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Sample records for les colloides radioactifs

  1. Colloidal Phenomena.

    ERIC Educational Resources Information Center

    Russel, William B.; And Others

    1979-01-01

    Described is a graduate level engineering course offered at Princeton University in colloidal phenomena stressing the physical and dynamical side of colloid science. The course outline, reading list, and requirements are presented. (BT)

  2. Hexadecapolar colloids

    PubMed Central

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-01-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously. PMID:26864184

  3. Colloidal polypyrrole

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized aromatic heterocyclic monomer, a stabilizing effective amount of a vinyl pyridine-containing polymer and dopant anions and a method of preparing such polymer compositions are disclosed.

  4. Hexadecapolar colloids

    NASA Astrophysics Data System (ADS)

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-02-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of `colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.

  5. Hexadecapolar colloids.

    PubMed

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M; Chernyshuk, Stanislav B; Smalyukh, Ivan I

    2016-01-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of 'colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously. PMID:26864184

  6. Hexadecapolar Colloids

    DOE PAGESBeta

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-02-11

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and forbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms’ displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. We describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Becausemore » of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and report the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.« less

  7. Topological colloids.

    PubMed

    Senyuk, Bohdan; Liu, Qingkun; He, Sailing; Kamien, Randall D; Kusner, Robert B; Lubensky, Tom C; Smalyukh, Ivan I

    2013-01-10

    Smoke, fog, jelly, paints, milk and shaving cream are common everyday examples of colloids, a type of soft matter consisting of tiny particles dispersed in chemically distinct host media. Being abundant in nature, colloids also find increasingly important applications in science and technology, ranging from direct probing of kinetics in crystals and glasses to fabrication of third-generation quantum-dot solar cells. Because naturally occurring colloids have a shape that is typically determined by minimization of interfacial tension (for example, during phase separation) or faceted crystal growth, their surfaces tend to have minimum-area spherical or topologically equivalent shapes such as prisms and irregular grains (all continuously deformable--homeomorphic--to spheres). Although toroidal DNA condensates and vesicles with different numbers of handles can exist and soft matter defects can be shaped as rings and knots, the role of particle topology in colloidal systems remains unexplored. Here we fabricate and study colloidal particles with different numbers of handles and genus g ranging from 1 to 5. When introduced into a nematic liquid crystal--a fluid made of rod-like molecules that spontaneously align along the so-called 'director'--these particles induce three-dimensional director fields and topological defects dictated by colloidal topology. Whereas electric fields, photothermal melting and laser tweezing cause transformations between configurations of particle-induced structures, three-dimensional nonlinear optical imaging reveals that topological charge is conserved and that the total charge of particle-induced defects always obeys predictions of the Gauss-Bonnet and Poincaré-Hopf index theorems. This allows us to establish and experimentally test the procedure for assignment and summation of topological charges in three-dimensional director fields. Our findings lay the groundwork for new applications of colloids and liquid crystals that range from

  8. Colloidal polyaniline

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized amino-substituted aromatic monomer, a stabilizing effective amount of a random copolymer containing amino-benzene type moieties as side chain constituents, and dopant anions, and a method of preparing such polymer compositions are provided.

  9. Soil colloidal behavior

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recent understanding that organic and inorganic contaminants are often transported via colloidal particles has increased interest in colloid science. The primary importance of colloids in soil science stems from their surface reactivity and charge characteristics. Characterizations of size, shape,...

  10. EDITORIAL: Colloidal suspensions Colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Petukhov, Andrei; Kegel, Willem; van Duijneveldt, Jeroen

    2011-05-01

    Special issue in honour of Henk Lekkerkerker's 65th birthday Professor Henk N W Lekkerkerker is a world-leading authority in the field of experimental and theoretical soft condensed matter. On the occasion of his 65th birthday in the summer of 2011, this special issue celebrates his many contributions to science. Henk Lekkerkerker obtained his undergraduate degree in chemistry at the University of Utrecht (1968) and moved to Calgary where he received his PhD in 1971. He moved to Brussels as a NATO fellow at the Université Libre de Bruxelles and was appointed to an assistant professorship (1974), an associate professorship (1977) and a full professorship (1980) in physical chemistry at the Vrije Universiteit Brussel. In 1985 he returned to The Netherlands to take up a professorship at the Van 't Hoff Laboratory, where he has been ever since. He has received a series of awards during his career, including the Onsager Medal (1999) of the University of Trondheim, the Bakhuys Roozeboom Gold Medal (2003) of the Royal Dutch Academy of Arts and Sciences (KNAW), the ECIS-Rhodia European Colloid and Interface Prize (2003), and the Liquid Matter Prize of the European Physical Society (2008). He was elected a member of KNAW in 1996, was awarded an Academy Chair position in 2005, and has held several visiting lectureships. Henk's work focuses on phase transitions in soft condensed matter, and he has made seminal contributions to both the theoretical and experimental aspects of this field. Here we highlight three major themes running through his work, and a few selected publications. So-called depletion interactions may lead to phase separation in colloid-polymer mixtures, and Henk realised that the partitioning of polymer needs to be taken into account to describe the phase behaviour correctly [1]. Colloidal suspensions can be used as model fluids, with the time- and length-scales involved leading to novel opportunities, notably the direct observation of capillary waves at a

  11. EDITORIAL: Colloidal suspensions Colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Petukhov, Andrei; Kegel, Willem; van Duijneveldt, Jeroen

    2011-05-01

    Special issue in honour of Henk Lekkerkerker's 65th birthday Professor Henk N W Lekkerkerker is a world-leading authority in the field of experimental and theoretical soft condensed matter. On the occasion of his 65th birthday in the summer of 2011, this special issue celebrates his many contributions to science. Henk Lekkerkerker obtained his undergraduate degree in chemistry at the University of Utrecht (1968) and moved to Calgary where he received his PhD in 1971. He moved to Brussels as a NATO fellow at the Université Libre de Bruxelles and was appointed to an assistant professorship (1974), an associate professorship (1977) and a full professorship (1980) in physical chemistry at the Vrije Universiteit Brussel. In 1985 he returned to The Netherlands to take up a professorship at the Van 't Hoff Laboratory, where he has been ever since. He has received a series of awards during his career, including the Onsager Medal (1999) of the University of Trondheim, the Bakhuys Roozeboom Gold Medal (2003) of the Royal Dutch Academy of Arts and Sciences (KNAW), the ECIS-Rhodia European Colloid and Interface Prize (2003), and the Liquid Matter Prize of the European Physical Society (2008). He was elected a member of KNAW in 1996, was awarded an Academy Chair position in 2005, and has held several visiting lectureships. Henk's work focuses on phase transitions in soft condensed matter, and he has made seminal contributions to both the theoretical and experimental aspects of this field. Here we highlight three major themes running through his work, and a few selected publications. So-called depletion interactions may lead to phase separation in colloid-polymer mixtures, and Henk realised that the partitioning of polymer needs to be taken into account to describe the phase behaviour correctly [1]. Colloidal suspensions can be used as model fluids, with the time- and length-scales involved leading to novel opportunities, notably the direct observation of capillary waves at a

  12. Colloidal Dispersions

    NASA Astrophysics Data System (ADS)

    Russel, W. B.; Saville, D. A.; Schowalter, W. R.

    1992-03-01

    The book covers the physical side of colloid science from the individual forces acting between submicron particles suspended in a liquid through the resulting equilibrium and dynamic properties. The relevant forces include Brownian motion, electrostatic repulsion, dispersion attraction, both attraction and repulsion due to soluble polymer, and viscous forces due to relative motion between the particles and the liquid. The balance among Brownian motion and the interparticle forces decides the questions of stability and phase behavior. Imposition of external fields produces complex effects, i.e. electrokinetic phenomena (electric field), sedimentation (gravitational field), diffusion (concentration/chemical potential gradient), and non-Newtonian rheology (shear field). The treatment aims to impart a sound, quantitative understanding based on fundamental theory and experiments with well-characterized model systems. This broad grasp of the fundamentals lends insight and helps to develop the intuitive sense needed to isolate essential features of technological problems and design critical experiments. Some exposure to fluid mechanics, statistical mechanics, and electricity and magnetism is assumed, but each subject is reintroduced in a self-contained manner.

  13. Colloidal Silver Products

    MedlinePlus

    ... can be dangerous to your health. What the Science Says About the Safety and Side Effects of ... homemade and commercial colloidal silver products. What the Science Says About the Effectiveness of Colloidal Silver Scientific ...

  14. What Is a Colloid?

    ERIC Educational Resources Information Center

    Lamb, William G.

    1985-01-01

    Describes the properties of colloids, listing those commonly encountered (such as whipped cream, mayonnaise, and fog). Also presents several experiments using colloids and discusses "Silly Putty," a colloid with viscoelastic properties whose counterintuitive properties result from its mixture of polymers. (DH)

  15. Electrohydrodynamically patterned colloidal crystals

    NASA Technical Reports Server (NTRS)

    Hayward, Ryan C. (Inventor); Poon, Hak F. (Inventor); Xiao, Yi (Inventor); Saville, Dudley A. (Inventor); Aksay, Ilhan A. (Inventor)

    2003-01-01

    A method for assembling patterned crystalline arrays of colloidal particles using ultraviolet illumination of an optically-sensitive semiconducting anode while using the anode to apply an electronic field to the colloidal particles. The ultraviolet illumination increases current density, and consequently, the flow of the colloidal particles. As a result, colloidal particles can be caused to migrate from non-illuminated areas of the anode to illuminated areas of the anode. Selective illumination of the anode can also be used to permanently affix colloidal crystals to illuminated areas of the anode while not affixing them to non-illuminated areas of the anode.

  16. Microfluidic colloid filtration

    PubMed Central

    Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J. C.; Wessling, Matthias

    2016-01-01

    Filtration of natural and colloidal matter is an essential process in today’s water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a “cake layer” – often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level. PMID:26927706

  17. Saturated Zone Colloid Transport

    SciTech Connect

    H. Viswanathan; P. Reimus

    2003-09-05

    Colloid retardation is influenced by the attachment and detachment of colloids from immobile surfaces. This analysis demonstrates the development of parameters necessary to estimate attachment and detachment of colloids and, hence, retardation in both fractured tuff and porous alluvium. Field and experimental data specific to fractured tuff are used for the analysis of colloid retardation in fractured tuff. Experimental data specific to colloid transport in alluvial material from Yucca Mountain as well as bacteriophage field studies in alluvial material, which are thought to be good analogs for colloid transport, are used to estimate attachment and detachment of colloids in the alluvial material. There are no alternative scientific approaches or technical methods for calculating these retardation factors.

  18. Microfluidic colloid filtration.

    PubMed

    Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J C; Wessling, Matthias

    2016-01-01

    Filtration of natural and colloidal matter is an essential process in today's water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a "cake layer" - often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level. PMID:26927706

  19. Microfluidic colloid filtration

    NASA Astrophysics Data System (ADS)

    Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J. C.; Wessling, Matthias

    2016-03-01

    Filtration of natural and colloidal matter is an essential process in today’s water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a “cake layer” - often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level.

  20. Saturated Zone Colloid Transport

    SciTech Connect

    H. S. Viswanathan

    2004-10-07

    This scientific analysis provides retardation factors for colloids transporting in the saturated zone (SZ) and the unsaturated zone (UZ). These retardation factors represent the reversible chemical and physical filtration of colloids in the SZ. The value of the colloid retardation factor, R{sub col} is dependent on several factors, such as colloid size, colloid type, and geochemical conditions (e.g., pH, Eh, and ionic strength). These factors are folded into the distributions of R{sub col} that have been developed from field and experimental data collected under varying geochemical conditions with different colloid types and sizes. Attachment rate constants, k{sub att}, and detachment rate constants, k{sub det}, of colloids to the fracture surface have been measured for the fractured volcanics, and separate R{sub col} uncertainty distributions have been developed for attachment and detachment to clastic material and mineral grains in the alluvium. Radionuclides such as plutonium and americium sorb mostly (90 to 99 percent) irreversibly to colloids (BSC 2004 [DIRS 170025], Section 6.3.3.2). The colloid retardation factors developed in this analysis are needed to simulate the transport of radionuclides that are irreversibly sorbed onto colloids; this transport is discussed in the model report ''Site-Scale Saturated Zone Transport'' (BSC 2004 [DIRS 170036]). Although it is not exclusive to any particular radionuclide release scenario, this scientific analysis especially addresses those scenarios pertaining to evidence from waste-degradation experiments, which indicate that plutonium and americium may be irreversibly attached to colloids for the time scales of interest. A section of this report will also discuss the validity of using microspheres as analogs to colloids in some of the lab and field experiments used to obtain the colloid retardation factors. In addition, a small fraction of colloids travels with the groundwater without any significant retardation

  1. Ring around the colloid

    NASA Astrophysics Data System (ADS)

    Cavallaro, Marcello, Jr.; Gharbi, Mohamed A.; Beller, Daniel A.; Čopar, Simon; Shi, Zheng; Kamien, Randall D.; Yang, Shu; Baumgart, Tobias; Stebe, Kathleen J.

    In this work, we show that Janus washers, genus-one colloids with hybrid anchoring conditions, form topologically required defects in nematic liquid crystals. Experiments under crossed polarizers reveal the defect structure to be a rigid disclination loop confined within the colloid, with an accompanying defect in the liquid crystal. When confined to a homeotropic cell, the resulting colloid-defect ring pair tilts relative to the far field director, in contrast to the behavior of toroidal colloids with purely homeotropic anchoring. We show that this tilting behavior can be reversibly suppressed by the introduction of a spherical colloid into the center of the toroid, creating a new kind of multi-shape colloidal assemblage.

  2. UZ Colloid Transport Model

    SciTech Connect

    M. McGraw

    2000-04-13

    The UZ Colloid Transport model development plan states that the objective of this Analysis/Model Report (AMR) is to document the development of a model for simulating unsaturated colloid transport. This objective includes the following: (1) use of a process level model to evaluate the potential mechanisms for colloid transport at Yucca Mountain; (2) Provide ranges of parameters for significant colloid transport processes to Performance Assessment (PA) for the unsaturated zone (UZ); (3) Provide a basis for development of an abstracted model for use in PA calculations.

  3. Analysis of colloid transport

    SciTech Connect

    Travis, B.J.; Nuttall, H.E.

    1985-12-31

    The population balance methodology is described and applied to the transport and capture of polydispersed colloids in packed columns. The transient model includes particle growth, capture, convective transport, and dispersion. We also follow the dynamic accumulation of captured colloids on the solids. The multidimensional parabolic partial differential equation was solved by a recently enhanced method of characteristics technique. This computational technique minimized numerical dispersion and is computationally very fast. The FORTRAN 77 code ran on a VAX-780 in less than a minute and also runs on an IBM-AT using the Professional FORTRAN compiler. The code was extensively tested against various simplified cases and against analytical models. The packed column experiments by Saltelli et al. were re-analyzed incorporating the experimentally reported size distribution of the colloid feed material. Colloid capture was modeled using a linear size dependent filtration function. The effects of a colloid size dependent filtration factor and various initial colloid size distributions on colloid migration and capture were investigated. Also, we followed the changing colloid size distribution as a function of position in the column. Some simple arguments are made to assess the likelihood of colloid migration at a potential NTS Yucca Mountain waste disposal site. 10 refs., 3 figs., 1 tab.

  4. Interface colloidal robotic manipulator

    DOEpatents

    Aronson, Igor; Snezhko, Oleksiy

    2015-08-04

    A magnetic colloidal system confined at the interface between two immiscible liquids and energized by an alternating magnetic field dynamically self-assembles into localized asters and arrays of asters. The colloidal system exhibits locomotion and shape change. By controlling a small external magnetic field applied parallel to the interface, structures can capture, transport, and position target particles.

  5. Driving magnetic colloidal polymers

    NASA Astrophysics Data System (ADS)

    Dempster, Joshua; Olvera de La Cruz, Monica

    Magnetic colloids are of growing interest for applications such as drug delivery and in vitro tissue growth. Recent experiments have synthesized 1D chains of magnetic colloids into permanent colloidal polymers. We study magnetic colloidal polymers theoretically and computationally under the influence of time-varying external fields and find a rich set of controllable, dynamic conformations. By iterating through a sequence of conformations, these polymers can perform mechanical functions. We discuss possible roles for these polymers beyond those considered for single colloids. This work was supported as part of the Center for Bio-Inspired Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0000989.

  6. Lock and key colloids.

    PubMed

    Sacanna, S; Irvine, W T M; Chaikin, P M; Pine, D J

    2010-03-25

    New functional materials can in principle be created using colloids that self-assemble into a desired structure by means of a programmable recognition and binding scheme. This idea has been explored by attaching 'programmed' DNA strands to nanometre- and micrometre- sized particles and then using DNA hybridization to direct the placement of the particles in the final assembly. Here we demonstrate an alternative recognition mechanism for directing the assembly of composite structures, based on particles with complementary shapes. Our system, which uses Fischer's lock-and-key principle, employs colloidal spheres as keys and monodisperse colloidal particles with a spherical cavity as locks that bind spontaneously and reversibly via the depletion interaction. The lock-and-key binding is specific because it is controlled by how closely the size of a spherical colloidal key particle matches the radius of the spherical cavity of the lock particle. The strength of the binding can be further tuned by adjusting the solution composition or temperature. The composite assemblies have the unique feature of having flexible bonds, allowing us to produce flexible dimeric, trimeric and tetrameric colloidal molecules as well as more complex colloidal polymers. We expect that this lock-and-key recognition mechanism will find wider use as a means of programming and directing colloidal self-assembly. PMID:20336142

  7. NOCHAR Polymers: An Aqueous and Organic Liquid Solidification Process for Cadarache LOR (Liquides Organiques Radioactifs) - 13195

    SciTech Connect

    Vaudey, Claire-Emilie; Renou, Sebastien; Porco, Julien; Kelley, Dennis; Cochaud, Chantal

    2013-07-01

    To handle the Very Low Level Waste (VLLW) and the Low Level Waste (LLW) in France, two options can be considered: the incineration at CENTRACO facility and the disposal facility on ANDRA sites. The waste acceptance in these radwaste routes is dependent upon the adequacy between the waste characteristics (physical chemistry and radiological) and the radwaste route specifications. If the waste characteristics are incompatible with the radwaste route specifications (presence of significant quantities of chlorine, fluorine, organic component etc or/and high activity limits), it is necessary to find an alternative solution that consists of a waste pre-treatment process. In the context of the problematic Cadarache LOR (Liquides Organiques Radioactifs) waste streams, two radioactive scintillation cocktails have to be treated. The first one is composed of organic liquids at 13.1 % (diphenyloxazol, mesitylene, TBP, xylene) and water at 86.9 %. The second one is composed of TBP at 8.6 % and water at 91.4 %. They contain chlorine, fluorine and sulphate and have got alpha/beta/gamma spectra with mass activities equal to some kBq.g{sup -1}. Therefore, tritium is present and creates the second problematic waste stream. As a consequence, in order for disposal acceptance at the ANDRA site, it is necessary to pre-treat the waste. The NOCHAR polymers as an aqueous and organic liquid solidification process seem to be an adequate solution. Indeed, these polymers constitute an important variety of products applied to the treatment of radioactive aqueous and organic liquids (solvent, oil, solvent/oil mixing etc) and sludge through a mechanical and chemical solidification process. For Cadarache LOR, N910 and N960 respectively dedicated to the organic and aqueous liquids solidification are considered. With the N910, the organic waste solidification occurs in two steps. As the organic liquid travels moves through the polymer strands, the strands swell and immobilise the liquid. Then as the

  8. Colloidal pen lithography.

    PubMed

    Xue, Mianqi; Cai, Xiaojing; Chen, Ghenfu

    2015-02-01

    Colloidal pen lithography, a low-cost, high-throughput scanning probe contact printing method, has been developed, which is based on self-assembled colloidal arrays embedded in a soft elastomeric stamp. Patterned protein arrays are demonstrated using this method, with a feature size ranging from 100 nm to several micrometers. A brief study into the specificity reorganization of protein gives evidence for the feasibility of this method for writing protein chips. PMID:25288364

  9. Spherical colloidal photonic crystals.

    PubMed

    Zhao, Yuanjin; Shang, Luoran; Cheng, Yao; Gu, Zhongze

    2014-12-16

    CONSPECTUS: Colloidal photonic crystals (PhCs), periodically arranged monodisperse nanoparticles, have emerged as one of the most promising materials for light manipulation because of their photonic band gaps (PBGs), which affect photons in a manner similar to the effect of semiconductor energy band gaps on electrons. The PBGs arise due to the periodic modulation of the refractive index between the building nanoparticles and the surrounding medium in space with subwavelength period. This leads to light with certain wavelengths or frequencies located in the PBG being prohibited from propagating. Because of this special property, the fabrication and application of colloidal PhCs have attracted increasing interest from researchers. The most simple and economical method for fabrication of colloidal PhCs is the bottom-up approach of nanoparticle self-assembly. Common colloidal PhCs from this approach in nature are gem opals, which are made from the ordered assembly and deposition of spherical silica nanoparticles after years of siliceous sedimentation and compression. Besides naturally occurring opals, a variety of manmade colloidal PhCs with thin film or bulk morphology have also been developed. In principle, because of the effect of Bragg diffraction, these PhC materials show different structural colors when observed from different angles, resulting in brilliant colors and important applications. However, this angle dependence is disadvantageous for the construction of some optical materials and devices in which wide viewing angles are desired. Recently, a series of colloidal PhC materials with spherical macroscopic morphology have been created. Because of their spherical symmetry, the PBGs of spherical colloidal PhCs are independent of rotation under illumination of the surface at a fixed incident angle of the light, broadening the perspective of their applications. Based on droplet templates containing colloidal nanoparticles, these spherical colloidal PhCs can be

  10. Viscosity of colloidal suspensions

    SciTech Connect

    Cohen, E.G.D.; Schepper, I.M. de

    1995-12-31

    Simple expressions are given for the effective Newtonian viscosity as a function of concentration as well as for the effective visco-elastic response as a function of concentration and imposed frequency, of monodisperse neutral colloidal suspensions over the entire fluid range. The basic physical mechanisms underlying these formulae are discussed. The agreement with existing experiments is very good.

