Self-consistent field theory and numerical scheme for calculating the phase diagram of wormlike diblock copolymers

NASA Astrophysics Data System (ADS)

Jiang, Ying; Chen, Jeff Z. Y.

2013-10-01

This paper concerns establishing a theoretical basis and numerical scheme for studying the phase behavior of AB diblock copolymers made of wormlike chains. The general idea of a self-consistent field theory is the combination of the mean-field approach together with a statistical weight that describes the configurational properties of a polymer chain. In recent years, this approach has been extensively used for structural prediction of block copolymers, based on the Gaussian-model description of a polymer chain. The wormlike-chain model has played an important role in the description of polymer systems, covering the semiflexible-to-rod crossover of the polymer properties and the highly stretching regime, which the Gaussian-chain model has difficulties to describe. Although the idea of developing a self-consistent field theory for wormlike chains could be traced back to early development in polymer physics, the solution of such a theory has been limited due to technical difficulties. In particular, a challenge has been to develop a numerical algorithm enabling the calculation of the phase diagram containing three-dimensional structures for wormlike AB diblock copolymers. This paper describes a computational algorithm that combines a number of numerical tricks, which can be used for such a calculation. A phase diagram covering major parameter areas was constructed for the wormlike-chain system and reported by us, where the ratio between the total length and the persistence length of a constituent polymer is suggested as another tuning parameter for the microphase-separated structures; all detailed technical issues are carefully addressed in the current paper.

Polyfibroblast: A Self-Healing and Galvanic Protection Additive

DTIC Science & Technology

2012-09-12

self-healing and galvanic protection capacity to the primer (Figure 1). Polyfibroblast consists of paint-filled microcapsules and zinc powder. It has...significant added cost. Microcapsule Figure 1. Polyfibroblast contains fresh paint encapsulated in polymer shells plus Zn powder. When scratched, resin...from the broken microcapsules fills the crack to form a polymer scar. Zn powder supplies galvanic protection in the event of incomplete healing

Self-consistent field theory of polymer-ionic molecule complexation.

PubMed

Nakamura, Issei; Shi, An-Chang

2010-05-21

A self-consistent field theory is developed for polymers that are capable of binding small ionic molecules (adsorbates). The polymer-ionic molecule association is described by Ising-like binding variables, C(i) ((a))(kDelta)(=0 or 1), whose average determines the number of adsorbed molecules, n(BI). Polymer gelation can occur through polymer-ionic molecule complexation in our model. For polymer-polymer cross-links through the ionic molecules, three types of solutions for n(BI) are obtained, depending on the equilibrium constant of single-ion binding. Spinodal lines calculated from the mean-field free energy exhibit closed-loop regions where the homogeneous phase becomes unstable. This phase instability is driven by the excluded-volume interaction due to the single occupancy of ion-binding sites on the polymers. Moreover, sol-gel transitions are examined using a critical degree of conversion. A gel phase is induced when the concentration of adsorbates is increased. At a higher concentration of the adsorbates, however, a re-entrance from a gel phase into a sol phase arises from the correlation between unoccupied and occupied ion-binding sites. The theory is applied to a model system, poly(vinyl alcohol) and borate ion in aqueous solution with sodium chloride. Good agreement between theory and experiment is obtained.

Polymers as Reference Partitioning Phase: Polymer Calibration for an Analytically Operational Approach To Quantify Multimedia Phase Partitioning.

PubMed

Gilbert, Dorothea; Witt, Gesine; Smedes, Foppe; Mayer, Philipp

2016-06-07

Polymers are increasingly applied for the enrichment of hydrophobic organic chemicals (HOCs) from various types of samples and media in many analytical partitioning-based measuring techniques. We propose using polymers as a reference partitioning phase and introduce polymer-polymer partitioning as the basis for a deeper insight into partitioning differences of HOCs between polymers, calibrating analytical methods, and consistency checking of existing and calculation of new partition coefficients. Polymer-polymer partition coefficients were determined for polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and organochlorine pesticides (OCPs) by equilibrating 13 silicones, including polydimethylsiloxane (PDMS) and low-density polyethylene (LDPE) in methanol-water solutions. Methanol as cosolvent ensured that all polymers reached equilibrium while its effect on the polymers' properties did not significantly affect silicone-silicone partition coefficients. However, we noticed minor cosolvent effects on determined polymer-polymer partition coefficients. Polymer-polymer partition coefficients near unity confirmed identical absorption capacities of several PDMS materials, whereas larger deviations from unity were indicated within the group of silicones and between silicones and LDPE. Uncertainty in polymer volume due to imprecise coating thickness or the presence of fillers was identified as the source of error for partition coefficients. New polymer-based (LDPE-lipid, PDMS-air) and multimedia partition coefficients (lipid-water, air-water) were calculated by applying the new concept of a polymer as reference partitioning phase and by using polymer-polymer partition coefficients as conversion factors. The present study encourages the use of polymer-polymer partition coefficients, recognizing that polymers can serve as a linking third phase for a quantitative understanding of equilibrium partitioning of HOCs between any two phases.

Origin of change in molecular-weight dependence for polymer surface tension.

PubMed

Thompson, R B; Macdonald, J R; Chen, P

2008-09-01

Self-consistent-field theory is used to reproduce the behavior of polymer surface tension with molecular-weight for both lower and higher molecular-weight polymers. The change in behavior of the surface tension between these two regimes is shown to be due to the almost total exclusion of polymer from the nonpolymer bulk phase. The predicted two regime surface tension behavior with molecular-weight and the exclusion explanation are shown to be valid for a range of different polymer compressibilities.

A New Self-Consistent Field Model of Polymer/Nanoparticle Mixture

NASA Astrophysics Data System (ADS)

Chen, Kang; Li, Hui-Shu; Zhang, Bo-Kai; Li, Jian; Tian, Wen-De

2016-02-01

Field-theoretical method is efficient in predicting assembling structures of polymeric systems. However, it’s challenging to generalize this method to study the polymer/nanoparticle mixture due to its multi-scale nature. Here, we develop a new field-based model which unifies the nanoparticle description with the polymer field within the self-consistent field theory. Instead of being “ensemble-averaged” continuous distribution, the particle density in the final morphology can represent individual particles located at preferred positions. The discreteness of particle density allows our model to properly address the polymer-particle interface and the excluded-volume interaction. We use this model to study the simplest system of nanoparticles immersed in the dense homopolymer solution. The flexibility of tuning the interfacial details allows our model to capture the rich phenomena such as bridging aggregation and depletion attraction. Insights are obtained on the enthalpic and/or entropic origin of the structural variation due to the competition between depletion and interfacial interaction. This approach is readily extendable to the study of more complex polymer-based nanocomposites or biology-related systems, such as dendrimer/drug encapsulation and membrane/particle assembly.

Dynamic Self-Consistent Field Theories for Polymer Blends and Block Copolymers

NASA Astrophysics Data System (ADS)

Kawakatsu, Toshihiro

Understanding the behavior of the phase separated domain structures and rheological properties of multi-component polymeric systems require detailed information on the dynamics of domains and that of conformations of constituent polymer chains. Self-consistent field (SCF) theory is a useful tool to treat such a problem because the conformation entropy of polymer chains in inhomogeneous systems can be evaluated quantitatively using this theory. However, when we turn our attention to the dynamic properties in a non-equilibrium state, the basic assumption of the SCF theory, i.e. the assumption of equilibrium chain conformation, breaks down. In order to avoid such a difficulty, dynamic SCF theories were developed. In this chapter, we give a brief review of the recent developments of dynamic SCF theories, and discuss where the cutting-edge of this theory is.

Bio-Based Nanocomposites: An Alternative to Traditional Composites

ERIC Educational Resources Information Center

Tate, Jitendra S.; Akinola, Adekunle T.; Kabakov, Dmitri

2009-01-01

Polymer matrix composites (PMC), often referred to as fiber reinforced plastics (FRP), consist of fiber reinforcement (E-glass, S2-glass, aramid, carbon, or natural fibers) and polymer matrix/resin (polyester, vinyl ester, polyurethane, phenolic, and epoxies). Eglass/ polyester and E-glass/vinyl ester composites are extensively used in the marine,…

Tire with Self-Repairing Mechanism

NASA Astrophysics Data System (ADS)

Nagaya, Kosuke; Ikai, Sigeo; Chiba, Manabu; Chao, Xujing

A new type of tire is presented, in which there is no air leakage when nails puncture the tire. The broken part is repaired automatically by a self-repairing mechanism. The self-repairing unit consists of two rubber sheets with internal lattices. Polymer particles, which expand their volume on adding water, are inserted into the lattices. The unit is adhered to the inside wall of the tire. Coolant fluid diluted with water is introduced to the polymers uniformly. In this system, the polymer particles expand with water-diluted coolant fluid, and become gel. Hence, they stop air leakages in the tire. Fundamental experiments are performed, and optimum conditions are found. This technique is also applied to real tires, and it is ascertained that there is no air leakage when the tire is punctured by nails.

Manipulating the ABCs of self-assembly via low-χ block polymer design

PubMed Central

Chang, Alice B.; Lee, Byeongdu; Garland, Carol M.; Jones, Simon C.; Matsen, Mark W.

2017-01-01

Block polymer self-assembly typically translates molecular chain connectivity into mesoscale structure by exploiting incompatible blocks with large interaction parameters (χij). In this article, we demonstrate that the converse approach, encoding low-χ interactions in ABC bottlebrush triblock terpolymers (χAC ≲ 0), promotes organization into a unique mixed-domain lamellar morphology, which we designate LAMP. Transmission electron microscopy indicates that LAMP exhibits ACBC domain connectivity, in contrast to conventional three-domain lamellae (LAM3) with ABCB periods. Complementary small-angle X-ray scattering experiments reveal a strongly decreasing domain spacing with increasing total molar mass. Self-consistent field theory reinforces these observations and predicts that LAMP is thermodynamically stable below a critical χAC, above which LAM3 emerges. Both experiments and theory expose close analogies to ABA′ triblock copolymer phase behavior, collectively suggesting that low-χ interactions between chemically similar or distinct blocks intimately influence self-assembly. These conclusions provide fresh opportunities for block polymer design with potential consequences spanning all self-assembling soft materials. PMID:28588139

Coarse-Graining Polymer Field Theory for Fast and Accurate Simulations of Directed Self-Assembly

NASA Astrophysics Data System (ADS)

Liu, Jimmy; Delaney, Kris; Fredrickson, Glenn

To design effective manufacturing processes using polymer directed self-assembly (DSA), the semiconductor industry benefits greatly from having a complete picture of stable and defective polymer configurations. Field-theoretic simulations are an effective way to study these configurations and predict defect populations. Self-consistent field theory (SCFT) is a particularly successful theory for studies of DSA. Although other models exist that are faster to simulate, these models are phenomenological or derived through asymptotic approximations, often leading to a loss of accuracy relative to SCFT. In this study, we employ our recently-developed method to produce an accurate coarse-grained field theory for diblock copolymers. The method uses a force- and stress-matching strategy to map output from SCFT simulations into parameters for an optimized phase field model. This optimized phase field model is just as fast as existing phenomenological phase field models, but makes more accurate predictions of polymer self-assembly, both in bulk and in confined systems. We study the performance of this model under various conditions, including its predictions of domain spacing, morphology and defect formation energies. Samsung Electronics.

The impact of fullerenes on the ordering of polyacrylonitrile during nanocomposites formation

DOE PAGES

Imel, Adam E.; Dadmun, Mark D.

2015-08-18

The production of polymer nanocomposites from solution consists of the mixing of the polymer and nanoparticle in solution and subsequent evaporation of the solvent. Here, we examine the formation of polyacrylonitrile and C60 fullerene nanocomposites, with a focus on monitoring these two steps.This study indicates that the nanoparticles are individually dispersed with the polymer chains in solution prior to deposition and in the final film. As the solution becomes more concentrated, the nanoparticles are sequestered to the outer edges of the polymer crystals, altering the detected crystal structure. The self-assembled structure of the crystalline polymer is directed by the additionmore » of C 60 and manifests itself as a peak in small-angle X-ray scattering on a length scale of ~150 . Moreover, our results suggest that the non-covalent molecular interactions between C60 and polyacrylonitrile matrix are sufficiently strong to alter the self-assembled morphology of the polymer and the meso- and nanoscale structures in the nanocomposite.« less

Functional level-set derivative for a polymer self consistent field theory Hamiltonian

NASA Astrophysics Data System (ADS)

Ouaknin, Gaddiel; Laachi, Nabil; Bochkov, Daniil; Delaney, Kris; Fredrickson, Glenn H.; Gibou, Frederic

2017-09-01

We derive functional level-set derivatives for the Hamiltonian arising in self-consistent field theory, which are required to solve free boundary problems in the self-assembly of polymeric systems such as block copolymer melts. In particular, we consider Dirichlet, Neumann and Robin boundary conditions. We provide numerical examples that illustrate how these shape derivatives can be used to find equilibrium and metastable structures of block copolymer melts with a free surface in both two and three spatial dimensions.

Modeling polymer-induced interactions between two grafted surfaces: comparison between interfacial statistical associating fluid theory and self-consistent field theory.

PubMed

Jain, Shekhar; Ginzburg, Valeriy V; Jog, Prasanna; Weinhold, Jeffrey; Srivastava, Rakesh; Chapman, Walter G

2009-07-28

The interaction between two polymer grafted surfaces is important in many applications, such as nanocomposites, colloid stabilization, and polymer alloys. In our previous work [Jain et al., J. Chem. Phys. 128, 154910 (2008)], we showed that interfacial statistical associating fluid density theory (iSAFT) successfully calculates the structure of grafted polymer chains in the absence/presence of a free polymer. In the current work, we have applied this density functional theory to calculate the force of interaction between two such grafted monolayers in implicit good solvent conditions. In particular, we have considered the case where the segment sizes of the free (sigma(f)) and grafted (sigma(g)) polymers are different. The interactions between the two monolayers in the absence of the free polymer are always repulsive. However, in the presence of the free polymer, the force either can be purely repulsive or can have an attractive minimum depending upon the relative chain lengths of the free (N(f)) and grafted polymers (N(g)). The attractive minimum is observed only when the ratio alpha = N(f)/N(g) is greater than a critical value. We find that these critical values of alpha satisfy the following scaling relation: rho(g) square root(N(g)) beta(3) proportional to alpha(-lambda), where beta = sigma(f)/sigma(g) and lambda is the scaling exponent. For beta = 1 or the same segment sizes of the free and grafted polymers, this scaling relation is in agreement with those from previous theoretical studies using self-consistent field theory (SCFT). Detailed comparisons between iSAFT and SCFT are made for the structures of the monolayers and their forces of interaction. These comparisons lead to interesting implications for the modeling of nanocomposite thermodynamics.

Monolithically Integrated Self-Charging Power Pack Consisting of a Silicon Nanowire Array/Conductive Polymer Hybrid Solar Cell and a Laser-Scribed Graphene Supercapacitor.

PubMed

Liu, Hanhui; Li, Mengping; Kaner, Richard B; Chen, Songyan; Pei, Qibing

2018-05-09

Owing to the need for portable and sustainable energy sources and the development trend for microminiaturization and multifunctionalization in the electronic components, the study of integrated self-charging power packs has attracted increasing attention. A new self-charging power pack consisting of a silicon nanowire array/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hybrid solar cell and a laser-scribed graphene (LSG) supercapacitor has been fabricated. The Si nanowire array/PEDOT:PSS hybrid solar cell structure exhibited a high power conversion efficiency (PCE) of 12.37%. The LSG demonstrated excellent energy storage capability for the power pack, with high current density, energy density, and cyclic stability when compared to other supercapacitor electrodes such as active carbon and conducting polymers. The overall efficiency of the power unit is 2.92%.

Neutron radiation shielding properties of polymer incorporated self compacting concrete mixes.

PubMed

Malkapur, Santhosh M; Divakar, L; Narasimhan, Mattur C; Karkera, Narayana B; Goverdhan, P; Sathian, V; Prasad, N K

2017-07-01

In this work, the neutron radiation shielding characteristics of a class of novel polymer-incorporated self-compacting concrete (PISCC) mixes are evaluated. Pulverized high density polyethylene (HDPE) material was used, at three different reference volumes, as a partial replacement to river sand in conventional concrete mixes. By such partial replacement of sand with polymer, additional hydrogen contents are incorporated in these concrete mixes and their effect on the neutron radiation shielding properties are studied. It has been observed from the initial set of experiments that there is a definite trend of reductions in the neutron flux and dose transmission factor values in these PISCC mixes vis-à-vis ordinary concrete mix. Also, the fact that quite similar enhanced shielding results are recorded even when reprocessed HDPE material is used in lieu of the virgin HDPE attracts further attention. Copyright © 2017 Elsevier Ltd. All rights reserved.

Scattering from Colloid-Polymer Conjugates with Excluded Volume Effect

DOE PAGES

Li, Xin; Sanchez-Diaz, Luis E.; Smith, Gregory Scott; ...

2015-01-13

This work presents scattering functions of conjugates consisting of a colloid particle and a self-avoiding polymer chain as a model for protein-polymer conjugates and nanoparticle-polymer conjugates in solution. The model is directly derived from the two-point correlation function with the inclusion of excluded volume effects. The dependence of the calculated scattering function on the geometric shape of the colloid and polymer stiffness is investigated. The model is able to describe the experimental scattering signature of the solutions of suspending hard particle-polymer conjugates and provide additional conformational information. This model explicitly elucidates the link between the global conformation of a conjugatemore » and the microstructure of its constituent components.« less

Development of a self-healing soft pneumatic actuator: a first concept.

PubMed

Terryn, Seppe; Mathijssen, Glenn; Brancart, Joost; Lefeber, Dirk; Assche, Guy Van; Vanderborght, Bram

2015-07-07

Inspired by the intrinsic softness and the corresponding embodied intelligence principles, soft pneumatic actuators (SPA) have been developed, which ensure safe interaction in unstructured, unknown environments. Due to their intrinsic softness, these actuators have the ability to resist large mechanical impacts. However, the soft materials used in these structures are in general susceptible to damage caused by sharp objects found in the unstructured environments. This paper proposes to integrate a self-healing (SH-) mechanism in SPAs, such that cuts, tears and perforations in the actuator can be self-healed. Diels-Alder (DA-) polymers, covalent polymer network systems based on the thermoreversible DA-reaction, were selected and their mechanical, as well as SH-properties, are described. To evaluate the feasibility of developing an SPA constructed out of SH-material, a single cell prototype, a SH-soft pneumatic cell (SH-SPC), was constructed entirely out of DA-polymers. Exploiting the SH-property of the DA-polymers, a completely new shaping process is presented in this paper, referred to as 'shaping through folding and self-healing'. 3D polygon structures, like the cubic SH-SPC, can be constructed by folding SH-polymer sheet. The sides of the structures can be sealed and made airtight using a SH-procedure at relatively low temperatures (<90 °C). Both the (thermo) mechanical and SH-properties of the SH-SPC prototype were experimentally validated and showed excellent performances. Macroscopic incisions in the prototype were completely healed using a SH-procedure (<70 °C). Starting from this single-cell prototype, it is straight-forward to develop a multi-cell prototype, the first SPA ever built completely out of SH-polymers.

Theoretical study of the self-assembly of Janus Bottlebrush Polymers from A-Branch-B Diblock Macromonomers

NASA Astrophysics Data System (ADS)

Gadelrab, Karim; Alexander-Katz, Alfredo; LaboratoryTheoretical Soft Materials Team

The self-assembly of block copolymers BCP has provided an impressive control over the nanoscale structure of soft matter. While the main focus of the research in the field has been directed towards simple linear diblocks, the development of advanced polymer architecture provided improved performance and access to new structures. In particular, bottlebrush BCPs (BBCPs) have interesting characteristics due to their dense functionality, high molecular weight, low levels of entanglement, and tendency to efficiently undergo rapid bulk phase separation. In this work, we are interested in theoretically studying the self-assembly of Janus-type ``A-branch-B'' BBCPs where A and B blocks can phase separate with the bottlebrush polymer backbone serving as the interface between the two blocks. Hence, the polymer backbone adds an extra constraint on the equilibrium spacing between neighboring linear diblock chains. In this regard, the segment length of the backbone separating the AB junctions has a direct effect of the observed domain spacing and effective segregation strength of the AB blocks. We employ self-consistent field theoretic SCFT simulations to capture the effect of volume fraction of different constituents and construct a phase diagram of the accessible morphologies of these BBCPs.

Manipulating the ABCs of self-assembly via low-χ block polymer design

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Alice B.; Bates, Christopher M.; Lee, Byeongdu

Block polymer self-assembly typically translates molecular chain connectivity into mesoscale structure by exploiting incompatible blocks with large interaction parameters (χ ij). In this report, we demonstrate that the converse approach, encoding low-χ interactions in ABC bottlebrush triblock terpolymers (χ AC ≲ 0), promotes organization into a unique mixed-domain lamellar morphology which we designate LAM P. Transmission electron microscopy indicates that LAMP exhibits ACBC domain connectivity, in contrast to conventional three-domain lamellae (LAM 3) with ABCB periods. Complementary small angle X-ray scattering experiments reveal a strongly decreasing domain spacing with increasing total molar mass. Self-consistent field theory reinforces these observations andmore » predicts that LAM P is thermodynamically stable below a critical χ AC, above which LAM 3 emerges. Both experiments and theory expose close analogies to ABA triblock copolymer phase behavior, collectively suggesting that low-χ interactions between chemically similar or distinct blocks intimately influence self-assembly. Furthermore, these conclusions provide new opportunities in block polymer design with potential consequences spanning all self-assembling soft materials.« less

Manipulating the ABCs of self-assembly via low-χ block polymer design

DOE PAGES

Chang, Alice B.; Bates, Christopher M.; Lee, Byeongdu; ...

2017-06-06

Block polymer self-assembly typically translates molecular chain connectivity into mesoscale structure by exploiting incompatible blocks with large interaction parameters (χ ij). In this report, we demonstrate that the converse approach, encoding low-χ interactions in ABC bottlebrush triblock terpolymers (χ AC ≲ 0), promotes organization into a unique mixed-domain lamellar morphology which we designate LAM P. Transmission electron microscopy indicates that LAMP exhibits ACBC domain connectivity, in contrast to conventional three-domain lamellae (LAM 3) with ABCB periods. Complementary small angle X-ray scattering experiments reveal a strongly decreasing domain spacing with increasing total molar mass. Self-consistent field theory reinforces these observations andmore » predicts that LAM P is thermodynamically stable below a critical χ AC, above which LAM 3 emerges. Both experiments and theory expose close analogies to ABA triblock copolymer phase behavior, collectively suggesting that low-χ interactions between chemically similar or distinct blocks intimately influence self-assembly. Furthermore, these conclusions provide new opportunities in block polymer design with potential consequences spanning all self-assembling soft materials.« less

Polarizable polymer chain under external electric field: Effects of many-body electrostatic dipole correlations.

PubMed

Budkov, Yu A; Kolesnikov, A L

2016-11-01

We present a new simple self-consistent field theory of a polarizable flexible polymer chain under an external constant electric field with account for the many-body electrostatic dipole correlations. We show the effects of electrostatic dipole correlations on the electric-field-induced globule-coil transition. We demonstrate that only when the polymer chain is in the coil conformation, the electrostatic dipole correlations of monomers can be considered as pairwise. However, when the polymer chain is in a collapsed state, the dipole correlations have to be considered at the many-body level.

Interactions between Nanoparticles and Polymer Brushes: Molecular Dynamics Simulations and Self-consistent Field Theory Calculations

NASA Astrophysics Data System (ADS)

Cheng, Shengfeng; Wen, Chengyuan; Egorov, Sergei

2015-03-01

Molecular dynamics simulations and self-consistent field theory calculations are employed to study the interactions between a nanoparticle and a polymer brush at various densities of chains grafted to a plane. Simulations with both implicit and explicit solvent are performed. In either case the nanoparticle is loaded to the brush at a constant velocity. Then a series of simulations are performed to compute the force exerted on the nanoparticle that is fixed at various distances from the grafting plane. The potential of mean force is calculated and compared to the prediction based on a self-consistent field theory. Our simulations show that the explicit solvent leads to effects that are not captured in simulations with implicit solvent, indicating the importance of including explicit solvent in molecular simulations of such systems. Our results also demonstrate an interesting correlation between the force on the nanoparticle and the density profile of the brush. We gratefully acknowledge the support of NVIDIA Corporation with the donation of the Tesla K40 GPU used for this research.

Pair interactions in polyelectrolyte-nanoparticle systems: Influence of dielectric inhomogeneities and the partial dissociation of polymers and nanoparticles.

PubMed

Pryamitsyn, Victor; Ganesan, Venkat

2015-10-28

We study the effective pair interactions between two charged spherical particles in polyelectrolyte solutions using polymer self-consistent field theory. In a recent study [V. Pryamitsyn and V. Ganesan, Macromolecules 47, 6095 (2015)], we considered a model in which the particles possess fixed charge density, the polymers contain a prespecified amount of dissociated charges and, the dielectric constant of the solution was assumed to be homogeneous in space and independent of the polymer concentration. In this article, we present results extending our earlier model to study situations in which either or both the particle and the polymers possess partially dissociable groups. Additionally, we also consider the case when the dielectric constant of the solution depends on the local concentration of the polymers and when the particle's dielectric constant is lower than that of the solvent. For each case, we quantify the polymer-mediated interactions between the particles as a function of the polymer concentrations and the degree of dissociation of the polymer and particles. Consistent with the results of our previous study, we observe that the polymer-mediated interparticle interactions consist of a short-range attraction and a long-range repulsion. The partial dissociablity of the polymer and particles was seen to have a strong influence on the strength of the repulsive portion of the interactions. Rendering the dielectric permittivity to be inhomogeneous has an even stronger effect on the repulsive interactions and results in changes to the qualitative nature of interactions in some parametric ranges.

Self-Consistent Field Theories for the Role of Large Length-Scale Architecture in Polymers

NASA Astrophysics Data System (ADS)

Wu, David

At large length-scales, the architecture of polymers can be described by a coarse-grained specification of the distribution of branch points and monomer types within a molecule. This includes molecular topology (e.g., cyclic or branched) as well as distances between branch points or chain ends. Design of large length-scale molecular architecture is appealing because it offers a universal strategy, independent of monomer chemistry, to tune properties. Non-linear analogs of linear chains differ in molecular-scale properties, such as mobility, entanglements, and surface segregation in blends that are well-known to impact rheological, dynamical, thermodynamic and surface properties including adhesion and wetting. We have used Self-Consistent Field (SCF) theories to describe a number of phenomena associated with large length-scale polymer architecture. We have predicted the surface composition profiles of non-linear chains in blends with linear chains. These predictions are in good agreement with experimental results, including from neutron scattering, on a range of well-controlled branched (star, pom-pom and end-branched) and cyclic polymer architectures. Moreover, the theory allows explanation of the segregation and conformations of branched polymers in terms of effective surface potentials acting on the end and branch groups. However, for cyclic chains, which have no end or junction points, a qualitatively different topological mechanism based on conformational entropy drives cyclic chains to a surface, consistent with recent neutron reflectivity experiments. We have also used SCF theory to calculate intramolecular and intermolecular correlations for polymer chains in the bulk, dilute solution, and trapped at a liquid-liquid interface. Predictions of chain swelling in dilute star polymer solutions compare favorably with existing PRISM theory and swelling at an interface helps explain recent measurements of chain mobility at an oil-water interface. In collaboration with: Renfeng Hu, Colorado School of Mines, and Mark Foster, University of Akron. This work was supported by NSF Grants No. CBET- 0730692 and No. CBET-0731319.

Triggered metal ion release and oxidation: Ferrocene as new mechanophore in polymers.

PubMed

Di Giannantonio, Michela; Ayer, Mathieu A; Verde-Sesto, Ester; Lattuada, Marco; Weder, Christoph; Fromm, Katharina M

2018-06-13

The introduction of mechanophores into polymers allows transducing mechanical forces into chemical reactions for e.g. self-healing, catalytic activity, or mechanochromic response. Here, the first example of mechanically induced metal ion release from a polymer is reported. Ferrocene (Fc) was incorporated as an Fe-ion releasing mechanophore into poly(methyl acrylate)s (PMAs) and polyurethanes (PUs). Sonication triggered the preferential cleavage of the polymers at the Fc units over other bonds, as shown by a kinetic study of the molar mass distribution of the cleaved Fc-containing and Fc-free reference polymers. The released and oxidized Fe2+ ions can be detected with KSCN to generate the red-colored [Fe(SCN)n(H2O)6-n)](3-n)+ or reacted with K4[Fe(CN)6] to afford Prussian blue. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Maier-Saupe model of polymer nematics: Comparing free energies calculated with Self Consistent Field theory and Monte Carlo simulations.

PubMed

Greco, Cristina; Jiang, Ying; Chen, Jeff Z Y; Kremer, Kurt; Daoulas, Kostas Ch

2016-11-14

Self Consistent Field (SCF) theory serves as an efficient tool for studying mesoscale structure and thermodynamics of polymeric liquid crystals (LC). We investigate how some of the intrinsic approximations of SCF affect the description of the thermodynamics of polymeric LC, using a coarse-grained model. Polymer nematics are represented as discrete worm-like chains (WLC) where non-bonded interactions are defined combining an isotropic repulsive and an anisotropic attractive Maier-Saupe (MS) potential. The range of the potentials, σ, controls the strength of correlations due to non-bonded interactions. Increasing σ (which can be seen as an increase of coarse-graining) while preserving the integrated strength of the potentials reduces correlations. The model is studied with particle-based Monte Carlo (MC) simulations and SCF theory which uses partial enumeration to describe discrete WLC. In MC simulations the Helmholtz free energy is calculated as a function of strength of MS interactions to obtain reference thermodynamic data. To calculate the free energy of the nematic branch with respect to the disordered melt, we employ a special thermodynamic integration (TI) scheme invoking an external field to bypass the first-order isotropic-nematic transition. Methodological aspects which have not been discussed in earlier implementations of the TI to LC are considered. Special attention is given to the rotational Goldstone mode. The free-energy landscape in MC and SCF is directly compared. For moderate σ the differences highlight the importance of local non-bonded orientation correlations between segments, which SCF neglects. Simple renormalization of parameters in SCF cannot compensate the missing correlations. Increasing σ reduces correlations and SCF reproduces well the free energy in MC simulations.

Statistics of wormlike chains. II. Phase transition of polymer liquid crystals and its mixture with low molecular weight liquid crystals

NASA Astrophysics Data System (ADS)

Zhang, W. X.; Zhao, S. R.; Sun, C. P.

1997-02-01

A general self-consistent field (SCF) for the mixture of polymer and low molecular weight (LMW) molecules has been derived by variation principle. Considering a Maier-Saupe type of interaction, the analytical expressions of the SCF for polymer liquid crystals (PLCs) and the mixture of PLCs and LMW liquid crystals are obtained, from which the phase behaviors of PLCs as well as the mixture are studied. The theoretical results are in agreement with experimental results by adjusting a parameter.

4D printing of a self-morphing polymer driven by a swellable guest medium.

PubMed

Su, Jheng-Wun; Tao, Xiang; Deng, Heng; Zhang, Cheng; Jiang, Shan; Lin, Yuyi; Lin, Jian

2018-01-31

There is a significant need of advanced materials that can be fabricated into functional devices with defined three-dimensional (3D) structures for application in tissue engineering, flexible electronics, and soft robotics. This need motivates an emerging four-dimensional (4D) printing technology, by which printed 3D structures consisting of active materials can transform their configurations over time in response to stimuli. Despite the ubiquity of active materials in performing self-morphing processes, their potential for 4D printing has not been fully explored to date. In this study, we demonstrate 4D printing of a commercial polymer, SU-8, which has not been reported to date in this field. The working principle is based on a self-morphing process of the printed SU-8 structures through spatial control of the swelling medium inside the polymer matrix by a modified process. To understand the self-morphing behavior, fundamental studies on the effect of the geometries including contours and filling patterns were carried out. A soft electronic device as an actuator was demonstrated to realize an application of this programmable polymer using the 3D printing technology. These studies provide a new paradigm for application of SU-8 in 4D printing, paving a new route to the exploration of more potential candidates by this demonstrated strategy.

Testing strong-segregation theory against self-consistent-field theory for block copolymer melts

NASA Astrophysics Data System (ADS)

Matsen, M. W.

2001-06-01

We introduce a highly efficient self-consistent-field theory (SCFT) method for examining the cylindrical and spherical block copolymer morphologies using a standard unit cell approximation (UCA). The method is used to calculate the classical diblock copolymer phase boundaries deep into the strong-segregation regime, where they can be compared with recent improvements to strong-segregation theory (SST). The comparison suggests a significant discrepancy between the two theories indicating that our understanding of strongly stretched polymer brushes is still incomplete.

Neural correlates of Self and its interaction with memory in healthy adolescents

PubMed Central

Dégeilh, Fanny; Guillery-Girard, Bérengère; Dayan, Jacques; Gaubert, Malo; Chételat, Gael; Egler, Pierre-Jean; Baleyte, Jean-Marc; Eustache, Francis; Viard, Armelle

2015-01-01

Adolescence is marked by the development of personal identity and is associated with structural and functional changes in brain regions associated with Self processing. Yet, little is known about the neural correlates of self-reference processing and self-reference effect in adolescents. This fMRI study consists in a self-reference paradigm followed by a recognition test proposed to 30 healthy adolescents aged 13–18 years old. Results showed that the rostral anterior cingulate cortex is specifically involved in self-reference processing and that this specialization develops gradually from 13 to 18 years old. The self-reference effect is associated with increased brain activation changes during encoding, suggesting that the beneficial effect of Self on memory may occur at encoding of self-referential information, rather than at retrieval. PMID:26443236

On the chain length dependence of local correlations in polymer melts and a perturbation theory of symmetric polymer blends.

PubMed

Morse, David C; Chung, Jun Kyung

2009-06-14

The self-consistent field (SCF) approach to the thermodynamics of dense polymer liquids is based on the idea that short-range correlations in a polymer liquid are almost independent of how monomers are connected into polymers over larger scales. Some limits of this idea are explored in the context of a perturbation theory for symmetric polymer blends. We consider mixtures of two structurally identical polymers, A and B, in which the AB monomer pair interaction differs slightly from the AA and BB interactions by an amount proportional to a parameter alpha. An expansion of the free energy to first order in alpha yields an excess free energy of mixing per monomer of the form alphaz(N)phi(A)phi(B) in both lattice and continuum models, where z(N) is a measure of the number of intermolecular near neighbors per monomer in a one-component (alpha=0) reference liquid with chains of length N. The quantity z(N) decreases slightly with increasing N because the concentration of intramolecular near neighbors is slightly higher for longer chains, creating a slightly deeper intermolecular correlation hole. We predict that z(N)=z(infinity)[1+betaN(-1/2)], where N is an invariant degree of polymerization and beta=(6/pi)(3/2) is a universal coefficient. This and related predictions about the slight N dependence of local correlations are confirmed by comparison to simulations of a continuum bead-spring model and to published lattice Monte Carlo simulations. We show that a renormalized one-loop theory for blends correctly describes this N dependence of local liquid structure. We also propose a way to estimate the effective interaction parameter appropriate for comparisons of simulation data to SCF theory and to coarse-grained theories of corrections to SCF theory, which is based on an extrapolation of perturbation theory to the limit N-->infinity.

2D mesoscale colloidal crystal patterns on polymer substrates

NASA Astrophysics Data System (ADS)

Bredikhin, Vladimir; Bityurin, Nikita

2018-05-01

The development of nanosphere lithography relies on the ability of depositing 2D colloidal crystals comprising micro- and nano-size elements on substrates of different materials. One of the most difficult problems here is deposition of coatings on hydrophobic substrates, e.g. polymers, from aqueous colloidal solutions. We use UV photooxidation for substrate hydrophilization. We demonstrate a new method of producing a two-dimensional ordered array of polymer microparticles (polystyrene microspheres ∼1 μm in diameter) on a polymer substrate (PMMA). We show that implementation of the new deposition technique for directed self-assembly of microspheres on an UV irradiated surface provides an opportunity to obtain coatings on a hydrophilized PMMA surface of large area (∼5 cm2). UV irradiation of the surface through masks allows creating 2D patterns consisting of mesoscale elements formed by the deposited self-assembled microparticles owing to the fact that the colloidal particles are deposited only on the irradiated area leaving the non-irradiated sections intact.

Observation of the Chiral and Achiral Hexatic Phases of Self-assembled Micellar polymers

PubMed Central

Pal, Antara; Kamal, Md. Arif; Raghunathan, V. A.

2016-01-01

We report the discovery of a thermodynamically stable line hexatic (N + 6) phase in a three-dimensional (3D) system made up of self-assembled polymer-like micelles of amphiphilic molecules. The experimentally observed phase transition sequence nematic (N)  N + 6  two-dimensional hexagonal (2D-H) is in good agreement with the theoretical predictions. Further, the present study also brings to light the effect of chirality on the N + 6 phase. In the chiral N + 6 phase the bond-orientational order within each “polymer” bundle is found to be twisted about an axis parallel to the average polymer direction. This structure is consistent with the theoretically envisaged Moiré state, thereby providing the first experimental demonstration of the Moiré structure. In addition to confirming the predictions of fundamental theories of two-dimensional melting, these results are relevant in a variety of situations in chemistry, physics and biology, where parallel packing of polymer-like objects are encountered. PMID:27577927

Novel protocol for highly efficient gas-phase chemical derivatization of surface amine groups using trifluoroacetic anhydride

NASA Astrophysics Data System (ADS)

Duchoslav, Jiri; Kehrer, Matthias; Hinterreiter, Andreas; Duchoslav, Vojtech; Unterweger, Christoph; Fürst, Christian; Steinberger, Roland; Stifter, David

2018-06-01

In the current work, chemical derivatization of amine (NH2) groups with trifluoroacetic anhydride (TFAA) as an analytical method to improve the information scope of X-ray photoelectron spectroscopy (XPS) is investigated. TFAA is known to successfully label hydroxyl (OH) groups. With the introduction of a newly developed gas-phase derivatization protocol conducted at ambient pressure and using a catalyst also NH2 groups can now efficiently be labelled with a high yield and without the formation of unwanted by-products. By establishing a comprehensive and self-consistent database of reference binding energies for XPS a promising approach for distinguishing hydroxyl from amine groups is presented. The protocol was verified on different polymers, including poly(allylamine), poly(ethyleneimine), poly(vinylalcohol) and chitosan, the latter one containing both types of addressed chemical groups.

Development of a Portable Taste Sensor with a Lipid/Polymer Membrane

PubMed Central

Tahara, Yusuke; Nakashi, Kenichi; Ji, Ke; Ikeda, Akihiro; Toko, Kiyoshi

2013-01-01

We have developed a new portable taste sensor with a lipid/polymer membrane and conducted experiments to evaluate the sensor's performance. The fabricated sensor consists of a taste sensor chip (40 mm × 26 mm × 2.2 mm) with working and reference electrodes and a portable sensor device (80 mm × 25 mm × 20 mm). The working electrode consists of a taste-sensing site comprising a poly(hydroxyethyl)methacrylate (pHEMA) hydrogel layer with KCl as the electrolyte layer and a lipid/polymer membrane as the taste sensing element. The reference electrode comprises a polyvinyl chloride (PVC) membrane layer with a small hole and a pHEMA layer with KCl. The whole device is the size of a USB memory stick, making it suitable for portable use. The sensor's response to tannic acid as the standard astringency substance showed good accuracy and reproducibility, and was comparable with the performance of a commercially available taste sensing system. Thus, it is possible for this sensor to be used for in-field evaluations and it can make a significant contribution to the food industry, as well as in various fields of research. PMID:23325168

A scattering function of star polymers including excluded volume effects

DOE PAGES

Li, Xin; Do, Changwoo; Liu, Yun; ...

2014-11-04

In this work we present a new model for the form factor of a star polymer consisting of self-avoiding branches. This new model incorporates excluded volume effects and is derived from the two point correlation function for a star polymer.. We compare this model to small angle neutron scattering (SANS) measurements from polystyrene (PS) stars immersed in a good solvent, tetrahydrofuran (THF). It is shown that this model provides a good description of the scattering signature originating from the excluded volume effect and it explicitly elucidates the connection between the global conformation of a star polymer and the local stiffnessmore » of its constituent branch.« less

Relaxation and Self-Diffusion of a Polymer Chain in a Melt

NASA Astrophysics Data System (ADS)

Hagita, Katsumi; Takano, Hiroshi

2004-04-01

Relaxation and self-diffusion of a polymer chain in a melt are discussed on the basis of the results of our recent Monte Carlo simulations of the bond fluctuation model, where only the excluded volume interaction is considered. Polymer chains are located on an L × L × L simple cubic lattice under periodic boundary conditions. Each chain consists of N segments, each of which occupies 2 × 2 × 2 unit cells. The results for N = 32, 48, 64, 96, 128, 192, 256, 384 and 512 at the volume fraction φ ≃ 0.5 are examined, where L = 128 for N ⩽ 256 and L = 192 for N ⩾ 384. The longest relaxation time τ is estimated by solving generalized eigenvalue problems for the equilibrium time correlation matrices of the positions of segments of a polymer chain. The self-diffusion constant D is estimated from the mean square displacements of the center of mass of a single polymer chain at the times larger than τ. From the data for N = 256, 384 and 512, the apparent exponents x r and xd, which describe the power law dependences of τ and D on N as τ ∝ N xr and D ∝ N-xd, are estimated to be xr ≃ 3.5 and xd ≃ 2.4, respectively. For N = 192, 256, 384 and 512, Dτ/ appears to be a constant, where denotes the mean square end-to-end distance of a polymer chain.

Self-reflection and self-transmission of pulsed radiation by laser-evaporated media

NASA Astrophysics Data System (ADS)

Furzikov, Nickolay P.

1991-05-01

Analysis of the known laser-induced evaporation (thermodestruction) model predicts the quasiperiodic oscillation of the effective absorption depth between its normal value and some minute quantity consisting of a part of the incident wavelength. This prediction explains the experimental data on the polymer laser ablation depth as well as the reflection transient drop of the laserdestructed aluminum.

Communication: Polarizable polymer chain under external electric field in a dilute polymer solution.

PubMed

Budkov, Yu A; Kolesnikov, A L; Kiselev, M G

2015-11-28

We study the conformational behavior of polarizable polymer chain under an external homogeneous electric field within the Flory type self-consistent field theory. We consider the influence of electric field on the polymer coil as well as on the polymer globule. We show that when the polymer chain conformation is a coil, application of external electric field leads to its additional swelling. However, when the polymer conformation is a globule, a sufficiently strong field can induce a globule-coil transition. We show that such "field-induced" globule-coil transition at the sufficiently small monomer polarizabilities goes quite smoothly. On the contrary, when the monomer polarizability exceeds a certain threshold value, the globule-coil transition occurs as a dramatic expansion in the regime of first-order phase transition. The developed theoretical model can be applied to predicting polymer globule density change under external electric field in order to provide more efficient processes of polymer functionalization, such as sorption, dyeing, and chemical modification.

Self-assembly of crystalline nanotubes from monodisperse amphiphilic diblock copolypeptoid tiles

DOE PAGES

Sun, Jing; Jiang, Xi; Lund, Reidar; ...

2016-03-28

The folding and assembly of sequence-defined polymers into precisely ordered nanostructures promises a class of well-defined biomimetic architectures with specific function. Amphiphilic diblock copolymers are known to self-assemble in water to form a variety of nanostructured morphologies including spheres, disks, cylinders, and vesicles. In all of these cases, the predominant driving force for assembly is the formation of a hydrophobic core that excludes water, whereas the hydrophilic blocks are solvated and extend into the aqueous phase. However, such polymer systems typically have broad molar mass distributions and lack the purity and sequence-defined structure often associated with biologically derived polymers. Here,more » we demonstrate that purified, monodisperse amphiphilic diblock copolypeptoids, with chemically distinct domains that are congruent in size and shape, can behave like molecular tile units that spontaneously assemble into hollow, crystalline nanotubes in water. The nanotubes consist of stacked, porous crystalline rings, and are held together primarily by side-chain van der Waals interactions. The peptoid nanotubes form without a central hydrophobic core, chirality, a hydrogen bond network, and electrostatic or π-π interactions. These results demonstrate the remarkable structure-directing influence of n-alkane and ethyleneoxy side chains in polymer self-assembly. More broadly, this work suggests that flexible, low-molecular-weight sequence-defined polymers can serve as molecular tile units that can assemble into precision supramolecular architectures.« less

Self-assembly of crystalline nanotubes from monodisperse amphiphilic diblock copolypeptoid tiles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Jing; Jiang, Xi; Lund, Reidar

The folding and assembly of sequence-defined polymers into precisely ordered nanostructures promises a class of well-defined biomimetic architectures with specific function. Amphiphilic diblock copolymers are known to self-assemble in water to form a variety of nanostructured morphologies including spheres, disks, cylinders, and vesicles. In all of these cases, the predominant driving force for assembly is the formation of a hydrophobic core that excludes water, whereas the hydrophilic blocks are solvated and extend into the aqueous phase. However, such polymer systems typically have broad molar mass distributions and lack the purity and sequence-defined structure often associated with biologically derived polymers. Here,more » we demonstrate that purified, monodisperse amphiphilic diblock copolypeptoids, with chemically distinct domains that are congruent in size and shape, can behave like molecular tile units that spontaneously assemble into hollow, crystalline nanotubes in water. The nanotubes consist of stacked, porous crystalline rings, and are held together primarily by side-chain van der Waals interactions. The peptoid nanotubes form without a central hydrophobic core, chirality, a hydrogen bond network, and electrostatic or π-π interactions. These results demonstrate the remarkable structure-directing influence of n-alkane and ethyleneoxy side chains in polymer self-assembly. More broadly, this work suggests that flexible, low-molecular-weight sequence-defined polymers can serve as molecular tile units that can assemble into precision supramolecular architectures.« less

Drag reduction by a linear viscosity profile.

PubMed

De Angelis, Elisabetta; Casciola, Carlo M; L'vov, Victor S; Pomyalov, Anna; Procaccia, Itamar; Tiberkevich, Vasil

2004-11-01

Drag reduction by polymers in turbulent flows raises an apparent contradiction: the stretching of the polymers must increase the viscosity, so why is the drag reduced? A recent theory proposed that drag reduction, in agreement with experiments, is consistent with the effective viscosity growing linearly with the distance from the wall. With this self-consistent solution the reduction in the Reynolds stress overwhelms the increase in viscous drag. In this Rapid Communication we show, using direct numerical simulations, that a linear viscosity profile indeed reduces the drag in agreement with the theory and in close correspondence with direct simulations of the FENE-P model at the same flow conditions.

Neural Correlates of Self and Its Interaction With Memory in Healthy Adolescents.

PubMed

Dégeilh, Fanny; Guillery-Girard, Bérengère; Dayan, Jacques; Gaubert, Malo; Chételat, Gaël; Egler, Pierre-Jean; Baleyte, Jean-Marc; Eustache, Francis; Viard, Armelle

2015-01-01

Adolescence is marked by the development of personal identity and is associated with structural and functional changes in brain regions associated with Self processing. Yet, little is known about the neural correlates of self-reference processing and self-reference effect in adolescents. This functional magnetic resonance imaging study consists of a self-reference paradigm followed by a recognition test proposed to 30 healthy adolescents aged 13-18 years old. Results showed that the rostral anterior cingulate cortex is specifically involved in self-reference processing and that this specialization develops gradually from 13 to 18 years old. The self-reference effect is associated with increased brain activation changes during encoding, suggesting that the beneficial effect of Self on memory may occur at encoding of self-referential information, rather than at retrieval. © 2015 The Authors. Child Development © 2015 Society for Research in Child Development, Inc.

Using multivalency to tailor the superselective binding of polymers on substrates

NASA Astrophysics Data System (ADS)

Tito, Nicholas; Frenkel, Daan

2014-03-01

Multivalency is a microscopic design concept in which a single nanoscopic entity contains multiple ligands, each of which may bind to multiple receptors on another entity. A useful property of many multivalent systems is ``superselectivity,'' where the fraction of the multivalent species bound to their complementary receptors grows sharply with the total number of receptors available. For example in the past two decades, multivalency has been exploited to develop DNA-coated nanoparticles that self-assemble into aggregates over an extremely narrow temperature window. In this talk, we use analytic and self-consistent field theories to explore the binding of multivalent polymers to receptors on a flat substrate. Discussion will focus on how the sequence, number, and binding strength of ligands along the polymer chain can be used to tune the superselectivity of the system. Comparison with recent experiments on model systems will be presented as time permits. We wish to thank ERC Advanced Grant 227758.

Extremely asymmetric phase diagram of homopolymer-monotethered nanoparticles: Competition between chain conformational entropy and particle steric interaction.

PubMed

Zhang, Tiancai; Fu, Chao; Yang, Yingzi; Qiu, Feng

2017-02-07

The phase behaviors of homopolymer-monotethered nanoparticles (HMNs) in melt are investigated via a theoretical method combining self-consistent field theory for polymers and density functional theory for hard spheres. An extremely asymmetric phase diagram is observed: (i) microphases are only possible for the volume fraction of the tethered polymer f A > 0.35; (ii) in addition to lamellar phase, the system can only self-assemble into various morphologies with a polymer-rich matrix, including gyroid phase, cylindrical phase, and spherical phase. In the frame of this theory, the critical point for HMNs' microphase separation is significantly lower than that of linear diblock copolymers. Furthermore, the characteristic length of microphase-separated structures of HMNs is much smaller than that of linear diblock copolymers with the same molecular weight. Our calculation results on morphologies and characteristic length agree well with recent simulations and experimental observations.

A study of metalized electrode self-clearing in electroactive polymer (EAP) based actuators

NASA Astrophysics Data System (ADS)

Ahmed, Saad; Ounaies, Zoubeida

2016-04-01

Electroactive polymer (EAP) based technologies have shown promise in areas such as artificial muscles, actuator, aerospace, medical and soft robotics. Still challenges remain such as low induced forces and defects-driven electrical breakdown, which impede the practical implementation of this technology. Multilayered or stacked configuration can address the low induced force issue whereas self-clearing can be a technique to improve breakdown limit of EAP based actuators. Self-clearing refers to the partial local breakdown of dielectric medium due to the presence of impurities, which in turn results in the evaporation of some of the metalized electrode. After this evaporation, the impurity is cleared and any current path would be safely cut off, which means the actuator continues to perform. It is a widely studied concept in the capacitor community, while it has not been studied much for EAP technologies. In this paper we report a systematic approach to precondition a silver-metalized electroactive polymer (EAP), more specifically P(VDF-TrFE-CTFE) terpolymer, using self-clearing concept. First, we show improvement in the dielectric breakdown strength of EAP based unimorph actuators after pre-clearing the impurities using low electric field (lower than dielectric breakdown of the terpolymer). Inspired by this improvement, we used Weibull statistics to systematically estimate the self-clearing/ preconditioning field needed to clear the defects. Then electrical breakdown experiments are conducted with and without preconditioning the samples to investigate its effect on the breakdown strength of the sample.

A finite element approach to self-consistent field theory calculations of multiblock polymers

NASA Astrophysics Data System (ADS)

Ackerman, David M.; Delaney, Kris; Fredrickson, Glenn H.; Ganapathysubramanian, Baskar

2017-02-01

Self-consistent field theory (SCFT) has proven to be a powerful tool for modeling equilibrium microstructures of soft materials, particularly for multiblock polymers. A very successful approach to numerically solving the SCFT set of equations is based on using a spectral approach. While widely successful, this approach has limitations especially in the context of current technologically relevant applications. These limitations include non-trivial approaches for modeling complex geometries, difficulties in extending to non-periodic domains, as well as non-trivial extensions for spatial adaptivity. As a viable alternative to spectral schemes, we develop a finite element formulation of the SCFT paradigm for calculating equilibrium polymer morphologies. We discuss the formulation and address implementation challenges that ensure accuracy and efficiency. We explore higher order chain contour steppers that are efficiently implemented with Richardson Extrapolation. This approach is highly scalable and suitable for systems with arbitrary shapes. We show spatial and temporal convergence and illustrate scaling on up to 2048 cores. Finally, we illustrate confinement effects for selected complex geometries. This has implications for materials design for nanoscale applications where dimensions are such that equilibrium morphologies dramatically differ from the bulk phases.

A finite element approach to self-consistent field theory calculations of multiblock polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackerman, David M.; Delaney, Kris; Fredrickson, Glenn H.

Self-consistent field theory (SCFT) has proven to be a powerful tool for modeling equilibrium microstructures of soft materials, particularly for multiblock polymers. A very successful approach to numerically solving the SCFT set of equations is based on using a spectral approach. While widely successful, this approach has limitations especially in the context of current technologically relevant applications. These limitations include non-trivial approaches for modeling complex geometries, difficulties in extending to non-periodic domains, as well as non-trivial extensions for spatial adaptivity. As a viable alternative to spectral schemes, we develop a finite element formulation of the SCFT paradigm for calculating equilibriummore » polymer morphologies. We discuss the formulation and address implementation challenges that ensure accuracy and efficiency. We explore higher order chain contour steppers that are efficiently implemented with Richardson Extrapolation. This approach is highly scalable and suitable for systems with arbitrary shapes. We show spatial and temporal convergence and illustrate scaling on up to 2048 cores. Finally, we illustrate confinement effects for selected complex geometries. This has implications for materials design for nanoscale applications where dimensions are such that equilibrium morphologies dramatically differ from the bulk phases.« less

Test of the ``radical-like polymerization'' scheme in molecular dynamics on the behavior of polymers under shock loading

NASA Astrophysics Data System (ADS)

Lemarchand, Claire; Bousquet, David; Schnell, Benoît; Pineau, Nicolas

2017-06-01

The behavior of polymer melts under shock loading is a question attracting more and more attention because of applications such as polymer-bonded explosives, light-weight armor and civilian protective equipment, like sports and car equipment. Molecular dynamics (MD) simulations are a very good tool to characterize the microscopic response of the polymer to a shock wave. To do so, the initial configuration of the polymer melt needs to be realistic. The ``radical-like polymerization'' scheme is a method to obtain near equilibrium configurations of a melt of long polymer chains. It consists in adding one neighboring monomer at a time to each growing chain. Between each polymerization step an MD run is performed to relax the new configuration. We test how details of our implementation of the ``radical-like polymerization'' scheme can impact or not Hugoniot curves and changes of chain configuration under shock. We compare our results to other simulation and experimental results on reference polymers.

Self-assembled morphologies of an amphiphilic Y-shaped weak polyelectrolyte in a thin film.

PubMed

Mu, Dan; Li, Jian-Quan; Feng, Sheng-Yu

2017-11-29

Different from the self-assembly of neutral polymers, polyelectrolytes self-assemble into smaller aggregates with a more loosely assembled structure, which results from the repulsive forces acting between similar electrical compositions with the introduction of ions. The Y-shaped weak polyelectrolytes self-assemble into a core-shell type cylindrical structure with a hexagonal arrangement in a thin film, whose thickness is smaller than the gyration radius of the polymer chain. The corresponding formation mechanism consists of enrichment of the same components, adjustment of the shape of the aggregate, and the subsequent separation into individual aggregates. With the increase in the thickness of the thin film until it exceeds the gyration radius of the polymer chain, combined with the greater freedom of movement along the direction of thin film thickness, the self-assembled structure changes into a micellar structure. Under confinement, the repulsive force to the polymeric components is weakened by the repulsive forces among polyelectrolyte components with like charges, and this helps in generating aggregates with more uniform size and density distribution. In particular, when the repulsive force between the walls and the core forming components is greater than that between the walls and the shell forming components, such asymmetric confinement produces a crossed-cylindrical structure with nearly perpendicular arrangement of two cylinder arrays. Similarly, a novel three-crossed cylinder morphology is self-assembled upon removal of confinement.

Elasticity Dominated Surface Segregation of Small Molecules in Polymer Mixtures

NASA Astrophysics Data System (ADS)

Krawczyk, Jarosław; Croce, Salvatore; McLeish, T. C. B.; Chakrabarti, Buddhapriya

2016-05-01

We study the phenomenon of migration of the small molecular weight component of a binary polymer mixture to the free surface using mean field and self-consistent field theories. By proposing a free energy functional that incorporates polymer-matrix elasticity explicitly, we compute the migrant volume fraction and show that it decreases significantly as the sample rigidity is increased. A wetting transition, observed for high values of the miscibility parameter can be prevented by increasing the matrix rigidity. Estimated values of the bulk modulus suggest that the effect should be observable experimentally for rubberlike materials. This provides a simple way of controlling surface migration in polymer mixtures and can play an important role in industrial formulations, where surface migration often leads to decreased product functionality.

Spatiotemporal evolution of hairpin eddies, Reynolds stress, and polymer torque in polymer drag-reduced turbulent channel flows.

PubMed

Kim, Kyoungyoun; Sureshkumar, Radhakrishna

2013-06-01

To study the influence of dynamic interactions between turbulent vortical structures and polymer stress on turbulent friction drag reduction, a series of simulations of channel flow is performed. We obtain self-consistent evolution of an initial eddy in the presence of polymer stresses by utilizing the finitely extensible nonlinear elastic-Peterlin (FENE-P) model. The initial eddy is extracted by the conditional averages for the second quadrant event from fully turbulent Newtonian flow, and the initial polymer conformation fields are given by the solutions of the FENE-P model equations corresponding to the mean shear flow in the Newtonian case. At a relatively low Weissenberg number We(τ) (=50), defined as the ratio of the polymer relaxation time to the wall time scale, the generation of new vortices is inhibited by polymer-induced countertorques. Thus fewer vortices are generated in the buffer layer. However, the head of the primary hairpin is unaffected by the polymer stress. At larger We(τ) values (≥100), the hairpin head becomes weaker and vortex autogeneration and Reynolds stress growth are almost entirely suppressed. The temporal evolution of the vortex strength and polymer torque magnitude reveals that polymer extension by the vortical motion results in a polymer torque that increases in magnitude with time until a maximum value is reached over a time scale comparable to the polymer relaxation time. The polymer torque retards the vortical motion and Reynolds stress production, which in turn weakens flow-induced chain extension and torque itself. An analysis of the vortex time scales reveals that with increasing We(τ), vortical motions associated with a broader range of time scales are affected by the polymer stress. This is qualitatively consistent with Lumley's time criterion for the onset of drag reduction.

Impact of Backbone Tether Length and Structure on the Electrochemical Performance of Viologen Redox Active Polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burgess, Mark; Chénard, Etienne; Hernández-Burgos, Kenneth

The design of chemically stable and electrochemically reversible redox active polymers (RAPs) is of great interest for energy storage technologies. Particularly, RAPs are new players for flow batteries relying on a size-exclusion based mechanism of electrolyte separation, but few studies have provided detailed molecular understanding of redox polymers in solution. Here, we use a systematic molecular design approach to investigate the impact of linker and redox-pendant electronic interactions on the performance of viologen RAPs. We used scanning electrochemical microscopy, cyclic voltammetry, bulk electrolysis, temperature-dependent absorbance, and spectroelectrochemistry to study the redox properties, charge transfer kinetics, and self-exchange of electrons throughmore » redox active dimers and their equivalent polymers. Stark contrast was observed between the electrochemical properties of viologen dimers and their corresponding polymers. Electron self-exchange kinetics in redox active dimers that only differ by their tether length and rigidity influences their charge transfer properties. Predictions from the Marcus Hush theory were consistent with observations in redox active dimers, but they failed to fully capture the behavior of macromolecular systems. For example, polymer bound viologen pendants, if too close in proximity, do not retain chemical reversibility. In contrast to polymer films, small modifications to the backbone structure decisively impact the bulk electrolysis of polymer solutions. This first comprehensive study highlights the careful balance between electronic interactions and backbone rigidity required to design RAPs with superior electrochemical performance.« less

Self-lubricating polymer composites and polymer transfer film lubrication for space applications

NASA Technical Reports Server (NTRS)

Fusaro, Robert L.

1990-01-01

The use of self-lubricating polymers and polymer composites in space is somewhat limited today. In general, they are only used when other methods are inadequate. There is potential, however, for these materials to make a significant impact on future space missions if properly utilized. Some of the different polymers and fillers used to make self-lubricating composites are surveyed. The mechanisms of composite lubrication and wear, the theory behind transfer film lubricating mechanisms, and some factors which affect polymer composite wear and transfer are examined. In addition, some of the current space tribology application areas for self-lubricating polymer composites and polymer transfer are mentioned.

Carbon Dots as Fillers Inducing Healing/Self-Healing and Anticorrosion Properties in Polymers.

PubMed

Zhu, Cheng; Fu, Yijun; Liu, Changan; Liu, Yang; Hu, Lulu; Liu, Juan; Bello, Igor; Li, Hao; Liu, Naiyun; Guo, Sijie; Huang, Hui; Lifshitz, Yeshayahu; Lee, Shuit-Tong; Kang, Zhenhui

2017-08-01

Self-healing is the way by which nature repairs damage and prolongs the life of bio entities. A variety of practical applications require self-healing materials in general and self-healing polymers in particular. Different (complex) methods provide the rebonding of broken bonds, suppressing crack, or local damage propagation. Here, a simple, versatile, and cost-effective methodology is reported for initiating healing in bulk polymers and self-healing and anticorrosion properties in polymer coatings: introduction of carbon dots (CDs), 5 nm sized carbon nanocrystallites, into the polymer matrix forming a composite. The CDs are blended into polymethacrylate, polyurethane, and other common polymers. The healing/self-healing process is initiated by interfacial bonding (covalent, hydrogen, and van der Waals bonding) between the CDs and the polymer matrix and can be optimized by modifying the functional groups which terminate the CDs. The healing properties of the bulk polymer-CD composites are evaluated by comparing the tensile strength of pristine (bulk and coatings) composites to those of fractured composites that are healed and by following the self-healing of scratches intentionally introduced to polymer-CD composite coatings. The composite coatings not only possess self-healing properties but also have superior anticorrosion properties compared to those of the pure polymer coatings. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular dynamics simulation of diffusion of gases in a carbon-nanotube-polymer composite

NASA Astrophysics Data System (ADS)

Lim, Seong Y.; Sahimi, Muhammad; Tsotsis, Theodore T.; Kim, Nayong

2007-07-01

Extensive molecular dynamics (MD) simulations were carried out to compute the solubilities and self-diffusivities of CO2 and CH4 in amorphous polyetherimide (PEI) and mixed-matrix PEI generated by inserting single-walled carbon nanotubes into the polymer. Atomistic models of PEI and its composites were generated using energy minimizations, MD simulations, and the polymer-consistent force field. Two types of polymer composite were generated by inserting (7,0) and (12,0) zigzag carbon nanotubes into the PEI structure. The morphologies of PEI and its composites were characterized by their densities, radial distribution functions, and the accessible free volumes, which were computed with probe molecules of different sizes. The distributions of the cavity volumes were computed using the Voronoi tessellation method. The computed self-diffusivities of the gases in the polymer composites are much larger than those in pure PEI. We find, however, that the increase is not due to diffusion of the gases through the nanotubes which have smooth energy surfaces and, therefore, provide fast transport paths. Instead, the MD simulations indicate a squeezing effect of the nanotubes on the polymer matrix that changes the composite polymers’ free-volume distributions and makes them more sharply peaked. The presence of nanotubes also creates several cavities with large volumes that give rise to larger diffusivities in the polymer composites. This effect is due to the repulsive interactions between the polymer and the nanotubes. The solubilities of the gases in the polymer composites are also larger than those in pure PEI, hence indicating larger gas permeabilities for mixed-matrix PEI than PEI itself.

[Self-judgment of personality traits and cognitive dimensions of the self].

PubMed

Horiuchi, T

1996-12-01

When people make a judgment as to whether a trait describes themselves or not, cognitive structure about the self must play an important role. Cognitive dimensions are a characteristic of such cognitive structure. The present study examined whether a self-referent information processing was mediated by cognitive dimensions of the self. For the purpose, Klein, Loftus, and Burton's task facilitation paradigm (1989) was adapted, which consisted of performing in succession two tasks, initial and target, for each trait adjective used. Experiment 1, which examined the evaluative dimension, showed that an evaluative processing in the target task was facilitated when the initial task was self-referent. Experiment 2, which examined six dimensions, showed that processing of the relevant dimension in the target task was facilitated when the initial task was self-referent. These results suggest that a self-referent information processing is mediated by cognitive dimensions of the self.

Reversible Shape Memory Polymers and Composites: Synthesis, Modeling and Design

DTIC Science & Technology

2013-03-01

Polymer; and (iii) Development of a Shape Memory Assisted Self - Healing Polymer. Page 3 of 19 Mather/FA9550-09-1-0195 IV(i) Modeling and Model...0195 IV(iii) Development of a Shape Memory Assisted Self - Healing Polymer Erika D. Rodriguez, X. Luo, and P.T. Mather, “Linear and Crosslinked...Poly (ε- Caprolactone) Polymers for Shape Memory Assisted Self - Healing (SMASH),” ACS Applied Materials and Interfaces 3 152-161 (2011). Self

Examining Associations between Narcissism, Behavior Problems, and Anxiety in Non-Referred Adolescents

ERIC Educational Resources Information Center

Lau, Katherine S. L.; Marsee, Monica A.; Kunimatsu, Melissa M.; Fassnacht, Gregory M.

2011-01-01

The present study examined associations between narcissism (total, adaptive, and maladaptive), self-esteem, and externalizing and internalizing problems in 157 non-referred adolescents (aged 14 to 18). Consistent with previous research, narcissism was positively associated with self-reported delinquency, overt aggression, and relational…

Fluorinated arene, imide and unsaturated pyrrolidinone based donor acceptor conjugated polymers: Synthesis, structure-property and device studies

NASA Astrophysics Data System (ADS)

Liyanage, Arawwawala Don Thilanga

After the discovery of doped polyacetylene, organic semiconductor materials are widely studied as high impending active components in consumer electronics. They have received substantial consideration due to their potential for structural tailoring, low cost, large area and mechanically flexible alternatives to common inorganic semiconductors. To acquire maximum use of these materials, it is essential to get a strong idea about their chemical and physical nature. Material chemist has an enormous role to play in this novel area, including development of efficient synthetic methodologies and control the molecular self-assembly and (opto)-electronic properties. The body of this thesis mainly focuses on the substituent effects: how different substituents affect the (opto)-electronic properties of the donor-acceptor (D-A) conjugated polymers. The main priority goes to understand, how different alkyl substituent effect to the polymer solubility, crystallinity, thermal properties (e.g.: glass transition temperature) and morphological order. Three classes of D-A systems were extensively studied in this work. The second chapter mainly focuses on the synthesis and structure-property study of fluorinated arene (TFB) base polymers. Here we used commercially available 1,4-dibromo-2,3,5,6-tetrafluorobenzene (TFB) as the acceptor material and prepare several polymers using 3,3'-dialkyl(3,3'-R2T2) or 3,3'-dialkoxy bithiophene (3,3'-RO2T2) units as electron donors. A detail study was done using 3,3'-bithiophene donor units incorporating branched alkoxy-functionalities by systematic variation of branching position and chain length. The study allowed disentangling the branching effects on (i) aggregation tendency, intermolecular arrangement, (iii) solid state optical energy gaps, and (iv) electronic properties in an overall consistent picture, which might guide future polymer synthesis towards optimized materials for opto-electronic applications. The third chapter mainly focused on the structure-property study of imide functionalized D-A polymers. Here we used thiophene-imide (TPD) as the acceptor moiety and prepare several D-A polymers by varying the donor units. When selecting the donor units, more priority goes to the fused ring systems. One main reason to use imide functionality is due to the, open position of the imide nitrogen, which provides an attaching position to alkyl substituent. Through this we can easily manipulate solubility and solid state packing arrangement. Also these imide acceptors have low-lying LUMOs due to their electron deficient nature and this will allow tuning the optical energy gap by careful choice of donor materials with different electron donating ability. The fourth chapter mainly contribute to the synthesis and structure property study of a completely novel electron acceptor moiety consist of a unsaturated pyrrolidinone unit known as Pechmann dye (PD) core. Pechmann dyes are closely related to the Indigo family. This can refer as 3-butenolide dimer connected via an alkene bridge, containing a benzene ring at the 5 and 5' positions of the lactone rings. We have prepared several D-A polymers using this PD system with benzodithiophene (BDT) as the donor unit. Different to common D-A polymers the HOMO and LUMO of the PD acceptor moiety are energetically located within the gap of the BDT, so that the electronic and optical properties (HOMO-LUMO transition) are dictated by the PD properties. The promising electronic properties, band gaps, high absorption coefficients and broad absorption suggest this new D-A polymers as an interesting donor material for organic solar cell (OSC) applications. KEY WORDS: Organic semiconductor materials, Self assembly, (opto)-electronic properties, Donor-Acceptor conjugated polymers, Fluorinated arene, 3,3'-bithiophene donors, Thiophene-imide (TPD), Pechmann dye, benzodithiophene, organic solar cell.

Mechanically Strong, Polymer Cross-linked Aerogels (X-Aerogels)

NASA Technical Reports Server (NTRS)

Leventis, Nicholas

2006-01-01

Aerogels comprise a class of low-density, high porous solid objects consisting of dimensionally quasi-stable self-supported three-dimensional assemblies of nanoparticles. Aerogels are pursued because of properties above and beyond those of the individual nanoparticles, including low thermal conductivity, low dielectric constant and high acoustic impedance. Possible applications include thermal and vibration insulation, dielectrics for fast electronics, and hosting of functional guests for a wide variety of optical, chemical and electronic applications. Aerogels, however, are extremely fragile materials, hence they have found only limited application in some very specialized environments, for example as Cerenkov radiation detectors in certain types of nuclear reactors, aboard spacecraft as collectors of hypervelocity particles (refer to NASA's Stardust program) and as thermal insulators on planetary vehicles on Mars (refer to Sojourner Rover in 1997 and Spirit and Opportunity in 2004). Along these lines, the X-Aerogel is a new NASA-developed strong lightweight material that has resolved the fragility problem of traditional (native) aerogels. X-Aerogels are made by applying a conformal polymer coating on the surfaces of the skeletal nanoparticles of native aerogels (see Scanning Electron Micrographs). Since the relative amounts of the polymeric crosslinker and the backbone are comparable, X-Aerogels can be viewed either as aerogels modified by the templated accumulation of polymer on the skeletal nanoparticles, or as nanoporous polymers made by remplated casting of polymer on a nanostructured framework. The most striking feature of X-Aerogels is that for a nominal 3-fold increase in density (still a ultralighweight material), the mechanical strength can be up to 300 times higher than the strength of the underlying native aerogel. Thus, X-Aerogels combine a multiple of the specific compressive strength of steel, with the the thermal conductivity of styrofoam. X-Aerogels have been demonstrated with several polymers such as polyurethanes/polyureas, epoxies and polyolefins, while crosslinking of approximately 35 different oxide aerogels yields a range of dimensionally stable, porous lightweight materials with unique combinations of structural, magnetic and optical properties. The main theme in materials development for space exploration is multifunction. For example, use of one material for thermal insulation/structural component will free weight for useful payload. In that regard, X-aerogels are evaluated at NASA for cryogenic fuel storage tanks and for spacesuits. Along the same lines, major impact fro X-Aerogels is also expected in commercial applications for thermal/acoustic insulation, in catalytic reformers and converters, in filtration membranes and membranes for fuel cells, as platforms for optical, electrical and magnetic sensors, and as lightweight structural component for aircraft and satellites.

Simple framework for understanding the universality of the maximum drag reduction asymptote in turbulent flow of polymer solutions

NASA Astrophysics Data System (ADS)

Li, Chang-Feng; Sureshkumar, Radhakrishna; Khomami, Bamin

2015-10-01

Self-consistent direct numerical simulations of turbulent channel flows of dilute polymer solutions exhibiting friction drag reduction (DR) show that an effective Deborah number defined as the ratio of polymer relaxation time to the time scale of fluctuations in the vorticity in the mean flow direction remains O (1) from the onset of DR to the maximum drag reduction (MDR) asymptote. However, the ratio of the convective time scale associated with streamwise vorticity fluctuations to the vortex rotation time decreases with increasing DR, and the maximum drag reduction asymptote is achieved when these two time scales become nearly equal. Based on these observations, a simple framework is proposed that adequately describes the influence of polymer additives on the extent of DR from the onset of DR to MDR as well as the universality of the MDR in wall-bounded turbulent flows with polymer additives.