  11. Les jeux de hasard chez les enfants et les adolescents

    PubMed Central

    Gupta, Rina; Pinzon, Jorge L

    2012-01-01

    RÉSUMÉ Même si, au Canada, les mineurs n’ont pas le droit de jouer à des jeux de hasard légalisés, les adolescents participent souvent à des jeux de hasard soit légalisés (produits de loterie, casino, terminaux de jeux vidéo), soit autonomes (jeux de cartes, paris sportifs, dés) à la maison et en milieu scolaire. Chez les adultes, le taux de prévalence de dépendance aux jeux de hasard au cours de la vie se situe entre 1 % et 2 %. D’après les données existantes, la prévalence chez les adolescents serait de deux à quatre fois plus élevée. On ne sait pas grand-chose des facteurs de risque d’apparition et de perpétuation d’une dépendance pathologique aux jeux de hasard. Le présent document de principes vise à informer les pédiatres, les médecins de famille et les autres professionnels de la santé des connaissances émergentes sur les jeux de hasard pendant l’enfance et l’adolescence et du risque de conséquences graves qui s’y rattachent. On y exhorte également les gouvernements fédéral, provinciaux et territoriaux à inclure cette question dans leur programme et à tenir compte des facteurs sociopolitiques associés aux jeux de hasard.

  12. COLLOIDS. Colloidal matter: Packing, geometry, and entropy.

    PubMed

    Manoharan, Vinothan N

    2015-08-28

    Colloidal particles with well-controlled shapes and interactions are an ideal experimental system for exploring how matter organizes itself. Like atoms and molecules, these particles form bulk phases such as liquids and crystals. But they are more than just crude analogs of atoms; they are a form of matter in their own right, with complex and interesting collective behavior not seen at the atomic scale. Their behavior is affected by geometrical or topological constraints, such as curved surfaces or the shapes of the particles. Because the interactions between the particles are often short-ranged, we can understand the effects of these constraints using geometrical concepts such as packing. The geometrical viewpoint gives us a window into how entropy affects not only the structure of matter, but also the dynamics of how it forms. PMID:26315444

  13. Colloidal Double Quantum Dots

    PubMed Central

    2016-01-01

    Conspectus Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single

  14. Colloidal Double Quantum Dots.

    PubMed

    Teitelboim, Ayelet; Meir, Noga; Kazes, Miri; Oron, Dan

    2016-05-17

    Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon

  15. Colloid migration in fractured media

    SciTech Connect

    Hunt, J.R. . Dept. of Civil Engineering)

    1989-09-15

    Field studies at the Nevada Test Site by researchers at Lawrence Livermore National Laboratory have demonstrated that radionuclides are being transported by colloidal material suspended in groundwater. This observation is counter to most predictions from contaminant transport models because the models assume adsorbed species are immobile. The purpose of this research is to quantify the transport processes for colloidal materials and develop the mechanistic understanding necessary to predict radionuclide transport in fractured media. There were three areas of investigation during this year that have addressed these issues: chemical control of colloid deposition on clean mineral surfaces, colloid accumulation on fracture surfaces, and the influence of deposited colloids on colloid and tracer migration. 7 refs.

  16. Magnetofluidic Tweezing of Nonmagnetic Colloids.

    PubMed

    Timonen, Jaakko V I; Demirörs, Ahmet F; Grzybowski, Bartosz A

    2016-05-01

    Magnetofluidic tweezing based on negative magnetophoresis and microfabricated core-shell magnetic microtips allows controlled on-demand assembly of colloids and microparticles into various static and dynamic structures such as colloidal crystals (as shown for 3.2 μm silica particles). PMID:26990182

  17. Colloidal aggregation in polymer blends.

    PubMed

    Benhamou, M; Ridouane, H; Hachem, E-K; Derouiche, A; Rahmoune, M

    2005-06-22

    We consider here a low-density assembly of colloidal particles immersed in a critical polymer mixture of two chemically incompatible polymers. We assume that, close to the critical point of the free mixture, the colloids prefer to be surrounded by one polymer (critical adsorption). As result, one is assisted to a reversible colloidal aggregation in the nonpreferred phase, due the existence of a long-range attractive Casimir force between particles. This aggregation is a phase transition driving the colloidal system from dilute to dense phases, as the usual gas-liquid transition. We are interested in a quantitative investigation of the phase diagram of the immersed colloids. We suppose that the positions of particles are disordered, and the disorder is quenched and follows a Gaussian distribution. To apprehend the problem, use is made of the standard phi(4) theory, where the field phi represents the composition fluctuation (order parameter), combined with the standard cumulant method. First, we derive the expression of the effective free energy of colloids and show that this is of Flory-Huggins type. Second, we find that the interaction parameter u between colloids is simply a linear combination of the isotherm compressibility and specific heat of the free mixture. Third, with the help of the derived effective free energy, we determine the complete shape of the phase diagram (binodal and spinodal) in the (Psi,u) plane, with Psi as the volume fraction of immersed colloids. The continuous "gas-liquid" transition occurs at some critical point K of coordinates (Psi(c) = 0.5,u(c) = 2). Finally, we emphasize that the present work is a natural extension of that, relative to simple liquid mixtures incorporating colloids. PMID:16035822

  18. Colloids in Acute Burn Resuscitation.

    PubMed

    Cartotto, Robert; Greenhalgh, David

    2016-10-01

    Colloids have been used in varying capacities throughout the history of formula-based burn resuscitation. There is sound experimental evidence that demonstrates colloids' ability to improve intravascular colloid osmotic pressure, expand intravascular volume, reduce resuscitation requirements, and limit edema in unburned tissue following a major burn. Fresh frozen plasma appears to be a useful and effective immediate burn resuscitation fluid but its benefits must be weighed against its costs, and risks of viral transmission and acute lung injury. Albumin, in contrast, is less expensive and safer and has demonstrated ability to reduce resuscitation requirements and possibly limit edema-related morbidity. PMID:27600123

  19. Two-dimensional dipolar nematic colloidal crystals.

    PubMed

    Skarabot, M; Ravnik, M; Zumer, S; Tkalec, U; Poberaj, I; Babic, D; Osterman, N; Musevic, I

    2007-11-01

    We study the interactions and directed assembly of dipolar nematic colloidal particles in planar nematic cells using laser tweezers. The binding energies for two stable configurations of a colloidal pair with homeotropic surface alignment are determined. It is shown that the orientation of the dipolar colloidal particle can efficiently be controlled and changed by locally quenching the nematic liquid crystal from the laser-induced isotropic phase. The interaction of a single colloidal particle with a single colloidal chain is determined and the interactions between pairs of colloidal chains are studied. We demonstrate that dipolar colloidal chains self-assemble into the two-dimensional (2D) dipolar nematic colloidal crystals. An odd-even effect is observed with increasing number of colloidal chains forming the 2D colloidal crystal. PMID:18233658

  20. Colloid labelled with radionuclide and method

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1990-01-01

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints.

  1. Method of making colloid labeled with radionuclide

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1991-01-01

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints.

  2. Colloid labelled with radionuclide and method

    DOEpatents

    Atcher, R.W.; Hines, J.J.

    1990-11-13

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints. No Drawings

  3. Emergent behavior in active colloids

    NASA Astrophysics Data System (ADS)

    Zöttl, Andreas; Stark, Holger

    2016-06-01

    Active colloids are microscopic particles, which self-propel through viscous fluids by converting energy extracted from their environment into directed motion. We first explain how artificial microswimmers move forward by generating near-surface flow fields via self-phoresis or the self-induced Marangoni effect. We then discuss generic features of the dynamics of single active colloids in bulk and in confinement, as well as in the presence of gravity, field gradients, and fluid flow. In the third section, we review the emergent collective behavior of active colloidal suspensions, focusing on their structural and dynamic properties. After summarizing experimental observations, we give an overview of the progress in modeling collectively moving active colloids. While active Brownian particles are heavily used to study collective dynamics on large scales, more advanced methods are necessary to explore the importance of hydrodynamic and phoretic particle interactions. Finally, the relevant physical approaches to quantify the emergent collective behavior are presented.

  4. Colloidal Suspended Iron in Rivers

    NASA Astrophysics Data System (ADS)

    Shiller, A. M.

    2009-12-01

    Iron is transported in most rivers predominantly in two physical-chemical forms: a) organic complexes of Fe(III) and b) crystalline or poorly-ordered suspended phases frequently dominated by iron oxides. These two forms have different properties with respect to transport, bioavailability, and sorption. For the suspended phase iron, the fraction in the colloidal size range may be especially important given the interactions of ferric oxide surfaces with dissolved metal ions and organic compounds. We report the concentrations of colloidal (20 - 450 nm) suspended particulate iron in a wide variety of rivers. Goals of this effort are to ascertain the ubiquity of this material and also to examine other fluvial variables as indicators of its sources and nature. This, in turn, should lead to an understanding of how landscape/climate change could affect fluvial colloidal suspended iron. Possible sources of suspended colloidal iron include ferric oxides precipitated from the oxidation of ferrous iron derived from reducing environments, alumino-silicates derived from physical weathering, products of chemical weathering, and flushing of soils. We observe most commonly that increasing concentrations of colloidal suspended iron follow indicators of reducing sources (e.g., higher dissolved Mn and Ce anomaly close to 1), suggesting that this material is dominated by freshly precipitated iron oxides. Only in glacial watersheds do we find colloidal suspended iron instead correlating with colloidal suspended Si, and hence, likely to be associated with alumino-silicates. We also observe that colloidal suspended iron correlates well with the UV absorbance associated with this size range (20 - 450 nm).

  5. Re-shaping colloidal clusters

    NASA Astrophysics Data System (ADS)

    Kraft, Daniela

    2015-03-01

    Controlling the geometry and yield of anisotropic colloidal particles remains a challenge for hierarchical self-assembly. I will discuss a synthetic strategy for fabricating colloidal clusters by creating order in randomly aggregated polymer spheres using surface tension and geometrical constraints. The technique can be extended to a variety of charge-stabilized polymer spheres and offers control over the cluster size distribution. VENI grant from The Netherlands Organization for Scientific Research (NWO).

  6. Mechanical Failure in Colloidal Gels

    NASA Astrophysics Data System (ADS)

    Kodger, Thomas Edward

    When colloidal particles in a dispersion are made attractive, they aggregate into fractal clusters which grow to form a space-spanning network, or gel, even at low volume fractions. These gels are crucial to the rheological behavior of many personal care, food products and dispersion-based paints. The mechanical stability of these products relies on the stability of the colloidal gel network which acts as a scaffold to provide these products with desired mechanical properties and to prevent gravitational sedimentation of the dispersed components. Understanding the mechanical stability of such colloidal gels is thus of crucial importance to predict and control the properties of many soft solids. Once a colloidal gel forms, the heterogeneous structure bonded through weak physical interactions, is immediately subject to body forces, such as gravity, surface forces, such as adhesion to a container walls and shear forces; the interplay of these forces acting on the gel determines its stability. Even in the absence of external stresses, colloidal gels undergo internal rearrangements within the network that may cause the network structure to evolve gradually, in processes known as aging or coarsening or fail catastrophically, in a mechanical instability known as syneresis. Studying gel stability in the laboratory requires model colloidal system which may be tuned to eliminate these body or endogenous forces systematically. Using existing chemistry, I developed several systems to study delayed yielding by eliminating gravitational stresses through density matching and cyclic heating to induce attraction; and to study syneresis by eliminating adhesion to the container walls, altering the contact forces between colloids, and again, inducing gelation through heating. These results elucidate the varied yet concomitant mechanisms by which colloidal gels may locally or globally yield, but then reform due to the nature of the physical, or non-covalent, interactions which form

  7. Aggregation of Heterogeneously Charged Colloids.

    PubMed

    Dempster, Joshua M; Olvera de la Cruz, Monica

    2016-06-28

    Patchy colloids are attractive as programmable building blocks for metamaterials. Inverse patchy colloids, in which a charged surface is decorated with patches of the opposite charge, are additionally noteworthy as models for heterogeneously charged biological materials such as proteins. We study the phases and aggregation behavior of a single charged patch in an oppositely charged colloid with a single-site model. This single-patch inverse patchy colloid model shows a large number of phases when varying patch size. For large patch sizes we find ferroelectric crystals, while small patch sizes produce cross-linked gels. Intermediate values produce monodisperse clusters and unusual worm structures that preserve finite ratios of area to volume. The polarization observed at large patch sizes is robust under extreme disorder in patch size and shape. We examine phase-temperature dependence and coexistence curves and find that large patch sizes produce polarized liquids, in contrast to mean-field predictions. Finally, we introduce small numbers of unpatched charged colloids. These can either suppress or encourage aggregation depending on their concentration and the size of the patches on the patched colloids. These effects can be exploited to control aggregation and to measure effective patch size. PMID:27253725

  8. Dielectrophoresis force of colloidal nanoparticles

    NASA Astrophysics Data System (ADS)

    Huang, Hao; Ou-Yang, Daniel

    Dielectrophoresis (DEP) is the motion of a polarizable colloidal particle in a non­uniform electric field. The magnitude of the DEP force is known to be proportional to the gradient of E2. The DEP force also depends on the relative polarizability of the particle to that of the surrounding medium. Due to its ease of use, DEP has been proposed for a variety of applications to manipulate colloidal particles in a microfluidic setting. However, accurate measurements of the DEP force on colloidal nanoparticles are lacking. A new method is proposed to measure accurately the DEP potential force of colloidal nanoparticles by using confocal fluorescence imaging to determine the density distributions of dilute colloidal nanoparticle in a DEP potential force field. The DEP potential field can be calculated from the particle density distributions since the spatial distribution of the particle number density follows the Boltzmann distribution of the DEP potential energy. The validity of the measured DEP force is tested by examining the force as a function of the E field strength and particle size. The classic Maxwell­Wagner­O'Konski is found to be inadequate to fully describe the frequency dependence of the DEP force. NSF 0928299, Emulsion Polymer Institute, Department of Physics of Lehigh University.

  9. PREFACE: Colloidal and molecular electro-optics Colloidal and molecular electro-optics

    NASA Astrophysics Data System (ADS)

    Palberg, Thomas; Löwen, Hartmut

    2010-12-01

    exciting trends and earn the interest of a good fraction of contemporary soft matter scientists. Note1 http://www.elopto2010.fb08.uni-mainz.de Note2 http://www.sfb-tr6.de References [1] Weinberger P 2008 John Kerr and his effects found in 1877 and 1878 Phil. Mag. Lett. 88 897-907 [2] Benoit H 1948 Calcul de l'écart quadratique moyen entre les extrémités de diverses chaînes moléculaires de type usuel J. Polym. Sci. 3 376-87 [3] Benoit H 1949 Sur un dispositif de mesure de l'effet Kerr par impulsions electriques isoles Comptes Rendus 228 1716-8 [4] Benoit H 1951 Contribution a l'etude de l'effet Kerr presente par les solutions diluees de macromolecules rigide Ann. Phys. 6 561-609 Colloidal and molecular electro-optics contents Electric dichroism transients of aqueous solutions of DNA J A Bertolotto, G M Corral, E M Farias de La Torre and G B Roston The role of effective charges in the electrophoresis of highly charged colloids Apratim Chatterji and Jürgen Horbach Nonlinear response of the electric birefringence of polyelectrolyte solutions J L Déjardin and J M Martinez Kerr constant of multi-subunit particles and semiflexible, wormlike chains J García de la Torre, F G Díaz Baños and H E Pérez Sánchez Self-assembling electroactive hydrogels for flexible display technology Scott L Jones, Kok Hou Wong, Pall Thordarson and François Ladouceur Electrooptical effects in colloid systems subjected to short pulses of strong electric field S A Klemeshev, M P Petrov, A A Trusov and A V Voitylov The effect of ionic strength on electrical properties of polyelectrolyte multilayers on colloidal particles V Milkova and Ts Radeva Charge transport and current in non-polar liquids Kristiaan Neyts, Filip Beunis, Filip Strubbe, Matthias Marescaux, Bart Verboven, Masoumeh Karvar and Alwin Verschueren Ionic concentration- and pH-dependent electrophoretic mobility as studied by single colloid electrophoresis I Semenov, P Papadopoulos, G Stober and F Kremer Effect of magnesium ions and

  10. Crack formation and prevention in colloidal drops.

    PubMed

    Kim, Jin Young; Cho, Kun; Ryu, Seul-A; Kim, So Youn; Weon, Byung Mook

    2015-01-01

    Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles. PMID:26279317

  11. Crack formation and prevention in colloidal drops

    NASA Astrophysics Data System (ADS)

    Kim, Jin Young; Cho, Kun; Ryu, Seul-A.; Kim, So Youn; Weon, Byung Mook

    2015-08-01

    Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles.

  12. Crack formation and prevention in colloidal drops

    PubMed Central

    Kim, Jin Young; Cho, Kun; Ryu, Seul-a; Kim, So Youn; Weon, Byung Mook

    2015-01-01

    Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles. PMID:26279317

  13. Entropy favours open colloidal lattices

    NASA Astrophysics Data System (ADS)

    Mao, Xiaoming; Chen, Qian; Granick, Steve

    2013-03-01

    Burgeoning experimental and simulation activity seeks to understand the existence of self-assembled colloidal structures that are not close-packed. Here we describe an analytical theory based on lattice dynamics and supported by experiments that reveals the fundamental role entropy can play in stabilizing open lattices. The entropy we consider is associated with the rotational and vibrational modes unique to colloids interacting through extended attractive patches. The theory makes predictions of the implied temperature, pressure and patch-size dependence of the phase diagram of open and close-packed structures. More generally, it provides guidance for the conditions at which targeted patchy colloidal assemblies in two and three dimensions are stable, thus overcoming the difficulty in exploring by experiment or simulation the full range of conceivable parameters.

  14. Doped colloidal artificial spin ice

    NASA Astrophysics Data System (ADS)

    Libál, A.; Olson Reichhardt, C. J.; Reichhardt, C.

    2015-10-01

    We examine square and kagome artificial spin ice for colloids confined in arrays of double-well traps. Unlike magnetic artificial spin ices, colloidal and vortex artificial spin ice realizations allow creation of doping sites through double occupation of individual traps. We find that doping square and kagome ice geometries produces opposite effects. For square ice, doping creates local excitations in the ground state configuration that produce a local melting effect as the temperature is raised. In contrast, the kagome ice ground state can absorb the doping charge without generating non-ground-state excitations, while at elevated temperatures the hopping of individual colloids is suppressed near the doping sites. These results indicate that in the square ice, doping adds degeneracy to the ordered ground state and creates local weak spots, while in the kagome ice, which has a highly degenerate ground state, doping locally decreases the degeneracy and creates local hard regions.

  15. Polymeric stabilization of colloidal asphaltenes

    NASA Astrophysics Data System (ADS)

    Hashmi, Sara; Firoozabadi, Abbas

    2010-03-01

    Asphaltenes, the heaviest component of crude oil, cause many problems in petroleum extraction and recovery. Operationally defined as insoluble in long chain alkanes but soluble in toluene, asphaltenes have been described by bulk thermodynamic models such as the Flory-Huggins theory. However, bulk models work well only for asphaltenes in good solvents. Characterization of asphaltenes in poor solvents remains elusive: molecular scale asphaltenes readily aggregate to the colloidal scale and become highly unstable in solution. We investigate the ability of polymers to stabilize colloidal asphaltene suspensions in heptane. In the absence of added polymer, sedimentation measurements reveal dynamics reminiscent of collapsing gels. Adding polymers to colloidal asphaltene suspensions can delay the characteristic sedimentation time by orders of magnitude. Light scattering results suggest that the mechanism of stabilization may be related to a decrease in both particle size and polydispersity as a function of added polymer.

  16. Gel transitions in colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Bergenholtz, J.; Fuchs, M.

    1999-12-01

    The idealized mode-coupling theory (MCT) is applied to colloidal systems interacting via short-range attractive interactions of Yukawa form. At low temperatures, MCT predicts a slowing down of the local dynamics and ergodicity-breaking transitions. The non-ergodicity transitions share many features with the colloidal gel transition, and are proposed to be the source of gelation in colloidal systems. Previous calculations of the phase diagram are complemented with additional data for shorter ranges of the attractive interaction, showing that the path of the non-ergodicity transition line is then unimpeded by the gas-liquid critical curve at low temperatures. Particular attention is given to the critical non-ergodicity parameters; this is motivated by recent experimental measurements. An asymptotic model is developed, valid for dilute systems of spheres interacting via strong short-range attractions, and is shown to capture all aspects of the low-temperature MCT non-ergodicity transitions.

  17. Colloidal particle assembly using piezoelectric inkjet printing of polystyrene colloidal ink formulations.

    PubMed

    Kwon, Younghwan

    2014-10-01

    We report the feasibility of piezoelectric inkjet printing of colloidal dispersion inks for geometrical patterning to arrange colloids in desired locations. Polystyrene colloid (dia. = 3 μm) inks dispersed with thermally curable binder in organic solvents are explored for fundamental study on colloidal patterning. The inkjet printability of colloidal inks is systematically investigated with different ink formulations and inkjet process variables. In addition, in order to maintain the structural stability of colloidal patterns fabricated on the substrate from externally applied forces such as mechanical, chemical and thermal stimuli, thermally curable binder was formulated into the colloidal ink formulations. PMID:25942838

  18. Colloid cyst: a case report.

    PubMed

    Grasu, Beatrice L; Alberico, Anthony M

    2011-01-01

    Colloid cysts are a rare clinical finding with a unique clinical presentation: non-specific paroxysmal headaches. The current recommended treatment is microsurgery, which poses the greatest risk to the patient but allows complete removal of the cyst to prevent recurrence. A 41-year old man presented with a colloid cyst located in the foramen of Monro causing obstructive hydrocephalus. He had paroxysmal headaches and memory and personality changes. Transcortical transventricle microsurgery was performed to remove the entire cyst. A temporary shunt was placed to prevent post-operative hydrocephalus. Normal neurological function returned upon cyst removal. PMID:22034805

  19. Synthesis and Characterization of Supramolecular Colloids.

    PubMed

    Vilanova, Neus; De Feijter, Isja; Voets, Ilja K

    2016-01-01

    Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer. PMID:27168201

  20. Colloids and Nucleation

    NASA Technical Reports Server (NTRS)

    Ackerson, Bruce

    1997-01-01

    The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range

  1. Colloid characterization and quantification in groundwater samples

    SciTech Connect

    K. Stephen Kung

    2000-06-01

    This report describes the work conducted at Los Alamos National Laboratory for studying the groundwater colloids for the Yucca Mountain Project in conjunction with the Hydrologic Resources Management Program (HRMP) and the Underground Test Area (UGTA) Project. Colloidal particle size distributions and total particle concentration in groundwater samples are quantified and characterized. Colloid materials from cavity waters collected near underground nuclear explosion sites by HRMP field sampling personnel at the Nevada Test Site (NTS) were quantified. Selected colloid samples were further characterized by electron microscope to evaluate the colloid shapes, elemental compositions, and mineral phases. The authors have evaluated the colloid size and concentration in the natural groundwater sample that was collected from the ER-20-5 well and stored in a 50-gallon (about 200-liter) barrel for several months. This groundwater sample was studied because HRMP personnel have identified trace levels of radionuclides in the water sample. Colloid results show that even though the water sample had filtered through a series of Millipore filters, high-colloid concentrations were identified in all unfiltered and filtered samples. They had studied the samples that were diluted with distilled water and found that diluted samples contained more colloids than the undiluted ones. These results imply that colloids are probably not stable during the storage conditions. Furthermore, results demonstrate that undesired colloids have been introduced into the samples during the storage, filtration, and dilution processes. They have evaluated possible sources of colloid contamination associated with sample collection, filtrating, storage, and analyses of natural groundwaters. The effects of container types and sample storage time on colloid size distribution and total concentration were studied to evaluate colloid stability by using J13 groundwater. The data suggests that groundwater samples

  2. Microbial effects on colloidal agglomeration

    SciTech Connect

    Hersman, L.

    1995-11-01

    Colloidal particles are known to enhance the transport of radioactive metals through soil and rock systems. This study was performed to determine if a soil microorganism, isolated from the surface samples collected at Yucca Mountain, NV, could affect the colloidal properties of day particles. The agglomeration of a Wyoming bentonite clay in a sterile uninoculated microbial growth medium was compared to the agglomeration in the medium inoculated with a Pseudomonas sp. In a second experiment, microorganisms were cultured in the succinate medium for 50 h and removed by centrifugation. The agglomeration of the clay in this spent was compared to sterile uninoculated medium. In both experiments, the agglomeration of the clay was greater than that of the sterile, uninoculated control. Based on these results, which indicate that this microorganism enhanced the agglomeration of the bentonite clay, it is possible to say that in the presence of microorganisms colloidal movement through a rock matrix could be reduced because of an overall increase in the size of colloidal particle agglomerates. 32 refs.

  3. Solid colloidal optical wavelength filter

    DOEpatents

    Alvarez, Joseph L.

    1992-01-01

    A solid colloidal optical wavelength filter includes a suspension of spheal particles dispersed in a coagulable medium such as a setting plastic. The filter is formed by suspending spherical particles in a coagulable medium; agitating the particles and coagulable medium to produce an emulsion of particles suspended in the coagulable medium; and allowing the coagulable medium and suspended emulsion of particles to cool.

  4. Sonochemical synthesis of iron colloids

    SciTech Connect

    Suslick, K.S.; Fang, M.; Hyeon, T.

    1996-11-27

    We present here a new method for the preparation of stable ferromagnetic colloids of iron using high-intensity ultrasound to sonochemically decompose volatile organometallic compounds. These colloids have narrow size distributions centered at a few nanometers and are found to be superparamagnetic. In conclusion, a simple synthetic method has been discovered to produce nanosized iron colloid using high-intensity ultrasound. Nanometer iron particles dispersed in polyvinylpyrrolidone (PVP) matrix or stabilized by adsorption of oleic acid have been synthesized by sonochemical decomposition of Fe(CO){sub 5}. Transmission electron micrographs show that the iron particles have a relatively narrow range in size from 3 to 8 nm for polyvinylpyrrolidone, while oleic acid gives an even more uniform distribution at 8 nm. magnetic measurements revealed that these nanometer iron particles are superparamagnetic with a saturation magnetization of 101 emu/g (Fe) at 290 K. This work is easily extended to colloids of other metals and to alloys of two or more metals, simply by using multiple volatile precursors. 29 refs., 4 figs.

  5. Physics of Colloids in Space

    NASA Technical Reports Server (NTRS)

    Weitz, Dave; Weeks, Eric; Gasser, Urs; Dinsmore, Tony; Mawley, Suliana; Segre, Phil; Cipelletti, Lucia

    2000-01-01

    This talk will present recent results from ground-based research to support the "Physics of Colloids in Space" project which is scheduled to fly in the ISS approximately one year from now. In addition, results supporting future planned flights will be discussed.

  6. Dynamics of evaporative colloidal patterning

    NASA Astrophysics Data System (ADS)

    Kaplan, C. Nadir; Wu, Ning; Mandre, Shreyas; Aizenberg, Joanna; Mahadevan, L.

    2015-09-01

    Drying suspensions often leave behind complex patterns of particulates, as might be seen in the coffee stains on a table. Here, we consider the dynamics of periodic band or uniform solid film formation on a vertical plate suspended partially in a drying colloidal solution. Direct observations allow us to visualize the dynamics of band and film deposition, where both are made of multiple layers of close packed particles. We further see that there is a transition between banding and filming when the colloidal concentration is varied. A minimal theory of the liquid meniscus motion along the plate reveals the dynamics of the banding and its transition to the filming as a function of the ratio of deposition and evaporation rates. We also provide a complementary multiphase model of colloids dissolved in the liquid, which couples the inhomogeneous evaporation at the evolving meniscus to the fluid and particulate flows and the transition from a dilute suspension to a porous plug. This allows us to determine the concentration dependence of the bandwidth and the deposition rate. Together, our findings allow for the control of drying-induced patterning as a function of the colloidal concentration and evaporation rate.

  7. Towards Structural Complexity with Colloids

    NASA Astrophysics Data System (ADS)

    Engel, Michael

    2012-02-01

    Colloids rather easily assemble into simple crystal structures like the face-centered cubic lattice or the body-centered cubic lattice. More complex phases are harder to achieve, but have recently been reported using a number of approaches. Yet, assembling complex structures often results from trial-and-error and is not well understood. In this presentation, we show how novel crystals, quasicrystals, and liquid crystals can be achieved with colloidal building blocks by varying the interactions and the shapes of the building blocks. Using computer simulations, we demonstrate the formation of unusually ordered phases both with isotropic pair potentials, as well as with facetted shapes like polyhedra. We describe new tools we have developed to perform complex structural analysis on simulated systems and show how they may be used to analyze real space images from colloid experiments. We also compare the assembled structures with densest packings of the building blocks and show that good packings can often be distinct from what is observed to assemble from the disordered state. This suggests that dense packings may not be illustrative of what is achievable in colloid experiments.

  8. Effective Forces Between Colloidal Particles

    NASA Technical Reports Server (NTRS)

    Tehver, Riina; Banavar, Jayanth R.; Koplik, Joel

    1999-01-01

    Colloidal suspensions have proven to be excellent model systems for the study of condensed matter and its phase behavior. Many of the properties of colloidal suspensions can be investigated with a systematic variation of the characteristics of the systems and, in addition, the energy, length and time scales associated with them allow for experimental probing of otherwise inaccessible regimes. The latter property also makes colloidal systems vulnerable to external influences such as gravity. Experiments performed in micro-ravity by Chaikin and Russell have been invaluable in extracting the true behavior of the systems without an external field. Weitz and Pusey intend to use mixtures of colloidal particles with additives such as polymers to induce aggregation and form weak, tenuous, highly disordered fractal structures that would be stable in the absence of gravitational forces. When dispersed in a polarizable medium, colloidal particles can ionize, emitting counterions into the solution. The standard interaction potential in these charged colloidal suspensions was first obtained by Derjaguin, Landau, Verwey and Overbeek. The DLVO potential is obtained in the mean-field linearized Poisson-Boltzmann approximation and thus has limited applicability. For more precise calculations, we have used ab initio density functional theory. In our model, colloidal particles are charged hard spheres, the counterions are described by a continuum density field and the solvent is treated as a homogeneous medium with a specified dielectric constant. We calculate the effective forces between charged colloidal particles by integrating over the solvent and counterion degrees of freedom, taking into account the direct interactions between the particles as well as particle-counterion, counterion-counterion Coulomb, counterion entropic and correlation contributions. We obtain the effective interaction potential between charged colloidal particles in different configurations. We evaluate two

  9. Diffusion dans les liquides

    NASA Astrophysics Data System (ADS)

    Dianoux, A. J.

    2003-09-01

    Après une brève introduction qui rappelle les concepts détaillés dans le cours de M. Bée, nous présentons un aperçu de trois de nos travaux sur l'étude de la diffusion. Tout d'abord la dynamique de l'eau, dans son état normal ou surfondu, révèle la complexité apportée par le réseau de liaisons hydrogène. Ensuite l'effet du confinement sur la dynamique de l'eau sera étudié dans le cas de la membrane Nafion. Enfin la diffusion dans les phases nématique et smectique A d'un cristal liquide permet d'obtenir la valeur du potentiel qui maintient les couches dans la phase smectique.

  10. Distorted colloidal arrays as designed template

    NASA Astrophysics Data System (ADS)

    Yu, Ye; Zhou, Ziwei; Möhwald, Helmuth; Ai, Bin; Zhao, Zhiyuan; Ye, Shunsheng; Zhang, Gang

    2015-01-01

    In this paper, a novel type of colloidal template with broken symmetry was generated using commercial, inductively coupled plasma reactive ion etching (ICP-RIE). With proper but simple treatment, the traditional symmetric non-close-packed colloidal template evolves into an elliptical profile with high uniformity. This unique feature can add flexibility to colloidal lithography and/or other lithography techniques using colloidal particles as building blocks to fabricate nano-/micro-structures with broken symmetry. Beyond that the novel colloidal template we developed possesses on-site tunability, i.e. the transformability from a symmetric into an asymmetric template. Sandwich-type particles with eccentric features were fabricated utilizing this tunable template. This distinguishing feature will provide the possibility to fabricate structures with unique asymmetric features using one set of colloidal template, providing flexibility and broad tunability to enable nano-/micro-structure fabrication with colloidal templates.

  11. Glass/Jamming Transition in Colloidal Aggregation

    NASA Technical Reports Server (NTRS)

    Segre, Philip N.; Prasad, Vikram; Weitz, David A.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    We have studied colloidal aggregation in a model colloid plus polymer system with short-range attractive interactions. By varying the colloid concentration and the strength of the attraction, we explored regions where the equilibrium phase is expected to consist of colloidal crystallites in coexistance with colloidal gas (i.e. monomers). This occurs for moderate values of the potential depth, U approximately equal to 2-5 kT. Crystallization was not always observed. Rather, over an extended sub-region two new metastable phases appear, one fluid-like and one solid-like. These were examined in detail with light scattering and microscopy techniques. Both phases consist of a near uniform distribution of small irregular shaped clusters of colloidal particles. The dynamical and structural characteristics of the ergodic-nonergodic transition between the two phases share much in common with the colloidal hard sphere glass transition.

  12. Colloid particle size-dependent dispersivity

    NASA Astrophysics Data System (ADS)

    Chrysikopoulos, C. V.; Katzourakis, V. E.

    2014-12-01

    Laboratory and field studies have demonstrated that dispersion coefficients evaluated by fitting advection-dispersion transport models to nonreactive tracer breakthrough curves do not adequately describe colloid transport under the same flow field conditions. Here an extensive laboratory study was undertaken to assess whether the dispersivity, which traditionally has been considered to be a property of the porous medium, is dependent on colloid particle size and interstitial velocity. A total of 49 colloid transport experiments were performed in columns packed with glass beads under chemically unfavorable colloid attachment conditions. Nine different colloid diameters, and various flow velocities were examined. The breakthrough curves were successfully simulated with a mathematical model describing colloid transport in homogeneous, water saturated porous media. The results demonstrated that the dispersivity is positively correlated with colloid particle size, and increases with increasing velocity.

  13. Colloidal aspects of texture perception.

    PubMed

    van Vliet, Ton; van Aken, George A; de Jongh, Harmen H J; Hamer, Rob J

    2009-08-30

    Recently, considerable attention has been given to the understanding of texture attributes that cannot directly be related to physical properties of food, such as creamy, crumbly and watery. The perception of these attributes is strongly related to the way the food is processed during food intake, mastication, swallowing of it and during the cleaning of the mouth after swallowing. Moreover, their perception is modulated by the interaction with other basic attributes, such as taste and aroma attributes (e.g. sourness and vanilla). To be able to link the composition and structure of food products to more complicated texture attributes, their initial physical/colloid chemical properties and the oral processing of these products must be well understood. Understanding of the processes in the mouth at colloidal length scales turned out to be essential to grasp the interplay between perception, oral physiology and food properties. In view of the huge differences in physical chemical properties between food products, it is practical to make a distinction between solid, semi-solid, and liquid food products. The latter ones are often liquid dispersions of emulsion droplets or particles in general. For liquid food products for instance flow behaviour and colloidal stability of dispersed particles play a main role in determining their textural properties. For most solid products stiffness and fracture behaviour in relation to water content are essential while for semi-solids a much larger range of mechanical properties will play a role. Examples of colloidal aspects of texture perception will be discussed for these three categories of products based on selected sensory attributes and/or relevant colloidal processes. For solid products some main factors determining crispness will be discussed. For crispiness of dry cellular solid products these are water content and the architecture of the product at mesoscopic length scales (20-1000 microm). In addition the distribution of

  14. Statistical Physics of Colloidal Dispersions.

    NASA Astrophysics Data System (ADS)

    Canessa, E.

    Available from UMI in association with The British Library. Requires signed TDF. This thesis is concerned with the equilibrium statistical mechanics of colloidal dispersions which represent useful model systems for the study of condensed matter physics; namely, charge stabilized colloidal dispersions and polymer stabilized colloidal dispersions. A one-component macroparticle approach is adopted in order to treat the macroscopic and microscopic properties of these systems in a simple and comprehensive manner. The thesis opens with the description of the nature of the colloidal state before reviewing some basic definitions and theory in Chapter II. In Chapter III a variational theory of phase equilibria based on the Gibbs-Bogolyobov inequality is applied to sterically stabilized colloidal dispersions. Hard spheres are chosen as the reference system for the disordered phases while an Einstein model is used for the ordered phases. The new choice of pair potential, taken for mathematical convenience, is a superposition of two Yukawa functions. By matching a double Yukawa potential to the van der Waals attractive potential at different temperatures and introducing a purely temperature dependent coefficient to the repulsive part, a rich variety of observed phase separation phenomena is qualitatively described. The behaviour of the potential is found to be consistent with a small decrease of the polymer layer thickness with increasing temperature. Using the same concept of a collapse transition the non-monotonic second virial coefficient is also explained and quantified. It is shown that a reduction of the effective macroparticle diameter with increasing temperature can only be partially examined from the point of view of a (binary-) polymer solution theory. This chapter concludes with the description of the observed, reversible, depletion flocculation behaviour. This is accomplished by using the variational formalism and by invoking the double Yukawa potential to allow

  15. What happens when pharmaceuticals meet colloids.

    PubMed

    Xing, Yingna; Chen, Xijuan; Zhuang, Jie; Chen, Xin

    2015-12-01

    Pharmaceuticals (PCs) have been widely detected in natural environment due to agricultural application of reclaimed water, sludge and animal wastes. Their potential risks to various ecosystems and even to human health have caused great concern; however, little was known about their environmental behaviors. Colloids (such as clays, metal oxides, and particulate organics) are kind of substances that are active and widespread in the environment. When PCs meet colloids, their interaction may influence the fate, transport, and toxicity of PCs. This review summarizes the progress of studies on the role of colloids in mediating the environmental behaviors of PCs. Synthesized results showed that colloids can adsorb PCs mainly through ion exchange, complexation and non-electrostatic interactions. During this process the structure of colloids and the stability of PCs may be changed. The adsorbed PCs may have higher risks to induce antibiotic resistance; besides, their transport may also be altered considering they have great chance to move with colloids. Solution conditions (such as pH, ionic strength, and cations) could influence these interactions between PCs and colloids, as they can change the forms of PCs and alter the primary forces between PCs and colloids in the solution. It could be concluded that PCs in natural soils could bind with colloids and then co-transport during the processes of irrigation, leaching, and erosion. Therefore, colloid-PC interactions need to be understood for risk assessment of PCs and the best management practices of various ecosystems (such as agricultural and wetland systems). PMID:26427370

  16. Preparatiion of metal colloids in inverse micelles

    SciTech Connect

    Wilcoxon, J.P.

    1990-11-23

    A method is provided for preparing catalytic elemental metal colloidal particles (e.g., gold, palladium, silver, rhodium, nickel, iron, platinum, molybdenum) or colloidal alloy particles (silver/iridium or platinum/gold). A homogenous inverse micelle solution of a metal salt is first formed in a metal-salt solvent comprised of a surfactant (e.g. a nonionic or cationic surfactant) and an organic solvent. The size and number of inverse micelles is controlled by the proportions of the surfactant and the solvent. Then, the metal salt is reduced (by chemical reduction or by a pulsed or continuous wave UV laser) to colloidal particles of elemental metal. After their formation, the colloidal metal particles can be stabilized by reaction with materials that permanently add surface stabilizing groups to the surface of the colloidal metal particles. The sizes of the colloidal elemental metal particles and their size distribution is determined by the size and number of the inverse micelles. A second salt can be added with further reduction to form the colloidal alloy particles. After the colloidal elemental metal particles are formed, the homogeneous solution distributes to two phases, one phase rich in colloidal elemental metal particles and the other phase rich in surfactant. The colloidal elemental metal particles from one phase can be dried to form a powder useful as a catalyst.

  17. Chancellor Water Colloids: Characterization and Radionuclide Association

    SciTech Connect

    Abdel-Fattah, Amr I.

    2012-06-18

    Concluding remarks about this paper are: (1) Gravitational settling, zeta potential, and ultrafiltration data indicate the existence of a colloidal phase of both the alpha and beta emitters in the Chancellor water; (2) The low activity combined with high dispersion homogeneity of the Chancellor water indicate that both alpha and beta emitters are not intrinsic colloids; (3) Radionuclides in the Chancellor water, particularly Pu, coexist as dissolved aqueous and sorbed phases - in other words the radionuclides are partitioned between the aqueous phase and the colloidal phase; (4) The presence of Pu as a dissolved species in the aqueous phase, suggests the possibility of Pu in the (V) oxidation state - this conclusion is supported by the similarity of the k{sub d} value of Pu determined in the current study to that determined for Pu(V) sorbed onto smectite colloids, and the similar electrokinetic behavior of the Chancellor water colloids to smectite colloids; (5) About 50% of the Pu(V) is in the aqueous phase and 50% is sorbed on colloids (mass concentration of colloids in the Chancellor water is 0.12 g/L); (6) The k{sub d} of the Pu and the beta emitters (fission products) between aqueous and colloidal phases in the Chancellor water is {approx}8.0 x 10{sup 3} mL/g using two different activity measurement techniques (LSC and alpha spectroscopy); (7) The gravitational settling and size distributions of the association colloids indicate that the properties (at least the physical ones) of the colloids to which the alpha emitters are associated with seem to be different that the properties of the colloids to which the beta emitters are associated with - the beta emitters are associated with very small particles ({approx}50 - 120 nm), while the alpha emitters are associated with relatively larger particles; and (8) The Chancellor water colloids are extremely stable under the natural pH and ionic strength conditions, indicating high potential for transport in the

  18. Electrokinetic properties of polymer colloids

    NASA Technical Reports Server (NTRS)

    Micale, F. J.; Fuenmayor, D. Y.

    1986-01-01

    The surface of polymer colloids, especially polystyrene latexes, were modified for the purpose of controlling the electrokinetic properties of the resulting colloids. Achievement required a knowledge of electrical double layer charging mechanism, as a function of the electrolyte conditions, at the polymer/water interface. The experimental approach is to control the recipe formulation in the emulsion polymerization process so as to systematically vary the strong acid group concentration on the surface of the polymer particles. The electrophoretic mobility of these model particles will then be measured as a function of surface group concentration and as a function of electrolyte concentration and type. An effort was also made to evaluate the electrophoretic mobility of polystyrene latexes made in space and to compare the results with latexes made on the ground.