Simple framework for understanding the universality of the maximum drag reduction asymptote in turbulent flow of polymer solutions.

PubMed

Li, Chang-Feng; Sureshkumar, Radhakrishna; Khomami, Bamin

2015-10-01

Self-consistent direct numerical simulations of turbulent channel flows of dilute polymer solutions exhibiting friction drag reduction (DR) show that an effective Deborah number defined as the ratio of polymer relaxation time to the time scale of fluctuations in the vorticity in the mean flow direction remains O(1) from the onset of DR to the maximum drag reduction (MDR) asymptote. However, the ratio of the convective time scale associated with streamwise vorticity fluctuations to the vortex rotation time decreases with increasing DR, and the maximum drag reduction asymptote is achieved when these two time scales become nearly equal. Based on these observations, a simple framework is proposed that adequately describes the influence of polymer additives on the extent of DR from the onset of DR to MDR as well as the universality of the MDR in wall-bounded turbulent flows with polymer additives.

Slippery self-lubricating polymer surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aizenberg, Joanna; Aizenberg, Michael; Cui, Jiaxi

The present disclosure describes a strategy to create self-healing, slippery self-lubricating polymers. Lubricating liquids with affinities to polymers can be utilized to get absorbed within the polymer and form a lubricant layer (of the lubricating liquid) on the polymer. The lubricant layer can repel a wide range of materials, including simple and complex fluids (water, hydrocarbons, crude oil and bodily fluids), restore liquid-repellency after physical damage, and resist ice, microorganisms and insects adhesion. Some exemplary applications where self-lubricating polymers will be useful include energy-efficient, friction-reduction fluid handling and transportation, medical devices, anti-icing, optical sensing, and as self-cleaning, and anti-fouling materialsmore » operating in extreme environments.« less

Generalizing the correlated chromophore domain model of reversible photodegradation to include the effects of an applied electric field

NASA Astrophysics Data System (ADS)

Anderson, Benjamin; Kuzyk, Mark G.

2014-03-01

All observations of photodegradation and self-healing follow the predictions of the correlated chromophore domain model [Ramini et al., Polym. Chem. 4, 4948 (2013), 10.1039/c3py00263b]. In the present work, we generalize the domain model to describe the effects of an electric field by including induced dipole interactions between molecules in a domain by means of a self-consistent field approach. This electric field correction is added to the statistical mechanical model to calculate the distribution of domains that are central to healing. Also included in the model are the dynamics due to the formation of an irreversibly damaged species, which we propose involves damage to the polymer mediated through energy transfer from a dopant molecule after absorbing a photon. As in previous studies, the model with one-dimensional domains best explains all experimental data of the population as a function of time, temperature, intensity, concentration, and now applied electric field. Though the precise nature of a domain is yet to be determined, the fact that only one-dimensional domain models are consistent with observations suggests that they might be made of correlated dye molecules along polymer chains. Furthermore, the voltage-dependent measurements suggest that the largest polarizability axis of the molecules are oriented perpendicular to the chain.

Effect of molecular properties on the performance of polymer light-emitting diodes

NASA Astrophysics Data System (ADS)

Ramos, Marta M. D.; Almeida, A. M.; Correia, Helena M. G.; Ribeiro, R. Mendes; Stoneham, A. M.

2004-11-01

The performance of a single layer polymer light-emitting diode depends on several interdependent factors, although recombination between electrons and holes within the polymer layer is believed to play an important role. Our aim is to carry out computer experiments in which bipolar charge carriers are injected in polymer networks made of poly(p-phenylene vinylene) chains randomly oriented. In these simulations, we follow the charge evolution in time from some initial state to the steady state. The intra-molecular properties of the polymer molecules obtained from self-consistent quantum molecular dynamics calculations are used in the mesoscopic model. The purpose of the present work is to clarify the effects of intra-molecular charge mobility and energy disorder on recombination efficiency. In particular, we find that charge mobility along the polymer chains has a serious influence on recombination within the polymer layer. Our results also show that energy disorder due to differences in ionization potential and electron affinity of neighbouring molecules affects mainly recombinations that occur near the electrodes at polymer chains parallel to them.

Comblike poly(ethylene oxide)/hydrophobic C6 branched chitosan surfactant polymers as anti-infection surface modifying agents.

PubMed

Mai-ngam, Katanchalee

2006-05-01

A series of structurally well-defined poly(ethylene oxide)/hydrophobic C6 branched chitosan surfactant polymers that undergo surface induced self assembly on hydrophobic biomaterial surfaces were synthesized and characterized. The surfactant polymers consist of low molecular weight (Mw) chitosan backbone with hydrophilic poly(ethylene oxide) (PEO) and hydrophobic hexyl pendant groups. Chitosan was depolymerized by nitrous acid deaminative cleavage. Hexanal and aldehyde-terminated PEO chains were simultaneously attached to low Mw chitosan hydrochloride via reductive amination. The surfactant polymers were prepared with various ratios of the two side chains. The molecular composition of the surfactant polymers was determined by FT-IR and 1H NMR. Surface active properties at the air-water interface were determined by Langmuir film balance measurements. The surfactant polymers with PEO/hexyl ratios of 1:3.0 and 1:14.4 were used as surface modifying agents to investigate their anti-infection properties. E. coli adhesion on Silastic surface was decreased significantly by the surfactant polymer with PEO/hexyl 1:3.0. Surface growth of adherent E. coli was effectively suppressed by both tested surfactant polymers.

Spinodal assisted growing dynamics of critical nucleus in polymer blends

NASA Astrophysics Data System (ADS)

Zhang, Xinghua; Qi, Shuanhu; Yan, Dadong

2012-11-01

In metastable polymer blends, nonclassical critical nucleus is not a drop of stable phase in core wrapped with a sharp interface, but a diffuse structure depending on the metastability. Thus, forming a critical nucleus does not mean the birth of a new phase. In the present work, the nonclassical growing dynamics of the critical nucleus is addressed in the metastable polymer blends by incorporating self-consistent field theory and external potential dynamics theory, which leads to an intuitionistic description for the scattering experiments. The results suggest that the growth of nonclassical critical nucleus is controlled by the spinodal-decomposition which happens in the region surrounding the nucleus. This leads to forming the shell structures around the nucleus.

Poly(ethylene oxide) surfactant polymers.

PubMed

Vacheethasanee, Katanchalee; Wang, Shuwu; Qiu, Yongxing; Marchant, Roger E

2004-01-01

We report on a series of structurally well-defined surfactant polymers that undergo surface-induced self-assembly on hydrophobic biomaterial surfaces. The surfactant polymers consist of a poly(vinyl amine) backbone with poly(ethylene oxide) and hexanal pendant groups. The poly(vinyl amine) (PVAm) was synthesized by hydrolysis of poly(N-vinyl formamide) following free radical polymerization of N-vinyl formamide. Hexanal and aldehyde-terminated poly(ethylene oxide) (PEO) were simultaneously attached to PVAm via reductive amination. Surfactant polymers with different PEO:hexanal ratios and hydrophilic/hydrophobic balances were prepared, and characterized by FT-IR, 1H-NMR and XPS spectroscopies. Surface active properties at the air/water interface were determined by surface tension measurements. Surface activity at a solid surface/water interface was demonstrated by atomic force microscopy, showing epitaxially molecular alignment for surfactant polymers adsorbed on highly oriented pyrolytic graphite. The surfactant polymers described in this report can be adapted for simple non-covalent surface modification of biomaterials and hydrophobic surfaces to provide highly hydrated interfaces.

Molecular self assembly of mixed comb-like dextran surfactant polymers for SPR virus detection.

PubMed

Mai-Ngam, Katanchalee; Kiatpathomchai, Wansika; Arunrut, Narong; Sansatsadeekul, Jitlada

2014-11-04

The synthesis of two comb-like dextran surfactant polymers, that are different in their dextran molecular weight (MW) distribution and the presence of carboxylic groups, and their characterization are reported. A bimodal carboxylic dextran surfactant polymer consists of poly(vinyl amine) (PVAm) backbone with carboxyl higher MW dextran, non-functionalized lower MW dextran and hydrophobic hexyl branches; while a monomodal dextran surfactant polymer is PVAm grafted with non-functionalized lower MW dextran and hexyl branches. Layer formation of non-covalently attached dextran chains with bimodal MW distributions on a surface plasmon resonance (SPR) chip was investigated from the perspective of mixed physisorption of the bimodal and monomodal surfactant polymers. Separation distances between the carboxylic longer dextran side chains within the bimodal surfactant polymer and between the whole bimodal surfactant molecules on the chip surface could be well-controlled. SPR analysis of shrimp yellow head virus using our mixed surfactant chips showed dependence on synergetic adjustment of these separation distances. Copyright © 2014 Elsevier Ltd. All rights reserved.

Preparation of candidate reference materials for the determination of phosphorus containing flame retardants in styrene-based polymers.

PubMed

Roth, Thomas; Urpi Bertran, Raquel; Latza, Andreas; Andörfer-Lang, Katrin; Hügelschäffer, Claudia; Pöhlein, Manfred; Puchta, Ralph; Placht, Christian; Maid, Harald; Bauer, Walter; van Eldik, Rudi

2015-04-01

Candidate reference materials (RM) for the analysis of phosphorus-based flame retardants in styrene-based polymers were prepared using a self-made mini-extruder. Due to legal requirements of the current restriction for the use of certain hazardous substances in electrical and electronic equipment, focus now is placed on phosphorus-based flame retardants instead of the brominated kind. Newly developed analytical methods for the first-mentioned substances also require RMs similar to industrial samples for validation and verification purposes. Hence, the prepared candidate RMs contained resorcinol-bis-(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), triphenyl phosphate and triphenyl phosphine oxide as phosphorus-based flame retardants. Blends of polycarbonate and acrylonitrile-co-butadiene-co-styrene as well as blends of high-impact polystyrene and polyphenylene oxide were chosen as carrier polymers. Homogeneity and thermal stability of the candidate RMs were investigated. Results showed that the candidate RMs were comparable to the available industrial materials. Measurements by ICP/OES, FTIR and NMR confirmed the expected concentrations of the flame retardants and proved that analyte loss and degradation, respectively, was below the uncertainty of measurement during the extrusion process. Thus, the candidate RMs were found to be suitable for laboratory use.

Predicting the Effective Elastic Properties of Polymer Bonded Explosives based on Micromechanical Methods

NASA Astrophysics Data System (ADS)

Wang, Jingcheng; Luo, Jingrun

2018-04-01

Due to the extremely high particle volume fraction (greater than 85%) and damage feature of polymer bonded explosives (PBXs), conventional micromechanical methods lead to inaccurate estimates on their effective elastic properties. According to their manufacture characteristics, a multistep approach based on micromechanical methods is proposed. PBXs are treated as pseudo poly-crystal materials consisting of equivalent composite particles (explosive crystals with binder coating), rather than two-phase composites composed of explosive particles and binder matrix. Moduli of composite spheres are obtained by generalized self-consistent method first, and the self-consistent method is modified to calculate the effective moduli of PBX. Defects and particle size distribution are considered by Mori-Tanaka method. Results show that when the multistep approach is applied to PBX 9501, estimates are far more accurate than the conventional micromechanical results. The bulk modulus is 5.75% higher, and shear modulus is 5.78% lower than the experimental values. Further analyses discover that while particle volume fraction and the binder's property have significant influences on the effective moduli of PBX, the moduli of particles present minor influences. Investigation of another particle size distribution indicates that the use of more fine particles will enhance the effective moduli of PBX.

Nanoporous polymer electrolyte

DOEpatents

Elliott, Brian [Wheat Ridge, CO; Nguyen, Vinh [Wheat Ridge, CO

2012-04-24

A nanoporous polymer electrolyte and methods for making the polymer electrolyte are disclosed. The polymer electrolyte comprises a crosslinked self-assembly of a polymerizable salt surfactant, wherein the crosslinked self-assembly includes nanopores and wherein the crosslinked self-assembly has a conductivity of at least 1.0.times.10.sup.-6 S/cm at 25.degree. C. The method of making a polymer electrolyte comprises providing a polymerizable salt surfactant. The method further comprises crosslinking the polymerizable salt surfactant to form a nanoporous polymer electrolyte.

Finite-size and asymptotic behaviors of the gyration radius of knotted cylindrical self-avoiding polygons.

PubMed

Shimamura, Miyuki K; Deguchi, Tetsuo

2002-05-01

Several nontrivial properties are shown for the mean-square radius of gyration R2(K) of ring polymers with a fixed knot type K. Through computer simulation, we discuss both finite size and asymptotic behaviors of the gyration radius under the topological constraint for self-avoiding polygons consisting of N cylindrical segments with radius r. We find that the average size of ring polymers with the knot K can be much larger than that of no topological constraint. The effective expansion due to the topological constraint depends strongly on the parameter r that is related to the excluded volume. The topological expansion is particularly significant for the small r case, where the simulation result is associated with that of random polygons with the knot K.

Application of encapsulated superabsorbent polymers in cementitious materials for stimulated autogenous healing

NASA Astrophysics Data System (ADS)

Pelto, Jani; Leivo, Markku; Gruyaert, Elke; Debbaut, Brenda; Snoeck, Didier; De Belie, Nele

2017-10-01

Superabsorbent polymers have shown potential for use in mortar and concrete as self-healing agents. The main drawback is, however, that these superabsorbent polymers also absorb mixing water during the preparation and casting of mortar or concrete, leading to a loss in workability. To avoid the absorption of mixing water, superabsorbent polymers were coated using a fluid bed spraying process. The barrier coating consisted of three successive coating layers: polyvinylbutyral as primer/wetting layer, cyclo-olefin copolymer as a barrier layer and a sol-gel derived zirconium-silicon oxide as an adhesion-promoting topcoat layer. The coated SAPs were characterized, and their swelling determined to quantify the delay in uptake of water and Ca(OH)2 solution. The last was considered as the most important, as the SAPs will finally be applied in mortar or concrete having a pore solution with high pH. The results showed that swelling could be delayed to a large extent, but for a short time. Results showed that the self-sealing efficiency of mortars was not affected by coating the SAPs. Moreover, due to the reduced uptake of mixing water, the strength reduction, noticed when uncoated SAPs were added to the mortar, could partly be compensated.

Highly dynamic biodegradable micelles capable of lysing Gram-positive and Gram-negative bacterial membrane.

PubMed

Qiao, Yuan; Yang, Chuan; Coady, Daniel J; Ong, Zhan Yuin; Hedrick, James L; Yang, Yi-Yan

2012-02-01

The development of biodegradable antimicrobial polymers adds to the toolbox of attractive antimicrobial agents against antibiotic-resistant microbes. To this end, the potential of polycarbonate polymers as such materials were explored. A series of random polycarbonate polymers consisting of monomers MTC-OEt and MTC-CH(2)CH(3)Cl were designed and synthesized using metal-free organocatalytic ring-opening polymerization. Random polycarbonate polymers self-assembled in solution but appeared highly dynamic; such behaviors are desirable as ready disassembly of polymers at the microbial membrane facilitates membrane disruption. Their activities against clinically relevant Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (E.coli and Pseudomonas aeruginosa) revealed that the hydrophobic-hydrophilic composition balance in polymers are important to render antimicrobial potency. Scanning electron microscopy (SEM) studies indicated microbial cell surface damage after treatment with polymers, and confocal microscopy studies also showed entry of FITC-dextran dye in Escherichia coli as a result of membrane disruption. On the other hand, the polymers exhibited minimal toxicity against red blood cells in hemolysis tests. Therefore, these random polycarbonate polymers are promising antimicrobial agents against both Gram-positive and Gram-negative bacteria for various biomedical applications. Copyright © 2011 Elsevier Ltd. All rights reserved.

Nanostructural self-organization and dynamic adaptation of metal-polymer tribosystems

NASA Astrophysics Data System (ADS)

Mashkov, Yu. K.

2017-02-01

The results of investigating the effect of nanosize modifiers of a polymer matrix on the nanostructural self-organization of polymer composites and dynamic adaptation of metal-polymer tribosystems, which considerably affect the wear resistance of polymer composite materials, have been analyzed. It has been shown that the physicochemical nanostructural self-organization processes are developed in metal-polymer tribosystems with the formation of thermotropic liquid-crystal structures of the polymer matrix, followed by the transition of the system to the stationary state with a negative feedback that ensures dynamic adaptation of the tribosystem to given operating conditions.

Orbitals, Occupation Numbers, and Band Structure of Short One-Dimensional Cadmium Telluride Polymers.

PubMed

Valentine, Andrew J S; Talapin, Dmitri V; Mazziotti, David A

2017-04-27

Recent work found that soldering CdTe quantum dots together with a molecular CdTe polymer yielded field-effect transistors with much greater electron mobility than quantum dots alone. We present a computational study of the CdTe polymer using the active-space variational two-electron reduced density matrix (2-RDM) method. While analogous complete active-space self-consistent field (CASSCF) methods scale exponentially with the number of active orbitals, the active-space variational 2-RDM method exhibits polynomial scaling. A CASSCF calculation using the (48o,64e) active space studied in this paper requires 10 24 determinants and is therefore intractable, while the variational 2-RDM method in the same active space requires only 2.1 × 10 7 variables. Natural orbitals, natural-orbital occupations, charge gaps, and Mulliken charges are reported as a function of polymer length. The polymer, we find, is strongly correlated, despite possessing a simple sp 3 -hybridized bonding scheme. Calculations reveal the formation of a nearly saturated valence band as the polymer grows and a charge gap that decreases sharply with polymer length.

Surface-induced effects in fluctuation-based measurements of single-polymer elasticity: A direct probe of the radius of gyration

NASA Astrophysics Data System (ADS)

Innes-Gold, Sarah N.; Morgan, Ian L.; Saleh, Omar A.

2018-03-01

Single-molecule measurements of polymer elasticity are powerful, direct probes of both biomolecular structure and principles of polymer physics. Recent work has revealed low-force regimes in which biopolymer elasticity is understood through blob-based scaling models. However, the small tensions required to observe these regimes have the potential to create measurement biases, particularly due to the increased interactions of the polymer chain with tethering surfaces. Here, we examine one experimentally observed bias, in which fluctuation-based estimates of elasticity report an unexpectedly low chain compliance. We show that the effect is in good agreement with predictions based on quantifying the exclusion effect of the surface through an image-method calculation of available polymer configurations. The analysis indicates that the effect occurs at an external tension inversely proportional to the polymer's zero-tension radius of gyration. We exploit this to demonstrate a self-consistent scheme for estimating the radius of gyration of the tethered polymer. This is shown in measurements of both hyaluronic acid and poly(ethylene glycol) chains.

Statistical Mechanical Theory of Penetrant Diffusion in Polymer Melts and Glasses

NASA Astrophysics Data System (ADS)

Zhang, Rui; Schweizer, Kenneth

We generalize our force-level, self-consistent nonlinear Langevin equation theory of activated diffusion of a dilute spherical penetrant in hard sphere fluids to predict the long-time diffusivity of molecular penetrants in supercooled polymer liquids and non-aging glasses. Chemical complexity is treated using an a priori mapping to a temperature-dependent hard sphere mixture model where polymers are disconnected into effective spheres based on the Kuhn length as the relevant coarse graining scale. A key parameter for mobility is the penetrant to polymer segment diameter ratio, R. Our calculations agree well with experimental measurements for a wide range of temperatures, penetrant sizes (from gas molecules with R ~0.3 to aromatic molecules with R ~1) and diverse amorphous polymers, over 10 decades variation of penetrant diffusivity. Structural parameter transferability is good. We have also formulated a theory at finite penetrant loading for the coupled penetrant-polymer dynamics in chemically (nearly) matched mixtures (e.g., toluene-polystyrene) which captures well the increase of penetrant diffusivity and decrease of polymer matrix vitrification temperature with increasing loading.

A new approach to modeling the effective thermal conductivity of ceramics porous media using a generalized self-consistent method

NASA Astrophysics Data System (ADS)

Edrisi, Siroos; Bidhendi, Norollah Kasiri; Haghighi, Maryam

2017-01-01

Effective thermal conductivity of the porous media was modeled based on a self-consistent method. This model estimates the heat transfer between insulator surface and air cavities accurately. In this method, the pore size and shape, the temperature gradient and other thermodynamic properties of the fluid was taken into consideration. The results are validated by experimental data for fire bricks used in cracking furnaces at the olefin plant of Maroon petrochemical complexes well as data published for polyurethane foam (synthetic polymers) IPTM and IPM. The model predictions present a good agreement against experimental data with thermal conductivity deviating <1 %.

Stochastic entangled chain dynamics of dense polymer solutions.

PubMed

Kivotides, Demosthenes; Wilkin, S Louise; Theofanous, Theo G

2010-10-14

We propose an adjustable-parameter-free, entangled chain dynamics model of dense polymer solutions. The model includes the self-consistent dynamics of molecular chains and solvent by describing the former via coarse-grained polymer dynamics that incorporate hydrodynamic interaction effects, and the latter via the forced Stokes equation. Real chain elasticity is modeled via the inclusion of a Pincus regime in the polymer's force-extension curve. Excluded volume effects are taken into account via the combined action of coarse-grained intermolecular potentials and explicit geometric tracking of chain entanglements. We demonstrate that entanglements are responsible for a new (compared to phantom chain dynamics), slow relaxation mode whose characteristic time scale agrees very well with experiment. Similarly good agreement between theory and experiment is also obtained for the equilibrium chain size. We develop methods for the solution of the model in periodic flow domains and apply them to the computation of entangled polymer solutions in equilibrium. We show that the number of entanglements Π agrees well with the number of entanglements expected on the basis of tube theory, satisfactorily reproducing the latter's scaling of Π with the polymer volume fraction φ. Our model predicts diminishing chain size with concentration, thus vindicating Flory's suggestion of excluded volume effects screening in dense solutions. The predicted scaling of chain size with φ is consistent with the heuristic, Flory theory based value.

Development of self-healing polymers via amine-epoxy chemistry: I. Properties of healing agent carriers and the modelling of a two-part self-healing system

NASA Astrophysics Data System (ADS)

Zhang, He; Yang, Jinglei

2014-06-01

Two types of healing agent carriers (microcapsules containing epoxy solution, referred to as EP-capsules, and etched hollow glass bubbles (HGBs) loaded with amine solution, referred to as AM-HGBs) used in self-healing epoxy systems were prepared and characterized in this study. The core percentages were measured at about 80 wt% and 33 wt% for EP-capsules and AM-HGBs, respectively. The loaded amine in AM-HGB, after incorporation into the epoxy matrix, showed high stability at ambient temperature, but diffused out gradually during heat treatment at 80 °C. The amount and the mass ratio of the two released healants at the crack plane were correlated with the size, concentration, and core percentage of the healing agent carriers. A simplified cubic array model for randomly distributed healing agent carriers was adopted to depict the longest diffusion distance of the released healants, which is inversely proportional to the cubic root of the carrier concentration.

Integral equation theory study on the phase separation in star polymer nanocomposite melts.

PubMed

Zhao, Lei; Li, Yi-Gui; Zhong, Chongli

2007-10-21

The polymer reference interaction site model theory is used to investigate phase separation in star polymer nanocomposite melts. Two kinds of spinodal curves were obtained: classic fluid phase boundary for relatively low nanoparticle-monomer attraction strength and network phase boundary for relatively high nanoparticle-monomer attraction strength. The network phase boundaries are much more sensitive with nanoparticle-monomer attraction strength than the fluid phase boundaries. The interference among the arm number, arm length, and nanoparticle-monomer attraction strength was systematically investigated. When the arm lengths are short, the network phase boundary shows a marked shift toward less miscibility with increasing arm number. When the arm lengths are long enough, the network phase boundaries show opposite trends. There exists a crossover arm number value for star polymer nanocomposite melts, below which the network phase separation is consistent with that of chain polymer nanocomposite melts. However, the network phase separation shows qualitatively different behaviors when the arm number is larger than this value.

Influence of pectins on the solubility and the molar mass distribution of dehydrogenative polymers (DHPs, lignin model compounds).

PubMed

Cathala, B; Monties, B

2001-07-19

Dehydrogenation polymers (DHPs, lignin model compounds) were synthesized in the presence of increasing pectin concentrations using two different methods. The first method ('Zutropfverfahren', ZT) consists in the slow adding of monomers whereas in the second method ('Zulaufverfahren', ZL) all the reactants are added simultaneously. DHPs solubility increases with the pectin concentration in the ZT experiments and remains stable in the ZL experiments. Covalent bonds between pectin and DHP are formed during ZT polymerization resulting in lignin carbohydrate complex (LCC) which keeps the unbound DHPs in solution by the formation of aggregate or micelle-like structures. In contrast LCC are not formed during the ZL process which behave like the DHP reference. The ZT DHP molar masses increase observed is attributed to the reactivity of the high molar mass polymer solubilized by the LCC whereas ZL higher molar mass polymers are precipitated out of the solution and cannot react further.

Predicting Flory-Huggins χ from Simulations

NASA Astrophysics Data System (ADS)

Zhang, Wenlin; Gomez, Enrique D.; Milner, Scott T.

2017-07-01

We introduce a method, based on a novel thermodynamic integration scheme, to extract the Flory-Huggins χ parameter as small as 10-3k T for polymer blends from molecular dynamics (MD) simulations. We obtain χ for the archetypical coarse-grained model of nonpolar polymer blends: flexible bead-spring chains with different Lennard-Jones interactions between A and B monomers. Using these χ values and a lattice version of self-consistent field theory (SCFT), we predict the shape of planar interfaces for phase-separated binary blends. Our SCFT results agree with MD simulations, validating both the predicted χ values and our thermodynamic integration method. Combined with atomistic simulations, our method can be applied to predict χ for new polymers from their chemical structures.

Novel Diels-Alder based self-healing epoxies for aerospace composites

NASA Astrophysics Data System (ADS)

Coope, T. S.; Turkenburg, D. H.; Fischer, H. R.; Luterbacher, R.; van Bracht, H.; Bond, I. P.

2016-08-01

Epoxy resins containing Diels-Alder (DA) furan and maleimide moieties are presented with the capability to self-heal after exposure to an external heat source. A conventional epoxy amine system has been combined with furfuryl and maleimide functional groups in a two-step process, to avoid major side-reactions, and the concentration of a thermo-reversibly binding cross-linker was considered to balance thermoset and thermoplastic behaviours, and the subsequent self-healing performance. In the context of self-repair technologies an inbuilt ‘intrinsic’ self-healing system is deemed favourable as the healing agent can be placed in known ‘hot spot’ regions (i.e. skin-stringer run outs, ply drops and around drilled holes) where operational damage predominately occurs in load bearing aerospace structures. In this study, the mechanical and self-healing performance of furan functionalised epoxy resins containing varying amounts (10, 20, 30 or 40 pph) of bismaleimide were investigated using a bulk epoxy polymer tapered double cantilever beam test specimen geometry. Two forms, a thin film and a bulk material, were evaluated to account for future integration methods into fibre reinforced polymer (FRP) composites. The highest healing efficiency, with respect to the obtained initial load value, was observed from the 20 pph bulk material derivative. The polymers were successful in achieving consistent multiple (three) healing cycles when heated at 150 °C for 5 min. This novel investigated DA material exhibits favourable processing characteristics for FRP composites as preliminary studies have shown successful coextrution with reinforcing fibres to form free standing films and dry fibre impregnation.

Nanostructure of propylammonium nitrate in the presence of poly(ethylene oxide) and halide salts

NASA Astrophysics Data System (ADS)

Stefanovic, Ryan; Webber, Grant B.; Page, Alister J.

2018-05-01

Nanoscale structure of protic ionic liquids is critical to their utility as molecular electrochemical solvents since it determines the capacity to dissolve salts and polymers such as poly(ethylene oxide) (PEO). Here we use quantum chemical molecular dynamics simulations to investigate the impact of dissolved halide anions on the nanostructure of an archetypal nanostructured protic ionic liquid, propylammonium nitrate (PAN), and how this impacts the solvation of a model PEO polymer. At the molecular level, PAN is nanostructured, consisting of charged/polar and uncharged/nonpolar domains. The charged domain consists of the cation/anion charge groups, and is formed by their electrostatic interaction. This domain solvophobically excludes the propyl chains on the cation, which form a distinct, self-assembled nonpolar domain within the liquid. Our simulations demonstrate that the addition of Cl- and Br- anions to PAN disrupts the structure within the PAN charged domain due to competition between nitrate and halide anions for the ammonium charge centre. This disruption increases with halide concentration (up to 10 mol. %). However, at these concentrations, halide addition has little effect on the structure of the PAN nonpolar domain. Addition of PEO to pure PAN also disrupts the structure within the charged domain of the liquid due to hydrogen bonding between the charge groups and the terminal PEO hydroxyl groups. There is little other association between the PEO structure and the surrounding ionic liquid solvent, with strong PEO self-interaction yielding a compact, coiled polymer morphology. Halide addition results in greater association between the ionic liquid charge centres and the ethylene oxide components of the PEO structure, resulting in reduced conformational flexibility, compared to that observed in pure PAN. Similarly, PEO self-interactions increase in the presence of Cl- and Br- anions, compared to PAN, indicating that the addition of halide salts to PAN decreases its utility as a molecular solvent for polymers such as PEO.

The self-assembly of particles with isotropic interactions: Using DNA coated colloids to create designer nanomaterials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thompson, R. B.; Dion, S.; Konigslow, K. von

Self-consistent field theory equations are presented that are suitable for use as a coarse-grained model for DNA coated colloids, polymer-grafted nanoparticles and other systems with approximately isotropic interactions. The equations are generalized for arbitrary numbers of chemically distinct colloids. The advantages and limitations of such a coarse-grained approach for DNA coated colloids are discussed, as are similarities with block copolymer self-assembly. In particular, preliminary results for three species self-assembly are presented that parallel results from a two dimensional ABC triblock copolymer phase. The possibility of incorporating crystallization, dynamics, inverse statistical mechanics and multiscale modelling techniques are discussed.

Membranes with artificial free-volume for biofuel production

PubMed Central

Petzetakis, Nikos; Doherty, Cara M.; Thornton, Aaron W.; Chen, X. Chelsea; Cotanda, Pepa; Hill, Anita J.; Balsara, Nitash P.

2015-01-01

Free-volume of polymers governs transport of penetrants through polymeric films. Control over free-volume is thus important for the development of better membranes for a wide variety of applications such as gas separations, pharmaceutical purifications and energy storage. To date, methodologies used to create materials with different amounts of free-volume are based primarily on chemical synthesis of new polymers. Here we report a simple methodology for generating free-volume based on the self-assembly of polyethylene-b-polydimethylsiloxane-b-polyethylene triblock copolymers. We have used this method to fabricate a series of membranes with identical compositions but with different amounts of free-volume. We use the term artificial free-volume to refer to the additional free-volume created by self-assembly. The effect of artificial free-volume on selective transport through the membranes was tested using butanol/water and ethanol/water mixtures due to their importance in biofuel production. We found that the introduction of artificial free-volume improves both alcohol permeability and selectivity. PMID:26104672

Membranes with artificial free-volume for biofuel production

NASA Astrophysics Data System (ADS)

Petzetakis, Nikos; Doherty, Cara M.; Thornton, Aaron W.; Chen, X. Chelsea; Cotanda, Pepa; Hill, Anita J.; Balsara, Nitash P.

2015-06-01

Free-volume of polymers governs transport of penetrants through polymeric films. Control over free-volume is thus important for the development of better membranes for a wide variety of applications such as gas separations, pharmaceutical purifications and energy storage. To date, methodologies used to create materials with different amounts of free-volume are based primarily on chemical synthesis of new polymers. Here we report a simple methodology for generating free-volume based on the self-assembly of polyethylene-b-polydimethylsiloxane-b-polyethylene triblock copolymers. We have used this method to fabricate a series of membranes with identical compositions but with different amounts of free-volume. We use the term artificial free-volume to refer to the additional free-volume created by self-assembly. The effect of artificial free-volume on selective transport through the membranes was tested using butanol/water and ethanol/water mixtures due to their importance in biofuel production. We found that the introduction of artificial free-volume improves both alcohol permeability and selectivity.

Piezoelectric and mechanical properties of fatigue resistant, self-healing PZT-ionomer composites

NASA Astrophysics Data System (ADS)

James, N. K.; Lafont, U.; van der Zwaag, S.; Groen, W. A.

2014-05-01

Piezoelectric ceramic-polymer composites with 0-3 connectivity were fabricated using lead zirconium titanate (PZT) powder dispersed in an ionomer (Zn ionomer) and its reference ethylene methacrylic acid copolymer (EMAA) polymer matrix. The PZT-Zn ionomer and PZT-EMAA composites were prepared by melt extrusion followed by hot pressing. The effects of poling conditions such as temperature, time and electric field on the piezoelectric properties of the composites were investigated. The experimentally observed piezoelectric charge coefficient and dielectric constant of the composites were compared with theoretical models. The results show that PZT-Zn ionomer composites have better piezoelectric properties compared to PZT-EMAA composites. The static and fatigue properties of the composites were investigated. The PZT-Zn ionomer composites were found to have excellent fatigue resistance even at strain levels of 4%. Due to the self-healing capabilities of the ionomer matrix, the loss of piezoelectric properties after high strain tensile cyclic loading could be partially recovered by thermal healing.

Membranes with artificial free-volume for biofuel production

DOE PAGES

Petzetakis, Nikos; Doherty, Cara M.; Thornton, Aaron W.; ...

2015-06-24

Free-volume of polymers governs transport of penetrants through polymeric films. Control over free-volume is thus important for the development of better membranes for a wide variety of applications such as gas separations, pharmaceutical purifications and energy storage. To date, methodologies used to create materials with different amounts of free-volume are based primarily on chemical synthesis of new polymers. Here we report a simple methodology for generating free-volume based on the self-assembly of polyethylene-b-polydimethylsiloxane-b-polyethylene triblock copolymers. Here, we have used this method to fabricate a series of membranes with identical compositions but with different amounts of free-volume. We use the termmore » artificial free-volume to refer to the additional free-volume created by self-assembly. The effect of artificial free-volume on selective transport through the membranes was tested using butanol/water and ethanol/water mixtures due to their importance in biofuel production. Moreover, we found that the introduction of artificial free-volume improves both alcohol permeability and selectivity.« less

Order and Disorder in Short Block Polymers

NASA Astrophysics Data System (ADS)

Bates, Frank S.

2015-03-01

Block polymers have captivated the interest of scientists and engineers for more than half a century. The phase behavior of this class of self-assembling soft material is well understood in the limit of infinite molecular weight, based on the self-consistent mean-field theory pioneered by Leibler. At practical molecular sizes, typically around N ~ 1000 repeat units, fluctuation effects become highly significant in the vicinity of the order disorder transition. One-loop corrections to mean-field theory, first described by Brazovski and applied to block polymers by Fredrickson and Helfand, are not expected to be applicable in this limit. Moreover, the drive towards ever smaller domain dimensions, and the opportunity to circumvent transport limitations associated with entanglements, have motivated experiments with yet lower molecular weight block polymers, N less than 100. This presentation will describe the consequences of fluctuations and the equilibrium structural properties of short model AB diblock polymers in the symmetric (f = 1/2) and asymmetric (f --> 0) regimes above and below the order-disorder transition. The consequences of fluctuations and access to equilibrium states will be described in the 1-dimensional stripped (lamellar) phase and the ordering of point particles in 3-dimensions, respectively. As N --> 1 computer simulation with realistic molecular detail becomes feasible presenting exciting opportunities to compliment the associated theoretical challenges. Research in collaboration with Sangwoo Lee, Chris Leighton and Timothy Gillard and Supported by NSF-DMR-1104368.

Elastin-like Polypeptide (ELP) Charge Influences Self-Assembly of ELP-mCherry Fusion Proteins.

PubMed

Mills, Carolyn E; Michaud, Zachary; Olsen, Bradley D

2018-05-23

Self-assembly of protein-polymer bioconjugates presents an elegant strategy for controlling nanostructure and orientation of globular proteins in functional materials. Recent work has shown that genetic fusion of globular protein mCherry to an elastin-like polypeptide (ELP) yields similar self-assembly behavior to these protein-polymer bioconjugates. In the context of studying protein-polymer bioconjugate self-assembly, the mutability of the ELP sequence allows several different properties of the ELP block to be tuned orthogonally while maintaining consistent polypeptide backbone chemistry. This work uses this ELP sequence tunability in combination with the precise control offered by genetic engineering of an amino acid sequence to generate a library of four novel ELP sequences that are used to study the combined effect of charge and hydrophobicity on ELP-mCherry fusion protein self-assembly. Concentrated solution self-assembly is studied by small-angle X-ray scattering (SAXS) and depolarized light scattering (DPLS). These experiments show that fusions containing a negatively charged ELP block do not assemble at all, and fusions with a charge balanced ELP block exhibit a weak propensity for assembly. By comparison, the fusion containing an uncharged ELP block starts to order at 40 wt % in solution and at all concentrations measured has sharper, more intense SAXS peaks than other fusion proteins. These experiments show that charge character of the ELP block is a stronger predictor of self-assembly behavior than the hydrophobicity of the ELP block. Dilute solution small-angle neutron scattering (SANS) on the ELPs alone suggests that all ELPs used in this study (including the uncharged ELP) adopt dilute solution conformations similar to those of traditional polymers, including polyampholytes and polyelectrolytes. Finally, dynamic light scattering studies on ELP-mCherry blends shows that there is no significant complexation between the charged ELPs and mCherry. Therefore, it is proposed that the superior self-assembly of fusion proteins containing uncharged ELP block is due to effective repulsions between charged and uncharged blocks due to local charge correlation effects and, in the case of anionic ELPs, repulsion between like charges within the ELP block.

Directed self-assembly of diblock copolymers in cylindrical confinement: effect of underfilling and air-polymer interactions on configurations

NASA Astrophysics Data System (ADS)

Carpenter, Corinne L.; Delaney, Kris T.; Laachi, Nabil; Fredrickson, Glenn H.

2015-03-01

Directed self-assembly (DSA) of block copolymers has attracted attention for its use as a simple, cost- effective patterning tool for creating vertical interconnect access (VIA) channels in nanoelectronic devices.1, 2 This technique supplements existing lithographic technologies to allow for the creation of high-resolution cylindrical holes whose diameter and placement can be precisely controlled. In this study, we use self-consistent field theory (SCFT) simulations to investigate the equilibrium configurations of under-filled DSA systems with air-polymer interactions. We report on a series of SCFT simulations of our three species (PMMA-b-PS diblock and air) model in cylindrical confinement to explore the role of template diameter, under-fill fraction (i.e. volume fraction of air), air-polymer surface interaction and polymer-side wall/substrate interactions on equilibrium morphologies in an under-filled template with a free top surface. We identify parameters and system configurations where a meniscus appears and explore cases with PMMA-attractive, PS-attractive, and all-neutral walls to understand the effects of wall properties on meniscus geometry and DSA morphology. An important outcome is an understanding of the parameters that control the contact angle of the meniscus with the wall, as it is one of the simplest quantitative measures of the meniscus shape. Ultimately, we seek to identify DSA formulations, templates, and surface treatments with predictable central cylinder diameter and a shallow contact angle, as these factors would facilitate broad process windows and ease of manufacturing.

Attraction between Opposing Planar Dipolar Polymer Brushes

DOE PAGES

Mahalik, J. P.; Sumpter, Bobby G.; Kumar, Rajeev

2017-08-01

In this paper, we use a field theory approach to study the effects of permanent dipoles on interpenetration and free energy changes as a function of distance between two identical planar polymer brushes. Melts (i.e., solvent-free) and solvated brushes made up of polymers grafted on nonadsorbing substrates are studied. In particular, the weak coupling limit of the dipolar interactions is considered, which leads to concentration-dependent pairwise interactions, and the effects of orientational order are neglected. It is predicted that a gradual increase in the dipole moment of the polymer segments can lead to attractive interactions between the brushes at intermediatemore » separation distances. Finally, because classical theory of polymer brushes based on the strong stretching limit (SSL) and the standard self-consistent field theory (SCFT) simulations using the Flory’s χ parameter always predicts repulsive interactions at all separations, our work highlights the importance of dipolar interactions in tailoring and accurately predicting forces between polar polymeric interfaces in contact with each other.« less

``Smart'' Surfaces of Polymer Brushes

NASA Astrophysics Data System (ADS)

Wang, Qiang; Meng, Dong

2009-03-01

``Smart'' surfaces, also known as stimuli-responsive surfaces, can change their properties (e.g., wettability, adhesion, friction, elasticity, and biocompatibility) in response to external stimuli (e.g., temperature, pressure, light, solvent selectivity, ionic strength, type of salt, pH, applied electric field, etc.). In this work, we use numerical self-consistent field calculations to study in detail the structure and stimuli- responses of various polymer brushes, including (1) the thermo- response of PNIPAM brushes in water, (2) solvent-response of uncharged diblock copolymer brushes, and (3) the stimuli- response of charged two-component polymer brushes (including both the binary A/B brushes and diblock copolymer A-B brushes) to ionic strength, pH, and applied electric field. Among the many design parameters (e.g., chain lengths, grafting densities, A-B incompatibility, degree of ionization of charged polymers, etc.) we identify those that strongly affect the surface switchability. Such knowledge is useful to the experimental design of these smart polymer brushes for their applications.

Interface Defect States and Charge Transport Properties in Low-Cost Photovoltaic Devices made from Scalable Deposition Methods

NASA Astrophysics Data System (ADS)

Marin, Andrew; Munoz-Rojas, David; Iza, Diana; Gershon, Talia; MacManus-Driscoll, Judith

2011-03-01

In-plane (parallel to the substrate) polymer diffusion at and near interfaces has significant implications for polymeric surfactants used in tertiary oil recovery, exfoliation of clay sheets in polymer nano-composites, and several other high technology applications. Here, we report a study on the in-plane diffusion of whole polymer chains confined between interfaces using fluorescence recovery after photobleaching. Adapted from quantitative biology, FRAP provides a platform to independently study the effect of temperature, molecular weight, and film thickness on in-plane diffusion of polymers confined between interfaces. Fluorescently labeled polymers were synthesized, spin coated onto quartz substrates and the self-diffusion coefficient was measured by irreversibly photobleaching fluorophores in a pre-defined pattern and monitoring recovery of fluorescence over time. Preliminary results indicate that for thick films the diffusion coefficient is consistent with bulk values. The authors would like to thank the Gates-Cambridge Trust and the International Copper Association.

Controlling microtube permeability via grafted polymers and solvent quality.

PubMed

Suo, Tongchuan; Whitmore, Mark D

2014-03-21

We examine pressure-driven flow through a microtube with grafted polymers using a "doubly self-consistent field" steady-state theory. Our focus is on the structure of the polymer layer, the tube permeability, and the effects of solvent quality, for different regimes of open and closed tubes. We find that, within experimentally attainable pressure gradients, the flow has very little effect on the grafted layer. However, the polymers, and in particular variations in the solvent quality and cylinder radii, can have large effects on the flow. We find that the permeability can either increase or decrease with either the radius or solvent quality, and we identify the regimes for different behaviors in terms of general parameters that can be used to generalize to other systems. This allows us to identify regimes where the systems are most sensitive to these "tuning" parameters, and we find that they correspond to the boundaries between open and closed tubes identified earlier.

Reversible clustering of pH- and temperature-responsive Janus magnetic nanoparticles.

PubMed

Isojima, Tatsushi; Lattuada, Marco; Vander Sande, John B; Hatton, T Alan

2008-09-23

Janus nanoparticles have been synthesized consisting of approximately 5 nm magnetite nanoparticles coated on one side with a pH-dependent and temperature-independent polymer (poly(acrylic acid), PAA), and functionalized on the other side by a second (tail) polymer that is either a pH-independent polymer (polystyrene sodium sulfonate, PSSNa) or a temperature-dependent polymer (poly(N-isopropyl acrylamide), PNIPAM). These Janus nanoparticles are dispersed stably as individual particles at high pH values and low temperatures, but can self-assemble at low pH values (PSSNa) or at high temperatures (>31 degrees C) (PNIPAM) to form stable dispersions of clusters of approximately 80-100 nm in hydrodynamic diameter. The Janus nanoparticle compositions were verified using FTIR and XPS, and their structures observed directly by TEM. Their clustering behavior is analyzed by dynamic light scattering and zeta potential measurements.

DNA-imprinted polymer nanoparticles with monodispersity and prescribed DNA-strand patterns

NASA Astrophysics Data System (ADS)

Trinh, Tuan; Liao, Chenyi; Toader, Violeta; Barłóg, Maciej; Bazzi, Hassan S.; Li, Jianing; Sleiman, Hanadi F.

2018-02-01

As colloidal self-assembly increasingly approaches the complexity of natural systems, an ongoing challenge is to generate non-centrosymmetric structures. For example, patchy, Janus or living crystallization particles have significantly advanced the area of polymer assembly. It has remained difficult, however, to devise polymer particles that associate in a directional manner, with controlled valency and recognition motifs. Here, we present a method to transfer DNA patterns from a DNA cage to a polymeric nanoparticle encapsulated inside the cage in three dimensions. The resulting DNA-imprinted particles (DIPs), which are 'moulded' on the inside of the DNA cage, consist of a monodisperse crosslinked polymer core with a predetermined pattern of different DNA strands covalently 'printed' on their exterior, and further assemble with programmability and directionality. The number, orientation and sequence of DNA strands grafted onto the polymeric core can be controlled during the process, and the strands are addressable independently of each other.

To what extent are microplastics from the open ocean weathered?

PubMed

Ter Halle, Alexandra; Ladirat, Lucie; Martignac, Marion; Mingotaud, Anne Françoise; Boyron, Olivier; Perez, Emile

2017-08-01

It is necessary to better characterize plastic marine debris in order to understand its fate in the environment and interaction with organisms, the most common type of debris being made of polyethylene (PE) and polypropylene (PP). In this work, plastic debris was collected in the North Atlantic sub-tropical gyre during the Expedition 7th Continent sea campaign and consisted mainly in PE. While the mechanisms of PE photodegradation and biodegradation in controlled laboratory conditions are well known, plastic weathering in the environment is not well understood. This is a difficult task to examine because debris comes from a variety of manufactured objects, the original compositions and properties of which vary considerably. A statistical approach was therefore used to compare four sample sets: reference PE, manufactured objects, mesoplastics (5-20 mm) and microplastics (0.3-5 mm). Infrared spectroscopy showed that the surface of all debris presented a higher oxidation state than the reference samples. Differential scanning calorimetry analysis revealed that the microplastics were more crystalline contrarily to the mesoplastics which were similar to references samples. Size exclusion chromatography showed that the molar mass decreased from the references to meso- and microplastics, revealing a clear degradation of the polymer chains. It was thus concluded that the morphology of marine microplastic was much altered and that an unambiguous shortening of the polymer chains took place even for this supposedly robust and inert polymer. Copyright © 2017 Elsevier Ltd. All rights reserved.

Manipulating polymers and composites from the nanoscopic to microscopic length scales

NASA Astrophysics Data System (ADS)

Gupta, Suresh

2008-10-01

This thesis focuses on the manipulation of polymers and composites on length scales ranging from the nanoscopic to microscopic. In particular, on the microscopic length scale electric fields were used to produce instabilities at the air surface and at polymer interfaces that lead to novel three dimensional structures and patterns. On the nanoscopic length scale, the interaction of ligands attached to nanoparticles and polymer matrix were used to induce self-assembly processes that, in turn, lead to systems that self-heal, self-corral, or are patterned. For manipulation at the micron length scale, electrohydrodynamic instabilities were used in trilayer system composed of a layer of poly(methyl methacrylate) (PMMA), a second layer of polystyrene (PS) and a third layer of air. Dewetting of the polymer at the substrate at the polymer/polymer interface under an applied electric field was used to generate novel three dimensional structures. Also, electrohydrodynamic instabilities were used to pattern thin polymer films in conjunction with ultrasonic vibrations and patterned upper electrodes. Self-assembly processes involving polymers and nanoparticles offer a unique means of generating pattern materials or materials that self heal. Simple polymer/nanoparticle composites were investigated. Here, in the absence of interactions between the poly(ethylene oxide) ligands attached to the nanoparticles and PMMA polymer matrix, the opportunity to generate self-healing systems was opened. The size of the nanoparticle was varied and the effect on diffusion of nanoparticle in the polymer matrix was studied. CdSe nanorods were also assembled on a substrate templated with or guided by microphase separated diblock copolymers. The nanorods were incorporated in the diblock copolymer thin films by spin coating the co-solution of nanorods and polymer, surface adsorption of nanorods on to the patterned diblock copolymer films and surface reconstruction of PS/PMMA diblock copolymer thin film. Further, the interactions between the PMMA polymer matrix and the tri n-octyl phosphine oxide ligands attached to an anisotropic nanoparticle, i.e. nanorods, were used to influence the dispersion of the nanorods in the polymer. This led to a novel assembly, termed self-corralling where under an applied electric field highly oriented, highly ordered arrays of nanorods form. Further, self corralling of nanorods was directed by chemically patterned substrates.

Communication: Relationship between solute localization and diffusion in a dynamically constrained polymer system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saylor, David M.; Jawahery, Sudi; Silverstein, Joshua S.

2016-07-21

We investigate the link between dynamic localization, characterized by the Debye–Waller factor, 〈u{sup 2}〉, and solute self-diffusivity, D, in a polymer system using atomistic molecular dynamics simulations and vapor sorption experiments. We find a linear relationship between lnD and 1/〈u{sup 2}〉 over more than four decades of D, encompassing most of the glass formation regime. The observed linearity is consistent with the Langevin dynamics in a periodically varying potential field and may offer a means to rapidly assess diffusion based on the characterization of dynamic localization.

Room-temperature healing of a thermosetting polymer using the Diels-Alder reaction.

PubMed

Peterson, Amy M; Jensen, Robert E; Palmese, Giuseppe R

2010-04-01

Self-healing materials are particularly desirable for load-bearing applications because they offer the potential for increased safety and material lifetimes. A furan-functionalized polymer network was designed that can heal via covalent bonding across the crack surface with the use of a healing agent consisting of a bismaleimide in solution. Average healing efficiencies of approximately 70% were observed. The healing ability of fiber-reinforced composite specimens was investigated with flexural, short beam shear, and double cantilever beam specimens. It was found that solvent amount and maleimide concentration play key roles in determining healing efficiency.

Quantifying Contributions to Transport in Ionic Polymers Across Multiple Length Scales

NASA Astrophysics Data System (ADS)

Madsen, Louis

Self-organized polymer membranes conduct mobile species (ions, water, alcohols, etc.) according to a hierarchy of structural motifs that span sub-nm to >10 μm in length scale. In order to comprehensively understand such materials, our group combines multiple types of NMR dynamics and transport measurements (spectroscopy, diffusometry, relaxometry, imaging) with structural information from scattering and microscopy as well as with theories of porous media,1 electrolytic transport, and oriented matter.2 In this presentation, I will discuss quantitative separation of the phenomena that govern transport in polymer membranes, from intermolecular interactions (<= 2 nm),3 to locally ordered polymer nanochannels (a few to 10s of nm),2 to larger polymer domain structures (10s of nm and larger).1 Using this multi-scale information, we seek to give informed feedback on the design of polymer membranes for use in, e . g . , efficient batteries, fuel cells, and mechanical actuators. References: [1] J. Hou, J. Li, D. Mountz, M. Hull, and L. A. Madsen. Journal of Membrane Science448, 292-298 (2013). [2] J. Li, J. K. Park, R. B. Moore, and L. A. Madsen. Nature Materials 10, 507-511 (2011). [3] M. D. Lingwood, Z. Zhang, B. E. Kidd, K. B. McCreary, J. Hou, and L. A. Madsen. Chemical Communications 49, 4283 - 4285 (2013).

Unified force-level theory of multiscale transient localization and emergent elasticity in polymer solutions and melts

NASA Astrophysics Data System (ADS)

Dell, Zachary E.; Schweizer, Kenneth S.

A unified, microscopic, theoretical understanding of polymer dynamics in concentrated liquids from segmental to macromolecular scales remains an open problem. We have formulated a statistical mechanical theory for this problem that explicitly accounts for intra- and inter-molecular forces at the Kuhn segment level. The theory is self-consistently closed at the level of a matrix of dynamical second moments of a tagged chain. Two distinct regimes of isotropic transient localization are predicted. In semidilute solutions, weak localization is predicted on a mesoscopic length scale between segment and chain scales which is a power law function of the invariant packing length. This is consistent with the breakdown of Rouse dynamics and the emergence of entanglements. The chain structural correlations in the dynamically arrested state are also computed. In dense melts, strong localization is predicted on a scale much smaller than the segment size which is weakly dependent on chain connectivity and signals the onset of glassy dynamics. Predictions of the dynamic plateau shear modulus are consistent with the known features of emergent rubbery and glassy elasticity. Generalizations to treat the effects of chemical crosslinking and physical bond formation in polymer gels are possible.

A thermodynamically consistent model of magneto-elastic materials under diffusion at large strains and its analysis

NASA Astrophysics Data System (ADS)

Roubíček, Tomáš; Tomassetti, Giuseppe

2018-06-01

A theory of elastic magnets is formulated under possible diffusion and heat flow governed by Fick's and Fourier's laws in the deformed (Eulerian) configuration, respectively. The concepts of nonlocal nonsimple materials and viscous Cahn-Hilliard equations are used. The formulation of the problem uses Lagrangian (reference) configuration while the transport processes are pulled back. Except the static problem, the demagnetizing energy is ignored and only local non-self-penetration is considered. The analysis as far as existence of weak solutions of the (thermo) dynamical problem is performed by a careful regularization and approximation by a Galerkin method, suggesting also a numerical strategy. Either ignoring or combining particular aspects, the model has numerous applications as ferro-to-paramagnetic transformation in elastic ferromagnets, diffusion of solvents in polymers possibly accompanied by magnetic effects (magnetic gels), or metal-hydride phase transformation in some intermetallics under diffusion of hydrogen accompanied possibly by magnetic effects (and in particular ferro-to-antiferromagnetic phase transformation), all in the full thermodynamical context under large strains.

Nanoparticle stability in semidilute and concentrated polymer solutions.

PubMed

Dutta, Nupur; Green, David

2008-05-20

The wetting of PDMS-grafted silica spheres (PDMS- g-silica) is connected to their depletion restabilization in semidilute and concentrated PDMS/cyohexane polymer solutions. Specifically, we found that a wetting diagram of chemically identical graft and free homopolymers predicts stability of hard, semisoft, and soft spheres as a function of the bulk free polymer volume fraction, graft density, and the graft and free polymer chain lengths. The transition between stable and aggregated regions is determined optically and with dynamic light scattering. The point of demarcation between the regions occurs when the graft and free polymer chains are equal in length. When graft chains are longer than free chains, the particles are stable; in contrast, the particles are unstable when the opposite is true. The regions of particle stability and instability are corroborated with theoretical self-consistent mean-field calculations, which not only show that the grafted brush is responsible for particle dispersion in the complete wetting region but also aggregation in the incomplete wetting region. Ultimately, our results indicate that depletion restabilization depends on the interfacial properties of the nanoparticles in semidilute and concentrated polymer solutions.

Forced unfolding of single-chain polymeric nanoparticles.

PubMed

Hosono, Nobuhiko; Kushner, Aaron M; Chung, Jaeyoon; Palmans, Anja R A; Guan, Zhibin; Meijer, E W

2015-06-03

Atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) is applied to single-chain polymeric nanoparticles (SCPNs) to acquire information about the internal folding structure of SCPNs and inherent kinetic parameters of supramolecular self-assembling motifs embedded into the SCPNs. The SCPNs used here are polyacrylate-based polymers carrying 2-ureido-4-[1H]-pyrimidinone (UPy) or benzene-1,3,5-tricarboxamide (BTA) pendants that induce an intramolecular chain collapse into nanoparticles consisting of one polymer chain only via internal supramolecular cross-linking. The SCPN is stretched by an AFM cantilever to unfold mechanically, which allows measuring of force-extension profiles of the SCPNs. Consecutive peaks observed in the force profiles are attributed to rupture events of self-assembled UPy/BTA units in the SCPNs. The force profiles have been analyzed statistically for a series of polymers with different UPy/BTA incorporation densities. The results provide insights into the internal conformation of SCPNs, where the folding structure can be changed with the incorporation density of UPy/BTA. In addition, dynamic loading rate analysis allows the determination of kinetic parameters of BTA self-assembly, which has not been accessible by any other method. This study offers a rational tool for understanding the folding structure, kinetics, and pathway of two series of SCPNs.

Atomic Origins of the Self-Healing Function in Cement–Polymer Composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Manh-Thuong; Wang, Zheming; Rod, Kenton A.

Motivated by recent advances in self-healing cement and epoxy polymer composites, we present a combined ab initio molecular dynamics and sum frequency generation (SFG) spectroscopy study of a calcium-silicate-hydrate/polymer interface. On stable, low-defect surfaces, the polymer only weakly adheres through coordination and hydrogen bonding interactions and can be easily mobilized towards defected surfaces. Conversely, on fractured surfaces, the polymer strongly anchors through ionic Ca-O bonds resulting from the deprotonation of polymer hydroxyl groups. In addition, polymer S-S groups are turned away from the cement/polymer interface, allowing for the self-healing function within the polymer. The overall elasticity and healing properties ofmore » these composites stem from a flexible hydrogen bonding network that can readily adapt to surface morphology. The theoretical vibrational signals associated with the proposed cement-polymer interfacial chemistry were confirmed experimentally by SFG spectroscopy.« less

Atomic Origins of the Self-Healing Function in Cement-Polymer Composites.

PubMed

Nguyen, Manh-Thuong; Wang, Zheming; Rod, Kenton A; Childers, M Ian; Fernandez, Carlos; Koech, Phillip K; Bennett, Wendy D; Rousseau, Roger; Glezakou, Vassiliki-Alexandra

2018-01-24

Motivated by recent advances in self-healing cement and epoxy polymer composites, we present a combined ab initio molecular dynamics and sum frequency generation (SFG) vibrational spectroscopy study of a calcium-silicate-hydrate/polymer interface. On stable, low-defect surfaces, the polymer only weakly adheres through coordination and hydrogen bonding interactions and can be easily mobilized toward defected surfaces. Conversely, on fractured surfaces, the polymer strongly anchors through ionic Ca-O bonds resulting from the deprotonation of polymer hydroxyl groups. In addition, polymer S-S groups are turned away from the cement-polymer interface, allowing for the self-healing function within the polymer. The overall elasticity and healing properties of these composites stem from a flexible hydrogen bonding network that can readily adapt to surface morphology. The theoretical vibrational signals associated with the proposed cement-polymer interfacial chemistry were confirmed experimentally by SFG vibrational spectroscopy.

Efficient Homodifunctional Bimolecular Ring-Closure Method for Cyclic Polymers by Combining RAFT and Self-Accelerating Click Reaction.

PubMed

Qu, Lin; Sun, Peng; Wu, Ying; Zhang, Ke; Liu, Zhengping

2017-08-01

An efficient metal-free homodifunctional bimolecular ring-closure method is developed for the formation of cyclic polymers by combining reversible addition-fragmentation chain transfer (RAFT) polymerization and self-accelerating click reaction. In this approach, α,ω-homodifunctional linear polymers with azide terminals are prepared by RAFT polymerization and postmodification of polymer chain end groups. By virtue of sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DBA) as small linkers, well-defined cyclic polymers are then prepared using the self-accelerating double strain-promoted azide-alkyne click (DSPAAC) reaction to ring-close the azide end-functionalized homodifunctional linear polymer precursors. Due to the self-accelerating property of DSPAAC ring-closing reaction, this novel method eliminates the requirement of equimolar amounts of telechelic polymers and small linkers in traditional bimolecular ring-closure methods. It facilitates this method to efficiently and conveniently produce varied pure cyclic polymers by employing an excess molar amount of DBA small linkers. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Surface segregation and surface tension of polydisperse polymer melts.

PubMed

Minnikanti, Venkatachala S; Qian, Zhenyu; Archer, Lynden A

2007-04-14

The effect of polydispersity on surface segregation of a lower molecular weight polymer component in a higher molecular weight linear polymer melt host is investigated theoretically. We show that the integrated surface excess zM of a polymer component of molecular weight M satisfies a simple relation zM=2Ue(M/Mw-1)phiM, where Mw is the weight averaged molecular weight, phiM is the polymer volume fraction, and Ue is the attraction of polymer chain ends to the surface. Ue is principally of entropic origin, but also reflects any energetic preference of chain ends to the surface. We further show that the surface tension gammaM of a polydisperse melt of high molar mass components depends on the number average degree of polymerization Mn as, gammaM=gammainfinity+2UerhobRT/Mn. The parameter gammainfinity is the asymptotic surface tension of an infinitely long polymer of the same chemistry, rhob is the bulk density of the polymer, R is the universal gas constant, and T is the temperature. The predicted gammaM compare favorably with surface tension values obtained from self-consistent field theory simulations that include equation of state effects, which account for changes in polymer density with molecular weight. We also compare the predicted surface tension with available experimental data.

Geometry in Biomimetic Network: Double Gyroid to Pseudo-Single Gyroid in Nanohybrid Materials

NASA Astrophysics Data System (ADS)

Hsueh, Han-Yu; Ho, Rong-Ming; Hung, Yu-Chueh; Ling, Yi-Chun; Hasegawa, Hirokazu

2013-03-01

Biological systems have developed delicately arranged micro- and architectures to produce striking optical effects since millions of years ago. Inspired by the textures of butterfly wings with single gyroid (SG) structure, herein, we aim to fabricate biocompatible and robust materials with SG-like structure in nanometer size so as to give new materials with unprecedented optical properties for applications. Biommicking from the biological photonic structures of butterfly wings, a double gyroid (DG) structure in nanometer size is obtained from the self-assembly of polystyrene-b-poly(L-lactide) (PS-PLLA). To acquire robust backbone networks, inorganic networks in polymer matrix are fabricated by using the hydrolyzed PS-PLLA with DG structure as a template for sol-gel reaction. Owing to the soft polymer matrix, two co-continuous inorganic networks embedded in the polymer matrix can be rearranged by thermal annealing at temperature above the glass transition of the polymer. Consequently, the rearrangement of these inorganic networks leads the formation of SG-like structure possessing unique nanohybrids with ordered texture. This unique nanomaterials with SG-like structure is referred as a pseudo-SG (p-SG) nanohybrids.

Lattice model of linear telechelic polymer melts. II. Influence of chain stiffness on basic thermodynamic properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Wen-Sheng, E-mail: wsxu@uchicago.edu; Freed, Karl F., E-mail: freed@uchicago.edu; Department of Chemistry, The University of Chicago, Chicago, Illinois 60637

2015-07-14

The lattice cluster theory (LCT) for semiflexible linear telechelic melts, developed in Paper I, is applied to examine the influence of chain stiffness on the average degree of self-assembly and the basic thermodynamic properties of linear telechelic polymer melts. Our calculations imply that chain stiffness promotes self-assembly of linear telechelic polymer melts that assemble on cooling when either polymer volume fraction ϕ or temperature T is high, but opposes self-assembly when both ϕ and T are sufficiently low. This allows us to identify a boundary line in the ϕ-T plane that separates two regions of qualitatively different influence of chainmore » stiffness on self-assembly. The enthalpy and entropy of self-assembly are usually treated as adjustable parameters in classical Flory-Huggins type theories for the equilibrium self-assembly of polymers, but they are demonstrated here to strongly depend on chain stiffness. Moreover, illustrative calculations for the dependence of the entropy density of linear telechelic polymer melts on chain stiffness demonstrate the importance of including semiflexibility within the LCT when exploring the nature of glass formation in models of linear telechelic polymer melts.« less

Puncture Self-Healing Polymers for Aerospace Applications

NASA Technical Reports Server (NTRS)

Gordon, Keith L.; Penner, Ronald K.; Bogert, Phil B.; Yost, W. T.; Siochi, Emilie J.

2011-01-01

Space exploration launch costs on the order of $10K per pound provide ample incentive to seek innovative, cost-effective ways to reduce structural mass without sacrificing safety and reliability. Damage-tolerant structural systems can provide a route to avoiding weight penalty while enhancing vehicle safety and reliability. Self-healing polymers capable of spontaneous puncture repair show great promise to mitigate potentially catastrophic damage from events such as micrometeoroid penetration. Effective self-repair requires these materials to heal instantaneously following projectile penetration while retaining structural integrity. Poly(ethylene-co-methacrylic acid) (EMMA), also known as Surlyn is an ionomer-based copolymer that undergoes puncture reversal (self-healing) following high impact puncture at high velocities. However EMMA is not a structural engineering polymer, and will not meet the demands of aerospace applications requiring self-healing engineering materials. Current efforts to identify candidate self-healing polymer materials for structural engineering systems are reported. Rheology, high speed thermography, and high speed video for self-healing semi-crystalline and amorphous polymers will be reported.

Polymers at interfaces and in colloidal dispersions.

PubMed

Fleer, Gerard J

2010-09-15

This review is an extended version of the Overbeek lecture 2009, given at the occasion of the 23rd Conference of ECIS (European Colloid and Interface Society) in Antalya, where I received the fifth Overbeek Gold Medal awarded by ECIS. I first summarize the basics of numerical SF-SCF: the Scheutjens-Fleer version of Self-Consistent-Field theory for inhomogeneous systems, including polymer adsorption and depletion. The conformational statistics are taken from the (non-SCF) DiMarzio-Rubin lattice model for homopolymer adsorption, which enumerates the conformational details exactly by a discrete propagator for the endpoint distribution but does not account for polymer-solvent interaction and for the volume-filling constraint. SF-SCF corrects for this by adjusting the field such that it becomes self-consistent. The model can be generalized to more complex systems: polydispersity, brushes, random and block copolymers, polyelectrolytes, branching, surfactants, micelles, membranes, vesicles, wetting, etc. On a mean-field level the results are exact; the disadvantage is that only numerical data are obtained. Extensions to excluded-volume polymers are in progress. Analytical approximations for simple systems are based upon solving the Edwards diffusion equation. This equation is the continuum variant of the lattice propagator, but ignores the finite segment size (analogous to the Poisson-Boltzmann equation without a Stern layer). By using the discrete propagator for segments next to the surface as the boundary condition in the continuum model, the finite segment size can be introduced into the continuum description, like the ion size in the Stern-Poisson-Boltzmann model. In most cases a ground-state approximation is needed to find analytical solutions. In this way realistic analytical approximations for simple cases can be found, including depletion effects that occur in mixtures of colloids plus non-adsorbing polymers. In the final part of this review I discuss a generalization of the free-volume theory (FVT) for the phase behavior of colloids and non-adsorbing polymer. In FVT the polymer is considered to be ideal: the osmotic pressure Pi follows the Van 't Hoff law, the depletion thickness delta equals the radius of gyration. This restricts the validity of FVT to the so-called colloid limit (polymer much smaller than the colloids). We have been able to find simple analytical approximations for Pi and delta which account for non-ideality and include established results for the semidilute limit. So we could generalize FVT to GFVT, and can now also describe the so-called protein limit (polymer larger than the 'protein-like' colloids), where the binodal polymer concentrations scale in a simple way with the polymer/colloid size ratio. For an intermediate case (polymer size approximately colloid size) we could give a quantitative description of careful experimental data. Copyright 2010 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saunders, C.B.; Dickson, L.W.; Singh, A.

A radiation-curable prepreg designed to meet the specifications set by a major aircraft company is described. The resin, consisting of a mixture of an epoxy diacrylate, polybutadiene diacrylate, and a multifunctional monomer, was used to impregnate a plain weave carbon fabric by a solvent process. The cured polymer, produced by irradiation in air to a dose of 40 kGy, is amorphous, with a gel fraction of 85 percent. The linear thermal expansion coefficient of the polymer was found to be 0.00017 m/m deg C from 25 to 150 C; it was not affected by varying the applied irradiation dose frommore » 30 to 50 kGy. 14 references.« less

Non-aqueous liquid compositions comprising ion exchange polymers reference to related application

DOEpatents

Kim,; Yu Seung, Lee [Los Alamos, NM; Kwan-Soo, Rockward [Los Alamos, NM; T, Tommy Q [Rio Rancho, NM

2012-08-07

Compositions, and methods of making thereof, comprising from about 1% to about 5% of a perfluorinated sulfonic acid ionomer or a hydrocarbon-based ionomer; and from about 95% to about 99% of a solvent, said solvent consisting essentially of a polyol; wherein said composition is substantially free of water and wherein said ionomer is uniformly dispersed in said solvent.

An all-solid-state reference electrode based on the layer-by-layer polymer coating.

PubMed

Kwon, Nak-Hyun; Lee, Kyung-Sun; Won, Mi-Sook; Shim, Yoon-Bo

2007-09-01

A solid-state reference electrode (SSRE) was fabricated by layering a silicone rubber (SR) film containing KCl on an AgCl surface, then a perfluorinated ionomer film, and finally a polyurethane-based membrane containing an ionophore, a lipophilic ionic additive, and a plasticizer, respectively. The addition of SiCl4 to the polyurethane-based membrane layer enhanced the strength of the membrane in an aqueous solution. The morphologies of the membranes were studied separately by SEM. The fabrication of the Ag/AgCl electrode through this layer-by-layer polymer coating improved the electrode stability enormously. In addition, the potential drift of the SSRE according to the pH of the medium was minimized by introducing a H+-ion-selective ionophore (tridodecylamine; TDDA) into the outmost polymer membrane. The cyclic voltammetric and potentiometric responses using the SSRE and a conventional reference electrode, respectively, were consistent. The SSRE exhibited little potential variation even in the case of the addition of very high concentrations of various salts, such as Na salicylate, LiCl, KCl, CaCl2, MgCl2, KNO3, NaCl, and NaHCO3. The practicability of the proposed SSRE was tested for the determination of blood pH and pCO2 in a flow cell system. The SSRE fabricated in the present study was stable over two years.

Self-Efficacy and Learning in Sorority and Fraternity Students

ERIC Educational Resources Information Center

Thompson, Jon G., Jr.; Oberle, Crystal D.; Lilley, Jennifer L.

2011-01-01

Past research consistently reveals that "self-efficacy," referring to one's perceived ability to obtain a desired outcome, in academic courses is linked to academic achievement and motivation in those courses. In particular, high self-efficacy in courses is associated with high academic performance, and low self-efficacy in courses is associated…

Encoding Personal Adjectives: The Effects of Depression on Self-Reference.

ERIC Educational Resources Information Center

Kuiper, Nicholas A.; Derry, Paul A.

A central tenet of a self-schema model for depression is the idea that severity of depression is a crucial determinant of the content and cohesiveness of the depressive's self-schema. Consistent with predictions generated form this model, sample nondepressives displayed superior recall for self-referenced, nondepressed-content adjectives. Recall…

Self-Assembly of Telechelic Tyrosine End-Capped PEO Star Polymers in Aqueous Solution.

PubMed

Edwards-Gayle, Charlotte J C; Greco, Francesca; Hamley, Ian W; Rambo, Robert P; Reza, Mehedi; Ruokolainen, Janne; Skoulas, Dimitrios; Iatrou, Hermis

2018-01-08

We investigate the self-assembly of two telechelic star polymer-peptide conjugates based on poly(ethylene oxide) (PEO) four-arm star polymers capped with oligotyrosine. The conjugates were prepared via N-carboxy anhydride-mediated ring-opening polymerization from PEO star polymer macroinitiators. Self-assembly occurs above a critical aggregation concentration determined via fluorescence probe assays. Peptide conformation was examined using circular dichroism spectroscopy. The structure of self-assembled aggregates was probed using small-angle X-ray scattering and cryogenic transmission electron microscopy. In contrast to previous studies on linear telechelic PEO-oligotyrosine conjugates that show self-assembly into β-sheet fibrils, the star architecture suppresses fibril formation and micelles are generally observed instead, a small population of fibrils only being observed upon pH adjustment. Hydrogelation is also suppressed by the polymer star architecture. These peptide-functionalized star polymer solutions are cytocompatible at sufficiently low concentration. These systems present tyrosine at high density and may be useful in the development of future enzyme or pH-responsive biomaterials.