  19. Predicting crystals of Janus colloids.

    PubMed

    Vissers, Teun; Preisler, Zdenek; Smallenburg, Frank; Dijkstra, Marjolein; Sciortino, Francesco

    2013-04-28

    We present a numerical study on the phase diagram for a simple model of Janus colloids, including ordered and disordered structures. Using a range of techniques, we generate a set of crystal structures and investigate their relative stability field in the pressure-temperature and temperature-density planes by means of free-energy calculations and thermodynamic integration schemes. We find that despite the Janus colloids' simple architecture, they form stable crystal structures with complicated bond-topologies on an underlying face-centered-cubic or hexagonal-close-packed lattice. In addition, we find a phase consisting of wrinkled bilayer sheets, competing with both the fluid and the crystal phases. We detect a metastable gas-liquid coexistence which displays a micellization-driven re-entrant behavior. PMID:23635155

  20. Magnetic Assisted Colloidal Pattern Formation

    NASA Astrophysics Data System (ADS)

    Yang, Ye

    Pattern formation is a mysterious phenomenon occurring at all scales in nature. The beauty of the resulting structures and myriad of resulting properties occurring in naturally forming patterns have attracted great interest from scientists and engineers. One of the most convenient experimental models for studying pattern formation are colloidal particle suspensions, which can be used both to explore condensed matter phenomena and as a powerful fabrication technique for forming advanced materials. In my thesis, I have focused on the study of colloidal patterns, which can be conveniently tracked in an optical microscope yet can also be thermally equilibrated on experimentally relevant time scales, allowing for ground states and transitions between them to be studied with optical tracking algorithms. In particular, I have focused on systems that spontaneously organize due to particle-surface and particle-particle interactions, paying close attention to systems that can be dynamically adjusted with an externally applied magnetic or acoustic field. In the early stages of my doctoral studies, I developed a magnetic field manipulation technique to quantify the adhesion force between particles and surfaces. This manipulation technique is based on the magnetic dipolar interactions between colloidal particles and their "image dipoles" that appear within planar substrate. Since the particles interact with their own images, this system enables massively parallel surface force measurements (>100 measurements) in a single experiment, and allows statistical properties of particle-surface adhesion energies to be extracted as a function of loading rate. With this approach, I was able to probe sub-picoNewton surface interactions between colloidal particles and several substrates at the lowest force loading rates ever achieved. In the later stages of my doctoral studies, I focused on studying patterns formed from particle-particle interaction, which serve as an experimental model of

  1. Phases transitions and interfaces in temperature-sensitive colloidal systems

    NASA Astrophysics Data System (ADS)

    Nguyen, Duc; Schall, Peter

    2013-03-01

    Colloids are widely used because of their exceptional properties. Beside their own applications in food, petrol, cosmetics and drug industries, photonic, optical filters and chemical sensor, they are also known as powerful model systems to study molecular phase behavior. Here, we examine both aspects of colloids using temperature-sensitive colloidal systems to fully investigate colloidal phase behavior and colloidal assembly.

  2. Superconductivity in colloidal lead nanocrystals

    NASA Astrophysics Data System (ADS)

    Zolotavin, Pavlo

    Monodisperse colloidal lead nanoparticles with diameters ranging from 4.4 to 20 nm were prepared by a self-limiting growth method. The nanoparticles are protected from oxidation by an amorphous lead-tin oxide shell of 1.5-2 nm thickness. The magnetic susceptibility of the particles was measured as a function of size, temperature and magnetic field. The Meissner effect was observed indicating the superconducting transition. For the 20 and 16 nm particles, the critical temperature is suppressed to 6.9 K from the bulk value of 7.2 K and is further reduced for smaller particles. Depending on the size of the particles, the critical field is enhanced by 60 to 140 times. The coupling between particles was in situ controlled through the conversion of the oxides present on the surface of the nanoparticles to chalcogenides. This transformation allows for a 109-fold increase in the conductivity. The temperature of the onset of the superconductivity was found to depend upon the degree of coupling of the nanoparticles in the vicinity of the insulator - superconductor transition. The critical current density of the best sample of Pb/PbSe nanocrystals at zero magnetic field was determined to be 4 x 103 A/cm 2. In turn, the critical field of the sample shows 50-fold enhancement compared to bulk Pb. A method to convert the original Pb/PbO nanocrystals into colloidal Pb/PbS (Se, Te) particle was developed. This alleviates the necessity of chemical post processing and provides a truly colloidal superconductor. Paramagnetic Meissner effect of abnormally large amplitude is observed for Pb/PbTe nanocrystal assemblies. The material described in this manuscript is the first nanostructured superconductor prepared by the bottom-up approach starting from colloidal nanoparticles.

  3. Linear viscoelasticity of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Cichocki, B.; Felderhof, B. U.

    1992-12-01

    We develop a phenomenological theory of the dynamic viscosity of colloidal suspensions, based on an extrapolation of the low-frequency behavior by use of a continued-fraction representation. In lowest approximation the dynamic viscosity depends on a small number of parameters, which may be determined experimentally. For semidilute suspensions the parameters may be found by theoretical calculation. The theory is tested by comparison with an exactly soluble model.

  4. Solid colloidal optical wavelength filter

    NASA Astrophysics Data System (ADS)

    Alvarez, J. L.

    1990-05-01

    A method for constructing a solid colloidal optical wavelength filter is discussed. The device was developed to filter optical wavelengths for spectroscopy, protection from intense radiation, monochromatizing, and analyzing optical radiation. The filter is formed by suspending spherical particles in a coagulable medium (such as setting plastic); agitating the particles and coagulable medium to produce an emulsion of particles suspended in the coagulable medium; and allowing the coagulable medium and suspended emulsion of particles to cool.

  5. Colloidal assembly by ice templating.

    PubMed

    Kumaraswamy, Guruswamy; Biswas, Bipul; Choudhury, Chandan Kumar

    2016-04-12

    We investigate ice templating of aqueous dispersions of polymer coated colloids and crosslinkers, at particle concentrations far below that required to form percolated monoliths. Freezing the aqueous dispersions forces the particles into close proximity to form clusters, that are held together as the polymer chains coating the particles are crosslinked. We observe that, with an increase in the particle concentration from about 10(6) to 10(8) particles per ml, there is a transition from isolated single particles to increasingly larger clusters. In this concentration range, most of the colloidal clusters formed are linear or sheet like particle aggregates. Remarkably, the cluster size distribution for clusters smaller than about 30 particles, as well as the size distribution of linear clusters, is only weakly dependent on the dispersion concentration in the range that we investigate. We demonstrate that the main features of cluster formation are captured by kinetic simulations that do not consider hydrodynamics or instabilities at the growing ice front due to particle concentration gradients. Thus, clustering of colloidal particles by ice templating dilute dispersions appears to be governed only by particle exclusion by the growing ice crystals that leads to their accumulation at ice crystal boundaries. PMID:26780838

  6. Colloidal thermoresponsive gel forming hybrids.

    PubMed

    Liu, Ruixue; Tirelli, Nicola; Cellesi, Francesco; Saunders, Brian R

    2010-09-15

    Colloidal hybrids comprise organic and inorganic components and are attracting considerable attention in the literature. Recently, we reported hybrid anisotropic microsheets that formed thermoresponsive gels in polymer solutions [Liu et al., Langmuir, 25, 490, 2009]. Here, we investigate the composition and properties of these hybrid colloids themselves in detail for the first time. Three different cationic PNIPAm (N-isopropylacrylamide) graft copolymers and two inorganic nanoparticle types (laponite and Ludox silica) were used to prepare a range of hybrids. Anisotropic microsheets only formed when laponite particles were added to the copolymer implying directed self-assembly. Aqueous dispersions of the microsheets spontaneously formed gels at room temperature and these gels were thermoresponsive. They represent a new class of gel forming colloid and are termed thermoresponsive gel forming hybrids. The compositions of the hybrids were determined from thermogravimetric analysis and those that gave gel forming behaviour identified. Variable-temperature rheology experiments showed that the elasticity of the gels increased linearly with temperature. The reversibility of the thermally-triggered changes in gel elasticity was investigated. The concentration dependence of the rheology data was well described by elastic percolation scaling theory and the data could be collapsed onto a master curve. The concentration exponent for the elastic modulus was 2.5. The strong attractive interactions that exist between the dispersed gel forming hybrids was demonstrated by the formation of stable thermoresponsive hybrid hydrogels through casting of hybrid dispersions. PMID:20561633

  7. Crystallization of DNA-coated colloids

    PubMed Central

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S.; Weck, Marcus; Pine, David J.

    2015-01-01

    DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids. PMID:26078020

  8. Crystallization of DNA-coated colloids.

    PubMed

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S; Weck, Marcus; Pine, David J

    2015-01-01

    DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids. PMID:26078020

  9. Binodal Colloidal Aggregation Test - 4: Polydispersion

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.

    2008-01-01

    Binodal Colloidal Aggregation Test - 4: Polydispersion (BCAT-4-Poly) will use model hard-spheres to explore seeded colloidal crystal nucleation and the effects of polydispersity, providing insight into how nature brings order out of disorder. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.

  10. Binary Colloidal Alloy Test Conducted on Mir

    NASA Technical Reports Server (NTRS)

    Hoffmann, Monica I.; Ansari, Rafat R.

    1999-01-01

    Colloids are tiny (submicron) particles suspended in fluid. Paint, ink, and milk are examples of colloids found in everyday life. The Binary Colloidal Alloy Test (BCAT) is part of an extensive series of experiments planned to investigate the fundamental properties of colloids so that scientists can make colloids more useful for technological applications. Some of the colloids studied in BCAT are made of two different sized particles (binary colloidal alloys) that are very tiny, uniform plastic spheres. Under the proper conditions, these colloids can arrange themselves in a pattern to form crystals. These crystals may form the basis of new classes of light switches, displays, and optical devices. Windows made of liquid crystals are already in the marketplace. These windows change their appearance from transparent to opaque when a weak electric current is applied. In the future, if the colloidal crystals can be made to control the passage of light through them, such products could be made much more cheaply. These experiments require the microgravity environment of space because good quality crystals are difficult to produce on Earth because of sedimentation and convection in the fluid. The BCAT experiment hardware included two separate modules for two different experiments. The "Slow Growth" hardware consisted of a 35-mm camera with a 250- exposure photo film cartridge. The camera was aimed toward the sample module, which contained 10 separate colloid samples. A rack of small lights provided backlighting for the photographs. The BCAT hardware was launched on the shuttle and was operated aboard the Russian space station Mir by American astronauts John Blaha and David Wolf (launched September 1996 and returned January 1997; reflown September 1997 and returned January 1998). To begin the experiment, one of these astronauts would mix the samples to disperse the colloidal particles and break up any crystals that might have already formed. Once the samples were mixed and

  11. Aggregation kinetics in a model colloidal suspension

    SciTech Connect

    Bastea, S

    2005-08-08

    The authors present molecular dynamics simulations of aggregation kinetics in a colloidal suspension modeled as a highly asymmetric binary mixture. Starting from a configuration with largely uncorrelated colloidal particles the system relaxes by coagulation-fragmentation dynamics to a structured state of low-dimensionality clusters with an exponential size distribution. The results show that short range repulsive interactions alone can give rise to so-called cluster phases. For the present model and probably other, more common colloids, the observed clusters appear to be equilibrium phase fluctuations induced by the entropic inter-colloidal attractions.

  12. Colloid Coalescence with Focused X Rays

    SciTech Connect

    Weon, B. M.; Kim, J. T.; Je, J. H.; Yi, J. M.; Wang, S.; Lee, W.-K.

    2011-07-01

    We show direct evidence that focused x rays enable us to merge polymer colloidal particles at room temperature. This phenomenon is ascribed to the photochemical scission of colloids with x rays, reducing the molecular weight, glass transition temperature, surface tension, and viscosity of colloids. The observation of the neck bridge growth with time shows that the x-ray-induced colloid coalescence is analogous to viscoelastic coalescence. This finding suggests a feasible protocol of photonic nanofabrication by sintering or welding of polymers, without thermal damage, using x-ray photonics.

  13. Conductivity maximum in a charged colloidal suspension

    SciTech Connect

    Bastea, S

    2009-01-27

    Molecular dynamics simulations of a charged colloidal suspension in the salt-free regime show that the system exhibits an electrical conductivity maximum as a function of colloid charge. We attribute this behavior to two main competing effects: colloid effective charge saturation due to counterion 'condensation' and diffusion slowdown due to the relaxation effect. In agreement with previous observations, we also find that the effective transported charge is larger than the one determined by the Stern layer and suggest that it corresponds to the boundary fluid layer at the surface of the colloidal particles.

  14. Collective motion in populations of colloidal bots

    NASA Astrophysics Data System (ADS)

    Bartolo, Denis

    One of the origins of active matter physics was the idea that flocks, herds, swarms and shoals could be quantitatively described as emergent ordered phases in self-driven materials. From a somehow dual perspective, I will show how to engineer active materials our of colloidal flocks. I will show how to motorize colloidal particles capable of sensing the orientation of their neighbors and how to handle them in microfluidic chips. These populations of colloidal bots display a non-equilibrium transition toward collective motion. A special attention will be paid to the robustness of the resulting colloidal flocks with respect to geometrical frustration and to quenched disorder.

  15. Nonequilibrium forces between dragged ultrasoft colloids.

    PubMed

    Singh, Sunil P; Winkler, Roland G; Gompper, Gerhard

    2011-10-01

    The dynamical deformation of ultrasoft colloids as well as their dynamic frictional forces are numerically investigated, when one colloid is dragged past another at constant velocity. Hydrodynamic interactions are captured by a particle-based mesoscopic simulation method. At vanishing relative velocity, the equilibrium repulsive force-distance curve is obtained. At large drag velocities, in contrast, we find an apparent attractive force for departing colloids along the dragging direction. The deformation, in the close encounter of colloids, and the energy dissipation are examined as a function of the drag velocity and their separation. PMID:22107322

  16. Colloid Titration--A Rapid Method for the Determination of Charged Colloid.

    ERIC Educational Resources Information Center

    Ueno, Keihei; Kina, Ken'yu

    1985-01-01

    "Colloid titration" is a volumetric method for determining charged polyelectrolytes in aqueous solutions. The principle of colloid titration, reagents used in the procedure, methods of endpoint detection, preparation of reagent solutions, general procedure used, results obtained, and pH profile of colloid titration are considered. (JN)

  17. SIGNIFICANCE OF STRAINING IN COLLOID DEPOSITION: EVIDENCE AND IMPLICATIONS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Filtration theory is often used to characterize colloid attachment when deposition is controlled by chemical interactions between colloids and grain surfaces. Over the past decade considerable research suggests that colloid deposition is frequently not consistent with filtration theory predictions u...

  18. Analysis of colloid and tracer breakthrough curves

    NASA Astrophysics Data System (ADS)

    Grindrod, Peter; Edwards, Mark S.; Higgo, Jenny J. W.; Williams, Geoffrey M.

    1996-02-01

    We consider the dispersion and elution of colloids and dissolved nonsorbing tracers within saturated heterogeneous porous media. Since flow path geometry in natural systems is often ill-characterized macroscopic (mean) flow rates and dispersion tensors are utilized in order to account for the sub-model scale microscopic fluctuations in media structure (and the consequent hydrodynamic profile). Even for tracer migration and dispersal this issue is far from settled. Here we consider how colloid and tracer migration phenomena can be treated consistently. Theoretical calculations for model flow geometries yield two quantitative predictions for the transport of free (not yet captured) colloids with reference to a non-sorbing dissolved tracer within the same medium: the average migration velocity of the free colloids is higher than that of the tracer; and that the ratio of the equivalent hydrodynamic dispersion rates of colloids and tracer is dependent only upon properties of the colloids and the porous medium, it is independent of pathlengths and fluid flux, once length scales are large enough. The first of these is well known, since even in simple flow paths free colloids must stay more centre stream. The second, if validated suggests how solute and colloid dispersion may be dealt with consistently in macroscopic migration models. This is crucial since dispersion is usually ill-characterized and unaddressed by the experimental literature. In this paper we present evidence based upon an existing Drigg field injection test for the validity of these predictions. We show that starting from experimental data the fitted dispersion rates of both colloids and non-sorbing tracers increase with the measured elution rates (obeying slightly different rules for tracers and colloids); and that the ratio of colloid and nonsorbing tracer elution rates, and the ratio of colloid and nonsorbing tracer dispersion rates may be dependent upon properties of the colloids and the medium (not

  19. Structural color from colloidal glasses

    NASA Astrophysics Data System (ADS)

    Magkiriadou, Sofia

    When a material has inhomogeneities at a lengthscale comparable to the wavelength of light, interference can give rise to structural colors: colors that originate from the interaction of the material's microstructure with light and do not require absorbing dyes. In this thesis we study a class of these materials, called photonic glasses, where the inhomogeneities form a dense and random arrangement. Photonic glasses have angle-independent structural colors that look like those of conventional dyes. However, when this work started, there was only a handful of colors accessible with photonic glasses, mostly hues of blue. We use various types of colloidal particles to make photonic glasses, and we study, both theoretically and experimentally, how the optical properties of these glasses relate to their structure and constituent particles. Based on our observations from glasses of conventional particles, we construct a theoretical model that explains the scarcity of yellow, orange, and red photonic glasses. Guided by this model, we develop novel colloidal systems that allow a higher degree of control over structural color. We assemble glasses of soft, core-shell particles with scattering cores and transparent shells, where the resonant wavelength can be tuned independently of the reflectivity. We then encapsulate glasses of these core-shell particles into emulsion droplets of tunable size; in this system, we observe, for the first time, angle-independent structural colors that cover the entire visible spectrum. To enhance color saturation, we begin experimenting with inverse glasses, where the refractive index of the particles is lower than the refractive index of the medium, with promising results. Finally, based on our theoretical model for scattering from colloidal glasses, we begin an exploration of the color gamut that could be achieved with this technique, and we find that photonic glasses are a promising approach to a new type of long-lasting, non-toxic, and

  20. Highly uniform polyhedral colloids formed by colloidal crystal templating

    NASA Astrophysics Data System (ADS)

    Wang, Yifan; McGinley, James; Crocker, John; Crocker Research Group Team

    2015-03-01

    We seek to create polyhedral solid particles by trapping oil droplets in a colloidal crystal, and polymerizing them in situ, resulting in polyhedral particles containing spherical dimples in an ordered arrangement. Specifically, highly monodisperse, micron-sized droplets of 3-methacryloxypropyl trimethoxysilane (TPM) were first prepared through a poly condensation reaction, following well established methods. The droplets were mixed with an excess of polystyrene(PS) particles (diameter in 2.58 μm), which formed close packed (FCC or HCP) colloidal crystals by natural sedimentation and compression under partial drying to an extent, with TPM oil droplets trapped into their tetrahedral and octahedral interstitial sites and wet PS particles. Depending on the initial particle volume fraction and extent of drying, a high yield of dimpled particles having different shapes including tetrahedra and cubes were obtained after oil initiated polymerization and dissolution of the host PS particles, as seen under SEM. The effects of TPM to PS particles size ratio, drying time, and other factors in relation to the yield of tetrahedral and cubic dimpled particles will be presented. Finally, fractionation techniques were used to obtain suspensions of uniform polyhedral particles of high purity.

  1. Active colloids at fluid interfaces.

    PubMed

    Malgaretti, P; Popescu, M N; Dietrich, S

    2016-05-01

    If an active Janus particle is trapped at the interface between a liquid and a fluid, its self-propelled motion along the interface is affected by a net torque on the particle due to the viscosity contrast between the two adjacent fluid phases. For a simple model of an active, spherical Janus colloid we analyze the conditions under which translation occurs along the interface and we provide estimates of the corresponding persistence length. We show that under certain conditions the persistence length of such a particle is significantly larger than the corresponding one in the bulk liquid, which is in line with the trends observed in recent experimental studies. PMID:27025167

  2. Colloidal entanglement in highly twisted chiral nematic colloids: twisted loops, Hopf links, and trefoil knots.

    PubMed

    Jampani, V S R; Škarabot, M; Ravnik, M; Čopar, S; Žumer, S; Muševič, I

    2011-09-01

    The topology and geometry of closed defect loops is studied in chiral nematic colloids with variable chirality. The colloidal particles with perpendicular surface anchoring of liquid crystalline molecules are inserted in a twisted nematic cell with the thickness that is only slightly larger than the diameter of the colloidal particle. The total twist of the chiral nematic structure in cells with parallel boundary conditions is set to 0, π, 2π, and 3π, respectively. We use the laser tweezers to discern the number and the topology of the -1/2 defect loops entangling colloidal particles. For a single colloidal particle, we observe that a single defect loop is winding around the particle, with the winding pattern being more complex in cells with higher total twist. We observe that colloidal dimers and colloidal clusters are always entangled by one or several -1/2 defect loops. For colloidal pairs in π-twisted cells, we identify at least 17 different entangled structures, some of them exhibiting linked defect loops-Hopf link. Colloidal entanglement is even richer with a higher number of colloidal particles, where we observe not only linked, but also colloidal clusters knotted into the trefoil knot. The experiments are in good agreement with numerical modeling using Landau-de Gennes theory coupled with geometrical and topological considerations using the method of tetrahedral rotation. PMID:22060386

  3. Colloid transport in dual-permeability media

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It has been widely reported that colloids can travel faster and over longer distances in natural structured porous media than in uniform structureless media used in laboratory studies. The presence of preferential pathways for colloids in the subsurface environment is of concern because of the incre...

  4. Colloidal Electrolytes and the Critical Micelle Concentration

    ERIC Educational Resources Information Center

    Knowlton, L. G.

    1970-01-01

    Describes methods for determining the Critical Micelle Concentration of Colloidal Electrolytes; methods described are: (1) methods based on Colligative Properties, (2) methods based on the Electrical Conductivity of Colloidal Electrolytic Solutions, (3) Dye Method, (4) Dye Solubilization Method, and (5) Surface Tension Method. (BR)

  5. Binary Colloidal Alloy Test-5: Aspheres

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.; Hollingsworth, Andrew D.

    2008-01-01

    The Binary Colloidal Alloy Test - 5: Aspheres (BCAT-5-Aspheres) experiment photographs initially randomized colloidal samples (tiny nanoscale spheres suspended in liquid) in microgravity to determine their resulting structure over time. BCAT-5-Aspheres will study the properties of concentrated systems of small particles when they are identical, but not spherical in microgravity..

  6. Stability of Ionic Colloidal Crystals (ICCs)

    NASA Astrophysics Data System (ADS)

    Maskaly, Garry R.; Garcia, R. Edwin; Carter, W. Craig; Chiang, Yet-Ming

    2003-03-01

    Ionic colloidal crystals (ICCs) are here defined as ordered multicomponent colloids formed by attractive electrostatic interactions. Compared to previous approaches to colloidal crystallization, the ICC approach holds the potential for self-assembly of a wide range of structures not easily accessible by other methods. In this work, the colloid-chemical conditions under which ICCs are stable have been theoretically analyzed. A model is presented in which two dimensionless parameters are found to fully characterize an ICC system. We calculate the Madelung constant for ICCs of several classical ionic crystal structures as a function of these two parameters, and discuss the parallels between the ICC Madelung constants and the classical ionic case. Experimentally accessible regions of surface charge, particle sizes, salt concentration, and temperature where ionic colloidal crystallization should be possible are identified.

  7. Shaping Colloids for Self-Assembly

    NASA Astrophysics Data System (ADS)

    Sacanna, Stefano; Yi, Gi-Ra; Pine, David

    2013-03-01

    The creation of a new material often starts from the design of its constituent building blocks at a smaller scale. From macromolecules to colloidal architectures, to granular systems, the interactions between basic units of matter can dictate the macroscopic behavior of the resulting engineered material and even regulate its genesis. Information can be imparted to the building units by altering their physical and chemical properties. In particular, the shape of building blocks plays a fundamental role at the colloidal scale, as it can govern the self-organization of particles into hierarchical structures and ultimately into the desired material. Herein we report a simple and general approach to generate an entire zoo of new anisotropic colloids. Our method is based on a controlled deformation of multiphase colloidal particles that can be selectively liquified, polymerized, dissolved and functionalized in bulk. We further demonstrate control over the particle functionalization and coating by realizing patchy and Janus colloids.

  8. Shaping colloids for self-assembly

    NASA Astrophysics Data System (ADS)

    Sacanna, Stefano; Korpics, Mark; Rodriguez, Kelvin; Colón-Meléndez, Laura; Kim, Seung-Hyun; Pine, David J.; Yi, Gi-Ra

    2013-04-01

    The creation of a new material often starts from the design of its constituent building blocks at a smaller scale. From macromolecules to colloidal architectures, to granular systems, the interactions between basic units of matter can dictate the macroscopic behaviour of the resulting engineered material and even regulate its genesis. Information can be imparted to the building units by altering their physical and chemical properties. In particular, the shape of building blocks has a fundamental role at the colloidal scale, as it can govern the self-organization of particles into hierarchical structures and ultimately into the desired material. Herein we report a simple and general approach to generate an entire zoo of new anisotropic colloids. Our method is based on a controlled deformation of multiphase colloidal particles that can be selectively liquified, polymerized, dissolved and functionalized in bulk. We further demonstrate control over the particle functionalization and coating by realizing patchy and Janus colloids.

  9. Les aspects psychosociaux de l’obésité chez les enfants et les adolescents

    PubMed Central

    Nieman, Peter; LeBlanc, Claire MA

    2012-01-01

    RÉSUMÉ En plus de donner des conseils aux familles au sujet de l’activité physique régulière et d’une saine alimentation, les cliniciens doivent déterminer les facteurs psychosociaux qui contribuent à l’obésité des enfants ou des adolescents et les aider à y faire face. Les personnes touchées peuvent souffrir de dépression, de mauvaise estime de soi, d’intimidation et de préjugés liés au poids, qui sont tous des expériences qui peuvent compliquer l’obtention des résultats de santé souhaités. Les cliniciens devraient tenter de déterminer les facteurs stressants sous-jacents et s’assurer de la mise en œuvre de conseils pertinents.

  10. Kinetically guided colloidal structure formation

    PubMed Central

    Hecht, Fabian M.; Bausch, Andreas R.

    2016-01-01

    The self-organization of colloidal particles is a promising approach to create novel structures and materials, with applications spanning from smart materials to optoelectronics to quantum computation. However, designing and producing mesoscale-sized structures remains a major challenge because at length scales of 10–100 μm equilibration times already become prohibitively long. Here, we extend the principle of rapid diffusion-limited cluster aggregation (DLCA) to a multicomponent system of spherical colloidal particles to enable the rational design and production of finite-sized anisotropic structures on the mesoscale. In stark contrast to equilibrium self-assembly techniques, kinetic traps are not avoided but exploited to control and guide mesoscopic structure formation. To this end the affinities, size, and stoichiometry of up to five different types of DNA-coated microspheres are adjusted to kinetically control a higher-order hierarchical aggregation process in time. We show that the aggregation process can be fully rationalized by considering an extended analytical DLCA model, allowing us to produce mesoscopic structures of up to 26 µm in diameter. This scale-free approach can easily be extended to any multicomponent system that allows for multiple orthogonal interactions, thus yielding a high potential of facilitating novel materials with tailored plasmonic excitation bands, scattering, biochemical, or mechanical behavior. PMID:27444018

  11. Synthesis of substantially monodispersed colloids

    NASA Technical Reports Server (NTRS)

    Klabunde, Kenneth J. (Inventor); Stoeva, Savka (Inventor); Sorensen, Christopher (Inventor)

    2003-01-01

    A method of forming ligated nanoparticles of the formula Y(Z).sub.x where Y is a nanoparticle selected from the group consisting of elemental metals having atomic numbers ranging from 21-34, 39-52, 57-83 and 89-102, all inclusive, the halides, oxides and sulfides of such metals, and the alkali metal and alkaline earth metal halides, and Z represents ligand moieties such as the alkyl thiols. In the method, a first colloidal dispersion is formed made up of nanoparticles solvated in a molar excess of a first solvent (preferably a ketone such as acetone), a second solvent different than the first solvent (preferably an organic aryl solvent such as toluene) and a quantity of ligand moieties; the first solvent is then removed under vacuum and the ligand moieties ligate to the nanoparticles to give a second colloidal dispersion of the ligated nanoparticles solvated in the second solvent. If substantially monodispersed nanoparticles are desired, the second dispersion is subjected to a digestive ripening process. Upon drying, the ligated nanoparticles may form a three-dimensional superlattice structure.

  12. Nonlinear rheology of colloidal dispersions.

    PubMed

    Brader, J M

    2010-09-15

    Colloidal dispersions are commonly encountered in everyday life and represent an important class of complex fluid. Of particular significance for many commercial products and industrial processes is the ability to control and manipulate the macroscopic flow response of a dispersion by tuning the microscopic interactions between the constituents. An important step towards attaining this goal is the development of robust theoretical methods for predicting from first-principles the rheology and nonequilibrium microstructure of well defined model systems subject to external flow. In this review we give an overview of some promising theoretical approaches and the phenomena they seek to describe, focusing, for simplicity, on systems for which the colloidal particles interact via strongly repulsive, spherically symmetric interactions. In presenting the various theories, we will consider first low volume fraction systems, for which a number of exact results may be derived, before moving on to consider the intermediate and high volume fraction states which present both the most interesting physics and the most demanding technical challenges. In the high volume fraction regime particular emphasis will be given to the rheology of dynamically arrested states. PMID:21386516

  13. Cocklebur-shaped colloidal dispersions.

    PubMed

    Lestage, David J; Urban, Marek W

    2005-11-01

    Unique cocklebur-shaped colloidal dispersions were prepared using a combination of a nanoextruder applied to the aqueous solution containing methyl methacrylate (MMA) and n-butyl acrylate (n-BA) with azo-bis-isobutyronitrile (AIBN) or potassium persulfate (KPS) initiators and stabilized by a mixture of sodium dioctyl sulfosuccinate (SDOSS) and 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DCPC) phospholipid. Upon extrusion and heating to 75 degrees C, methyl methacrylate/n-butyl acrylate (MMA/nBA) colloidal particles containing tubules pointing outward were obtained as a result of DCPC phospholipids present at the particle surfaces. The same cocklebur-shaped particles were obtained when classical polymerization was used without a nanoextruder under similar compositional and thermal conditions, giving a particle size of 159 nm. However, when Ca(2+) ions are present during polymerization, cocklebur morphologies are disrupted. Because DCPC tubules undergo a transition at 38 degrees C, such cocklebur morphologies may offer numerous opportunities for devices with stimuli-responsive characteristics. PMID:16262269

  14. Colloid-Associated Radionuclide Concentration Limits: ANL

    SciTech Connect

    C. Mertz

    2000-12-21

    The purpose and scope of this report is to describe the analysis of available colloidal data from waste form corrosion tests at Argonne National Laboratory (ANL) to extract characteristics of these colloids that can be used in modeling their contribution to the source term for sparingly soluble radioelements (e.g., Pu). Specifically, the focus is on developing a useful description of the following waste form colloid characteristics: (1) composition, (2) size distribution, and (3) quantification of the rate of waste form colloid generation. The composition and size distribution information are intended to support analysis of the potential transport of the sparingly soluble radionuclides associated with the waste form colloids. The rate of colloid generation is intended to support analysis of the waste form colloid-associated radionuclide concentrations. In addressing the above characteristics, available data are interpreted to address mechanisms controlling colloid formation and stability. This report was developed in accordance with the ''Technical Work Plan for Waste Form Degradation Process Model Report for SR'' (CRWMS M&O 2000). Because the end objective is to support the source term modeling we have organized the conclusions into two categories: (1) data analysis conclusions and (2) recommendations for colloid source term modeling. The second category is included to facilitate use of the conclusions from the data analysis in the abstraction of a colloid source term model. The data analyses and conclusions that are presented in this report are based on small-scale laboratory tests conducted on a limited number of waste glass compositions and spent fuel types.

  15. Plutonium and Cesium Colloid Mediated Transport

    NASA Astrophysics Data System (ADS)

    Boukhalfa, H.; Dittrich, T.; Reimus, P. W.; Ware, D.; Erdmann, B.; Wasserman, N. L.; Abdel-Fattah, A. I.

    2013-12-01

    Plutonium and cesium have been released to the environment at many different locations worldwide and are present in spent fuel at significant levels. Accurate understanding of the mechanisms that control their fate and transport in the environment is important for the management of contaminated sites, for forensic applications, and for the development of robust repositories for the disposal of spent nuclear fuel and nuclear waste. Plutonium, which can be present in the environment in multiple oxidations states and various chemical forms including amorphous oxy(hydr)oxide phases, adsorbs/adheres very strongly to geological materials and is usually immobile in all its chemical forms. However, when associated with natural colloids, it has the potential to migrate significant distances from its point of release. Like plutonium, cesium is not very mobile and tends to remain adhered to geological materials near its release point, although its transport can be enhanced by natural colloids. However, the reactivity of plutonium and cesium are very different, so their colloid-mediated transport might be significantly different in subsurface environments. In this study, we performed controlled experiments in two identically-prepared columns; one dedicated to Pu and natural colloid transport experiments, and the other to Cs and colloid experiments. Multiple flow-through experiments were conducted in each column, with the effluent solutions being collected and re-injected into the same column two times to examine the persistence and scaling behavior of the natural colloids, Pu and Cs. The data show that that a significant fraction of colloids were retained in the first elution through each column, but the eluted colloids collected from the first run transported almost conservatively in subsequent runs. Plutonium transport tracked natural colloids in the first run but deviated from the transport of natural colloids in the second and third runs. Cesium transport tracked natural

  16. Colloid Transport in Saturated Porous Media: Elimination of Attachment Efficiency in a New Colloid Transport Model

    SciTech Connect

    Landkamer, Lee L.; Harvey, Ronald W.; Scheibe, Timothy D.; Ryan, Joseph N.

    2013-05-11

    A new colloid transport model is introduced that is conceptually simple but captures the essential features of complicated attachment and detachment behavior of colloids when conditions of secondary minimum attachment exist. This model eliminates the empirical concept of collision efficiency; the attachment rate is computed directly from colloid filtration theory. Also, a new paradigm for colloid detachment based on colloid population heterogeneity is introduced. Assuming the dispersion coefficient can be estimated from tracer behavior, this model has only two fitting parameters: (1) the fraction of colloids that attach irreversibly and (2) the rate at which reversibly attached colloids leave the surface. These two parameters were correlated to physical parameters that control colloid transport such as the depth of the secondary minimum and pore water velocity. Given this correlation, the model serves as a heuristic tool for exploring the influence of physical parameters such as surface potential and fluid velocity on colloid transport. This model can be extended to heterogeneous systems characterized by both primary and secondary minimum deposition by simply increasing the fraction of colloids that attach irreversibly.

  17. Polymer-Induced Depletion Interaction and Its Effect on Colloidal Sedimentation in Colloid-Polymer Mixtures

    NASA Technical Reports Server (NTRS)

    Tong, Penger

    1996-01-01

    In this paper we focus on the polymer-induced depletion attraction and its effect on colloidal sedimentation in colloid-polymer mixtures. We first report a small angle neutron scattering (SANS) study of the depletion effect in a mixture of hard-sphere-like colloid and non-adsorbing polymer. Then we present results of our recent sedimentation measurements in the same colloid-polymer mixture. A key parameter in controlling the sedimentation of heavy colloidal particles is the interparticle potential U(tau), which is the work required to bring two colloidal particles from infinity to a distance tau under a give solvent condition. This potential is known to affect the average settling velocity of the particles and experimentally one needs to have a way to continuously vary U(tau) in order to test the theory. The interaction potential U(tau) can be altered by adding polymer molecules into the colloidal suspension. In a mixture of colloid and non-adsorbing polymer, the potential U(tau) can develop an attractive well because of the depletion effect, in that the polymer chains are expelled from the region between two colloidal particles when their surface separation becomes smaller than the size of the polymer chains. The exclusion of polymer molecules from the space between the colloidal particles leads to an unbalanced osmotic pressure difference pushing the colloidal particles together, which results in an effective attraction between the two colloidal particles. The polymer-induced depletion attraction controls the phase stability of many colloid-polymer mixtures, which are directly of interest to industry.

  18. Structural evolution of Colloidal Gels under Flow

    NASA Astrophysics Data System (ADS)

    Boromand, Arman; Maia, Joao; Jamali, Safa

    Colloidal suspensions are ubiquitous in different industrial applications ranging from cosmetic and food industries to soft robotics and aerospace. Owing to the fact that mechanical properties of colloidal gels are controlled by its microstructure and network topology, we trace the particles in the networks formed under different attraction potentials and try to find a universal behavior in yielding of colloidal gels. Many authors have implemented different simulation techniques such as molecular dynamics (MD) and Brownian dynamics (BD) to capture better picture during phase separation and yielding mechanism in colloidal system with short-ranged attractive force. However, BD neglects multi-body hydrodynamic interactions (HI) which are believed to be responsible for the second yielding of colloidal gels. We envision using dissipative particle dynamics (DPD) with modified depletion potential and hydrodynamic interactions, as a coarse-grain model, can provide a robust simulation package to address the gel formation process and yielding in short ranged-attractive colloidal systems. The behavior of colloidal gels with different attraction potentials under flow is examined and structural fingerprints of yielding in these systems will be discussed.

  19. Quantification of hydrophobic interaction affinity of colloids

    NASA Astrophysics Data System (ADS)

    Saini, G.; Nasholm, N.; Wood, B. D.

    2009-12-01

    Colloids play an important role in a wide variety of disciplines, including water and wastewater treatment, subsurface transport of metals and organic contaminants, migration of fines in oil reservoirs, biocolloid (virus and bacteria) transport in subsurface, and are integral to laboratory transport studies. Although the role of hydrophobicity in adhesion and transport of colloids, particularly bacteria, is well known; there is scarcity of literature regarding hydrophobicity measurement of non-bacterial colloids and other micron-sized particles. Here we detail an experimental approach based on differential partitioning of colloids between two liquid phases (hydrocarbon and buffer) as a measure of the hydrophobic interaction affinity of colloids. This assay, known as Microbial adhesion to hydrocarbons or MATH, is frequently used in microbiology and bacteriology for quantifying the hydrophobicity of microbes. Monodispersed colloids and particles, with sizes ranging from 1 micron to 33 micron, were used for the experiments. A range of hydrophobicity values were observed for different particles. The hydrophobicity results are also verified against water contact angle measurements of these particles. This liquid-liquid partitioning assay is quick, easy-to-perform and requires minimal instrumentation. Estimation of the hydrophobic interaction affinity of colloids would lead to a better understanding of their adhesion to different surfaces and subsequent transport in porous media.

  20. Interactions between radioactively labeled colloids and natural particles: Evidence for colloidal pumping

    NASA Astrophysics Data System (ADS)

    Wen, Liang-Saw; Santschi, Peter H.; Tang, Degui

    1997-07-01

    It has been hypothesized that colloidal forms of trace metals can be reactive intermediaries in the scavenging processes leading to the removal of their particulate forms. A series of radiotracer experiments using natural colloidal organic matter from Galveston Bay, USA were carried out in order to test this hypothesis. Suspended particle uptake of originally colloidally bound trace metals occurred in a matter of hours to days in estuarine waters. After ten days, the majority (>50%) of the colloidal trace metals had been transferred into the particulate phase (≥0.45 μm), except for 65Zn. Two distinctively different temporal regions of removal of colloidal trace metals were identified: a faster reaction during the first four hours, followed by a slower reaction after approximately one day. In a separate river water-seawater mixing experiment, the solid/solution partitioning of the radiotracers was investigated in the absence of suspended matter. About 30% of most of the elements, except Ag and Fe (˜60%), were associated with a newly formed particulate phase after eight days. There were two major trends: (1) the particulate fraction of 59Fe and 110Ag increased while the colloidal fraction decreased, suggesting a colloidal pumping mechanism. (2) The particulate fraction of 54Mn, 133Ba, 65Zn, 109Cd, 113Sn, and 60CO increased while the LMW (≤ 1 kDa) fraction decreased, suggesting a direct uptake into the particulate fraction with less involvement of a transitory colloidal phase. The values of the particle-water ( Kd) and colloid-water partitioning ( Kc) coefficients for most trace metals were similar to those observed in Galveston Bay waters, suggesting complementary results to field studies. The results from these experiments suggested two different pathways for colloidal tracer uptake by particles: (1) colloidal pumping of a major component (e.g., biopolymer) of the colloidal pool and (2) coagulation of trace components (e.g., phytochelatins) with varying

  1. Assembly of open clusters of colloidal dumbbells via droplet evaporation

    NASA Astrophysics Data System (ADS)

    Pham Van, Hai; Fortini, Andrea; Schmidt, Matthias

    2016-05-01

    We investigate the behavior of a mixture of asymmetric colloidal dumbbells and emulsion droplets by means of kinetic Monte Carlo simulations. The evaporation of the droplets and the competition between droplet-colloid attraction and colloid-colloid interactions lead to the formation of clusters built up of colloid aggregates with both closed and open structures. We find that stable packings and hence complex colloidal structures can be obtained by changing the relative size of the colloidal spheres and/or their interfacial tension with the droplets.

  2. Colloidal Synthesis of Gold Semishells

    PubMed Central

    Rodríguez-Fernández, Denis; Pérez-Juste, Jorge; Pastoriza-Santos, Isabel; Liz-Marzán, Luis M

    2012-01-01

    This work describes a novel and scalable colloid chemistry strategy to fabricate gold semishells based on the selective growth of gold on Janus silica particles (500 nm in diameter) partly functionalized with amino groups. The modulation of the geometry of the Janus silica particles allows us to tune the final morphology of the gold semishells. This method also provides a route to fabricating hollow gold semishells through etching of the silica cores with hydrofluoric acid. The optical properties were characterized by visible near-infrared (vis-NIR) spectroscopy and compared with simulations performed using the boundary element method (BEM). These revealed that the main optical features are located beyond the NIR region because of the large core size. PMID:24551496

  3. Colloids at NAPL-Interfaces

    NASA Astrophysics Data System (ADS)

    Baumann, Thomas; Metz, Christian

    2014-05-01

    Non-aqueous phase liquids in subsurface are relevant in the scope of contaminated sites as well as for enhanced oil recovery. In both cases colloids and engineered nanoparticles are applied to increase the efficiency of NAPL removal. Particle tracking experiments using fluoresecent latex beads and opaque particles have been run in micromodels mimicking the pore structure of subsurface media. The results show that the interface between NAPL and water is highly dynamic, especially in its early stage. There is a distinct circular flow pattern at the interface, effectively increasing the interfacial area. Concentration gradients measured with Raman Microspectrometry at low Peclet numbers suggest that the mass transfer of dissolved contaminants from the NAPL into the water is highly affected by the interface dynamics. On the other hand the interfaces themselves are less accessible, which has implications for the remediation of contaminated sites.

  4. Colloidal QDs-polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Gordillo, H.; Suárez, I.; Rodríguez-Cantó, P.; Abargues, R.; García-Calzada, R.; Chyrvony, V.; Albert, S.; Martínez-Pastor, J.

    2012-04-01

    Nanometer-size colloidal semiconductor nanocrystals, or Quantum Dots (NQD), are very prospective active centers because their light emission is highly efficient and temperature-independent. Nanocomposites based on the incorporation of QDs inside a polymer matrix are very promising materials for application in future photonic devices because they combine the properties of QDs with the technological feasibility of polymers. In the present work some basic applications of these new materials have been studied. Firstly, the fabrication of planar and linear waveguides based on the incorporation of CdS, CdSe and CdTe in PMMA and SU-8 are demonstrated. As a result, photoluminescence (PL) of the QDs are coupled to a waveguide mode, being it able to obtain multicolor waveguiding. Secondly, nanocomposite films have been evaluated as photon energy down-shifting converters to improve the efficiency of solar cells.

  5. Three-dimensional ultrasonic colloidal crystals

    NASA Astrophysics Data System (ADS)

    Caleap, Mihai; Drinkwater, Bruce W.