Effects of Prior Aging at 288 deg C in Argon Environment on Creep Response of Carbon Fiber Reinforced PMR-15 Composite with + or - 45 deg Fiber Orientation at 288 deg C

DTIC Science & Technology

2009-06-01

typically consists of a thermoset or thermoplastic polymer matrix reinforced with fibers that are much stronger and stiffer than the matrix. The PMCs are...high thermal or electrical conductivity, stealth characteristics , the ability to self-heal, communication, and sensor capabilities. The multi...have factual evidence of limitations and characteristics so as to utilize the material in a manner consistent with its strengths and weaknesses

Self-assembly and glass-formation in a lattice model of telechelic polymer melts: Influence of stiffness of the sticky bonds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Wen-Sheng, E-mail: wsxu@uchicago.edu; Freed, Karl F., E-mail: freed@uchicago.edu; Department of Chemistry, The University of Chicago, Chicago, Illinois 60637

2016-06-07

Telechelic polymers are chain macromolecules that may self-assemble through the association of their two mono-functional end groups (called “stickers”). A deep understanding of the relation between microscopic molecular details and the macroscopic physical properties of telechelic polymers is important in guiding the rational design of telechelic polymer materials with desired properties. The lattice cluster theory (LCT) for strongly interacting, self-assembling telechelic polymers provides a theoretical tool that enables establishing the connections between important microscopic molecular details of self-assembling polymers and their bulk thermodynamics. The original LCT for self-assembly of telechelic polymers considers a model of fully flexible linear chains [J.more » Dudowicz and K. F. Freed, J. Chem. Phys. 136, 064902 (2012)], while our recent work introduces a significant improvement to the LCT by including a description of chain semiflexibility for the bonds within each individual telechelic chain [W.-S. Xu and K. F. Freed, J. Chem. Phys. 143, 024901 (2015)], but the physically associative (or called “sticky”) bonds between the ends of the telechelics are left as fully flexible. Motivated by the ubiquitous presence of steric constraints on the association of real telechelic polymers that impart an additional degree of bond stiffness (or rigidity), the present paper further extends the LCT to permit the sticky bonds to be semiflexible but to have a stiffness differing from that within each telechelic chain. An analytical expression for the Helmholtz free energy is provided for this model of linear telechelic polymer melts, and illustrative calculations demonstrate the significant influence of the stiffness of the sticky bonds on the self-assembly and thermodynamics of telechelic polymers. A brief discussion is also provided for the impact of self-assembly on glass-formation by combining the LCT description for this extended model of telechelic polymers with the Adam-Gibbs relation between the structural relaxation time and the configurational entropy.« less

Mechanochemically-Active Polymer Composites

DTIC Science & Technology

2013-09-13

Jackson, Jonathan A. Bartelt, Paul V. Braun. Transparent Self - Healing Polymers Based on Encapsulated Plasticizers in a Thermoplastic Matrix...08/28/2008 4.00 J.P. Youngblood, N.R. Sottos. bioinspired materials for self cleaning and self healing , MRS Bulletin, ( ): . doi: 08/28/2008 5.00...H.M.Anderson, M.W.Keller, J.S. Moore, N.R. Sottos, S.R. White. Self Healing Polymers and Composites , , ( ): . doi: TOTAL: 35 (b) Papers published in

Evaluation of two polyimides and of an improved liner retention design for self-lubricating bushings

NASA Technical Reports Server (NTRS)

Sliney, H. E.

1984-01-01

Two different polyimide polymers were studied and the effectiveness of a design feature to improve retention of the self lubricating composite liners under high load was evaluated. The basic bearing design consisted of a molded layer of chopped graphite-fiber-reinforced-polyimide (GFRP) composite bonded to the bore of a steel bushing. The friction, wear, and load carrying ability of the bushings were determined in oscillating tests at 25, 260 and 315 C at radial unit loads up to 260 MPa. Friction coefficients were typically 0.15 to 0.25. Bushings with liners containing a new partially fluorinated polymer were functional, but had a lower load capacity and higher wear rate than those containing a more conventional, high temperature polyimide. The liner retention design feature reduced the tendency of the liners to crack and work out of the contact zone under high oscillating loads.

Density functional theory for polymeric systems in 2D.

PubMed

Słyk, Edyta; Roth, Roland; Bryk, Paweł

2016-06-22

We propose density functional theory for polymeric fluids in two dimensions. The approach is based on Wertheim's first order thermodynamic perturbation theory (TPT) and closely follows density functional theory for polymers proposed by Yu and Wu (2002 J. Chem. Phys. 117 2368). As a simple application we evaluate the density profiles of tangent hard-disk polymers at hard walls. The theoretical predictions are compared against the results of the Monte Carlo simulations. We find that for short chain lengths the theoretical density profiles are in an excellent agreement with the Monte Carlo data. The agreement is less satisfactory for longer chains. The performance of the theory can be improved by recasting the approach using the self-consistent field theory formalism. When the self-avoiding chain statistics is used, the theory yields a marked improvement in the low density limit. Further improvements for long chains could be reached by going beyond the first order of TPT.

Coherent states field theory in supramolecular polymer physics

NASA Astrophysics Data System (ADS)

Fredrickson, Glenn H.; Delaney, Kris T.

2018-05-01

In 1970, Edwards and Freed presented an elegant representation of interacting branched polymers that resembles the coherent states (CS) formulation of second-quantized field theory. This CS polymer field theory has been largely overlooked during the intervening period in favor of more conventional "auxiliary field" (AF) interacting polymer representations that form the basis of modern self-consistent field theory (SCFT) and field-theoretic simulation approaches. Here we argue that the CS representation provides a simpler and computationally more efficient framework than the AF approach for broad classes of reversibly bonding polymers encountered in supramolecular polymer science. The CS formalism is reviewed, initially for a simple homopolymer solution, and then extended to supramolecular polymers capable of forming reversible linkages and networks. In the context of the Edwards model of a non-reacting homopolymer solution and one and two-component models of telechelic reacting polymers, we discuss the structure of CS mean-field theory, including the equivalence to SCFT, and show how weak-amplitude expansions (random phase approximations) can be readily developed without explicit enumeration of all reaction products in a mixture. We further illustrate how to analyze CS field theories beyond SCFT at the level of Gaussian field fluctuations and provide a perspective on direct numerical simulations using a recently developed complex Langevin technique.

Organic electronics with polymer dielectrics on plastic substrates fabricated via transfer printing

NASA Astrophysics Data System (ADS)

Hines, Daniel R.

Printing methods are fast becoming important processing techniques for the fabrication of flexible electronics. Some goals for flexible electronics are to produce cheap, lightweight, disposable radio frequency identification (RFID) tags, very large flexible displays that can be produced in a roll-to-roll process and wearable electronics for both the clothing and medical industries. Such applications will require fabrication processes for the assembly of dissimilar materials onto a common substrate in ways that are compatible with organic and polymeric materials as well as traditional solid-state electronic materials. A transfer printing method has been developed with these goals and application in mind. This printing method relies primarily on differential adhesion where no chemical processing is performed on the device substrate. It is compatible with a wide variety of materials with each component printed in exactly the same way, thus avoiding any mixed processing steps on the device substrate. The adhesion requirements of one material printed onto a second are studied by measuring the surface energy of both materials and by surface treatments such as plasma exposure or the application of self-assembled monolayers (SAM). Transfer printing has been developed within the context of fabricating organic electronics onto plastic substrates because these materials introduce unique opportunities associated with processing conditions not typically required for traditional semiconducting materials. Compared to silicon, organic semiconductors are soft materials that require low temperature processing and are extremely sensitive to chemical processing and environmental contamination. The transfer printing process has been developed for the important and commonly used organic semiconducting materials, pentacene (Pn) and poly(3-hexylthiophene) (P3HT). A three-step printing process has been developed by which these materials are printed onto an electrode subassembly consisting of previously printed electrodes separated by a polymer dielectric layer all on a plastic substrate. These bottom contact, flexible organic thin-film transistors (OTFT) have been compared to unprinted (reference) devices consisting of top contact electrodes and a silicon dioxide dielectric layer on a silicon substrate. Printed Pn and P3HT TFTs have been shown to out-perform the reference devices. This enhancement has been attributed to an annealing under pressure of the organic semiconducting material.

The special theory of Brownian relativity: equivalence principle for dynamic and static random paths and uncertainty relation for diffusion.

PubMed

Mezzasalma, Stefano A

2007-03-15

The theoretical basis of a recent theory of Brownian relativity for polymer solutions is deepened and reexamined. After the problem of relative diffusion in polymer solutions is addressed, its two postulates are formulated in all generality. The former builds a statistical equivalence between (uncorrelated) timelike and shapelike reference frames, that is, among dynamical trajectories of liquid molecules and static configurations of polymer chains. The latter defines the "diffusive horizon" as the invariant quantity to work with in the special version of the theory. Particularly, the concept of universality in polymer physics corresponds in Brownian relativity to that of covariance in the Einstein formulation. Here, a "universal" law consists of a privileged observation, performed from the laboratory rest frame and agreeing with any diffusive reference system. From the joint lack of covariance and simultaneity implied by the Brownian Lorentz-Poincaré transforms, a relative uncertainty arises, in a certain analogy with quantum mechanics. It is driven by the difference between local diffusion coefficients in the liquid solution. The same transformation class can be used to infer Fick's second law of diffusion, playing here the role of a gauge invariance preserving covariance of the spacetime increments. An overall, noteworthy conclusion emerging from this view concerns the statistics of (i) static macromolecular configurations and (ii) the motion of liquid molecules, which would be much more related than expected.

An ecotoxicological study on tin- and bismuth-catalysed PDMS based coatings containing a surface-active polymer.

PubMed

Pretti, Carlo; Oliva, Matteo; Mennillo, Elvira; Barbaglia, Martina; Funel, Marco; Reddy Yasani, Bhaskar; Martinelli, Elisa; Galli, Giancarlo

2013-12-01

Novel films were prepared by condensation curing reaction of a poly(dimethyl siloxane) (PDMS) matrix with bismuth neodecanoate and dibutyltin diacetate catalysts. An ecotoxicological study was performed on the leachates of the coatings using the bacterium Vibrio fischeri, the unicellular alga Dunaliella tertiolecta, the crustacean Artemia salina and the fish Sparus aurata (larvae) as testing organisms. A copper-based self-polishing commercial paint was also tested as reference. The results showed that the tin-catalysed coatings and the copper paint were highly toxic against at least two of the four test organisms, whereas bismuth-catalysed coatings did not show any toxic effect. Moreover, the same biological assessment was also carried out on PDMS coatings containing a surface-active fluorinated polymer. The toxicity of the entire polymeric system resulted only from the tin catalyst used for the condensation curing reaction, as the bismuth catalysed coatings incorporating the surface-active polymer remained atoxic toward all the tested organisms. © 2013 Elsevier Inc. All rights reserved.

Hydrodynamically Coupled Brownian Dynamics: A coarse-grain particle-based Brownian dynamics technique with hydrodynamic interactions for modeling self-developing flow of polymer solutions

NASA Astrophysics Data System (ADS)

Ahuja, V. R.; van der Gucht, J.; Briels, W. J.

2018-01-01

We present a novel coarse-grain particle-based simulation technique for modeling self-developing flow of dilute and semi-dilute polymer solutions. The central idea in this paper is the two-way coupling between a mesoscopic polymer model and a phenomenological fluid model. As our polymer model, we choose Responsive Particle Dynamics (RaPiD), a Brownian dynamics method, which formulates the so-called "conservative" and "transient" pair-potentials through which the polymers interact besides experiencing random forces in accordance with the fluctuation dissipation theorem. In addition to these interactions, our polymer blobs are also influenced by the background solvent velocity field, which we calculate by solving the Navier-Stokes equation discretized on a moving grid of fluid blobs using the Smoothed Particle Hydrodynamics (SPH) technique. While the polymers experience this frictional force opposing their motion relative to the background flow field, our fluid blobs also in turn are influenced by the motion of the polymers through an interaction term. This makes our technique a two-way coupling algorithm. We have constructed this interaction term in such a way that momentum is conserved locally, thereby preserving long range hydrodynamics. Furthermore, we have derived pairwise fluctuation terms for the velocities of the fluid blobs using the Fokker-Planck equation, which have been alternatively derived using the General Equation for the Non-Equilibrium Reversible-Irreversible Coupling (GENERIC) approach in Smoothed Dissipative Particle Dynamics (SDPD) literature. These velocity fluctuations for the fluid may be incorporated into the velocity updates for our fluid blobs to obtain a thermodynamically consistent distribution of velocities. In cases where these fluctuations are insignificant, however, these additional terms may well be dropped out as they are in a standard SPH simulation. We have applied our technique to study the rheology of two different concentrations of our model linear polymer solutions. The results show that the polymers and the fluid are coupled very well with each other, showing no lag between their velocities. Furthermore, our results show non-Newtonian shear thinning and the characteristic flattening of the Poiseuille flow profile typically observed for polymer solutions.

Hydrodynamically Coupled Brownian Dynamics: A coarse-grain particle-based Brownian dynamics technique with hydrodynamic interactions for modeling self-developing flow of polymer solutions.

PubMed

Ahuja, V R; van der Gucht, J; Briels, W J

2018-01-21

We present a novel coarse-grain particle-based simulation technique for modeling self-developing flow of dilute and semi-dilute polymer solutions. The central idea in this paper is the two-way coupling between a mesoscopic polymer model and a phenomenological fluid model. As our polymer model, we choose Responsive Particle Dynamics (RaPiD), a Brownian dynamics method, which formulates the so-called "conservative" and "transient" pair-potentials through which the polymers interact besides experiencing random forces in accordance with the fluctuation dissipation theorem. In addition to these interactions, our polymer blobs are also influenced by the background solvent velocity field, which we calculate by solving the Navier-Stokes equation discretized on a moving grid of fluid blobs using the Smoothed Particle Hydrodynamics (SPH) technique. While the polymers experience this frictional force opposing their motion relative to the background flow field, our fluid blobs also in turn are influenced by the motion of the polymers through an interaction term. This makes our technique a two-way coupling algorithm. We have constructed this interaction term in such a way that momentum is conserved locally, thereby preserving long range hydrodynamics. Furthermore, we have derived pairwise fluctuation terms for the velocities of the fluid blobs using the Fokker-Planck equation, which have been alternatively derived using the General Equation for the Non-Equilibrium Reversible-Irreversible Coupling (GENERIC) approach in Smoothed Dissipative Particle Dynamics (SDPD) literature. These velocity fluctuations for the fluid may be incorporated into the velocity updates for our fluid blobs to obtain a thermodynamically consistent distribution of velocities. In cases where these fluctuations are insignificant, however, these additional terms may well be dropped out as they are in a standard SPH simulation. We have applied our technique to study the rheology of two different concentrations of our model linear polymer solutions. The results show that the polymers and the fluid are coupled very well with each other, showing no lag between their velocities. Furthermore, our results show non-Newtonian shear thinning and the characteristic flattening of the Poiseuille flow profile typically observed for polymer solutions.

Paintable band-edge liquid crystal lasers.

PubMed

Gardiner, Damian J; Morris, Stephen M; Hands, Philip J W; Mowatt, Carrie; Rutledge, Rupert; Wilkinson, Timothy D; Coles, Harry J

2011-01-31

In this paper we demonstrate photonic band-edge laser emission from emulsion-based polymer dispersed liquid crystals. The lasing medium consists of dye-doped chiral nematic droplets dispersed within a polymer matrix that spontaneously align as the film dries. Such lasers can be easily formed on single substrates with no alignment layers. The system combines the self-organizing periodic structure of chiral nematic liquid crystals with the simplicity of the emulsion procedure so as to produce a material that retains the emission characteristics of band-edge lasers yet can be readily coated. Sequential and stacked layers demonstrate the possibility of achieving simultaneous multi-wavelength laser output from glass, metallic, and flexible substrates.

Satiety and the self-regulation of food intake in children: A potential for gene-environment interplay

USDA-ARS?s Scientific Manuscript database

Child eating self-regulation refers to behaviors that enable children to start and stop eating in a manner consistent with maintaining energy balance. Perturbations in these behaviors, manifesting as poorer child eating self-regulation, are associated with higher child weight status. Initial researc...

FY08 Chemical Synthesis for the Self-Decontaminating Coatings Project

DTIC Science & Technology

2013-08-01

These synthesized materials consist of Boltorn hyperbranched polymers that are functionalized with hydantoin, alkyl, and perfluorinated groups. 15...envisioned that completely prevents sorption of chemical agents, enables autonomous decontamination, reduces the volume of cleaning solution...modified with perfluorinated octanoic acid (PFOA), lauric acid, and a hydantoin moiety. HO OH CH3 HO O 3 Figure 2. Synthetic targets 1–3

Self-consistent field theory of tethered polymers: one dimensional, three dimensional, strong stretching theories and the effects of excluded-volume-only interactions.

PubMed

Suo, Tongchuan; Whitmore, Mark D

2014-11-28

We examine end-tethered polymers in good solvents, using one- and three-dimensional self-consistent field theory, and strong stretching theories. We also discuss different tethering scenarios, namely, mobile tethers, fixed but random ones, and fixed but ordered ones, and the effects and important limitations of including only binary interactions (excluded volume terms). We find that there is a "mushroom" regime in which the layer thickness is independent of the tethering density, σ, for systems with ordered tethers, but we argue that there is no such plateau for mobile or disordered anchors, nor is there one in the 1D theory. In the other limit of brushes, all approaches predict that the layer thickness scales linearly with N. However, the σ(1/3) scaling is a result of keeping only excluded volume interactions: when the full potential is included, the dependence is faster and more complicated than σ(1/3). In fact, there does not appear to be any regime in which the layer thickness scales in the combination Nσ(1/3). We also compare the results for two different solvents with each other, and with earlier Θ solvent results.

Self-assembling nucleic acid delivery vehicles via linear, water-soluble, cyclodextrin-containing polymers.

PubMed

Davis, M E; Pun, S H; Bellocq, N C; Reineke, T M; Popielarski, S R; Mishra, S; Heidel, J D

2004-01-01

Non-viral (synthetic) nucleic acid delivery systems have the potential to provide for the practical application of nucleic acid-based therapeutics. We have designed and prepared a tunable, non-viral nucleic acid delivery system that self-assembles with nucleic acids and centers around a new class of polymeric materials; namely, linear, water-soluble cyclodextrin-containing polymers. The relationships between polymer structure and gene delivery are illustrated, and the roles of the cyclodextrin moieties for minimizing toxicity and forming inclusion complexes in the self-assembly processes are highlighted. This vehicle is the first example of a polymer-based gene delivery system formed entirely by self-assembly.

Effects of polymer additives on Rayleigh-Taylor turbulence.

PubMed

Boffetta, G; Mazzino, A; Musacchio, S

2011-05-01

The role of polymer additives on the turbulent convective flow of a Rayleigh-Taylor system is investigated by means of direct numerical simulations of Oldroyd-B viscoelastic model. The dynamics of polymer elongations follows adiabatically the self-similar evolution of the turbulent mixing layer and shows the appearance of a strong feedback on the flow which originates a cutoff for polymer elongations. The viscoelastic effects on the mixing properties of the flow are twofold. Mixing is appreciably enhanced at large scales (the mixing layer growth rate is larger than that of the purely Newtonian case) and depleted at small scales (thermal plumes are more coherent with respect to the Newtonian case). The observed speed up of the thermal plumes, together with an increase of the correlations between temperature field and vertical velocity, contributes to a significant enhancement of heat transport. Our findings are consistent with a scenario of drag reduction induced by polymers. A weakly nonlinear model proposed by Fermi for the growth of the mixing layer is reported in the Appendix. © 2011 American Physical Society

Generation of Well-Relaxed All-Atom Models of Large Molecular Weight Polymer Melts: A Hybrid Particle-Continuum Approach Based on Particle-Field Molecular Dynamics Simulations.

PubMed

De Nicola, Antonio; Kawakatsu, Toshihiro; Milano, Giuseppe

2014-12-09

A procedure based on Molecular Dynamics (MD) simulations employing soft potentials derived from self-consistent field (SCF) theory (named MD-SCF) able to generate well-relaxed all-atom structures of polymer melts is proposed. All-atom structures having structural correlations indistinguishable from ones obtained by long MD relaxations have been obtained for poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO) melts. The proposed procedure leads to computational costs mainly related on system size rather than to the chain length. Several advantages of the proposed procedure over current coarse-graining/reverse mapping strategies are apparent. No parametrization is needed to generate relaxed structures of different polymers at different scales or resolutions. There is no need for special algorithms or back-mapping schemes to change the resolution of the models. This characteristic makes the procedure general and its extension to other polymer architectures straightforward. A similar procedure can be easily extended to the generation of all-atom structures of block copolymer melts and polymer nanocomposites.

Many Body Effects on Particle Diffusion in Polymer Nanocomposites

NASA Astrophysics Data System (ADS)

Dell, Zachary E.; Schweizer, Kenneth S.

2014-03-01

Recent statistical mechanical theories of nanoparticle motion in polymer melts and networks have focused on the dilute particle limit. By combining PRISM theory predictions for microscopic structural correlations, and a new formulation of self-consistent dynamical mode coupling theory, we extend dilute theories to finite filler loading. As a minimalist model, the polymer dynamics are first assumed to be unperturbed by the presence of the nanoparticles. The long time particle diffusivity in unentangled and entangled melts is determined as a function of polymer tube diameter and radius of gyration, nanoparticle diameter, and polymer-filler attraction strength under both constant volume and constant pressure situations. The influence of nanocomposite statistical structure (depletion, steric stabilization, bridging) on dynamics is also investigated. Using recent theoretical developments for predicting tube diameters in nanocomposites, the consequences of filler-induced tube dilation on nanoparticle motion is established. In entangled melts, increasing filler loading first modestly speeds up diffusion, and then dramatically when the inter-filler separation becomes smaller than the tube diameter. At very high loadings, a filler glass transition is generically predicted.

Simple triple-state polymer actuators with controllable folding characteristics

NASA Astrophysics Data System (ADS)

Chen, Shuyang; Li, Jing; Fang, Lichen; Zhu, Zeyu; Kang, Sung Hoon

2017-03-01

Driven by the interests in self-folding, there have been studies developing artificial self-folding structures at different length scales based on various polymer actuators that can realize dual-state actuation. However, their unidirectional nature limits the applicability of the actuators for a wide range of multi-state self-folding behaviors. In addition, complex fabrication and programming procedures hinder broad applications of existing polymer actuators. Moreover, few of the existing polymer actuators are able to show the self-folding behaviors with the precise control of curvature and force. To address these issues, we report an easy-to-fabricate triple-state actuator with controllable folding behaviors based on bilayer polymer composites with different glass transition temperatures. Initially, the fabricated actuator is in the flat state, and it can sequentially self-fold to angled folding states of opposite directions as it is heated up. Based on an analytical model and measured partial recovery behaviors of polymers, we can accurately control the folding characteristics (curvature and force) for the rational design. To demonstrate an application of our triple-state actuator, we have developed a self-folding transformer robot which self-folds from a two-dimensional sheet into a three-dimensional boat-like configuration and transforms from the boat shape to a car shape with the increase in the temperature applied to the actuator. Our findings offer a simple approach to generate multiple configurations from a single system by harnessing behaviors of polymers with the rational design.

Development of New Supramolecular Lyotropic Liquid Crystals and Their Application as Alignment Media for Organic Compounds.

PubMed

Leyendecker, Martin; Meyer, Nils-Christopher; Thiele, Christina M

2017-09-11

Most alignment media for the residual dipolar coupling (RDC) based molecular structure determination of small organic compounds consist of rod-like polymers dissolved in organic solvents or of swollen cross-linked polymer gels. Thus far, the synthesis of polymer-based alignment media has been a challenging process, which is often followed by a time-consuming sample preparation. We herein propose the use of non-polymeric alignment media based on benzenetricarboxamides (BTAs), which self-assemble into rod-like supramolecules. Our newly found supramolecular lyotropic liquid crystals (LLCs) are studied in terms of their LLC properties and their suitability as alignment media in NMR spectroscopy. Scalable enantiodifferentiating properties are introduced through a sergeant-and-soldier principle by blending achiral with chiral substituted BTAs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Role of Monomer Sequence, Hydrogen Bonding and Mesoscale Architecture in Marine Antifouling Coatings

NASA Astrophysics Data System (ADS)

Segalman, Rachel

Polypeptoids are non-natural, sequence specific polymers that offer the opportunity to probe the effect of monomer sequence, chirality, and chain shape on self-assembly and surface properties. Additionally, polypeptoid synthesis is more scaleable than traditional polypeptides suggesting their utility in large area applications. We have designed efficient marine anti-fouling coatings by using triblock copolymer scaffolds to which polypeptoids are tethered in order to tune both the modulus and surface energies with great precision. Surprisingly, when short sequences are tethered to a polymer backbone, polypeptoids consistently outperform analogous polypeptides in antifouling properties. We hypothesize that the hydrogen bonding inherent to the polypeptide backbone drives the observed differences in performance. We also find that the polymer scaffold housing the polypeptoids also plays a crucial role in directing surface presentation and therefore the overall coating properties.

Effectiveness of External Electric Field Treatment of Conjugated Polymers in Bulk-Heterojunction Solar Cells.

PubMed

Solanki, Ankur; Bagui, Anirban; Long, Guankui; Wu, Bo; Salim, Teddy; Chen, Yongsheng; Lam, Yeng Ming; Sum, Tze Chien

2016-11-30

External electric field treatment (EFT) on P3HT:PCBM bulk heterojunction (BHJ) devices was recently found to be a viable approach for improving the power conversion efficiencies (PCEs) through modulating the blend nanomorphology. However, its effectiveness over the broad family of polymer-fullerene blends remains unclear. Herein, we investigate the effects of external EFT on various polymer-fullerene blends with distinct morphologies stemming from the difference in molecular structure of the polymers (i.e., semicrystalline vs amorphous) in a bid to establish a clear morphology-function-charge dynamics relationship to the photovoltaic performance. Our findings reveal that EFT promotes self-organization of the semicrystalline thiophene-based conjugated polymers (i.e., P3HT and P3BT) while it was ineffective for the amorphous polymers (i.e., PTB7 and PCPDTBT) even at the maximum applied E-field of 8 kV cm -1 . Transient absorption spectroscopy shows an improvement in the initial charge-carrier and polaron formation from delocalized excitons in the E-field treated semicrystalline blends compared to their untreated reference samples. Interfacial trap-assisted monomolecular and trap-free bimolecular recombination at nanosecond-microsecond time scale in the E-field treated P3BT:PC60BM devices are significantly suppressed. Importantly, our findings shed new light and provide guidelines on the effectiveness of utilizing external EFT to enhance the PCEs of a larger family of conjugated polymer-based BHJ OSCs.

Light Irradiation as Key to Shape and Function of Nano-Assemblies in Solution

NASA Astrophysics Data System (ADS)

Groehn, Franziska

Developing strategies to exploit solar energy become more and more important. Inspired by natural systems it is highly promising to self-assemble functional species into effective tailored supramolecular units. Here we report self-assembled polymer structures in solution, taking advantage of optical properties of hybrid structures and light responsiveness. A new type of photocatalytically active self-assembled polymer structure in aqueous solution consists of supramolecular nano-objects obtained from macroions and multivalent inorganic ``counterions'' such as nanoparticles or clusters. These can exhibit expressed selectivity or even allow catalytic reactions in solution that are not possible with the building blocks only. Further, polyelectrolyte-porphyrin nanoscale assemblies exhibit tunable optical properties including strong fluorescence and an up to 20-fold higher photocatalytic activity than without polymeric template. A different approach is to transfer light energy into mechanical energy. Here, light energy is converted into nanoscale shape changes. This route for the conversion of light is highly promising for applications in drug delivery, nanosensors and solar energy conversion. Membership of DPG, Germany ID 153159-.

Bioelectrochemical control of neural cell development on conducting polymers.

PubMed

Collazos-Castro, Jorge E; Polo, José L; Hernández-Labrado, Gabriel R; Padial-Cañete, Vanesa; García-Rama, Concepción

2010-12-01

Electrically conducting polymers hold promise for developing advanced neuroprostheses, bionic systems and neural repair devices. Among them, poly(3, 4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) exhibits superior physicochemical properties but biocompatibility issues have limited its use. We describe combinations of electrochemical and molecule self-assembling methods to consistently control neural cell development on PEDOT:PSS while maintaining very low interfacial impedance. Electro-adsorbed polylysine enabled long-term neuronal survival and growth on the nanostructured polymer. Neurite extension was strongly inhibited by an additional layer of PSS or heparin, which in turn could be either removed electrically or further coated with spermine to activate cell growth. Binding basic fibroblast growth factor (bFGF) to the heparin layer inhibited neurons but promoted proliferation and migration of precursor cells. This methodology may orchestrate neural cell behavior on electroactive polymers, thus improving cell/electrode communication in prosthetic devices and providing a platform for tissue repair strategies. Copyright © 2010 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahalik, J. P.; Sumpter, Bobby G.; Kumar, Rajeev

In this paper, we use a field theory approach to study the effects of permanent dipoles on interpenetration and free energy changes as a function of distance between two identical planar polymer brushes. Melts (i.e., solvent-free) and solvated brushes made up of polymers grafted on nonadsorbing substrates are studied. In particular, the weak coupling limit of the dipolar interactions is considered, which leads to concentration-dependent pairwise interactions, and the effects of orientational order are neglected. It is predicted that a gradual increase in the dipole moment of the polymer segments can lead to attractive interactions between the brushes at intermediatemore » separation distances. Finally, because classical theory of polymer brushes based on the strong stretching limit (SSL) and the standard self-consistent field theory (SCFT) simulations using the Flory’s χ parameter always predicts repulsive interactions at all separations, our work highlights the importance of dipolar interactions in tailoring and accurately predicting forces between polar polymeric interfaces in contact with each other.« less

Improvement of mechanical robustness of the superhydrophobic wood surface by coating PVA/SiO2 composite polymer

NASA Astrophysics Data System (ADS)

Liu, Feng; Wang, Shuliang; Zhang, Ming; Ma, Miaolian; Wang, Chengyu; Li, Jian

2013-09-01

Improvement of the robustness of superhydrophobic surfaces is crucial for the purpose of achieving commercial applications of these surfaces in such various areas as self-cleaning, water repellency and corrosion resistance. We have investigated a fabrication of polyvinyl alcohol (PVA)/silica (SiO2) composite polymer coating on wooden substrates with super repellency toward water, low sliding angles, low contact angle hysteresis, and relatively better mechanical robustness. The composite polymer slurry, consisting of well-mixing SiO2 particles and PVA, is prepared simply and subsequently coated over wooden substrates with good adhesion. In this study, the mechanical robustness of superhydrophobic wood surfaces was evaluated. The effect of petaloid structures of the composite polymer on robustness was investigated using an abrasion test and the results were compared with those of superhydrophobic wood surfaces fabricated by other processes. The produced wood surfaces exhibited promising superhydrophobic properties with a contact angle of 159̊ and a sliding angle of 4̊, and the relatively better mechanical robustness.

Similarity to the Self Affects Memory for Impressions of Others in Younger and Older Adults

PubMed Central

Park, Jung M.; Gutchess, Angela H.

2015-01-01

Objectives. Similarity to the self has been shown to affect memory for impressions in younger adults, suggesting a self-reference effect in person memory. Because older adults show comparable self-reference effects, but prioritize memory for positive over negative information relative to young adults, we examined age differences in self-similarity effects on memory for positive and negative impressions. Method. Younger and older adults formed positive and negative impressions of others differing in the degree of similarity to the self (high, medium, low). Results. For positive impressions, both groups showed enhanced memory for self-similar others relative to dissimilar others, whereas for negative impressions, memory was poorer for those similar to the self. When collapsed across similarity to the self, younger adults remembered negative impressions better than older adults, but interestingly, older adults exhibited a trend for better memory for the positive impressions. Discussion. Results suggest that self-reference effects in impression memory are preserved with age and that older adults exhibit positivity effects in person memory consistent with previous findings. PMID:24389124

Extreme Activity of Drug Nanocrystals Coated with A Layer of Non-Covalent Polymers from Self-Assembled Boric Acid

NASA Astrophysics Data System (ADS)

Zhan, Honglei; Liang, Jun F.

2016-12-01

Non-covalent polymers have remarkable advantages over synthetic polymers for wide biomedical applications. In this study, non-covalent polymers from self-assembled boric acid were used as the capping reagent to replace synthetic polymers in drug crystallization. Under acidic pH, boric acid self-assembled on the surface of drug nanocrystals to form polymers with network-like structures held together by hydrogen bonds. Coating driven by boric acid self-assembly had negligible effects on drug crystallinity and structure but resulted in drug nanocrystals with excellent dispersion properties that aided in the formation of a more stable suspension. Boric acid coating improved drug stability dramatically by preventing drug molecules from undergoing water hydrolysis in a neutral environment. More importantly, the specific reactivity of orthoboric groups to diols in cell glycocalyx facilitated a rapid cross-membrane translocation of drug nanocrystals, leading to efficient intracellular drug delivery, especially on cancer cells with highly expressed sialic acids. Boric acid coated nanocrystals of camptothecin, an anticancer drug with poor aqueous solubility and stability, demonstrated extreme cytotoxic activity (IC50 < 5.0 μg/mL) to cancer cells compared to synthetic polymer coated CPT nanocrystals and free CPT. Surface coating using non-covalent polymers from self-assembled boric acid will have wide biomedical applications especially in biomaterials and drug delivery field.

Extreme Activity of Drug Nanocrystals Coated with A Layer of Non-Covalent Polymers from Self-Assembled Boric Acid.

PubMed

Zhan, Honglei; Liang, Jun F

2016-12-09

Non-covalent polymers have remarkable advantages over synthetic polymers for wide biomedical applications. In this study, non-covalent polymers from self-assembled boric acid were used as the capping reagent to replace synthetic polymers in drug crystallization. Under acidic pH, boric acid self-assembled on the surface of drug nanocrystals to form polymers with network-like structures held together by hydrogen bonds. Coating driven by boric acid self-assembly had negligible effects on drug crystallinity and structure but resulted in drug nanocrystals with excellent dispersion properties that aided in the formation of a more stable suspension. Boric acid coating improved drug stability dramatically by preventing drug molecules from undergoing water hydrolysis in a neutral environment. More importantly, the specific reactivity of orthoboric groups to diols in cell glycocalyx facilitated a rapid cross-membrane translocation of drug nanocrystals, leading to efficient intracellular drug delivery, especially on cancer cells with highly expressed sialic acids. Boric acid coated nanocrystals of camptothecin, an anticancer drug with poor aqueous solubility and stability, demonstrated extreme cytotoxic activity (IC 50  < 5.0 μg/mL) to cancer cells compared to synthetic polymer coated CPT nanocrystals and free CPT. Surface coating using non-covalent polymers from self-assembled boric acid will have wide biomedical applications especially in biomaterials and drug delivery field.

Extreme Activity of Drug Nanocrystals Coated with A Layer of Non-Covalent Polymers from Self-Assembled Boric Acid

PubMed Central

Zhan, Honglei; Liang, Jun F.

2016-01-01

Non-covalent polymers have remarkable advantages over synthetic polymers for wide biomedical applications. In this study, non-covalent polymers from self-assembled boric acid were used as the capping reagent to replace synthetic polymers in drug crystallization. Under acidic pH, boric acid self-assembled on the surface of drug nanocrystals to form polymers with network-like structures held together by hydrogen bonds. Coating driven by boric acid self-assembly had negligible effects on drug crystallinity and structure but resulted in drug nanocrystals with excellent dispersion properties that aided in the formation of a more stable suspension. Boric acid coating improved drug stability dramatically by preventing drug molecules from undergoing water hydrolysis in a neutral environment. More importantly, the specific reactivity of orthoboric groups to diols in cell glycocalyx facilitated a rapid cross-membrane translocation of drug nanocrystals, leading to efficient intracellular drug delivery, especially on cancer cells with highly expressed sialic acids. Boric acid coated nanocrystals of camptothecin, an anticancer drug with poor aqueous solubility and stability, demonstrated extreme cytotoxic activity (IC50 < 5.0 μg/mL) to cancer cells compared to synthetic polymer coated CPT nanocrystals and free CPT. Surface coating using non-covalent polymers from self-assembled boric acid will have wide biomedical applications especially in biomaterials and drug delivery field. PMID:27934922

On the kinetics of body versus end evaporation and addition of supramolecular polymers.

PubMed

Tiwari, Nitin S; van der Schoot, Paul

2017-06-01

The kinetics of the self-assembly of supramolecular polymers is dictated by how monomers, dimers, trimers etc., attach to and detach from each other. It is for this reasons that researchers have proposed a plethora of pathways to explain the kinetics of various self-assembling supramolecules, including sulfur, linear micelles, living polymers and protein fibrils. Recent observations hint at the importance of a hitherto ignored molecular aggregation pathway that we refer to as "body evaporation and addition". In this pathway, monomers can enter at or dissociate from any point along the backbone of the polymer. In this paper, we compare predictions for the well-established end evaporation and addition pathway with those that we obtained for the newly proposed body evaporation and addition model. We quantify the lag time, characteristic of nucleated reversible polymerisation, in terms of the time it takes to obtain half of the steady-state polymerised fraction and the apparent growth rate at that point, and obtain power laws for both as a function of the total monomer concentration. We find, perhaps not entirely unexpectedly, that the body evaporation and addition pathway speeds up the relaxation of the polymerised monomeric mass relative to that of the end evaporation and addition. However, the presence of the body evaporation and addition pathway does not affect the dependence of the lag time on the total monomer concentration and it remains the same as that for the case of end evaporation and addition. The scaling of the lag time with the forward rate is different for the two models, suggesting that they may be distinguished experimentally.

Thin Polymer Films with Continuous Vertically Aligned 1 nm Pores Fabricated by Soft Confinement

DOE PAGES

Feng, Xunda; Nejati, Siamak; Cowan, Matthew G.; ...

2015-12-03

Membrane separations are critically important in areas ranging from health care and analytical chemistry to bioprocessing and water purification. An ideal nanoporous membrane would consist of a thin film with physically continuous and vertically aligned nanopores and would display a narrow distribution of pore sizes. However, the current state of the art departs considerably from this ideal and is beset by intrinsic trade-offs between permeability and selectivity. We demonstrate an effective and scalable method to fabricate polymer films with ideal membrane morphologies consisting of submicron thickness films with physically continuous and vertically aligned 1 nm pores. The approach is basedmore » on soft confinement to control the orientation of a cross-linkable mesophase in which the pores are produced by self-assembly. The scalability, exceptional ease of fabrication, and potential to create a new class of nanofiltration membranes stand out as compelling aspects.« less

Towards an automated and efficient calculation of resonating vibrational states based on state-averaged multiconfigurational approaches

NASA Astrophysics Data System (ADS)

Meier, Patrick; Oschetzki, Dominik; Pfeiffer, Florian; Rauhut, Guntram

2015-12-01

Resonating vibrational states cannot consistently be described by single-reference vibrational self-consistent field methods but request the use of multiconfigurational approaches. Strategies are presented to accelerate vibrational multiconfiguration self-consistent field theory and subsequent multireference configuration interaction calculations in order to allow for routine calculations at this enhanced level of theory. State-averaged vibrational complete active space self-consistent field calculations using mode-specific and state-tailored active spaces were found to be very fast and superior to state-specific calculations or calculations with a uniform active space. Benchmark calculations are presented for trans-diazene and bromoform, which show strong resonances in their vibrational spectra.

Towards an automated and efficient calculation of resonating vibrational states based on state-averaged multiconfigurational approaches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meier, Patrick; Oschetzki, Dominik; Pfeiffer, Florian

Resonating vibrational states cannot consistently be described by single-reference vibrational self-consistent field methods but request the use of multiconfigurational approaches. Strategies are presented to accelerate vibrational multiconfiguration self-consistent field theory and subsequent multireference configuration interaction calculations in order to allow for routine calculations at this enhanced level of theory. State-averaged vibrational complete active space self-consistent field calculations using mode-specific and state-tailored active spaces were found to be very fast and superior to state-specific calculations or calculations with a uniform active space. Benchmark calculations are presented for trans-diazene and bromoform, which show strong resonances in their vibrational spectra.

Self-Assembly of Diblock Molecular Polymer Brushes in the Spherical Confinement of Nanoemulsion Droplets.

PubMed

Steinhaus, Andrea; Pelras, Théophile; Chakroun, Ramzi; Gröschel, André H; Müllner, Markus

2018-05-02

Understanding the self-assembly behavior of polymers of various topologies is key to a reliable design of functional polymer materials. Self-assembly under confinement conditions emerges as a versatile avenue to design polymer particles with complex internal morphologies while simultaneously facilitating scale-up. However, only linear block copolymers have been studied to date, despite the increasing control over macromolecule composition and architecture available. This study extends the investigation of polymer self-assembly in confinement from regular diblock copolymers to diblock molecular polymer brushes (MPBs). Block-type MPBs with polystyrene (PS) and polylactide (PLA) compartments of different sizes are incorporated into surfactant-stabilized oil-in-water (chloroform/water) emulsions. The increasing confinement in the nanoemulsion droplets during solvent evaporation directs the MPBs to form solid nano/microparticles. Microscopy studies reveal an intricate internal particle structure, including interpenetrating networks and axially stacked lamellae of PS and PLA, depending on the PS/PLA ratio of the brushes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

NMR Water Self-Diffusion and Relaxation Studies on Sodium Polyacrylate Solutions and Gels in Physiologic Ionic Solutions.

PubMed

Bai, Ruiliang; Basser, Peter J; Briber, Robert M; Horkay, Ferenc

2014-03-15

Water self-diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca 2+ and Na + . Several physical models describing the self-diffusion of the solvent were applied and compared. A free-volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non-linear behavior at higher concentrations. Both the water self-diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na + on the mobility of water molecules was practically undetectable. By contrast, addition of Ca 2+ strongly increased the longitudinal relaxation rate while its effect on the self-diffusion coefficient was much less pronounced.

Compartmentalization Technologies via Self-Assembly and Cross-Linking of Amphiphilic Random Block Copolymers in Water.

PubMed

Matsumoto, Mayuko; Terashima, Takaya; Matsumoto, Kazuma; Takenaka, Mikihito; Sawamoto, Mitsuo

2017-05-31

Orthogonal self-assembly and intramolecular cross-linking of amphiphilic random block copolymers in water afforded an approach to tailor-make well-defined compartments and domains in single polymer chains and nanoaggregates. For a double compartment single-chain polymer, an amphiphilic random block copolymer bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dodecyl, benzyl, and olefin pendants was synthesized by living radical polymerization (LRP) and postfunctionalization; the dodecyl and benzyl units were incorporated into the different block segments, whereas PEG pendants were statistically attached along a chain. The copolymer self-folded via the orthogonal self-assembly of hydrophobic dodecyl and benzyl pendants in water, followed by intramolecular cross-linking, to form a single-chain polymer carrying double yet distinct hydrophobic nanocompartments. A single-chain cross-linked polymer with a chlorine terminal served as a globular macroinitiator for LRP to provide an amphiphilic tadpole macromolecule comprising a hydrophilic nanoparticle and a hydrophobic polymer tail; the tadpole thus self-assembled into multicompartment aggregates in water.

The Evolution of Thin-Film Structure in pi-Conjugated System: Implications for Devices

DTIC Science & Technology

2015-07-09

dependent, polymer self - assembly (Chem Matls, 2015). The results provide vital insights into factors leading to organized conjugated polymer nanostructures...34Liquid Crystalline Poly(3-hexylthiophene) Solutions Revisited: Role of Time- dependent Self - Assembly ", Chemistry of Materials (2015), 27(7), 2687-2694...period (if none, report none): For the first time, we demonstrated that π-conjugated polymers self - assemble and exhibit liquid crystal ordering

Mechanophores for Self-Healing Applications

DTIC Science & Technology

2013-09-09

macroscopic failure. One of the first discovered mechanochemical reactions was the self - healing of vulcanized rubber . Damaging mechanical force...therefore have potential self - healing features. Using the serendipitous case of rubber as a model, mechanophores that produce reactive species under...Mechanophores for Self - Healing Applications Supramolecular polymers held together by hydrogen bonds make efficient self - healing systems. A rubber -like polymer

Interface-engineering additives of poly(oxyethylene tridecyl ether) for low-band gap polymer solar cells consisting of PCDTBT:PCBM₇₀ bulk-heterojunction layers.

PubMed

Huh, Yoon Ho; Park, Byoungchoo

2013-01-14

We herein report on the improved photovoltaic (PV) effects of using a polymer bulk-heterojunction (BHJ) layer that consists of a low-band gap electron donor polymer of poly(N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)) (PCDTBT) and an acceptor of [6,6]-phenyl C₇₁ butyric acid methyl ester (PCBM₇₀), doped with an interface-engineering surfactant additive of poly(oxyethylene tridecyl ether) (PTE). The presence of an interface-engineering additive in the PV layer results in excellent performance; the addition of PTE to a PCDTBT:PCBM₇₀ system produces a power conversion efficiency (PCE) of 6.0%, which is much higher than that of a reference device without the additive (4.9%). We attribute this improvement to an increased charge carrier lifetime, which is likely to be the result of the presence of PTE molecules oriented at the interfaces between the BHJ PV layer and the anode and cathode, as well as at the interfaces between the phase-separated BHJ domains. Our results suggest that the incorporation of the PTE interface-engineering additive in the PCDTBT:PCBM₇₀ PV layer results in a functional composite system that shows considerable promise for use in efficient polymer BHJ PV cells.

Optical sensor in planar configuration based on multimode interference

NASA Astrophysics Data System (ADS)

Blahut, Marek

2017-08-01

In the paper a numerical analysis of optical sensors based on multimode interference in planar one-dimensional step-index configuration is presented. The structure consists in single-mode input and output waveguides and multimode waveguide which guide only few modes. Material parameters discussed refer to a SU8 polymer waveguide on SiO2 substrate. The optical system described will be designed to the analysis of biological substances.

Effects of self-healing microcapsules on bending performance in composite brake pads

NASA Astrophysics Data System (ADS)

Zhang, Li; Dong, Xiu-ping; Wang, Hui

2009-07-01

For the purpose of reducing self-weight, friction noise and cost, improving shock absorption, enhancing corrosion and wear resistance, brake pads made of composite materials with self-healing function are prepared to substitute metal ones by designing ingredients and applying optimized production technology. As self-healing capsules are chosen, new method with technology of self-healing microcapsules, dicyclpentadiene (DCPD) microcapsules coated with poly (urea-formaldehyde), is put forward in this paper. In the crack's extending process, the stress is concentrated at the crack end, where the microcapsule is designed to be located. When the stress goes through the microcapsules and causes them to break, the self-healing liquid runs out to fill the crack by the capillary and it will poly-react with catalyst in the composite. As a result, the crack is healed. In this paper, polymer matrix composite brake pads with 6 prescriptions are prepared and studied. Three-point bending tests are carried out according to standards in GB/T 3356-1999 and the elastic constants of these polymer matrix composites are obtained by experiments. In accordance with the law of the continuous fiber composite, elastic constants of the short-fiber composite can be calculated by proportions of each ingredient. Results show that the theoretical expected results and the experimental values are consistent. 0.3-1.2 % mass proportion of microcapsules has little effects on the composite's bending intensity and modulus of elasticity. These studies also show that self-healing microcapsules used in composite brake pads is feasible.

Recognition-Mediated Assembly of Quantum Dot Polymer Conjugates with Controlled Morphology

PubMed Central

Nandwana, Vikas; Subramani, Chandramouleeswaran; Eymur, Serkan; Yeh, Yi-Cheun; Tonga, Gulen Yesilbag; Tonga, Murat; Jeong, Youngdo; Yang, Boqian; Barnes, Michael D.; Cooke, Graeme; Rotello, Vincent M.

2011-01-01

We have demonstrated a polymer mediated “bricks and mortar” method for the self-assembly of quantum dots (QDs). This strategy allows QDs to self-assemble into structured aggregates using complementary three-point hydrogen bonding. The resulting nanocomposites have distinct morphologies and inter-particle distances based on the ratio between QDs and polymer. Time resolved photoluminescence measurements showed that the optical properties of the QDs were retained after self-assembly. PMID:22016664

Self-healing polymers and composites based on thermal activation

NASA Astrophysics Data System (ADS)

Wang, Ying; Bolanos, Ed; Wudl, Fred; Hahn, Thomas; Kwok, Nathan

2007-04-01

Structural polymer composites are susceptible to premature failure in the form of microcracks in the matrix. Although benign initially when they form, these matrix cracks tend to coalesce and lead in service to critical damage modes such as ply delamination. The matrix cracks are difficult to detect and almost impossible to repair because they form inside the composite laminate. Therefore, polymers with self-healing capability would provide a promising potential to minimize maintenance costs while extending the service lifetime of composite structures. In this paper we report on a group of polymers and their composites which exhibit mendable property upon heating. The failure and healing mechanisms of the polymers involve Diels-Alder (DA) and retro-Diels-Alder (RDA) reactions on the polymer back-bone chain, which are thermally reversible reactions requiring no catalyst. The polymers exhibited good healing property in bulk form. Composite panels were prepared by sandwiching the monomers between carbon fiber fabric layers and cured in autoclave. Microcracks were induced on the resin-rich surface of composite with Instron machine at room temperature by holding at 1% strain for 1 min. The healing ability of the composite was also demonstrated by the disappearance of microcracks after heating. In addition to the self-healing ability, the polymers and composites also exhibited shape memory property. These unique properties may provide the material multi-functional applications. Resistance heating of traditional composites and its applicability in self-healing composites is also studied to lay groundwork for a fully integrated self-healing composite.

Synthesis of a Self-Healing Polymer Based on Reversible Diels-Alder Reaction: An Advanced Undergraduate Laboratory at the Interface of Organic Chemistry and Materials Science

ERIC Educational Resources Information Center

Weizman, Haim; Nielsen, Christian; Weizman, Or S.; Nemat-Nasser, Sia

2011-01-01

This laboratory experiment exposes students to the chemistry of self-healing polymers based on a Diels-Alder reaction. Students accomplish a multistep synthesis of a monomer building block and then polymerize it to form a cross-linked polymer. The healing capability of the polymer is verified by differential scanning calorimetry (DSC) experiments.…

Factors affecting the stability of drug-loaded polymeric micelles and strategies for improvement

NASA Astrophysics Data System (ADS)

Zhou, Weisai; Li, Caibin; Wang, Zhiyu; Zhang, Wenli; Liu, Jianping

2016-09-01

Polymeric micelles (PMs) self-assembled by amphiphilic block copolymers have been used as promising nanocarriers for tumor-targeted delivery due to their favorable properties, such as excellent biocompatibility, prolonged circulation time, favorable particle sizes (10-100 nm) to utilize enhanced permeability and retention effect and the possibility for functionalization. However, PMs can be easily destroyed due to dilution of body fluid and the absorption of proteins in system circulation, which may induce drug leakage from these micelles before reaching the target sites and compromise the therapeutic effect. This paper reviewed the factors that influence stability of micelles in terms of thermodynamics and kinetics consist of the critical micelle concentration of block copolymers, glass transition temperature of hydrophobic segments and polymer-polymer and polymer-cargo interaction. In addition, some effective strategies to improve the stability of micelles were also summarized.

Fabrication of porous hierarchical polymer/ceramic composites by electron irradiation of organic/inorganic polymers: route to a highly durable, large-area superhydrophobic coating.

PubMed

Lee, Eun Je; Kim, Jae Joon; Cho, Sung Oh

2010-03-02

Polymer/ceramic composite films with micro- and nanocombined hierarchical structures are fabricated by electron irradiation of poly(methyl methacrylate) (PMMA) microspheres/silicone grease. Electron irradiation induces volume contraction of PMMA microspheres and simultaneously transforms silicone grease into a ceramic material of silicon oxycarbide with many nanobumps. As a result, highly porous structures that consist of micrometer-sized pores and microparticles decorated with nanobumps are created. The fabricated films with the porous hierarchical structure exhibit good superhydrophobicity with excellent self-cleaning and antiadhesion properties after surface treatment with fluorosilane. In addition, the porous hierarchical structures are covered with silicon oxycarbide, and thus the superhydrophobic coatings have high hardness and strong adhesion to the substrate. The presented technique provides a straightforward route to producing large-area, mechanically robust superhydrophobic films on various substrate materials.

Sequence heuristics to encode phase behaviour in intrinsically disordered protein polymers

PubMed Central

Quiroz, Felipe García; Chilkoti, Ashutosh

2015-01-01

Proteins and synthetic polymers that undergo aqueous phase transitions mediate self-assembly in nature and in man-made material systems. Yet little is known about how the phase behaviour of a protein is encoded in its amino acid sequence. Here, by synthesizing intrinsically disordered, repeat proteins to test motifs that we hypothesized would encode phase behaviour, we show that the proteins can be designed to exhibit tunable lower or upper critical solution temperature (LCST and UCST, respectively) transitions in physiological solutions. We also show that mutation of key residues at the repeat level abolishes phase behaviour or encodes an orthogonal transition. Furthermore, we provide heuristics to identify, at the proteome level, proteins that might exhibit phase behaviour and to design novel protein polymers consisting of biologically active peptide repeats that exhibit LCST or UCST transitions. These findings set the foundation for the prediction and encoding of phase behaviour at the sequence level. PMID:26390327

Integrated Multilayer Insulation

NASA Technical Reports Server (NTRS)

Dye, Scott

2009-01-01

Integrated multilayer insulation (IMLI) is being developed as an improved alternative to conventional multilayer insulation (MLI), which is more than 50 years old. A typical conventional MLI blanket comprises between 10 and 120 metallized polymer films separated by polyester nets. MLI is the best thermal- insulation material for use in a vacuum, and is the insulation material of choice for spacecraft and cryogenic systems. However, conventional MLI has several disadvantages: It is difficult or impossible to maintain the desired value of gap distance between the film layers (and consequently, it is difficult or impossible to ensure consistent performance), and fabrication and installation are labor-intensive and difficult. The development of IMLI is intended to overcome these disadvantages to some extent and to offer some additional advantages over conventional MLI. The main difference between IMLI and conventional MLI lies in the method of maintaining the gaps between the film layers. In IMLI, the film layers are separated by what its developers call a micro-molded discrete matrix, which can be loosely characterized as consisting of arrays of highly engineered, small, lightweight, polymer (typically, thermoplastic) frames attached to, and placed between, the film layers. The term "micro-molded" refers to both the smallness of the frames and the fact that they are fabricated in a process that forms precise small features, described below, that are essential to attainment of the desired properties. The term "discrete" refers to the nature of the matrix as consisting of separate frames, in contradistinction to a unitary frame spanning entire volume of an insulation blanket.

Panoramic View of Electrochemical Pseudocapacitor and Organic Solar Cell Research in Molecularly Engineered Energy Materials (MEEM)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aguirre, Jordan C.; Ferreira, Amy; Ding, Hong

2014-07-09

Our program on capacitive energy storage is a comprehensive one that combines experimental and computational components to achieve a fundamental understanding of charge storage processes in redox-based materials, specifically transition metal oxides. Some of the highlights of this program are the identification of intercalation pseudocapacitance in Nb2O5, which enables high energy density to be achieved at high rates, and the development of a new route for synthesizing mesoporous films in which preformed nanocrystal building blocks are used in combination with polymer templating. The resulting material architectures have large surface areas and enable electrolyte access to the redox active pore walls,more » while the interconnected mesoporous film provides good electronic conductivity. Select first-principles density-functional theory studies of prototypical pseudocapacitor materials are reviewed, providing insight into the key physical and chemical features involved in charge transfer and ion diffusion. Rigorous multiscale physical models and numerical tools have been developed and used to reproduce electrochemical properties of carbon-based electrochemical capacitors with the ultimate objective of facilitating the optimization of electrode design. For the organic photovoltaic (OPV) program, our focus has been ongoing beyond the trial-and-error Edisonian approaches that have been responsible for the increase in power conversion efficiency of blend-cast (BC) bulk heterojunction blends of polymers and fullerenes. Our first approach has been to use molecular self-assembly to create the ideal nanometer-scale architecture using thermodynamics rather than relying on the kinetics of spontaneous phase segregation. We have created fullerenes that self-assemble into one-dimensional stacks and have shown that use of these self-assembled fullerenes lead to dramatically enhanced OPV performance relative to fullerenes that do not assemble. We also have created self-assembling conjugated polymers that form gels based on electrically continuous cross-linked micelles in solution, opening the possibility for water-processable “green” production of OPVs based on these materials. Our second approach has been to avoid kinetic control over phase separation by using a sequential processing (SqP) technique to deposit the polymer and fullerene materials in separate deposition steps. The polymer layer is deposited first, using solvents and deposition conditions that optimize the polymer crystallinity for swelling and hole mobility. The fullerene layer is then deposited in a second step from a solvent that swells the polymer but does not dissolve it, allowing the fullerene to penetrate into the polymer underlayer to the desired degree. Careful comparison of composition- and thickness-matched BC and SqP devices shows that SqP not only produces more efficient devices but also leads to devices that behave more consistently.« less

How interfaces affect hydrophobically driven polymer folding.

PubMed

Jamadagni, Sumanth N; Godawat, Rahul; Dordick, Jonathan S; Garde, Shekhar

2009-04-02

Studies of folding-unfolding of hydrophobic polymers in water provide an excellent starting point to probe manybody hydrophobic interactions in the context of realistic self-assembly processes. Such studies in bulk water have highlighted the similarities between thermodynamics of polymer collapse and of protein folding, and emphasized the role of hydration-water structure, density, and fluctuations-in the folding kinetics. Hydrophobic polymers are interfacially active-that is, they prefer locations at aqueous interfaces relative to bulk water-consistent with their low solubility. How does the presence of a hydrophobic solid surface or an essentially hydrophobic vapor-water interface affect the structural, thermodynamic, and kinetic aspects of polymer folding? Using extensive molecular dynamics simulations, we show that the large hydrophobic driving force for polymer collapse in bulk water is reduced at a solid alkane-water interface and further reduced at a vapor-water interface. As a result, at the solid-water interface, folded structures are marginally stable, whereas the vapor-liquid interface unfolds polymers completely. Structural sampling is also significantly affected by the interface. For example, at the solid-water interface, polymer conformations are quasi-2- dimensional, with folded states being pancake-like structures. At the vapor-water interface, the hydrophobic polymer is significantly excluded from the water phase and freely samples a broad range of compact to extended structures. Interestingly, although the driving force for folding is considerably lower, kinetics of folding are faster at both interfaces, highlighting the role of enhanced water fluctuations and dynamics at a hydrophobic interface.

Cooperative Activated Transport of Dilute Penetrants in Viscous Molecular and Polymer Liquids

NASA Astrophysics Data System (ADS)

Schweizer, Kenneth; Zhang, Rui

We generalize the force-level Elastically Collective Nonlinear Langevin Equation theory of activated relaxation in one-component supercooled liquids to treat the hopping transport of a dilute penetrant in a dense hard sphere fluid. The new idea is to explicitly account for the coupling between penetrant displacement and a local matrix cage re-arrangement which facilitates its hopping. A temporal casuality condition is employed to self-consistently determine a dimensionless degree of matrix distortion relative to the penetrant jump distance using the dynamic free energy concept. Penetrant diffusion becomes increasingly coupled to the correlated matrix displacements for larger penetrant to matrix particle size ratio (R) and/or attraction strength (physical bonds), but depends weakly on matrix packing fraction. In the absence of attractions, a nearly exponential dependence of penetrant diffusivity on R is predicted in the intermediate range of 0.2

Self-folding polymeric containers for encapsulation and delivery of drugs

PubMed Central

Fernandes, Rohan; Gracias, David H.

2012-01-01

Self-folding broadly refers to self-assembly processes wherein thin films or interconnected planar templates curve, roll-up or fold into three dimensional (3D) structures such as cylindrical tubes, spirals, corrugated sheets or polyhedra. The process has been demonstrated with metallic, semiconducting and polymeric films and has been used to curve tubes with diameters as small as 2 nm and fold polyhedra as small as 100 nm, with a surface patterning resolution of 15 nm. Self-folding methods are important for drug delivery applications since they provide a means to realize 3D, biocompatible, all-polymeric containers with well-tailored composition, size, shape, wall thickness, porosity, surface patterns and chemistry. Self-folding is also a highly parallel process, and it is possible to encapsulate or self-load therapeutic cargo during assembly. A variety of therapeutic cargos such as small molecules, peptides, proteins, bacteria, fungi and mammalian cells have been encapsulated in self-folded polymeric containers. In this review, we focus on self-folding of all-polymeric containers. We discuss the mechanistic aspects of self-folding of polymeric containers driven by differential stresses or surface tension forces, the applications of self-folding polymers in drug delivery and we outline future challenges. PMID:22425612

Supramolecular Polymer Network-Mediated Self-Assembly of Semicrystalline Polymers with Excellent Crystalline Performance.

PubMed

Cheng, Chih-Chia; Chuang, Wei-Tsung; Lee, Duu-Jong; Xin, Zhong; Chiu, Chih-Wei

2017-03-01

A novel application of supramolecular interactions within semicrystalline polymers, capable of self-assembling into supramolecular polymer networks via self-complementary multiple hydrogen-bonded complexes, is demonstrated for efficient construction of highly controlled self-organizing hierarchical structures to offer a direct, efficient nucleation pathway resulting in superior crystallization performance. Herein, a novel functionalized poly(ε-caprolactone) containing self-complementary sextuple hydrogen-bonded uracil-diamidopyridine (U-DPy) moieties is successfully developed and demonstrated excellent thermal and viscoelastic properties as well as high dynamic structural stability in the bulk state due to physical cross-linking created by reversible sextuple hydrogen bonding between U-DPy units. Due to the ability to vary the extent of the reversible network by tuning the U-DPy content, this newly developed material can be readily adjusted to obtain the desired crystalline products with specific characteristics. Importantly, incorporating only 0.1% U-DPy resulted in a polymer with a high crystallization rate constant, short crystallization half-time, and much more rapid crystallization kinetics than pristine PCL, indicating a low content of U-DPy moieties provides highly efficient nucleation sites that manipulate the nucleation and growth processes of polymer crystals to promote crystallization and chain alignment in bulk. This new system is suggested as a potential new route to substantially improve the performance of polymer crystallization. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-healing composites and applications thereof

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tee, Chee Keong; Wang, Chao; Cui, Yi

A battery electrode includes an electrochemically active material and a binder covering the electrochemically active material. The binder includes a self-healing polymer and conductive additives dispersed in the self-healing polymer to provide an electrical pathway across at least a portion of the binder.

Liquid crystalline order in mucus

NASA Technical Reports Server (NTRS)

Viney, C.; Huber, A. E.; Verdugo, P.

1993-01-01

Mucus plays an exceptionally wide range of important biological roles. It operates as a protective, exchange, and transport medium in the digestive, respiratory, and reproductive systems of humans and other vertebrates. Mucus is a polymer hydrogel. It is secreted as discrete packages (secretory granules) by specialized secretory cells. Mucus hydrogel is stored in a condensed state inside the secretory granules. Depending upon the architecture of their constituent macromolecules and on the composition of the solvent, polymer gels can form liquid crystalline microstructures, with orientational order being exhibited over optically resolvable distances. Individual mucin molecules consist of alternating rigid segments (heavily glycosylated; hydrophilic) and flexible segments (nonglycosylated; hydrophobic). Polymer molecules consisting of rigid units linked by flexible spacers are frequently associated with liquid crystalline behavior, which again raises the possibility that mucus could form anisotropic fluid phases. Suggestions that mucins may be self-associating in dilute solution have previously been challenged on the basis of sedimentation-equilibrium studies performed on mucus in which potential sites of association were competitively blocked with inhibitors. However, the formation of stable liquid crystalline phases does not depend on the existence of inter- or intramolecular associations; these phases can form on the basis of steric considerations alone.

Strong Selective Adsorption of Polymers.

PubMed

Ge, Ting; Rubinstein, Michael

2015-06-09

A scaling theory is developed for selective adsorption of polymers induced by the strong binding between specific monomers and complementary surface adsorption sites. By "selective" we mean specific attraction between a subset of all monomers, called "sticky", and a subset of surface sites, called "adsorption sites". We demonstrate that, in addition to the expected dependence on the polymer volume fraction ϕ bulk in the bulk solution, selective adsorption strongly depends on the ratio between two characteristic length scales, the root-mean-square distance l between neighboring sticky monomers along the polymer, and the average distance d between neighboring surface adsorption sites. The role of the ratio l / d arises from the fact that a polymer needs to deform to enable the spatial commensurability between its sticky monomers and the surface adsorption sites for selective adsorption. We study strong selective adsorption of both telechelic polymers with two end monomers being sticky and multisticker polymers with many sticky monomers between sticky ends. For telechelic polymers, we identify four adsorption regimes at l / d < 1 that are characterized by the fraction of occupied adsorption sites and whether the dominant conformation of adsorbed chains is a single-end-adsorbed "mushroom" or double-end-adsorbed loop. For l / d > 1, we expect that the adsorption layer at exponentially low ϕ bulk consists of separated unstretched loops, while as ϕ bulk increases the layer crosses over to a brush of extended loops with a second layer of weakly overlapping tails. For multisticker chains, in the limit of exponentially low ϕ bulk , adsorbed polymers are well separated from each other. As l / d increases, the conformation of an individual polymer changes from a single-end-adsorbed "mushroom" to a random walk of loops. For high ϕ bulk , adsorbed polymers at small l / d are mushrooms that cover all the adsorption sites. At sufficiently large l / d , adsorbed multisticker polymers strongly overlap. We anticipate the formation of a self-similar carpet and with increasing l / d a two-layer structure with a brush of loops covered by a self-similar carpet. As l / d exceeds the threshold determined by the adsorption energy, the brush of loops under the carpet reaches a saturated state, resulting in a l / d -independent brush-under-carpet structure, which can also be applied to describe adsorbed multisticker polymers in nonselective adsorption where a sticker can strongly bind to any place on the adsorption surface. We examine the adsorbed amount Γ of multisticker polymers in different regimes for selective adsorption. If the adsorbed multisticker polymers are nonoverlapping mushrooms, the adsorbed amount Γ increases linearly with the surface density of adsorption sites Σ ≈ 1/ d 2 . In the self-similar carpet regime, Γ increases sublinearly as Σ 0.15 in a good solvent, while only logarithmically in a theta solvent. Formation of a brush layer under the carpet contributes an additional adsorbed amount. This additional amount increases linearly with Σ and eventually dominates the overall adsorbed amount Γ before saturating at a plateau value controlled by the adsorption energy.

Tailoring the mucoadhesive and sustained release characteristics of mesalamine loaded formulations for local treatment of distal forms of ulcerative colitis.

PubMed

Ali, Hany S M; Hanafy, Ahmed F; El Achy, Samar N

2016-10-10

Direct delivery of sustained therapeutic levels of mesalamine (MS) via rectal systems to manage distal forms of ulcerative colitis was studied. The High molecular weight hydroxypropyl methylcellulose (HPMC K4M) polymer was combined with hydrophilic surfactants to control polymer hydration process allowing optimization of the mucoadhesive and controlled drug release properties for the rectal systems. Physical mixtures and granules of MS and HPMC K4M were prepared and in vitro characterized using scanning electron microscope, differential scanning calorimetry and X-ray diffraction techniques. Rectal formulations were prepared utilizing MS-HPMC K4M mixtures in different polyethylene glycol (PEG) combination bases. The developed rectal formulations were investigated for physical, mucoadhesion, in-vitro drug release and swelling characteristics. Results revealed acceptable physical characteristics of the prepared formulations with good content uniformity and minimum weight variation. Sustained release patterns of MS form HPMC K4M based formulations were observed. Formulations prepared using high proportions of the polymer or PEG 400 showed higher extent of mucoadhesion, swelling and greatly extended drug release time. Efficacy of an optimized formulation was assessed using the acetic acid induced colitis model in rats and compared to a reference polymer-free formulation of the drug. Clinical evaluation included bleeding from rectum, consistency of animal stool and colon/body weight ratio. Furthermore, histopathological analysis was carried out to evaluate the degree of inflammation and mucosal damage. Overall results showed a significant enhancement in the clinical pictures and colon histopathology of animals treated by the sustained release mucoadhesive formulation compared to the reference polymer free formulation and the non-treated colitis group. Copyright © 2016 Elsevier B.V. All rights reserved.

Microsecond MD Simulations of Nano-patterned Polymer Brushes on Self-Assembled Monolayers

NASA Astrophysics Data System (ADS)

Buie, Creighton; Qiu, Liming; Cheng, Kwan; Park, Soyeun

2010-03-01

Nano-patterned polymer brushes end-grafted onto self-assembled monolayers have gained increasing research interests due to their unique thermodynamic properties and their chemical and biomedical applications in colloids, biosensing and tissue engineering. So far, the interactions between the polymer brushes with the surrounding environments such as the floor and solvent at the nanometer length scale and microsecond time scale are still difficult to obtained experimentally and computationally. Using a Coarse-Grained MD approach, polymer brushes of different monomeric lengths, grafting density and hydrophobicity of the monomers grafted on self-assembled monolayers and in explicit solvent were studied. Molecular level information, such as lateral diffusion, transverse height and volume contour of the brushes, were calculated from our microsecond-MD simulations. Our results demonstrated the significance of the hydration of the polymer in controlling the conformational arrangement of the polymer brushes.

Self Diffusion in Nano Filled Polymer Melts: a Molecular Dynamics Simulation Study

NASA Astrophysics Data System (ADS)

Desai, Tapan; Keblinski, Pawel

2003-03-01

SELF DIFFUSION IN NANO FILLED POLYMER MELTS: A MOLECULAR DYNAMICS SIMULATION STUDY* T. G. Desai,P. Keblinski, Material Science and Engineering Department, Rensselaer Polytechnic Institute, Troy, NY. Using molecular dynamics simulations, we studied the dynamics of the polymeric systems containing immobile and analytically smooth spherical nanoparticles. Each chain consisted of N monomers connected by an anharmonic springs described by the finite extendible nonlinear elastic, FENE potential. The system comprises of 3nanoparticles and the rest by freely rotating but not overlapping chains. The longest chain studied has a Radius of gyration equal to particle size radius and comparable to inter-particle distance. There is no effect on the structural characteristics such as Radius of gyration or end to end distance due to the nanoparticles. Diffusion of polymeric chains is not affected by the presence of either attractive or repulsive nanoparticles. In all cases Rouse dynamics is observed for short chains with a crossover to reptation dynamics for longer chains.

Effect of bidispersity in grafted chain length on grafted chain conformations and potential of mean force between polymer grafted nanoparticles in a homopolymer matrix.

PubMed

Nair, Nitish; Wentzel, Nathaniel; Jayaraman, Arthi

2011-05-21

In efforts to produce polymeric materials with tailored physical properties, significant interest has grown around the ability to control the spatial organization of nanoparticles in polymer nanocomposites. One way to achieve controlled particle arrangement is by grafting the nanoparticle surface with polymers that are compatible with the matrix, thus manipulating the interfacial interactions between the nanoparticles and the polymer matrix. Previous work has shown that the molecular weight of the grafted polymer, both at high grafting density and low grafting density, plays a key role in dictating the effective inter-particle interactions in a polymer matrix. At high grafting density nanoparticles disperse (aggregate) if the graft molecular weight is higher (lower) than the matrix molecular weight. At low grafting density the longer grafts can better shield the nanoparticle surface from direct particle-particle contacts than the shorter grafts and lead to the dispersion of the grafted particles in the matrix. Despite the importance of graft molecular weight, and evidence of non-trivial effects of polydispersity of chains grafted on flat surfaces, most theoretical work on polymer grafted nanoparticles has only focused on monodisperse grafted chains. In this paper, we focus on how bidispersity in grafted chain lengths affects the grafted chain conformations and inter-particle interactions in an implicit solvent and in a dense homopolymer polymer matrix. We first present the effects of bidispersity on grafted chain conformations in a single polymer grafted particle using purely Monte Carlo (MC) simulations. This is followed by calculations of the potential of mean force (PMF) between two grafted particles in a polymer matrix using a self-consistent Polymer Reference Interaction Site Model theory-Monte Carlo simulation approach. Monte Carlo simulations of a single polymer grafted particle in an implicit solvent show that in the bidisperse polymer grafted particles with an equal number of short and long grafts at low to medium grafting density, the short grafts are in a more coiled up conformation (lower radius of gyration) than their monodisperse counterparts to provide a larger free volume to the longer grafts so they can gain conformational entropy. The longer grafts do not show much difference in conformation from their monodisperse counterparts at low grafting density, but at medium grafting density the longer grafts exhibit less stretched conformations (lower radius of gyration) as compared to their monodisperse counterparts. In the presence of an explicit homopolymer matrix, the longer grafts are more compressed by the matrix homopolymer chains than the short grafts. We observe that the potential of mean force between bidisperse grafted particles has features of the PMF of monodisperse grafted particles with short grafts and monodisperse grafted particles with long grafts. The value of the PMF at contact is governed by the short grafts and values at large inter-particle distances are governed by the longer grafts. Further comparison of the PMF for bidisperse and monodisperse polymer grafted particles in a homopolymer matrix at varying parameters shows that the effects of matrix chain length, matrix packing fraction, grafting density, and particle curvature on the PMF between bidisperse polymer grafted particles are similar to those seen between monodisperse polymer grafted particles. © 2011 American Institute of Physics.