    2016-05-01

    Colloidal assembly represents a powerful method for the fabrication of functional materials. In this article, we describe how acoustic radiation forces can guide the assembly of colloidal particles into structures that serve as microscopic elements in novel acoustic metadevices or act as phononic crystals. Using a simple three-dimensional orthogonal system, we show that a diversity of colloidal structures with orthorhombic symmetry can be assembled with megahertz-frequency (MHz) standing pressure waves. These structures allow rapid tuning of acoustic properties and provide a new platform for dynamic metamaterial applications. xml:lang="fr"

  6. Transport in charged colloids driven by thermoelectricity.

    PubMed

    Würger, Alois

    2008-09-01

    We study the thermal diffusion coefficient D{T} of a charged colloid in a temperature gradient, and find that it is to a large extent determined by the thermoelectric response of the electrolyte solution. The thermally induced salinity gradient leads in general to a strong increase with temperature. The difference of the heat of transport of coions and counterions gives rise to a thermoelectric field that drives the colloid to the cold or to the warm, depending on the sign of its charge. Our results provide an explanation for recent experimental findings on thermophoresis in colloidal suspensions. PMID:18851262

  7. A colloidal quantum dot spectrometer

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

    Spectroscopy is carried out in almost every field of science, whenever light interacts with matter. Although sophisticated instruments with impressive performance characteristics are available, much effort continues to be invested in the development of miniaturized, cheap and easy-to-use systems. Current microspectrometer designs mostly use interference filters and interferometric optics that limit their photon efficiency, resolution and spectral range. Here we show that many of these limitations can be overcome by replacing interferometric optics with a two-dimensional absorptive filter array composed of colloidal quantum dots. Instead of measuring different bands of a spectrum individually after introducing temporal or spatial separations with gratings or interference-based narrowband filters, a colloidal quantum dot spectrometer measures a light spectrum based on the wavelength multiplexing principle: multiple spectral bands are encoded and detected simultaneously with one filter and one detector, respectively, with the array format allowing the process to be efficiently repeated many times using different filters with different encoding so that sufficient information is obtained to enable computational reconstruction of the target spectrum. We illustrate the performance of such a quantum dot microspectrometer, made from 195 different types of quantum dots with absorption features that cover a spectral range of 300 nanometres, by measuring shifts in spectral peak positions as small as one nanometre. Given this performance, demonstrable avenues for further improvement, the ease with which quantum dots can be processed and integrated, and their numerous finely tuneable bandgaps that cover a broad spectral range, we expect that quantum dot microspectrometers will be useful in applications where minimizing size, weight, cost and complexity of the spectrometer are critical.

  8. Colloid-Facilitated Transport of Radionuclides through the Vadose Zone

    SciTech Connect

    Flury, Markus; Harsh, James B.; Zachara, John M.; McCarthy, John F.; Lichtner, Peter C.

    2006-05-31

    This project seeks to improve the basic understanding of the role of colloids in facilitating the transport of contaminants in the vadose zone. We focus on three major thrusts: (1) thermodynamic stability and mobility of colloids formed by reactions of sediments with highly alkaline tank waste solutions, (2) colloid-contaminant interactions, and (3) in-situ colloid mobilization and colloid facilitated contaminant transport occurring in both contaminated and uncontaminated Hanford sediments.

  9. Polarity inversion of ζ-potential in concentrated colloidal dispersions.

    PubMed

    Manzanilla-Granados, Héctor M; Jiménez-Ángeles, Felipe; Lozada-Cassou, Marcelo

    2011-10-27

    A concentrated colloidal dispersion is studied by applying an integral equations theory to the colloidal primitive model fluid. Important effects, attributed to large size and charge and to the finite concentration of colloidal particles, are found. We observe a polarity inversion of ζ-potential for concentrated colloidal dispersions, while it is not present for a single colloidal particle at infinite dilution. An excellent qualitative agreement between our theoretical predictions and our computer simulations is observed. PMID:21928833

  10. Colloidal suspension simulates linear dynamic pressure profile

    NASA Technical Reports Server (NTRS)

    Mc Cann, R. J.

    1966-01-01

    Missile nose fairings immersed in colloidal suspension prepared with various specific gravities simulate pressure profiles very similar to those encountered during reentry. Stress and deflection conditions similar to those expected during atmospheric reentry are thus attained in the laboratory.

  11. Mesoscopic modelling of colloids in chiral nematics.

    PubMed

    Ravnik, Miha; Alexander, Gareth P; Yeomans, Julia M; Zumer, Slobodan

    2010-01-01

    We present numerical modelling of colloidal particles in chiral nematics with cubic symmetry (blue phases) within the framework of the Landau-de Gennes free energy. The interaction potential of a single, nano-sized colloidal particle with a -1/2 disclination line is calculated as a generic trapping mechanism for particles within the cholesteric blue phases. The interaction potential is shown to be highly anisotropic and have threefold rotational symmetry. We discuss the equilibration of the colloidal texture with respect to particle positions and the unit cell size of the blue phase. We also describe how preservation of the liquid crystal volume and the number of particles allows blue phase colloidal structures with different unit cell sizes and configurations to be compared numerically. PMID:20158028

  12. Polydispersity effects in colloid-polymer mixtures.

    PubMed

    Liddle, S M; Narayanan, T; Poon, W C K

    2011-05-18

    We study phase separation and transient gelation experimentally in a mixture consisting of polydisperse colloids (polydispersity: ≈ 6%) and non-adsorbing polymers, where the ratio of the average size of the polymer to that of the colloid is ≈ 0.062. Unlike what has been reported previously for mixtures with somewhat lower colloid polydispersity (≈ 5%), the addition of polymers does not expand the fluid-solid coexistence region. Instead, we find a region of fluid-solid coexistence which has an approximately constant width but an unexpected re-entrant shape. We detect the presence of a metastable gas-liquid binodal, which gives rise to two-stepped crystallization kinetics that can be rationalized as the effect of fractionation. Finally, we find that the separation into multiple coexisting solid phases at high colloid volume fractions predicted by equilibrium statistical mechanics is kinetically suppressed before the system reaches dynamical arrest. PMID:21525554

  13. Ultrasonically assisted deposition of colloidal crystals

    SciTech Connect

    Wollmann, Sabine; Patel, Raj B.; Wixforth, Achim; Krenner, Hubert J.

    2014-07-21

    Colloidal particles are a versatile physical system which have found uses across a range of applications such as the simulation of crystal kinetics, etch masks for fabrication, and the formation of photonic band-gap structures. Utilization of colloidal particles often requires a means to produce highly ordered, periodic structures. One approach is the use of surface acoustic waves (SAWs) to direct the self-assembly of colloidal particles. Previous demonstrations using standing SAWs were shown to be limited in terms of crystal size and dimensionality. Here, we report a technique to improve the spatial alignment of colloidal particles using traveling SAWs. Through control of the radio frequency power, which drives the SAW, we demonstrate enhanced quality and dimensionality of the crystal growth. We show that this technique can be applied to a range of particle sizes in the μm-regime and may hold potential for particles in the sub-μm-regime.

  14. A Course in Colloid and Surface Science.

    ERIC Educational Resources Information Center

    Scamehorn, John F.

    1984-01-01

    Describes a course for chemical engineers, chemists, and petroleum engineers that focuses on colloid and surface science. Major topic areas in the course include capillarity, surface thermodynamics, adsorption contact angle, micelle formation, solubilization in micelles, emulsions, foams, and applications. (JN)

  15. Dynamical Threshold of Diluteness of Soft Colloids

    SciTech Connect

    Chen, Wei-Ren; Do, Changwoo; Egami, T; Falus, Peter; Li, Xin; Liu, Dazhi; Porcar, L.; Sanchez-Diaz, Luis E; Smith, Gregory Scott; Wu, Bin

    2014-01-01

    The dynamics of soft colloids in solutions is characterized by internal collective motion as well as center-of-mass diffusion. Using neutron scattering we demonstrate that the competition between the relaxation processes associated with these two degrees of freedom results in strong dependence of dynamics and structure on colloid concentration, c, well below the overlap concentration c*. Triggered by the increasing inter-particle collisions, substantial structural dehydration and slowing-down of internal dynamics occurs before geometrically defined colloidal overlap develops. This observation is surprising since it is generally believed that the internal dynamics and conformation of soft colloidal particles essentially remain invariant below c*. The competition between these two relaxation processes gives rise to a new dynamically-defined dilute threshold concentration well below c*.

  16. Colloidal gold: a pluripotent receptor probe.

    PubMed

    Handley, D A; Chien, S

    1983-10-01

    Colloidal gold is an electron-dense, lyophobic colloid that readily forms a stable electrostatic interaction with a variety of macromolecules. Monodispersed colloids ranging from 3-150 nm in diameter can be produced to provide the researcher with flexibility in selecting the optimally sized probe. Gold labeling of antibodies and lectins has been extensively used to study surface antigens and cell components. Recently, the use of gold labeling has been extended to study receptor-ligand binding, enzyme-substrate reactions, and transcellular pathways. Published applications include gold labeling of metabolites (low-density lipoproteins), enzymes (DNAase and RNAase, RNA polymerase, thrombin, collagenase, elastase), hormones (insulin, epidermal growth factor, glucagon), circulating plasma proteins (asialoglycoprotein, alpha 2-macroglobulin, factor VIII-von Willebrand factor), and endotoxins (tetanus toxin, cholera toxin). This broad spectrum of applications emphasizes the versatility and usefulness of colloidal gold as a probe in areas of cell biology related to receptors, endocytosis, transport, and functions of proteins. PMID:6356133

  17. Self-similarity in active colloid motion

    NASA Astrophysics Data System (ADS)

    Constant, Colin; Sukhov, Sergey; Dogariu, Aristide

    The self-similarity of displacements among randomly evolving systems has been used to describe the foraging patterns of animals and predict the growth of financial systems. At micron scales, the motion of colloidal particles can be analyzed by sampling their spatial displacement in time. For self-similar systems in equilibrium, the mean squared displacement increases linearly in time. However, external forces can take the system out of equilibrium, creating active colloidal systems, and making this evolution more complex. A moment scaling spectrum of the distribution of particle displacements quantifies the degree of self-similarity in the colloid motion. We will demonstrate that, by varying the temporal and spatial characteristics of the external forces, one can control the degree of self-similarity in active colloid motion.

  18. Sulfonated nanoporous colloidal films and membranes

    NASA Astrophysics Data System (ADS)

    Smith, Joanna Jane

    The objective of this thesis is to describe the preparation and investigation of a new class of proton-conducting membrane materials, namely, nanoporous colloidal membranes whose proton conductivity results from the nanopore surface modification with organic molecules carrying acid functionalities. Both the proton transport and ion transport were studied in nanoporous silica colloidal crystals that were surface modified with sulfonic groups. First, the transport of ions was studied through sulfonated silica colloidal films that were supported on platinum electrodes using cyclic voltammetry. The surface of self-assembled nanoporous silica colloidal crystalline films was sulfonated using 1,3-propanesultone. We found that the flux of anions through the sulfonated colloidal films is reduced, while the flux of cations is increased, compared to the unmodified colloidal films. Second, the proton transport in free-standing assemblies of surface-sulfonated silica nanospheres, either randomly packed or self-assembled into a close-packed arrangement, were studied. It was demonstrated that colloidal assemblies prepared using surface-sulfonated silica nanospheres posses proton conductivity that depends on the ordering of the material, temperature and relative humidity. Based on the comparison between the close-packed and disordered assemblies made of the same spheres, we conclude that the increase in structural organization of the self-assembled colloidal materials leads to increased proton conductivity and better water retention. Next free-standing colloidal membranes with a relatively large area and no mechanical defects were prepared by sintering silica colloidal films. The sintered membranes were then surface rehydroxylated, which restores the surface silanol groups, and then can be chemically modified. Finally, sintered self-assembled nanoporous silica colloidal crystals were modified with poly(sulfopropyl-methacrylate) (pSPM) and poly(stryrenesulfonic acid) (pSSA) brushes

  19. Colloids generation from metallic uranium fuel

    SciTech Connect

    Metz, C.; Fortner, J.; Goldberg, M.; Shelton-Davis, C.

    2000-07-20

    The possibility of colloid generation from spent fuel in an unsaturated environment has significant implications for storage of these fuels in the proposed repository at Yucca Mountain. Because colloids can act as a transport medium for sparingly soluble radionuclides, it might be possible for colloid-associated radionuclides to migrate large distances underground and present a human health concern. This study examines the nature of colloidal materials produced during corrosion of metallic uranium fuel in simulated groundwater at elevated temperature in an unsaturated environment. Colloidal analyses of the leachates from these corrosion tests were performed using dynamic light scattering and transmission electron microscopy. Results from both techniques indicate a bimodal distribution of small discrete particles and aggregates of the small particles. The average diameters of the small, discrete colloids are {approximately}3--12 nm, and the large aggregates have average diameters of {approximately}100--200 nm. X-ray diffraction of the solids from these tests indicates a mineral composition of uranium oxide or uranium oxy-hydroxide.

  20. Sterically stabilized colloids with tunable repulsions.

    PubMed

    van Gruijthuijsen, Kitty; Obiols-Rabasa, Marc; Heinen, Marco; Nägele, Gerhard; Stradner, Anna

    2013-09-10

    When studying tunable electrostatic repulsions in aqueous suspensions of charged colloids, irreversible colloid aggregation or gelation may occur at high salt concentrations. For many commonly used synthetic colloids, such as polystyrene and silica particles, the reason for coagulation is the presence of unbalanced, strongly attractive, and short-ranged van der Waals (VDW) forces. Here, we present an aqueous polystyrene model colloid that is sterically stabilized against VDW attractions. We show that the synthesis procedure, based on a neutral initiator couple and a nonionic surfactant, introduces surface charges that can be further increased by the addition of charged comonomer methacrylic acid. Thus, the interactions between the polystyrene spheres can be conveniently tuned from hard-sphere-like to charge-stabilized with long-ranged electrostatic repulsions described by a Yukawa-type pair potential. The particle size, grafting density, core-shell structure, and surface charge are characterized by light and neutron scattering. Using X-ray and neutron scattering in combination with an accurate analytic integral equation scheme for the colloidal static structure factor, we deduce effective particle charges for colloid volume fractions ≥0.1 and salt concentrations in the range of 1.5 to 50 mM. PMID:23937718

  1. Self-replication with magnetic dipolar colloids

    NASA Astrophysics Data System (ADS)

    Dempster, Joshua M.; Zhang, Rui; Olvera de la Cruz, Monica

    2015-10-01

    Colloidal self-replication represents an exciting research frontier in soft matter physics. Currently, all reported self-replication schemes involve coating colloidal particles with stimuli-responsive molecules to allow switchable interactions. In this paper, we introduce a scheme using ferromagnetic dipolar colloids and preprogrammed external magnetic fields to create an autonomous self-replication system. Interparticle dipole-dipole forces and periodically varying weak-strong magnetic fields cooperate to drive colloid monomers from the solute onto templates, bind them into replicas, and dissolve template complexes. We present three general design principles for autonomous linear replicators, derived from a focused study of a minimalist sphere-dimer magnetic system in which single binding sites allow formation of dimeric templates. We show via statistical models and computer simulations that our system exhibits nonlinear growth of templates and produces nearly exponential growth (low error rate) upon adding an optimized competing electrostatic potential. We devise experimental strategies for constructing the required magnetic colloids based on documented laboratory techniques. We also present qualitative ideas about building more complex self-replicating structures utilizing magnetic colloids.

  2. Self-replication with magnetic dipolar colloids.

    PubMed

    Dempster, Joshua M; Zhang, Rui; Olvera de la Cruz, Monica

    2015-10-01

    Colloidal self-replication represents an exciting research frontier in soft matter physics. Currently, all reported self-replication schemes involve coating colloidal particles with stimuli-responsive molecules to allow switchable interactions. In this paper, we introduce a scheme using ferromagnetic dipolar colloids and preprogrammed external magnetic fields to create an autonomous self-replication system. Interparticle dipole-dipole forces and periodically varying weak-strong magnetic fields cooperate to drive colloid monomers from the solute onto templates, bind them into replicas, and dissolve template complexes. We present three general design principles for autonomous linear replicators, derived from a focused study of a minimalist sphere-dimer magnetic system in which single binding sites allow formation of dimeric templates. We show via statistical models and computer simulations that our system exhibits nonlinear growth of templates and produces nearly exponential growth (low error rate) upon adding an optimized competing electrostatic potential. We devise experimental strategies for constructing the required magnetic colloids based on documented laboratory techniques. We also present qualitative ideas about building more complex self-replicating structures utilizing magnetic colloids. PMID:26565238

  3. Autonomous colloidal crystallization in a galvanic microreactor

    NASA Astrophysics Data System (ADS)

    Punckt, Christian; Jan, Linda; Jiang, Peng; Frewen, Thomas A.; Saville, Dudley A.; Kevrekidis, Ioannis G.; Aksay, Ilhan A.

    2012-10-01

    We report on a technique that utilizes an array of galvanic microreactors to guide the assembly of two-dimensional colloidal crystals with spatial and orientational order. Our system is comprised of an array of copper and gold electrodes in a coplanar arrangement, immersed in a dilute hydrochloric acid solution in which colloidal micro-spheres of polystyrene and silica are suspended. Under optimized conditions, two-dimensional colloidal crystals form at the anodic copper with patterns and crystal orientation governed by the electrode geometry. After the aggregation process, the colloidal particles are cemented to the substrate by co-deposition of reaction products. As we vary the electrode geometry, the dissolution rate of the copper electrodes is altered. This way, we control the colloidal motion as well as the degree of reaction product formation. We show that particle motion is governed by a combination of electrokinetic effects acting directly on the colloidal particles and bulk electrolyte flow generated at the copper-gold interface.

  4. Linked topological colloids in a nematic host.

    PubMed

    Martinez, Angel; Hermosillo, Leonardo; Tasinkevych, Mykola; Smalyukh, Ivan I

    2015-04-14

    Geometric shape and topology of constituent particles can alter many colloidal properties such as Brownian motion, self-assembly, and phase behavior. Thus far, only single-component building blocks of colloids with connected surfaces have been studied, although topological colloids, with constituent particles shaped as freestanding knots and handlebodies of different genus, have been recently introduced. Here we develop a topological class of colloids shaped as multicomponent links. Using two-photon photopolymerization, we fabricate colloidal microparticle analogs of the classic examples of links studied in the field of topology, the Hopf and Solomon links, which we disperse in nematic fluids that possess orientational ordering of anisotropic rod-like molecules. The surfaces of these particles are treated to impose tangential or perpendicular boundary conditions for the alignment of liquid crystal molecules, so that they generate a host of topologically nontrivial field and defect structures in the dispersing nematic medium, resulting in an elastic coupling between the linked constituents. The interplay between the topologies of surfaces of linked colloids and the molecular alignment field of the nematic host reveals that linking of particle rings with perpendicular boundary conditions is commonly accompanied by linking of closed singular defect loops, laying the foundations for fabricating complex composite materials with interlinking-based structural organization. PMID:25825765

  5. Colloidal diffusion over a periodic energy landscape

    NASA Astrophysics Data System (ADS)

    Ma, Xiao-Guang; Lai, Pik-Yin; Tong, Penger

    2014-03-01

    A two-layer colloidal system is developed for the study of colloidal diffusion over a two-dimensional periodic energy landscape. The energy landscape is made from the bottom layer of colloidal spheres forming a honey-comb crystalline pattern above a glass substrate. The corrugated surface of the bottom colloidal crystal provides a gravitational potential field for the diffusing particles in the top layer. The obtained population probability histogram P(x , y) of the diffusing particles is used to fully characterize the energy landscape U(x , y) via the Boltzmann distribution. The dynamical properties of the diffusing particle, such as its escape time tR and diffusion coefficient D are simultaneously measured from the particle's trajectories. The long-time diffusion coefficients D is found to be in good agreement with the theory for all colloidal samples studied. The experiment demonstrates the applications of this newly constructed colloidal energy landscape. *Work supported in part by the Research Grants Council of Hong Kong SAR.

  6. Inventions Utilizing Microfluidics and Colloidal Particles

    NASA Technical Reports Server (NTRS)

    Marr, David W.; Gong, Tieying; Oakey, John; Terray, Alexander V.; Wu, David T.

    2009-01-01

    Several related inventions pertain to families of devices that utilize microfluidics and/or colloidal particles to obtain useful physical effects. The families of devices can be summarized as follows: (1) Microfluidic pumps and/or valves wherein colloidal-size particles driven by electrical, magnetic, or optical fields serve as the principal moving parts that propel and/or direct the affected flows. (2) Devices that are similar to the aforementioned pumps and/or valves except that they are used to manipulate light instead of fluids. The colloidal particles in these devices are substantially constrained to move in a plane and are driven to spatially order them into arrays that function, variously, as waveguides, filters, or switches for optical signals. (3) Devices wherein the ultra-laminar nature of microfluidic flows is exploited to effect separation, sorting, or filtering of colloidal particles or biological cells in suspension. (4) Devices wherein a combination of confinement and applied electrical and/or optical fields forces the colloidal particles to become arranged into three-dimensional crystal lattices. Control of the colloidal crystalline structures could be exploited to control diffraction of light. (5) Microfluidic devices, incorporating fluid waveguides, wherein switching of flows among different paths would be accompanied by switching of optical signals.

  7. Linked topological colloids in a nematic host

    PubMed Central

    Martinez, Angel; Hermosillo, Leonardo; Tasinkevych, Mykola; Smalyukh, Ivan I.

    2015-01-01

    Geometric shape and topology of constituent particles can alter many colloidal properties such as Brownian motion, self-assembly, and phase behavior. Thus far, only single-component building blocks of colloids with connected surfaces have been studied, although topological colloids, with constituent particles shaped as freestanding knots and handlebodies of different genus, have been recently introduced. Here we develop a topological class of colloids shaped as multicomponent links. Using two-photon photopolymerization, we fabricate colloidal microparticle analogs of the classic examples of links studied in the field of topology, the Hopf and Solomon links, which we disperse in nematic fluids that possess orientational ordering of anisotropic rod-like molecules. The surfaces of these particles are treated to impose tangential or perpendicular boundary conditions for the alignment of liquid crystal molecules, so that they generate a host of topologically nontrivial field and defect structures in the dispersing nematic medium, resulting in an elastic coupling between the linked constituents. The interplay between the topologies of surfaces of linked colloids and the molecular alignment field of the nematic host reveals that linking of particle rings with perpendicular boundary conditions is commonly accompanied by linking of closed singular defect loops, laying the foundations for fabricating complex composite materials with interlinking-based structural organization. PMID:25825765

  8. Tunable Time-Dependent Colloidal Interactions

    NASA Astrophysics Data System (ADS)

    Bergman, Andrew M.; Rogers, W. Benjamin; Manoharan, Vinothan N.