Modeling and control of a self-sensing polymer metal composite actuator

NASA Astrophysics Data System (ADS)

Nam, Doan Ngoc Chi; Ahn, Kyoung Kwan

2014-02-01

An ion polymer metal composite (IPMC) is an electro-active polymer (EAP) that bends in response to a small applied electrical field as a result of mobility of cations in the polymer network and vice versa. One drawback in the use of an IPMC is the sensing problem for such a small size actuator. The aim of this paper is to develop a physical model for a self-sensing IPMC actuator and to verify its applicability for practical position control. Firstly, ion dynamics inside a polymer membrane is investigated with an asymmetric solution in the presence of distributed surface resistance. Based on this analysis, a modified equivalent circuit and a simple configuration to realize the self-sensing IPMC actuator are proposed. Mathematical modelling and experimental evaluation indicate that the bending curvature can be obtained accurately using several feedback voltage signals along with the IPMC length. Finally, the controllability of the developed self-sensing IPMC actuator is investigated using a robust position control. Experimental results prove that the self-sensing characteristics can be applied in engineering control problems to provide a more convenient sensing method for IPMC actuating systems.

Self-healing in single and multiple fiber(s) reinforced polymer composites

NASA Astrophysics Data System (ADS)

Woldesenbet, E.

2010-06-01

You Polymer composites have been attractive medium to introduce the autonomic healing concept into modern day engineering materials. To date, there has been significant research in self-healing polymeric materials including several studies specifically in fiber reinforced polymers. Even though several methods have been suggested in autonomic healing materials, the concept of repair by bleeding of enclosed functional agents has garnered wide attention by the scientific community. A self-healing fiber reinforced polymer composite has been developed. Tensile tests are carried out on specimens that are fabricated by using the following components: hollow and solid glass fibers, healing agent, catalysts, multi-walled carbon nanotubes, and a polymer resin matrix. The test results have demonstrated that single fiber polymer composites and multiple fiber reinforced polymer matrix composites with healing agents and catalysts have provided 90.7% and 76.55% restoration of the original tensile strength, respectively. Incorporation of functionalized multi-walled carbon nanotubes in the healing medium of the single fiber polymer composite has provided additional efficiency. Healing is found to be localized, allowing multiple healing in the presence of several cracks.

Low Leachable Container System Consisting of a Polymer-Based Syringe with Chlorinated Isoprene Isobutene Rubber Plunger Stopper.

PubMed

Kiminami, Hideaki; Takeuchi, Katsuyuki; Nakamura, Koji; Abe, Yoshihiko; Lauwers, Philippe; Dierick, William; Yoshino, Keisuke; Suzuki, Shigeru

2015-01-01

A 36 month leachable study on water for injection in direct contact within a polymer-based prefillable syringe consisting of a cyclo olefin polymer barrel, a chlorinated isoprene isobutene rubber plunger stopper, a polymer label attached on the barrel, and a secondary packaging was conducted at 25 ± 2 °C and 60 ± 5% relative humidity. Through the various comparison studies, no difference in the leachable amounts was observed between this polymer-based prefilled syringe and a glass bottle as a blank sample reference by 36 months. No influence on the leachables study outcome was noted from the printed label and/or label adhesive or from the secondary packaging. In an additional study, no acrylic acid used as the label adhesive leachable was detected by an extended storage for 45 months at 25 ± 2 °C and 60 ± 5% relative humidity as a worst case. To obtain more details, a comparison extractable study was conducted between a cyclo olefin polymer barrel and a glass barrel. In addition, chlorinated isoprene isobutene rubber and bromo isoprene isobutene rubber were compared. As a result, no remarkable difference was found in the organic extractables for syringe barrels. On the other hand, in the case of element extractable analysis, the values for the cyclo olefin polymer barrel were lower than that for the glass barrel. For the plunger stoppers, the chlorinated isoprene isobutene rubber applied in this study was showing a lower extractable profile as compared to the bromo isoprene isobutene rubber, both for organic and element extractables. In conclusion, the proposed polymer-based prefillable syringe system has great potential and represents a novel alternative that can achieve very low level extractable profiles and can bring additional value to the highly sensitive biotech drug market. A 36 month leachable study on water for injection in direct contact within a cyclo olefin polymer barrel and chlorinated isoprene isobutene rubber plunger stopper that has a polymer label attached to the barrel and is wrapped into a secondary packaging was conducted at 25 °C and 60% relative humidity. Through the various comparison studies, no difference in the leachable amounts was observed between polymer-based prefilled syringes and a glass bottle as a blank sample reference by 36 months. No influences on the leachables study outcome were noted from the secondary packaging. To obtain more details, a comparison extractable study was conducted between the cyclo olefin polymer and the glass barrel. In addition, chlorinated isoprene isobutene rubber and bromo isoprene isobutene rubber plunger stoppers were compared as well. As a result, no remarkable difference was found in the organic extractables for barrels. As for element extractable analysis, the values for the cyclo olefin polymer barrel were lower than that for the glass barrel. For the plunger stoppers, the chlorinated isoprene isobutene rubber applied in this study was showing a lower extractable profile as compared to the bromo isoprene isobutene rubber, both for organic and element extractables. In conclusion, the proposed polymer-based prefillable syringe system has great potential and represents a novel alternative that can achieve very low level extractable profiles and can bring additional value to the highly sensitive biotech drug market. © PDA, Inc. 2015.

Structure and Conductivity of Semiconducting Polymer Hydrogels.

PubMed

Huber, Rachel C; Ferreira, Amy S; Aguirre, Jordan C; Kilbride, Daniel; Toso, Daniel B; Mayoral, Kenny; Zhou, Z Hong; Kopidakis, Nikos; Rubin, Yves; Schwartz, Benjamin J; Mason, Thomas G; Tolbert, Sarah H

2016-07-07

Poly(fluorene-alt-thiophene) (PFT) is a conjugated polyelectrolyte that self-assembles into rod-like micelles in water, with the conjugated polymer backbone running along the length of the micelle. At modest concentrations (∼10 mg/mL in aqueous solutions), PFT forms hydrogels, and this work focuses on understanding the structure and intermolecular interactions in those gel networks. The network structure can be directly visualized using cryo electron microscopy. Oscillatory rheology studies further tell us about connectivity within the gel network, and the data are consistent with a picture where polymer chains bridge between micelles to hold the network together. Addition of tetrahydrofuran (THF) to the gels breaks those connections, but once the THF is removed, the gel becomes stronger than it was before, presumably due to the creation of a more interconnected nanoscale architecture. Small polymer oligomers can also passivate the bridging polymer chains, breaking connections between micelles and dramatically weakening the hydrogel network. Fits to solution-phase small-angle X-ray scattering data using a Dammin bead model support the hypothesis of a bridging connection between PFT micelles, even in dilute aqueous solutions. Finally, time-resolved microwave conductivity measurements on dried samples show an increase in carrier mobility after THF annealing of the PFT gel, likely due to increased connectivity within the polymer network.

Self-healing hyperbranched poly(aroyltriazole)s

PubMed Central

Wei, Qiang; Wang, Jian; Shen, Xiaoyuan; Zhang, Xiao A.; Sun, Jing Zhi; Qin, Anjun; Tang, Ben Zhong

2013-01-01

The research on self-healing polymers has been a hot topic. The encapsulated-monomer/catalyst, supramolecular self-assembly, and reversible or dynamic covalent bond formation are the prevailingly adopted strategies. The alternative of irreversible covalent bond formation is, however, to be further developed. In this contribution, self-healing hyperbranched poly(aroyltriazole)s of PI and PII sharing such mechanism were developed. The polymers were synthesized by our developed metal-free click polymerizations of bis(aroylacetylene)s and triazide. They are processible and have excellent film-forming ability. High quality homogeneous films and sticks free from defects could be obtained by casting. The scratched films could be self-repaired upon general heating. The cut films and sticks could be healed by stacking or pressing the halves together at elevated temperature. Thus, these hyperbranched polymers could find broad applications in diverse areas, and our design concept for self-healing materials should be generally applicable to other hyperbranched polymers with reactive groups on their peripheries.

Ion solvation in polymer blends and block copolymer melts: effects of chain length and connectivity on the reorganization of dipoles.

PubMed

Nakamura, Issei

2014-05-29

We studied the thermodynamic properties of ion solvation in polymer blends and block copolymer melts and developed a dipolar self-consistent field theory for polymer mixtures. Our theory accounts for the chain connectivity of polymerized monomers, the compressibility of the liquid mixtures under electrostriction, the permanent and induced dipole moments of monomers, and the resultant dielectric contrast among species. In our coarse-grained model, dipoles are attached to the monomers and allowed to rotate freely in response to electrostatic fields. We demonstrate that a strong electrostatic field near an ion reorganizes dipolar monomers, resulting in nonmonotonic changes in the volume fraction profile and the dielectric function of the polymers with respect to those of simple liquid mixtures. For the parameter sets used, the spatial variations near an ion can be in the range of 1 nm or larger, producing significant differences in the solvation energy among simple liquid mixtures, polymer blends, and block copolymers. The solvation energy of an ion depends substantially on the chain length in block copolymers; thus, our theory predicts the preferential solvation of ions arising from differences in chain length.

Synthesis and Study of Guest-Rebinding of MIP Based on MAA Prepared using Theophylline Template

NASA Astrophysics Data System (ADS)

Nurhayati, T.; Yanti; Royani, I.; Widayani; Khairurrijal

2016-08-01

A molecularly imprinted polymer (MIP) based on methacrylic acid (MAA) monomer and theophylline template has been synthesized using a modified bulk polymerization method. Theophylline was employed as a template and it formed a complex with MAA through hydrogen bonding. Self-assembly of template-monomer was followed by cross-linking process using ethylene glycol dimethacrylate (EGDMA) cross-linker. The polymerization process was initiated by thermal decomposition of benzoyl peroxide (BPO) as the initiator at 60oC after cooling treatment at -5oC. After 7 hours, a rigid polymer was obtained and followed by grinding the polymer and removing the template. As a reference, a nonimprinted polymer (NIP) has also been synthesized using similar procedure by excluding the template. FTIR study was carried out to investigate the presence of theophylline in the as- prepared polymer, MIP, and NIP. The spectra indicated that theophylline was successfully incorporated in the as-prepared polymer. This result was also confirmed by EDS analysis showing that N atoms of the as-prepared polymer were derived from amino group of theophylline. Furthermore, the polymer particles of MIP were irregular in shape and size as shown by its SEM image. The capability of guest-rebinding of the MIP was analyzed through Batchwise guest-binding experiment. The results showed that for initial concentration of theophylline in methanol/chloroform (1/1, v/v) of 0.333 mM, the binding capacity of the MIP was 23.22 /mol/g. Compared to the MIP, the adsorption capacity of the NIP was only 3.73 /mol/g. This result shows that MIP has higher affinity than NIP.

Controlled Supramolecular Self-Assembly of Super-charged β-Lactoglobulin A-PEG Conjugates into Nanocapsules.

PubMed

Khan, Amit Kumar; Gudlur, Sushanth; de Hoog, Hans-Peter M; Siti, Winna; Liedberg, Bo; Nallani, Madhavan

2017-09-18

The synthesis and characterization of a new protein-polymer conjugate composed of β lactoglobulin A (βLG A) and poly(ethylene glycol) PEG is described. βLG A was selectively modified to self-assemble by super-charging via amination or succinylation followed by conjugation with PEG. An equimolar mixture of the oppositely charged protein-polymer conjugates self-assemble into spherical capsules of 80-100 nm in diameter. The self-assembly proceeds by taking simultaneous advantage of the amphiphilicity and polyelectrolyte nature of the protein-polymer conjugate. These protein-polymer capsules or proteinosomes are reminiscent of protein capsids, and are capable of encapsulating solutes in their interior. We envisage this approach to be applicable to other globular proteins. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tough Self-Healing Elastomers by Molecular Enforced Integration of Covalent and Reversible Networks.

PubMed

Wu, Jinrong; Cai, Li-Heng; Weitz, David A

2017-10-01

Self-healing polymers crosslinked by solely reversible bonds are intrinsically weaker than common covalently crosslinked networks. Introducing covalent crosslinks into a reversible network would improve mechanical strength. It is challenging, however, to apply this concept to "dry" elastomers, largely because reversible crosslinks such as hydrogen bonds are often polar motifs, whereas covalent crosslinks are nonpolar motifs. These two types of bonds are intrinsically immiscible without cosolvents. Here, we design and fabricate a hybrid polymer network by crosslinking randomly branched polymers carrying motifs that can form both reversible hydrogen bonds and permanent covalent crosslinks. The randomly branched polymer links such two types of bonds and forces them to mix on the molecular level without cosolvents. This enables a hybrid "dry" elastomer that is very tough with fracture energy 13500 Jm -2 comparable to that of natural rubber. Moreover, the elastomer can self-heal at room temperature with a recovered tensile strength 4 MPa, which is 30% of its original value, yet comparable to the pristine strength of existing self-healing polymers. The concept of forcing covalent and reversible bonds to mix at molecular scale to create a homogenous network is quite general and should enable development of tough, self-healing polymers of practical usage. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-curing concrete with different self-curing agents

NASA Astrophysics Data System (ADS)

Gopala krishna sastry, K. V. S.; manoj kumar, Putturu

2018-03-01

Concrete is recognised as a versatile construction material globally. Properties of concrete depend upon, to a greater extent, the hydration of cement and microstructure of hydrated cement. Congenial atmosphere would aid the hydration of cement and hence curing of concrete becomes essential, till a major portion of the hydration process is completed. But in areas of water inadequacy and concreting works at considerable heights, curing is problematic. Self-Curing or Internal Curing technique overcomes these problems. It supplies redundant moisture, for more than sufficient hydration of cement and diminish self-desiccation. Self-Curing agents substantially help in the conservation of water in concrete, by bringing down the evaporation during the hydration of Concrete. The present study focuses on the impact of self-curing agents such as Poly Ethylene Glycol (PEG), Poly Vinyl Alcohol (PVA) and Super Absorbent Polymer (SAP) on the concrete mix of M25 grade (reference mix). The effect of these agents on strength properties of Concrete such as compressive strength, split tensile strength and flexural strength was observed on a comparative basis which revealed that PEG 4000 was the most effective among all the agents.

Self-Assembled Core-Shell-Type Lipid-Polymer Hybrid Nanoparticles: Intracellular Trafficking and Relevance for Oral Absorption.

PubMed

Li, Qiuxia; Xia, Dengning; Tao, Jinsong; Shen, Aijun; He, Yuan; Gan, Yong; Wang, Chi

2017-10-01

Lipid-polymer hybrid nanoparticles (NPs) are advantageous for drug delivery. However, their intracellular trafficking mechanism and relevance for oral drug absorption are poorly understood. In this study, self-assembled core-shell lipid-polymer hybrid NPs made of poly(lactic-co-glycolic acid) (PLGA) and various lipids were developed to study their differing intracellular trafficking in intestinal epithelial cells and their relevance for oral absorption of a model drug saquinavir (SQV). Our results demonstrated that the endocytosis and exocytosis of hybrid NPs could be changed by varying the kind of lipid. A glyceride mixture (hybrid NPs-1) decreased endocytosis but increased exocytosis in Caco-2 cells, whereas the phospholipid (E200) (hybrid NPs-2) decreased endocytosis but exocytosis was unaffected as compared with PLGA nanoparticles. The transport of hybrid NPs-1 in cells involved various pathways, including caveolae/lipid raft-dependent endocytosis, and clathrin-mediated endocytosis and macropinocytosis, which was different from the other groups of NPs that involved only caveolae/lipid raft-dependent endocytosis. Compared with that of the reference formulation (nanoemulsion), the oral absorption of SQV-loaded hybrid NPs in rats was poor, probably due to the limited drug release and transcytosis of NPs across the intestinal epithelium. In conclusion, the intracellular processing of hybrid NPs in intestinal epithelia can be altered by adding lipids to the NP. However, it appears unfavorable to use PLGA-based NPs to improve oral absorption of SQV compared with nanoemulsion. Our findings will be essential in the development of polymer-based NPs for the oral delivery of drugs with the purpose of improving their oral absorption. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Bis-urea-based supramolecular polymer: the first self-assembled drag reducer for hydrocarbon solvents.

PubMed

Sabadini, Edvaldo; Francisco, Kelly R; Bouteiller, Laurent

2010-02-02

The hydrodynamic drag reduction phenomenon, also termed the Toms effect, is an unusual case involving macromolecules in solution in which the resistance to flow is reduced comparatively to that of the pure solvent. Although the effect is relatively well characterized, it is still unclear from the molecular viewpoint. The presence of some amount of a polymer with high molecular weight can produce large levels of drag reduction in turbulent flow as a result of the interactions of the long structures with the small vortices developed during the flow. For this reason, the effect is very attractive in the pumping process because a significant amount of energy can be saved. In aqueous systems, giant micelles can be spontaneously formed, driven by the hydrophobic effect, and are effective drag reducers. Giant micelles are interesting in promoting drag reduction because the noncovalent and reversible aggregation of the surfactant molecules avoids mechanical degradation, which typically occurs with classical polymers, due to irreversible scission of the backbone. In this letter, we present the first hydrodynamic drag reducer for hydrocarbons based on a self-assembled polymer formed from the reversible aggregation of bis-urea monomers. This system forms two competitive polymeric structures--the tube (T) and the filament (F) forms--which are in equilibrium with each other. Our rheology results in octane and toluene are fully consistent with calorimetry data and show that only the longest form, T, is able to promote the drag reduction effect.

Star-like supramolecular polymers fabricated by a Keplerate cluster with cationic terminated polymers and their self-assembly into vesicles.

PubMed

Zhang, Qian; He, Lipeng; Wang, Hui; Zhang, Cheng; Liu, Weisheng; Bu, Weifeng

2012-07-18

The electrostatic combination of a Keplerate cluster, [Mo(132)O(372)(CH(3)COO)(30)(H(2)O)(72)](42-) with cationic terminated poly(styrene) yields polyoxometalate-based supramolecular star polymers, which can further self-assemble into vesicular aggregates in CHCl(3)-MeOH mixed solvent.

Simulation of self-assembly of polyzwitterions into vesicles

DOE PAGES

Mahalik, Jyoti P.; Muthukumar, Murugappan

2016-08-19

Using the Langevin dynamics method and a coarse-grained model, we have researched the formation of vesicles by hydrophobic polymers consisting of periodically placed zwitterion side groups in dilute salt-free aqueous solutions. The zwitterions, being permanent charge dipoles, provide long-range electrostatic correlations which are interfered by the conformational entropy of the polymer. Our simulations are geared towards gaining conceptual understanding in these correlated dipolar systems, where theoretical calculations are at present formidable. A competition between hydrophobic interactions and dipole-dipole interactions leads to a series of self-assembled structures. As the spacing d between the successive zwitterion side groups decreases, single chains undergomore » globule → disk → worm-like structures. We have calculated the Flory-Huggins χ parameter for these systems in terms of d and monitored the radius of gyration, hydrodynamic radius, spatial correlations among hydrophobic and dipole monomers, and dipole-dipole orientational correlation functions. During the subsequent stages of self-assembly, these structures lead to larger globules and vesicles as d is decreased up to a threshold value, below which no large scale morphology forms. Finally the vesicles form via a polynucleation mechanism whereby disk-like structures form first, followed by their subsequent merger.« less

NMR Water Self–Diffusion and Relaxation Studies on Sodium Polyacrylate Solutions and Gels in Physiologic Ionic Solutions

PubMed Central

Bai, Ruiliang; Basser, Peter J.; Briber, Robert M.; Horkay, Ferenc

2013-01-01

Water self-diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca2+ and Na+. Several physical models describing the self-diffusion of the solvent were applied and compared. A free-volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non-linear behavior at higher concentrations. Both the water self-diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na+ on the mobility of water molecules was practically undetectable. By contrast, addition of Ca2+ strongly increased the longitudinal relaxation rate while its effect on the self-diffusion coefficient was much less pronounced. PMID:24409001

Self-referential processing is distinct from semantic elaboration: evidence from long-term memory effects in a patient with amnesia and semantic impairments.

PubMed

Sui, Jie; Humphreys, Glyn W

2013-11-01

We report data demonstrating that self-referential encoding facilitates memory performance in the absence of effects of semantic elaboration in a severely amnesic patient also suffering semantic problems. In Part 1, the patient, GA, was trained to associate items with the self or a familiar other during the encoding phase of a memory task (self-ownership decisions in Experiment 1 and self-evaluation decisions in Experiment 2). Tests of memory showed a consistent self-reference advantage, relative to a condition where the reference was another person in both experiments. The pattern of the self-reference advantage was similar to that in healthy controls. In Part 2 we demonstrate that GA showed minimal effects of semantic elaboration on memory for items he semantically classified, compared with items subject to physical size decisions; in contrast, healthy controls demonstrated enhanced memory performance after semantic relative to physical encoding. The results indicate that self-referential encoding, not semantic elaboration, improves memory in amnesia. Self-referential processing may provide a unique scaffold to help improve learning in amnesic cases. Copyright © 2013 Elsevier Ltd. All rights reserved.

Bone repair using a new injectable self-crosslinkable bone substitute.

PubMed

Fellah, Borhane H; Weiss, Pierre; Gauthier, Olivier; Rouillon, Thierry; Pilet, Paul; Daculsi, Guy; Layrolle, Pierre

2006-04-01

A new injectable and self-crosslinkable bone substitute (IBS2) was developed for filling bone defects. The IBS2 consisted of a chemically modified polymer solution mixed with biphasic calcium phosphate (BCP) ceramic particles. The polymer hydroxypropylmethyl cellulose was functionalized with silanol groups (Si-HPMC) and formed a viscous solution (3 wt %) in alkaline medium. With a decrease in pH, self-hardening occurred due to the formation of intermolecular -Si-O- bonds. During setting, BCP particles, 40 to 80 microm in diameter, were added to the polymer solution at a weight ratio of 50/50. The resulting injectable material was bilaterally implanted into critically sized bone defects at the distal femoral epiphyses of nine New Zealand White rabbits. The IBS2 filled the bone defects entirely and remained in place. After 8 weeks, bone had grown centripetally and progressed towards the center of the defects. Newly formed bone, ceramic, and nonmineralized tissue ratios were 24.6% +/- 5.6%, 21.6% +/- 5.8%, and 53.7% +/- 0.1%, respectively. Mineralized and mature bone was observed between and in contact with the BCP particles. The bone/ceramic apposition was 73.4% +/- 10.6%. The yield strength for the IBS2-filled defects was 16.4 +/- 7.2 MPa, significantly higher than for the host trabecular bone tissue (2.7 +/- 0.4 MPa). This study showed that BCP particles supported the bone healing process by osteoconduction while the Si-HPMC hydrogel created intergranular space for bone ingrowth. This new injectable and self-crosslinkable bone substitute could be used conveniently in orthopedic surgery for filling critical-size bone defects. Copyright 2006 Orthopaedic Research Society

Examining the Self-Assembly of Rod-Coil Block Copolymers via Physics Based Polymer Models and Polarized X-Ray Scattering

NASA Astrophysics Data System (ADS)

Hannon, Adam; Sunday, Daniel; Windover, Donald; Liman, Christopher; Bowen, Alec; Khaira, Gurdaman; de Pablo, Juan; Delongchamp, Dean; Kline, R. Joseph

Photovoltaics, flexible electronics, and stimuli-responsive materials all require enhanced methodology to examine their nanoscale molecular orientation. The mechanical, electronic, optical, and transport properties of devices made from these materials are all a function of this orientation. The polymer chains in these materials are best modeled as semi-flexible to rigid rods. Characterizing the rigidity and molecular orientation of these polymers non-invasively is currently being pursued by using polarized resonant soft X-ray scattering (P-RSoXS). In this presentation, we show recent work on implementing such a characterization process using a rod-coil block copolymer system in the rigid-rod limit. We first demonstrate how we have used physics based models such as self-consistent field theory (SCFT) in non-polarized RSoXS work to fit scattering profiles for thin film coil-coil PS- b-PMMA block copolymer systems. We then show by using a wormlike chain partition function in the SCFT formulism to model the rigid-rod block, the methodology can be used there as well to extract the molecular orientation of the rod block from a simulated P-RSoXS experiment. The results from the work show the potential of the technique to extract thermodynamic and morphological sample information.

Host polymer influence on dilute polystyrene segmental dynamics

NASA Astrophysics Data System (ADS)

Lutz, T. R.

2005-03-01

We have utilized deuterium NMR to investigate the segmental dynamics of dilute (2%) d3-polystyrene (PS) chains in miscible polymer blends with polybutadiene, poly(vinyl ethylene), polyisoprene, poly(vinyl methylether) and poly(methyl methacrylate). In the dilute limit, we find qualitative differences depending upon whether the host polymer has dynamics that are faster or slower than that of pure PS. In blends where PS is the fast (low Tg) component, segmental dynamics are slowed upon blending and can be fit by the Lodge-McLeish model. When PS is the slow (high Tg) component, PS segmental dynamics speed up upon blending, but cannot be fit by the Lodge-McLeish model unless a temperature dependent self-concentration is employed. These results are qualitatively consistent with a recent suggestion by Kant, Kumar and Colby (Macromolecules, 2003, 10087), based upon data at higher concentrations. Furthermore, as the slow component, we find the segmental dynamics of PS has a temperature dependence similar to that of its host. This suggests viewing the high Tg component dynamics in a miscible blend as similar to a polymer in a low molecular weight solvent.

Elasticity dominated surface segregation of small molecules in polymer mixtures

NASA Astrophysics Data System (ADS)

Croce, Salvatore; Krawczyk, Jaroslaw; McLeish, Tom; Chakrabarti, Buddhapriya

When a binary polymer mixture with mobile components is left to equilibrate, the low molecular weight component migrates to the free surface. A balance between loss of translational entropy and gain in surface energy dictates the equilibrium partitioning ratio and the migrant fraction. Despite its ubiquity and several theoretical and experimental investigations, the phenomenon is not fully understood. Further, methods by which migration can be controlled are in its nascent stage of development. We propose a new phenomenological free energy functional that incorporates the elasticity of bulk polymer mixtures (reticulated networks and gels) and show (using mean field and self-consistent field theories) that the migrant fraction decreases with increasing the bulk modulus of the system. Further, a wetting transition observed otherwise for large values of miscibility parameter and polymerization index can be avoided by increasing the elastic modulus of the system. Estimated values of moduli (for the effect to be observable) are akin to those of rubbery polymers. Our work paves the way for controlling surface migration in complex industrial formulations with polymeric ingredients where this effect leads to decreased product stability and performance.

Nature's Mechanisms for Tough, Self-healing Polymers and Polymer Adhesives

NASA Astrophysics Data System (ADS)

Hansma, Paul

2007-03-01

Spider silk^2 and the natural polymer adhesives in abalone shells^3 and bone^4,5 can give us insights into nature's mechanisms for tough, self-healing polymers and polymer adhesives. The natural polymer adhesives in biomaterials have been optimized by evolution. An optimized polymer adhesive has five characteristics. 1) It holds together the strong elements of the composite. 2) It yields just before the strong elements would otherwise break. 3) It dissipates large amounts of energy as it yields. 4) It self heals after it yields. 5) It takes just a few percent by weight. Both natural polymer adhesives and silk rely on sacrificial bonds and hidden length for toughness and self-healing.^6 A relatively large energy, of order 100eV, is required to stretch a polymer molecule after a weak bond, a sacrificial bond, breaks and liberates hidden length, which was previously hidden, typically in a loop or folded domain, from whatever was stretching the polymer. The bond is called sacrificial if it breaks at forces well below the forces that could otherwise break the polymer backbone, typically greater than 1nN. In many biological cases, the breaking of sacrificial bonds has been found to be reversible, thereby also providing a ``self-healing'' property to the material.^2-4 Individual polymer adhesive molecules based on sacrificial bonds and hidden length can supply forces of order 300pN over distances of 100s of nanometers. Model calculations show that a few percent by weight of adhesives based on these principles could be optimized adhesives for high performance composite materials including nanotube and graphene sheet composites. ^2N. Becker, E. Oroudjev, S. Mutz et al., Nature Materials 2 (4), 278 (2003). ^3B. L. Smith, T. E. Schaffer, M. Viani et al., Nature 399 (6738), 761 (1999). ^4J. B. Thompson, J. H. Kindt, B. Drake et al., Nature 414 (6865), 773 (2001). ^5G. E. Fantner, T. Hassenkam, J. H. Kindt et al., Nature Materials 4, 612 (2005). ^6G. E. Fantner, E. Oroudjev, G. Schitter et al., Biophysical Journal 90 (4), 1411 (2006).

A self-healing PDMS polymer with solvatochromic properties.

PubMed

Jia, Xiao-Yong; Mei, Jin-Feng; Lai, Jian-Cheng; Li, Cheng-Hui; You, Xiao-Zeng

2015-05-28

Coordination bonds are effective for constructing functional self-healing materials due to their tunable bond strength and metal-ion-induced functionalities. In this work, we incorporate a cobalt(II) triazole complex into a polydimethylsiloxane (PDMS) matrix. The resulting polymers show solvatochromic behaviour as well as self-healing properties.

Two-Dimensional Self-Consistent Radio Frequency Plasma Simulations Relevant to the Gaseous Electronics Conference RF Reference Cell

PubMed Central

Lymberopoulos, Dimitris P.; Economou, Demetre J.

1995-01-01

Over the past few years multidimensional self-consistent plasma simulations including complex chemistry have been developed which are promising tools for furthering our understanding of reactive gas plasmas and for reactor design and optimization. These simulations must be benchmarked against experimental data obtained in well-characterized systems such as the Gaseous Electronics Conference (GEC) reference cell. Two-dimensional simulations relevant to the GEC Cell are reviewed in this paper with emphasis on fluid simulations. Important features observed experimentally, such as off-axis maxima in the charge density and hot spots of metastable species density near the electrode edges in capacitively-coupled GEC cells, have been captured by these simulations. PMID:29151756

Time-dependent density functional theory (TD-DFT) coupled with reference interaction site model self-consistent field explicitly including spatial electron density distribution (RISM-SCF-SEDD)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yokogawa, D., E-mail: d.yokogawa@chem.nagoya-u.ac.jp; Institute of Transformative Bio-Molecules

2016-09-07

Theoretical approach to design bright bio-imaging molecules is one of the most progressing ones. However, because of the system size and computational accuracy, the number of theoretical studies is limited to our knowledge. To overcome the difficulties, we developed a new method based on reference interaction site model self-consistent field explicitly including spatial electron density distribution and time-dependent density functional theory. We applied it to the calculation of indole and 5-cyanoindole at ground and excited states in gas and solution phases. The changes in the optimized geometries were clearly explained with resonance structures and the Stokes shift was correctly reproduced.

Second-order perturbation theory with a density matrix renormalization group self-consistent field reference function: theory and application to the study of chromium dimer.

PubMed

Kurashige, Yuki; Yanai, Takeshi

2011-09-07

We present a second-order perturbation theory based on a density matrix renormalization group self-consistent field (DMRG-SCF) reference function. The method reproduces the solution of the complete active space with second-order perturbation theory (CASPT2) when the DMRG reference function is represented by a sufficiently large number of renormalized many-body basis, thereby being named DMRG-CASPT2 method. The DMRG-SCF is able to describe non-dynamical correlation with large active space that is insurmountable to the conventional CASSCF method, while the second-order perturbation theory provides an efficient description of dynamical correlation effects. The capability of our implementation is demonstrated for an application to the potential energy curve of the chromium dimer, which is one of the most demanding multireference systems that require best electronic structure treatment for non-dynamical and dynamical correlation as well as large basis sets. The DMRG-CASPT2/cc-pwCV5Z calculations were performed with a large (3d double-shell) active space consisting of 28 orbitals. Our approach using large-size DMRG reference addressed the problems of why the dissociation energy is largely overestimated by CASPT2 with the small active space consisting of 12 orbitals (3d4s), and also is oversensitive to the choice of the zeroth-order Hamiltonian. © 2011 American Institute of Physics

Nanostructure Control of Biologically Inspired Polymers

NASA Astrophysics Data System (ADS)

Rosales, Adrianne Marie

Biological polymers, such as polypeptides, are responsible for many of life's most sophisticated functions due to precisely evolved hierarchical structures. These protein structures are the result of monodisperse sequences of amino acids that fold into well-defined chain shapes and tertiary structures. Recently, there has been much interest in the design of such sequence-specific polymers for materials applications in fields ranging from biotechnology to separations membranes. Non-natural polymers offer the stability and robustness necessary for materials applications; however, our ability to control monomer sequence in non-natural polymers has traditionally operated on a much simpler level. In addition, the relationship between monomer sequence and self-assembly is not well understood for biological molecules, much less synthetic polymers. Thus, there is a need to explore self-assembly phase space with sequence using a model system. Polypeptoids are non-natural, sequence-specific polymers that offer the opportunity to probe the effect of sequence on self-assembly. A variety of monomer interactions have an impact on polymer properties, such as chirality, hydrophobicity, and electrostatic interactions. Thus, a necessary starting point for this project was to investigate monomer sequence effects on the bulk properties of polypeptoid homopolymers. It was found that several polypeptoids have experimentally accessible melting transitions that are dependent on the choice of side chains, and it was shown that this transition is tuned by the incorporation of "defects" or a comonomer. The polypeptoid chain shape is also controlled with the choice of monomer and monomer sequence. By using at least 50% monomers with bulky, chiral side chains, the polypeptoid backbone is sterically twisted into a helix, and as found for the first time in this work, the persistence length is increased. However, this persistence length, which is a measure of the stiffness of the polymer, is small compared to other folded helices, indicating the conformational flexibility of polypeptoid chains. With a firmer understanding of how monomer sequence and composition influence polypeptoid bulk properties, we designed block copolymer systems for self-assembly. Because the governing parameters of block copolymer self-assembly are well understood, this architecture provides a convenient starting point for probing the effect of changing polymer sequence. We found that polystyrene-polypeptoid block copolymers readily self-assemble into hexagonally-packed and lamellar morphologies with long range order, and furthermore, sequence control of the polypeptoid block enables us to tune the strength of segregation (and therefore the order-disorder transition) of the block copolymer. Polypeptoid chain shape also affects self-assembly. In classical synthetic block copolymers, it has typically been difficult to change chain shape without also changing polymer chemistry and therefore other factors affecting self-assembly. The advantage of the polypeptoid system is that it is modular, as the side chain chemistry (and therefore polymer properties) can easily be changed without changing the backbone chemistry. Thus, we have decoupled conformational effects from chemical composition by comparing the self-assembly of block copolymers containing either a helical peptoid block or its racemic, non-helical analog. The increase in the persistence length of the peptoid block due to helicity translates to an increase in the morphological domain spacing. In this work, we further the understanding of the effect of monomer sequence on bulk polypeptoid properties and self-assembly. Our findings pave the way for the rational design of structured synthetic polymers with tunable, sequence-specific properties.

Microfabricated ommatidia using a laser induced self-writing process for high resolution artificial compound eye optical systems.

PubMed

Jung, Hyukjin; Jeong, Ki-Hun

2009-08-17

A microfabricated compound eye, comparable to a natural compound eye shows a spherical arrangement of integrated optical units called artificial ommatidia. Each consists of a self-aligned microlens and waveguide. The increase of waveguide length is imperative to obtain high resolution images through an artificial compound eye for wide field-of - view imaging as well as fast motion detection. This work presents an effective method for increasing the waveguide length of artificial ommatidium using a laser induced self-writing process in a photosensitive polymer resin. The numerical and experimental results show the uniform formation of waveguides and the increment of waveguide length over 850 microm. (c) 2009 Optical Society of America

Self-Injurious Behavior in Correctional and Noncorrectional Psychiatric Patients.

ERIC Educational Resources Information Center

Hillbrand, Marc

1993-01-01

Examined prevalence and selected correlates of self-injurious behavior (SIB) among inmates (n=23) referred for treatment to maximum-security forensic hospital, non-SIB inmates (n=23), and noncorrections SIB patients (n=30). Found two distinct patterns of SIB: pattern consistent with conceptualization of SIB as expression of generalized behavioral…

Enhanced stiffness of silk-like fibers by loop formation in the corona leads to stronger gels.

PubMed

Rombouts, Wolf H; Domeradzka, Natalia E; Werten, Marc W T; Leermakers, Frans A M; de Vries, Renko J; de Wolf, Frits A; van der Gucht, Jasper

2016-11-01

We study the self-assembly of protein polymers consisting of a silk-like block flanked by two hydrophilic blocks, with a cysteine residue attached to the C-terminal end. The silk blocks self-assemble to form fibers while the hydrophilic blocks form a stabilizing corona. Entanglement of the fibers leads to the formation of hydrogels. Under oxidizing conditions the cysteine residues form disulfide bridges, effectively connecting two corona chains at their ends to form a loop. We find that this leads to a significant increase in the elastic modulus of the gels. Using atomic force microscopy, we show that this stiffening is due to an increase of the persistence length of the fibers. Self-consistent-field calculations indicate a slight decrease of the lateral pressure in the corona upon loop formation. We argue that this small decrease in the repulsive interactions affects the stacking of the silk-like blocks in the core, resulting in a more rigid fiber. © 2016 Wiley Periodicals, Inc.

Thermoreversible Morphology and Conductivity of a Conjugated Polymer Network Embedded in Block Copolymer Self-Assemblies

DOE PAGES

Han, Youngkyu; Carrillo, Jan-Michael Y.; Zhang, Zhe; ...

2016-07-19

Self-assembly of block copolymers provides numerous opportunities to create functional materials, utilizing self-assembled microdomains with a variety of morphology and periodic architectures as templates for functional nanofillers. Here new progress is reported toward the fabrication of thermally responsive and electrically conductive polymeric self-assemblies made from a water-soluble poly(thiophene) derivative with short poly(ethylene oxide) side chains and Pluronic L62 block copolymer solution in water. The structural and electrical properties of conjugated polymer-embedded self-assembled architectures are investigated by combining small-angle neutron and X-ray scattering, coarse-grained molecular dynamics simulations, and impedance spectroscopy. The L62 solution template organizes the conjugated polymers by stably incorporatingmore » them into the hydrophilic domains thus inhibiting aggregation. The changing morphology of L62 during the micellarto- lamellar phase transition defines the embedded conjugated polymer network. As a result, the conductivity is strongly coupled to the structural change of the templating L62 phase and exhibits thermally reversible behavior with no signs of quenching of the conductivity at high temperature. In conclusion, this study shows promise for enabling more flexibility in processing and utilizing water-soluble conjugated polymers in aqueous solutions for self-assembly based fabrication of stimuli-responsive nanostructures and sensory materials.« less

Thermoreversible Morphology and Conductivity of a Conjugated Polymer Network Embedded in Block Copolymer Self-Assemblies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Youngkyu; Carrillo, Jan-Michael Y.; Zhang, Zhe

Self-assembly of block copolymers provides numerous opportunities to create functional materials, utilizing self-assembled microdomains with a variety of morphology and periodic architectures as templates for functional nanofillers. Here new progress is reported toward the fabrication of thermally responsive and electrically conductive polymeric self-assemblies made from a water-soluble poly(thiophene) derivative with short poly(ethylene oxide) side chains and Pluronic L62 block copolymer solution in water. The structural and electrical properties of conjugated polymer-embedded self-assembled architectures are investigated by combining small-angle neutron and X-ray scattering, coarse-grained molecular dynamics simulations, and impedance spectroscopy. The L62 solution template organizes the conjugated polymers by stably incorporatingmore » them into the hydrophilic domains thus inhibiting aggregation. The changing morphology of L62 during the micellarto- lamellar phase transition defines the embedded conjugated polymer network. As a result, the conductivity is strongly coupled to the structural change of the templating L62 phase and exhibits thermally reversible behavior with no signs of quenching of the conductivity at high temperature. In conclusion, this study shows promise for enabling more flexibility in processing and utilizing water-soluble conjugated polymers in aqueous solutions for self-assembly based fabrication of stimuli-responsive nanostructures and sensory materials.« less

Morphology of Block Copolymer Electrolytes: A Numerical Self-Consistent Field Theory Study

NASA Astrophysics Data System (ADS)

Hou, Kevin; Qin, Jian

Engineering the morphology of ion-containing block copolymers is imperative for the optimization of their charge-transport and mechanical properties. Existing experiments have demonstrated that the addition of ions has a dramatic effect on the morphology and thermodynamic behavior of these structured electrolytes. We have developed an efficient, symmetry-adapted algorithm to calculate the ionic interactions in the SCFT for ion-containing polymers. We present the results of a numerical SCFT study examining how dielectric heterogeneity, ion concentration, and ion solvation affect morphology, domain spacing, ion distribution, and polymer density profiles. Particular attention is given to the detailed morphological analysis of the bicontinuous gyroidal phase, as well as the relevance of the aforementioned results to ionic conductivity.

Shape-Controlled Fabrication of the Polymer-Based Micromotor Based on the Polydimethylsiloxane Template.

PubMed

Su, Miaoda; Liu, Mei; Liu, Limei; Sun, Yunyu; Li, Mingtong; Wang, Dalei; Zhang, Hui; Dong, Bin

2015-11-03

We report the utilization of the polydimethylsiloxane template to construct polymer-based autonomous micromotors with various structures. Solid or hollow micromotors, which consist of polycaprolactone and platinum nanoparticles, can be obtained with controllable sizes and shapes. The resulting micromotor can not only be self-propelled in solution based on the bubble propulsion mechanism in the presence of the hydrogen peroxide fuel, but also exhibit structure-dependent motion behavior. In addition, the micromotors can exhibit various functions, ranging from fluorescence, magnetic control to cargo transportation. Since the current method can be extended to a variety of organic and inorganic materials, we thus believe it may have great potential in the fabrication of different functional micromotors for diverse applications.

A switchable polymer layer: Chain folding in end-charged polymer brushes

NASA Astrophysics Data System (ADS)

Heine, David; Wu, David T.

2001-03-01

We use a self-consistent field approximation to model the configurations of end-charged homopolymer and block copolymer brushes in response to an external electric field due to charges on the grafting surface. By varying the charge density on the grafting surface, we can cause the chains either to extend outward, greatly increasing the brush height, or to loop back to the grafting surface. We show that such a copolymer brush can present one block at the exposed surface in the extended state and present the other block in the retracted state. This occurs for both a solvated brush and a dry brush. We also compare these results to those of a modified Alexander-de Gennes model for the end-charged homopolymer brush.

A primer on polymer nomenclature: Structure-based, sourced-based and trade names

USDA-ARS?s Scientific Manuscript database

Polymer nomenclature is important because it is part of the language of polymer science and is needed for polymer identification, reference, and documentation. A primer on polymer nomenclature is provided herein for people new to the field or for instructional use. Both structure-based and source-...

Energy dissipation in polymer-polymer adhesion contacts

NASA Astrophysics Data System (ADS)

Garif, Yev Skip

This study focuses on self-adhesion in elastomers as a way of approaching a broader polymer adhesion problem. The model systems studied are cross-linked acrylic pressure-sensitive adhesives (PSA-LNs) synthesized to attain four surface types: neutral, acidic, basic, and polar. As the study progressed, it distinguished itself as the first of its kind to consistently report the effect of temperature on measurable intrinsic parameters of polymer adhesion. The main goal of the study was to understand why the magnitude of the practical adhesion energies of the four PSA-LN systems tested varies disproportionately greater than their respective surface energies. To achieve this goal, continuous sweeps of adhesion energy as a function of rate of interfacial separation were performed using three different adhesion-probing techniques--- peel, micro-scratch, and normal contact. The answer was found in the sub-micron-per-second limit of separation rates. In approaching this limit, the power law behavior of adhesion gradually transitioned into a linear region of markedly weaker sensitivity to rate. Referred to as the "intrinsic window", this linear region was characterized by three parameters: (1) the intrinsic adhesion energy at zero rate of separation; (2) the intrinsic rate sensitivity equal to the proportionality constant of the linear fit; and (3) the critical separation rate in the middle of the transition to the power law. All three were found to be thermally activated. Activation energies suggested that interfacial processes are attributed mainly to dispersive and electrostatic molecular interactions such as hydrogen bonding or van der Waals attraction. Comparative analysis of the intrinsic window of the four PSA-LNs tested showed that an increase in the intrinsic adhesion energy associated with higher surface energy is inherently coupled with an increase in the intrinsic rate sensitivity and reduction in the critical separation rate. When combined, the three parameters reshape the intrinsic window such that the entire power-law portion of the adhesion response is shifted to a level that appears disproportionately high based on the false assumption that there is only one intrinsic parameter contributing to the shift. Thus, the goal of explaining this disproportionality was achieved.

Supramolecular polymerization of a prebiotic nucleoside provides insights into the creation of sequence-controlled polymers.

PubMed

Wang, Jun; Bonnesen, Peter V; Rangel, E; Vallejo, E; Sanchez-Castillo, Ariadna; James Cleaves Ii, H; Baddorf, Arthur P; Sumpter, Bobby G; Pan, Minghu; Maksymovych, Petro; Fuentes-Cabrera, Miguel

2016-01-04

Self-assembly of a nucleoside on Au(111) was studied to ascertain whether polymerization on well-defined substrates constitutes a promising approach for making sequence-controlled polymers. Scanning tunneling microscopy and density functional theory were used to investigate the self-assembly on Au(111) of (RS)-N(9)-(2,3-dihydroxypropyl)adenine (DHPA), a plausibly prebiotic nucleoside analog of adenosine. It is found that DHPA molecules self-assemble into a hydrogen-bonded polymer that grows almost exclusively along the herringbone reconstruction pattern, has a two component sequence that is repeated over hundreds of nanometers, and is erasable with electron-induced excitation. Although the sequence is simple, more complicated ones are envisioned if two or more nucleoside types are combined. Because polymerization occurs on a substrate in a dry environment, the success of each combination can be gauged with high-resolution imaging and accurate modeling techniques. These characteristics make nucleoside self-assembly on a substrate an attractive approach for designing sequence-controlled polymers. Further, by choosing plausibly prebiotic nucleosides, insights may be provided into how nature created the first sequence-controlled polymers capable of storing information. Such insights, in turn, can inspire new ways of synthesizing sequence-controlled polymers.

Chemical and charge transfer studies on interfaces of a conjugated polymer and ITO

NASA Astrophysics Data System (ADS)

David, Tanya M. S.; Arasho, Wondwosson; Smith, O'Neil; Hong, Kunlun; Bonner, Carl; Sun, Sam-Shajing

2017-08-01

Conjugated oligomers and polymers are very attractive for potential future plastic electronic and opto-electronic device applications such as plastic photo detectors and solar cells, thermoelectric devices, field effect transistors, and light emitting diodes. Understanding and optimizing charge transport between an active polymer layer and conductive substrate is critical to the optimization of polymer based electronic and opto-electronic devices. This study focused on the design, synthesis, self-assembly, and electron transfers and transports of a phosphonic acid end-functionalized polyphenylenevinylene (PPV) that was covalently attached and self-assembled onto an Indium Tin Oxide (ITO) substrate. This study demonstrated how atomic force microscopy (AFM) can be an effective characterization technique in conjunction with conventional electron transfer methods, including cyclic voltammetry (CV), towards determining electron transfer rates in polymer and polymer/conductor interface systems. This study found that the electron transfer rates of covalently attached and self-assembled films were much faster than the spin coated films. The knowledge from this study can be very useful for designing potential polymer based electronic and opto-electronic thin film devices.

Interfacial self-healing of nanocomposite hydrogels: Theory and experiment

NASA Astrophysics Data System (ADS)

Wang, Qiming; Gao, Zheming; Yu, Kunhao

2017-12-01

Polymers with dynamic bonds are able to self-heal their fractured interfaces and restore the mechanical strengths. It is largely elusive how to analytically model this self-healing behavior to construct the mechanistic relationship between the self-healing properties (e.g., healed interfacial strength and equilibrium healing time) and the material compositions and healing conditions. Here, we take a self-healable nanocomposite hydrogel as an example to illustrate an interfacial self-healing theory for hydrogels with dynamic bonds. In the theory, we consider the free polymer chains diffuse across the interface and reform crosslinks to bridge the interface. We analytically reveal that the healed strengths of nanocomposite hydrogels increase with the healing time in an error-function-like form. The equilibrium self-healing time of the full-strength recovery decreases with the temperature and increases with the nanoparticle concentration. We further analytically reveal that the healed interfacial strength decreases with increasing delaying time before the healing process. The theoretical results quantitatively match with our experiments on nanosilica hydrogels, and also agree well with other researchers' experiments on nanoclay hydrogels. We expect that this theory would open promising avenues for quantitative understanding of the self-healing mechanics of various polymers with dynamic bonds, and offer insights for designing high-performance self-healing polymers.

Shear History Extensional Rheology Experiment: A Proposed ISS Experiment

NASA Technical Reports Server (NTRS)

Hall, Nancy R.; Logsdon, Kirk A.; Magee, Kevin S.

2007-01-01

The Shear History Extensional Rheology Experiment (SHERE) is a proposed International Space Station (ISS) glovebox experiment designed to study the effect of preshear on the transient evolution of the microstructure and viscoelastic tensile stresses for monodisperse dilute polymer solutions. Collectively referred to as Boger fluids, these polymer solutions have become a popular choice for rheological studies of non-Newtonian fluids and are the non-Newtonian fluid used in this experiment. The SHERE hardware consists of the Rheometer, Camera Arm, Interface Box, Cabling, Keyboard, Tool Box, Fluid Modules, and Stowage Tray. Each component will be described in detail in this paper. In the area of space exploration, the development of in-situ fabrication and repair technology represents a critical element in evolution of autonomous exploration capability. SHERE has the capability to provide data for engineering design tools needed for polymer parts manufacturing systems to ensure their rheological properties have not been impacted in the variable gravity environment and this will be briefly addressed.

Toward a versatile toolbox for cucurbit[n]uril-based supramolecular hydrogel networks through in situ polymerization.

PubMed

Liu, Ji; Soo Yun Tan, Cindy; Lan, Yang; Scherman, Oren A

2017-09-15

The success of exploiting cucurbit[ n ]uril (CB[ n ])-based molecular recognition in self-assembled systems has sparked a tremendous interest in polymer and materials chemistry. In this study, polymerization in the presence of host-guest complexes is applied as a modular synthetic approach toward a diverse set of CB[8]-based supramolecular hydrogels with desirable properties, such as mechanical strength, toughness, energy dissipation, self-healing, and shear-thinning. A range of vinyl monomers, including acrylamide-, acrylate-, and imidazolium-based hydrophilic monomers, could be easily incorporated as the polymer backbones, leading to a library of CB[8] hydrogel networks. This versatile strategy explores new horizons for the construction of supramolecular hydrogel networks and materials with emergent properties in wearable and self-healable electronic devices, sensors, and structural biomaterials. © 2017 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3105-3109.

Micro- and nanostructured electro-active polymer actuators as smart muscles for incontinence treatment

NASA Astrophysics Data System (ADS)

Osmani, Bekim; Töpper, Tino; Deschenaux, Christian; Nohava, Jiri; Weiss, Florian M.; Leung, Vanessa; Müller, Bert

2015-02-01

Treatments of severe incontinence are currently based on purely mechanical systems that generally result in revision after three to five years. Our goal is to develop a prototype acting in a natural-analogue manner as artificial muscle, which is based on electro-active polymers. Dielectric actuators have outstanding performances including millisecond response times, mechanical strains of more than 10 % and power to mass densities similar to natural muscles. They basically consist of polymer films sandwiched between two compliant electrodes. The incompressible but elastic polymer film transduces the electrical energy into mechanical work according to the Maxwell pressure. Available polymer films are micrometers thick and voltages as large as kV are necessary to obtain 10 % strain. For medical implants, polymer films should be nanometer thin to realize actuation below 48 V. The metallic electrodes have to be stretchable to follow the strain of 10 % and remain conductive. Recent results on the stress/strain behavior of anisotropic EAP-cantilevers have shown dependencies on metal electrode preparation. We have investigated tunable anisotropic micro- and nanostructures for metallic electrodes. They show a preferred actuation direction with improved stress-strain behavior. The bending of the cantilever has been characterized by the laser beam deflection method. The impact of the electrode on the effective Young's Modulus is measured using an Ultra Nanoindentation Tester with an integrated reference system for soft polymer surfaces. Once ten thousand layers of nanometer-thin EAP actuators are available, devices beyond the envisioned application will flood the market.

Polymer Self-Assembled Nanostructures as Innovative Drug Nanocarrier Platforms.

PubMed

Pippa, Natassa; Pispas, Stergios; Demetzos, Costas

2016-01-01

Polymer self-assembled nanostructures are used in pharmaceutical sciences as bioactive molecules' delivery systems for therapeutic and diagnostic purposes. Micelles, polyelectrolyte complexes, polymersomes, polymeric nanoparticles, nanogels and polymer grafted liposomes represent delivery vehicles that are marketed and/or under clinical development, as drug formulations. In this mini-review, these, recently appeared in the literature, innovative polymer drug nanocarrier platforms are discussed, starting from their technological development in the laboratory to their potential clinical use, through studies of their biophysics, thermodynamics, physical behavior, morphology, bio-mimicry, therapeutic efficacy and safety. The properties of an ideal drug delivery system are the structural control over size and shape of drug or imaging agent cargo/domain, biocompatibility, nontoxic polymer/ pendant functionality and the precise, nanoscale container and/or scaffolding properties with high drug or imaging agent capacity features. Self-assembled polymer nanostructures exhibit all these properties and could be considered as ideal drug nanocarriers through control of their size, structure and morphology, with the aid of a large variety of parameters, in vitro and in vivo. These modern trends reside at the interface of soft matter self-assembly and pharmaceutical sciences and the technologies for health. Great advantages related to basic science and applications are expected by understanding the self-assembly behavior of these polymeric nanotechnological drug delivery systems, created through bio-inspiration and biomimicry and have potential utilization into clinical applications.

Assessing Prevalence of Overweight and Obesity through Self-Reports of Height and Weight by High School Students in Taipei, Taiwan

ERIC Educational Resources Information Center

Page, Randy M.; Lee, Ching-Mei; Miao, Nae-Fang

2004-01-01

This study compared consistency of age- and gender-specific self-reported height and weight and calculated body mass index among a sample of high school students in Taipei County, Taiwan to reference values for Taiwanese school-aged youth obtained through national studies. Taipei high school students provided self-reports of height and weight that…

Softening of the stiffness of bottle-brush polymers by mutual interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bolisetty, S.; Airaud, C.; Rosenfeldt, S.

2007-04-15

We study bottle-brush macromolecules in a good solvent by small-angle neutron scattering (SANS), static light scattering (SLS), and dynamic light scattering (DLS). These polymers consist of a linear backbone to which long side chains are chemically grafted. The backbone contains about 1600 monomer units (weight average) and every second monomer unit carries side chains with approximately 60 monomer units. The SLS and SANS data extrapolated to infinite dilution lead to the form factor of the polymer that can be described in terms of a wormlike chain with a contour length of 380 nm and a persistence length of 17.5 nm.more » An analysis of the DLS data confirms these model parameters. The scattering intensities taken at finite concentration can be modeled using the polymer reference interaction site model. It reveals a softening of the bottle-brush polymers caused by their mutual interaction. We demonstrate that the persistence decreases from 17.5 nm down to 5 nm upon increasing the concentration from dilute solution to the highest concentration (40.59 g/l) under consideration. The observed softening of the chains is comparable to the theoretically predicted decrease of the electrostatic persistence length of linear polyelectrolyte chains at finite concentrations.« less

Electrochemical energy storage devices comprising self-compensating polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Paul; Bautista-Martinez, Jose Antonio; Friesen, Cody

The disclosed technology relates generally to devices comprising conductive polymers and more particularly to electrochemical devices comprising self-compensating conductive polymers. In one aspect, electrochemical energy storage device comprises a negative electrode comprising an active material including a redox-active polymer. The device additionally comprises a positive electrode comprising an active material including a redox-active polymer. The device further comprises an electrolyte material interposed between the negative electrode and positive electrode and configured to conduct mobile counterions therethrough between the negative electrode and positive electrode. At least one of the negative electrode redox-active polymer and the positive electrode redox-active polymer comprises amore » zwitterionic polymer unit configured to reversibly switch between a zwitterionic state in which the zwitterionic polymer unit has first and second charge centers having opposite charge states that compensate each other, and a non-zwitterionic state in which the zwitterionic polymer unit has one of the first and second charge centers whose charge state is compensated by mobile counterions.« less

Polymer blend lithography: A versatile method to fabricate nanopatterned self-assembled monolayers.

PubMed

Huang, Cheng; Moosmann, Markus; Jin, Jiehong; Heiler, Tobias; Walheim, Stefan; Schimmel, Thomas

2012-01-01

A rapid and cost-effective lithographic method, polymer blend lithography (PBL), is reported to produce patterned self-assembled monolayers (SAM) on solid substrates featuring two or three different chemical functionalities. For the pattern generation we use the phase separation of two immiscible polymers in a blend solution during a spin-coating process. By controlling the spin-coating parameters and conditions, including the ambient atmosphere (humidity), the molar mass of the polystyrene (PS) and poly(methyl methacrylate) (PMMA), and the mass ratio between the two polymers in the blend solution, the formation of a purely lateral morphology (PS islands standing on the substrate while isolated in the PMMA matrix) can be reproducibly induced. Either of the formed phases (PS or PMMA) can be selectively dissolved afterwards, and the remaining phase can be used as a lift-off mask for the formation of a nanopatterned functional silane monolayer. This "monolayer copy" of the polymer phase morphology has a topographic contrast of about 1.3 nm. A demonstration of tuning of the PS island diameter is given by changing the molar mass of PS. Moreover, polymer blend lithography can provide the possibility of fabricating a surface with three different chemical components: This is demonstrated by inducing breath figures (evaporated condensed entity) at higher humidity during the spin-coating process. Here we demonstrate the formation of a lateral pattern consisting of regions covered with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) and (3-aminopropyl)triethoxysilane (APTES), and at the same time featuring regions of bare SiO(x). The patterning process could be applied even on meter-sized substrates with various functional SAM molecules, making this process suitable for the rapid preparation of quasi two-dimensional nanopatterned functional substrates, e.g., for the template-controlled growth of ZnO nanostructures [1].

Photothermal triggering of self-healing processes applied to the reparation of bio-based polymer networks

NASA Astrophysics Data System (ADS)

Altuna, F. I.; Antonacci, J.; Arenas, G. F.; Pettarin, V.; Hoppe, C. E.; Williams, R. J. J.

2016-04-01

Green laser irradiation successfully activated self-healing processes in epoxy-acid networks modified with low amounts of gold nanoparticles (NPs). A bio-based polymer matrix, obtained by crosslinking epoxidized soybean oil (ESO) with an aqueous citric acid (CA) solution, was self-healed through molecular rearrangements produced by transesterification reactions of β-hydroxyester groups generated in the polymerization reaction. The temperature increase required for the triggering of these thermally activated reactions was attained by green light irradiation of the damaged area. Compression force needed to assure a good contact between crack faces was achieved by volume dilatation generated by the same temperature rise. Gold NPs dispersed in the polymer efficiently generated heat in the presence of electromagnetic radiation under plasmon resonance, acting as nanometric heating sources and allowing remote activation of the self-healing in the crosslinked polymer.

Life extension of self-healing polymers with rapidly growing fatigue cracks.

PubMed

Jones, A S; Rule, J D; Moore, J S; Sottos, N R; White, S R

2007-04-22

Self-healing polymers, based on microencapsulated dicyclopentadiene and Grubbs' catalyst embedded in the polymer matrix, are capable of responding to propagating fatigue cracks by autonomic processes that lead to higher endurance limits and life extension, or even the complete arrest of the crack growth. The amount of fatigue-life extension depends on the relative magnitude of the mechanical kinetics of crack propagation and the chemical kinetics of healing. As the healing kinetics are accelerated, greater fatigue life extension is achieved. The use of wax-protected, recrystallized Grubbs' catalyst leads to a fourfold increase in the rate of polymerization of bulk dicyclopentadiene and extends the fatigue life of a polymer specimen over 30 times longer than a comparable non-healing specimen. The fatigue life of polymers under extremely fast fatigue crack growth can be extended through the incorporation of periodic rest periods, effectively training the self-healing polymeric material to achieve higher endurance limits.

High Performance Solid Polymer Electrolytes for Rechargeable Batteries: A Self-Catalyzed Strategy toward Facile Synthesis.

PubMed

Cui, Yanyan; Liang, Xinmiao; Chai, Jingchao; Cui, Zili; Wang, Qinglei; He, Weisheng; Liu, Xiaochen; Liu, Zhihong; Cui, Guanglei; Feng, Jiwen

2017-11-01

It is urgent to seek high performance solid polymer electrolytes (SPEs) via a facile chemistry and simple process. The lithium salts are composed of complex anions that are stabilized by a Lewis acid agent. This Lewis acid can initiate the ring opening polymerization. Herein, a self-catalyzed strategy toward facile synthesis of crosslinked poly(ethylene glycol) diglycidyl ether-based solid polymer electrolyte (C-PEGDE) is presented. It is manifested that the poly(ethylene glycol) diglycidyl ether-based solid polymer electrolyte possesses a superior electrochemical stability window up to 4.5 V versus Li/Li + and considerable ionic conductivity of 8.9 × 10 -5 S cm -1 at ambient temperature. Moreover, the LiFePO 4 /C-PEGDE/Li batteries deliver stable charge/discharge profiles and considerable rate capability. It is demonstrated that this self-catalyzed strategy can be a very effective approach for high performance solid polymer electrolytes.

A rapidly self-healing supramolecular polymer hydrogel with photostimulated room-temperature phosphorescence responsiveness.

PubMed

Chen, Hui; Ma, Xiang; Wu, Shuaifan; Tian, He

2014-12-15

Development of self-healing and photostimulated luminescent supramolecular polymeric materials is important for artificial soft materials. A supramolecular polymeric hydrogel is reported based on the host-guest recognition between a β-cyclodextrin (β-CD) host polymer (poly-β-CD) and an α-bromonaphthalene (α-BrNp) polymer (poly-BrNp) without any additional gelator, which can self-heal within only about one minute under ambient atmosphere without any additive. This supramolecular polymer system can be excited to engender room-temperature phosphorescence (RTP) signals based on the fact that the inclusion of β-CD macrocycle with α-BrNp moiety is able to induce RTP emission (CD-RTP). The RTP signal can be adjusted reversibly by competitive complexation of β-CD with azobenzene moiety under specific irradiation by introducing another azobenzene guest polymer (poly-Azo). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Functional Supramolecular Polymers*

PubMed Central

Aida, T.; Meijer, E.W.; Stupp, S.I.

2012-01-01

Supramolecular polymers can be random and entangled coils with the mechanical properties of plastics and elastomers, but with great capacity for processability, recycling, and self-healing due to their reversible monomer-to-polymer transitions. At the other extreme, supramolecular polymers can be formed by self-assembly among designed subunits to yield shape-persistent and highly ordered filaments. The use of strong and directional interactions among molecular subunits can achieve not only rich dynamic behavior but also high degrees of internal order that are not known in ordinary polymers. They can resemble, for example, the ordered and dynamic one-dimensional supramolecular assemblies of the cell cytoskeleton, and possess useful biological and electronic functions. PMID:22344437

Proposal of simple and novel method of capacity fading analysis using pseudo-reference electrode in lithium ion cells: Application to solvent-free lithium ion polymer batteries

NASA Astrophysics Data System (ADS)

Shono, Kumi; Kobayashi, Takeshi; Tabuchi, Masato; Ohno, Yasutaka; Miyashiro, Hajime; Kobayashi, Yo

2014-02-01

We propose a simple procedure for introducing a pseudo-reference electrode (PRE) to lithium ion batteries using isometric lithium metal placed between the cathode and anode, and we successfully obtained the cathode and anode voltage profiles, individual interfacial impedances, and the misalignment of the operation range between the cathode and anode after cycle operation. The proposed procedure is applicable to lithium ion battery systems using a solid electrolyte to prepare two cells with a lithium counter electrode. We determined the capacity decrease of a solvent-free lithium ion polymer battery consisting of a LiNi1/3Mn1/3Co1/3O2 (NMC), a polyether-based solid polymer electrolyte (SPE), and a graphite (Gr) with the proposed PRE over 1000 cycles. The capacity retention of the [Gr|SPE|NMC] cell reached 50% at the 1000th cycle upon the optimization of cell preparation, and we found that the main factor of the capacity decrease was the continuous irreversible loss of active lithium at the graphite anode, not the oxidation of the SPE. Our findings suggest that we should reconsider combining a polyether-based SPE with a conventionally used 4 V class cathode and a graphite anode to develop an innovative, safe, and low-cost battery for the expected large lithium ion battery systems for stationary use.

Self-folding polymeric containers for encapsulation and delivery of drugs.

PubMed

Fernandes, Rohan; Gracias, David H

2012-11-01

Self-folding broadly refers to self-assembly processes wherein thin films or interconnected planar templates curve, roll-up or fold into three dimensional (3D) structures such as cylindrical tubes, spirals, corrugated sheets or polyhedra. The process has been demonstrated with metallic, semiconducting and polymeric films and has been used to curve tubes with diameters as small as 2nm and fold polyhedra as small as 100nm, with a surface patterning resolution of 15nm. Self-folding methods are important for drug delivery applications since they provide a means to realize 3D, biocompatible, all-polymeric containers with well-tailored composition, size, shape, wall thickness, porosity, surface patterns and chemistry. Self-folding is also a highly parallel process, and it is possible to encapsulate or self-load therapeutic cargo during assembly. A variety of therapeutic cargos such as small molecules, peptides, proteins, bacteria, fungi and mammalian cells have been encapsulated in self-folded polymeric containers. In this review, we focus on self-folding of all-polymeric containers. We discuss the mechanistic aspects of self-folding of polymeric containers driven by differential stresses or surface tension forces, the applications of self-folding polymers in drug delivery and we outline future challenges. Copyright © 2012 Elsevier B.V. All rights reserved.

Packaging of Polyelectrolytes in Viral Capsids: The Interplay Between Polymer Length and Capsid Size

NASA Astrophysics Data System (ADS)

Knobler, Charles

2008-03-01

Each particle of the Cowpea Chlorotic Mottle Virus (CCMV) has a very small ``parts list,'' consisting of two components: a molecule of single-stranded RNA and a 190-residue protein that makes up the 28-nm diameter icosahedral capsid. When purified viral RNA and capsid protein are mixed in solution at an appropriate pH and ionic strength, infectious wild-type viruses form spontaneously. Virus-like particles (VLPs) are formed when the protein self assembles around other anionic polymers such as poly(styrene sulfonate) (PSS). Under different pH and ionic strength conditions the capsid protein can assemble by itself into empty capsids, multishell structures, tubes and sheets. To explore the effect on virion size of the competition between the preferred curvature of the protein and the size of the packaged cargo we have examined the formation of VLPs around PSS polymers with molecular weights ranging from 400 kDa to 3.4 MDa. Two distinct sizes are observed -- 22 nm for the lower molecular weights, jumping to 27 nm at 2 MDa. While under given conditions the size of PSS in solution is directly determined by its molecular weight, the self-complementarity of RNA makes its solution structure dependent on the nucleotide sequence as well. We have therefore employed Small-Angle X-ray Scattering and Fluorescence Correlation Spectroscopy to examine the sizes of viral and non-viral RNAs of identical lengths. A model for the assembly that includes both the self-interactions of the polyelectrolyte and the capsid proteins and the interactions between them provides insight into the experimental results.

Lattice cluster theory for dense, thin polymer films.

PubMed

Freed, Karl F

2015-04-07

While the application of the lattice cluster theory (LCT) to study the miscibility of polymer blends has greatly expanded our understanding of the monomer scale molecular details influencing miscibility, the corresponding theory for inhomogeneous systems has not yet emerged because of considerable technical difficulties and much greater complexity. Here, we present a general formulation enabling the extension of the LCT to describe the thermodynamic properties of dense, thin polymer films using a high dimension, high temperature expansion. Whereas the leading order of the LCT for bulk polymer systems is essentially simple Flory-Huggins theory, the highly non-trivial leading order inhomogeneous LCT (ILCT) for a film with L layers already involves the numerical solution of 3(L - 1) coupled, highly nonlinear equations for the various density profiles in the film. The new theory incorporates the essential "transport" constraints of Helfand and focuses on the strict imposition of excluded volume constraints, appropriate to dense polymer systems, rather than the maintenance of chain connectivity as appropriate for lower densities and as implemented in self-consistent theories of polymer adsorption at interfaces. The ILCT is illustrated by presenting examples of the computed profiles of the density, the parallel and perpendicular bonds, and the chain ends for free standing and supported films as a function of average film density, chain length, temperature, interaction with support, and chain stiffness. The results generally agree with expected general trends.

Photoresponsive polymer design for solar concentrator self-steering heliostats

NASA Astrophysics Data System (ADS)

Barker, Jessica; Basnet, Amod; Bhaduri, Moinak; Burch, Caroline; Chow, Amenda; Li, Xue; Oates, William S.; Massad, Jordan E.; Smith, Ralph

2014-03-01

Concentrating solar energy and transforming it into electricity is clean, economical and renewable. One design of solar power plants consists of an array of heliostats which redirects sunlight to a fixed receiver tower and the generated heat is converted into electricity. Currently, the angles of elevation of heliostats are controlled by motors and drives that are costly and require diverting power that can otherwise be used for producing electricity. We consider replacing the motor and drive system of the heliostat with a photosensitive polymer design that can tilt the mirror using the ability of the polymer to deform when subjected to light. The light causes the underlying molecular structure to change and subsequently, the polymer deforms. The deformation of the polymer is quantified in terms of photostrictive constitutive relations. A mathematical model is derived governing the behaviour of the angle of elevation as the photostrain varies. Photostrain depends on the composition of the polymer, intensity and temperature of light and angle of light polarization. Preliminary findings show a photomechanical rod structural design can provide 60° elevation for temperatures of about 40°C. A photomechanical beam structural design can generate more tilt at lower temperatures. The mathematical analysis illustrates that photostrains on the order of 1% to 10% are desired for both rod and beam designs to produce sufficient tilt under most heliostat field conditions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmitt, Adam K.; Mahanthappa, Mahesh K.

Using a combination of small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), we document the composition-dependent morphologies of 39 new poly(lactide-block-1,4-butadiene-block-lactide) (LBL) block polymers, comprising a broad dispersity B segment (Mn = 4.5–17.7 kg/mol;more » $$\\def\\eth{{\\specialfont\\char238}}$$ = Mw/Mn = 1.72–1.88) and narrow dispersity L end blocks (Mn = 0.6–15.3 kg/mol; $$\\def\\eth{{\\specialfont\\char238}}$$ = 1.10–1.21) with volume fractions 0.26 ≤ fB ≤ 0.95. A subset of these samples undergo melt self-assembly into cylindrical, lamellar, and apparently bicontinuous morphologies. By assessing the states of order and disorder in these triblock polymer melts using temperature-dependent SAXS, we find that broad B segment dispersity increases the minimum segregation strength χN ≳ 27 required for LBL triblock self-assembly relative to the self-consistent mean-field theory prediction χN ≥ 17.9 for narrow dispersity analogues. While B segment dispersity has previously been shown to thermodynamically stabilize the self-assembled morphologies of low χ/high N ABA triblocks, the present study indicates that broad B block dispersity in related high χ/low N systems destabilizes the microphase-separated melt. These observations are rationalized in terms of recent theories that suggest that broad segmental dispersity substantially enhances fluctuation effects at low N, thus disfavoring melt segregation.« less

Reliability study of an emerging fire suppression system

DOE PAGES

Miller, David A.; Rossati, Lyric M.; Fritz, Nathan K.; ...