    Self-assembly of colloidal particles can be driven by changes in temperature, density, or the concentration of solutes, and it is even possible to program the thermal response and equilibrium phase transitions of such systems. It is still difficult, however, to tune how the self-assembly process varies in time. We demonstrate control over the time-dependence of colloidal interactions, using DNA-functionalized colloidal particles with binding energies that are set by the concentration of a free linker strand in solution. We control the rate at which this free strand is consumed using a catalytic DNA reaction, whose rate is governed by the concentration of a catalyst strand. Varying the concentration of the linker, its competitor, and the catalyst at a fixed temperature, we can tune the rate and degree of the formation of colloidal aggregates and their following disassembly. Close to the colloidal melting point, the timescales of these out-of-equilibrium assembly and disassembly processes are determined by the rate of the catalytic reaction. Far below the colloidal melting point, however, the effects from varying our linker and competitor concentrations dominate.

  9. Interactions between radioactively labeled colloids and natural particles: Evidence for colloidal pumping

    SciTech Connect

    Wen, L.S.; Santschi, P.H.; Tang, D.

    1997-07-01

    It has been hypothesized that colloidal forms of trace metals can be reactive intermediaries in the scavenging processes leading to the removal of their particulate forms. A series of radiotracer experiments using natural colloidal organic matter from Galveston Bay, USA were carried out in order to test this hypothesis. Suspended particle uptake of originally colloidally bound trace metals occurred in a matter of hours to days in estuarine waters. After ten days, the majority ( >50%) of the colloidal trace metals had been transferred into the particulate phase ({ge} 0.45{mu}m), except for {sup 65}Zn. Two distinctively different temporal regions of removal of colloidal trace metals were identified: a faster reaction during the first four hours, followed by a slower reaction after approximately one day. In a separate river water-seawater mixing experiment, the solid/solution partitioning of the radiotracers was investigated in the absence of suspended matter. About 30% of most of the elements, except Ag and Fe ({approximately}60%), were associated with a newly formed particulate phase after eight days. There were two major trends: (1) the particulate fraction of {sup 59}Fe and {sup 110}Ag increased while the colloidal fraction decreased, suggesting a colloidal pumping mechanism. (2) The particulate fraction of {sup 54}Mn, {sup 133}Ba, {sup 65}Zn, {sup 109}Cd, {sup 113}Sn, and {sup 60}Co increased while the LMW({le}1 kDa) fraction decreased, suggesting a direct uptake into the particulate fraction with less involvement of a transitory colloidal phase. The results from these experiments suggested two different pathways for colloidal tracer uptake by particles: (1) colloidal pumping of a major component (e.g., biopolymer) of the colloidal pool and (2) coagulation of trace components (e.g., phytochelatins) with varying affinities for different trace metals. 39 refs., 8 figs., 3 tabs.

  10. Magnetic nanostructures by colloidal lithography

    NASA Astrophysics Data System (ADS)

    Zhu, Frank Qing

    Structural, magnetic and in some cases magneto-transport properties of (1) symmetric and asymmetric ferromagnetic nanorings and (2) single layer, multilayer, and exchange biased ferromagnetic nanodots prepared by colloidal lithography are presented. A fast, reliable and cost effective method has been developed to fabricate large number (˜ 109) of magnetic nanorings over macroscopic areas (˜ cm2) with large areal densities (up to 45 rings/mum 2). Cobalt nanorings with diameters ranging from 100 nm to 500 nm have been fabricated by sputtering Co onto nanosphere-coated substrates followed by ion beam etching. X-ray diffraction verifies that the Co nanorings still have hexagonal close-packed (hcp) structure. Scanning electron microscopy reveals that the cross-section of the symmetric nanoring is tapered and uniform along the circumference, and the cross-section of the asymmetric nanoring changes progressively along the circumference. Two magnetic reversal processes have been found in magnetic nanorings---the vortex formation process and the onion rotation process. The co-existence of these two processes is the manifestation of the competition between the exchange energy and the magnetostatic energy in the nanorings. Micromagnetics simulations have been carried out to reveal the details of the magnetic reversals. The experimental and the computed hysteresis loops agree both qualitatively and quantitatively. For the 100 nm symmetric Co nanorings, the vortex formation process has a probability of about 40%, while the onion rotation process has 60% chances. To increase the probability of vortex formation process, a desirable process for application, asymmetric nanorings have been fabricated by ion beam etching at oblique angles. Unlike the symmetric nanorings, the probability of the vortex formation process in asymmetric nanorings can be controlled by the direction of the external field. For the 100 nm asymmetric nanorings, the fraction of the vortex formation process

  11. Les violences conjugales à Dakar

    PubMed Central

    Soumah, Mohamed Maniboliot; Issa, Abdoul Wahab; Ndiaye, Mor; Ndoye, El Hadj Oumar; Sow, Mamadou Lamine

    2015-01-01

    L'objectif était d’évaluer les aspects épidémiologiques des violences conjugales, identifier les facteurs de risques et les différents types de violences conjugales, évaluer les conséquences des violences conjugales sur la santé des victimes, afin d'améliorer la prise en charge des victimes et la prévention du phénomène. Il s'est agit d'une étude transversale effectuée de décembre 2012 à janvier 2013 à Dakar. Les données ont été recueillies, après consentement, sur fiche d'enquête anonyme soumise à toute personne volontaire vivant en couple et résidant à Dakar. L'analyse statistique a été effectuée avec le logiciel SPSS 13.0. Le nombre de personnes victimes de violences conjugales était de 60 soit 37,30% dont 31 femmes (51,70%) et 29 hommes (48,30%). Le sex-ratio était de 0,93. Parmi les victimes, 53 étaient scolarisées soit 88,30%. Le régime matrimonial était de type monogame dans 39 cas (65%) et polygame dans 21 cas (35%). La vie en couple durait depuis moins de 11 ans dans 60% des cas et durait de 11 ans à 20 ans au plus dans 26,6% des cas. L’étude des types de violences montrait la fréquence des agressions physiques. Les armes utilisées étaient surtout les armes naturelles. Les principaux facteurs de risque de violence conjugale sont les facteurs sociodémographiques, culturels et économiques comme le jeune âge, l'inégalité du genre, les jeunes couples, la précarité, le niveau d'instruction élevé. La prise en charge des victimes et la prévention du phénomène restent insuffisantes dans nos pays. PMID:26918077

  12. Statistical thermodynamics of charge-stabilized colloids

    NASA Astrophysics Data System (ADS)

    Torres Valderrama, A.

    2008-06-01

    This thesis is a theoretical study of equilibrium statistical thermodynamic properties of colloidal systems in which electrostatic interactions play a dominant role, namely, charge-stabilized colloidal suspensions. Such systems are fluids consisting of a mixture of a large number of mesoscopic particles and microscopic ions which interact via the Coulomb force, suspended in a molecular fluid. Quantum statistical mechanics is essential to fully understand the properties and stability of such systems. A less fundamental but for many purposes, sufficient description, is provided by classical statistical mechanics. In such approximation the system is considered as composed of a great number of charged classical particles with additional hard-core repulsions. The kinetic energy or momentum integrals become independent Gaussians, and hence their contribution to the free energy can be trivially evaluated. The contribution of the potential energy to the free energy on the other hand, depends upon the configuration of all the particles and becomes highly non-trivial due to the long-range character of the Coulomb force and the extremely different length scales involved in the problem. Using the microscopic model described above, we focus on the calculation of equilibrium thermodynamic properties (response functions), correlations (structure factors), and mechanical properties (forces and stresses), which can be measured in experiments and computed by Monte Carlo simulations. This thesis is divided into three parts. In part I, comprising chapters 2 and 3, we focus on finite-thickness effects in colloidal platelets and rigid planar membranes. In chapter 2 we study electrolyte-mediated interactions between two of such colloidal objects. Several aspects of these interactions are considered including the nature (attractive or repulsive) of the force between the objects, the osmotic properties for different types of surfaces and image charge effects. In part II, which includes

  13. Colloidal Gelation-2 and Colloidal Disorder-Order Transition-2 Investigations Conducted on STS-95

    NASA Technical Reports Server (NTRS)

    Hoffmann, Monica T.

    2000-01-01

    The Colloidal Gelation-2 (CGEL 2) and Colloidal Disorder-Order Transition-2 (CDOT 2) investigations flew on Space Shuttle Discovery mission STS-95 (also known as the John Glenn Mission). These investigations were part of a series of colloid experiments designed to help scientists answer fundamental science questions and reduce the trial and error involved in developing new and better materials. Industries dealing with semiconductors, electro-optics, ceramics, and composites are just a few that may benefit from this knowledge. The goal of the CGEL 2 investigation was to study the fundamental properties of colloids to help scientists better understand their nature and make them more useful for technology. Colloids consist of very small (submicron) particles suspended in a fluid. They play a critical role in the technology of this country, finding uses in materials ranging from paints and coatings to drugs, cosmetics, food, and drink. Although these products are routinely produced and used, there are still many aspects of their behavior about which scientists know little. Understanding their structures may allow scientists to manipulate the physical properties of colloids (a process called "colloidal engineering") to produce new materials and products. Colloid research may even improve the processing of known products to enhance their desirable properties.

  14. Colloids in the River Inn

    NASA Astrophysics Data System (ADS)

    Ueckert, Martina; Baumann, Thomas

    2014-05-01

    In the light of an increasing number of technical applications using nanoparticles and reports of adverse effects of engineered nanoparticles, research on the occurrence and stability of particles in all compartments has to be intensified. Colloids in river water represent the geologic setting, environmental conditions, and the anthropogenic use in its catchment. The river not only acts as a sink for nanoparticles but also as the source term due to exchange in the hyporheic zone and in bank filtration setups. The concentration, size distribution and elemental composition of particles in the River Inn were studied from the source in the Swiss Alps to the river mouth at Passau. Samples were collected after each tributary from a sub-catchment and filtered on-site. The elemental composition was determined after acid digestion with ICP/MS. SEM/EDX analyses provided morphological and elemental information for single particles. A complementary chemical analysis of the river water was performed to assess the geochemical stability of indvidual particles. Particles in the upper, rural parts mainly reveal changes in the geological setting of the tributary catchments. Not unexpectedly, particles originating from crystalline rocks, were more stable than particles originating from calcareous rocks. Anthropogenic and industrial influences increase in the lower parts. This went together with a change of the size distribution, an increase of the number of organic particles, and a decrease of the microfauna. Interestingly, specific leisure activities in a sub-catchment, like extensive downhill skiing, manifest itself in the particle composition.

  15. Colloidal Bandpass and Bandgap Filters

    NASA Astrophysics Data System (ADS)

    Yellen, Benjamin; Tahir, Mukarram; Ouyang, Yuyu; Nori, Franco

    2013-03-01

    Thermally or deterministically-driven transport of objects through asymmetric potential energy landscapes (ratchet-based motion) is of considerable interest as models for biological transport and as methods for controlling the flow of information, material, and energy. Here, we provide a general framework for implementing a colloidal bandpass filter, in which particles of a specific size range can be selectively transported through a periodic lattice, whereas larger or smaller particles are dynamically trapped in closed-orbits. Our approach is based on quasi-static (adiabatic) transition in a tunable potential energy landscape composed of a multi-frequency magnetic field input signal with the static field of a spatially-periodic magnetization. By tuning the phase shifts between the input signal and the relative forcing coefficients, large-sized particles may experience no local energy barriers, medium-sized particles experience only one local energy barrier, and small-sized particles experience two local energy barriers. The odd symmetry present in this system can be used to nudge the medium-sized particles along an open pathway, whereas the large or small beads remain trapped in a closed-orbit, leading to a bandpass filter, and vice versa for a bandgap filter. NSF CMMI - 0800173, Youth 100 Scholars Fund

  16. Seismic stress mobilization of natural colloids in a porous rock

    SciTech Connect

    Roberts, Peter M; Abdel-fattah, Amr I

    2008-01-01

    Stress oscillations at 26 Hz enhanced the release of natural micro-particles (colloids) in a porous rock sample. Micron-scale effects were induced by meter-scale wavelengths. The results are attributed to altering the release rate coefficient for colloids trapped in pores. The rate change did not depend on colloid size and thus is not due to altering colloid-pore-wall interactions. Enhanced colloid detachment from pore walls and flushing from dead-end pores are likely mechanisms. This phenomenon could impact a broad range of physical sciences involving colloid dynamics and porous transport.

  17. Modeling colloid transport for performance assessment.

    PubMed

    Contardi, J S; Turner, D R; Ahn, T M

    2001-02-01

    The natural system is expected to contribute to isolation at the proposed high-level nuclear waste (HLW) geologic repository at Yucca Mountain, NV (YM). In developing performance assessment (PA) computer models to simulate long-term behavior at YM, colloidal transport of radionuclides has been proposed as a critical factor because of the possible reduced interaction with the geologic media. Site-specific information on the chemistry and natural colloid concentration of saturated zone groundwaters in the vicinity of YM is combined with a surface complexation sorption model to evaluate the impact of natural colloids on calculated retardation factors (RF) for several radioelements of concern in PA. Inclusion of colloids into the conceptual model can reduce the calculated effective retardation significantly. Strongly sorbed radionuclides such as americium and thorium are most affected by pseudocolloid formation and transport, with a potential reduction in RF of several orders of magnitude. Radioelements that are less strongly sorbed under YM conditions, such as uranium and neptunium, are not affected significantly by colloid transport, and transport of plutonium in the valence state is only moderately enhanced. Model results showed no increase in the peak mean annual total effective dose equivalent (TEDE) within a compliance period of 10,000 years, although this is strongly dependent on container life in the base case scenario. At longer times, simulated container failures increase and the TEDE from the colloidal models increased by a factor of 60 from the base case. By using mechanistic models and sensitivity analyses to determine what parameters and transport processes affect the TEDE, colloidal transport in future versions of the TPA code can be represented more accurately. PMID:11288586

  18. Interparticle interactions and polarization effects in colloids

    SciTech Connect

    Hayter, J.B.

    1987-01-01

    The physics of simple colloidal systems is usually dominated by three independent length scales: the particle size, the average interparticle distance, and the range of the interparticle potential. The dispersed particles typically have characteristic dimensions in the range 5 to 100 nm, often with spherical or cylindrical symmetry. Dispersion densities vary over volume fractions ranging from 0.5 to 10/sup -4/, with the corresponding mean interparticle distances ranging from about 1 to 10 diameters (in spherical systems). The interaction potential may be very short ranged (hard sphere), very long ranged (Coulomb or dipolar), or anywhere in between (screened Coulomb), and the correlations exhibited in the dispersion may be gas-like, liquid-like or crystalline, depending on the range of the potential relative to the interparticle distance. This rich phase behavior is responsible for the remarkable importance of colloidal studies in many areas of condensed matter physics and biophysics, but it poses often intractable problems in developing the statistical mechanical descriptions necessary for an understanding of scattering data from colloids. This paper will review the considerable recent progress in this field, in the context of SANS experiments on colloids in which the potentials are dominated by either screened Coulomb or magnetic dipolar interactions; in the case of magnetic colloids (ferrofluids), the use of polarization analysis will also be discussed. 32 refs., 4 figs.

  19. Diffusing colloidal probes of cell surfaces.

    PubMed

    Duncan, Gregg A; Fairbrother, D Howard; Bevan, Michael A

    2016-05-25

    Measurements and analyses are reported to quantify dynamic and equilibrium interactions between colloidal particles and live cell surfaces using dark field video microscopy. Two-dimensional trajectories of micron-sized polyethylene glycol (PEG)-coated silica colloids relative to adherent epithelial breast cancer cell perimeters are determined allowing measurement of position dependent diffusivities and interaction potentials. PEG was chosen as the material system of interest to assess non-specific interactions with cell surfaces and establishes a basis for investigation of specific interactions in future studies. Analysis of measured potential energies on cell surfaces reveals the spatial dependence in cell topography. With the measured cell topography and models for particle-cell surface hydrodynamic interactions, excellent agreement is obtained between theoretical and measured colloidal transport on cell surfaces. Quantitative analyses of association lifetimes showed that PEG coatings act to stabilize colloids above the cell surface through net repulsive, steric interactions. Our results demonstrate a self-consistent analysis of diffusing colloidal probe interactions due to conservative and non-conservative forces to characterize biophysical cell surface properties. PMID:27117575

  20. Method for electrohydrodynamically assembling patterned colloidal structures

    NASA Technical Reports Server (NTRS)

    Trau, Mathias (Inventor); Aksay, Ilhan A. (Inventor); Saville, Dudley A. (Inventor)

    1999-01-01

    A method apparatus is provided for electrophoretically depositing particles onto an electrode, and electrohydrodynamically assembling the particles into crystalline structures. Specifically, the present method and apparatus creates a current flowing through a solution to cause identically charged electrophoretically deposited colloidal particles to attract each other over very large distances (<5 particle diameters) on the surface of electrodes to form two-dimensional colloidal crystals. The attractive force can be created with both DC and AC fields and can modulated by adjusting either the field strength or frequency of the current. Modulating this lateral attraction between the particles causes the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows for the formation of two or three-dimensional colloidal crystals, as well as more complex designed structures. Once the required structures are formed, these three-dimension colloidal crystals can be permanently frozen or glued by controlled coagulation induced by to the applied field to form a stable crystalline structure.

  1. Apparatus for electrohydrodynamically assembling patterned colloidal structures

    NASA Technical Reports Server (NTRS)

    Trau, Mathias (Inventor); Aksay, Ilhan A. (Inventor); Saville, Dudley A. (Inventor)

    2000-01-01

    A method apparatus is provided for electrophoretically depositing particles onto an electrode, and electrohydrodynamically assembling the particles into crystalline structures. Specifically, the present method and apparatus creates a current flowing through a solution to cause identically charged electrophoretically deposited colloidal particles to attract each other over very large distances (<5 particle diameters) on the surface of electrodes to form two-dimensional colloidal crystals. The attractive force can be created with both DC and AC fields and can modulated by adjusting either the field strength or frequency of the current. Modulating this lateral attraction between the particles causes the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows for the formation of two or three-dimensional colloidal crystals, as well as more complex designed structures. Once the required structures are formed, these three-dimension colloidal crystals can be permanently frozen or glued by controlled coagulation induced by to the applied field to form a stable crystalline structure.

  2. Colloidal spirals in nematic liquid crystals.

    PubMed

    Senyuk, Bohdan; Pandey, Manoj B; Liu, Qingkun; Tasinkevych, Mykola; Smalyukh, Ivan I

    2015-12-01

    One of the central experimental efforts in nematic colloids research aims to explore how the interplay between the geometry of particles along with the accompanying nematic director deformations and defects around them can provide a means of guiding particle self-assembly and controlling the structure of particle-induced defects. In this work, we design, fabricate, and disperse low-symmetry colloidal particles with shapes of spirals, double spirals, and triple spirals in a nematic fluid. These spiral-shaped particles, which are controlled by varying their surface functionalization to provide tangential or perpendicular boundary conditions of the nematic molecular alignment, are found inducing director distortions and defect configurations with non-chiral or chiral symmetry. Colloidal particles also exhibit both stable and metastable multiple orientational states in the nematic host, with a large number of director configurations featuring both singular and solitonic nonsingular topological defects accompanying them, which can result in unusual forms of colloidal self-assembly. Our findings directly demonstrate how the symmetry of particle-generated director configurations can be further lowered, or not, as compared to the low point group symmetry of solid micro-inclusions, depending on the nature of induced defects while satisfying topological constraints. We show that achiral colloidal particles can cause chiral symmetry breaking of elastic distortions, which is driven by complex three-dimensional winding of induced topological line defects and solitons. PMID:26358649

  3. Colloids with continuously tunable surface charge.

    PubMed

    van Ravensteijn, Bas G P; Kegel, Willem K

    2014-09-01

    In this paper, we present a robust way to tune the surface potential of polystyrene colloids without changing the pH, ionic strength, etc. The colloids are composed of a cross-linked polystyrene core and a cross-linked vinylbenzyl chloride layer. Besides the chlorine groups, the particle surface contains sulfate/sulfonate groups (arising from the polymerization initiators) that provide a negative surface potential. Performing a Menschutkin reaction on the surface chlorine groups with tertiary amines allows us to introduce quaternary, positively charged amines. The overall charge on the particles is then determined by the ratio between the sulfate/sulfonate moieties and the quaternary amines. Using this process, we were able to invert the charge in a continuous manner without losing colloidal stability upon passing the isoelectric point. The straightforward reaction mechanism together with the fact that the reaction could be quenched rapidly resulted in a colloidal system in which the ζ potential can be tuned between -80 and 45 mV. As proof of principle, the positively charged particles were used in heterocoagulation experiments with nanometer- and micrometer-sized negatively charged silica particles to create geometrically well-defined colloidal (nano) clusters. PMID:25127340

  4. Une vie active saine pour les enfants et les adolescents

    PubMed Central

    2002-01-01

    De mauvais modes de vie, comme une alimentation malsaine et l’inactivité physique, sont d'importants facteurs contributifs à une augmentation de la morbidité et de la mortalité secondaires à des maladies chroniques à l’âge adulte. Depuis dix ans, on remarque une augmentation du mode de vie sédentaire et de l’obésité chez les enfants et les adolescents, tant en Amérique du Nord qu’ailleurs dans le monde. Les médecins doivent être conscients de l’importance du problème, fournir des conseils de prévention aux familles et promouvoir une vie active saine dans leur pratique.

  5. ["Les Impatients": expression through art].