2015-11-01

Self-contained fire extinguishers are a robust, reliable and minimally invasive means of fire suppression for gloveboxes. Plutonium gloveboxes are known to present harsh environmental conditions for polymer materials, these include radiation damage and chemical exposure, both of which tend to degrade the lifetime of engineered polymer components. The primary component of interest in self-contained fire extinguishers is the nylon 6-6 machined tube that comprises the main body of the system.Thermo-mechanical modeling and characterization of nylon 6-6 for use in plutonium glovebox applications has been carried out. Data has been generated regarding property degradation leading to poor, or reduced, engineering performancemore » of nylon 6-6 components. In this study, nylon 6-6 tensile specimens conforming to the casing of self-contained fire extinguisher systems have been exposed to hydrochloric, nitric, and sulfuric acids. This information was used to predict the performance of a load bearing engineering component comprised of nylon 6-6 and designed to operate in a consistent manner over a specified time period. The study provides a fundamental understanding of the engineering performance of the fire suppression system and the effects of environmental degradation due to acid exposure on engineering performance. Data generated help identify the limitations of self-contained fire extinguishers. No critical areas of concern for plutonium glovebox applications of nylon 6-6 have been identified when considering exposure to mineral acid.« less

Reliability study of an emerging fire suppression system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, David A.; Rossati, Lyric M.; Fritz, Nathan K.

Self-contained fire extinguishers are a robust, reliable and minimally invasive means of fire suppression for gloveboxes. Plutonium gloveboxes are known to present harsh environmental conditions for polymer materials, these include radiation damage and chemical exposure, both of which tend to degrade the lifetime of engineered polymer components. The primary component of interest in self-contained fire extinguishers is the nylon 6-6 machined tube that comprises the main body of the system.Thermo-mechanical modeling and characterization of nylon 6-6 for use in plutonium glovebox applications has been carried out. Data has been generated regarding property degradation leading to poor, or reduced, engineering performancemore » of nylon 6-6 components. In this study, nylon 6-6 tensile specimens conforming to the casing of self-contained fire extinguisher systems have been exposed to hydrochloric, nitric, and sulfuric acids. This information was used to predict the performance of a load bearing engineering component comprised of nylon 6-6 and designed to operate in a consistent manner over a specified time period. The study provides a fundamental understanding of the engineering performance of the fire suppression system and the effects of environmental degradation due to acid exposure on engineering performance. Data generated help identify the limitations of self-contained fire extinguishers. No critical areas of concern for plutonium glovebox applications of nylon 6-6 have been identified when considering exposure to mineral acid.« less

Redox-responsive self-healing materials formed from host–guest polymers

PubMed Central

Nakahata, Masaki; Takashima, Yoshinori; Yamaguchi, Hiroyasu; Harada, Akira

2011-01-01

Expanding the useful lifespan of materials is becoming highly desirable, and self-healing and self-repairing materials may become valuable commodities. The formation of supramolecular materials through host–guest interactions is a powerful method to create non-conventional materials. Here we report the formation of supramolecular hydrogels and their redox-responsive and self-healing properties due to host–guest interactions. We employ cyclodextrin (CD) as a host molecule because it is environmentally benign and has diverse applications. A transparent supramolecular hydrogel quickly forms upon mixing poly(acrylic acid) (pAA) possessing β-CD as a host polymer with pAA possessing ferrocene as a guest polymer. Redox stimuli induce a sol−gel phase transition in the supramolecular hydrogel and can control self-healing properties such as re-adhesion between cut surfaces. PMID:22027591

Self-organization of glucose oxidase-polymer surfactant nanoconstructs in solvent-free soft solids and liquids.

PubMed

Sharma, Kamendra P; Zhang, Yixiong; Thomas, Michael R; Brogan, Alex P S; Perriman, Adam W; Mann, Stephen

2014-10-02

An anisotropic glucose oxidase-polymer surfactant nanoconjugate is synthesized and shown to exhibit complex temperature-dependent phase behavior in the solvent-free state. At close to room temperature, the nanoconjugate crystallizes as a mesolamellar soft solid with an expanded interlayer spacing of ca. 12 nm and interchain correlation lengths consistent with alkyl tail-tail and PEO-PEO ordering. The soft solid displays a birefringent spherulitic texture and melts at 40 °C to produce a solvent-free liquid protein without loss of enzyme secondary structure. The nanoconjugate melt exhibits a birefringent dendritic texture below the conformation transition temperature (Tc) of glucose oxidase (58 °C) and retains interchain PEO-PEO ordering. Our results indicate that the shape anisotropy of the protein-polymer surfactant globular building block plays a key role in directing mesolamellar formation in the solvent-free solid and suggests that the microstructure observed in the solvent-free liquid protein below Tc is associated with restrictions in the intramolecular motions of the protein core of the nanoconjugate.

Computer Simulation of Spatial Arrangement and Connectivity of Particles in Three-Dimensional Microstructure: Application to Model Electrical Conductivity of Polymer Matrix Composite

NASA Technical Reports Server (NTRS)

Louis, P.; Gokhale, A. M.

1996-01-01

Computer simulation is a powerful tool for analyzing the geometry of three-dimensional microstructure. A computer simulation model is developed to represent the three-dimensional microstructure of a two-phase particulate composite where particles may be in contact with one another but do not overlap significantly. The model is used to quantify the "connectedness" of the particulate phase of a polymer matrix composite containing hollow carbon particles in a dielectric polymer resin matrix. The simulations are utilized to estimate the morphological percolation volume fraction for electrical conduction, and the effective volume fraction of the particles that actually take part in the electrical conduction. The calculated values of the effective volume fraction are used as an input for a self-consistent physical model for electrical conductivity. The predicted values of electrical conductivity are in very good agreement with the corresponding experimental data on a series of specimens having different particulate volume fraction.

Synergistic toughening of composite fibres by self-alignment of reduced graphene oxide and carbon nanotubes.

PubMed

Shin, Min Kyoon; Lee, Bommy; Kim, Shi Hyeong; Lee, Jae Ah; Spinks, Geoffrey M; Gambhir, Sanjeev; Wallace, Gordon G; Kozlov, Mikhail E; Baughman, Ray H; Kim, Seon Jeong

2012-01-31

The extraordinary properties of graphene and carbon nanotubes motivate the development of methods for their use in producing continuous, strong, tough fibres. Previous work has shown that the toughness of the carbon nanotube-reinforced polymer fibres exceeds that of previously known materials. Here we show that further increased toughness results from combining carbon nanotubes and reduced graphene oxide flakes in solution-spun polymer fibres. The gravimetric toughness approaches 1,000 J g(-1), far exceeding spider dragline silk (165 J g(-1)) and Kevlar (78 J g(-1)). This toughness enhancement is consistent with the observed formation of an interconnected network of partially aligned reduced graphene oxide flakes and carbon nanotubes during solution spinning, which act to deflect cracks and allow energy-consuming polymer deformation. Toughness is sensitive to the volume ratio of the reduced graphene oxide flakes to the carbon nanotubes in the spinning solution and the degree of graphene oxidation. The hybrid fibres were sewable and weavable, and could be shaped into high-modulus helical springs.

Developing Flexible, High Performance Polymers with Self-Healing Capabilities

NASA Technical Reports Server (NTRS)

Jolley, Scott T.; Williams, Martha K.; Gibson, Tracy L.; Caraccio, Anne J.

2011-01-01

Flexible, high performance polymers such as polyimides are often employed in aerospace applications. They typically find uses in areas where improved physical characteristics such as fire resistance, long term thermal stability, and solvent resistance are required. It is anticipated that such polymers could find uses in future long duration exploration missions as well. Their use would be even more advantageous if self-healing capability or mechanisms could be incorporated into these polymers. Such innovative approaches are currently being studied at the NASA Kennedy Space Center for use in high performance wiring systems or inflatable and habitation structures. Self-healing or self-sealing capability would significantly reduce maintenance requirements, and increase the safety and reliability performance of the systems into which these polymers would be incorporated. Many unique challenges need to be overcome in order to incorporate a self-healing mechanism into flexible, high performance polymers. Significant research into the incorporation of a self-healing mechanism into structural composites has been carried out over the past decade by a number of groups, notable among them being the University of I1linois [I]. Various mechanisms for the introduction of self-healing have been investigated. Examples of these are: 1) Microcapsule-based healant delivery. 2) Vascular network delivery. 3) Damage induced triggering of latent substrate properties. Successful self-healing has been demonstrated in structural epoxy systems with almost complete reestablishment of composite strength being achieved through the use of microcapsulation technology. However, the incorporation of a self-healing mechanism into a system in which the material is flexible, or a thin film, is much more challenging. In the case of using microencapsulation, healant core content must be small enough to reside in films less than 0.1 millimeters thick, and must overcome significant capillary and surface tension forces to flow, mix and react to achieve healing. Vascular networks small enough to fit into such films must also overcome these same flow limitations. Self-healing has also been demonstrated in ionomeric substrates such as Surlyn , wherein the heat generated by a projectile impact triggers the latent ability of this substrate to flow back to its original shape. Recent work using Diels-Alder reactions have shown promise in bringing about actual reforming of broken chemical bonds to achieve self-healing [2]. All self-healing mechanisms that rely on the use of inherent latent substrate properties require some degree of polymer chain flow to achieve any significant level of healing.

Van der Waals pressure sensors using reduced graphene oxide composites

NASA Astrophysics Data System (ADS)

Jung, Ju Ra; Ahn, Sung Il

2018-04-01

Reduced graphene oxide (RGO) films intercalated with various polymers were fabricated by reaction-based self-assembly, and their characteristics as vacuum pressure sensors based on van der Waals interactions were studied. At low temperature, the electrical resistances of the samples decrease linearly with increasing vacuum pressure, whereas at high temperature the variation of the electrical resistance shows secondary order curves. Among all samples, the poly vinyl alcohol intercalated RGO shows the highest sensitivity, being almost two times more sensitive than reference RGO. All samples show almost the same signal for repetitive sudden pressure changes, indicating reasonable reproducibility and durability.

Calculating permittivity of semi-conductor fillers in composites based on simplified effective medium approximation models

NASA Astrophysics Data System (ADS)

Feng, Yefeng; Wu, Qin; Hu, Jianbing; Xu, Zhichao; Peng, Cheng; Xia, Zexu

2018-03-01

Interface induced polarization has a significant impact on permittivity of 0–3 type polymer composites with Si based semi-conducting fillers. Polarity of Si based filler, polarity of polymer matrix and grain size of filler are closely connected with induced polarization and permittivity of composites. However, unlike 2–2 type composites, the real permittivity of Si based fillers in 0–3 type composites could be not directly measured. Therefore, achieving the theoretical permittivity of fillers in 0–3 composites through effective medium approximation (EMA) models should be very necessary. In this work, the real permittivity results of Si based semi-conducting fillers in ten different 0–3 polymer composite systems were calculated by linear fitting of simplified EMA models, based on particularity of reported parameters in those composites. The results further confirmed the proposed interface induced polarization. The results further verified significant influences of filler polarity, polymer polarity and filler size on induced polarization and permittivity of composites as well. High self-consistency was gained between present modelling and prior measuring. This work might offer a facile and effective route to achieve the difficultly measured dielectric performances of discrete filler phase in some special polymer based composite systems.

Supramolecular polymerization of a prebiotic nucleoside provides insights into the creation of sequence-controlled polymers

DOE PAGES

Wang, Jun; Bonnesen, Peter V; Rangel, E.; ...

2016-01-04

The self-assembly of a nucleoside on Au(111) was studied to ascertain whether polymerization on well-defined substrates constitutes a promising approach for making sequence-controlled polymers. Scanning tunneling microscopy and density functional theory were used to investigate the self-assembly on Au(111) of (RS)-N9-(2,3-dihydroxypropyl)adenine (DHPA), a plausibly prebiotic nucleoside analog of adenosine. It is found that DHPA molecules self-assemble into a hydrogen-bonded polymer that grows almost exclusively along the herringbone reconstruction pattern, has a two component sequence that is repeated over hundreds of nanometers, and is erasable with electron-induced excitation. Although the sequence is simple, more complicated ones are envisioned if two ormore » more nucleoside types are combined. Because polymerization occurs on a substrate in a dry environment, the success of each combination can be gauged with high-resolution imaging and accurate modeling techniques. The resulting characteristics make nucleoside self-assembly on a substrate an attractive approach for designing sequence-controlled polymers. Moreover, by choosing plausibly prebiotic nucleosides, insights may be provided into how nature created the first sequence-controlled polymers capable of storing information. Such insights, in turn, can inspire new ways of synthesizing sequence-controlled polymers.« less

Supramolecular polymerization of a prebiotic nucleoside provides insights into the creation of sequence-controlled polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jun; Bonnesen, Peter V; Rangel, E.

The self-assembly of a nucleoside on Au(111) was studied to ascertain whether polymerization on well-defined substrates constitutes a promising approach for making sequence-controlled polymers. Scanning tunneling microscopy and density functional theory were used to investigate the self-assembly on Au(111) of (RS)-N9-(2,3-dihydroxypropyl)adenine (DHPA), a plausibly prebiotic nucleoside analog of adenosine. It is found that DHPA molecules self-assemble into a hydrogen-bonded polymer that grows almost exclusively along the herringbone reconstruction pattern, has a two component sequence that is repeated over hundreds of nanometers, and is erasable with electron-induced excitation. Although the sequence is simple, more complicated ones are envisioned if two ormore » more nucleoside types are combined. Because polymerization occurs on a substrate in a dry environment, the success of each combination can be gauged with high-resolution imaging and accurate modeling techniques. The resulting characteristics make nucleoside self-assembly on a substrate an attractive approach for designing sequence-controlled polymers. Moreover, by choosing plausibly prebiotic nucleosides, insights may be provided into how nature created the first sequence-controlled polymers capable of storing information. Such insights, in turn, can inspire new ways of synthesizing sequence-controlled polymers.« less

Assembling new technologies at the interface of materials science and biology

NASA Astrophysics Data System (ADS)

Stendahl, John C.

Molecular self-assembly can be used to construct advanced materials by taking cues from nature and harnessing noncovalent interactions. This bottom-up approach affords molecular level precision that can cultivate pathways to improved materials function. The graduate research presented in this thesis integrates molecular self-assembly with traditional concepts in chemistry and materials science, with the ultimate goal of developing innovative solutions in technology and medicine. In the field of polymer engineering, self-assembly was used to create supramolecular nanoribbons that, when incorporated into polystyrene, modify its microstructure and significantly enhance its toughness and ductility. In medicine, self-assembly was used to create ordered, chemically functional materials to improve interactions with cells and other constituents of the biological environment. One system that was investigated is based on a triblock molecule in which cholesterol is connected to a lysine dendron by a flexible oligo-(L-lactic acid) spacer. These molecules self-assemble into polar surface coatings on fibrous poly(L-lactic acid) scaffolds that improve the scaffold's wettability and increase its retention of cells during seeding. Another self-assembling system that was investigated for biomedical applications is a family of molecules referred to as peptide amphiphiles (PA's). PA's consist of hydrophobic alkyl tails connected to short, hydrophilic peptides that incorporate biological signaling epitopes. These molecules spontaneously assemble into networks of well-defined nanofibers in aqueous environments, with the signaling epitopes presented in high density on the nanofiber exteriors. Nanofiber assembly is triggered by charge screening on the peptides and is able to produce self-supporting gels in concentrations of less than 1.0 wt.-%. The assembly process and mechanical properties of PA gels was investigated in detail with vibrational spectroscopy and oscillatory rheology. PA nanofibers were used in conjunction with fibrous poly(L-lactic acid] fabrics to create chemically functional scaffolds to facilitate islet cell transplantation. In transplant studies in diabetic mice, the use of scaffolds for islet delivery was shown to significantly improve transplant outcomes over free islet injections. Together, these studies illustrate that molecular self-assembly can be used to create functional materials for a variety of applications. These materials utilize noncovalent interactions to produce supramolecular structures that have important impacts on properties.

A Primer on Polymer Nomenclature: Structure-Based, Sourced- Based, and Trade Names

ERIC Educational Resources Information Center

Cheng, H. N.; Howell, Bob A.

2017-01-01

Polymer nomenclature is important because it is part of the language of polymer science and is needed for polymer identification, reference, and documentation. A primer on polymer nomenclature is provided herein for people new to the field or for instructional use. Both structurebased and source-based nomenclatures, together with trivial and trade…

Tuning the entropic spring to dictate order and functionality in polymer conjugated peptide biomaterials

NASA Astrophysics Data System (ADS)

Keten, Sinan

Hybrid peptide-polymer conjugates have the potential to combine the advantages of natural proteins and synthetic polymers, resulting in biomaterials with improved stability, controlled assembly, and tailored functionalities. However, the effect of polymer conjugation on peptide structural organization and functionality, along with the behavior of polymers at the interface with biomolecules remain to be fully understood. This talk will summarize our recent efforts towards establishing a modeling framework to design entropic forces in helix-polymer conjugates and polymer-conjugated peptide nanotubes to achieve hierarchical self-assembling systems with predictable order. The first part of the talk will discuss how self-assembly principles found in biology, combined with polymer physics concepts can be used to create artificial membranes that mimic certain features of ion channels. Thermodynamics and kinetics aspects of self-assembly and how it governs the growth and stacking sequences of peptide nanotubes will be discussed, along with its implications for nanoscale transport. The second part of the talk will review advances related to modeling polymer conjugated coiled coils at relevant length and time scales. Atomistic simulations combined with sampling techniques will be presented to discuss the energy landscapes governing coiled-coil stability, revealing cascades of events governing disassembly. This will be followed by a discussion of mechanisms through which polymers can stabilize small proteins, such as shielding of solvents, and how specific peptide sequences can reciprocate by altering polymer conformations. Correlations between mechanical and thermal stability of peptides will be discussed. Finally, coarse-grained simulations will provide insight into how the location of polymer attachment changes entropic forces and higher-level organization in helix bundle assemblies. Our findings set the stage for a materials-by-design capability towards dictating complex topologies of polymer-peptide conjugate systems.

Self-monitoring fiber reinforced polymer strengthening system for civil engineering infrastructures

NASA Astrophysics Data System (ADS)

Jiang, Guoliang; Dawood, Mina; Peters, Kara; Rizkalla, Sami

2008-03-01

Fiber reinforced polymer (FRP) materials are currently used for strengthening civil engineering infrastructures. The strengthening system is dependant on the bond characteristics of the FRP to the external surface of the structure to be effective in resisting the applied loads. This paper presents an innovative self-monitoring FRP strengthening system. The system consists of two components which can be embedded in FRP materials to monitor the global and local behavior of the strengthened structure respectively. The first component of the system is designed to evaluate the applied load acting on a structure based on elongation of the FRP layer along the entire span of the structure. Success of the global system has been demonstrated using a full-scale prestressed concrete bridge girder which was loaded up to failure. The test results indicate that this type of sensor can be used to accurately determine the load prior to failure within 15 percent of the measured value. The second sensor component consists of fiber Bragg grating sensors. The sensors were used to monitor the behavior of steel double-lap shear splices tested under tensile loading up to failure. The measurements were used to identify abnormal structural behavior such as epoxy cracking and FRP debonding. Test results were also compared to numerical values obtained from a three dimensional shear-lag model which was developed to predict the sensor response.

Monoglyceride-based self-assembling copolymers as carriers for poorly water-soluble drugs.

PubMed

Rouxhet, L; Dinguizli, M; Latere Dwan'isa, J P; Ould-Ouali, L; Twaddle, P; Nathan, A; Brewster, M E; Rosenblatt, J; Ariën, A; Préat, V

2009-12-01

To develop self-assembling polymers forming polymeric micelles and increasing the solubility of poorly soluble drugs, amphiphilic polymers containing a hydrophilic PEG moiety and a hydrophobic moiety derived from monoglycerides and polyethers were designed. The biodegradable copolymers were obtained via a polycondensation reaction of polyethylene glycol (PEG), monooleylglyceride (MOG) and succinic anhydride (SA). Polymers with molecular weight below 10,000 g/mol containing a minimum of 40 mol% PEG and a maximum of 10 mol% MOG self-assembled spontaneously in aqueous media upon gentle mixing. They formed particles with a diameter of 10 nm although some aggregation was evident. The critical micellar concentration varied between 3x10(-4) and 4x10(-3) g/ml, depending on the polymer. The cloud point (> or = 66 degrees C) and flocculation point (> or = 0.89 M) increased with the PEG chain length. At a 1% concentration, the polymers increased the solubility of poorly water-soluble drug candidates up to 500-fold. Drug solubility increased as a function of the polymer concentration. HPMC capsules filled with these polymers disintegrated and released model drugs rapidly. Polymer with long PEG chains had a lower cytotoxicity (MTT test) on Caco-2 cells. All of these data suggest that the object polymers, in particular PEG1000/MOG/SA (45/5/50) might be potential candidates for improving the oral biopharmaceutical performance of poorly soluble drugs.

21 CFR 175.270 - Poly(vinyl fluoride) resins.

Code of Federal Regulations, 2013 CFR

2013-04-01

... polymerization of vinyl fluoride. (b) The poly(vinyl fluoride) basic resins have an intrinsic viscosity of not... Dilute Solution Viscosity of Vinyl Chloride Polymers,” which is incorporated by reference. Copies may be... Solution Viscosity of Vinyl Chloride Polymers,” which is incorporated by reference; see paragraph (b) of...

21 CFR 175.270 - Poly(vinyl fluoride) resins.

Code of Federal Regulations, 2012 CFR

2012-04-01

... polymerization of vinyl fluoride. (b) The poly(vinyl fluoride) basic resins have an intrinsic viscosity of not... Dilute Solution Viscosity of Vinyl Chloride Polymers,” which is incorporated by reference. Copies may be... Solution Viscosity of Vinyl Chloride Polymers,” which is incorporated by reference; see paragraph (b) of...

Precise control of polymer coated nanopores by nanoparticle additives: Insights from computational modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eskandari Nasrabad, Afshin; Coalson, Rob D.; Jasnow, David

Polymer-nanoparticle composites are a promising new class of materials for creation of controllable nano-patterned surfaces and nanopores. We use coarse-grained molecular dynamics simulations augmented with analytical theory to study the structural transitions of surface grafted polymer layers (brushes) induced by infiltration of nanoparticles that are attracted to the polymers in the layer. We systematically compare two different polymer brush geometries: one where the polymer chains are grafted to a planar surface and the other where the chains are grafted to the inside of a cylindrical nanochannel. We perform a comprehensive study of the effects of the material parameters such asmore » the polymer chain length, chain grafting density, nanoparticle size, strength of attraction between nanoparticles and polymer monomers, and, in the case of the cylindrically grafted brush, the radius of the cylinder. We find a very general behavioral motif for all geometries and parameter values: the height of the polymer brush is non-monotonic in the nanoparticle concentration in solution. As the nanoparticle concentration increases, the brush height first decreases and after passing through a minimum value begins to increase, resulting in the swelling of the nanoparticle infused brush. These morphological features may be useful for devising tunable “smart” nano-devices whose effective dimensions can be reversibly and precisely adjusted by changing the nanoparticle concentration in solution. The results of approximate Self-Consistent Field Theory (SCFT) calculations, applicable in the regime of strong brush stretching, are compared to the simulation results. The SCFT calculations are found to be qualitatively, even semi-quantitatively, accurate when applied within their intended regime of validity, and provide a useful and efficient tool for modeling such materials.« less

Micellar Self-Assembly of Recombinant Resilin-/Elastin-Like Block Copolypeptides.

PubMed

Weitzhandler, Isaac; Dzuricky, Michael; Hoffmann, Ingo; Garcia Quiroz, Felipe; Gradzielski, Michael; Chilkoti, Ashutosh

2017-08-14

Reported here is the synthesis of perfectly sequence defined, monodisperse diblock copolypeptides of hydrophilic elastin-like and hydrophobic resilin-like polypeptide blocks and characterization of their self-assembly as a function of structural parameters by light scattering, cryo-TEM, and small-angle neutron scattering. A subset of these diblock copolypeptides exhibit lower critical solution temperature and upper critical solution temperature phase behavior and self-assemble into spherical or cylindrical micelles. Their morphologies are dictated by their chain length, degree of hydrophilicity, and hydrophilic weight fraction of the ELP block. We find that (1) independent of the length of the corona-forming ELP block there is a minimum threshold in the length of the RLP block below which self-assembly does not occur, but that once that threshold is crossed, (2) the RLP block length is a unique molecular parameter to independently tune self-assembly and (3) increasing the hydrophobicity of the corona-forming ELP drives a transition from spherical to cylindrical morphology. Unlike the self-assembly of purely ELP-based block copolymers, the self-assembly of RLP-ELPs can be understood by simple principles of polymer physics relating hydrophilic weight fraction and polymer-polymer and polymer-solvent interactions to micellar morphology, which is important as it provides a route for the de novo design of desired nanoscale morphologies from first principles.

Coordination Polymer Gels with Modular Nanomorphologies, Tunable Emissions, and Stimuli-Responsive Behavior Based on an Amphiphilic Tripodal Gelator.

PubMed

Sutar, Papri; Maji, Tapas Kumar

2017-08-21

The recent upsurge in research on coordination polymer gels (CPGs) stems from their synthetic modularity, nanoscale processability, and versatile functionalities. Here we report self-assembly of an amphiphilic, tripodal low-molecular weight gelator (L) that consists of 4,4',4-[1,3,5-phenyl-tri(methoxy)]-tris-benzene core and 2,2':6',2″-terpyridyl termini, with different metal ions toward the formation of CPGs that show controllable nanomorphologies, tunable emission, and stimuli-responsive behaviors. L can also act as a selective chemosensor for Zn II with very low limit of detection (0.18 ppm) in aqueous medium. Coordination-driven self-assembly of L with Zn II in H 2 O/MeOH solvent mixture results in a coordination polymer hydrogel (ZnL) that exhibits sheet like morphology and charge-transfer emission. On the other hand, coordination of L with Tb III and Eu III in CHCl 3 /tetrahydrofuran solvent mixture results in green- and red-emissive CPGs, respectively, with nanotubular morphology. Moreover, precise stoichiometric control of L/Eu III /Tb III ratio leads to the formation of bimetallic CPGs that show emissions over a broad spectral range, including white-light-emission. We also explore the multistimuli responsive properties of the white-light-emitting CPG by exploiting the dynamics of Ln III -tpy coordination.

Clever and crude but not kind: narcissism, self-esteem, and the self-reference effect.

PubMed

Jones, Lara L; Brunell, Amy B

2014-01-01

According to the agency model of narcissism (Campbell, Brunell, & Finkel, 2006) narcissists view themselves as high on agentic traits but low on communal traits. To test if this self-view extends to recall, two experiments examined the extent to which narcissism was associated with self-ratings and recall of agentic and communal traits that varied in valence. Across both experiments a trait description task was followed by a surprise recall task for the trait words and then completion of the Narcissistic Personality Inventory (NPI; Raskin & Terry, 1988). Within the self-reference condition narcissism was related to higher selection in the trait description task and to higher recall of positive-agentic (e.g., clever) traits. This general pattern of results occurred for narcissism even while controlling for the related personality variables of self-esteem, agency, and communion. In contrast to narcissism, within the self-referent group self-esteem predicted higher recall for positive-communal traits (e.g., kind) but lower recall for negative-communal traits, a finding consistent with mnemic neglect. Overall, results supported the agency model of narcissism and extended this model to suggest that narcissists rate themselves more highly not only on positive-agentic traits but also on negative-communal traits.

A Brief Experimental Analysis of Reinforcer and Response Dimensions Related to Self-Control in an Outpatient Clinic

ERIC Educational Resources Information Center

Falcomata, Terry S.; Cooper-Brown, Linda J.; Wacker, David P.; Gardner, Andrew W.; Boelter, Eric W.

2010-01-01

We conducted an assessment of self-control and impulsivity with 9 children referred to an outpatient clinic for impulsive, inattentive, and hyperactive behaviors. Each condition of the assessment consisted of a choice between 2 concurrently presented math or writing tasks, with 1 alternative reflecting impulsive responding and 1 alternative…

Routing of individual polymers in designed patterns

NASA Astrophysics Data System (ADS)

Knudsen, Jakob Bach; Liu, Lei; Bank Kodal, Anne Louise; Madsen, Mikael; Li, Qiang; Song, Jie; Woehrstein, Johannes B.; Wickham, Shelley F. J.; Strauss, Maximilian T.; Schueder, Florian; Vinther, Jesper; Krissanaprasit, Abhichart; Gudnason, Daniel; Smith, Anton Allen Abbotsford; Ogaki, Ryosuke; Zelikin, Alexander N.; Besenbacher, Flemming; Birkedal, Victoria; Yin, Peng; Shih, William M.; Jungmann, Ralf; Dong, Mingdong; Gothelf, Kurt V.

2015-10-01

Synthetic polymers are ubiquitous in the modern world, but our ability to exert control over the molecular conformation of individual polymers is very limited. In particular, although the programmable self-assembly of oligonucleotides and proteins into artificial nanostructures has been demonstrated, we currently lack the tools to handle other types of synthetic polymers individually and thus the ability to utilize and study their single-molecule properties. Here we show that synthetic polymer wires containing short oligonucleotides that extend from each repeat can be made to assemble into arbitrary routings. The wires, which can be more than 200 nm in length, are soft and bendable, and the DNA strands allow individual polymers to self-assemble into predesigned routings on both two- and three-dimensional DNA origami templates. The polymers are conjugated and potentially conducting, and could therefore be used to create molecular-scale electronic or optical wires in arbitrary geometries.

Self-Healing of biocompatible polymeric nanocomposities

NASA Astrophysics Data System (ADS)

Espino, Omar; Chipara, Dorina

2014-03-01

Polymers are vulnerable to damage in form of cracks deep within the structure, where detection is difficult and repair is near to impossible. These cracks lead to mechanical degradation of the polymer. A method has been created to solve this problem named polymeric self healing. Self healing capabilities implies the dispersion within the polymeric matrix of microcapsules filled with a monomer and of catalyst. Poly urea-formaldehyde microcapsules used in this method are filled with dicyclopentadiene that is liberated after being ruptured by the crack propagation in the material. Polymerization is assisted by a catalyst FGGC that ignites the self healing process. Nanocomposites, such as titanium oxide, will be used as an integration of these polymers that will be tested by rupturing mechanically slowly. In order to prove the self healing process, Raman spectroscopy, FTIR, and SEM are used.

Single molecule atomic force microscopy and force spectroscopy of chitosan.

PubMed

Kocun, Marta; Grandbois, Michel; Cuccia, Louis A

2011-02-01

Atomic force microscopy (AFM) and AFM-based force spectroscopy was used to study the desorption of individual chitosan polymer chains from substrates with varying chemical composition. AFM images of chitosan adsorbed onto a flat mica substrate show elongated single strands or aggregated bundles. The aggregated state of the polymer is consistent with the high level of flexibility and mobility expected for a highly positively charged polymer strand. Conversely, the visualization of elongated strands indicated the presence of stabilizing interactions with the substrate. Surfaces with varying chemical composition (glass, self-assembled monolayer of mercaptoundecanoic acid/decanethiol and polytetrafluoroethylene (PTFE)) were probed with chitosan modified AFM tips and the corresponding desorption energies, calculated from plateau-like features, were attributed to the desorption of individual polymer strands. Desorption energies of 2.0±0.3×10(-20)J, 1.8±0.3×10(-20)J and 3.5±0.3×10(-20)J were obtained for glass, SAM of mercaptoundecanoic/dodecanethiol and PTFE, respectively. These single molecule level results can be used as a basis for investigating chitosan and chitosan-based materials for biomaterial applications. Copyright © 2010 Elsevier B.V. All rights reserved.

Micro- and nanostructured electro-active polymer actuators as smart muscles for incontinence treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Osmani, Bekim, E-mail: bekim.osmani@unibas.ch, E-mail: tino.toepper@unibas.ch; Töpper, Tino, E-mail: bekim.osmani@unibas.ch, E-mail: tino.toepper@unibas.ch; Weiss, Florian M., E-mail: vanessa.leung@unibas.ch, E-mail: bert.mueller@unibas.ch

2015-02-17

Treatments of severe incontinence are currently based on purely mechanical systems that generally result in revision after three to five years. Our goal is to develop a prototype acting in a natural-analogue manner as artificial muscle, which is based on electro-active polymers. Dielectric actuators have outstanding performances including millisecond response times, mechanical strains of more than 10 % and power to mass densities similar to natural muscles. They basically consist of polymer films sandwiched between two compliant electrodes. The incompressible but elastic polymer film transduces the electrical energy into mechanical work according to the Maxwell pressure. Available polymer films aremore » micrometers thick and voltages as large as kV are necessary to obtain 10 % strain. For medical implants, polymer films should be nanometer thin to realize actuation below 48 V. The metallic electrodes have to be stretchable to follow the strain of 10 % and remain conductive. Recent results on the stress/strain behavior of anisotropic EAP-cantilevers have shown dependencies on metal electrode preparation. We have investigated tunable anisotropic micro- and nanostructures for metallic electrodes. They show a preferred actuation direction with improved stress-strain behavior. The bending of the cantilever has been characterized by the laser beam deflection method. The impact of the electrode on the effective Young's Modulus is measured using an Ultra Nanoindentation Tester with an integrated reference system for soft polymer surfaces. Once ten thousand layers of nanometer-thin EAP actuators are available, devices beyond the envisioned application will flood the market.« less

Near-infrared (NIR) emitting conjugated polymers for biomedical applications (Presentation Recording)

NASA Astrophysics Data System (ADS)

Repenko, Tatjana; Kuehne, Alexander J. C.

2015-10-01

Fluorescent biomedical markers of today such as dye-infiltrated colloids, microgels and quantum dots suffer from fast bleaching, lack surface functionality (for targets or pharmaceutical agents) and potentially leach heavy metals in case of quantum dots (e.g. Cd). By contrast, conjugated polymer particles are non-cytotoxic, exhibit reduced bleaching, as the entire particle consists of fluorophore, they are hydrophobic and show high quantum yields. Consequently, conjugated polymer particles represent ideal materials for biological applications and imaging. However currently, conjugated polymer particles for biomedical imaging usually lack near-infrared (NIR) emission and are polydisperse. Fluorescent agents with emission in the NIR spectrum are interesting for biomedical applications due to their low photo-damage towards biological species and the ability of NIR radiation to penetrate deep into biological tissue.. I will present the development and synthesis of new conjugated polymers particles with fluorescence in the NIR spectral region for bio-imaging and clinical diagnosis. The particle synthesis proceeds in a one-step Pd or Ni-catalyzed dispersion polymerization of functional NIR emitters. The resulting monodisperse conjugated polymer particles are obtained as a dispersion in a non-hazardous solvent. Different sizes in the sub-micrometer range with a narrow size distribution can be produced. Furthermore biological recognition motifs can be easily attached to the conjugated polymers via thiol-yne click-chemistry providing specific tumor targeting without quenching of the fluorescence. References [1] Kuehne AJC, Gather MC, Sprakel J., Nature Commun. 2012, 3, 1088. [2] Repenko T, Fokong S, De Laporte L, Go D, Kiessling F, Lammers T, Kuehne AJC.,Chem Commun 2015, accepted.

Age Differences in Self-Referencing: Evidence for Common and Distinct Encoding Strategies

PubMed Central

Gutchess, Angela H.; Sokal, Rebecca; Coleman, Jennifer A.; Gotthilf, Gina; Grewal, Lauren; Rosa, Nicole

2014-01-01

Although engagement of medial prefrontal cortex (MPFC) underlies self-referencing of information for younger and older adults, the region has not consistently been implicated across age groups for the encoding of self-referenced information. We sought to determine whether making judgments about others as well as the self influenced findings in the previous study. During an fMRI session, younger and older adults encoded adjectives using only a self-reference task. For items later remembered compared to those later forgotten, both age groups robustly recruited medial prefrontal cortex, indicating common neural regions support encoding across younger and older adults when participants make only self-reference judgments. Focal age differences emerged in regions related to emotional processing and cognitive control, though these differences are more limited than in tasks in which judgments also are made about others. We conclude that making judgments about another person differently affects the ways that younger and older adults make judgments about the self, with results of a follow-up behavioral study supporting this interpretation. PMID:25223905

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Tzu-Pin; Chang, Alice B.; Luo, Shao-Xiong

Grafting density is an important structural parameter that imparts significant influences over the physical properties of architecturally complex polymers. In this paper, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization (ROMP). ω-norbornenyl poly(D,L-lactide) (PLA) and polystyrene (PS) macromonomers were copolymerized with discrete co-monomers in different feed ratios, enabling precise control over the grafting density. Small-angle X-ray scattering (SAXS) experiments demonstrate that these graft block polymers can self-assemble into long-range-orderedmore » lamellar structures. For seventeen series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ~ N bb α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, instead of segregation strengths. A model is pro-posed in which the characteristic ratio (C ∞), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ~ N bb f(z). To the best of our knowledge, this report represents the first study of scaling behavior for the self-assembly of block polymers with variable grafting density. Lastly, the relationships disclosed herein provide valuable insights into conformational changes with grafting density, thus introducing new opportunities for future block polymer design.« less

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

DOE PAGES

Lin, Tzu-Pin; Chang, Alice B.; Luo, Shao-Xiong; ...

2017-10-26

Grafting density is an important structural parameter that imparts significant influences over the physical properties of architecturally complex polymers. In this paper, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization (ROMP). ω-norbornenyl poly(D,L-lactide) (PLA) and polystyrene (PS) macromonomers were copolymerized with discrete co-monomers in different feed ratios, enabling precise control over the grafting density. Small-angle X-ray scattering (SAXS) experiments demonstrate that these graft block polymers can self-assemble into long-range-orderedmore » lamellar structures. For seventeen series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ~ N bb α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, instead of segregation strengths. A model is pro-posed in which the characteristic ratio (C ∞), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ~ N bb f(z). To the best of our knowledge, this report represents the first study of scaling behavior for the self-assembly of block polymers with variable grafting density. Lastly, the relationships disclosed herein provide valuable insights into conformational changes with grafting density, thus introducing new opportunities for future block polymer design.« less

Toughening and healing of continuous fibre reinforced composites with bis-maleimide based pre-pregs

NASA Astrophysics Data System (ADS)

Kostopoulos, V.; Kotrotsos, A.; Tsantzalis, S.; Tsokanas, P.; Christopoulos, A. C.; Loutas, T.

2016-08-01

Unidirectional (UD) pre-pregs containing self-healing materials based on Diels-Alder reaction bis-maleimide (BMI) polymers were successfully incorporated on the mid-plane of UD carbon fibre reinforced polymers. The fracture toughness of these composites and the introduced healing capability were measured under mode I loading. The interlaminar fracture toughness was enhanced considerably, since the maximum load (P max) of the modified composite increased approximately 1.5 times and the mode I fracture energy (G IC) displayed a significant increase of almost 3.5 times when compared to the reference composites. Furthermore the modified composites displayed a healing efficiency (HE) value of about 30% for P max and 20% for G IC after the first healing, appearing to be an almost stable behaviour after the third healing cycle. The HE displayed a decrease of 20% and 15% for P max and G IC values, respectively, after the fifth healing cycle. During the tests, the monitored acoustic emission (AE) activity of the samples showed that there is no significant difference due to the presence of BMI polymer in terms of AE hits. Moreover, optical microscopy not only showed that the epoxy matrix at the interface is partly infiltrated by the BMI polymer, but it also revealed the presence of pulled out fibres at the fractured surface, indicating ductile behaviour.

Tolerance to structural disorder and tunable mechanical behavior in self-assembled superlattices of polymer-grafted nanocrystals

DOE PAGES

Gu, X. Wendy; Ye, Xingchen; Koshy, David M.; ...

2017-02-27

Large, freestanding membranes with remarkably high elastic modulus ( > 10 GPa) have been fabricated through the self-Assembly of ligand-stabilized inorganic nanocrystals, even though these nanocrystals are connected only by soft organic ligands (e.g., dodecanethiol or DNA) that are not cross-linked or entangled. Recent developments in the synthesis of polymer-grafted nanocrystals have greatly expanded the library of accessible superlattice architectures,which allows superlattice mechanical behavior to be linked to specific structural features. Here, colloidal self-Assembly is used to organize polystyrene-grafted Au nanocrystals at a fluid interface to form ordered solids with sub-10-nm periodic features. We used thin-film buckling and nanoindentation tomore » evaluate the mechanical behavior of polymer-grafted nanocrystal superlattices while exploring the role of polymer structural conformation, nanocrystal packing, and superlattice dimensions. Superlattices containing 3-20 vol % Au are found to have an elastic modulus of ~6-19 GPa, and hardness of ~120-170 MPa. We also found that rapidly self-Assembled superlattices have the highest elastic modulus, despite containing significant structural defects. Polymer extension, interdigitation, and grafting density are determined to be critical parameters that govern superlattice elastic and plastic deformation.« less

Thermo-reversible morphology and conductivity of a conjugated polymer network embedded in polymeric self-assembly

NASA Astrophysics Data System (ADS)

Han, Youngkyu; Carrillo, Jan-Michael Y.; Zhang, Zhe; Li, Yunchao; Hong, Kunlun; Sumpter, Bobby G.; Ohl, Michael; Paranthaman, Mariappan Parans; Smith, Gregory S.; Do, Changwoo

Self-assembly of block copolymers provides opportunities to create nano hybrid materials, utilizing self-assembled micro-domains with a variety of morphology and periodic architectures as templates for functional nano-fillers. Here we report new progress towards the fabrication of a thermally responsive conducting polymer self-assembly made from a water-soluble poly(thiophene) derivative with short PEO side chains and Pluronic L62 solution in water. The structural and electrical properties of conjugated polymer-embedded nanostructures were investigated by combining SANS, SAXS, CGMD simulations, and impedance spectroscopy. The L62 solution template organizes the conjugated polymers by stably incorporating them into the hydrophilic domains thus inhibiting aggregation. The changing morphology of L62 during the micellar-to-lamellar phase transition defines the embedded conjugated polymer network. The conductivity is strongly coupled to the structural change of the templating L62 phase and exhibits thermally reversible behavior with no signs of quenching of the conductivity at high temperature. The research was sponsored by the Scientific User Facilities Division, Office of BES, U.S. DOE and Laboratory Directed Research and Development Program of ORNL, managed by UT-Battelle, LLC.

Tolerance to structural disorder and tunable mechanical behavior in self-assembled superlattices of polymer-grafted nanocrystals

NASA Astrophysics Data System (ADS)

Gu, X. Wendy; Ye, Xingchen; Koshy, David M.; Vachhani, Shraddha; Hosemann, Peter; Alivisatos, A. Paul

2017-03-01

Large, freestanding membranes with remarkably high elastic modulus (>10 GPa) have been fabricated through the self-assembly of ligand-stabilized inorganic nanocrystals, even though these nanocrystals are connected only by soft organic ligands (e.g., dodecanethiol or DNA) that are not cross-linked or entangled. Recent developments in the synthesis of polymer-grafted nanocrystals have greatly expanded the library of accessible superlattice architectures, which allows superlattice mechanical behavior to be linked to specific structural features. Here, colloidal self-assembly is used to organize polystyrene-grafted Au nanocrystals at a fluid interface to form ordered solids with sub-10-nm periodic features. Thin-film buckling and nanoindentation are used to evaluate the mechanical behavior of polymer-grafted nanocrystal superlattices while exploring the role of polymer structural conformation, nanocrystal packing, and superlattice dimensions. Superlattices containing 3-20 vol % Au are found to have an elastic modulus of ˜6-19 GPa, and hardness of ˜120-170 MPa. We find that rapidly self-assembled superlattices have the highest elastic modulus, despite containing significant structural defects. Polymer extension, interdigitation, and grafting density are determined to be critical parameters that govern superlattice elastic and plastic deformation.

Self-consistent clustering analysis: an efficient multiscale scheme for inelastic heterogeneous materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Z.; Bessa, M. A.; Liu, W.K.

A predictive computational theory is shown for modeling complex, hierarchical materials ranging from metal alloys to polymer nanocomposites. The theory can capture complex mechanisms such as plasticity and failure that span across multiple length scales. This general multiscale material modeling theory relies on sound principles of mathematics and mechanics, and a cutting-edge reduced order modeling method named self-consistent clustering analysis (SCA) [Zeliang Liu, M.A. Bessa, Wing Kam Liu, “Self-consistent clustering analysis: An efficient multi-scale scheme for inelastic heterogeneous materials,” Comput. Methods Appl. Mech. Engrg. 306 (2016) 319–341]. SCA reduces by several orders of magnitude the computational cost of micromechanical andmore » concurrent multiscale simulations, while retaining the microstructure information. This remarkable increase in efficiency is achieved with a data-driven clustering method. Computationally expensive operations are performed in the so-called offline stage, where degrees of freedom (DOFs) are agglomerated into clusters. The interaction tensor of these clusters is computed. In the online or predictive stage, the Lippmann-Schwinger integral equation is solved cluster-wise using a self-consistent scheme to ensure solution accuracy and avoid path dependence. To construct a concurrent multiscale model, this scheme is applied at each material point in a macroscale structure, replacing a conventional constitutive model with the average response computed from the microscale model using just the SCA online stage. A regularized damage theory is incorporated in the microscale that avoids the mesh and RVE size dependence that commonly plagues microscale damage calculations. The SCA method is illustrated with two cases: a carbon fiber reinforced polymer (CFRP) structure with the concurrent multiscale model and an application to fatigue prediction for additively manufactured metals. For the CFRP problem, a speed up estimated to be about 43,000 is achieved by using the SCA method, as opposed to FE2, enabling the solution of an otherwise computationally intractable problem. The second example uses a crystal plasticity constitutive law and computes the fatigue potency of extrinsic microscale features such as voids. This shows that local stress and strain are capture sufficiently well by SCA. This model has been incorporated in a process-structure-properties prediction framework for process design in additive manufacturing.« less

Self assembled linear polymeric chains with tuneable semiflexibility using isotropic interactions.

PubMed

Abraham, Alex; Chatterji, Apratim

2018-04-21

We propose a two-body spherically symmetric (isotropic) potential such that particles interacting by the potential self-assemble into linear semiflexible polymeric chains without branching. By suitable control of the potential parameters, we can control the persistence length of the polymer and can even introduce a controlled number of branches. Thus we show how to achieve effective directional interactions starting from spherically symmetric potentials. The self-assembled polymers have an exponential distribution of chain lengths akin to what is observed for worm-like micellar systems. On increasing particle density, the polymeric chains self-organize to an ordered line-hexagonal phase where every chain is surrounded by six parallel chains, the transition is first order. On further increase in monomer density, the order is destroyed and we get a branched gel-like phase. This potential can be used to model semi-flexible equilibrium polymers with tunable semiflexibility and excluded volume. The use of the potential is computationally cheap and hence can be used to simulate and probe equilibrium polymer dynamics with long chains. The potential also gives a plausible method of tuning colloidal interactions in experiments such that one can obtain self-assembling polymeric chains made up of colloids and probe polymer dynamics using an optical microscope. Furthermore, we show how a modified potential leads to the observation of an intermediate nematic phase of self-assembled chains in between the low density disordered phase and the line-ordered hexagonal phase.

Self assembled linear polymeric chains with tuneable semiflexibility using isotropic interactions

NASA Astrophysics Data System (ADS)

Abraham, Alex; Chatterji, Apratim

2018-04-01

We propose a two-body spherically symmetric (isotropic) potential such that particles interacting by the potential self-assemble into linear semiflexible polymeric chains without branching. By suitable control of the potential parameters, we can control the persistence length of the polymer and can even introduce a controlled number of branches. Thus we show how to achieve effective directional interactions starting from spherically symmetric potentials. The self-assembled polymers have an exponential distribution of chain lengths akin to what is observed for worm-like micellar systems. On increasing particle density, the polymeric chains self-organize to an ordered line-hexagonal phase where every chain is surrounded by six parallel chains, the transition is first order. On further increase in monomer density, the order is destroyed and we get a branched gel-like phase. This potential can be used to model semi-flexible equilibrium polymers with tunable semiflexibility and excluded volume. The use of the potential is computationally cheap and hence can be used to simulate and probe equilibrium polymer dynamics with long chains. The potential also gives a plausible method of tuning colloidal interactions in experiments such that one can obtain self-assembling polymeric chains made up of colloids and probe polymer dynamics using an optical microscope. Furthermore, we show how a modified potential leads to the observation of an intermediate nematic phase of self-assembled chains in between the low density disordered phase and the line-ordered hexagonal phase.

Dispersion of the Photosensitizer 5,10,15,20-Tetrakis(4-Sulfonatophenyl)-porphyrin by the Amphiphilic Polymer Poly(vinylpirrolidone) in Highly Porous Solid Materials Designed for Photodynamic Therapy.

PubMed

Díaz, Claudia; Catalán-Toledo, José; Flores, Mario E; Orellana, Sandra L; Pesenti, Héctor; Lisoni, Judit; Moreno-Villoslada, Ignacio

2017-08-03

The ability of the amphiphilic and biocompatible poly(vinylpyrrolidone) to avoid self-aggregation of the photosensitizer 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin in aqueous solution in the presence of the biocompatible polycation chitosan, polymer that induces the dye self-aggregation, is shown. This is related to the tendency of the dye to undergo preferential solvation by the amphiphilic polymer. Importantly, the dispersant ability of this polymer is transferred to the solid state. Thus, aerogels made of the biocompatible polymers chitosan and chondroitin sulfate, and containing the photosensitizer dispersed by the amphiphilic polymer have been synthesized. Production of reactive oxygen species by the aerogel containing the amphiphilic polymer was faster than when the polymer was absent, correlating with the relative concentration of dyes dispersed as monomers. The aerogels presented here constitute low cost biocompatible materials bearing a conventional photosensitizer for photodynamic therapy, easy to produce, store, transport, and manage in clinical practice.

Self-healing pH-sensitive poly[(methyl vinyl ether)-alt-(maleic acid)]-based supramolecular hydrogels formed by inclusion complexation between cyclodextrin and adamantane.

PubMed

Ma, Xiaoe; Zhou, Naizhen; Zhang, Tianzhu; Hu, Wanjun; Gu, Ning

2017-04-01

Self-healing materials are of interest for drug delivery, cell and gene therapy, tissue engineering, and other biomedical applications. In this work, on the base of biocompatible polymer poly(methyl vinyl ether-alt-maleic acid) (P(MVE-alt-MA)), host polymer β-cyclodextrin-grafted P(MVE-alt-MA) (P(MVE-alt-MA)-g-β-CD) and guest polymer adamantane-grafted P(MVE-alt-MA) (P(MVE-alt-MA)-g-Ad) were first prepared. Then through taking advantage of the traditional host-guest interaction of β-cyclodextrin and adamantane, a novel self-healing pH-sensitive physical P(MVE-alt-MA)-g-β-CD/P(MVE-alt-MA)-g-Ad supramolecular hydrogels were obtained after simply mixing the aqueous solution of host polymer and guest polymer. This kind of supramolecular hydrogels not only possess pH-sensitivity, but also possess the ability to repair themselves after being damaged. Copyright © 2016 Elsevier B.V. All rights reserved.

Evaluation of dose dependent antimicrobial activity of self-assembled chitosan, nano silver and chitosan-nano silver composite against several pathogens.

PubMed

Tareq, Foysal Kabir; Fayzunnesa, Mst; Kabir, Md Shahariar; Nuzat, Musrat

2018-01-01

The aim of this investigation to preparation of silver nanoparticles organized chitosan nano polymer, which effective against microbial and pathogens, when apply to liquid medium and edible food products surface, will rescue the growth of microbes. Self-assembly approach used to synthesis of silver nanoparticles and silver nanoparticles organized chitosan nano polymer. Silver nanoparticles and silver nanoparticles organized chitosan nano polymer and film characterized using Ultra-violate visible spectrometer (UV-vis), X-ray diffraction (X-ray), and Scanning electronic microscope (SEM). The crystalline structured protein capped nano silver successfully synthesized at range of 12 nm-29 nm and organized into chitosan nano polymer. Antimicrobial ingredient in liquid medium and food product surface provide to rescue oxidative change and growth of microorganism to provide higher safety. The silver nanoparticles organized chitosan nano polymer caused the death of microorganism. The materials in nano scale synthesized successfully using self-assembly method, which showed good antimicrobial properties. Copyright © 2017 Elsevier Ltd. All rights reserved.

Metal fume fever and polymer fume fever.

PubMed

Greenberg, Michael I; Vearrier, David

2015-05-01

Inhalational exposure to metal-containing fumes generated by welding and related processes may result in the development of the clinical syndrome known as "metal fume fever." Polymer fume fever is a separate and distinct but related disorder that has been associated with inhalational exposure to specific fluorinated polymer products, such as polytetrafluoroethylene or Teflon(®). We undertook a review of the peer-reviewed medical literature as it relates to these two disease entities in order to describe their epidemiology, pathophysiology, clinical presentation, diagnosis, treatment, prevention, and prognosis. We performed a search of the PubMed ( www.pubmed.com ) and Ovid MEDLINE (ovidsp.tx.ovid.com) databases for keywords "metal fume fever," "polymer fume fever," and "fume fever," covering the period 1946 to September 2014, which resulted in a total of 141 citations. Limiting the search to articles published in the English language yielded 115 citations. These 115 articles were manually reviewed for relevance. In addition, the reference lists in each article retrieved were reviewed for additional relevant references. This left 48 relevant citations. Metal fume fever occurs most commonly as an occupational disease in individuals who perform welding and other metal-joining activities for a living. It is estimated that 1,500-2,500 cases of metal fume fever occur annually in the United States. Polymer fume fever was initially identified as an occupational disease but increased regulations have resulted in decreased incidence in the occupational setting. Overheating of Teflon(®)-coated cookware is one of the more common mechanisms for exposure. While the precise pathophysiology associated with the development of metal fume fever is yet to be elucidated, suggested pathophysiologic mechanisms include pro-inflammatory cytokine release, neutrophil activation, and oxygen radical formation. The pathophysiologic mechanism for polymer fume fever has not been definitively elucidated but may involve similar mechanisms to those proposed for metal fume fever. Metal fume fever typically presents with generally non-specific complaints including influenza-like symptoms, fever, shaking chills, arthalgias, myalgias, headache, and malaise. Onset of symptoms typically occurs 4-10 h following the exposure to metal-containing fumes. While metal fume fever is typically benign and self-limited, severe cases of the disease have been reported. In patients with ongoing metal fume exposure over the course of a workweek, tachyphylaxis occurs resulting in improvement in symptoms over the course of the workweek and maximal symptoms occurring after an exposure-free period such as a weekend. The clinical presentation of polymer fume fever is indistinguishable from metal fume fever, with an exposure history being necessary to distinguish the two entities. Chest radiographs are typically normal in cases of metal fume fever and polymer fume fever; however, mild vascular congestion may be demonstrated and severe cases may feature diffuse patchy infiltrates. Laboratory studies are typically not necessary but may demonstrate leukocytosis with leftward shift or an elevated erythrocyte sedimentation rate. The primary treatment for both metal fume fever and polymer fume fever is supportive and directed at symptom relief. Oral hydration, rest, and the use of antipyretics and anti-inflammatory medications (e.g., non-steroidal anti-inflammatory drugs and aspirin) are recommended. A careful workplace exposure assessment analysis conducted by an occupational medicine specialist or clinical toxicologist in concert with a qualified industrial hygienist should be performed. A careful workplace exposure assessment including measurement of ambient zinc and other metal (e.g., chrome, nickel, copper and manganese) fume concentrations or concentrations of fluorocarbon polymer decomposition products at different locations within the workplace should be performed. Metal fume fever is typically a benign and self-limited disease entity that resolves over 12-48 h following cessation of exposure. Metal and polymer fume fevers generally follow a benign course with spontaneous resolution of symptoms, though both have the potential to be serious, especially in those with significant preexisting cardiorespiratory disease.

Internal Reflection Spectra of Surface Compounds and Adsorbed Molecules

NASA Astrophysics Data System (ADS)

Zolotarev, V. M.; Lygin, V. I.; Tarasevich, B. N.

1981-01-01

The application of attenuated total reflection (ATR) spectroscopy in surface studies of inorganic adsorbents and catalysts, polymers, and optically transparent electrodes is discussed. The basic principles of ATR spectroscopy as applied to surface phenomena are considered, with special reference to thin films, industrial adsorbents and catalysts, and polymer degradation processes. 276 references.

Simulation of macromolecule self-assembly in solution: A multiscale approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavino, Alessio D., E-mail: alessiodomenico.lavino@studenti.polito.it; Barresi, Antonello A., E-mail: antonello.barresi@polito.it; Marchisio, Daniele L., E-mail: daniele.marchisio@polito.it

2015-12-17

One of the most common processes to produce polymer nanoparticles is to induce self-assembly by using the solvent-displacement method, in which the polymer is dissolved in a “good” solvent and the solution is then mixed with an “anti-solvent”. The polymer ability to self-assemble in solution is therefore determined by its structural and transport properties in solutions of the pure solvents and at the intermediate compositions. In this work, we focus on poly-ε-caprolactone (PCL) which is a biocompatible polymer that finds widespread application in the pharmaceutical and biomedical fields, performing simulation at three different scales using three different computational tools: fullmore » atomistic molecular dynamics (MD), population balance modeling (PBM) and computational fluid dynamics (CFD). Simulations consider PCL chains of different molecular weight in solution of pure acetone (good solvent), of pure water (anti-solvent) and their mixtures, and mixing at different rates and initial concentrations in a confined impinging jets mixer (CIJM). Our MD simulations reveal that the nano-structuring of one of the solvents in the mixture leads to an unexpected identical polymer structure irrespectively of the concentration of the two solvents. In particular, although in pure solvents the behavior of the polymer is, as expected, very different, at intermediate compositions, the PCL chain shows properties very similar to those found in pure acetone as a result of the clustering of the acetone molecules in the vicinity of the polymer chain. We derive an analytical expression to predict the polymer structural properties in solution at different solvent compositions and use it to formulate an aggregation kernel to describe the self-assembly in the CIJM via PBM and CFD. Simulations are eventually validated against experiments.« less

Active self-healing encapsulation of vaccine antigens in PLGA microspheres

PubMed Central

Desai, Kashappa-Goud H.; Schwendeman, Steven P.

2013-01-01

Herein, we describe the detailed development of a simple and effective method to microencapsulate vaccine antigens in poly(lactic-co-glycolic acid) (PLGA) by simple mixing of preformed active self-microencapsulating (SM) PLGA microspheres in a low concentration aqueous antigen solution at modest temperature (10-38 °C). Co-encapsulating protein-sorbing vaccine adjuvants and polymer plasticizers were used to “actively” load the protein in the polymer pores and facilitate polymer self-healing at temperature > hydrated polymer glass transition temperature, respectively. The microsphere formulation parameters and loading conditions to provide optimal active self-healing microencapsulation of vaccine antigen in PLGA was investigated. Active self-healing encapsulation of two vaccine antigens, ovalbumin and tetanus toxoid (TT), in PLGA microspheres was adjusted by preparing blank microspheres containing different vaccine adjuvant (aluminum hydroxide (Al(OH)3) or calcium phosphate). Active loading of vaccine antigen in Al(OH)3-PLGA microspheres was found to: a) increase proportionally with an increasing loading of Al(OH)3 (0.88-3 wt%) and addition of porosigen, b) decrease when the inner Al(OH)3/trehalose phase to 1 mL outer oil phase and size of microspheres was respectively > 0.2 mL and 63 μm, and c) change negligibly by PLGA concentration and initial incubation (loading) temperature. Encapsulation of protein sorbing Al(OH)3 in PLGA microspheres resulted in suppression of self-healing of PLGA pores, which was then overcome by improving polymer chain mobility, which in turn was accomplished by coincorporating hydrophobic plasticizers in PLGA. Active self-healing microencapsulation of manufacturing process-labile TT in PLGA was found to: a) obviate micronization- and organic solvent-induced TT degradation, b) improve antigen loading (1.4-1.8 wt% TT) and encapsulation efficiency (~ 97%), c) provide nearly homogeneous distribution and stabilization of antigen in polymer, and d) provide improved in vitro controlled release of antigenic TT. PMID:23103983

Polymer damage mitigation---predictive lifetime models of polymer insulation degradation and biorenewable thermosets through cationic polymerization for self-healing applications

NASA Astrophysics Data System (ADS)

Hondred, Peter Raymond

Over the past 50 years, the industrial development and applications for polymers and polymer composites has become expansive. However, as with any young technology, the techniques for predicting material damage and resolving material failure are in need of continued development and refinement. This thesis work takes two approaches to polymer damage mitigation---material lifetime prediction and spontaneous damage repair through self-healing while incorporating bio-renewable feedstock. First, material lifetime prediction offers the benefit of identifying and isolating material failures before the effects of damage results in catastrophic failure. Second, self-healing provides a systematic approach to repairing damaged polymer composites, specifically in applications where a hands-on approach or removing the part from service are not feasible. With regard to lifetime prediction, we investigated three specific polymeric materials---polytetrafluoroethylene (PTFE), poly(ethylene-alt-tetrafluoroethylene) (ETFE), and Kapton. All three have been utilized extensively in the aerospace field as a wire insulation coating. Because of the vast amount of electrical wiring used in aerospace constructions and the potential for electrical and thermal failure, this work develops mathematical models for both the thermal degradation kinetics as well as a lifetime prediction model for electrothermal breakdown. Isoconversional kinetic methods, which plot activation energy as a function of the extent of degradation, present insight into the development each kinetic model. The models for PTFE, ETFE, and Kapton are one step, consecutive three-step, and competitive and consecutive five-step respectively. Statistical analysis shows that an nth order autocatalytic reaction best defined the reaction kinetics for each polymer's degradation. Self-healing polymers arrest crack propagation through the use of an imbedded adhesive that reacts when cracks form. This form of damage mitigation focuses on repairing damage before the damage causes a failure in the polymer's function. In this work, the healing agent (adhesive) is developed using bio-renewable oils instead of solely relying on petroleum based feedstocks. Several bio-renewable thermosetting polymers were successfully prepared from tung oil through cationic polymerization for the use as the healing agent in self-healing microencapsulated applications. Modifications to both the monomers in the resin and the catalyst for polymerization were made and the subsequent changes to mechanical, thermal, and structural properties were identified. Furthermore, compressive lap shear testing was used to confirm that the adhesive properties would be beneficial for self-healing applications. Finally, scanning electron microscopy of the crack plane was used to study the fracture mechanism of the crack.

Estimating loblolly pine size-density trajectories across a range of planting densities

Treesearch

Curtis L. VanderSchaaf; Harold E. Burkhart

2013-01-01

Size-density trajectories on the logarithmic (ln) scale are generally thought to consist of two major stages. The first is often referred to as the density-independent mortality stage where the probability of mortality is independent of stand density; in the second, often referred to as the density-dependent mortality or self-thinning stage, the probability of...

Self-Renewing Microns-Thick Biopolymer Brush Made of Hyaluronan under Active Synthesis

NASA Astrophysics Data System (ADS)

Wei, W.; Washburn, J.; Weigel, P.; Curtis, J. E.

Hyaluronan (HA) is a large anionic polysaccharide distributed throughout many vertebrate tissues. We introduce a technology to produce dynamic HA polymer brush interfaces. The strategy relies on the enzyme hyaluronan synthase (HA synthase), which synthesizes and extrudes HA polymers up to 20 microns in length. We show that interfaces decorated by HA synthase-rich membrane fragments robustly produce polymer brushes of predictable heights and concentration profiles. The brush thickness can be tuned by the duration of growth or the enzyme density in the membranes. The system is self-renewing in that old polymers desorb and new polymers are produced. The brush can also be replenished after enzymatic removal multiple times. The large extent of the polymer interface allows for characterization of the brush architecture and for studying dynamic processes inside the brush using optical microscopy. At low ionic strengths (1 mM), we measure one of the largest polymer brushes yet reported, an average of 7.8 microns thick. For applications that require a stable brush interface, we have covalently reinforced the HA to the surfaces, and demonstrated that the brush is stable for at least two months. This self-renewing, dynamic biopolymer brush has great potential as a new biomaterial for implants, antifouling, tissue engineering and drug delivery.

Self-Healing Polymer Dielectric for a High Capacitance Gate Insulator.

PubMed

Ko, Jieun; Kim, Young-Jae; Kim, Youn Sang

2016-09-14

Self-healing materials are required for development of various flexible electronic devices to repair cracks and ruptures caused by repetitive bending or folding. Specifically, a self-healing dielectric layer has huge potential to achieve healing electronics without mechanical breakdown in flexible operations. Here, we developed a high performance self-healing dielectric layer with an ionic liquid and catechol-functionalized polymer which exhibited a self-healing ability for both bulk and film states under mild self-healing conditions at 55 °C for 30 min. Due to the sufficient ion mobility of the ionic liquid in the polymer matrix, it had a high capacitance value above 1 μF/cm(2) at 20 Hz. Moreover, zinc oxide (ZnO) thin-film transistors (TFTs) with a self-healing dielectric layer exhibited a high field-effect mobility of 16.1 ± 3.07 cm(2) V(-1) s(-1) at a gate bias of 3 V. Even after repetitive self-healing of the dielectric layer from mechanical breaking, the electrical performance of the TFTs was well-maintained.

Dynamic Scaling Theory of the Forced Translocation of a Semi-flexible Polymer Through a Nanopore

NASA Astrophysics Data System (ADS)

Lam, Pui-Man; Zhen, Yi

2015-10-01

We present a theoretical description of the dynamics of a semi-flexible polymer being pulled through a nanopore by an external force acting at the pore. Our theory is based on the tensile blob picture of Pincus in which the front of the tensile force propagates through the backbone of the polymer, as suggested by Sakaue and recently applied to study a completely flexible polymer with self-avoidance, by Dubbledam et al. For a semi-flexible polymer with a persistence length P, its statistics is self-avoiding for a very long chain. As the local force increases, the blob size starts to decrease. At the blob size , where a is the size of a monomer, the statistics becomes that of an ideal chain. As the blob size further decreases to below the persistence length P, the statistics is that of a rigid rod. We argue that semi-flexible polymer in translocation should include the three regions: a self-avoiding region, an ideal chain region and a rigid rod region, under uneven tension propagation, instead of a uniform scaling picture as in the case of a completely flexible polymer. In various regimes under the effect of weak, intermediate and strong driving forces we derive equations from which we can calculate the translocation time of the polymer. The translocation exponent is given by , where is an effective exponent for the end-to-end distance of the semi-flexible polymer, having a value between 1/2 and 3/5, depending on the total contour length of the polymer. Our results are of relevance for forced translocation of biological polymers such as DNA through a nanopore.

Novel guanidinylated bioresponsive poly(amidoamine)s designed for short hairpin RNA delivery

PubMed Central

Yu, Jiankun; Zhang, Jinmin; Xing, Haonan; Sun, Yanping; Yang, Zhen; Yang, Tianzhi; Cai, Cuifang; Zhao, Xiaoyun; Yang, Li; Ding, Pingtian

2016-01-01

Two different disulfide (SS)-containing poly(amidoamine) (PAA) polymers were constructed using guanidino (Gua)-containing monomers (ie, arginine [Arg] and agmatine [Agm]) and N,N′-cystamine bisacrylamide (CBA) by Michael-addition polymerization. In order to characterize these two Gua-SS-PAA polymers and investigate their potentials as short hairpin RNA (shRNA)-delivery carriers, pSilencer 4.1-CMV FANCF shRNA was chosen as a model plasmid DNA to form complexes with these two polymers. The Gua-SS-PAAs and plasmid DNA complexes were determined with particle sizes less than 90 nm and positive ζ-potentials under 20 mV at nucleic acid:polymer weight ratios lower than 1:24. Bioresponsive release of plasmid DNA was observed from both newly constructed complexes. Significantly lower cytotoxicity was observed for both polymer complexes compared with polyethylenimine and Lipofectamine 2000, two widely used transfection reagents as reference carriers. Arg-CBA showed higher transfection efficiency and gene-silencing efficiency in MCF7 cells than Agm-CBA and the reference carriers. In addition, the cellular uptake of Arg-CBA in MCF7 cells was found to be higher and faster than Agm-CBA and the reference carriers. Similarly, plasmid DNA transport into the nucleus mediated by Arg-CBA was more than that by Agm-CBA and the reference carriers. The study suggested that guanidine and carboxyl introduced into Gua-SS-PAAs polymers resulted in a better nuclear localization effect, which played a key role in the observed enhancement of transfection efficiency and low cytotoxicity. Overall, two newly synthesized Gua-SS-PAAs polymers demonstrated great potential to be used as shRNA carriers for gene-therapy applications. PMID:27994462

Applicability of mode-coupling theory to polyisobutylene: a molecular dynamics simulation study.

PubMed

Khairy, Y; Alvarez, F; Arbe, A; Colmenero, J

2013-10-01

The applicability of Mode Coupling Theory (MCT) to the glass-forming polymer polyisobutylene (PIB) has been explored by using fully atomistic molecular dynamics simulations. MCT predictions for the so-called asymptotic regime have been successfully tested on the dynamic structure factor and the self-correlation function of PIB main-chain carbons calculated from the simulated cell. The factorization theorem and the time-temperature superposition principle are satisfied. A consistent fitting procedure of the simulation data to the MCT asymptotic power-laws predicted for the α-relaxation regime has delivered the dynamic exponents of the theory-in particular, the exponent parameter λ-the critical non-ergodicity parameters, and the critical temperature T(c). The obtained values of λ and T(c) agree, within the uncertainties involved in both studies, with those deduced from depolarized light scattering experiments [A. Kisliuk et al., J. Polym. Sci. Part B: Polym. Phys. 38, 2785 (2000)]. Both, λ and T(c)/T(g) values found for PIB are unusually large with respect to those commonly obtained in low molecular weight systems. Moreover, the high T(c)/T(g) value is compatible with a certain correlation of this parameter with the fragility in Angell's classification. Conversely, the value of λ is close to that reported for real polymers, simulated "realistic" polymers and simple polymer models with intramolecular barriers. In the framework of the MCT, such finding should be the signature of two different mechanisms for the glass-transition in real polymers: intermolecular packing and intramolecular barriers combined with chain connectivity.

Self-assembled hydrogels utilizing polymer-nanoparticle interactions

NASA Astrophysics Data System (ADS)

Appel, Eric A.; Tibbitt, Mark W.; Webber, Matthew J.; Mattix, Bradley A.; Veiseh, Omid; Langer, Robert

2015-02-01

Mouldable hydrogels that flow on applied stress and rapidly self-heal are increasingly utilized as they afford minimally invasive delivery and conformal application. Here we report a new paradigm for the fabrication of self-assembled hydrogels with shear-thinning and self-healing properties employing rationally engineered polymer-nanoparticle (NP) interactions. Biopolymer derivatives are linked together by selective adsorption to NPs. The transient and reversible interactions between biopolymers and NPs enable flow under applied shear stress, followed by rapid self-healing when the stress is relaxed. We develop a physical description of polymer-NP gel formation that is utilized to design biocompatible gels for drug delivery. Owing to the hierarchical structure of the gel, both hydrophilic and hydrophobic drugs can be entrapped and delivered with differential release profiles, both in vitro and in vivo. The work introduces a facile and generalizable class of mouldable hydrogels amenable to a range of biomedical and industrial applications.

Is negative self-referent bias an endophenotype for depression? An fMRI study of emotional self-referent words in twins at high vs. low risk of depression.

PubMed

Miskowiak, K W; Larsen, J E; Harmer, C J; Siebner, H R; Kessing, L V; Macoveanu, J; Vinberg, M

2018-01-15

Negative cognitive bias and aberrant neural processing of self-referent emotional words seem to be trait-marks of depression. However, it is unclear whether these neurocognitive changes are present in unaffected first-degree relatives and constitute an illness endophenotype. Fifty-three healthy, never-depressed monozygotic or dizygotic twins with a co-twin history of depression (high-risk group: n = 26) or no first-degree family history of depression (low-risk group: n = 27) underwent neurocognitive testing and functional magnetic imaging (fMRI) as part of a follow-up cohort study. Participants performed a self-referent emotional word categorisation task and free word recall task followed by a recognition task during fMRI. Participants also completed questionnaires assessing mood, personality traits and coping strategies. High-risk and low-risk twins (age, mean ± SD: 40 ± 11) were well-balanced for demographic variables, mood, coping and neuroticism. High-risk twins showed lower accuracy during self-referent categorisation of emotional words independent of valence and more false recollections of negative words than low-risk twins during free recall. Functional MRI yielded no differences between high-risk and low-risk twins in retrieval-specific neural activity for positive or negative words or during the recognition of negative versus positive words within the hippocampus or prefrontal cortex. The subtle display of negative recall bias is consistent with the hypothesis that self-referent negative memory bias is an endophenotype for depression. High-risk twins' lower categorisation accuracy adds to the evidence for valence-independent cognitive deficits in individuals at familial risk for depression. Copyright © 2017 Elsevier B.V. All rights reserved.

Quantum non-objectivity from performativity of quantum phenomena

NASA Astrophysics Data System (ADS)

Khrennikov, Andrei; Schumann, Andrew

2014-12-01

We analyze the logical foundations of quantum mechanics (QM) by stressing non-objectivity of quantum observables, which is a consequence of the absence of logical atoms in QM. We argue that the matter of quantum non-objectivity is that, on the one hand, the formalism of QM constructed as a mathematical theory is self-consistent, but, on the other hand, quantum phenomena as results of experimenters’ performances are not self-consistent. This self-inconsistency is an effect of the language of QM differing greatly from the language of human performances. The former is the language of a mathematical theory that uses some Aristotelian and Russellian assumptions (e.g., the assumption that there are logical atoms). The latter language consists of performative propositions that are self-inconsistent only from the viewpoint of conventional mathematical theory, but they satisfy another logic that is non-Aristotelian. Hence, the representation of quantum reality in linguistic terms may be different: the difference between a mathematical theory and a logic of performative propositions. To solve quantum self-inconsistency, we apply the formalism of non-classical self-referent logics.

An iterative method for hydrodynamic interactions in Brownian dynamics simulations of polymer dynamics

NASA Astrophysics Data System (ADS)

Miao, Linling; Young, Charles D.; Sing, Charles E.

2017-07-01

Brownian Dynamics (BD) simulations are a standard tool for understanding the dynamics of polymers in and out of equilibrium. Quantitative comparison can be made to rheological measurements of dilute polymer solutions, as well as direct visual observations of fluorescently labeled DNA. The primary computational challenge with BD is the expensive calculation of hydrodynamic interactions (HI), which are necessary to capture physically realistic dynamics. The full HI calculation, performed via a Cholesky decomposition every time step, scales with the length of the polymer as O(N3). This limits the calculation to a few hundred simulated particles. A number of approximations in the literature can lower this scaling to O(N2 - N2.25), and explicit solvent methods scale as O(N); however both incur a significant constant per-time step computational cost. Despite this progress, there remains a need for new or alternative methods of calculating hydrodynamic interactions; large polymer chains or semidilute polymer solutions remain computationally expensive. In this paper, we introduce an alternative method for calculating approximate hydrodynamic interactions. Our method relies on an iterative scheme to establish self-consistency between a hydrodynamic matrix that is averaged over simulation and the hydrodynamic matrix used to run the simulation. Comparison to standard BD simulation and polymer theory results demonstrates that this method quantitatively captures both equilibrium and steady-state dynamics after only a few iterations. The use of an averaged hydrodynamic matrix allows the computationally expensive Brownian noise calculation to be performed infrequently, so that it is no longer the bottleneck of the simulation calculations. We also investigate limitations of this conformational averaging approach in ring polymers.

Novel Self-Assembling Amino Acid-Derived Block Copolymer with Changeable Polymer Backbone Structure.

PubMed

Koga, Tomoyuki; Aso, Eri; Higashi, Nobuyuki

2016-11-29

Block copolymers have attracted much attention as potentially interesting building blocks for the development of novel nanostructured materials in recent years. Herein, we report a new type of self-assembling block copolymer with changeable polymer backbone structure, poly(Fmoc-Ser) ester -b-PSt, which was synthesized by combining the polycondensation of 9-fluorenylmethoxycarbonyl-serine (Fmoc-Ser) with the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St). This block copolymer showed the direct conversion of the backbone structure from polyester to polypeptide through a multi O,N-acyl migration triggered by base-induced deprotection of Fmoc groups in organic solvent. Such polymer-to-polymer conversion was found to occur quantitatively without decrease in degree of polymerization and to cause a drastic change in self-assembling property of the block copolymer. On the basis of several morphological analyses using FTIR spectroscopy, atomic force, and transmission and scanning electron microscopies, the resulting peptide block copolymer was found to self-assemble into a vesicle-like hollow nanosphere with relatively uniform diameter of ca. 300 nm in toluene. In this case, the peptide block generated from polyester formed β-sheet structure, indicating the self-assembly via peptide-guided route. We believe the findings presented in this study offer a new concept for the development of self-assembling block copolymer system.

Identity processing styles and the need for self-esteem in middle-aged and older adults.

PubMed

Sneed, J R; Whitbourne, S K

2001-01-01

This study was a test of the relationship between self-esteem and the identity processing styles of identity assimilation (i.e., maintaining consistent views of the self), accommodation (i.e., changing the self ), and a balance between consistency seeking and identity change. A community sample of 242 older adults ranging in age from forty to ninety-five (M = 63.31) completed measures of identity processing and self-esteem. Previous research has demonstrated that identity assimilation increases with age in order to maintain self-esteem in the domain of physical and cognitive functioning; this is referred to as the identity assimilation effect (IAE). Based on this research, a similar result was expected in the domain of personality. Although identity assimilation and balance predicted increases in self-esteem, and identity accommodation predicted decreases in self-esteem, as predicted, no interaction effects were observed. The results of this study suggest the IAE may be domain specific to physical and cognitive functioning.

``Coffee-ring'' patterns of polymer droplets

NASA Astrophysics Data System (ADS)

Biswas, Nupur; Datta, Alokmay

2013-02-01

Dried droplets of polymer solutions carries the self-assembly behavior of polymer molecules by forming various patterns. Pattern formation is a consequence of deposition of molecules depending on motion of the contact line during the drying process. The contact line motion depends on initial polymer concentrations and hence entanglement. Thus depending on entanglement the patterns represent the `particle' like or `collective' behavior of polymer molecules.

Self-organization of oligopeptides obtained on dissolution of feather keratins in superheated water.

PubMed

Yin, Jie; Rastogi, Sanjay; Terry, Ann E; Popescu, Crisan

2007-03-01

Keratins are self-organized proteins that are abundantly available in wool, feather, human hair, etc., making them a potential cheap feedstock for the modification of amino acids. This paper explores the hydrolysis of keratin in water under specific pressure-temperature conditions where the hydrolysis through scission of the protein chain yields oligopeptides. Here we report for the first time that, under appropriate conditions, these oligopeptides self-assemble into a hierarchical architecture, the process being followed in time by optical microscopy. Birefringent needle-like crystals are observed which tend to nucleate heterogeneously. When given sufficient time, these needles become tens of microns in length and act as further nuclei, developing a highly repetitive structure of several hundreds of microns in size. Micro-focus X-ray diffraction studies supported by in situ microscopy reveal that these needles have a crystal structure similar to that of the native protein, although better organized along the ab-plane. Spectroscopic studies on these structures show crystalline bands that disappear above 150 degrees C, coinciding with an endothermic peak in DSC. Amino acid analysis shows that the self-assembled birefringent entities are indeed oligopeptides, consisting of sequences of approximately 40 amino acids. The proposed ecofriendly route provides an effective route for obtaining oligopeptides that can be used as important building blocks for the synthesis of a range of novel polymers. The oligopeptides obtained from the sustainable source can be used as important building blocks for the synthesis of a range of novel polymers.

Artificial Informational Polymers and Nanomaterials from Ring-Opening Metathesis Polymerization

NASA Astrophysics Data System (ADS)

James, Carrie Rae

Inspired by naturally occurring polymers (DNA, polypeptides, polysaccharides, etc.) that can self-assemble on the nanoscale into complex, information-rich architectures, we have synthesized nucleic acid based polymers using ROMP. These polymers were synthesized using a graft-through strategy, whereby nucleic acids bearing a strained cyclic olefin were directly polymerized. This is the first example of the graft-through polymerization of nucleic acids. Our approach takes advantage of non-charged peptide nucleic acids (PNAs) as elements to incorporate into ROMP polymer backbones. PNA is a synthetic nucleic acid analogue known for its increased affinity and specificity for complementary DNA or RNA. To accomplish the graft-through polymerization of PNA, we conjugated PNA to strained cyclic olefins using solid phase peptide conjugation chemistry. These PNA monomers were then directly polymerized into homo and block copolymers forming brushes, or comb-like arrangements, of information. Block copolymer amphiphiles of these materials, where the PNA brush served as the hydrophilic portion, were capable of self-assembly into spherical nanoparticles (PNA NPs). These PNA NPs were then studied with respect to their ability to hybridize complementary DNA sequences, as well as their ability to undergo cellular internalization. PNA NPs consisting of densely packed brushes of nucleic acids possessed increased thermal stability when mixed with their complementary DNA sequence, indicating a greater DNA binding affinity over their unpolymerized PNA counterparts. In addition, by arranging the PNA into dense brushes at the surface of the nanoparticle, Cy5.5 labeled PNA NPs were able to undergo cellular internalization into HeLa cells without the need for an additional cellular delivery device. Importantly, cellular internalization of PNA has remained a significant challenge in the literature due to the neutrally charged amino-ethyl glycine backbone of PNA. Therefore, this represents a novel way of facilitating cellular uptake of PNA. This materials strategy represents the first direct polymerization of nucleic acids, and presents a novel method for arranging biological information on the nanoscale at high density in order to confer novel attributes.

Chemical Interactions and Their Role in the Microphase Separation of Block Copolymer Thin Films

PubMed Central

Farrell, Richard A.; Fitzgerald, Thomas G.; Borah, Dipu; Holmes, Justin D.; Morris, Michael A.

2009-01-01

The thermodynamics of self-assembling systems are discussed in terms of the chemical interactions and the intermolecular forces between species. It is clear that there are both theoretical and practical limitations on the dimensions and the structural regularity of these systems. These considerations are made with reference to the microphase separation that occurs in block copolymer (BCP) systems. BCP systems self-assemble via a thermodynamic driven process where chemical dis-affinity between the blocks driving them part is balanced by a restorative force deriving from the chemical bond between the blocks. These systems are attracting much interest because of their possible role in nanoelectronic fabrication. This form of self-assembly can obtain highly regular nanopatterns in certain circumstances where the orientation and alignment of chemically distinct blocks can be guided through molecular interactions between the polymer and the surrounding interfaces. However, for this to be possible, great care must be taken to properly engineer the interactions between the surfaces and the polymer blocks. The optimum methods of structure directing are chemical pre-patterning (defining regions on the substrate of different chemistry) and graphoepitaxy (topographical alignment) but both centre on generating alignment through favourable chemical interactions. As in all self-assembling systems, the problems of defect formation must be considered and the origin of defects in these systems is explored. It is argued that in these nanostructures equilibrium defects are relatively few and largely originate from kinetic effects arising during film growth. Many defects also arise from the confinement of the systems when they are ‘directed’ by topography. The potential applications of these materials in electronics are discussed. PMID:19865513

NMR investigations of self-aggregation characteristics of SDS in a model assembled tri-block copolymer solution.

PubMed

Kumar, B V N Phani; Priyadharsini, S Umayal; Prameela, G K S; Mandal, Asit Baran

2011-08-01

The present work was undertaken with a view to understand the influence of a model non-ionic tri-block copolymer PEO-PPO-PEO (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)) with molecular weight 5800 i.e., P123 [(EO)(20)-(PO)(70)-(EO)(20)] on the self-aggregation characteristics of the anionic surfactant sodium dodecylsulfate (SDS) in aqueous solution (D(2)O) using NMR chemical shift, self-diffusion and nuclear spin-relaxation as suitable experimental probes. In addition, polymer diffusion has been monitored as a function of SDS concentration. The concentration-dependent chemical shift, diffusion data and relaxation data indicated the significant interaction of polymeric micelles with SDS monomers and micelles at lower and intermediate concentrations of SDS, whereas the weak interaction of the polymer with SDS micelles at higher concentrations of SDS. It has been observed that SDS starts aggregating on the polymer at a lower concentration i.e., critical aggregation concentration (cac=1.94 mM) compared to polymer-free situation, and the onset of secondary micelle concentration (C(2)=27.16 mM) points out the saturation of the 0.2 wt% polymer or free SDS monomers/micelles at higher concentrations of SDS. It has also been observed that the parameter cac is almost independent in the polymer concentrations of study. The TMS (tetramethylsilane) has been used as a solubilizate to measure the bound diffusion coefficient of SDS-polymer mixed system. The self-diffusion data were analyzed using two-site exchange model and the obtained information on aggregation dynamics was commensurate with that inferred from chemical shift and relaxation data. The information on slow motions of polymer-SDS system was also extracted using spin-spin and spin-lattice relaxation rate measurements. The relaxation data points out the disintegration of polymer network at higher concentrations of SDS. The present NMR investigations have been well corroborated by surface tension and conductivity measurements. Copyright © 2011 Elsevier Inc. All rights reserved.

Cognitive indicators of social anxiety in youth: a structural equation analysis.

PubMed

Rudy, Brittany M; Davis, Thompson E; Matthews, Russell A

2014-01-01

Previous studies have demonstrated significant relationships among various cognitive variables such as negative cognition, self-efficacy, and social anxiety. Unfortunately, few studies focus on the role of cognition among youth, and researchers often fail to use domain-specific measures when examining cognitive variables. Therefore, the purpose of the present study was to examine domain-specific cognitive variables (i.e., socially oriented negative self-referent cognition and social self-efficacy) and their relationships to social anxiety in children and adolescents using structural equation modeling techniques. A community sample of children and adolescents (n=245; 55.9% female; 83.3% Caucasian, 9.4% African American, 2% Asian, 2% Hispanic, 2% "other," and 1.2% not reported) completed questionnaires assessing social cognition and social anxiety symptomology. Three latent variables were created to examine the constructs of socially oriented negative self-referent cognition (as measured by the SONAS scale), social self-efficacy (as measured by the SEQSS-C), and social anxiety (as measured by the SPAI-C and the Brief SA). The resulting measurement model of latent variables fit the data well. Additionally, consistent with the study hypothesis, results indicated that social self-efficacy likely mediates the relationship between socially oriented negative self-referent cognition and social anxiety, and socially oriented negative self-referent cognition yields significant direct and indirect effects on social anxiety. These findings indicate that socially oriented negative cognitions are associated with youth's beliefs about social abilities and the experience of social anxiety. Future directions for research and study limitations, including use of cross-sectional data, are discussed. © 2013.

Electrostatic stiffening and induced persistence length for coassembled molecular bottlebrushes

NASA Astrophysics Data System (ADS)

Storm, Ingeborg M.; Stuart, Martien A. Cohen; de Vries, Renko; Leermakers, Frans A. M.

2018-03-01

A self-consistent field analysis for tunable contributions to the persistence length of isolated semiflexible polymer chains including electrostatically driven coassembled deoxyribonucleic acid (DNA) bottlebrushes is presented. When a chain is charged, i.e., for polyelectrolytes, there is, in addition to an intrinsic rigidity, an electrostatic stiffening effect, because the electric double layer resists bending. For molecular bottlebrushes, there is an induced contribution due to the grafts. We explore cases beyond the classical phantom main-chain approximation and elaborate molecularly more realistic models where the backbone has a finite volume, which is necessary for treating coassembled bottlebrushes. We find that the way in which the linear charge density or the grafting density is regulated is important. Typically, the stiffening effect is reduced when there is freedom for these quantities to adapt to the curvature stresses. Electrostatically driven coassembled bottlebrushes, however, are relatively stiff because the chains have a low tendency to escape from the compressed regions and the electrostatic binding force is largest in the convex part. For coassembled bottlebrushes, the induced persistence length is a nonmonotonic function of the polymer concentration: For low polymer concentrations, the stiffening grows quadratically with coverage; for semidilute polymer concentrations, the brush chains retract and regain their Gaussian size. When doing so, they lose their induced persistence length contribution. Our results correlate well with observed physical characteristics of electrostatically driven coassembled DNA-bioengineered protein-polymer bottlebrushes.

Liquid crystal Janus emulsion droplets: preparation, tumbling, and swimming.

PubMed

Jeong, Joonwoo; Gross, Adam; Wei, Wei-Shao; Tu, Fuquan; Lee, Daeyeon; Collings, Peter J; Yodh, A G

2015-09-14

This study introduces liquid crystal (LC) Janus droplets. We describe a process for the preparation of these droplets, which consist of nematic LC and polymer compartments. The process employs solvent-induced phase separation in emulsion droplets generated by microfluidics. The droplet morphology was systematically investigated and demonstrated to be sensitive to the surfactant concentration in the background phase, the compartment volume ratio, and the possible coalescence of multiple Janus droplets. Interestingly, the combination of a polymer and an anisotropic LC introduces new functionalities into Janus droplets, and these properties lead to unusual dynamical behaviors. The different densities and solubilities of the two compartments produce gravity-induced alignment, tumbling, and directional self-propelled motion of Janus droplets. LC Janus droplets with remarkable optical properties and dynamical behaviors thus offer new avenues for applications of Janus colloids and active soft matter.

Rapid Self-healing Nanocomposite Hydrogel with Tunable Dynamic Mechanics

NASA Astrophysics Data System (ADS)

Li, Qiaochu; Mishra, Sumeet; Chapman, Brian; Chen, Pangkuan; Tracy, Joseph; Holten-Andersen, Niels

The macroscopic healing rate and efficiency in self-repairing hydrogel materials are largely determined by the dissociation dynamics of their polymer network, which is hardly achieved in a controllable manner. Inspired by mussel's adhesion chemistry, we developed a novel approach to assemble inorganic nanoparticles and catechol-decorated PEG polymer into a hydrogel network. When utilized as reversible polymer-particle crosslinks, catechol-metal coordination bonds yield a unique gel network with dynamic mechanics controlled directly by interfacial crosslink structure. Taking advantage of this structure-property relationship at polymer-particle interfaces, we designed a hierarchically structured hybrid gel with two distinct relaxation timescales. By tuning the relative contribution of the two relaxation modes, we are able to finely control the gel's dynamic mechanical behavior from a viscoelastic fluid to a stiff solid, yet preserving its rapid self-healing property without the need for external stimuli.

Self-assembled dye-doped polymer microspheres as whispering gallery mode lasers

NASA Astrophysics Data System (ADS)

Chen, Xiaogang; Sun, Hongyi; Yang, Hongqin; Wu, Xiang; Xie, Shusen

2016-10-01

Microlasers based on high-Q whispering-gallery-mode (WGM) resonances are promising low-threshold laser sources for bio-sensing and imaging applications. In this talk, we demonstrate a cost effective approach to obtain size-controllable polymer microspheres, which can be served as good WGM microcavities. By injecting SU-8 solution into low-refractiveindex UV polymer, self-assembled spherical droplet with smooth surface can be created inside the elastic medium and then solidified by UV exposure. The size of the microspheres can be tuned from several to hundreds of microns. WGM Lasing has been achieved by optically pumping the dye-doped microspheres with ns lasers. Experimental results show that the microsphere lasers have high quality factors and low lasing thresholds. The self-assembled dye-doped polymer microspheres would provide an excellent platform for the micro-laser sources in on-chip biosensing and imaging systems.

Self-formation of polymer nanostructures in plasma etching: mechanisms and applications

NASA Astrophysics Data System (ADS)

Du, Ke; Jiang, Youhua; Huang, Po-Shun; Ding, Junjun; Gao, Tongchuan; Choi, Chang-Hwan

2018-01-01

In recent years, plasma-induced self-formation of polymer nanostructures has emerged as a simple, scalable and rapid nanomanufacturing technique to pattern sub-100 nm nanostructures. High-aspect-ratio nanostructures (>20:1) are fabricated on a variety of polymer surfaces such as poly(methylmethacrylate) (PMMA), polystyrene (PS), polydimethylsiloxane (PDMS), and fluorinated ethylene propylene (FEP). Sub-100 nm nanostructures (i.e. diameter  ⩽  50 nm) are fabricated in this one-step process without relying on slow and expensive nanolithography techniques. This review starts with discussion of the self-formation mechanisms including surface modulation, random masks, and materials impurities. Emphasis is put on the applications of polymer nanostructures in the fields of hierarchical nanostructures, liquid repellence, adhesion, lab-on-a-chip, surface enhanced Raman scattering (SERS), organic light emitting diode (OLED), and energy harvesting. The unique advantages of this nanomanufacturing technique are illustrated, followed by prospects.

Analysis and experiment on a self-sensing ionic polymer-metal composite actuator

NASA Astrophysics Data System (ADS)

Nam, Doan Ngoc Chi; Ahn, Kyoung Kwan

2014-07-01

An ionic polymer-metal composite (IPMC) actuator is an electro-active polymer (EAP) that bends in response to a small applied electrical field as a result of the mobility of cations in the polymer network. This paper aims to develop a self-sensing actuator for practical use, since current sensing methods generally face limitations due to the compact size and mobility of the IPMC actuator. Firstly, the variation of surface resistance during bending operations is investigated. Then, the behavior of IPMC corresponding to the variation of surface resistance is mathematically analyzed. Based on the analysis results, a simple configuration to realize the self-sensing behavior is introduced. In this technique, the bending curvature of an IPMC can be obtained accurately by employing several feedback voltage signals along with the IPMC length. Finally, experimental evaluations proved the ability of the proposed scheme to estimate the bending behavior of IPMC actuators.

Application of Bottlebrush Block Copolymers as Photonic Crystals.

PubMed

Liberman-Martin, Allegra L; Chu, Crystal K; Grubbs, Robert H

2017-07-01

Brush block copolymers are a class of comb polymers that feature polymeric side chains densely grafted to a linear backbone. These polymers display interesting properties due to their dense functionality, low entanglement, and ability to rapidly self-assemble to highly ordered nanostructures. The ability to prepare brush polymers with precise structures has been enabled by advancements in controlled polymerization techniques. This Feature Article highlights the development of brush block copolymers as photonic crystals that can reflect visible to near-infrared wavelengths of light. Fabrication of these materials relies on polymer self-assembly processes to achieve nanoscale ordering, which allows for the rapid preparation of photonic crystals from common organic chemical feedstocks. The characteristic physical properties of brush block copolymers are discussed, along with methods for their preparation. Strategies to induce self-assembly at ambient temperatures and the use of blending techniques to tune photonic properties are emphasized. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-Assembling Brush Polymers Bearing Multisaccharides.

PubMed

Lee, Jongchan; Kim, Jin Chul; Lee, Hoyeol; Song, Sungjin; Kim, Heesoo; Ree, Moonhor

2017-06-01

Three different series of brush polymers bearing glucosyl, maltosyl, or maltotriosyl moiety at the bristle end are successfully prepared by using cationic ring-opening polymerization and two sequential postmodification reactions. All brush polymers, except for the polymer containing 100 mol% maltotriosyl moiety, demonstrate the formation of multibilayer structure in films, always providing saccharide-enriched surface. These self-assembling features are remarkable, regarding the bulkiness of saccharide moieties and the kink in the bristle due to the triazole linker. The saccharide-enriched film surfaces reveal exceptionally high specific binding affinity to concanavalin A but suppress nonspecific binding of plasma proteins severely. Overall, the brush polymers bearing saccharide moieties of various kinds in this study are highly suitable materials for biomedical applications including biosensors. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Role of Nanofillers in Polymer Nanocomposites

NASA Astrophysics Data System (ADS)

Xu, Di

Polymer nanocomposites have been widely used in many fields. By introducing nanoparticles as fillers, researchers are able to get reinforced materials and new materials with novel properties, such as stronger mechanics, enhanced optical properties and improved conductivity. Though experimental techniques have rapidly advanced to enable better control of materials at atomic level, there is still a lack of a fundamental understanding of the dynamics and structure-properties relations in polymer nanocomposites. In this thesis, we use computer simulations to study the molecular structure and connections between microstate to macro properties of a variety of nanocomposites. Our goal is to understand the role of nanofillers in complex nanocomposite systems and to assist nanocomposite design. Nanoplatelet fillers, such as clays, have shown superior effects on the properties of polymer gels. We used molecular dynamic simulation to study nanoplatelet-filled composite gel system, in which short-range attraction exists between the polymer and nanoplatelet fillers. We show that the polymers and nanoplatelet fillers formed organic-inorganic networks with nanoplatelets acting as crosslink junctions, and the network eventually percolates the system as fillers reached a critical concentration. Stress auto-correlation and step-strain test were applied to investigate the mechanical properties; the results show the simulated composites changed from fluid-like to solid-like. The mechanical changes were consistent with the percolation transition, and gelation mechanism was therefore believed to be similar to those pure polymer physical gels. It was observed platelets aggregated into a local intercalation structure, which significantly differs from typical spherical fillers. This unique intercalation structure was examined by radial distribution function and ordering parameters. We discussed how intercalation would affect the properties of the platelet composites by comparing them with spherical fillers. Nanofillers have been widely used in polymer blends to improve the interfacial compatibility of otherwise immiscible polymers. In the second system, we investigated the interfacial behavior of binary polymer blends with different types of fillers. The interfacial tension and shear resistance were studied as a function of filler-polymer interaction, filler concentration and species of fillers. We found filler-polymer interaction is the key factor to improve the interfacial compatibility. The results show that nanofillers reduce both interfacial tension and interfacial slip at strong filler-polymer interaction. The effects of nanofillers however differ significantly from each other by their shapes. We analyzed the structure of nanofillers at the interface and their effects on the interfacial behaviors. The self-assembly of polymers into a columnar structure, while subject to a thin film environment, provides an economic route to fabricate polymer solar cell (PSC) with high conversion efficiency. In our work, we showed that two immiscible polymer segregates into to a percolating columnar structure when confined to a thin film. By adding nanofillers, with specific functionality, we can template the segregation of nanofillers to the polymer-polymer interface. We prove this process is surface tension driven and is a result that is particular for thin film geometries, where the thickness is under critical value. The results provide a theoretical basis for the column structure forming in a self-assembled PSC system, and can help to select polymer candidates that optimize PSC efficiency. These studies serve as theoretical guideline for engineering novel nanocomposites, and could lead to the design of materials with new and improved properties.

Self-Healing of Unentangled Polymer Networks with Reversible Bonds

PubMed Central

Stukalin, Evgeny B.; Cai, Li-Heng; Kumar, N. Arun; Leibler, Ludwik; Rubinstein, Michael

2013-01-01

Self-healing polymeric materials are systems that after damage can revert to their original state with full or partial recovery of mechanical strength. Using scaling theory we study a simple model of autonomic self-healing of unentangled polymer networks. In this model one of the two end monomers of each polymer chain is fixed in space mimicking dangling chains attachment to a polymer network, while the sticky monomer at the other end of each chain can form pairwise reversible bond with the sticky end of another chain. We study the reaction kinetics of reversible bonds in this simple model and analyze the different stages in the self-repair process. The formation of bridges and the recovery of the material strength across the fractured interface during the healing period occur appreciably faster after shorter waiting time, during which the fractured surfaces are kept apart. We observe the slowest formation of bridges for self-adhesion after bringing into contact two bare surfaces with equilibrium (very low) density of open stickers in comparison with self-healing. The primary role of anomalous diffusion in material self-repair for short waiting times is established, while at long waiting times the recovery of bonds across fractured interface is due to hopping diffusion of stickers between different bonded partners. Acceleration in bridge formation for self-healing compared to self-adhesion is due to excess non-equilibrium concentration of open stickers. Full recovery of reversible bonds across fractured interface (formation of bridges) occurs after appreciably longer time than the equilibration time of the concentration of reversible bonds in the bulk. PMID:24347684

Measuring self-aligned quadruple patterning pitch walking with scatterometry-based metrology utilizing virtual reference

NASA Astrophysics Data System (ADS)

Kagalwala, Taher; Vaid, Alok; Mahendrakar, Sridhar; Lenahan, Michael; Fang, Fang; Isbester, Paul; Shifrin, Michael; Etzioni, Yoav; Cepler, Aron; Yellai, Naren; Dasari, Prasad; Bozdog, Cornel

2016-10-01

Advanced technology nodes, 10 nm and beyond, employing multipatterning techniques for pitch reduction pose new process and metrology challenges in maintaining consistent positioning of structural features. A self-aligned quadruple patterning (SAQP) process is used to create the fins in FinFET devices with pitch values well below optical lithography limits. The SAQP process bears the compounding effects from successive reactive ion etch and spacer depositions. These processes induce a shift in the pitch value from one fin compared to another neighboring fin. This is known as pitch walking. Pitch walking affects device performance as well as later processes, which work on an assumption that there is consistent spacing between fins. In SAQP, there are three pitch walking parameters of interest, each linked to specific process steps in the flow. These pitch walking parameters are difficult to discriminate at a specific process step by singular evaluation technique or even with reference metrology, such as transmission electron microscopy. We will utilize a virtual reference to generate a scatterometry model to measure pitch walk for SAQP process flow.

Synthetic Reference Materials Based on Polymer Films for the Control of Welding Fumes Composition

NASA Astrophysics Data System (ADS)

Kuznetsova, O. V.; Kuznetsova, A. N.; Begunova, L. A.

2017-04-01

Analysis of the current hygienic situation in the welding production showed that the intensification of welding processes involves the deterioration of air quality, which negatively affects the welders health. Welders are exposed to a variety of metal fumes, including manganese that may elevate the risk for neurological diseases. The control of metals concentration in the air of the working area is difficult due to the lack of reference materials. The creation of reference materials of welding fumes composition is a challenge due to chemical characteristics of their physical properties. Synthetic samples in a form of the polymer film containing powder particles of welding fumes were create. Studies on the selection of the polymer were done. Experiments proved that the qualitative materials of synthetic welding fumes are obtained by using polyvinyl alcohol. The metals concentration in the samples was determined by X-ray fluorescence analysis. The obtained data demonstrates indirectly the uniform distribution of welding fumes powder particles on the polymer film.

Bio-inspired Self-healing Composite Hydrogel with Iron Oxide Nanoparticle as Coordination Crosslinker

NASA Astrophysics Data System (ADS)

Li, Qiaochu; Barret, Devin G.; Messersmith, Phillip B.; Holten-Andersen, Niels

2014-03-01

Polymer-nanoparticle (NP) composites have attracted renewed attention due to enhanced mechanical strength combined with various functionalities, but controlling the interfacial chemistry between NPs and polymer matrix, which is crucial for the composite's mechanical behavior, remains a major challenge. Inspired by the adhesion chemistry of mussel fibers, we investigated a novel approach to incorporate Fe3O4 NPs into hydrogel matrix. A polyethylene glycol polymer is designed with both ends conjugated by catechol groups, which have strong coordination affinity to Fe. The polymer network is crosslinked via coordination bonding at the surface of Fe3O4 NPs, yielding a stiff nanocomposite hydrogel. Due to the reversible nature of coordination bonding, the hydrogel presents self-healing behavior. Oscillatory rheology allows comparative kinetic studies of self-healing driven by catechol bonding at Fe3O4 NP interfaces and by catechol-Fe3+ coordination complexes. Furthermore, the superparamagnetic property of Fe3O4 NP is preserved after gelation, allowing for response to external stimuli. This gelation motif can serve as a versatile platform for tuning functional and mechanical properties for future polymer nanocomposite materials.

Centro-Apical Self-Organization of Organic Semiconductors in a Line-Printed Organic Semiconductor: Polymer Blend for One-Step Printing Fabrication of Organic Field-Effect Transistors

PubMed Central

Jin Lee, Su; Kim, Yong-Jae; Young Yeo, So; Lee, Eunji; Sun Lim, Ho; Kim, Min; Song, Yong-Won; Cho, Jinhan; Ah Lim, Jung

2015-01-01

Here we report the first demonstration for centro-apical self-organization of organic semiconductors in a line-printed organic semiconductor: polymer blend. Key feature of this work is that organic semiconductor molecules were vertically segregated on top of the polymer phase and simultaneously crystallized at the center of the printed line pattern after solvent evaporation without an additive process. The thickness and width of the centro-apically segregated organic semiconductor crystalline stripe in the printed blend pattern were controlled by varying the relative content of the organic semiconductors, printing speed, and solution concentrations. The centro-apical self-organization of organic semiconductor molecules in a printed polymer blend may be attributed to the combination of an energetically favorable vertical phase-separation and hydrodynamic fluids inside the droplet during solvent evaporation. Finally, a centro-apically phase-separated bilayer structure of organic semiconductor: polymer blend was successfully demonstrated as a facile method to form the semiconductor and dielectric layer for OFETs in one- step. PMID:26359068

Centro-Apical Self-Organization of Organic Semiconductors in a Line-Printed Organic Semiconductor: Polymer Blend for One-Step Printing Fabrication of Organic Field-Effect Transistors.

PubMed

Lee, Su Jin; Kim, Yong-Jae; Yeo, So Young; Lee, Eunji; Lim, Ho Sun; Kim, Min; Song, Yong-Won; Cho, Jinhan; Lim, Jung Ah

2015-09-11

Here we report the first demonstration for centro-apical self-organization of organic semiconductors in a line-printed organic semiconductor: polymer blend. Key feature of this work is that organic semiconductor molecules were vertically segregated on top of the polymer phase and simultaneously crystallized at the center of the printed line pattern after solvent evaporation without an additive process. The thickness and width of the centro-apically segregated organic semiconductor crystalline stripe in the printed blend pattern were controlled by varying the relative content of the organic semiconductors, printing speed, and solution concentrations. The centro-apical self-organization of organic semiconductor molecules in a printed polymer blend may be attributed to the combination of an energetically favorable vertical phase-separation and hydrodynamic fluids inside the droplet during solvent evaporation. Finally, a centro-apically phase-separated bilayer structure of organic semiconductor: polymer blend was successfully demonstrated as a facile method to form the semiconductor and dielectric layer for OFETs in one- step.

Synergistic toughening of composite fibres by self-alignment of reduced graphene oxide and carbon nanotubes

PubMed Central

Shin, Min Kyoon; Lee, Bommy; Kim, Shi Hyeong; Lee, Jae Ah; Spinks, Geoffrey M.; Gambhir, Sanjeev; Wallace, Gordon G.; Kozlov, Mikhail E.; Baughman, Ray H.; Kim, Seon Jeong

2012-01-01

The extraordinary properties of graphene and carbon nanotubes motivate the development of methods for their use in producing continuous, strong, tough fibres. Previous work has shown that the toughness of the carbon nanotube-reinforced polymer fibres exceeds that of previously known materials. Here we show that further increased toughness results from combining carbon nanotubes and reduced graphene oxide flakes in solution-spun polymer fibres. The gravimetric toughness approaches 1,000 J g−1, far exceeding spider dragline silk (165 J g−1) and Kevlar (78 J g−1). This toughness enhancement is consistent with the observed formation of an interconnected network of partially aligned reduced graphene oxide flakes and carbon nanotubes during solution spinning, which act to deflect cracks and allow energy-consuming polymer deformation. Toughness is sensitive to the volume ratio of the reduced graphene oxide flakes to the carbon nanotubes in the spinning solution and the degree of graphene oxidation. The hybrid fibres were sewable and weavable, and could be shaped into high-modulus helical springs. PMID:22337128

Magnetic field gradient driven self-assembly of superparamagnetic nanoparticles using programmable magnetically-recorded templates

NASA Astrophysics Data System (ADS)

Ye, L.; Qi, B.; Lawton, T. G.; Mefford, O. T.; Rinaldi, C.; Garzon, S.; Crawford, T. M.

2013-03-01

Using the enormous magnetic field gradients (100 MT/m @ z =20 nm) present near the surface of magnetic recording media, we demonstrate the fabrication of diffraction gratings with lines consisting entirely of magnetic nanoparticles assembled from a colloidal fluid onto a disk drive medium, followed by transfer to a flexible and transparent polymer thin film. These nanomanufactured gratings have line spacings programmed with commercial magnetic recording and are inherently concave with radii of curvature controlled by varying the polymer film thickness. The diffracted intensity increases non-monotonically with the length of time the colloidal fluid remains on the disk surface. In addition to comparing longitudinal and perpendicular magnetic recording, a combination of spectral diffraction efficiency measurements, magnetometry, scanning electron microscopy and inductively coupled plasma atomic emmission spectroscopy of these gratings are employed to understand colloidal nanoparticle dynamics in this extreme gradient limit. Such experiments are necessary to optimize nanoparticle assembly and obtain uniform patterned features. This low-cost and sustainable approach to nanomanufacturing could enable low-cost, high-quality diffraction gratings as well as more complex polymer nanocomposite materials assembled with single-nanometer precision.

Chasing Extreme Polymer Morphologies with Ed

NASA Astrophysics Data System (ADS)

Fredrickson, Glenn

I was privileged to have a seventeen year friendship and scientific collaboration with Edward J. Kramer that produced 55 papers and countless student and postdoc co-advisements. This talk will discuss our last project together; an ongoing research program to achieve thermoplastic polymer materials that are uniquely hard, tough, and elastic, with moduli greater than 100 MPa and elastic recovery greater than 0.9 at strains of 1 or more. The targeted materials are based on an A(BA')n mikto-arm block copolymer architecture, and alloys of these molecules with A homopolymer. The molecular design of the miktopolymer was optimized using self-consistent field theory and the materials realized in a polystyrene (A)-polyisoprene (B) system. TEM, SAXS, and tensile mechanical tests were used to validate the designs and probe microstructure/mechanics relationships. An unexpected discovery was the emergence of a new structured disordered phase - the bricks and mortar phase -in which the A domains remain discrete at up to a volume fraction of 0.7. Field-theoretic simulations have been used to understand the origins of this new fluctuation-stabilized equilibrium phase, which has no precedent in the polymer physics literature.

In situ characterization of the oxidative degradation of a polymeric light emitting device

NASA Astrophysics Data System (ADS)

Cumpston, B. H.; Parker, I. D.; Jensen, K. F.

1997-04-01

Light-emitting devices with polymeric emissive layers have great promise for the production of large-area, lightweight, flexible color displays, but short lifetimes currently limit applications. We address mechanisms of bulk polymer degradation in these devices and show through in situ Fourier transform infrared characterization of working light-emitting devices with active layers of poly[2-methoxy,5-(2'-ethyl-hexoxy)-1,4-phenylene vinylene] that oxygen is responsible for the degradation of the polymer film. A mechanism is given based on the formation of singlet oxygen from oxygen impurities in the film via energy transfer from a nonradiative exciton. Fourier transform infrared and x-ray photoelectron spectroscopy results are consistent with the mechanism, involving singlet oxygen attack followed by free radical processes. We further show that oxygen readily diffuses into the active polymer layer, changing the electrical characteristics of the film even at low concentrations. Thus, polyphenylene-vinylene-based light-emitting devices will self-destruct during operation if fabricated without special attention to eliminating oxygen contamination during fabrication and device operation.

Balanced Ambipolar Organic Field-Effect Transistors by Polymer Preaggregation.

PubMed

Janasz, Lukasz; Luczak, Adam; Marszalek, Tomasz; Dupont, Bertrand G R; Jung, Jaroslaw; Ulanski, Jacek; Pisula, Wojciech

2017-06-21

Ambipolar organic field-effect transistors (OFETs) based on heterojunction active films still suffer from an imbalance in the transport of electrons and holes. This problem is related to an uncontrolled phase separation between the donor and acceptor organic semiconductors in the thin films. In this work, we have developed a concept to improve the phase separation in heterojunction transistors to enhance their ambipolar performance. This concept is based on preaggregation of the donor polymer, in this case poly(3-hexylthiophene) (P3HT), before solution mixing with the small-molecular-weight acceptor, phenyl-C61-butyric acid methyl ester (PCBM). The resulting heterojunction transistor morphology consists of self-assembled P3HT fibers embedded in a PCBM matrix, ensuring balanced mobilities reaching 0.01 cm 2 /V s for both holes and electrons. These are the highest mobility values reported so far for ambipolar OFETs based on P3HT/PCBM blends. Preaggregation of the conjugated polymer before fabricating binary blends can be regarded as a general concept for a wider range of semiconducting systems applicable in organic electronic devices.

Self-assembled hybrid polymer-TiO2 nanotube array heterojunction solar cells.

PubMed

Shankar, Karthik; Mor, Gopal K; Prakasam, Haripriya E; Varghese, Oomman K; Grimes, Craig A

2007-11-20

Films comprised of 4 microm long titanium dioxide nanotube arrays were fabricated by anodizing Ti foils in an ethylene glycol based electrolyte. A carboxylated polythiophene derivative was self-assembled onto the TiO2 nanotube arrays by immersing them in a solution of the polymer. The binding sites of the carboxylate moiety along the polymer chain provide multiple anchoring sites to the substrate, making for a stable rugged film. Backside illuminated liquid junction solar cells based on TiO2 nanotube films sensitized by the self-assembled polymeric layer showed a short-circuit current density of 5.5 mA cm-2, a 0.7 V open circuit potential, and a 0.55 fill factor yielding power conversion efficiencies of 2.1% under AM 1.5 sun. A backside illuminated single heterojunction solid state solar cell using the same self-assembled polymer was demonstrated and yielded a photocurrent density as high as 2.0 mA cm-2. When a double heterojunction was formed by infiltrating a blend of poly(3-hexylthiophene) (P3HT) and C60-methanofullerene into the self-assembled polymer coated nanotube arrays, a photocurrent as high as 6.5 mA cm-2 was obtained under AM 1.5 sun with a corresponding efficiency of 1%. The photocurrent action spectra showed a maximum incident photon-to-electron conversion efficiency (IPCE) of 53% for the liquid junction cells and 25% for the single heterojunction solid state solar cells.

Facile synthesis of polymeric fluorescent organic nanoparticles based on the self-polymerization of dopamine for biological imaging.

PubMed

Shi, Yingge; Jiang, Ruming; Liu, Meiying; Fu, Lihua; Zeng, Guangjian; Wan, Qing; Mao, Liucheng; Deng, Fengjie; Zhang, Xiaoyong; Wei, Yen

2017-08-01

Polymeric fluorescent organic nanoparticles (polymer-FONs) have raised considerable research attention for biomedical applications owing to their advantages as compared with fluorescent inorganic nanoparticles and small organic molecules. In this study, we presented an efficient, facile and environment-friendly strategy to produce polymer-FONs, which relied on the self-polymerization of dopamine and polyethyleneimine (PEI) in rather mild conditions. To obtain the final polymer-FONs, aldehyde group-containing copolymers (named as poly(UA-co-PEGMA)) were synthesized by reversible addition-fragmentation chain-transfer polymerization using polyethylene glycol methyl ether methacrylate (PEGMA) and 1-undecen-10-al (UA) as monomers. The dopamine was conjugated onto poly(UA-co-PEGMA) through a multicomponent reaction between UA and dopamine to obtain poly(UA-co-PEGMA)-DA, which was further utilized for preparation of polymer-FONs through self-polymerization of dopamine and PEI. 1 H nuclear magnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy and fluorescence spectroscopy were employed to characterize the structure, morphology, compositions and optical properties of these polymer-FONs. Cell viability and cell uptake behavior results suggested that these polymer-FONs possess good biocompatibility and can be potentially utilized for biomedical applications. More importantly, the method can be also applied to fabricate many other multifunctional polymer-FONs with great potential for biomedical applications. Copyright © 2017 Elsevier B.V. All rights reserved.

The Iranian Version of the Exercise Self-Efficacy Scale (ESES): Factor Structure, Internal Consistency and Construct Validity

ERIC Educational Resources Information Center

Noroozi, Azita; Ghofranipour, Fazlollah; Heydarnia, Ali Reza; Nabipour, Iraj; Tahmasebi, Rahim; Tavafian, Sedighe Sadat

2011-01-01

Purpose: The exercise self-efficacy scale (ESES) is largely used among diabetic patients to enhance exercise behaviour. However, the Iranian version of ESES was not available. The aim of this study was to validate ESES in this country. Method: Data were collected from 348 women who referred to a diabetes institute in Iran through convenience…

Highly Flexible Self-Assembled V2O5 Cathodes Enabled by Conducting Diblock Copolymers

PubMed Central

An, Hyosung; Mike, Jared; Smith, Kendall A.; Swank, Lisa; Lin, Yen-Hao; L. Pesek, Stacy; Verduzco, Rafael; Lutkenhaus, Jodie L.

2015-01-01

Mechanically robust battery electrodes are desired for applications in wearable devices, flexible displays, and structural energy and power. In this regard, the challenge is to balance mechanical and electrochemical properties in materials that are inherently brittle. Here, we demonstrate a unique water-based self-assembly approach that incorporates a diblock copolymer bearing electron- and ion-conducting blocks, poly(3-hexylthiophene)-block-poly(ethyleneoxide) (P3HT-b-PEO), with V2O5 to form a flexible, tough, carbon-free hybrid battery cathode. V2O5 is a promising lithium intercalation material, but it remains limited by its poor conductivity and mechanical properties. Our approach leads to a unique electrode structure consisting of interlocking V2O5 layers glued together with micellar aggregates of P3HT-b-PEO, which results in robust mechanical properties, far exceeding the those obtained from conventional fluoropolymer binders. Only 5 wt % polymer is required to triple the flexibility of V2O5, and electrodes comprised of 10 wt % polymer have unusually high toughness (293 kJ/m3) and specific energy (530 Wh/kg), both higher than reduced graphene oxide paper electrodes. Furthermore, addition of P3HT-b-PEO enhances lithium-ion diffusion, eliminates cracking during cycling, and boosts cyclability relative to V2O5 alone. These results highlight the importance of tradeoffs between mechanical and electrochemical performance, where polymer content can be used to tune both aspects. PMID:26391053

Highly Flexible Self-Assembled V 2O 5 Cathodes Enabled by Conducting Diblock Copolymers

DOE PAGES

An, Hyosung; Mike, Jared; Smith, Kendall A.; ...

2015-09-22

Mechanically robust battery electrodes are desired for applications in wearable devices, flexible displays, and structural energy and power. In this regard, the challenge is to balance mechanical and electrochemical properties in materials that are inherently brittle. Here, we demonstrate a unique water-based self-assembly approach that incorporates a diblock copolymer bearing electron- and ion-conducting blocks, poly(3-hexylthiophene)-block-poly(ethyleneoxide) (P3HT-b-PEO), with V 2O 5 to form a flexible, tough, carbon-free hybrid battery cathode. V 2O 5 is a promising lithium intercalation material, but it remains limited by its poor conductivity and mechanical properties. Our approach leads to a unique electrode structure consisting of interlockingmore » V 2O 5 layers glued together with micellar aggregates of P3HT-b-PEO, which results in robust mechanical properties, far exceeding the those obtained from conventional fluoropolymer binders. Only 5 wt % polymer is required to triple the flexibility of V 2O 5, and electrodes comprised of 10 wt % polymer have unusually high toughness (293 kJ/m 3) and specific energy (530 Wh/kg), both higher than reduced graphene oxide paper electrodes. Furthermore, addition of P3HT-b-PEO enhances lithium-ion diffusion, eliminates cracking during cycling, and boosts cyclability relative to V 2O 5 alone. These results highlight the importance of tradeoffs between mechanical and electrochemical performance, where polymer content can be used to tune both aspects.« less

Genetically engineered silk-collagen-like copolymer for biomedical applications: production, characterization and evaluation of cellular response.

PubMed

Włodarczyk-Biegun, Małgorzata K; Werten, Marc W T; de Wolf, Frits A; van den Beucken, Jeroen J J P; Leeuwenburgh, Sander C G; Kamperman, Marleen; Cohen Stuart, Martien A

2014-08-01

Genetically engineered protein polymers (GEPP) are a class of multifunctional materials with precisely controlled molecular structure and property profile. Representing a promising alternative for currently used materials in biomedical applications, GEPP offer multiple benefits over natural and chemically synthesized polymers. However, producing them in sufficient quantities for preclinical research remains challenging. Here, we present results from an in vitro cellular response study of a recombinant protein polymer that is soluble at low pH but self-organizes into supramolecular fibers and physical hydrogels at neutral pH. It has a triblock structure denoted as C2S(H)48C2, which consists of hydrophilic collagen-inspired and histidine-rich silk-inspired blocks. The protein was successfully produced by the yeast Pichia pastoris in laboratory-scale bioreactors, and it was purified by selective precipitation. This efficient and inexpensive production method provided material of sufficient quantities, purity and sterility for cell culture study. Rheology and erosion studies showed that it forms hydrogels exhibiting long-term stability, self-healing behavior and tunable mechanical properties. Primary rat bone marrow cells cultured in direct contact with these hydrogels remained fully viable; however, proliferation and mineralization were relatively low compared to collagen hydrogel controls, probably because of the absence of cell-adhesive motifs. As biofunctional factors can be readily incorporated to improve material performance, our approach provides a promising route towards biomedical applications. Copyright © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Polymer-stabilized liquid crystalline topological defect network for micro-pixelated optical devices

NASA Astrophysics Data System (ADS)

Araoka, Fumito; Le, Khoa V.; Fujii, Shuji; Orihara, Hiroshi; Sasaki, Yuji

2018-02-01

Spatially and temporally controlled topological defects in nematic liquid crystals (NLCs) are promising for its potential in optical applications. Utilization of self-organization is a key to fabricate complex micro- and nano-structures which are often difficult to obtain by conventional lithographic tools. Using photo-polymerization technique, here we show a polymer-stabilized NLC having a micro-pixelated structure of regularly ordered umbilical defects which are induced by an electric field. Due to the formation of polymer network, the self-organized pattern is kept stable without deterioration. Moreover, the polymer network allows to template other LCs whose optical properties can be tuned with external stimuli such as temperature and electric fields.

Shape Memory Polymers for Body Motion Energy Harvesting and Self-Powered Mechanosensing.

PubMed

Liu, Ruiyuan; Kuang, Xiao; Deng, Jianan; Wang, Yi-Cheng; Wang, Aurelia C; Ding, Wenbo; Lai, Ying-Chih; Chen, Jun; Wang, Peihong; Lin, Zhiqun; Qi, H Jerry; Sun, Baoquan; Wang, Zhong Lin

2018-02-01

Growing demand in portable electronics raises a requirement to electronic devices being stretchable, deformable, and durable, for which functional polymers are ideal choices of materials. Here, the first transformable smart energy harvester and self-powered mechanosensation sensor using shape memory polymers is demonstrated. The device is based on the mechanism of a flexible triboelectric nanogenerator using the thermally triggered shape transformation of organic materials for effectively harvesting mechanical energy. This work paves a new direction for functional polymers, especially in the field of mechanosensation for potential applications in areas such as soft robotics, biomedical devices, and wearable electronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tritium containing polymers having a polymer backbone substantially void of tritium

DOEpatents

Jensen, G.A.; Nelson, D.A.; Molton, P.M.

1992-03-31

A radioluminescent light source comprises a solid mixture of a phosphorescent substance and a tritiated polymer. The solid mixture forms a solid mass having length, width, and thickness dimensions, and is capable of self-support. In one aspect of the invention, the phosphorescent substance comprises solid phosphor particles supported or surrounded within a solid matrix by a tritium containing polymer. The tritium containing polymer comprises a polymer backbone which is essentially void of tritium. 2 figs.

Tritium containing polymers having a polymer backbone substantially void of tritium

DOEpatents

Jensen, George A.; Nelson, David A.; Molton, Peter M.

1992-01-01

A radioluminescent light source comprises a solid mixture of a phosphorescent substance and a tritiated polymer. The solid mixture forms a solid mass having length, width, and thickness dimensions, and is capable of self-support. In one aspect of the invention, the phosphorescent substance comprises solid phosphor particles supported or surrounded within a solid matrix by a tritium containing polymer. The tritium containing polymer comprises a polymer backbone which is essentially void of tritium.

Metastable Polymers for On Demand Transient Electronic Packaging

DTIC Science & Technology

2018-01-17

a triggerable polymer for engineering applications. 25 Approved for public release; distribution is unlimited. 6 REFERENCES (1) Aso, C.; Tagami, S...R. Advanced Materials 2014, 26, 7637. (4) Ito, H.; Willson, C. G. Polymer Engineering & Science 1983, 23, 1012. (5) Ito, H.; England, W. P.; Ueda, M

Theoretical studies of electronically excited states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Besley, Nicholas A.

2014-10-06

Time-dependent density functional theory is the most widely used quantum chemical method for studying molecules in electronically excited states. However, excited states can also be computed within Kohn-Sham density functional theory by exploiting methods that converge the self-consistent field equations to give excited state solutions. The usefulness of single reference self-consistent field based approaches for studying excited states is demonstrated by considering the calculation of several types of spectroscopy including the infrared spectroscopy of molecules in an electronically excited state, the rovibrational spectrum of the NO-Ar complex, core electron binding energies and the emission spectroscopy of BODIPY in water.

Combination of SEDDS and Preactivated Thiomer Technology: Incorporation of a Preactivated Thiolated Amphiphilic Polymer into Self-Emulsifying Delivery Systems.

PubMed

Hetényi, Gergely; Griesser, Janine; Nardin, Isabelle; Bernkop-Schnürch, Andreas

2017-06-01

The aim of the study was to create novel mucoadhesive drug delivery systems by incorporating amphiphilic hydrophobically modified, thiolated and preactivated polymers (preactivated thiomers) into self-emulsifying drug delivery systems (SEDDS). L-Cysteine methyl ester was covalently attached to the polymeric backbone of Pemulen TR-2 and preactivated using 2-mercaptonicotinic acid (2-MNA). These thiomers were incorporated in a concentration of 0.3% (w/v) into SEDDS. The size distribution and the zeta potential of the emulsions were evaluated by dynamic light scattering. Mucoadhesive properties of thiomers-SEDDS spiked with FDA (fluorescein diacetate) were examined utilizing rheological measurement, permeation studies and in vitro residence time study on porcine mucosa. Cell viability tests were additionally performed. 734 ± 58 μmol L-Cysteine methyl ester and 562 ± 71 μmol 2-MNA could be attached per gram polymer of Pemulen TR-2. Emulsions exhibited a droplet size range between 180 and 270 nm. Blank SEDDS possessed a zeta potential value between -5.7 and -8.6 mV, whereas thiomers-SEDDS between -14.6 and -17.2 mV. Viscous modulus of thiomer and preactivated thiomer containing SEDDS-mucus mixture was 8-fold and 11-fold increased in comparison to reference. The amount of FDA permeated the mucus layer was 2-fold lower in case of thiomers-SEDDS compared to blank SEDDS. A prolonged residence time was observed for thiomers-SEDDS over 45 min. During cell viability studies no severe toxic effects were detected. The novel developed SEDDS with incorporated thiomers might be a promising tool for mucoadhesive oral drug delivery.

Self-assembled tunable networks of sticky colloidal particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demortiere, Arnaud; Snezhko, Oleksiy Alexey; Sapozhnikov, Maksim

Self-assembled tunable networks of microscopic polymer fibers ranging from wavy colloidal "fur" to highly interconnected networks are created from polymer systems and an applied electric field. The networks emerge via dynamic self-assembly in an alternating (ac) electric field from a non-aqueous suspension of "sticky" polymeric colloidal particles with a controlled degree of polymerization. The resulting architectures are tuned by the frequency and amplitude of the electric field and surface properties of the particles.

Rigid Origami via Optical Programming and Deferred Self-Folding of a Two-Stage Photopolymer.

PubMed

Glugla, David J; Alim, Marvin D; Byars, Keaton D; Nair, Devatha P; Bowman, Christopher N; Maute, Kurt K; McLeod, Robert R

2016-11-02

We demonstrate the formation of shape-programmed, glassy origami structures using a single-layer photopolymer with two mechanically distinct phases. The latent origami pattern consisting of rigid, high cross-link density panels and flexible, low cross-link density creases is fabricated using a series of photomask exposures. Strong optical absorption of the polymer formulation creates depth-wise gradients in the cross-link density of the creases, enforcing directed folding which enables programming of both mountain and valley folds within the same sheet. These multiple photomask patterns can be sequentially applied because the sheet remains flat until immersed into a photopolymerizable monomer solution that differentially swells the polymer to fold and form the origami structure. After folding, a uniform photoexposure polymerizes the absorbed solution, permanently fixing the shape of the folded structure while simultaneously increasing the modulus of the folds. This approach creates sharp folds by mimicking the stiff panels and flexible creases of paper origami while overcoming the traditional trade-off of self-actuated materials that require low modulus for folding and high modulus for mechanical robustness. Using this process, we demonstrate a waterbomb base capable of supporting 1500 times its own weight.

Lipid-peptide-polymer conjugates and nanoparticles thereof

DOEpatents

Xu, Ting; Dong, He; Shu, Jessica

2015-06-02

The present invention provides a conjugate having a peptide with from about 10 to about 100 amino acids, wherein the peptide adopts a helical structure. The conjugate also includes a first polymer covalently linked to the peptide, and a hydrophobic moiety covalently linked to the N-terminus of the peptide, wherein the hydrophobic moiety comprises a second polymer or a lipid moiety. The present invention also provides helix bundles form by self-assembling the conjugates, and particles formed by self-assembling the helix bundles. Methods of preparing the helix bundles and particles are also provided.

Active Curved Polymers Form Vortex Patterns on Membranes.

PubMed

Denk, Jonas; Huber, Lorenz; Reithmann, Emanuel; Frey, Erwin

2016-04-29

Recent in vitro experiments with FtsZ polymers show self-organization into different dynamic patterns, including structures reminiscent of the bacterial Z ring. We model FtsZ polymers as active particles moving along chiral, circular paths by Brownian dynamics simulations and a Boltzmann approach. Our two conceptually different methods point to a generic phase behavior. At intermediate particle densities, we find self-organization into vortex structures including closed rings. Moreover, we show that the dynamics at the onset of pattern formation is described by a generalized complex Ginzburg-Landau equation.

Towards a unified description of the charge transport mechanisms in conductive atomic force microscopy studies of semiconducting polymers.

PubMed

Moerman, D; Sebaihi, N; Kaviyil, S E; Leclère, P; Lazzaroni, R; Douhéret, O

2014-09-21

In this work, conductive atomic force microscopy (C-AFM) is used to study the local electrical properties in thin films of self-organized fibrillate poly(3-hexylthiophene) (P3HT), as a reference polymer semiconductor. Depending on the geometrical confinement in the transport channel, the C-AFM current is shown to be governed either by the charge transport in the film or by the carrier injection at the tip-sample contact, leading to either bulk or local electrical characterization of the semiconducting polymer, respectively. Local I-V profiles allow discrimination of the different dominating electrical mechanisms, i.e., resistive in the transport regime and space charge limited current (SCLC) in the local regime. A modified Mott-Gurney law is analytically derived for the contact regime, taking into account the point-probe geometry of the contact and the radial injection of carriers. Within the SCLC regime, the probed depth is shown to remain below 12 nm with a lateral electrical resolution below 5 nm. This confirms that high resolution is reached in those C-AFM measurements, which therefore allows for the analysis of single organic semiconducting nanostructures. The carrier density and mobility in the volume probed under the tip under steady-state conditions are also determined in the SCLC regime.

Nonequilibrium self-energy functional theory

NASA Astrophysics Data System (ADS)

Hofmann, Felix; Eckstein, Martin; Arrigoni, Enrico; Potthoff, Michael

2013-10-01

The self-energy functional theory (SFT) is generalized to describe the real-time dynamics of correlated lattice-fermion models far from thermal equilibrium. This is achieved by starting from a reformulation of the original equilibrium theory in terms of double-time Green's functions on the Keldysh-Matsubara contour. With the help of a generalized Luttinger-Ward functional, we construct a functional Ω̂[Σ] which is stationary at the physical (nonequilibrium) self-energy Σ and which yields the grand potential of the initial thermal state Ω at the physical point. Nonperturbative approximations can be defined by specifying a reference system that serves to generate trial self-energies. These self-energies are varied by varying the reference system's one-particle parameters on the Keldysh-Matsubara contour. In the case of thermal equilibrium, this approach reduces to the conventional SFT. Contrary to the equilibrium theory, however, “unphysical” variations, i.e., variations that are different on the upper and the lower branches of the Keldysh contour, must be considered to fix the time dependence of the optimal physical parameters via the variational principle. Functional derivatives in the nonequilibrium SFT Euler equation are carried out analytically to derive conditional equations for the variational parameters that are accessible to a numerical evaluation via a time-propagation scheme. Approximations constructed by means of the nonequilibrium SFT are shown to be inherently causal, internally consistent, and to respect macroscopic conservation laws resulting from gauge symmetries of the Hamiltonian. This comprises the nonequilibrium dynamical mean-field theory but also dynamical-impurity and variational-cluster approximations that are specified by reference systems with a finite number of degrees of freedom. In this way, nonperturbative and consistent approximations can be set up, the numerical evaluation of which is accessible to an exact-diagonalization approach.

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

PubMed Central

Copic, Davor; Park, Sei Jin; Tawfick, Sameh; De Volder, Michael; Hart, A. John

2012-01-01

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3. PMID:22806089

Fabrication, densification, and replica molding of 3D carbon nanotube microstructures.

PubMed

Copic, Davor; Park, Sei Jin; Tawfick, Sameh; De Volder, Michael; Hart, A John

2012-07-02

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques (1, 2), and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization (3).

Phases and Dynamics of Self-Assembled DNA Programmed Nanocubes

NASA Astrophysics Data System (ADS)

Knorowski, Christopher; Travesset, Alex

2013-03-01

Systems of Nanoparticles grafted with complementary DNA strands have been shown to self-assemble into an array of superlattices. In this talk, we extend our previous model, which successfully predicted equilibrium phases and dynamics of assembly for spherical Nanoparticles without fitting parameters, to the case of nanocubes. We show that the phase diagram consists of bcc and sc lattices, depending on DNA length. The bcc lattices are either rotator and orientational glass or cubatic. For temperatures above the DNA melting temperature, the system is equivalent to f-star polymer systems, and consist of bcc, also with rotator, orientational glass or cubatic orientational order as well as sc. We also provide a characterization of the dynamics, including the role of topological defects in crystal nucleation and growth. This work is funded by DOE through the Ames Lab under Contract DE-AC02-07CH11358. Most simulations are performed on the Exalted GPU cluster, which is funded by a grant from Iowa State University and Nvidia Corp.

Modification of polymers by polymeric additives

NASA Astrophysics Data System (ADS)

Nesterov, A. E.; Lebedev, E. V.

1989-08-01

The conditions for the thermodynamic compatibility of polymers and methods for its enhancement are examined. The study of the influence of various factors on the concentration-temperature limits of compatibility, dispersion stabilisation processes, and methods for the improvement of adhesion between phases in mixtures of thermodynamically incompatible polymers is described. Questions concerning the improvement of the physicomechanical characteristics of polymer dispersions are considered. The bibliography includes 200 references.

Self-Healing Nanocomposite Hydrogel with Well-Controlled Dynamic Mechanics

NASA Astrophysics Data System (ADS)

Li, Qiaochu; Mishra, Sumeet; Chen, Pangkuan; Tracy, Joseph; Holten-Andersen, Niels

Network dynamics is a crucial factor that determines the macroscopic self-healing rate and efficiency in polymeric hydrogel materials, yet its controllability is seldom studied in most reported self-healing hydrogel systems. Inspired by mussel's adhesion chemistry, we developed a novel approach to assemble inorganic nanoparticles and catechol-decorated PEG polymer into a hydrogel network. When utilized as reversible polymer-particle crosslinks, catechol-metal coordination bonds yield a unique gel network with dynamic mechanics controlled directly by interfacial crosslink structure. Taking advantage of this structure-property relationship at polymer-particle interfaces, we next designed a hierarchically structured hybrid gel with two distinct relaxation timescales. By tuning the relative contribution of the two hierarchical relaxation modes, we are able to finely control the gel's dynamic mechanical behavior from a viscoelastic fluid to a stiff solid, yet preserving its fast self-healing property without the need for external stimuli.

Phenomenological modelling of self-healing polymers based on integrated healing agents

NASA Astrophysics Data System (ADS)

Mergheim, Julia; Steinmann, Paul

2013-09-01

The present contribution introduces a phenomenological model for self-healing polymers. Self-healing polymers are a promising class of materials which mimic nature by their capability to autonomously heal micro-cracks. This self-healing is accomplished by the integration of microcapsules containing a healing agent and a dispersed catalyst into the matrix material. Propagating microcracks may then break the capsules which releases the healing agent into the microcracks where it polymerizes with the catalyst, closes the crack and 'heals' the material. The present modelling approach treats these processes at the macroscopic scale, the microscopic details of crack propagation and healing are thus described by means of continuous damage and healing variables. The formulation of the healing model accounts for the fact that healing is directly associated with the curing process of healing agent and catalyst. The model is implemented and its capabilities are studied by means of numerical examples.

STANDARD REFERENCE MATERIALS FOR THE POLYMERS INDUSTRY.

PubMed

McDonough, Walter G; Orski, Sara V; Guttman, Charles M; Migler, Kalman D; Beers, Kathryn L

2016-01-01

The National Institute of Standards and Technology (NIST) provides science, industry, and government with a central source of well-characterized materials certified for chemical composition or for some chemical or physical property. These materials are designated Standard Reference Materials ® (SRMs) and are used to calibrate measuring instruments, to evaluate methods and systems, or to produce scientific data that can be referred readily to a common base. In this paper, we discuss the history of polymer based SRMs, their current status, and challenges and opportunities to develop new standards to address industrial measurement challenges.

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush.

PubMed

Lin, Tzu-Pin; Chang, Alice B; Luo, Shao-Xiong; Chen, Hsiang-Yun; Lee, Byeongdu; Grubbs, Robert H

2017-11-28

Grafting density is an important structural parameter that exerts significant influences over the physical properties of architecturally complex polymers. In this report, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization. ω-Norbornenyl poly(d,l-lactide) and polystyrene macromonomers were copolymerized with discrete comonomers in different feed ratios, enabling precise control over both the grafting density and molecular weight. Small-angle X-ray scattering experiments demonstrate that these graft block polymers self-assemble into long-range-ordered lamellar structures. For 17 series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ∼ N bb α ) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, not segregation effects. A model is proposed in which the characteristic ratio (C ∞ ), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ∼ N bb f(z) . The scaling behavior disclosed herein provides valuable insights into conformational changes with grafting density, thus introducing opportunities for block polymer and material design.

Homopolymer self-assembly into stable nanoparticles: concerted action of hydrophobic association and hydrogen bonding in thermoresponsive poly(alkylacrylic acid)s.

PubMed

Sedlák, Marián

2012-03-01

A new approach to polymer self-assembly was presented recently [M. Sedlák, Č. Koňák, J. Dybal, Macromolecules 2009, 2, 7430-7438 and 7439-7446.] (1, 2) where stable polymeric nanoparticles were formed from poly(ethylacrylic acid) homopolymers without any assembly triggering additives, simply by heating polymer solution under conditions of thermosensitivity to certain temperature. In the current Article, we present successful results on poly(propylacrylic acid), which is a more hydrophobic polymer. We also present results on a less hydrophobic polymer from this series, poly(methacrylic acid), from which nanoparticles cannot be formed. Comparison of results on all three polymers gives a solid physicochemical insight and supports the molecular mechanism of the self-assembly previously suggested: The solvent quality gradually worsens upon heating of a thermosensitive polymer solution, and polymer-polymer contacts are preferred over polymer-solvent contacts, which leads to the formation of polymer assemblies. The presence of a significant amount of charge on chains prevents macroscopic phase separation. Upon subsequent cooling to laboratory temperature, the assemblies (nanoparticles) should eventually dissolve; however, this is not the case due to the fact that polymer chains brought to a close proximity at elevated temperatures become hydrogen-bonded. In addition, hydrogen bonds strengthen upon cooling. Mainly carboxylic-carboxylate hydrogen bonds (COOH····COO(-)) are responsible for the irreversibility of the process and the stability of nanoparticles. Conclusions are supported by results from static and dynamic light scattering, FTIR spectroscopy, and cryo-TEM microscopy. Size of nanoparticles can be monitored during the growth and custom-tailored by tuning critical parameters, especially the degree of ionization, temperature, and time of heating. Nanoparticles are stable over long periods of time. They are stable in a broad range of salt concentrations, including physiological conditions, and possess a mild acceptable degree of polydispersity.

A highly stretchable autonomous self-healing elastomer

NASA Astrophysics Data System (ADS)

Li, Cheng-Hui; Wang, Chao; Keplinger, Christoph; Zuo, Jing-Lin; Jin, Lihua; Sun, Yang; Zheng, Peng; Cao, Yi; Lissel, Franziska; Linder, Christian; You, Xiao-Zeng; Bao, Zhenan

2016-06-01

It is a challenge to synthesize materials that possess the properties of biological muscles—strong, elastic and capable of self-healing. Herein we report a network of poly(dimethylsiloxane) polymer chains crosslinked by coordination complexes that combines high stretchability, high dielectric strength, autonomous self-healing and mechanical actuation. The healing process can take place at a temperature as low as -20 °C and is not significantly affected by surface ageing and moisture. The crosslinking complexes used consist of 2,6-pyridinedicarboxamide ligands that coordinate to Fe(III) centres through three different interactions: a strong pyridyl-iron one, and two weaker carboxamido-iron ones through both the nitrogen and oxygen atoms of the carboxamide groups. As a result, the iron-ligand bonds can readily break and re-form while the iron centres still remain attached to the ligands through the stronger interaction with the pyridyl ring, which enables reversible unfolding and refolding of the chains. We hypothesize that this behaviour supports the high stretchability and self-healing capability of the material.

Sequential Self-Folding Structures by 3D Printed Digital Shape Memory Polymers

NASA Astrophysics Data System (ADS)

Mao, Yiqi; Yu, Kai; Isakov, Michael S.; Wu, Jiangtao; Dunn, Martin L.; Jerry Qi, H.

2015-09-01

Folding is ubiquitous in nature with examples ranging from the formation of cellular components to winged insects. It finds technological applications including packaging of solar cells and space structures, deployable biomedical devices, and self-assembling robots and airbags. Here we demonstrate sequential self-folding structures realized by thermal activation of spatially-variable patterns that are 3D printed with digital shape memory polymers, which are digital materials with different shape memory behaviors. The time-dependent behavior of each polymer allows the temporal sequencing of activation when the structure is subjected to a uniform temperature. This is demonstrated via a series of 3D printed structures that respond rapidly to a thermal stimulus, and self-fold to specified shapes in controlled shape changing sequences. Measurements of the spatial and temporal nature of self-folding structures are in good agreement with the companion finite element simulations. A simplified reduced-order model is also developed to rapidly and accurately describe the self-folding physics. An important aspect of self-folding is the management of self-collisions, where different portions of the folding structure contact and then block further folding. A metric is developed to predict collisions and is used together with the reduced-order model to design self-folding structures that lock themselves into stable desired configurations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bleiziffer, Patrick, E-mail: patrick.bleiziffer@fau.de; Krug, Marcel; Görling, Andreas

A self-consistent Kohn-Sham method based on the adiabatic-connection fluctuation-dissipation (ACFD) theorem, employing the frequency-dependent exact exchange kernel f{sub x} is presented. The resulting SC-exact-exchange-only (EXX)-ACFD method leads to even more accurate correlation potentials than those obtained within the direct random phase approximation (dRPA). In contrast to dRPA methods, not only the Coulomb kernel but also the exact exchange kernel f{sub x} is taken into account in the EXX-ACFD correlation which results in a method that, unlike dRPA methods, is free of self-correlations, i.e., a method that treats exactly all one-electron systems, like, e.g., the hydrogen atom. The self-consistent evaluation ofmore » EXX-ACFD total energies improves the accuracy compared to EXX-ACFD total energies evaluated non-self-consistently with EXX or dRPA orbitals and eigenvalues. Reaction energies of a set of small molecules, for which highly accurate experimental reference data are available, are calculated and compared to quantum chemistry methods like Møller-Plesset perturbation theory of second order (MP2) or coupled cluster methods [CCSD, coupled cluster singles, doubles, and perturbative triples (CCSD(T))]. Moreover, we compare our methods to other ACFD variants like dRPA combined with perturbative corrections such as the second order screened exchange corrections or a renormalized singles correction. Similarly, the performance of our EXX-ACFD methods is investigated for the non-covalently bonded dimers of the S22 reference set and for potential energy curves of noble gas, water, and benzene dimers. The computational effort of the SC-EXX-ACFD method exhibits the same scaling of N{sup 5} with respect to the system size N as the non-self-consistent evaluation of only the EXX-ACFD correlation energy; however, the prefactor increases significantly. Reaction energies from the SC-EXX-ACFD method deviate quite little from EXX-ACFD energies obtained non-self-consistently with dRPA orbitals and eigenvalues, and the deviation reduces even further if the Coulomb kernel is scaled by a factor of 0.75 in the dRPA to reduce self-correlations in the dRPA correlation potential. For larger systems, such a non-self-consistent EXX-ACFD method is a competitive alternative to high-level wave-function-based methods, yielding higher accuracy than MP2 and CCSD methods while exhibiting a better scaling of the computational effort than CCSD or CCSD(T) methods. Moreover, EXX-ACFD methods were shown to be applicable in situation characterized by static correlation.« less

Understanding the effect of nanoporosity on optimizing the performance of self-healing materials for anti-corrosion applications

NASA Astrophysics Data System (ADS)

Sellaiyan, S.; Smith, S. V.; Hughes, A. E.; Miller, A.; Jenkins, D. R.; Uedono, A.

2011-01-01

The chromate-based epoxy primer film was prepared on glass and metal surfaces using various graded doctor blades. The quality and consistency of the films was assessed using scanning electron microscopy and the porosity within the film characterized by positron annihilation lifetime spectroscopy. The positron lifetime (τ) distribution for the epoxy polymer matrix was resolved using the CONTIN program. The free volume was found from the ortho-positronium component. The optimum thickness for the films was established for future structure/activity studies.

Communication: Dominance of extreme statistics in a prototype many-body Brownian ratchet.

PubMed

Hohlfeld, Evan; Geissler, Phillip L

2014-10-28

Many forms of cell motility rely on Brownian ratchet mechanisms that involve multiple stochastic processes. We present a computational and theoretical study of the nonequilibrium statistical dynamics of such a many-body ratchet, in the specific form of a growing polymer gel that pushes a diffusing obstacle. We find that oft-neglected correlations among constituent filaments impact steady-state kinetics and significantly deplete the gel's density within molecular distances of its leading edge. These behaviors are captured quantitatively by a self-consistent theory for extreme fluctuations in filaments' spatial distribution.

Conformational Asymmetry and Quasicrystal Approximants in Linear Diblock Copolymers

NASA Astrophysics Data System (ADS)

Schulze, Morgan W.; Lewis, Ronald M.; Lettow, James H.; Hickey, Robert J.; Gillard, Timothy M.; Hillmyer, Marc A.; Bates, Frank S.

2017-05-01

Small angle x-ray scattering experiments on three model low molar mass diblock copolymer systems containing minority polylactide and majority hydrocarbon blocks demonstrate that conformational asymmetry stabilizes the Frank-Kasper σ phase. Differences in block flexibility compete with space filling at constant density inducing the formation of polyhedral shaped particles that assemble into this low symmetry ordered state with local tetrahedral coordination. These results confirm predictions from self-consistent field theory that establish the origins of symmetry breaking in the ordering of block polymer melts subjected to compositional and conformational asymmetry.

Morphological Consequences of Frustration in ABC Triblock Polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radlauer, Madalyn R.; Sinturel, Christophe; Asai, Yusuke

2016-12-19

Three poly(styrene)-block-poly(isoprene)-block-poly(lactide) (PS-b-PI-b-PLA, SIL) triblock terpolymers were synthesized and characterized in the bulk and as thin films. The pronounced incompatibility of the covalently connected PI and PLA led to significant frustration and the tendency to minimize their intermaterial dividing surface area. This resulted in the formation of a core–shell cylinder morphology with exaggerated nonconstant mean curvature from triblock polymers with equal block volume fractions rather than the more typical lamellar morphology. The effect of frustration was magnified in thin films by both confinement and interfacial interactions such that the PI domains became discontinuous. Self-consistent field theory (SCFT) calculations emphasize thatmore » the marked difference in the PS/PI and PI/PLA interaction parameters promotes the formation of nonlamellar morphologies. However, SCFT predicts that lamellar morphology is more stable than the observed cylindrical morphology, demonstrating a limitation that arises from the underlying assumptions.« less

Micelle Morphology and Mechanical Response of Triblock Gels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seitz, Michelle E.; Burghardt, Wesley R.; Shull, Kenneth R.

2010-01-12

The effect of polymer concentration on mechanical response and micelle morphology of ABA and AB copolymers in B-selective solvents has been systematically studied. Micelle morphology was determined using a combination of small-angle X-ray scattering, shear, and birefringence while mechanical response at low and high strains was determined using indentation techniques. Self-consistent field theory calculations were used to determine micelle volume fraction profiles and to construct an equilibrium phase map. The transition from spherical to cylindrical micelles increases the triblock gel modulus and energy dissipation. Combining knowledge of gel relaxation time, which determines the rate at which the gel can equilibratemore » its micelle structure, with the equilibrium phase map allows estimation of the experimental temperatures and time scales over which kinetic trapping will arrest micelle structure evolution. Kinetic trapping enables cylindrical morphologies to be obtained at significantly lower polymer fractions than is possible in equilibrated systems.« less

Thin film surface treatments for lowering dust adhesion on Mars Rover calibration targets

NASA Astrophysics Data System (ADS)

Sabri, F.; Werhner, T.; Hoskins, J.; Schuerger, A. C.; Hobbs, A. M.; Barreto, J. A.; Britt, D.; Duran, R. A.

The current generation of calibration targets on Mars Rover serve as a color and radiometric reference for the panoramic camera. They consist of a transparent silicon-based polymer tinted with either color or grey-scale pigments and cast with a microscopically rough Lambertian surface for a diffuse reflectance pattern. This material has successfully withstood the harsh conditions existent on Mars. However, the inherent roughness of the Lambertian surface (relative to the particle size of the Martian airborne dust) and the tackiness of the polymer in the calibration targets has led to a serious dust accumulation problem. In this work, non-invasive thin film technology was successfully implemented in the design of future generation calibration targets leading to significant reduction of dust adhesion and capture. The new design consists of a μm-thick interfacial layer capped with a nm-thick optically transparent layer of pure metal. The combination of these two additional layers is effective in burying the relatively rough Lambertian surface while maintaining diffuse properties of the samples which is central to the correct operation as calibration targets. A set of these targets are scheduled for flight on the Mars Phoenix mission.

Smart Materials for Advanced Applications: Self-Decontaminating Polymers, Photofunctional Composites, and Electroconductive Fibers

NASA Astrophysics Data System (ADS)

Little, Brian Kevin

2011-12-01

Materials capable of providing multifunctional properties controllable by some external stimulus (pH, light, temperature, etc) are highly desirable and obtainable given recent advancements in material science. Development of these so called "Smart" materials spanned across many disciplines of science with applications in industrial areas such as medical, military, security, and environmental. Furthermore, next-generation materials require the ability to not only sense/respond to changes in their external/internal environment, but process information in regards to these changes and adapt accordingly in a dynamic fashion, autonomously, so called "Intelligent" materials. Findings reported in this manuscript detail the synthesis, characterization, and application of smart materials in the following three areas: (1) self-cleaning polymers (2) photoresponsive composites and (3) electroconductive fibers. Self-Cleaning Polymers: Self-decontaminating polymers are unique materials capable of degrading toxic organic chemicals (TOCs). Barriers composed of or coated with our photochemical reactive polymer matrix could be applied to multiple surfaces for defense against TOCs; for example, military garments for protection against chemical warfare agents. This study investigates conditions necessary for formation of peroxides via O2 reduction induced by long-lived, strongly reducing benzophenyl ketyl (BPK) polymer radicals. Photolysis of aqueous solutions composed of sulphonated poly(ether etherketone), SPEEK, and poly(vinyl alcohol), PVA lead to the formation of the BPK radicals. Experiments investigate the formation and decomposition of peroxides in aqueous solutions of SPEEK/PVA under photolysis. Photofunctional Composites: Photoresponsive nanoporous (PN) films and powders were studied and evaluated as possible additives to sensitize the initiation of CH3NO2 via a mechanism involving coalescence of reaction sites. Such materials consist of a 3-D mesoporous silica framework possessing open interconnected pores. Attached to the pore walls are azobenzene ligands that undergo trans to cis isomerization upon exposure to 350--360 nm photons; the reverse reaction occurs with heat or under illumination with lambda > 420 nm. PN films were studied to ascertain the mass transport properties for the filling/releasing of CH 3NO2 from within the pores of the films in the absence/presence of UV-Vis light. PN powders were evaluated for pore morphology, ligand mobility, and particle size and shape in order to determine their ability to be utilized as an effective sensitizing agent. Electroconductive Fibers: This study investigates electroless and electrochemical techniques for purposes of producing highly conductive metal coatings on the surface of high strength fibers. Metallized fibers were envisioned to be utilized as high strength low weight tethers for space applications. Findings suggest that these materials could be valuable as components within "Intelligent" textiles, but, at present, not suitable for conditions witnessed in space (high energy UV irradiation, Atomic Oxygen, etc). Kevlar fibers were coated utilizing an electroless and then electrochemical deposition processes. Metallized fibers were evaluated for their resistivity, power output, tensile strength, uniform coverage, and mass gain. Presented in this section are the results of such measurements.

Self-interacting polymer chains terminally anchored to adsorbing surfaces of three-dimensional fractal lattices

NASA Astrophysics Data System (ADS)

Živić, I.; Elezović-Hadžić, S.; Milošević, S.

2018-01-01

We have studied the adsorption problem of self-attracting linear polymers, modeled by self-avoiding walks (SAWs), situated on three-dimensional fractal structures, exemplified by 3d Sierpinski gasket (SG) family of fractals as containers of a poor solvent. Members of SG family are enumerated by an integer b (b ≥ 2), and it is assumed that one side of each SG fractal is an impenetrable adsorbing surface. We calculate the critical exponents γ1 ,γ11, and γs, which are related to the numbers of all possible SAWs with one, both, and no ends anchored to the adsorbing boundary, respectively. By applying the exact renormalization group (RG) method (for the first three members of the SG fractal family, b = 2 , 3, and 4), we have obtained specific values of these exponents, for θ-chain and globular polymer phase. We discuss their mutual relations and relations with corresponding values pertinent to extended polymer chain phase.

Formulation and in-vitro evaluation of directly compressed controlled release matrices of Losartan Potassium using Ethocel Grade 100 as rate retarding agent.

PubMed

Khan, Kamran Ahmad; Khan, Gul Majid; Zeeshan Danish, Muhammad; Akhlaq; Khan, Haroon; Rehman, Fazal; Mehsud, Saifullah

2015-12-30

Current study was aimed to develop 200mg controlled release matrix tablets of Losartan Potassium using Ethocel 100 Premium and Ethocel 100 FP Premium as rate controlling polymer. In-vitro studies were performed according to USP Method-I in phosphate buffer (PH 6.8) using pharma test dissolution apparatus. The temperature of the dissolution medium was kept constant at 37±0.5°C at 100rpm. Flow properties, physical quality control tests, effect of polymer size and drug-to-polymers ratios were studied using different kinetics models such as 1st-order, zero-order, Hixon Crowell model, Highuchi model and Power law. Difference factor f1 and similarity factor f2 were applied for dissolution profiles against Cardaktin® tablets used as a reference formulation. The matrices with polymer ethocel 100 FP Premiums have prolonged the drug release rate as compared to polymer ethocel 100 Premiums. The n values matrices with polymer ethocel grade 100 ranged from 0.603 to 0.857 indicating that the drug release occurred by anomalous non fickian diffusion kinetics while then value of reference Cardaktin® tablet was measured as 0.125 indicating that these tablets do not follow power law. The dissolution profiles of test formulations were different than that of reference Cardaktin®. This suggests the polymer Ethocel grade 100 can be proficiently incorporated in fabrication and development of once a day controlled release matrix tablets. Copyright © 2015. Published by Elsevier B.V.

Molecular Strategies for Morphology Control in Semiconducting Polymers for Optoelectronics.

PubMed

Rahmanudin, Aiman; Sivula, Kevin

2017-06-28

Solution-processable semiconducting polymers have been explored over the last decades for their potential applications in inexpensively fabricated transistors, diodes and photovoltaic cells. However, a remaining challenge in the field is to control the solid-state self-assembly of polymer chains in thin films devices, as the aspects of (semi)crystallinity, grain boundaries, and chain entanglement can drastically affect intra-and inter-molecular charge transport/transfer and thus device performance. In this short review we examine how the aspects of molecular weight and chain rigidity affect solid-state self-assembly and highlight molecular engineering strategies to tune thin film morphology. Side chain engineering, flexibly linking conjugation segments, and block co-polymer strategies are specifically discussed with respect to their effect on field effect charge carrier mobility in transistors and power conversion efficiency in solar cells. Example systems are taken from recent literature including work from our laboratories to illustrate the potential of molecular engineering semiconducting polymers.

Bioinspired synthesis and self-assembly of hybrid organic–inorganic nanomaterials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Honghu

Nature is replete with complex organic–inorganic hierarchical materials of diverse yet specific functions. These materials are intricately designed under physiological conditions through biomineralization and biological self-assembly processes. Tremendous efforts have been devoted to investigating mechanisms of such biomineralization and biological self-assembly processes as well as gaining inspiration to develop biomimetic methods for synthesis and self-assembly of functional nanomaterials. In this work, we focus on the bioinspired synthesis and self-assembly of functional inorganic nanomaterials templated by specialized macromolecules including proteins, DNA and polymers. The in vitro biomineralization process of the magnetite biomineralizing protein Mms6 has been investigated using small-angle X-ray scattering.more » Templated by Mms6, complex magnetic nanomaterials can be synthesized on surfaces and in the bulk. DNA and synthetic polymers have been exploited to construct macroscopic two- and three-dimensional (2D and 3D) superlattices of gold nanocrystals. Employing X-ray scattering and spectroscopy techniques, the self-assembled structures and the self-assembly mechanisms have been studied, and theoretical models have been developed. Our results show that specialized macromolecules including proteins, DNA and polymers act as effective templates for synthesis and self-assembly of nanomaterials. These bottom-up approaches provide promising routes to fabricate hybrid organic–inorganic nanomaterials with rationally designed hierarchical structures, targeting specific functions.« less

Electron propagator calculations on the ionization energies of CrH -, MnH - and FeH -

NASA Astrophysics Data System (ADS)

Lin, Jyh-Shing; Ortiz, J. V.

1990-08-01

Electron propagator calculations with unrestricted Hartree-Fock reference states yield the ionization energies of the title anions. Spin contamination in the anionic reference state is small, enabling the use of second-and third-order self-energies in the Dyson equation. Feynman-Dyson amplitudes for these ionizations are essentially identical to canonical spin-orbitals. For most of the final states, these consist of an antibonding combination of an sp metal hybrid, polarized away from the hydrogen, and hydroegen s functions. In one case, the Feynman-Dyson amplitude consists of nonbonding d functions. Calculated ionization energies are within 0.5 eV of experiment.

Creating "hotels" for cells by electrospinning honeycomb-like polymeric structures.

PubMed

Liang, T; Mahalingam, S; Edirisinghe, M

2013-10-01

It is well established that three-dimensional honeycomb-like nanofibrous structures enhance cell activity. In this work, we report that electrospun polymer nanofibres self-assemble into three-dimensional honeycomb-like structures. The underlying mechanism is studied by varying the polymer solution concentration, collecting substrates and working distance. The polymer solution concentration has a significant effect on the size of the electrospun nanofibres. The collection substrate and working distance affect the electric field strength, the evaporation of solvent and the discharging of nanofibres and consequently these two had a significant influence on the self-assembly of nanofibres. © 2013.

Nanopatterns by phase separation of patterned mixed polymer monolayers

DOEpatents

Huber, Dale L; Frischknecht, Amalie

2014-02-18

Micron-size and sub-micron-size patterns on a substrate can direct the self-assembly of surface-bonded mixed polymer brushes to create nanoscale patterns in the phase-separated mixed polymer brush. The larger scale features, or patterns, can be defined by a variety of lithographic techniques, as well as other physical and chemical processes including but not limited to etching, grinding, and polishing. The polymer brushes preferably comprise vinyl polymers, such as polystyrene and poly(methyl methacrylate).

Thermoresponsive AuNPs Stabilized by Pillararene-Containing Polymers.

PubMed

Liao, Xiaojuan; Guo, Lei; Chang, Junxia; Liu, Sha; Xie, Meiran; Chen, Guosong

2015-08-01

Pillararene-containing thermoresponsive polymers are synthesized via reversible addition-fragmentation chain transfer polymerization using pillararene derivatives as the effective chain transfer agents for the first time. These polymers can self-assemble into micelles and form vesicles after guest molecules are added. Furthermore, such functional polymers can be further applied to prepare hybrid gold nanoparticles, which integrate the thermoresponsivity of polymers and molecular recognition of pillararenes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Differentially photo-crosslinked polymers enable self-assembling microfluidics

PubMed Central

Jamal, Mustapha; Zarafshar, Aasiyeh M.; Gracias, David H.

2012-01-01

An important feature of naturally self-assembled systems such as leaves and tissues is that they are curved and have embedded fluidic channels that enable the transport of nutrients to, or removal of waste from, specific three-dimensional (3D) regions. Here, we report the self-assembly of photopatterned polymers, and consequently microfluidic devices, into curved geometries. We discovered that differentially photo-crosslinked SU-8 films spontaneously and reversibly curved upon film de-solvation and re-solvation. Photolithographic patterning of the SU-8 films enabled the self-assembly of cylinders, cubes, and bidirectionally folded sheets. We integrated polydimethylsiloxane (PDMS) microfluidic channels with these SU-8 films to self-assemble curved microfluidic networks. PMID:22068594

Development of polymer-biomolecule core-shell particles for biomedical applications

NASA Astrophysics Data System (ADS)

Suthiwangcharoen, Nisaraporn

Developing efficient strategies to introduce biomolecules around polymeric nanoparticles (NPs) is critical for targeted delivery of therapeutic or diagnostic agents. Although polymeric NPs have been well established, problems such as toxicity, stability, and immunoresistance remain potential concerns. The first part of this dissertation focuses on the development of nanosized targeted drug delivery vehicle in cancer chemotherapy. The vehicle was created by the self-assembly of folate-grafted filamentous bacteriophage M13 with poly(caprolactone- b-2-vinylpyridine) while doxorubicin, the antitumor drugs, was successfully loaded in the interior of the vehicles. These particles offer unique properties of being able to selectively target tumor cells while appearing to be safe and non-toxic to normal cells. Although they have shown great prospects in many biomedical applications, less is known about the interactions between biomolecules and polymers. The next part of the dissertation focuses on the self-assembly of proteins and polymers to create polymer-protein core-shell nanoparticles (PPCS-NPs). Several proteins with different isoelectric points and molecular weights were employed to demonstrate a versatility of our assembly method while a series of esterified derivatives of poly(2-hydroxyethyl methacrylate) (pHEMA) were synthesized to evaluate the interaction between proteins and polymers. Our data indicated that the polymers containing pyridine residues can successfully assemble with proteins, and the mechanism is mainly governed by hydrogen bonding and the hydrophobic/hydrophilic interactions. This in turn helps retaining proteins' folding conformation and functionality, which are also demonstrated in the in vitro/in vivo cellular uptake of the PPCS-NPs in endothelial cells. The last part of the dissertation focuses on the self-assembly of the bienzyme-polymer NPs. Glucose oxidase (GOX) together with horseradish peroxidase (HRP) were employed to construct bienzyme-NPs. GOX was initially used as a model enzyme to assemble with pyridine-modified pHEMA, and its enzymatic activity was shown to increase after self-assembly. When both GOX and HRP were assembled with the polymers, the activity was shown to be even greater than that of the single enzyme-polymer NPs or a free enzyme. The results indicated that NPs enhance enzymatic activity, likely due to an increase in enzyme localization, and the assembly between GOX and polymers might prevent conformational transitions of these enzymes.

Biodegradability and biodegradation rate of poly(caprolactone)-starch blend and poly(butylene succinate) biodegradable polymer under aerobic and anaerobic environment.

PubMed

Cho, H S; Moon, H S; Kim, M; Nam, K; Kim, J Y

2011-03-01

The biodegradability and the biodegradation rate of two kinds biodegradable polymers; poly(caprolactone) (PCL)-starch blend and poly(butylene succinate) (PBS), were investigated under both aerobic and anaerobic conditions. PCL-starch blend was easily degraded, with 88% biodegradability in 44 days under aerobic conditions, and showed a biodegradation rate of 0.07 day(-1), whereas the biodegradability of PBS was only 31% in 80 days under the same conditions, with a biodegradation rate of 0.01 day(-1). Anaerobic bacteria degraded well PCL-starch blend (i.e., 83% biodegradability for 139 days); however, its biodegradation rate was relatively slow (6.1 mL CH(4)/g-VS day) compared to that of cellulose (13.5 mL CH(4)/g-VS day), which was used as a reference material. The PBS was barely degraded under anaerobic conditions, with only 2% biodegradability in 100 days. These results were consistent with the visual changes and FE-SEM images of the two biodegradable polymers after the landfill burial test, showing that only PCL-starch blend had various sized pinholes on the surface due to attack by microorganisms. This result may be use in deciding suitable final disposal approaches of different types of biodegradable polymers in the future. Copyright © 2010 Elsevier Ltd. All rights reserved.

Recent progress in the synthesis of poly(organo)phosphazenes and their applications in tissue engineering and drug delivery

NASA Astrophysics Data System (ADS)

Khan, R. U.; Wang, L.; Yu, H.; Zain-ul-Abdin; Akram, M.; Wu, J.; Haroon, M.; Ullah, R. S.; Deng, Zh; Xia, X.

2018-02-01

It is a highly desirable goal of researchers to develop effective biomaterials with minimum recovery time and affordable treatment expense for tissue engineering and drug delivery. In this scenario, numerous synthetic and natural polymers have been used. Among those synthetic polymers, polyorganophosphazenes (POPs) have got much attention as highly promising candidates for applications in tissue engineering and drug delivery. Polyorganophosphazenes are hybrid polymers containing inorganic backbone consisting of alternating nitrogen and phosphorus atoms with two organic side groups. POPs possess a wide range of unique properties, i.e., synthetic flexibility, biocompatibility, osteocompatibility, osteoinductivity, sustainability and degradability into harmless end products with predictable degradation rate and adjustable mechanical strength. Moreover, their tunable hydrophilic/hydrophobic and stimuli responsive properties add extra points to their use in biomedical applications. In addition, their various polymeric forms, i.e., microspheres, nano/microfibres, micelles, membranes, polymersomes, hydrogels and nano-conjugate linear polymers provide different carriers to efficiently deliver various hydrophilic/hydrophobic therapeutic agents both in vitro and in vivo. This review focuses on the most recent progress that has been made in the synthesis and applications of POPs in tissue engineering and their different polymeric forms used for drug delivery. Moreover, we have also summarized the effect of different side groups on the overall efficiency of POPs. The bibliography includes 239 references.

Nanoconfinement: an effective way to enhance PVDF piezoelectric properties.

PubMed

Cauda, Valentina; Stassi, Stefano; Bejtka, Katarzyna; Canavese, Giancarlo

2013-07-10

The dimensional confinement and oriented crystallization are both key factors in determining the piezoelectric properties of a polymeric nanostructured material. Here we prepare arrays of one-dimensional polymeric nanowires showing piezoelectric features by template-wetting two distinct polymers into anodic porous alumina (APA) membranes. In particular, poly(vinylidene fluoride), PVDF, and its copolymer poly(vinylidene fluoride-trifluoroethylene), PVTF, are obtained in commercially available APA, showing a final diameter of about 200 nm and several micrometers in length, reflecting the templating matrix features. We show that the crystallization of both polymers into a ferroelectric phase is directed by the nanotemplate confinement. Interestingly, the PVDF nanowires mainly crystallize into the β-phase in the nanoporous matrix, whereas the reference thin film of PVDF crystallizes in the α nonpolar phase. In the case of the PVTF nanowires, needle-like crystals oriented perpendicularly to the APA channel walls are observed, giving insight on the molecular orientation of the polymer within the nanowire structure. A remarkable piezoelectric behavior of both 1-D polymeric nanowires is observed, upon recording ferroelectric polarization, hysteresis, and displacement loops. In particular, an outstanding piezoelectric effect is observed for the PVDF nanowires with respect to the polymeric thin film, considering that no poling was carried out. Current versus voltage (I-V) characteristics showed a consistent switching behavior of the ferroelectric polar domains, thus revealing the importance of the confined and oriented crystallization of the polymer in monodimensional nanoarchitectures.

21 CFR 177.1560 - Polyarylsulfone resins.

Code of Federal Regulations, 2012 CFR

2012-04-01

... polymer units. The copolymers have a minimum reduced viscosity of 0.40 deciliter per gram in 1-methyl-2... Solution Viscosity of Polymers,” which is incorporated by reference. Copies may be obtained from the...

21 CFR 177.1560 - Polyarylsulfone resins.

Code of Federal Regulations, 2013 CFR

2013-04-01

... polymer units. The copolymers have a minimum reduced viscosity of 0.40 deciliter per gram in 1-methyl-2... Solution Viscosity of Polymers,” which is incorporated by reference. Copies may be obtained from the...

21 CFR 177.1560 - Polyarylsulfone resins.

Code of Federal Regulations, 2011 CFR

2011-04-01

... polymer units. The copolymers have a minimum reduced viscosity of 0.40 deciliter per gram in 1-methyl-2... Solution Viscosity of Polymers,” which is incorporated by reference. Copies may be obtained from the...

21 CFR 177.1560 - Polyarylsulfone resins.

Code of Federal Regulations, 2010 CFR

2010-04-01

... polymer units. The copolymers have a minimum reduced viscosity of 0.40 deciliter per gram in 1-methyl-2... Solution Viscosity of Polymers,” which is incorporated by reference. Copies may be obtained from the...

Fluorinated monomers useful for preparing fluorinated polyquinoline polymers

NASA Technical Reports Server (NTRS)

Hendricks, Neil H. (Inventor)

1994-01-01

A new class of polymers is provided, as well as the monomers used for their preparation. The polymers provided in accordance with practice of the present invention include repeating units comprising one or more quinoline groups, wherein at least a portion of the repeating units includes a hexafluoroisopropylidene (6F) group or a 1-aryl-2,2,2-trifluoroethylidene (3F) group, or both. The hexafluoroisopropylidene group is referred to herein as a 6F group and has the following structure: ##STR1## The 6F group includes a tetravalent carbon atom bound to two trifluoromethyl moieties, with its other two bonds forming linkages in the polymer chain. The 1-aryl-2,2,2-trifluoroethylidene group is referred to herein as a 3F group and has the following structure: ##STR2## wherein Ar' is an aryl group.

Autonomously Propelled Motors for Value-Added Product Synthesis and Purification.

PubMed

Srivastava, Sarvesh K; Schmidt, Oliver G

2016-06-27

A proof-of-concept design for autonomous, self-propelling motors towards value-added product synthesis and separation is presented. The hybrid motor design consists of two distinct functional blocks. The first, a sodium borohydride (NaBH4 ) granule, serves both as a reaction prerequisite for the reduction of vanillin and also as a localized solid-state fuel in the reaction mixture. The second capping functional block consisting of a graphene-polymer composite serves as a hydrophobic matrix to attract the reaction product vanillyl alcohol (VA), resulting in facile separation of this edible value-added product. These autonomously propelled motors were fabricated at a length scale down to 400 μm, and once introduced in the reaction environment showed rapid bubble-propulsion followed by high-purity separation of the reaction product (VA) by the virtue of the graphene-polymer cap acting as a mesoporous sponge. The concept has excellent potential towards the synthesis/isolation of industrially important compounds, affinity-based product separation, pollutant remediation (such as heavy metal chelation/adsorption), as well as localized fuel-gradients as an alternative to external fuel dependency. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Benchmarking the Bethe–Salpeter Formalism on a Standard Organic Molecular Set

PubMed Central

2015-01-01

We perform benchmark calculations of the Bethe–Salpeter vertical excitation energies for the set of 28 molecules constituting the well-known Thiel’s set, complemented by a series of small molecules representative of the dye chemistry field. We show that Bethe–Salpeter calculations based on a molecular orbital energy spectrum obtained with non-self-consistent G0W0 calculations starting from semilocal DFT functionals dramatically underestimate the transition energies. Starting from the popular PBE0 hybrid functional significantly improves the results even though this leads to an average −0.59 eV redshift compared to reference calculations for Thiel’s set. It is shown, however, that a simple self-consistent scheme at the GW level, with an update of the quasiparticle energies, not only leads to a much better agreement with reference values, but also significantly reduces the impact of the starting DFT functional. On average, the Bethe–Salpeter scheme based on self-consistent GW calculations comes close to the best time-dependent DFT calculations with the PBE0 functional with a 0.98 correlation coefficient and a 0.18 (0.25) eV mean absolute deviation compared to TD-PBE0 (theoretical best estimates) with a tendency to be red-shifted. We also observe that TD-DFT and the standard adiabatic Bethe–Salpeter implementation may differ significantly for states implying a large multiple excitation character. PMID:26207104

Self-oscillating AB diblock copolymer developed by post modification strategy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ueki, Takeshi, E-mail: ueki@cross.t.u-tokyo.ac.jp, E-mail: ryo@cross.t.u-tokyo.ac.jp; Onoda, Michika; Tamate, Ryota

We prepared AB diblock copolymer composed of hydrophilic poly(ethylene oxide) segment and self-oscillating polymer segment. In the latter segment, ruthenium tris(2,2′-bipyridine) (Ru(bpy){sub 3}), a catalyst of the Belousov-Zhabotinsky reaction, is introduced into the polymer architecture based on N-isopropylacrylamide (NIPAAm). The Ru(bpy){sub 3} was introduced into the polymer segment by two methods; (i) direct random copolymerization (DP) of NIPAAm and Ru(bpy){sub 3} vinyl monomer and (ii) post modification (PM) of Ru(bpy){sub 3} with random copolymer of NIPAAm and N-3-aminopropylmethacrylamide. For both the diblock copolymers, a bistable temperature region (the temperature range; ΔT{sub m}), where the block copolymer self-assembles into micelle atmore » reduced Ru(bpy){sub 3}{sup 2+} state whereas it breaks-up into individual polymer chain at oxidized Ru(bpy){sub 3}{sup 3+} state, monotonically extends as the composition of the Ru(bpy){sub 3} increases. The ΔT{sub m} of the block copolymer prepared by PM is larger than that by DP. The difference in ΔT{sub m} is rationalized from the statistical analysis of the arrangement of the Ru(bpy){sub 3} moiety along the self-oscillating segments. By using the PM method, the well-defined AB diblock copolymer having ΔT{sub m} (ca. 25 °C) large enough to cause stable self-oscillation can be prepared. The periodic structural transition of the diblock copolymer in a dilute solution ([Polymer] = 0.1 wt. %) is closely investigated in terms of the time-resolved dynamic light scattering technique at constant temperature in the bistable region. A macroscopic viscosity oscillation of a concentrated polymer solution (15 wt. %) coupled with the periodic microphase separation is also demonstrated.« less

Functional nanocomposites prepared by self-assembly and polymerization of diacetylene surfactants and silicic acid

NASA Technical Reports Server (NTRS)

Yang, Yi; Lu, Yunfeng; Lu, Mengcheng; Huang, Jinman; Haddad, Raid; Xomeritakis, George; Liu, Nanguo; Malanoski, Anthony P.; Sturmayr, Dietmar; Fan, Hongyou;

Polymer brush coatings for DNA: fundamental polymer physics and nanofabrication applications

NASA Astrophysics Data System (ADS)

de Vries, Renko

Recombinant DNA technology allows for the production of precisely defined self-assembling protein-based polymers. So far, the major applications for such protein-based polymers have been self-assembling hydrogels and micellar structures with biomedical application. Inspired by minimal models for the self-ssembly of rod-shaped viruses such as the tobacco mosaic virus, I have developed protein-polymers that co-assemble with DNA into rod-shaped virus-like particles, and protein-polymers that provide brush coatings around single DNA molecules. In this presentation I will focus on the latter, showing that on the one hand brush coated DNA is a rich model system for exploring the physics of bottle-brush polymers, while on the other hand brush coatings of DNA can also play an important practical role in nanofabrication. A key problem in the physics of bottle-brush polymers that I will address is the scale-dependence of bottle-brush elasticity. For long-wavelength thermal deformations probed by AFM imaging I will demonstrate that there is significant stiffening due to the brush coating, while for short wavelength thermal deformations probed by force spectroscopy, we find that stiffening due to the brush coating disappears completely. DNA brush coatings can also play an important practical role in nanofabrication by acting as a compatibilizer between chemically different building blocks. I will explore the example of DNA origami in combination with gold nanoparticles: while Mg2+ ions and high concentrations of monovalent salts are crucial for the stability of DNA origami, such solution conditions are typically incompatible with the colloidal stability of gold nanoparticles.I will show how DNA brush coatings can dramatically enhance the yield of formation of isolated DNA-gold nanoparticle composite nanostructures.

Self-doped microphase separated block copolymer electrolyte

DOEpatents

Mayes, Anne M.; Sadoway, Donald R.; Banerjee, Pallab; Soo, Philip; Huang, Biying

2002-01-01

A polymer electrolyte includes a self-doped microphase separated block copolymer including at least one ionically conductive block and at least one second block that is immiscible in the ionically conductive block, an anion immobilized on the polymer electrolyte and a cationic species. The ionically conductive block provides a continuous ionically conductive pathway through the electrolyte. The electrolyte may be used as an electrolyte in an electrochemical cell.

Microscopic theory for dynamics in entangled polymer nanocomposites

NASA Astrophysics Data System (ADS)

Yamamoto, Umi

New microscopic theories for describing dynamics in polymer nanocomposites are developed and applied. The problem is addressed from two distinct perspectives and using two different theoretical approaches. The first half of this dissertation studies the long-time and intermediate-time dynamics of nanoparticles in entangled and unentangled polymer melts for dilute particle concentrations. Using a combination of mode-coupling, Brownian motion, and polymer physics ideas, the nanoparticle long-time diffusion coefficients is formulated in terms of multiple length-scales, packing microstructures, and spatially-resolved polymer density fluctuation dynamics. The key motional mechanism is described via the parallel relaxation of the force exerted on the particle controlled by collective polymer constraint-release and the particle self-motion. A sharp but smooth crossover from the hydrodynamic to the non-hydrodynamic regime is predicted based on the Stokes-Einstein violation ratio as a function of all the system variables. Quantitative predictions are made for the recovery of the Stokes-Einstein law, and the diffusivity in the crossover regime agrees surprisingly well with large-scale molecular dynamics simulations for all particle sizes and chain lengths studied. The approach is also extended to address intermediate-time anomalous transport of a single nanoparticle and two-particle relative diffusion. The second half of this dissertation focuses on developing a novel dynamical theory for a liquid of infinitely-thin rods in the presence of hard spherical obstacles, aiming at a technical and conceptual extension of the existing paradigm for entangled polymer dynamics. As a fundamental theoretical development, the two-component generalization of a first-principles dynamic meanfield approach is presented. The theory enforces inter-needle topological uncrossability and needlesphere impenetrability in a unified manner, leading to a generalized theory of entanglements that includes the sphere excluded volume effect. Coupled self-consistent equations for the generalized diffusion tensors are constructed, and the expressions for the transverse localization lengths and the long-time diffusion coefficients are derived. In the static sphere limit, we find the effective tube diameter is generally reduced as a function of a single confinement parameter that quantifies the number of particles penetrating into the pure-polymer tube. A preliminary extension to treat flexible chain melts has also been achieved, and shown to agree reasonably well with simulations. The anisotropic needle diffusion constants are rich functions of the length-scale ratios, needle concentration and particle volume fraction. We show that the steric blocking of the longitudinal motion causes a literal and simultaneous localization of the two diffusion channels, and entangled needles can diffuse via a modified reptation dynamics over a window of polymer concentration but the compression of the tube and the blocking of the reptation motion must be accounted for. Generalization to treat mobile spheres is also possible and fully formulated.

Shrink-induced graphene sensor for alpha-fetoprotein detection with low-cost self-assembly and label-free assay

NASA Astrophysics Data System (ADS)

Sando, Shota; Zhang, Bo; Cui, Tianhong

2017-12-01

Combination of shrink induced nano-composites technique and layer-by-layer (LbL) self-assembled graphene challenges controlling surface morphology. Adjusting shrink temperature achieves tunability on graphene surface morphology on shape memory polymers, and it promises to be an alternative in fields of high-surface-area conductors and molecular detection. In this study, self-assembled graphene on a shrink polymer substrate exhibits nanowrinkles after heating. Induced nanowrinkles on graphene with different shrink temperature shows distinct surface roughness and wettability. As a result, it becomes more hydrophilic with higher shrink temperatures. The tunable wettability promises to be utilized in, for example, microfluidic devices. The graphene on shrink polymer also exhibits capability of being used in sensing applications for pH and alpha-fetoprotein (AFP) detection with advantages of label free and low cost, due to self-assembly technique, easy functionalization, and antigen-antibody reaction on graphene surface. The detection limit of AFP detection is down to 1 pg/mL, and therefore the sensor also has a significant potential for biosensing as it relies on low-cost self-assembly and label-free assay.

Ratiometric fluorescence detection of superoxide anion based on AuNPs-BSA@Tb/GMP nanoscale coordination polymers.

PubMed

Liu, Nan; Hao, Juan; Cai, Keying; Zeng, Mulan; Huang, Zhenzhong; Chen, Lili; Peng, Bingxian; Li, Ping; Wang, Li; Song, Yonghai

2018-02-01

A novel ratiometric fluorescence nanosensor for superoxide anion (O 2 •- ) detection was designed with gold nanoparticles-bovine serum albumin (AuNPs-BSA)@terbium/guanosine monophosphate disodium (Tb/GMP) nanoscale coordination polymers (NCPs) (AuNPs-BSA@Tb/GMP NCPs). The abundant hydroxyl and amino groups of AuNPs-BSA acted as binding points for the self-assembly of Tb 3+ and GMP to form core-shell AuNPs-BSA@Tb/GMP NCP nanosensors. The obtained probe exhibited the characteristic fluorescence emission of both AuNPs-BSA and Tb/GMP NCPs. The AuNPs-BSA not only acted as a template to accelerate the growth of Tb/GMP NCPs, but also could be used as the reference fluorescence for the detection of O 2 •- . The resulting AuNPs-BSA@Tb/GMP NCP ratiometric fluorescence nanosensor for the detection of O 2 •- demonstrated high sensitivity and selectivity with a wide linear response range (14 nM-10 μM) and a low detection limit (4.7 nM). Copyright © 2017 John Wiley & Sons, Ltd.

Age differences in self-referencing: Evidence for common and distinct encoding strategies.

PubMed

Gutchess, Angela H; Sokal, Rebecca; Coleman, Jennifer A; Gotthilf, Gina; Grewal, Lauren; Rosa, Nicole

2015-07-01

Although engagement of medial prefrontal cortex (MPFC) underlies self-referencing of information for younger and older adults, the region has not consistently been implicated across age groups for the encoding of self-referenced information. We sought to determine whether making judgments about others as well as the self influenced findings in the previous study. During an fMRI session, younger and older adults encoded adjectives using only a self-reference task. For items later remembered compared to those later forgotten, both age groups robustly recruited medial prefrontal cortex, indicating common neural regions support encoding across younger and older adults when participants make only self-reference judgments. Focal age differences emerged in regions related to emotional processing and cognitive control, though these differences are more limited than in tasks in which judgments also are made about others. We conclude that making judgments about another person differently affects the ways that younger and older adults make judgments about the self, with results of a follow-up behavioral study supporting this interpretation. This article is part of a Special Issue entitled Memory and Aging. Copyright © 2014 Elsevier B.V. All rights reserved.

Cicada-Wing-Inspired Self-Cleaning Antireflection Coatings on Polymer Substrates.

PubMed

Chen, Ying-Chu; Huang, Zhe-Sheng; Yang, Hongta

2015-11-18

The cicada has transparent wings with remarkable self-cleaning properties and high transmittance over the whole visible spectral range, which is derived from periodic conical structures covering the wing surface. Here we report a scalable self-assembly technique for fabricating multifunctional optical coatings that mimic cicada-wing structures. Spin-coated two-dimensional non-close-packed colloidal crystals are utilized as etching masks to pattern subwavelength-structured cone arrays directly on polymer substrates. The resulting gratings exhibit broadband antireflection performance and superhydrophobic properties after surface modification. The dependence of the cone shape and size on the antireflective and self-cleaning properties has also been investigated in this study.

Molecular dynamics simulation studies of tailored nanostructured polymers

NASA Astrophysics Data System (ADS)

Liu, Lixin

With recent advancements in the synthesis and characterization of polymeric materials, scientists are able to create multi-scale novel polymers with various cases of chemical functionalities, diversified topologies, as well as cross-linking networks. Due to those remarkable achievements, there are a broad range of possible applications of smart polymers in catalysis, in environmental remediation, and especially in drug-delivery. Because of rising interest in developing therapeutic drug binding to specific treating target, polymer chemists are in particular interests in design and engineering the drug delivery materials to be not only bio-compatible, but also to be capable of self-assembly at various in-vivo physiological stimulus. Both experimental and theoretical work indicate that the thermodynamic properties relating to the hydrophobic effect play an important role in determining self-assembly process. At the same time, computational simulation and modeling are powerful instruments to contribute to microscopic thermodynamics' understanding toward self-assembly phenomenon. Along with statistical approaches, constructing empirical model based on simulation results would also help predict for further development of tailored nano-structured materials. My Research mainly focused on investigating physical and chemical characteristics of polymer materials through molecular dynamics simulation and probing the fundamental thermodynamic driving force of self-assembly behavior. We tried to surmount technological obstacles in computational chemistry and build an efficient scheme to identify the physical and chemical Feature of molecules, to reproduce underlying properties, to understand the origin of thermodynamic signatures, and to speed up current trial and error process in screening new materials.

Self-healing multiphase polymers via dynamic metal-ligand interactions.

PubMed

Mozhdehi, Davoud; Ayala, Sergio; Cromwell, Olivia R; Guan, Zhibin

2014-11-19

A new self-healing multiphase polymer is developed in which a pervasive network of dynamic metal-ligand (zinc-imidazole) interactions are programmed in the soft matrix of a hard/soft two-phase brush copolymer system. The mechanical and dynamic properties of the materials can be tuned by varying a number of molecular parameters (e.g., backbone/brush degree of polymerization and brush density) as well as the ligand/metal ratio. Following mechanical damage, these thermoplastic elastomers show excellent self-healing ability under ambient conditions without any intervention.

Investigating the Modification of Spontaneous Emission using Layer-by-Layer Self-Assembly

NASA Astrophysics Data System (ADS)

Ashry, Islam Ahmed Ibrahim Youssef

The process of spontaneous emission can be dramatically modified by optical micro- and nanostructures. We studied the modification of fluorescence dynamics using a polymer spacer layer fabricated through layer-by-layer (LbL) self-assembly. The advantages of this method are numerous: The self-assembled spacers can possess exceptional smooth surface morphology; The thickness of the spacer can be controlled with nanometer accuracy; And depending on fabrication conditions, the spacer layer is stimuli responsive and its thickness can be dynamically tuned. This thesis contains three interlinked components. First, we vary LbL spacer layer thickness and explore the change in fluorescence lifetime induced by the modified photonic density of states (PDOS), i.e., Purcell effects. Our experimental results agree well with theoretical predictions based on a classical dipole model, which also yields consistent values for the fluorophores' intrinsic fluorescence lifetime and quantum yield near a dielectric as well as a plasmonic interface. Based on this observation, we further demonstrate that self-assembled fluorophores can be used to probe the modified PDOS near optical micro- and nano-structures. These results naturally lead to the second component of our research. In particularly, based on the PDOS-induced changes in fluorescent lifetime, we develop a non-contact method that can measure morphological changes with nanoscale resolution. Our method relies on quantitatively linking fluorophore position with PDOS, and is validated through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. To demonstrate the potential application of this method, we investigated the swelling/deswelling of LbL films induced by pH changes. Our results indicate significant difference between a LbL film composed of a single polymer monolayer and a LbL film with 3 monolayers. Such stimuli-responsive polymers can be used to construct active and tunable plasmonic nano-devices. As a proof-of-principle demonstration, we experimentally confirm that it is possible to utilize the swelling/deswelling behavior of stimuli-responsive films to dynamically control the separation between Au nanoparticles and Texas Red (TR) dyes. This result is based on the strong correlation of TR fluorescence lifetime and nanoparticles-TR separation. Finally, we investigate the impact of different lithography processes on the fluorescence properties of self-assembled fluorophores. We consider three methods: direct fluorophore patterning through ultraviolet (UV) ablation, focused ion beam (FIB) milling of self-assembled fluorophores, and self-assembly of fluorescent materials over plasmonic nano-patterns.

Potential of thermally conductive polymers for the cooling of mechatronic parts

NASA Astrophysics Data System (ADS)

Heinle, C.; Drummer, D.

Adding thermally conductive fillers to polymers the thermal conductivity can be raised significantly. Thermal conductive polymers (TC-plastics) open up a vast range of options to set up novel concepts of polymer technological system solutions in the area of mechatronics. Heating experiment of cooling ribs show the potential in thermal management of mechatronic parts with TC-polymers in comparison with widely used reference materials copper and aluminum. The results demonstrate that especially for certain thermal boundary conditions comparable performance between these two material grades can be measured.

Aggregation and network formation in self-assembly of protein (H3.1) by a coarse-grained Monte Carlo simulation.

PubMed

Pandey, R B; Farmer, B L

2014-11-07

Multi-scale aggregation to network formation of interacting proteins (H3.1) are examined by a knowledge-based coarse-grained Monte Carlo simulation as a function of temperature and the number of protein chains, i.e., the concentration of the protein. Self-assembly of corresponding homo-polymers of constitutive residues (Cys, Thr, and Glu) with extreme residue-residue interactions, i.e., attractive (Cys-Cys), neutral (Thr-Thr), and repulsive (Glu-Glu), are also studied for comparison with the native protein. Visual inspections show contrast and similarity in morphological evolutions of protein assembly, aggregation of small aggregates to a ramified network from low to high temperature with the aggregation of a Cys-polymer, and an entangled network of Glu and Thr polymers. Variations in mobility profiles of residues with the concentration of the protein suggest that the segmental characteristic of proteins is altered considerably by the self-assembly from that in its isolated state. The global motion of proteins and Cys polymer chains is enhanced by their interacting network at the low temperature where isolated chains remain quasi-static. Transition from globular to random coil transition, evidenced by the sharp variation in the radius of gyration, of an isolated protein is smeared due to self-assembly of interacting networks of many proteins. Scaling of the structure factor S(q) with the wave vector q provides estimates of effective dimension D of the mass distribution at multiple length scales in self-assembly. Crossover from solid aggregates (D ∼ 3) at low temperature to a ramified fibrous network (D ∼ 2) at high temperature is observed for the protein H3.1 and Cys polymers in contrast to little changes in mass distribution (D ∼ 1.6) of fibrous Glu- and Thr-chain configurations.

Aggregation and network formation in self-assembly of protein (H3.1) by a coarse-grained Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Pandey, R. B.; Farmer, B. L.

2014-11-01

Multi-scale aggregation to network formation of interacting proteins (H3.1) are examined by a knowledge-based coarse-grained Monte Carlo simulation as a function of temperature and the number of protein chains, i.e., the concentration of the protein. Self-assembly of corresponding homo-polymers of constitutive residues (Cys, Thr, and Glu) with extreme residue-residue interactions, i.e., attractive (Cys-Cys), neutral (Thr-Thr), and repulsive (Glu-Glu), are also studied for comparison with the native protein. Visual inspections show contrast and similarity in morphological evolutions of protein assembly, aggregation of small aggregates to a ramified network from low to high temperature with the aggregation of a Cys-polymer, and an entangled network of Glu and Thr polymers. Variations in mobility profiles of residues with the concentration of the protein suggest that the segmental characteristic of proteins is altered considerably by the self-assembly from that in its isolated state. The global motion of proteins and Cys polymer chains is enhanced by their interacting network at the low temperature where isolated chains remain quasi-static. Transition from globular to random coil transition, evidenced by the sharp variation in the radius of gyration, of an isolated protein is smeared due to self-assembly of interacting networks of many proteins. Scaling of the structure factor S(q) with the wave vector q provides estimates of effective dimension D of the mass distribution at multiple length scales in self-assembly. Crossover from solid aggregates (D ˜ 3) at low temperature to a ramified fibrous network (D ˜ 2) at high temperature is observed for the protein H3.1 and Cys polymers in contrast to little changes in mass distribution (D ˜ 1.6) of fibrous Glu- and Thr-chain configurations.

Directed Self-Assembly of Block Copolymers for High Breakdown Strength Polymer Film Capacitors.

PubMed

Samant, Saumil P; Grabowski, Christopher A; Kisslinger, Kim; Yager, Kevin G; Yuan, Guangcui; Satija, Sushil K; Durstock, Michael F; Raghavan, Dharmaraj; Karim, Alamgir

2016-03-01

Emerging needs for fast charge/discharge yet high-power, lightweight, and flexible electronics requires the use of polymer-film-based solid-state capacitors with high energy densities. Fast charge/discharge rates of film capacitors on the order of microseconds are not achievable with slower charging conventional batteries, supercapacitors and related hybrid technologies. However, the current energy densities of polymer film capacitors fall short of rising demand, and could be significantly enhanced by increasing the breakdown strength (EBD) and dielectric permittivity (εr) of the polymer films. Co-extruded two-homopolymer component multilayered films have demonstrated much promise in this regard showing higher EBD over that of component polymers. Multilayered films can also help incorporate functional features besides energy storage, such as enhanced optical, mechanical, thermal and barrier properties. In this work, we report accomplishing multilayer, multicomponent block copolymer dielectric films (BCDF) with soft-shear driven highly oriented self-assembled lamellar diblock copolymers (BCP) as a novel application of this important class of self-assembling materials. Results of a model PS-b-PMMA system show ∼50% enhancement in EBD of self-assembled multilayer lamellar BCP films compared to unordered as-cast films, indicating that the breakdown is highly sensitive to the nanostructure of the BCP. The enhancement in EBD is attributed to the "barrier effect", where the multiple interfaces between the lamellae block components act as barriers to the dielectric breakdown through the film. The increase in EBD corresponds to more than doubling the energy storage capacity using a straightforward directed self-assembly strategy. This approach opens a new nanomaterial paradigm for designing high energy density dielectric materials.

Directed self-assembly of block copolymers for high breakdown strength polymer film capacitors

DOE PAGES

Samant, Saumil P.; Grabowski, Christopher A.; Kisslinger, Kim; ...

2016-03-04

Emerging needs for fast charge/discharge yet high-power, lightweight, and flexible electronics requires the use of polymer-film-based solid-state capacitors with high energy densities. Fast charge/discharge rates of film capacitors on the order of microseconds are not achievable with slower charging conventional batteries, supercapacitors and related hybrid technologies. However, the current energy densities of polymer film capacitors fall short of rising demand, and could be significantly enhanced by increasing the breakdown strength (E BD) and dielectric permittivity (ε r) of the polymer films. Co-extruded two-homopolymer component multilayered films have demonstrated much promise in this regard showing higher E BD over that ofmore » component polymers. Multilayered films can also help incorporate functional features besides energy storage, such as enhanced optical, mechanical, thermal and barrier properties. In this work, we report accomplishing multilayer, multicomponent block copolymer dielectric films (BCDF) with soft-shear driven highly oriented self-assembled lamellar diblock copolymers (BCP) as a novel application of this important class of self-assembling materials. Results of a model PS- b-PMMA system show ~50% enhancement in E BD of self-assembled multilayer lamellar BCP films compared to unordered as-cast films, indicating that the breakdown is highly sensitive to the nanostructure of the BCP. The enhancement in E BD is attributed to the “barrier effect”, where the multiple interfaces between the lamellae block components act as barriers to the dielectric breakdown through the film. The increase in E BD corresponds to more than doubling the energy storage capacity using a straightforward directed self-assembly strategy. Lastly, this approach opens a new nanomaterial paradigm for designing high energy density dielectric materials.« less

Enthalpic and Entropic Competition in Blends of Self-Suspended Hairy Nanoparticles

NASA Astrophysics Data System (ADS)

Choudhury, Snehashis; Agrawal, Akanksha; Archer, Lynden

Self-suspended hairy nanoparticles, where polymer chains are grafted onto nanoparticles, have attracted significant recent attention. These materials have been reported to manifest several interesting phenomena like thermal jamming, slowing-down of polymer chain dynamics, as well as small-strain stress overshoots during start-up of steady shear. The entropic penalty on tethered polymers produced by the requirement that they fill the space between the nanoparticle cores explain most of these behaviors. Here, we show that the entropic attraction between tethered polymer chains can be manipulated in mixtures of hairy nanoparticles using different polymer chemistry to design materials with unusual characteristics. Specifically, the degree of interpenetration of polymer chains can be controlled by tuning their interaction parameter (χ) . For SiO2-PEG/SiO2-PMMA blends, oscillatory rheological measurements show that the plateau modulus and yielding energy are significantly increased, while an opposite effect is seen with SiO2-PEG/SiO2-PI blends. More subtle effects of this enthalpy-entropy competition are well captured in Dielectric Spectroscopy measurements and SAXS experiments that can be used to quantify the degree of stretch and interdigitation of polymer chains.

Surface properties of functional polymer systems

NASA Astrophysics Data System (ADS)

Wong, Derek

Polymer surface modification typically involves blending with other polymers or chemical modification of the parent polymer. Such strategies inevitably result in polymer systems that are spatially and chemically heterogeneous, and which exhibit the phenomenon of surface segregation. This work investigates the effects of chain architecture on the surface segregation behavior of such functionally modified polymers using a series of end- and center-fluorinated poly(D,L-lactide). Surface segregation of the fluorinated functional groups was observed in both chain architectures via AMPS and water contact angle. Higher surface segregation was noted for functional groups located at the chain end as opposed to those in the middle of the chain. A self-consistent mean-field lattice theory was used to model the composition depth profiles of functional groups and excellent agreement was found between the model predictions and the experimental AMPS data in both chain architectures. Polymer properties are also in general dependent on both time and temperature, and exhibit a range of relaxation times in response to environmental stimuli. This behavior arises from the characteristic frequencies of molecular motions of the polymer chain and the interrelationship between time and temperature has been widely established for polymer bulk properties. There is evidence that surface properties also respond in a manner that is time and temperature dependent and that this dependence may not be the same as that observed for bulk properties. AMPS and water contact angle experiments were used to investigate the surface reorganization behavior of functional groups using a series of anionically synthesized end-fluorinated and end-carboxylated poly(styrene). It was found that both types of functional end-groups reorganized upon a change in the polarity of the surface environment in order to minimize the surface free energy. ADXPS and contact angle results suggest that the reorganization depth was confined to the top 2--3 nm of the surface. Contact angle results showed also that the reorganization process proceeded as a function of (time) 1/2, indicating that it is likely diffusion controlled. The magnitudes of the activation energies determined from the experimental data according to the Arhenius equation, suggest that the process is possibly correlated with known bulk beta and gamma relaxations in the polymer.

Towards a unification of the hierarchical reference theory and the self-consistent Ornstein-Zernike approximation.

PubMed

Reiner, A; Høye, J S

2005-12-01

The hierarchical reference theory and the self-consistent Ornstein-Zernike approximation are two liquid state theories that both furnish a largely satisfactory description of the critical region as well as phase coexistence and the equation of state in general. Furthermore, there are a number of similarities that suggest the possibility of a unification of both theories. As a first step towards this goal, we consider the problem of combining the lowest order gamma expansion result for the incorporation of a Fourier component of the interaction with the requirement of consistency between internal and free energies, leaving aside the compressibility relation. For simplicity, we restrict ourselves to a simplified lattice gas that is expected to display the same qualitative behavior as more elaborate models. It turns out that the analytically tractable mean spherical approximation is a solution to this problem, as are several of its generalizations. Analysis of the characteristic equations shows the potential for a practical scheme and yields necessary conditions that any closure to the Ornstein-Zernike relation must fulfill for the consistency problem to be well posed and to have a unique differentiable solution. These criteria are expected to remain valid for more general discrete and continuous systems, even if consistency with the compressibility route is also enforced where possible explicit solutions will require numerical evaluations.

Self-assembly of nucleic acids, silk and hybrid materials thereof.

PubMed

Humenik, Martin; Scheibel, Thomas

2014-12-17

Top-down approaches based on etching techniques have almost reached their limits in terms of dimension. Therefore, novel assembly strategies and types of nanomaterials are required to allow technological advances. Self-assembly processes independent of external energy sources and unlimited in dimensional scaling have become a very promising approach. Here,we highlight recent developments in self-assembled DNA-polymer, silk-polymer and silk-DNA hybrids as promising materials with biotic and abiotic moieties for constructing complex hierarchical materials in ‘bottom-up’ approaches. DNA block copolymers assemble into nanostructures typically exposing a DNA corona which allows functionalization, labeling and higher levels of organization due to its specific addressable recognition properties. In contrast, self-assembly of natural silk proteins as well as their recombinant variants yields mechanically stable β-sheet rich nanostructures. The combination of silk with abiotic polymers gains hybrid materials with new functionalities. Together, the precision of DNA hybridization and robustness of silk fibrillar structures combine in novel conjugates enable processing of higher-order structures with nanoscale architecture and programmable functions.

Self-assembly of nucleic acids, silk and hybrid materials thereof

NASA Astrophysics Data System (ADS)

Humenik, Martin; Scheibel, Thomas

2014-12-01

Top-down approaches based on etching techniques have almost reached their limits in terms of dimension. Therefore, novel assembly strategies and types of nanomaterials are required to allow technological advances. Self-assembly processes independent of external energy sources and unlimited in dimensional scaling have become a very promising approach. Here, we highlight recent developments in self-assembled DNA-polymer, silk-polymer and silk-DNA hybrids as promising materials with biotic and abiotic moieties for constructing complex hierarchical materials in ‘bottom-up’ approaches. DNA block copolymers assemble into nanostructures typically exposing a DNA corona which allows functionalization, labeling and higher levels of organization due to its specific addressable recognition properties. In contrast, self-assembly of natural silk proteins as well as their recombinant variants yields mechanically stable β-sheet rich nanostructures. The combination of silk with abiotic polymers gains hybrid materials with new functionalities. Together, the precision of DNA hybridization and robustness of silk fibrillar structures combine in novel conjugates enable processing of higher-order structures with nanoscale architecture and programmable functions.

Polymer adsorption-driven self-assembly of nanostructures.

PubMed

Chakraborty, A K; Golumbfskie, A J

2001-01-01

Driven by prospective applications, there is much interest in developing materials that can perform specific functions in response to external conditions. One way to design such materials is to create systems which, in response to external inputs, can self-assemble to form structures that are functionally useful. This review focuses on the principles that can be employed to design macromolecules that when presented with an appropriate two-dimensional surface, will self-assemble to form nanostructures that may be functionally useful. We discuss three specific examples: (a) biomimetic recognition between polymers and patterned surfaces. (b) control and manipulation of nanomechanical motion generated by biopolymer adsorption and binding, and (c) creation of patterned nanostructuctures by exposing molten diblock copolymers to patterned surfaces. The discussion serves to illustrate how polymer sequence can be manipulated to affect self-assembly characteristics near adsorbing surfaces. The focus of this review is on theoretical and computational work aimed toward elucidating the principles underlying the phenomena pertinent to the three topics noted above. However, synergistic experiments are also described in the appropriate context.

Poly(ethylene oxide) Chains Are Not ``Hydrophilic'' When They Exist As Polymer Brush Chains

NASA Astrophysics Data System (ADS)

Lee, Hoyoung; Kim, Dae Hwan; Witte, Kevin N.; Ohn, Kimberly; Choi, Je; Kim, Kyungil; Meron, Mati; Lin, Binhua; Akgun, Bulent; Satija, Sushil; Won, You-Yeon

2012-02-01

By using a combined experimental and theoretical approach, a model poly(ethylene oxide) (PEO) brush system, prepared by spreading a poly(ethylene oxide)-poly(n-butyl acrylate) (PEO-PnBA) amphiphilic diblock copolymer onto an air-water interface, was investigated. The polymer segment density profiles of the PEO brush in the direction normal to the air-water interface under various grafting density conditions were determined from combined X-ray and neutron reflectivity data. In order to achieve a theoretically sound analysis of the reflectivity data, we developed a new data analysis method that uses the self-consistent field theoretical modeling as a tool for predicting expected reflectivity results for comparison with the experimental data. Using this new data analysis method, we discovered that the effective Flory-Huggins interaction parameter of the PEO brush chains is significantly greater than that corresponding to the theta condition, suggesting that contrary to what is more commonly observed for PEO in normal situations, the PEO chains are actually not ``hydrophilic'' when they exist as polymer brush chains, because of the many body interactions forced to be effective in the brush situation.

Redox polymer and probe DNA tethered to gold electrodes for enzyme-amplified amperometric detection of DNA hybridization.

PubMed

Kavanagh, Paul; Leech, Dónal

2006-04-15

The detection of nucleic acids based upon recognition surfaces formed by co-immobilization of a redox polymer mediator and DNA probe sequences on gold electrodes is described. The recognition surface consists of a redox polymer, [Os(2,2'-bipyridine)2(polyvinylimidazole)(10)Cl](+/2+), and a model single DNA strand cross-linked and tethered to a gold electrode via an anchoring self-assembled monolayer (SAM) of cysteamine. Hybridization between the immobilized probe DNA of the recognition surface and a biotin-conjugated target DNA sequence (designed from the ssrA gene of Listeria monocytogenes), followed by addition of an enzyme (glucose oxidase)-avidin conjugate, results in electrical contact between the enzyme and the mediating redox polymer. In the presence of glucose, the current generated due to the catalytic oxidation of glucose to gluconolactone is measured, and a response is obtained that is binding-dependent. The tethering of the probe DNA and redox polymer to the SAM improves the stability of the surface to assay conditions of rigorous washing and high salt concentration (1 M). These conditions eliminate nonspecific interaction of both the target DNA and the enzyme-avidin conjugate with the recognition surfaces. The sensor response increases linearly with increasing concentration of target DNA in the range of 1 x 10(-9) to 2 x 10(-6) M. The detection limit is approximately 1.4 fmol, (corresponding to 0.2 nM of target DNA). Regeneration of the recognition surface is possible by treatment with 0.25 M NaOH solution. After rehybridization of the regenerated surface with the target DNA sequence, >95% of the current is recovered, indicating that the redox polymer and probe DNA are strongly bound to the surface. These results demonstrate the utility of the proposed approach.

Theoretical study of geometrical and electronic structures of various thiophene-based tricyclic polymers

NASA Astrophysics Data System (ADS)

Hong, Sung Y.; Song, Jung M.

1997-12-01

A theoretical study of a variety of tricyclic polymers [-(C8H2X2Y)n-] with two different types of bridging groups was performed, X=S and Y=CH2, SiH2, C=O, C=S, or C=CH2 for the fused bithiophene system and vice versa for the thieno-bicyclic system. These two types of the bridging groups are different from each other in that S favors the aromatic form of a cyclic polymer and the other groups prefer the quinonoid form. Geometrical structures of the polymers were obtained from semiempirical self-consistent-field (SCF) band calculations and the electronic properties from the modified extended Hückel band calculations. It is found that the ground-state geometrical structures of the tricyclic polymers are determined by the bridging groups in the outer rings. That is, the fused bithiophene system is aromatic in the ground state and the thieno-bicyclic system is quinonoid. The ground-state band gaps (which correspond to the absorption peaks of π-π* band transition) of the polymers were estimated to be in the range of 0.7-2.0 eV. The band gaps were analyzed in terms of the bond-length alternation along the conjugated carbon backbone, the C1-C4 interactions, and the electronic effect of the bridging groups. We also investigated the geometrical and electronic structures of polydicyanomethylene-cyclopenta-dicyclopentadiene (PDICNCY). Unlike the theoretical predictions of Toussaint and Bredas [Synth. Met. 69, 637 (1995)], PDICNCY in the ground state was estimated to be of the quinonoid form and to possess a large band gap (2.55 eV) comparable with the gap of polythiophene.

Self-Assembled CNT-Polymer Hybrids in Single-Walled Carbon Nanotubes Dispersed Aqueous Triblock Copolymer Solutions

NASA Astrophysics Data System (ADS)

Vijayaraghavan, D.; Manjunatha, A. S.; Poojitha, C. G.

2018-04-01

We have carried out scanning electron microscopy (SEM), differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), electrical conductivity, and 1H NMR studies as a function of temperature on single-walled carbon nanotubes (SWCNTs) dispersed aqueous triblock copolymer (P123) solutions. The single-walled carbon nanotubes in this system aggregate to form bundles, and the bundles aggregate to form net-like structures. Depending on the temperature and phases of the polymer, this system exhibits three different self-assembled CNT-polymer hybrids. We find CNT-unimer hybrid at low temperatures, CNT-micelle hybrid at intermediate temperatures wherein the polymer micelles are adsorbed in the pores of the CNT nets, and another type of CNT-micelle hybrid at high temperatures wherein the polymer micelles are adsorbed on the surface of the CNT bundles. Our DSC thermogram showed two peaks related to these structural changes in the CNT-polymer hybrids. Temperature dependence of the 1H NMR chemical shifts of the molecular groups of the polymer and the AC electrical conductivity of the composite also showed discontinuous changes at the temperatures at which the CNT-polymer hybrid's structural changes are seen. Interestingly, for a higher CNT concentration (0.5 wt.%) in the system, the aggregated polymer micelles adsorbed on the CNTs exhibit cone-like and cube-like morphologies at the intermediate and at high temperatures respectively.

Self Assembly and Interface Engineering of Organic Functional Materials for High Performance Polymer Solar Cells

NASA Astrophysics Data System (ADS)

Jen, Alex

2010-03-01

The performance of polymer solar cells are strongly dependent on the efficiency of light harvesting, exciton dissociation, charge transport, and charge collection at the metal/organic, metal/metal oxide, and organic/metal oxide interfaces. To improve the device performance, two parallel approaches were used: 1) developing novel low band gap conjugated polymers with good charge-transporting properties and 2) modifying the interfaces between the organic/metal oxide and organic/metal layers with functional self-assembling monolayers to tune their energy barriers. Moreover, the molecule engineering approach was also used to tune the energy level, charge mobility, and morphology of organic semiconductors.

Superfast Near-Infrared Light-Driven Polymer Multilayer Rockets.

PubMed

Wu, Zhiguang; Si, Tieyan; Gao, Wei; Lin, Xiankun; Wang, Joseph; He, Qiang

2016-02-03

A gold nanoshell-functionalized polymer multilayer nanorocket performs self-propulsion upon the irradiation with NIR light in the absence of chemical fuel. Theoretical simulations reveal that the NIR light-triggered self-thermophoresis drives the propulsion of the nanorocket. The nanorocket also displays -efficient NIR light-triggered propulsion in -biofluids and thus holds considerable promise for various potential biomedical applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Formation of Supramolecular Nanotubes by Self-assembly of a Phosphate-linked Dimeric Anthracene in Water.

PubMed

Yu, Hao; Sabetti, Mattia; Häner, Robert

2018-04-16

The assembly of supramolecular polymers from a phosphodiester-linked dimeric anthracene is described. AFM and TEM imaging reveals that the supramolecular polymers self-assemble into nanotubes in water. Subsequent photodimerization experiments indicate that the supramolecular polymerization occurs via end-to-end stacking rather than an interdigitation arrangement of the building blocks. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Roles of Segmental and Oligomeric Diffusion on the Gel Effect in Free Radical Polymerization

NASA Astrophysics Data System (ADS)

Wisnudel, M. B.; Torkelson, J. M.

1996-03-01

Termination between radicals has been simulated by phosphorescence quenching, showing strong roles for segmental and oligomeric radical self-diffusion in the origin of the gel effect. Quenching rate constants (k_q) were measured between benzil-terminated polymer as a function of anthracene-terminated polymer in polymer solutions. In dilute solution, interactions between 10k or 73k MW benzil-terminated polystyrene (PS- B) and anthracence-terminated polystyrene (PS-A) of varying MW, the MW effect is weaker than the Smoluchowski eq. prediction (kq MW^- 0.5). At higher concentration, interactions of PS-B and PS-A of like MW show only weak dependence of kq on MW and a concentration dependence similar to that of segmental mobility, indicating that segmental diffusion is important in termination. Finally, with interactions between 73k MW PS-B and PS-A of varying MW at 35 wt% PS, kq decreases by a factor of 10 in going from MW's of 100 to 1000 g/mol; beyond 1000 g/mol, kq is MW independent. Such effects cannot be explained by polymer-radical self-diffusion. However, they support the notion that the gel effect onset is associated with the concentration dependence of oligomeric radical self-diffusion and polymer radical chain-end segmental mobility.

Polysoaps: Configurations and Elasticity

NASA Astrophysics Data System (ADS)

Halperin, A.

1997-03-01

Simple polymers are very long, flexible, linear molecules. Amphiphiles, soaps, are small molecules comprising of a part that prefers water over oil and a part that prefers oil over water. By combining the two we arrive at an interesting, little explored, class of materials: Polysoaps. These comprise of a water soluble backbone incorporating, at intervals, covalently bound amphiphilic monomers. In water, the polymerised amphiphiles aggregate into self assembled units known as micelles. This induces a dramatic modification of the spatial configurations of the polymers. What were featureless random coils now exhibit intramolecular, hierachial self organisation. Due to this self organisation it is necessary to modify the paradigms describing the large scale behaviour of these polymers: Their configurations, dimensions and elasticity. Understanding the behaviour of these polymers is of practical interest because of their wide range of industrial applications, ranging from cosmetics to paper coating. It is of fundamental interest because polysoaps are characterised by a rugged free energy landscape that is reminiscent of complex systems such as proteins and glasses. The talk concerns theoretical arguments regarding the following issues: (i) The design parameters that govern the spatial configurations of the polysoaps, (ii) The interaction between polysoaps and free amphiphiles, (iii) The effect of the intramolecular self organisation on the elasticity of the chains.

Metal- and Polymer-Matrix Composites: Functional Lightweight Materials for High-Performance Structures

NASA Astrophysics Data System (ADS)

Gupta, Nikhil; Paramsothy, Muralidharan

2014-06-01

The special topic "Metal- and Polymer-Matrix Composites" is intended to capture the state of the art in the research and practice of functional composites. The current set of articles related to metal-matrix composites includes reviews on functionalities such as self-healing, self-lubricating, and self-cleaning capabilities; research results on a variety of aluminum-matrix composites; and investigations on advanced composites manufacturing methods. In addition, the processing and properties of carbon nanotube-reinforced polymer-matrix composites and adhesive bonding of laminated composites are discussed. The literature on functional metal-matrix composites is relatively scarce compared to functional polymer-matrix composites. The demand for lightweight composites in the transportation sector is fueling the rapid development in this field, which is captured in the current set of articles. The possibility of simultaneously tailoring several desired properties is attractive but very challenging, and it requires significant advancements in the science and technology of composite materials. The progress captured in the current set of articles shows promise for developing materials that seem capable of moving this field from laboratory-scale prototypes to actual industrial applications.

Synthesis of pH-responsive β-CD-based star polymer and impact of its self-assembly behavior on pectinase activity.

PubMed

Hu, Dong; Yang, Hong; Liu, Jiangtao; Lei, Zhongli

2017-03-01

A novel type of pH-responsive star polymer based on β-cyclodextrin (β-CD) was synthesized and further covalently conjugated with enzyme. The impact of its self-assembly behavior on enzyme activity was investigated. In our design, azide containing the polymer (N 3 ) 7 -β-CD-(PtBA) 14 was synthesized via atom transfer radical polymerization of tert-butyl acrylate using (N 3 ) 7 -β-CD-(Br) 14 as the multifunctional initiator. The final product (N 3 ) 7 -β-CD-(PAA) 14 was obtained via hydrolysis and covalently conjugating pectinase onto pH-responsive polyacrylic acid (PAA) arms. PAA can change its conformation with the self-assembly by altered pH, leading its nanostructure into micellar nanoparticles in aqueous solution and further affecting the activity of immobilized pectinase. The results were proved by fluorescence spectroscopy and dynamic light scattering. This system proves that the activity of immobilized enzyme can be tailored predictably, and this pH-responsive polymer holds great potential for controllable delivery of enzymes. © 2016 International Union of Biochemistry and Molecular Biology, Inc.

New developments in thermally stable polymers

NASA Technical Reports Server (NTRS)

Hergenrother, Paul M.

1991-01-01

Advances in high-temperature polymers since 1985 are discussed with the emphasis on the chemistry. High-temperature polymers refer to materials that exhibit glass-transition temperatures greater than 200 C and have the chemical structure expected to provide high thermooxidative stability. Specific polymers or series of polymers were selected to show how the chemical structure influences certain properties. Poly(arylene ethers) and polyimides are the two principal families of polymers discussed. Recent work on poly(arylene ethers) has concentrated on incorporating heterocyclic units within the polymer backbone. Recent polyimide work has centered on the synthesis of new polymers from novel monomers, several containing the trifluoromethyl group strategically located on the molecule. Various members in each of these polymer families display a unique combination of properties, heretofore unattainable. Other families of polymers are also briefly discussed with a polymer from an AB maleimidobenzocyclobutene exhibiting an especially attractive combination of properties.

Hierarchical self-assembly: Self-organized nanostructures in a nematically ordered matrix of self-assembled polymeric chains

NASA Astrophysics Data System (ADS)

Mubeena, Shaikh; Chatterji, Apratim

2015-03-01

We report many different nanostructures which are formed when model nanoparticles of different sizes (diameter σn) are allowed to aggregate in a background matrix of semiflexible self-assembled polymeric wormlike micellar chains. The different nanostructures are formed by the dynamical arrest of phase-separating mixtures of micellar monomers and nanoparticles. The different morphologies obtained are the result of an interplay of the available free volume, the elastic energy of deformation of polymers, the density (chemical potential) of the nanoparticles in the polymer matrix, and, of course, the ratio of the size of self-assembling nanoparticles and self-avoidance diameter of polymeric chains. We have used a hybrid semi-grand-canonical Monte Carlo simulation scheme to obtain the (nonequilibrium) phase diagram of the self-assembled nanostructures. We observe rodlike structures of nanoparticles which get self-assembled in the gaps between the nematically ordered chains, as well as percolating gel-like network of conjoined nanotubes. We also find a totally unexpected interlocked crystalline phase of nanoparticles and monomers, in which each crystal plane of nanoparticles is separated by planes of perfectly organized polymer chains. We identified the condition which leads to such interlocked crystal structure. We suggest experimental possibilities of how the results presented in this paper could be used to obtain different nanostructures in the laboratory.

Quickly updatable hologram images with high performance photorefractive polymer composites

NASA Astrophysics Data System (ADS)

Tsutsumi, Naoto; Kinashi, Kenji; Nonomura, Asato; Sakai, Wataru

2012-02-01

We present here quickly updatable hologram images using high performance photorefractive (PR) polymer composite based on poly(N-vinyl carbazole) (PVCz). PVCz is one of the pioneer materials for photoconductive polymer. PVCz/7- DCST/CzEPA/TNF (44/35/20/1 by wt) gives high diffraction efficiency of 68 % at E = 45 V/μm with fast response speed. Response speed of optical diffraction is the key parameter for real-time 3D holographic display. Key parameter for obtaining quickly updatable hologram images is to control the glass transition temperature lower enough to enhance chromophore orientation. Object image of the reflected coin surface recorded with reference beam at 532 nm (green beam) in the PR polymer composite is simultaneously reconstructed using a red probe beam at 642 nm. Instead of using coin object, object image produced by a computer was displayed on a spatial light modulator (SLM) is used as an object for hologram. Reflected object beam from a SLM interfered with reference beam on PR polymer composite to record a hologram and simultaneously reconstructed by a red probe beam. Movie produced in a computer was recorded as a realtime hologram in the PR polymer composite and simultaneously clearly reconstructed with a video rate.

Recent progress in nanocomposites based on conducting polymer: application as electrochemical sensors

NASA Astrophysics Data System (ADS)

El Rhazi, Mama; Majid, Sanaa; Elbasri, Miloud; Salih, Fatima Ezzahra; Oularbi, Larbi; Lafdi, Khalid

2018-06-01

Over the years, intensive research works have been devoted to conducting polymers due to their potential application in many fields such as fuel cell, sensors, and capacitors. To improve the properties of these compounds, several new approaches have been developed which consist in combining conducting polymers and nanoparticles. Then, this review intends to give a clear overview on nanocomposites based on conducting polymers, synthesis, characterization, and their application as electrochemical sensors. For this, the paper is divided into two parts: the first part will highlight the nanocomposites synthesized by combination of carbon nanomaterials (CNMs) and conducting polymers. The preparation of polymer/CNMs such as graphene and carbon nanotube modified electrode is presented coupled with relevant applications. The second part consists of a review of nanocomposites synthesized by combination of metal nanoparticles and conducting polymers.

Fluorine-Rich Planetary Environments as Possible Habitats for Life

PubMed Central

Budisa, Nediljko; Kubyshkin, Vladimir; Schulze-Makuch, Dirk

2014-01-01

In polar aprotic organic solvents, fluorine might be an element of choice for life that uses selected fluorinated building blocks as monomers of choice for self-assembling of its catalytic polymers. Organofluorine compounds are extremely rare in the chemistry of life as we know it. Biomolecules, when fluorinated such as peptides or proteins, exhibit a “fluorous effect”, i.e., they are fluorophilic (neither hydrophilic nor lipophilic). Such polymers, capable of creating self-sorting assemblies, resist denaturation by organic solvents by exclusion of fluorocarbon side chains from the organic phase. Fluorous cores consist of a compact interior, which is shielded from the surrounding solvent. Thus, we can anticipate that fluorine-containing “teflon”-like or “non-sticking” building blocks might be monomers of choice for the synthesis of organized polymeric structures in fluorine-rich planetary environments. Although no fluorine-rich planetary environment is known, theoretical considerations might help us to define chemistries that might support life in such environments. For example, one scenario is that all molecular oxygen may be used up by oxidation reactions on a planetary surface and fluorine gas could be released from F-rich magma later in the history of a planetary body to result in a fluorine-rich planetary environment. PMID:25370378

Properties of knotted ring polymers. I. Equilibrium dimensions.

PubMed

Mansfield, Marc L; Douglas, Jack F

2010-07-28

We report calculations on three classes of knotted ring polymers: (1) simple-cubic lattice self-avoiding rings (SARs), (2) "true" theta-state rings, i.e., SARs generated on the simple-cubic lattice with an attractive nearest-neighbor contact potential (theta-SARs), and (3) ideal, Gaussian rings. Extrapolations to large polymerization index N imply knot localization in all three classes of chains. Extrapolations of our data are also consistent with conjectures found in the literature which state that (1) R(g)-->AN(nu) asymptotically for ensembles of random knots restricted to any particular knot state, including the unknot; (2) A is universal across knot types for any given class of flexible chains; and (3) nu is equal to the standard self-avoiding walk (SAW) exponent (congruent with 0.588) for all three classes of chains (SARs, theta-SARs, and ideal rings). However, current computer technology is inadequate to directly sample the asymptotic domain, so that we remain in a crossover scaling regime for all accessible values of N. We also observe that R(g) approximately p(-0.27), where p is the "rope length" of the maximally inflated knot. This scaling relation holds in the crossover regime, but we argue that it is unlikely to extend into the asymptotic scaling regime where knots become localized.

Collapsed state of polyglutamic acid results in amyloid spherulite formation

PubMed Central

Stehli, Daniel; Mulaj, Mentor; Miti, Tatiana; Traina, Joshua; Foley, Joseph; Muschol, Martin

2015-01-01

Self-assembly of proteins and peptides into amyloid fibrils involves multiple distinct intermediates and late-stage fibrillar polymorphs. Understanding the conditions and mechanisms that promote the formation of one type of intermediate and polymorph over the other represents a fundamental challenge. Answers to this question are also of immediate biomedical relevance since different amyloid aggregate species have been shown to have distinct pathogenic potencies. One amyloid polymorph that has received comparatively little attention are amyloid spherulites. Here we report that self-assembly of the intrinsically disordered polymer poly(L-glutamic) acid (PLE) can generate amyloid spherulites. We characterize spherulite growth kinetics, as well as the morphological, optical and tinctorial features of this amyloid polymorph previously unreported for PLE. We find that PLE spherulites share both tinctorial and structural characteristics with their amyloid fibril counterparts. Differences in PLE's molecular weight, polydispersity or chemistry could not explain the selective propensity toward either fibril or spherulite formation. Instead, we provide evidence that PLE polymers can exist in either a collapsed globule or an extended random coil conformation. The collapsed globule consistently produces spherulites while the extended coil assembles into disordered fibril bundles. This results suggests that these 2 PLE conformers directly affect the morphology of the resulting macroscopic amyloid assembly. PMID:28232889

Collapsed state of polyglutamic acid results in amyloid spherulite formation.

PubMed

Stehli, Daniel; Mulaj, Mentor; Miti, Tatiana; Traina, Joshua; Foley, Joseph; Muschol, Martin

2015-01-01

Self-assembly of proteins and peptides into amyloid fibrils involves multiple distinct intermediates and late-stage fibrillar polymorphs. Understanding the conditions and mechanisms that promote the formation of one type of intermediate and polymorph over the other represents a fundamental challenge. Answers to this question are also of immediate biomedical relevance since different amyloid aggregate species have been shown to have distinct pathogenic potencies. One amyloid polymorph that has received comparatively little attention are amyloid spherulites. Here we report that self-assembly of the intrinsically disordered polymer poly(L-glutamic) acid (PLE) can generate amyloid spherulites. We characterize spherulite growth kinetics, as well as the morphological, optical and tinctorial features of this amyloid polymorph previously unreported for PLE. We find that PLE spherulites share both tinctorial and structural characteristics with their amyloid fibril counterparts. Differences in PLE's molecular weight, polydispersity or chemistry could not explain the selective propensity toward either fibril or spherulite formation. Instead, we provide evidence that PLE polymers can exist in either a collapsed globule or an extended random coil conformation. The collapsed globule consistently produces spherulites while the extended coil assembles into disordered fibril bundles. This results suggests that these 2 PLE conformers directly affect the morphology of the resulting macroscopic amyloid assembly.

Olefin metathesis for effective polymer healing via dynamic exchange of strong carbon-carbon bonds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guan, Zhibin; Lu, Yixuan

A method of preparing a malleable and/or self-healing polymeric or composite material is provided. The method includes providing a polymeric or composite material comprising at least one alkene-containing polymer, combining the polymer with at least one homogeneous or heterogeneous transition metal olefin metathesis catalyst to form a polymeric or composite material, and performing an olefin metathesis reaction on the polymer so as to form reversible carbon-carbon double bonds in the polymer. Also provided is a method of healing a fractured surface of a polymeric material. The method includes bringing a fractured surface of a first polymeric material into contact withmore » a second polymeric material, and performing an olefin metathesis reaction in the presence of a transition metal olefin metathesis catalyst such that the first polymeric material forms reversible carbon-carbon double bonds with the second polymeric material. Compositions comprising malleable and/or self-healing polymeric or composite material are also provided.« less

Graphene Oxide-Polymer Composite Langmuir Films Constructed by Interfacial Thiol-Ene Photopolymerization

NASA Astrophysics Data System (ADS)

Luo, Xiaona; Ma, Kai; Jiao, Tifeng; Xing, Ruirui; Zhang, Lexin; Zhou, Jingxin; Li, Bingbing

2017-02-01

The effective synthesis and self-assembly of graphene oxide (GO) nanocomposites are of key importance for a broad range of nanomaterial applications. In this work, a one-step chemical strategy is presented to synthesize stable GO-polymer Langmuir composite films by interfacial thiol-ene photopolymerization at room temperature, without use of any crosslinking agents and stabilizing agents. It is discovered that photopolymerization reaction between thiol groups modified GO sheets and ene in polymer molecules is critically responsible for the formation of the composite Langmuir films. The film formed by Langmuir assembly of such GO-polymer composite films shows potential to improve the mechanical and chemical properties and promotes the design of various GO-based nanocomposites. Thus, the GO-polymer composite Langmuir films synthesized by interfacial thiol-ene photopolymerization with such a straightforward and clean manner, provide new alternatives for developing chemically modified GO-based hybrid self-assembled films and nanomaterials towards a range of soft matter and graphene applications.

Dispersions of polymer ionomers: I.

PubMed

Capek, Ignác

2004-12-31

The principal subject discussed in the current paper is the effect of ionic functional groups in polymers on the formation of nontraditional polymer materials, polymer blends or polymer dispersions. Ionomers are polymers that have a small amount of ionic groups distributed along a nonionic hydrocarbon chain. Specific interactions between components in a polymer blend can induce miscibility of two or more otherwise immiscible polymers. Such interactions include hydrogen bonding, ion-dipole interactions, acid-base interactions or transition metal complexation. Ion-containing polymers provide a means of modifying properties of polymer dispersions by controlling molecular structure through the utilization of ionic interactions. Ionomers having a relatively small number of ionic groups distributed usually along nonionic organic backbone chains can agglomerate into the following structures: (1) multiplets, consisting of a small number of tightly packed ion pairs; and (2) ionic clusters, larger aggregates than multiplets. Ionomers exhibit unique solid-state properties as a result of strong associations among ionic groups attached to the polymer chains. An important potential application of ionomers is in the area of thermoplastic elastomers, where the associations constitute thermally reversible cross-links. The ionic (anionic, cationic or polar) groups are spaced more or less randomly along the polymer chain. Because in this type of ionomer an anionic group falls along the interior of the chain, it trails two hydrocarbon chain segments, and these must be accommodated sterically within any domain structure into which the ionic group enters. The primary effects of ionic functionalization of a polymer are to increase the glass transition temperature, the melt viscosity and the characteristic relaxation times. The polymer microstructure is also affected, and it is generally agreed that in most ionomers, microphase-separated, ion-rich aggregates form as a result of strong ion-dipole attractions. As a consequence of this new phase, additional relaxation processes are often observed in the viscoelastic behavior of ionomers. Light functionalization of polymers can increase the glass transition temperature and gives rise to two new features in viscoelastic behavior: (1) a rubbery plateau above T(g) and (2) a second loss process at elevated temperatures. The rubbery plateau was due to the formation of a physical network. The major effect of the ionic aggregate was to increase the longer time relaxation processes. This in turn increases the melt viscosity and is responsible for the network-like behavior of ionomers above the glass transition temperature. Ionomers rich in polar groups can fulfill the criteria for the self-assembly formation. The reported phenomenon of surface micelle formation has been found to be very general for these materials.

Theoretical study of solvent effects on the coil-globule transition

NASA Astrophysics Data System (ADS)

Polson, James M.; Opps, Sheldon B.; Abou Risk, Nicholas

2009-06-01

The coil-globule transition of a polymer in a solvent has been studied using Monte Carlo simulations of a single chain subject to intramolecular interactions as well as a solvent-mediated effective potential. This solvation potential was calculated using several different theoretical approaches for two simple polymer/solvent models, each employing hard-sphere chains and hard-sphere solvent particles as well as attractive square-well potentials between some interaction sites. For each model, collapse is driven by variation in a parameter which changes the energy mismatch between monomers and solvent particles. The solvation potentials were calculated using two fundamentally different methodologies, each designed to predict the conformational behavior of polymers in solution: (1) the polymer reference interaction site model (PRISM) theory and (2) a many-body solvation potential (MBSP) based on scaled particle theory introduced by Grayce [J. Chem. Phys. 106, 5171 (1997)]. For the PRISM calculations, two well-studied solvation monomer-monomer pair potentials were employed, each distinguished by the closure relation used in its derivation: (i) a hypernetted-chain (HNC)-type potential and (ii) a Percus-Yevick (PY)-type potential. The theoretical predictions were each compared to results obtained from explicit-solvent discontinuous molecular dynamics simulations on the same polymer/solvent model systems [J. Chem. Phys. 125, 194904 (2006)]. In each case, the variation in the coil-globule transition properties with solvent density is mostly qualitatively correct, though the quantitative agreement between the theory and prediction is typically poor. The HNC-type potential yields results that are more qualitatively consistent with simulation. The conformational behavior of the polymer upon collapse predicted by the MBSP approach is quantitatively correct for low and moderate solvent densities but is increasingly less accurate for higher densities. At high solvent densities, the PRISM-HNC and MBSP approaches tend to overestimate, while the PRISM-PY approach underestimates the tendency of the solvent to drive polymer collapse.

Performance of local orbital basis sets in the self-consistent Sternheimer method for dielectric matrices of extended systems

NASA Astrophysics Data System (ADS)

Hübener, H.; Pérez-Osorio, M. A.; Ordejón, P.; Giustino, F.

2012-09-01

We present a systematic study of the performance of numerical pseudo-atomic orbital basis sets in the calculation of dielectric matrices of extended systems using the self-consistent Sternheimer approach of [F. Giustino et al., Phys. Rev. B 81, 115105 (2010)]. In order to cover a range of systems, from more insulating to more metallic character, we discuss results for the three semiconductors diamond, silicon, and germanium. Dielectric matrices of silicon and diamond calculated using our method fall within 1% of reference planewaves calculations, demonstrating that this method is promising. We find that polarization orbitals are critical for achieving good agreement with planewaves calculations, and that only a few additional ζ's are required for obtaining converged results, provided the split norm is properly optimized. Our present work establishes the validity of local orbital basis sets and the self-consistent Sternheimer approach for the calculation of dielectric matrices in extended systems, and prepares the ground for future studies of electronic excitations using these methods.

Repair and Rehabilitation of Dams: Case Studies

DTIC Science & Technology

1999-09-01

with fiber - reinforced , acrylic- polymer modi- fied concrete (FRAPMC) and eliminating leakage into the trunnion recesses. FRAPMC consists of mortar...coarse aggregate, and reinforcement fibers . It is mixed in a mortar mixer as a two-component system consisting of a liquid polymer emulsion of...seat was removed and replaced with fiber - reinforced , acrylic- polymer modified concrete (FRAPMC). New bridge seats were installed, allowing for more

End-anchored polymers in good solvents from the single chain limit to high anchoring densities.

PubMed

Whitmore, Mark D; Grest, Gary S; Douglas, Jack F; Kent, Michael S; Suo, Tongchuan

2016-11-07

An increasing number of applications utilize grafted polymer layers to alter the interfacial properties of solid substrates, motivating refinement in our theoretical understanding of such layers. To assess existing theoretical models of them, we have investigated end-anchored polymer layers over a wide range of grafting densities, σ, ranging from a single chain to high anchoring density limits, chain lengths ranging over two orders of magnitude, for very good and marginally good solvent conditions. We compare Monte Carlo and molecular dynamics simulations, numerical self-consistent field calculations, and experimental measurements of the average layer thickness, h, with renormalization group theory, the Alexander-de Gennes mushroom theory, and the classical brush theory. Our simulations clearly indicate that appreciable inter-chain interactions exist at all simulated areal anchoring densities so that there is no mushroom regime in which the layer thickness is independent of σ. Moreover, we find that there is no high coverage regime in which h follows the predicted scaling, h ∼ Nσ 1/3 , for classical polymer brushes either. Given that no completely adequate analytic theory seems to exist that spans wide ranges of N and σ, we applied scaling arguments for h as a function of a suitably defined reduced anchoring density, defined in terms of the solution radius of gyration of the polymer chains and N. We find that such a scaling approach enables a smooth, unified description of h in very good solvents over the full range of anchoring density and chain lengths, although this type of data reduction does not apply to marginal solvent quality conditions.

In vitro characterization of self-assembled anterior cruciate ligament cell spheroids for ligament tissue engineering.

PubMed

Hoyer, M; Meier, C; Breier, A; Hahner, J; Heinrich, G; Drechsel, N; Meyer, M; Rentsch, C; Garbe, L-A; Ertel, W; Lohan, A; Schulze-Tanzil, G

2015-03-01

Tissue engineering of an anterior cruciate ligament (ACL) implant with functional enthesis requires site-directed seeding of different cell types on the same scaffold. Therefore, we studied the suitability of self-assembled three-dimensional spheroids generated by lapine ACL ligament fibroblasts for directed scaffold colonization. The spheroids were characterized in vitro during 14 days in static and 7 days in dynamic culture. Size maintenance of self-assembled spheroids, the vitality, the morphology and the expression pattern of the cells were monitored. Additionally, we analyzed the total sulfated glycosaminoglycan, collagen contents and the expression of the ligament components type I collagen, decorin and tenascin C on protein and for COL1A1, DCN and TNMD on gene level in the spheroids. Subsequently, the cell colonization of polylactide-co-caprolactone [P(LA-CL)] and polydioxanone (PDS) polymer scaffolds was assessed in response to a directed, spheroid-based seeding technique. ACL cells were able to self-assemble spheroids and survive over 14 days. The spheroids decreased in size but not in cellularity depending on the culture time and maintained or even increased their differentiation state. The area of P[LA-CL] scaffolds, colonized after 14 days by the cells of one spheroid, was in average 4.57 ± 2.3 mm(2). Scaffolds consisting of the polymer P[LA-CL] were more suitable for colonization by spheroids than PDS embroideries. We conclude that ACL cell spheroids are suitable as site-directed seeding strategy for scaffolds in ACL tissue engineering approaches and recommend the use of freshly assembled spheroids for scaffold colonization, due to their balanced proliferation and differentiation.

Polymer-mediated nanorod self-assembly predicted by dissipative particle dynamics simulations.

PubMed

Khani, Shaghayegh; Jamali, Safa; Boromand, Arman; Hore, Michael J A; Maia, Joao

2015-09-14

Self-assembly of nanoparticles in polymer matrices is an interesting and growing subject in the field of nanoscience and technology. We report herein on modelling studies of the self-assembly and phase behavior of nanorods in a homopolymer matrix, with the specific goal of evaluating the role of deterministic entropic and enthalpic factors that control the aggregation/dispersion in such systems. Grafting polymer brushes from the nanorods is one approach to control/impact their self-assembly capabilities within a polymer matrix. From an energetic point of view, miscible interactions between the brush and the matrix are required for achieving a better dispersibility; however, grafting density and brush length are the two important parameters in dictating the morphology. Unlike in previous computational studies, the present Dissipative Particle Dynamics (DPD) simulation framework is able to both predict dispersion or aggregation of nanorods and determine the self-assembled structure, allowing for the determination of a phase diagram, which takes all of these factors into account. Three types of morphologies are predicted: dispersion, aggregation and partial aggregation. Moreover, favorable enthalpic interactions between the brush and the matrix are found to be essential for expanding the window for achieving a well-dispersed morphology. A three-dimensional phase diagram is mapped on which all the afore-mentioned parameters are taken into account. Additionally, in the case of immiscibility between brushes and the matrix, simulations predict the formation of some new and tunable structures.

The influence of polymer architecture on the assembly of poly(ethylene oxide) grafted C60 fullerene clusters in aqueous solution: a molecular dynamics simulation study.

PubMed

Hooper, Justin B; Bedrov, Dmitry; Smith, Grant D

2009-03-28

The effect of polymer architecture on the aggregation behavior of C60 fullerenes tethered with a single chain of poly(ethylene oxide) (PEO) in aqueous solution has been investigated using coarse-grained, implicit solvent molecular dynamics simulations. The PEO-grafted fullerenes were comprised of a single tether of 60 repeat units represented as a linear polymer, a three-arm star (20 repeat units/arm) or a six-arm star (10 repeat units/arm). Additionally, the influence of arm length on self-assembly of the PEO-fullerene conjugates was investigated for the three-arm stars. Self-assembly is driven by favorable fullerene-fullerene and fullerene-PEO interactions. Our simulations reveal that it should be possible to control the size and geometry of the self-assembled fullerene aggregates in water through variation of PEO architecture and PEO molecular weight. We found that aggregate size and shape could be understood qualitatively in terms of the packing parameter concept that has been employed for diblock polymer and surfactant self-assembly. Higher molecular weight PEO (longer arms) and more compact PEO (more arms for the same molecular weight) resulted in greater steric repulsion between fullerenes, engendering greater aggregate surface curvature and hence the formation of smaller, more spherically shaped aggregates. Finally, weak attractive interactions between PEO and the fullerenes were found to play an important role in determining aggregate shape, size and the dynamics of self-assembly.

Nanospace-Mediated Self-Organization of Nanoparticles in Flexible Porous Polymer Templates.

PubMed

Kuroda, Yoshiyuki; Muto, Itaru; Shimojima, Atsushi; Wada, Hiroaki; Kuroda, Kazuyuki

2017-09-12

Self-organization is a fundamental process for the construction of complex hierarchically ordered nanostructures, which are widespread in biological systems. However, precise control of size, shape, and surface properties is required for self-organization of nanoparticles. Here, we demonstrate a novel self-organization phenomenon mediated by flexible nanospaces in templates. Inorganic nanoparticles (e.g., silica, zirconia, and titania) are deposited in porous polymer thin films with randomly distributed pores on the surface, leaving a partially filled nanospace in each pore. Heating at temperatures beyond the glass transition temperature of the template leads to self-organization of the inorganic nanoparticles into one-dimensional chainlike networks. The self-organization is mediated by the deformation and fusion of the residual nanospaces, and it can be rationally controlled by sequential heat treatments. These results show that a nanospace, defined by the nonexistence of matter, interacts indirectly with matter and can be used as a component of self-organization systems.

Diels-Alder Trapping of Photochemically Generated o-Xylenols: Application in the Synthesis of Novel Organic Molecules and Polymers

NASA Technical Reports Server (NTRS)

Meador, Michael A.

2003-01-01

Bis(o-xylenol) equivalents are useful synthetic intermediates in the construction of polymers and hydroxyl substituted organic molecules which can organize by hydrogen bonded self-assembly into unique supramolecular structures. These polymers and supramolecular materials have potential use as coatings and thin films in aerospace, electronic and biomedical applications.

Lack of guilt, guilt, and shame: a multi-informant study on the relations between self-conscious emotions and psychopathology in clinically referred children and adolescents.

PubMed

Muris, Peter; Meesters, Cor; Heijmans, Jolina; van Hulten, Sandra; Kaanen, Linsy; Oerlemans, Birgit; Stikkelbroeck, Tessa; Tielemans, Tim

2016-04-01

The present study examined the relationships between dysregulations in self-conscious emotions and psychopathology in clinically referred children and adolescents. For this purpose, parent-, teacher-, and self-report Achenbach System of Empirically Based Assessment data of 1000 youth aged 4-18 years was analyzed as this instrument not only provides information on the intensity levels of lack of guilt, guilt, and shame, but also on the severity of various types of psychopathology. The results first of all indicated that dysregulations of self-conscious emotions were more common in this clinical sample than in the general population. Further, a consistent pattern was found with regard to the relationships between self-conscious emotions and childhood psychopathology. That is, lack of guilt was predominantly associated with oppositional defiant and conduct (i.e., externalizing) problems, while guilt and shame were primarily linked with affective and anxiety (i.e., internalizing) problems. By and large, these findings confirm what has been found in non-clinical youth, and suggest that self-conscious emotions play a small but significant role in the psychopathology of children and adolescents.

Cognitive vulnerabilities and depression versus other psychopathology symptoms and diagnoses in early adolescence.

PubMed

Alloy, Lauren B; Black, Shimrit K; Young, Mathew E; Goldstein, Kim E; Shapero, Benjamin G; Stange, Jonathan P; Boccia, Angelo S; Matt, Lindsey M; Boland, Elaine M; Moore, Lauren C; Abramson, Lyn Y

2012-01-01

We examined the concurrent associations between multiple cognitive vulnerabilities to depression featured in hopelessness theory, Beck's theory, and response styles theory and depressive symptoms and diagnoses in a sample of early adolescents. We also examined the specificity of these cognitive vulnerabilities to depression versus anxiety and externalizing psychopathology, controlling for co-occurring symptoms and diagnoses. Male and female, Caucasian and African American, 12- to 13-year-old adolescents were assessed in a cross-sectional design. Cognitive vulnerabilities of hopelessness, inferential style, rumination, and self-referent information processing were assessed with self-reports and behavioral tasks. Symptoms and diagnoses of depressive, anxiety, and externalizing disorders were assessed with self-report questionnaires and diagnostic interviews. Hopelessness exhibited the greatest specificity to depressive symptoms and diagnoses, whereas negative inferential styles, rumination, and negative self-referent information processing were associated with both depressive and anxiety symptoms and diagnoses and, in some cases, with externalizing disorders. Consistent with cognitive theories of depression, hopelessness, negative inferential styles, rumination, and negative self-referent information processing were associated with depressive symptoms and diagnoses. However, with the exception of hopelessness, most of the remaining cognitive vulnerabilities were not specific to depression. With further maturation of our sample, these cognitive vulnerabilities may become more specific to depression as cognitive styles further develop and consolidate, the rates of depression increase, and individuals' presentations of psychopathology become more differentiated.

Cognitive Vulnerabilities and Depression versus Other Psychopathology Symptoms and Diagnoses in Early Adolescence

PubMed Central

Alloy, Lauren B.; Black, Shimrit K.; Young, Mathew E.; Goldstein, Kim E.; Shapero, Benjamin G.; Stange, Jonathan P.; Boccia, Angelo S.; Matt, Lindsey M.; Boland, Elaine M.; Moore, Lauren C.; Abramson, Lyn Y.

2012-01-01

Objective We examined the concurrent associations between multiple cognitive vulnerabilities to depression featured in Hopelessness Theory, Beck’s Theory, and Response Styles Theory and depressive symptoms and diagnoses in a sample of early adolescents. We also examined the specificity of these cognitive vulnerabilities to depression versus anxiety and externalizing psychopathology, controlling for co-occurring symptoms and diagnoses. Method Male and female, Caucasian and African-American, 12–13 year old adolescents were assessed in a cross-sectional design. Cognitive vulnerabilities of hopelessness, inferential style, rumination, and self-referent information processing were assessed with self-reports and behavioral tasks. Symptoms and diagnoses of depressive, anxiety, and externalizing disorders were assessed with self-report questionnaires and diagnostic interviews. Results Hopelessness exhibited the greatest specificity to depressive symptoms and diagnoses, whereas negative inferential styles, rumination, and negative self-referent information processing were associated with both depressive and anxiety symptoms and diagnoses and, in some cases, with externalizing disorders. Conclusions Consistent with cognitive theories of depression, hopelessness, negative inferential styles, rumination, and negative self-referent information processing were associated with depressive symptoms and diagnoses. However, with the exception of hopelessness, most of the remaining cognitive vulnerabilities were not specific to depression. With further maturation of our sample, these cognitive vulnerabilities may become more specific to depression as cognitive styles further develop and consolidate, the rates of depression increase, and individuals’ presentations of psychopathology become more differentiated. PMID:22853629

Thermodynamic and dynamic behaviors of self-organizing polymeric systems

NASA Astrophysics Data System (ADS)

Zhao, Yiqiang

Two topics of self-organizing polymeric systems are explored in this work: thermodynamic and dynamic properties of liquid crystal polymers in solutions and rheological behaviors of self-organizing gels. For dilute nematic solutions of end-on side-chain liquid crystal polysiloxanes (SCLCP) dissolved in 5CB, the chain anisotropies R∥/R ⊥, obtained from electrorheological(ER) analysis based on the Brochard model, are consistent with independent measurements of Rg∥/R g⊥ via small-angle neutron scattering (SANS), which unambiguously demonstrating a slightly prolate SCLCP chain conformation. Dissolution of this prolate SCLCP in flow-aligning 5CB produces a tumbling flow, clearly indicating a discrepancy with the Brochard hydrodynamic theory which predicts such a transition only for oblate conformation. A numerical comparison using a modified version of the Brochard model leads to improved self-consistent agreement between SANS, ER and shear transient experiments. The molecular weight dependence of the chain conformational relaxation time it indicates an extended SCLCP chain conformation in 5CB. SANS analysis suggests that the SCLCP conformation is sensitive to the solvent interaction, i.e. a more extended conformation is observed in isotropic acetone-d6 than in nematic 5CB. A SANS conformational study of SCLCCs with methoxyphenylbenzoate mesogenic side group in CDC13 demonstrates that the form factor of a single comb-like SCLCP chain is well described by a wormlike chain model with finite cross-sectional thickness over the entire q range, taking into account the molecular weight polydispersity. Consistent with measurement of a large R g from low q analysis, the resulting persistence length lp is in the range 28˜32 A, substantially larger than that of unsubstituted polydimethylsiloxane (PDMS) chain (l p =5.8 A), which suggests a relatively rigid SCLCP chain due to the influence of densely attached mesogenic groups. For nematic mixtures of copolysiloxane SCLCP in 5OCB, a metastably extended miscible nematic range is observed at low SCLCP concentration upon cooling. Onset of an induced smectic phase occurs upon cooling at 60%wt SCLCP concentration which corresponds to 48:52 molar ratio of mesogens. Dielectric spectra of these mixtures over a wide concentration range exhibit two distinct regimes of relaxation behavior reflecting the crossover from dilute and semidilute to concentrated regime. Rheological behavior of a metallo-supramolecular gel with thixotropic feature is explored to understand the viscoelastic behaviors of self-assembling networks consisting of "living polymers". A well-defined yield point and non-linear viscoelasticity at small strain are probed via the controlled-stress and controlled-strain measurements, respectively. The self-assembled network is readily presheared into a Newtonian sol and displays a three-stage kinetic recovery process, closely associated with the metal ion-ligand binding kinetics and related phase behaviors. Finally, we investigate the viscoelastic properties of a novel colloidal gel in which macrocycles self-assemble into interconnected self-organized clusters. A series of rheological experiments are combined to reveal the shear responsive nature as well as linear and nonlinear viscoelasticity of this gel. Certain features of observed viscoelastic properties demonstrate the characteristics of the behavior of colloidal gels which show slow glassy dynamics. The negative temperature dependence of the storage modulus at low frequency suggests that enthalpic contributions to elasticity need to be considered, presumably due to internal energy changes upon deformation.

Chromatographic evaluation of self-immobilized stationary phases for reversed-phase liquid chromatography.

PubMed

Bottoli, Carla B G; Collins, Kenneth E; Collins, Carol H

2003-02-14

The preparation of stationary phases for HPLC using polymers deposited on silica usually includes an immobilization step involving cross-linking by free radicals induced by ionizing radiation or by other radical initiators. The present paper reports changes which occur at ambient temperature in the character of poly(methyloctylsiloxane) deposited on porous silica particles as a function of the time interval between particle loading and column packing. Column performance and retention factors increase with time and these changes are attributed to rearrangement (self-assembly) which result in "self-immobilization" of the polymer molecules on the silica surface.

Emergent Vortex Patterns in Systems of Self-Propelled, Chiral Particles

NASA Astrophysics Data System (ADS)

Huber, Lorenz; Denk, Jonas; Reithmann, Emanuel; Frey, Erwin

Self-organization of FtsZ polymers is vital for Z-ring assembly during bacterial cell division, and has been studied using reconstituted in vitro model systems. Employing Brownian dynamics simulations and a Boltzmann approach, we model FtsZ polymers as active particles moving along chiral circular paths. With both theoretical approaches we find self-organization into vortex structures and characterize different states in parameter states. Our work demonstrates that these patterns are robust and are generic for active chiral matter. Moreover, we show that the dynamics at the onset of pattern formation is described by a generalized complex Ginzburg-Landau equation.

A process for preparing an ultra-thin, adhesiveless, multi-layered, patterned polymer substrate

NASA Technical Reports Server (NTRS)

Bryant, Robert G. (Inventor); Kruse, Nancy H. M. (Inventor); Fox, Robert L. (Inventor); Tran, Sang Q. (Inventor)

1995-01-01

A process for preparing an ultra-thin, adhesiveless, multi-layered, patterned polymer substrate is disclosed. The process may be used to prepare both rigid and flexible cables and circuit boards. A substrate is provided and a polymeric solution comprising a self-bonding, soluble polymer and a solvent is applied to the substrate. Next, the polymer solution is dried to form a polymer coated substrate. The polymer coated substrate is metallized and patterned. At least one additional coating of the polymeric solution is applied to the metallized, patterned, polymer coated substrate and the steps of metallizing and patterning are repeated. Lastly, a cover coat is applied. When preparing a flexible cable and flexible circuit board, the polymer coating is removed from the substrate.

A polymer scaffold for self-healing perovskite solar cells

NASA Astrophysics Data System (ADS)

Zhao, Yicheng; Wei, Jing; Li, Heng; Yan, Yin; Zhou, Wenke; Yu, Dapeng; Zhao, Qing

2016-01-01

Advancing of the lead halide perovskite solar cells towards photovoltaic market demands large-scale devices of high-power conversion efficiency, high reproducibility and stability via low-cost fabrication technology, and in particular resistance to humid environment for long-time operation. Here we achieve uniform perovskite film based on a novel polymer-scaffold architecture via a mild-temperature process. These solar cells exhibit efficiency of up to ~16% with small variation. The unencapsulated devices retain high output for up to 300 h in highly humid environment (70% relative humidity). Moreover, they show strong humidity resistant and self-healing behaviour, recovering rapidly after removing from water vapour. Not only the film can self-heal in this case, but the corresponding devices can present power conversion efficiency recovery after the water vapour is removed. Our work demonstrates the value of cheap, long chain and hygroscopic polymer scaffold in perovskite solar cells towards commercialization.

Self-constructed tree-shape high thermal conductivity nanosilver networks in epoxy.

PubMed

Pashayi, Kamyar; Fard, Hafez Raeisi; Lai, Fengyuan; Iruvanti, Sushumna; Plawsky, Joel; Borca-Tasciuc, Theodorian

2014-04-21

We report the formation of high aspect ratio nanoscale tree-shape silver networks in epoxy, at low temperatures (<150 °C) and atmospheric pressures, that are correlated to a ∼200 fold enhancement of thermal conductivity (κ) of the nanocomposite compared to the polymer matrix. The networks form through a three-step process comprising of self-assembly by diffusion limited aggregation of polyvinylpyrrolidone (PVP) coated nanoparticles, removal of PVP coating from the surface, and sintering of silver nanoparticles in high aspect ratio networked structures. Controlling self-assembly and sintering by carefully designed multistep temperature and time processing leads to κ of our silver nanocomposites that are up to 300% of the present state of the art polymer nanocomposites at similar volume fractions. Our investigation of the κ enhancements enabled by tree-shaped network nanocomposites provides a basis for the development of new polymer nanocomposites for thermal transport and storage applications.

Hierarchical nanoparticle assemblies formed by decorating breath figures.

PubMed

Böker, Alexander; Lin, Yao; Chiapperini, Kristen; Horowitz, Reina; Thompson, Mike; Carreon, Vincent; Xu, Ting; Abetz, Clarissa; Skaff, Habib; Dinsmore, A D; Emrick, Todd; Russell, Thomas P

2004-05-01

The combination of two self-assembly processes on different length scales leads to the formation of hierarchically structured nanoparticle arrays. Here, the formation of spherical cavities, or 'breath figures'-made by the condensation of micrometre-sized water droplets on the surface of a polymer solution-that self-assemble into a well-ordered hexagonal array, is combined with the self-assembly of CdSe nanoparticles at the polymer solution-water droplet interface. Complete evaporation of the solvent and water confines the particle assembly to an array of spherical cavities and allows for ex situ investigation. Fluorescence confocal, transmission electron and scanning electron microscope images show the preferential segregation of the CdSe nanoparticles to the polymer solution-water interface where they form a 5-7-nm-thick layer, thus functionalizing the walls of the holes. This process opens a new route to fabricating highly functionalized ordered microarrays of nanoparticles, potentially useful in sensory, separation membrane or catalytic applications.

A polymer scaffold for self-healing perovskite solar cells

PubMed Central

Zhao, Yicheng; Wei, Jing; Li, Heng; Yan, Yin; Zhou, Wenke; Yu, Dapeng; Zhao, Qing

2016-01-01

Advancing of the lead halide perovskite solar cells towards photovoltaic market demands large-scale devices of high-power conversion efficiency, high reproducibility and stability via low-cost fabrication technology, and in particular resistance to humid environment for long-time operation. Here we achieve uniform perovskite film based on a novel polymer-scaffold architecture via a mild-temperature process. These solar cells exhibit efficiency of up to ∼16% with small variation. The unencapsulated devices retain high output for up to 300 h in highly humid environment (70% relative humidity). Moreover, they show strong humidity resistant and self-healing behaviour, recovering rapidly after removing from water vapour. Not only the film can self-heal in this case, but the corresponding devices can present power conversion efficiency recovery after the water vapour is removed. Our work demonstrates the value of cheap, long chain and hygroscopic polymer scaffold in perovskite solar cells towards commercialization. PMID:26732479

A polymer scaffold for self-healing perovskite solar cells.

PubMed

Zhao, Yicheng; Wei, Jing; Li, Heng; Yan, Yin; Zhou, Wenke; Yu, Dapeng; Zhao, Qing

2016-01-06

Advancing of the lead halide perovskite solar cells towards photovoltaic market demands large-scale devices of high-power conversion efficiency, high reproducibility and stability via low-cost fabrication technology, and in particular resistance to humid environment for long-time operation. Here we achieve uniform perovskite film based on a novel polymer-scaffold architecture via a mild-temperature process. These solar cells exhibit efficiency of up to ∼ 16% with small variation. The unencapsulated devices retain high output for up to 300 h in highly humid environment (70% relative humidity). Moreover, they show strong humidity resistant and self-healing behaviour, recovering rapidly after removing from water vapour. Not only the film can self-heal in this case, but the corresponding devices can present power conversion efficiency recovery after the water vapour is removed. Our work demonstrates the value of cheap, long chain and hygroscopic polymer scaffold in perovskite solar cells towards commercialization.

Relationship between Coping Strategies and Depression in Caregivers of Alzheimer Patients.

ERIC Educational Resources Information Center

Ambinder, Abby

This research examined whether a multicomponent program consisting of individual and family counseling intervention for spouse caregivers of Alzheimer's disease patients can affect caregiver depression. Self-referred spouse caregivers (N=52) completed an intensive assessment battery on their perception of patient and personal status at entry into…

On-Chip Chemical Self-Assembly of Semiconducting Single-Walled Carbon Nanotubes (SWNTs): Toward Robust and Scale Invariant SWNTs Transistors.

PubMed

Derenskyi, Vladimir; Gomulya, Widianta; Talsma, Wytse; Salazar-Rios, Jorge Mario; Fritsch, Martin; Nirmalraj, Peter; Riel, Heike; Allard, Sybille; Scherf, Ullrich; Loi, Maria A

2017-06-01

In this paper, the fabrication of carbon nanotubes field effect transistors by chemical self-assembly of semiconducting single walled carbon nanotubes (s-SWNTs) on prepatterned substrates is demonstrated. Polyfluorenes derivatives have been demonstrated to be effective in selecting s-SWNTs from raw mixtures. In this work the authors functionalized the polymer with side chains containing thiols, to obtain chemical self-assembly of the selected s-SWNTs on substrates with prepatterned gold electrodes. The authors show that the full side functionalization of the conjugated polymer with thiol groups partially disrupts the s-SWNTs selection, with the presence of metallic tubes in the dispersion. However, the authors determine that the selectivity can be recovered either by tuning the number of thiol groups in the polymer, or by modulating the polymer/SWNTs proportions. As demonstrated by optical and electrical measurements, the polymer containing 2.5% of thiol groups gives the best s-SWNT purity. Field-effect transistors with various channel lengths, using networks of SWNTs and individual tubes, are fabricated by direct chemical self-assembly of the SWNTs/thiolated-polyfluorenes on substrates with lithographically defined electrodes. The network devices show superior performance (mobility up to 24 cm 2 V -1 s -1 ), while SWNTs devices based on individual tubes show an unprecedented (100%) yield for working devices. Importantly, the SWNTs assembled by mean of the thiol groups are stably anchored to the substrate and are resistant to external perturbation as sonication in organic solvents. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polymers for Traveling Wave Ion Mobility Spectrometry Calibration

NASA Astrophysics Data System (ADS)

Duez, Quentin; Chirot, Fabien; Liénard, Romain; Josse, Thomas; Choi, ChangMin; Coulembier, Olivier; Dugourd, Philippe; Cornil, Jérôme; Gerbaux, Pascal; De Winter, Julien

2017-07-01

One of the main issues when using traveling wave ion mobility spectrometry (TWIMS) for the determination of collisional cross-section (CCS) concerns the need for a robust calibration procedure built from referent ions of known CCS. Here, we implement synthetic polymer ions as CCS calibrants in positive ion mode. Based on their intrinsic polydispersities, polymers offer in a single sample the opportunity to generate, upon electrospray ionization, numerous ions covering a broad mass range and a large CCS window for different charge states at a time. In addition, the key advantage of polymer ions as CCS calibrants lies in the robustness of their gas-phase structure with respect to the instrumental conditions, making them less prone to collisional-induced unfolding (CIU) than protein ions. In this paper, we present a CCS calibration procedure using sodium cationized polylactide and polyethylene glycol, PLA and PEG, as calibrants with reference CCS determined on a home-made drift tube. Our calibration procedure is further validated by testing the polymer calibration to determine CCS of numerous different ions for which CCS are reported in the literature. [Figure not available: see fulltext.

Tile-based self-assembly of a triple-helical polysaccharide into cell wall-like mesoporous nanocapsules.

PubMed

Wu, Chaoxi; Wang, Xiaoying; Wang, Jianjing; Zhang, Zhen; Wang, Zhiping; Wang, Yifei; Tang, Shunqing

2017-07-20

Tile-based self-assembly is a robust system in the construction of three-dimensional DNA nanostructures but it has been rarely applied to other helical biopolymers. β-Glucan is an immunoactive natural polymer which exists in a triple helical conformation. Herein, we report that β-glucan, after modification using two types of short chain acyl groups, can self-assemble into tiles with inactivated sticky ends at the interface of two solvents. These tiles consist of a single layer of helices laterally aligned, and the sticky ends can be activated when a few acyl groups at the ends are removed; these tiles can further pack into mesoporous nanocapsules, in a similar process as the sticky DNA tiles pack into complex polyhedral nano-objects. These nanocapsules were found to have targeted effects to antigen presenting cells in a RAW264.7 cell model. Our study suggests that tile-based self-assembly can be a general strategy for helical biopolymers, and on fully exploiting this strategy, various new functional nanostructures will become accessible in the future.

Nanohelices from planar polymer self-assembled in carbon nanotubes

PubMed Central

Fu, Hongjin; Xu, Shuqiong; Li, Yunfang

2016-01-01

The polymer possessing with planar structure can be activated and guided to encapsulate the inner space of SWNT and form a helix through van der Waals interaction and the π-π stacking effect between the polymer and the inner surface of SWNT. The SWNT size, the nanostructure and flexibility of polymer chain are all determine the final structures. The basic interaction between the polymer and the nanotubes is investigated, and the condition and mechanism of the helix-forming are explained particularly. Hybrid polymers improve the ability of the helix formation. This study provides scientific basis for fabricating helical polymers encapsulated in SWNTs and eventually on their applications in various areas. PMID:27440493

Linking topology of tethered polymer rings with applications to chromosome segregation and estimation of the knotting length.

PubMed

Marko, John F

2009-05-01

The Gauss linking number (Ca) of two flexible polymer rings which are tethered to one another is investigated. For ideal random walks, mean linking-squared varies with the square root of polymer length while for self-avoiding walks, linking-squared increases logarithmically with polymer length. The free-energy cost of linking of polymer rings is therefore strongly dependent on degree of self-avoidance, i.e., on intersegment excluded volume. Scaling arguments and numerical data are used to determine the free-energy cost of fixed linking number in both the fluctuation and large-Ca regimes; for ideal random walks, for |Ca|>N;{1/4} , the free energy of catenation is found to grow proportional, variant|Ca/N;{1/4}|;{4/3} . When excluded volume interactions between segments are present, the free energy rapidly approaches a linear dependence on Gauss linking (dF/dCa approximately 3.7k_{B}T) , suggestive of a novel "catenation condensation" effect. These results are used to show that condensation of long entangled polymers along their length, so as to increase excluded volume while decreasing number of statistical segments, can drive disentanglement if a mechanism is present to permit topology change. For chromosomal DNA molecules, lengthwise condensation is therefore an effective means to bias topoisomerases to eliminate catenations between replicated chromatids. The results for mean-square catenation are also used to provide a simple approximate estimate for the "knotting length," or number of segments required to have a knot along a single circular polymer, explaining why the knotting length ranges from approximately 300 for an ideal random walk to 10;{6} for a self-avoiding walk.

Improving the representation of peptide-like inhibitor and antibiotic molecules in the Protein Data Bank

PubMed Central

Dutta, Shuchismita; Dimitropoulos, Dimitris; Feng, Zukang; Persikova, Irina; Sen, Sanchayita; Shao, Chenghua; Westbrook, John; Young, Jasmine; Zhuravleva, Marina A; Kleywegt, Gerard J; Berman, Helen M

2014-01-01

With the accumulation of a large number and variety of molecules in the Protein Data Bank (PDB) comes the need on occasion to review and improve their representation. The Worldwide PDB (wwPDB) partners have periodically updated various aspects of structural data representation to improve the integrity and consistency of the archive. The remediation effort described here was focused on improving the representation of peptide-like inhibitor and antibiotic molecules so that they can be easily identified and analyzed. Peptide-like inhibitors or antibiotics were identified in over 1000 PDB entries, systematically reviewed and represented either as peptides with polymer sequence or as single components. For the majority of the single-component molecules, their peptide-like composition was captured in a new representation, called the subcomponent sequence. A novel concept called “group” was developed for representing complex peptide-like antibiotics and inhibitors that are composed of multiple polymer and nonpolymer components. In addition, a reference dictionary was developed with detailed information about these peptide-like molecules to aid in their annotation, identification and analysis. Based on the experience gained in this remediation, guidelines, procedures, and tools were developed to annotate new depositions containing peptide-like inhibitors and antibiotics accurately and consistently. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 659–668, 2014. PMID:24173824

The effect of side-chain substitution and hot processing on diketopyrrolopyrrole-based polymers for organic solar cells.

PubMed

Heintges, Gaël H L; Leenaers, Pieter J; Janssen, René A J

2017-07-14

The effects of cold and hot processing on the performance of polymer-fullerene solar cells are investigated for diketopyrrolopyrrole (DPP) based polymers that were specifically designed and synthesized to exhibit a strong temperature-dependent aggregation in solution. The polymers, consisting of alternating DPP and oligothiophene units, are substituted with linear and second position branched alkyl side chains. For the polymer-fullerene blends that can be processed at room temperature, hot processing does not enhance the power conversion efficiencies compared to cold processing because the increased solubility at elevated temperatures results in the formation of wider polymer fibres that reduce charge generation. Instead, hot processing seems to be advantageous when cold processing is not possible due to a limited solubility at room temperature. The resulting morphologies are consistent with a nucleation-growth mechanism for polymer fibres during drying of the films.

Orbital-free bond breaking via machine learning

NASA Astrophysics Data System (ADS)

Snyder, John C.; Rupp, Matthias; Hansen, Katja; Blooston, Leo; Müller, Klaus-Robert; Burke, Kieron

2013-12-01

Using a one-dimensional model, we explore the ability of machine learning to approximate the non-interacting kinetic energy density functional of diatomics. This nonlinear interpolation between Kohn-Sham reference calculations can (i) accurately dissociate a diatomic, (ii) be systematically improved with increased reference data and (iii) generate accurate self-consistent densities via a projection method that avoids directions with no data. With relatively few densities, the error due to the interpolation is smaller than typical errors in standard exchange-correlation functionals.

Squaramide-Based Supramolecular Materials for Three-Dimensional Cell Culture of Human Induced Pluripotent Stem Cells and Their Derivatives

PubMed Central

2018-01-01

Synthetic hydrogel materials can recapitulate the natural cell microenvironment; however, it is equally necessary that the gels maintain cell viability and phenotype while permitting reisolation without stress, especially for use in the stem cell field. Here, we describe a family of synthetically accessible, squaramide-based tripodal supramolecular monomers consisting of a flexible tris(2-aminoethyl)amine (TREN) core that self-assemble into supramolecular polymers and eventually into self-recovering hydrogels. Spectroscopic measurements revealed that monomer aggregation is mainly driven by a combination of hydrogen bonding and hydrophobicity. The self-recovering hydrogels were used to encapsulate NIH 3T3 fibroblasts as well as human-induced pluripotent stem cells (hiPSCs) and their derivatives in 3D. The materials reported here proved cytocompatible for these cell types with maintenance of hiPSCs in their undifferentiated state essential for their subsequent expansion or differentiation into a given cell type and potential for facile release by dilution due to their supramolecular nature. PMID:29528623

Self-healable electrically conducting wires for wearable microelectronics.

PubMed

Sun, Hao; You, Xiao; Jiang, Yishu; Guan, Guozhen; Fang, Xin; Deng, Jue; Chen, Peining; Luo, Yongfeng; Peng, Huisheng

2014-09-01

Electrically conducting wires play a critical role in the advancement of modern electronics and in particular are an important key to the development of next-generation wearable microelectronics. However, the thin conducting wires can easily break during use, and the whole device fails to function as a result. Herein, a new family of high-performance conducting wires that can self-heal after breaking has been developed by wrapping sheets of aligned carbon nanotubes around polymer fibers. The aligned carbon nanotubes offer an effective strategy for the self-healing of the electric conductivity, whereas the polymer fiber recovers its mechanical strength. A self-healable wire-shaped supercapacitor fabricated from a wire electrode of this type maintained a high capacitance after breaking and self-healing. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

On the impact of self-clearing on electroactive polymer (EAP) actuators

NASA Astrophysics Data System (ADS)

Ahmed, Saad; Ounaies, Zoubeida; Lanagan, Michael T.

2017-10-01

Electroactive polymer (EAP)-based actuators have large potential for a wide array of applications; however, their practical implementation is still a challenge because of the requirement of high driving voltage, which most often leads to premature defect-driven electrical breakdown. Polymer-based capacitors have the ability to clear defects with partial electrical breakdown and subsequent removal of a localized electrode section near the defect. In this study, this process, which is known as self-clearing, is adopted for EAP technologies. We report a methodical approach to self-clear an EAP, more specifically P(VDF-TrFE-CTFE) terpolymer, to delay premature defect-driven electrical breakdown of the terpolymer actuators at high operating electric fields. Breakdown results show that electrical breakdown strength is improved up to 18% in comparison to a control sample after self-clearing. Furthermore, the electromechanical performance in terms of blocked force and free displacement of P(VDF-TrFE-CTFE) terpolymer-based bending actuators are examined after self-clearing and precleared samples show improved blocked force, free displacement and maximum sustainable electric field compared to control samples. The study demonstrates that controlled self-clearing of EAPs improves the breakdown limit and reliability of the EAP actuators for practical applications without impeding their electromechanical performance.

Self-assembled multilayers and photoluminescence properties of a new water-soluble poly(para-phenylene)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, X.; Li, D.; Luett, M.

1998-07-01

This paper reports the synthesis and characterizations of a new water-soluble poly(paraphenylene) (PPP) and its applications in preparing self-assembled multi-layer films. This new water-soluble conducting polymer was prepared through the sulfonation reaction of poly(p-quarterphenylene-2,2{prime}-dicarboxylic acid). The incorporation of sulfonate groups has dramatically improved PPP's solubility in water at a wide pH range, whereas previous PPP is only slightly soluble in basic solutions. Dilute aqueous solutions of this polymer with acidic, neutral or basic pH emit brilliant blue light while irradiated with UV light. The sulfonated PPP emits from 350 nm to 455 nm with a maximum intensity at 380 nm.more » Self-assembled multilayers of this sulfonated PPP were constructed with a positively charged polymer poly(diallyl dimethyl ammonium chloride) and characterized with various surface analyses. Conductive (RuO{sub 2} and ITO), semiconductive (Si wafer), and non-conductive (SiO{sub 2}) substrates were used in the preparation of self-assembled multilayers. Electrical, optical and structural properties of these novel self-assembled thin films will be discussed.« less

Self-assembled multilayers and photoluminescence properties of a new water-soluble poly(para-phenylene)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, X.; Li, D.Q.; Luett, M.

1998-03-01

This paper reports the synthesis and characterizations of a new water-soluble poly(para-phenylene) (PPP) and its applications in preparing self-assembled multilayer films. This new water-soluble conducting polymer was prepared through the sulfonation reaction of poly(p-quarterphenylene-2,2{prime}-dicarboxylic acid). The incorporation of sulfonate groups has dramatically improved PPP`s solubility in water at a wide pH range, whereas previous PPP is only slightly soluble in basic solutions. Dilute aqueous solutions of this polymer with acidic, neutral or basic pH emit brilliant blue light while irradiated with UV light. The sulfonated PPP emits from 350 nm to 455 nm with a maximum intensity at 380 nm.more » Self-assembled multilayers of this sulfonated PPP were constructed with a positively charged polymer poly(diallyl dimethyl ammonium chloride) and characterized with various surface analyses. Conductive (RuO{sub 2} and ITO), semiconductive (Si wafer), and non-conductive (SiO{sub 2}) substrates were used in the preparation of self-assembled multilayers. Electrical, optical and structural properties of these novel self-assembled thin films will be discussed.« less

Smart and functional polymer materials for smart and functional microfluidic instruments

NASA Astrophysics Data System (ADS)

Gray, Bonnie L.

2014-04-01

As microfluidic systems evolve from "chip-in-the-lab" to true portable lab-on-a-chip (LoC) or lab-in-a-package (LiP) microinstrumentation, there is a need for increasingly miniaturized sensors, actuators, and integration/interconnect technologies with high levels of functionality and self-direction. Furthermore, as microfluidic instruments are increasingly realized in polymer-based rather than glass- or silicon- based platforms, there is a need to realize these highly functional components in materials that are polymer-compatible. Polymers that are altered to possess basic functionality, and even higher-functioning "smart" polymer materials, may help to realize high-functioning and selfdirecting portable microinstrumentation. Stimuli-responsive hydrogels have been recognized for over a decade as beneficial to the development of smart microfluidics systems and instrumentation. In addition, functional materials such as conductive and magnetic composite polymers are being increasingly employed to push microfluidics systems to greater degrees of functionality, portability, and/or flexibility for wearable/implantable systems. Functional and smart polymer materials can be employed to realize electrodes, electronic routing, heaters, mixers, valves, pumps, sensors, and interconnect structures in polymer-based microfluidic systems. Stimuli for such materials can be located on-chip or in a small package, thus greatly increasing the degree of portability and the potential for mechanical flexibility of such systems. This paper will examine the application of functional polymer materials to the development of high-functioning microfluidics instruments with a goal towards self-direction.

Self-supported fibrin-polyvinyl alcohol interpenetrating polymer networks: an easily handled and rehydratable biomaterial.

PubMed

Bidault, Laurent; Deneufchatel, Marie; Vancaeyzeele, Cédric; Fichet, Odile; Larreta-Garde, Véronique

2013-11-11

A fibrin hydrogel at physiological concentration (5 mg/mL) was associated with polyvinyl alcohol (PVA) inside an interpenetrating polymer networks (IPN) architecture. Previously, PVA has been modified with methacrylate functions in order to cross-link it by free-radical polymerization. The fibrin network was synthesized by the enzymatic hydrolysis of fibrinogen by thrombin. The resulting self-supported materials simultaneously exhibit the properties of the fibrin hydrogel and those of the synthetic polymer network. Their storage modulus is 50-fold higher than that of the fibrin hydrogel and they are completely rehydratable. These materials are noncytotoxic toward human fibroblast and the fibrin present on the surface of PVAm-based IPNs favors cell development.

Quantifying the value of information for uncertainty reduction in chemical EOR modeling

NASA Astrophysics Data System (ADS)

Leray, Sarah; Yeates, Christopher; Douarche, Frédéric; Roggero, Frédéric

2016-04-01

Reservoir modeling is a powerful tool to assess the technical and economic feasibility of chemical Enhanced Oil Recovery methods such as the joint injection of surfactant and polymer. Laboratory recovery experiments are usually undertaken on cores to understand recovery mechanisms and to estimate properties, that will be further used to build large scale models. To capture the different processes involved in chemical EOR, models are described by a large number of parameters which are basically only partially constrained by recovery experiments and additional characterizations, mainly because of cost and time restrictions or limited representativeness. Among the most uncertain properties, features the surfactant adsorption which cannot be straightforwardly derived from bulk or simplified dynamic measurements (e.g. single phase dynamic adsorption experiments). It is unfortunately critical for the economics of the process. Identifying the most informative observations (e.g. saturation scans, pressure differential, surfactant production, oil recovery) is of primary interest to compensate deficiency of some characterizations and improve models robustness and their predictive capability. Building a consistent set of recovery experiments that will allow to seize recovery mechanisms is critical as well. To address these inverse methodology issues, we create a synthetic numerical model with a well-defined set of parameter values, considered to be our reference case. This choice of model is based on a similar real data set and a broad literature review. It consists of a water-wet sandstone subject to typical surfactant-polymer injections. We first study the effect of a salinity gradient injected after a surfactant-polymer slug, as it is known to significantly improve oil recovery. We show that reaching optimal conditions of salinity gradient is a fragile balance between surfactant desorption and interfacial tension increase. This high dependence on surfactant adsorption properties indicates that two recovery tests with and without salinity gradient are of great interest for model inversion and characterization of surfactant adsorption. Second, we analyze our capacity to find again the reference model using an assisted history matching method to reproduce a set of synthetic core-scale experiments. To do so, we use the reference model over five configurations with respect to chemicals injection to provide baseline recovery data. Then, we consider some uncertainty on model parameters, regarding surfactant adsorption properties amongst others, leading to a total of twelve uncertain parameters. Finally, we extensively explore the parameter space to find several reasonable matches. We show that an additional sixth recovery experiment is necessary to fully constrain the model, and specifically characterize surfactant adsorption. We besides show that production data are not equally informative: pressure differential is for instance the less informative data while a saturation scan at the end of the polymer post-flush can greatly help in the inversion. The inverse methodology carried out here has also been successfully tested with a real set of coreflood experiments.

Helically assembled π-conjugated polymers with circularly polarized luminescence.

PubMed

Watanabe, Kazuyoshi; Akagi, Kazuo

2014-08-01

We review the recent progress in the field of helically assembled π -conjugated polymers, focusing on aromatic conjugated polymers with interchain helical π -stacking that exhibit circularly polarized luminescence (CPL). In Part 1, we discuss optically active polymers with white-colored CPL and the amplification of the circular polarization through liquid crystallinity. In Part 2, we focus on the stimuli-responsive CPL that results from changes in the conformation and aggregation state of π -conjugated molecules and polymers. In Part 3, we discuss the self-assembly of achiral cationic π -conjugated polymers into circularly polarized luminescent supramolecular nanostructures with the aid of other chiral molecules.

An experimental study of the PTC properties of polymers with carbon black fillers

NASA Astrophysics Data System (ADS)

Lin, Jianlian

The Positive Temperature Coefficient (PTC) phenomenon, first discovered by Harman in 1957, is defined as the sharp increase of the electrical resistivity of the material with temperature, especially at the Curie transition temperature. Polymeric PTC materials have been widely used since 1975 as self-regulating components, over current or over heat protectors, sensors, etc. In this project a detailed study of polymeric PTC materials has been carried out. Polymeric PTC materials consist of a non-conducting polymeric phase in which conductive particles, such as CB's, are added. Previously most of the studies of the polymer matrices of PTC materials were limited to single component semi-crystalline polymers, such as HDPE, LDPE, EVA etc. In this work, the PTC effects of carbon black filled binary polymer blends, such as LDPE/EPDM, HDPD/EPDM, HDPE/EVA, etc. are mainly studied. For the LDPE/EPDM/CB system, it is found that the PTC intensity of the blends after gamma-ray irradiation increases by almost 5 orders of magnitude compared with that of irradiated LDPE/CB compound. This increase in PTC intensity is due to the greater thermal expansion coefficient of the rubber (EPDM) phase. In addition, a comparison of E-beam and gamma-ray irradiation is made and the resulting effect on the PTC properties of LDPE/EPDM/CB blends is studied in detail. It is found that with higher dose of gamma-ray, the material undergoes significant radiation damage, while irradiation with E-beam prevents radiation damage due to shorter exposure time. The influence of using treated carbon blacks on the PTC/NTC effects of the composites is also studied. The polymer blends filled with oxidized carbon black display higher PTC intensity followed by a weaker NTC effect, which is due to stronger interactions between oxidized CB's & polymer. It is concluded that strong interactions between polymers and fillers suppress the NTC effect. Finally ESR analysis is used to study the interactions between the polymer blends and fillers. It is found that relatively high structure CB's (CSF-III) have a strong interaction with the polymer blend. Based on all the work done, it is concluded that a blend of high polymer with a crystalline rubber filled with relatively high structure carbon blacks that is irradiated by E-beam will be a good polymer PTC material.

Virtex-5QV Self Scrubber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wojahn, Christopher K.

2015-10-20

This HDL code (hereafter referred to as "software") implements circuitry in Xilinx Virtex-5QV Field Programmable Gate Array (FPGA) hardware. This software allows the device to self-check the consistency of its own configuration memory for radiation-induced errors. The software then provides the capability to correct any single-bit errors detected in the memory using the device's inherent circuitry, or reload corrupted memory frames when larger errors occur that cannot be corrected with the device's built-in error correction and detection scheme.

Enhancing the effectiveness of antismoking messages via self-congruent appeals.

PubMed

Chang, Chingching

2009-01-01

A self-congruent effect model was applied to understand adolescents' responses to antismoking advertising that referred to the self or others. Experiment 1 showed that self-referring ads generated more negative smoking attitudes than other-referring ads among adolescents with independent self-construals, whereas other-referring ads generated more negative smoking attitudes than self-referring ads among adolescents with interdependent self-construals. A survey further showed that smokers rated themselves higher on a measure of independent self-construal than nonsmokers. Experiment 2 then found that self-referring ads are more effective than other-referring ads for smokers, who have independent self-construals. Findings supported the idea that health communication campaign designers can maximize message effectiveness by developing different messages for different target segments of the population based on their self-construals.

Liquid-Solid Self-Lubricated Coatings

NASA Astrophysics Data System (ADS)

Armada, S.; Schmid, R.; Equey, S.; Fagoaga, I.; Espallargas, N.

2013-02-01

Self-lubricated coatings have been a major topic of interest in thermal spray in the last decades. Self-lubricated coatings obtained by thermal spray are exclusively based on solid lubricants (PTFE, h-BN, graphite, MoS2, etc.) embedded in the matrix. Production of thermal spray coatings containing liquid lubricants has not yet been achieved because of the complexity of keeping a liquid in a solid matrix during the spraying process. In the present article, the first liquid-solid self-lubricating thermal spray coatings are presented. The coatings are produced by inserting lubricant-filled capsules inside a polymeric matrix. The goal of the coating is to release lubricant to the system when needed. The first produced coatings consisted solely of capsules for confirming the feasibility of the process. For obtaining such a coating, the liquid-filled capsules were injected in the thermal spray flame without any other feedstock material. Once the concept and the idea were proven, a polymer was co-sprayed together with the capsules to obtain a coating containing the lubricant-filled capsules distributed in the solid polymeric matrix. The coatings and the self-lubricated properties have been investigated by means of optical microscopy, Scanning Electron Microscopy, and tribological tests.

DFTB3: Extension of the self-consistent-charge density-functional tight-binding method (SCC-DFTB).

PubMed

Gaus, Michael; Cui, Qiang; Elstner, Marcus

2012-04-10

The self-consistent-charge density-functional tight-binding method (SCC-DFTB) is an approximate quantum chemical method derived from density functional theory (DFT) based on a second-order expansion of the DFT total energy around a reference density. In the present study we combine earlier extensions and improve them consistently with, first, an improved Coulomb interaction between atomic partial charges, and second, the complete third-order expansion of the DFT total energy. These modifications lead us to the next generation of the DFTB methodology called DFTB3, which substantially improves the description of charged systems containing elements C, H, N, O, and P, especially regarding hydrogen binding energies and proton affinities. As a result, DFTB3 is particularly applicable to biomolecular systems. Remaining challenges and possible solutions are also briefly discussed.

Pseudo-conformer models for linear molecules: Joint treatment of spectroscopic, electron diffraction and ab initio data for the C3O2 molecule

NASA Astrophysics Data System (ADS)

Tarasov, Yury I.; Kochikov, Igor V.

2018-06-01

Dynamic analysis of the molecules with large-amplitude motions (LAM) based on the pseudo-conformer approach has been successfully applied to various molecules. Floppy linear molecules present a special class of molecular structures that possess a pair of conjugate LAM coordinates but allow one-dimensional treatment. In this paper, previously developed treatment for the semirigid molecules is applied to the carbon suboxide molecule. This molecule characterized by the extremely large CCC bending has been thoroughly investigated by spectroscopic and ab initio methods. However, the earlier electron diffraction investigations were performed within a static approach, obtaining thermally averaged parameters. In this paper we apply a procedure aimed at obtaining the short list of self-consistent reference geometry parameters of a molecule, while all thermally averaged parameters are calculated based on reference geometry, relaxation dependencies and quadratic and cubic force constants. We show that such a model satisfactorily describes available electron diffraction evidence with various QC bending potential energy functions when r.m.s. CCC angle is in the interval 151 ± 2°. This leads to a self-consistent molecular model satisfying spectroscopic and GED data. The parameters for linear reference geometry have been defined as re(CO) = 1.161(2) Å and re(CC) = 1.273(2) Å.

Stuttering Thoughts: Negative Self-Referent Thinking Is Less Sensitive to Aversive Outcomes in People with Higher Levels of Depressive Symptoms

PubMed Central

Iijima, Yudai; Takano, Keisuke; Boddez, Yannick; Raes, Filip; Tanno, Yoshihiko

2017-01-01

Learning theories of depression have proposed that depressive cognitions, such as negative thoughts with reference to oneself, can develop through a reinforcement learning mechanism. This negative self-reference is considered to be positively reinforced by rewarding experiences such as genuine support from others after negative self-disclosure, and negatively reinforced by avoidance of potential aversive situations. The learning account additionally predicts that negative self-reference would be maintained by an inability to adjust one’s behavior when negative self-reference no longer leads to such reward. To test this prediction, we designed an adapted version of the reversal-learning task. In this task, participants were reinforced to choose and engage in either negative or positive self-reference by probabilistic economic reward and punishment. Although participants were initially trained to choose negative self-reference, the stimulus-reward contingencies were reversed to prompt a shift toward positive self-reference (Study 1) and a further shift toward negative self-reference (Study 2). Model-based computational analyses showed that depressive symptoms were associated with a low learning rate of negative self-reference, indicating a high level of reward expectancy for negative self-reference even after the contingency reversal. Furthermore, the difficulty in updating outcome predictions of negative self-reference was significantly associated with the extent to which one possesses negative self-images. These results suggest that difficulty in adjusting action-outcome estimates for negative self-reference increases the chance to be faced with negative aspects of self, which may result in depressive symptoms. PMID:28824511

Stuttering Thoughts: Negative Self-Referent Thinking Is Less Sensitive to Aversive Outcomes in People with Higher Levels of Depressive Symptoms.

PubMed

Iijima, Yudai; Takano, Keisuke; Boddez, Yannick; Raes, Filip; Tanno, Yoshihiko

2017-01-01

Learning theories of depression have proposed that depressive cognitions, such as negative thoughts with reference to oneself, can develop through a reinforcement learning mechanism. This negative self-reference is considered to be positively reinforced by rewarding experiences such as genuine support from others after negative self-disclosure, and negatively reinforced by avoidance of potential aversive situations. The learning account additionally predicts that negative self-reference would be maintained by an inability to adjust one's behavior when negative self-reference no longer leads to such reward. To test this prediction, we designed an adapted version of the reversal-learning task. In this task, participants were reinforced to choose and engage in either negative or positive self-reference by probabilistic economic reward and punishment. Although participants were initially trained to choose negative self-reference, the stimulus-reward contingencies were reversed to prompt a shift toward positive self-reference (Study 1) and a further shift toward negative self-reference (Study 2). Model-based computational analyses showed that depressive symptoms were associated with a low learning rate of negative self-reference, indicating a high level of reward expectancy for negative self-reference even after the contingency reversal. Furthermore, the difficulty in updating outcome predictions of negative self-reference was significantly associated with the extent to which one possesses negative self-images. These results suggest that difficulty in adjusting action-outcome estimates for negative self-reference increases the chance to be faced with negative aspects of self, which may result in depressive symptoms.