    PubMed

    Lamontagne, Céline; Palardy, Lorraine

    2015-01-01

    The organization called "Les Impatients" was founded in 1992. Using a unique model, Les Impatients welcomes those with mental health issues who would like to express themselves through art. Les Impatients offers free creative workshops and encourages exchanges with the community through the sharing of its participants' creations. The name Les Impatients reinforces the idea that the organization does not consider those attending its workshops as patients, but rather creators who are eager to heal, develop their craft and find their place in society. The participants contribute to the collective objective of breaking down the stigma that surrounds mental illness.Les Impatients collaborates with various mental health organizations in Quebec, such as the Institut universitaire en santé mentale de Montréal (IUSMM) affiliated to the Université de Montréal, Douglas Mental Health University Institute (DMHUI), the Centre de santé et services sociaux Drummond (CSSS Drummond) and the Centre de santé et services sociaux Pierre-Boucher (CSSS Pierre-Boucher). Les Impatients offers more than 48 workshops in eight different locations to around 450 participants each week.Dissemination activities, remarkable events, original projects: Les Impatients stands out through its realizations. Examples are exhibitions, collections of love letters, comic books, CD, concerts, and reading nights. The organization's originality resides in the exploration of the links between the work of the participants and that of professional artists. An illustration of this interest is the annual Parle-moi d'amour auction-exhibition, which has been one of Les Impatients' major events since 1999.As part of its mission, Les Impatients conserves the works of art created by the participants during the workshops. Its collection includes more than 15,000 works of art from Les Impatients as well as pieces donated by collectors of unconventional art, commonly known as "art brut" or "outsider art". The

  6. Influence of heteroaggregation processes between intrinsic colloids and carrier colloids on cerium(III) mobility through fractured carbonate rocks.

    PubMed

    Tran, Emily; Klein Ben-David, Ofra; Teutch, Nadya; Weisbrod, Noam

    2016-09-01

    Colloid facilitated transport of radionuclides has been implicated as a major transport vector for leaked nuclear waste in the subsurface. Sorption of radionuclides onto mobile carrier colloids such as bentonite and humic acid often accelerates their transport through saturated rock fractures. Here, we employ column studies to investigate the impact of intrinsic, bentonite and humic acid colloids on the transport and recovery of Ce(III) through a fractured chalk core. Ce(III) recovery where either bentonite or humic colloids were added was 7.7-26.9% Ce for all experiments. Greater Ce(III) recovery was observed when both types of carrier colloids were present (25.4-37.4%). When only bentonite colloids were present, Ce(III) appeared to be fractionated between chemical sorption to the bentonite colloid surfaces and heteroaggregation of bentonite colloids with intrinsic carbonate colloids, precipitated naturally in solution. However, scanning electron microscope (SEM) images and colloid stability experiments reveal that in suspensions of humic acid colloids, colloid-facilitated Ce(III) migration results only from the latter attachment mechanism rather than from chemical sorption. This observed heteroaggregation of different colloid types may be an important factor to consider when predicting potential mobility of leaked radionuclides from geological repositories for spent fuel located in carbonate rocks. PMID:27183207

  7. Technetium-99m antimony colloid for bone-marrow imaging

    SciTech Connect

    Martindale, A.A.; Papadimitriou, J.M.; Turner, J.H.

    1980-11-01

    Technetium-99m antimony colloid was prepared in our laboratory for bone-marrow imaging. Optimal production of colloid particles of size range 1 to 13 nm was achieved by the use of polyvinylpyrrolidone of mol. wt. 44,000. Electron microscopy was used to size the particles. Studies in rabbits showed exclusive concentration in the subendothelial dendritic phagocytes of the bone marrow. Pseudopods from these cells were found to traverse interendothelial junctions and concentrate colloid from the sinusoids. Imaging studies of bone marrow in rabbits showed the superiority of the Tc-99m antimony colloid over the much larger colloidal particle of Tc-99m sulfur colloid. Tissue distribution studies in the rat confirmed that bone-marrow uptake of Tc-99m antimony colloid was greater than that of Tc-99m sulfur colloid, although blood clearance was much slower.

  8. COLLOIDAL CONSIDERATIONS IN GROUNDWATER SAMPLING AND CONTAMINANT TRANSPORT PREDICTIONS

    EPA Science Inventory

    The association of contaminants with suspended colloidal material in groundwater is a possible transport mechanism and a complicating factor for accurate estimations of the aqueous geochemistry of subsurface systems. esearch to date indicates colloidal facilitated transport of co...

  9. Industrial application of surface and colloid science

    SciTech Connect

    Borgarello, E.

    1995-12-01

    Interfacial phenomena are playing a key role in several industrial processes such as oil production and refining, synthesis of chemicals and catalytic reactions. Eniricerche has gained a quite wide experience in applied colloid science in the last fifteen years working together with the Operating Companies of the ENI group. The main areas of interest have been oil production and transportation, fuel formulation, lubrication, bitumen, detergency, reactions in microemulsions, gels for cosmetics, blood substitutes, and photocatalytic degradation of pollutants in colloidal dispersions. The understanding of the interfacial phenomena occurring at the solid-liquid or at the liquid-liquid interface has been a major contribution to the solution of industrial problems. After a short description of Eniricerche activities in applied colloid science, two examples will be described: the hydroformulation of olefines in a microemulsion and the transportation of heavy oil in an oil-in-water emulsion.

  10. Nematic colloidal tilings as photonic materials

    NASA Astrophysics Data System (ADS)

    Ravnik, M.; Dontabhaktuni, J.; Cancula, M.; Zumer, S.

    2014-02-01

    Colloidal platelets are explored as elementary building blocks for the shape-controlled assembly of crystalline and quasicrystalline tilings. Using three-dimensional (3D) numerical modelling based on the minimization of Landau-de Gennes free energy for modelling of colloids combined with Finite Difference Time Domain calculations for optics, we demonstrate the self-assembly and optical (transmission) properties of triangular, square and pentagonal sub-micrometer sized platelets in a thin layer of nematic liquid crystal. Interactions between platelets are explored, providing an insight into the assembly process. Two-dimensional tilings of various-shaped colloidal platelets are demonstrated, and their use as diffraction layers is explored by using FDTD simulations. Designing symmetry-breaking surface anchoring profiles on pentagonal platelets opens also a possibility to achieve interactions that could lead to tilings with non-crystalline symmetry.

  11. Shape-shifting colloids via stimulated dewetting

    NASA Astrophysics Data System (ADS)

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-07-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly.

  12. Colloids in food: ingredients, structure, and stability.

    PubMed

    Dickinson, Eric

    2015-01-01

    This article reviews progress in the field of food colloids with particular emphasis on advances in novel functional ingredients and nanoscale structuring. Specific aspects of ingredient development described here are the stabilization of bubbles and foams by the protein hydrophobin, the emulsifying characteristics of Maillard-type protein-polysaccharide conjugates, the structural and functional properties of protein fibrils, and the Pickering stabilization of dispersed droplets by food-grade nanoparticles and microparticles. Building on advances in the nanoscience of biological materials, the application of structural design principles to the fabrication of edible colloids is leading to progress in the fabrication of functional dispersed systems-multilayer interfaces, multiple emulsions, and gel-like emulsions. The associated physicochemical insight is contributing to our mechanistic understanding of oral processing and textural perception of food systems and to the development of colloid-based strategies to control delivery of nutrients during food digestion within the human gastrointestinal tract. PMID:25422877

  13. Dynamic Assembly of Magnetic Colloidal Vortices.

    PubMed

    Mohorič, Tomaž; Kokot, Gašper; Osterman, Natan; Snezhko, Alexey; Vilfan, Andrej; Babič, Dušan; Dobnikar, Jure

    2016-05-24

    Magnetic colloids in external time-dependent fields are subject to complex induced many-body interactions governing their self-assembly into a variety of equilibrium and out-of-equilibrium structures such as chains, networks, suspended membranes, and colloidal foams. Here, we report experiments, simulations, and theory probing the dynamic assembly of superparamagnetic colloids in precessing external magnetic fields. Within a range of field frequencies, we observe dynamic large-scale structures such as ordered phases composed of precessing chains, ribbons, and rotating fluidic vortices. We show that the structure formation is inherently coupled to the buildup of torque, which originates from internal relaxation of induced dipoles and from transient correlations among the particles as a result of short-lived chain formation. We discuss in detail the physical properties of the vortex phase and demonstrate its potential in particle-coating applications. PMID:27128501

  14. Collective behavior of thermally active colloids.

    PubMed

    Golestanian, Ramin

    2012-01-20

    Colloids with patchy metal coating under laser irradiation could act as local heat sources and generate temperature gradients that could induce self-propulsion and interactions between them. The collective behavior of a dilute solution of such thermally active particles is studied using a stochastic formulation. It is found that when the Soret coefficient is positive, the system could be described in a stationary state by the nonlinear Poisson-Boltzmann equation and could adopt density profiles with significant depletion in the middle region when confined. For colloids with a negative Soret coefficient, the system can be described as a dissipative equivalent of a gravitational system. It is shown that in this case the thermally active colloidal solution could undergo an instability at a critical laser intensity, which has similarities to a supernova explosion. PMID:22400792

  15. Collective Behavior of Thermally Active Colloids

    NASA Astrophysics Data System (ADS)

    Golestanian, Ramin

    2012-01-01

    Colloids with patchy metal coating under laser irradiation could act as local heat sources and generate temperature gradients that could induce self-propulsion and interactions between them. The collective behavior of a dilute solution of such thermally active particles is studied using a stochastic formulation. It is found that when the Soret coefficient is positive, the system could be described in a stationary state by the nonlinear Poisson-Boltzmann equation and could adopt density profiles with significant depletion in the middle region when confined. For colloids with a negative Soret coefficient, the system can be described as a dissipative equivalent of a gravitational system. It is shown that in this case the thermally active colloidal solution could undergo an instability at a critical laser intensity, which has similarities to a supernova explosion.

  16. Boundaries Matter for Confined Colloidal Glasses

    NASA Astrophysics Data System (ADS)

    Hunter, Gary L.; Edmond, Kazem V.; Weeks, Eric R.

    2012-02-01

    We confine dense colloidal suspensions within emulsion droplets to examine how confinement and properties of the confining medium affect the colloidal glass transition. Samples are imaged via fast confocal microscopy. By observing a wide range of droplet sizes and varying the viscosity of the external continuous phase, we separate finite size and boundary effects on particle motions within the droplet. Suspensions are composed of binary PMMA spheres in organic solvents while the external phases are simple mixtures of water and glycerol. In analogy with molecular super-cooled liquids and thin-film polymers, we find that confinement effects in colloidal systems are not merely functions of the finite size of the system, but are strongly dependent on the viscosity of the confining medium and interactions between particles and the interface of the two phases.

  17. Shape-shifting colloids via stimulated dewetting.

    PubMed

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-01-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly. PMID:27426418

  18. Convection of a stratified colloidal suspension

    SciTech Connect

    Cherepanov, I. N.; Smorodin, B. L.

    2013-11-15

    The convection of a colloidal suspension, which is a binary mixture of a carrier medium with an admixture of nanoparticles having a large positive thermal diffusion parameter, has been studied for the case of the heating of a horizontal cell from below and periodic conditions at the vertical boundaries corresponding to the experimental situation of ring channels. Bifurcation diagrams have been constructed for vibrational and monotonic regimes of the convection of the colloidal mixture. The time dependences of the maximum stream function and the stream function at a fixed point of the cell, as well as the spatial distributions of the concentration field of the colloid admixture, have been obtained. It has been shown that a stable regime of traveling waves exists in a certain region of the parameters of the problem (Boltzmann and Rayleigh numbers characterizing the gravitational stratification and intensity of the thermal effect, respectively)

  19. Premelting at Defects Within Bulk Colloidal Crystals

    NASA Astrophysics Data System (ADS)

    Alsayed, A. M.; Islam, M. F.; Zhang, J.; Collings, P. J.; Yodh, A. G.

    2005-08-01

    Premelting is the localized loss of crystalline order at surfaces and defects at temperatures below the bulk melting transition. It can be thought of as the nucleation of the melting process. Premelting has been observed at the surfaces of crystals but not within. We report observations of premelting at grain boundaries and dislocations within bulk colloidal crystals using real-time video microscopy. The crystals are equilibrium close-packed, three-dimensional colloidal structures made from thermally responsive microgel spheres. Particle tracking reveals increased disorder in crystalline regions bordering defects, the amount of which depends on the type of defect, distance from the defect, and particle volume fraction. Our observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and atomic-scale crystals.

  20. Targeted delivery of colloids by swimming bacteria

    PubMed Central

    Koumakis, N.; Lepore, A.; Maggi, C.; Di Leonardo, R.

    2013-01-01

    The possibility of exploiting motile microorganisms as tiny propellers represents a fascinating strategy for the transport of colloidal cargoes. However, delivery on target sites usually requires external control fields to steer propellers and trigger cargo release. The need for a constant feedback mechanism prevents the design of compact devices where biopropellers could perform their tasks autonomously. Here we show that properly designed three-dimensional (3D) microstructures can define accumulation areas where bacteria spontaneously and efficiently store colloidal beads. The process is stochastic in nature and results from the rectifying action of an asymmetric energy landscape over the fluctuating forces arising from collisions with swimming bacteria. As a result, the concentration of colloids over target areas can be strongly increased or depleted according to the topography of the underlying structures. Besides the significance to technological applications, our experiments pose some important questions regarding the structure of stationary probability distributions in non-equilibrium systems. PMID:24100868

  1. Shape-shifting colloids via stimulated dewetting

    PubMed Central

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-01-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly. PMID:27426418

  2. Colloidal Disorder-Order Transition (CDOT-2)

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This is an image of a colloidal crystal from the CDOT-2 investigation flown on STS-95. There are so many colloidal particles in this sample that it behaves like a glass. In the laboratory on Earth, the sample remained in an amorphous state, showing no sign of crystal growth. In microgravity the sample crystallized in 3 days, as did the other glassy colloidal samples examined in the CDOT-2 experiment. During the investigation, crystallization occurred in samples that had a volume fraction (number of particles per total volume) larger than the formerly reported glass transition of 0.58. This has great implications for theories of the structural glass transition. These crystals were strong enough to survive space shuttle re-entry and landing.

  3. Phosphate binding by natural iron-rich colloids in streams.

    PubMed

    Baken, Stijn; Moens, Claudia; van der Grift, Bas; Smolders, Erik

    2016-07-01

    Phosphorus (P) in natural waters may be bound to iron (Fe) bearing colloids. However, the natural variation in composition and P binding strength of these colloids remain unclear. We related the composition of "coarse colloids" (colloids in the 0.1-1.2 μm size range) in 47 Belgian streams to the chemical properties of the streamwater. On average, 29% of the P in filtered (<1.2 μm) samples of these streams is present in coarse colloids. The concentration of Fe-rich colloids in streams decreases with increasing water hardness and pH. The P bearing colloids in these streams mostly consist of Fe hydroxyphosphates and of Fe oxyhydroxides with surface adsorbed P, which is underpinned by geochemical speciation calculations. In waters with molar P:Fe ratios above 0.5, only a minor part of the P is bound to coarse colloids. In such waters, the colloids have molar P:Fe ratios between 0.2 and 1 and are, therefore, nearly saturated with P. Conversely, in streams with molar P:Fe ratios below 0.1, most of the P is bound to Fe-rich colloids. Equilibration of synthetic and natural Fe and P bearing colloids with a zero sink reveals that colloids with low molar P:Fe ratios contain mostly nonlabile P, whereas P-saturated colloids contain mostly labile P which can be released within 7 days. Equilibration at a fixed free orthophosphate activity shows that the Fe-rich colloids may bind only limited P through surface adsorption, in the range of 0.02-0.04 mol P (mol Fe)(-1). The P:Fe ratios measured in naturally occurring Fe and P bearing colloids is clearly higher (between 0.05 and 1). These colloids are therefore likely formed by coprecipitation of P during oxidation of Fe(II), which leads to the formation of Fe hydroxyphosphate minerals. PMID:27110889

  4. Colloidal-gold electrosensor measuring device

    DOEpatents

    Wegner, Steven; Harpold, Michael A.; McCaffrey, Terence M.; Morris, Susan E.; Wojciechowski, Marek; Zhao, Junguo; Henkens, Robert W.; Naser, Najih; O'Daly, John P.

    1995-01-01

    The present invention provides a new device for use in measuring lead levels in biological and environmental samples. Using square wave coulometry and colloidal gold particles impregnated on carbon electrodes, the present invention provides a rapid, reliable, portable and inexpensive means of detecting low lead levels. The colloidal gold modified electrodes have microelectrode array characteristics and produce significantly higher stripping detection signals for lead than are produced at bulk gold electrode surfaces. The method is effective in determining levels of lead down to at least 5 .mu.g/dL in blood samples as small as 10 .mu.L.

  5. Dynamic Light Scattering From Colloidal Gels

    NASA Technical Reports Server (NTRS)

    Krall, A. H.; Weitz, David A.

    1996-01-01

    We present a brief, preliminary account of the interpretation of dynamic light scattering from fractal colloidal gels. For small scattering angles, and for high initial colloid particle volume fractions, the correlation functions exhibit arrested decay, reflecting the non-ergodic nature of these systems and allowing us to directly determine the elastic modulus of the gels. For smaller initial volume fractions, the correlation functions decay completely. In all cases, the initial decay is not exponential, but is instead described by a stretched exponential. We summarize the principles of a model that accounts for these data and discuss the scaling behavior of the measured parameters.

  6. Wetting reversal in colloid-polymer systems.

    PubMed

    Blokhuis, Edgar M; Kuipers, Joris

    2010-05-01

    The wetting of a phase-separated colloid-polymer mixture in contact with a hard wall is analyzed using free volume theory in a Nakanishi-Fisher-type approach. We present results for the wetting phase diagram for several model approximations. Our analysis is compared with a previous analysis by Aarts [J. Chem. Phys. 120, 1973 (2004)]. We find that there is a crossover from wetting to drying at a threshold value for the colloid-polymer size ratio and that the transitions are close to the critical point and of second order in nature. PMID:20866234

  7. Fabrication of anisotropic multifunctional colloidal carriers

    NASA Astrophysics Data System (ADS)

    Jerri, Huda A.

    The field of colloidal assembly has grown tremendously in recent years, although the direct or template-assisted methods used to fabricate complex colloidal constructions from monodisperse micro- and nanoparticles have been generally demonstrated on model materials. In this work, novel core particle syntheses, particle functionalizations and bottom-up assembly techniques are presented to create functional colloidal devices. Using particle lithography, high-information colloidal vectors have been developed and modified with imaging and targeting agents. Localized nanoscale patches have been reliably positioned on microparticles to serve as foundations for further chemical or physical modifications. Site-specific placement of RGD targeting ligands has been achieved in these lithographed patches. Preferential uptake of these targeted vectors by RGD-specific 3T3 fibroblasts was verified using confocal laser scanning microscopy. A transition was made from the functionalization of model imaging core particles to the lithography of colloidal cartridges, in an effort to construct colloidal syringes with specialized, programmable release profiles. A variety of functional, pH-sensitive fluorescent cores were engineered to respond to solution conditions. When triggered, the diverse composite core microparticles and reservoir microcapsules released embedded fluorescent moieties such as dye molecules, and fluorophore-conjugated nanoparticles. The microcapsules, created using layer-by-layer polyelectrolyte deposition on sacrificial templates, were selectively modified with a robust coating. The pH-responsive anisotropic reservoir microcapsules were extremely stable in solution, and exhibited a "Lazarus" functionality of rehydrating to their original state following desiccation. A snapshot of focused-release of core constituents through the lone opening in colloidal monotremes has been obtained by anisotropically-functionalizing degradable cores with barrier shells. Additionally

  8. Synthesis of Ionic Colloidal Crystals (ICCs)

    NASA Astrophysics Data System (ADS)

    Maskaly, Garry R.; Garcia, R. Edwin; Carter, W. Craig; Chiang, Yet-Ming

    2003-03-01

    Binary ionic colloidal crystals (ICCs) have been produced by ordered heterocoagulation of colloidal mixtures of silica (negative surface charge) and polystyrene functionalized with amidine (positive surface charge) suspended in isopropanol. Experimental conditions predicted by the theoretical model discussed in a separate talk have been implemented to obtain heterocoagulation of these particles in the rocksalt structure. To our knowledge, this is the first experimental demonstration of the ICC concept. The importance of various experimental parameters on ICC formation is discussed. Particle dynamics simulations are carried out to provide insight into the kinetics of ICCs. Potential applications are discussed.

  9. Colloidal-gold electrosensor measuring device

    DOEpatents

    Wegner, S.; Harpold, M.A.; McCaffrey, T.M.; Morris, S.E.; Wojciechowski, M.; Zhao, J.; Henkens, R.W.; Naser, N.; O`Daly, J.P.

    1995-11-21

    The present invention provides a new device for use in measuring lead levels in biological and environmental samples. Using square wave coulometry and colloidal gold particles impregnated on carbon electrodes, the present invention provides a rapid, reliable, portable and inexpensive means of detecting low lead levels. The colloidal gold modified electrodes have microelectrode array characteristics and produce significantly higher stripping detection signals for lead than are produced at bulk gold electrode surfaces. The method is effective in determining levels of lead down to at least 5 {micro}g/dL in blood samples as small as 10 {micro}L. 9 figs.

  10. Controlling colloidal interaction through asymetric functionalization

    NASA Astrophysics Data System (ADS)

    Snyder, Charles E.

    The use of colloids and nanoparticles is becoming more and more prevalent across all scientific disciplines. The ability to control how these particles interact may yield new structures with unique and useful properties. This thesis contributes a new method of creating dual functionality on colloids, "particle lithography". These modified colloids may be used to bottom-up assemble asymmetric colloidal aggregate structures. Particle lithography allows for the site specific functionalization of a colloid at a single site. The technique is not limited to any specific material and is scalable. The ability to control the patch's size is demonstrated. Characterization of the patch confirms the ability to control the patch size through varying the size of the colloid, the hydrodynamic radius of the coating particles or molecules, and the salt concentration at which the coating is applied. The effects of other experimental conditions on the particle lithography process, such as sonication, are examined. The particle lithography process is extended to functionalize a colloid at two sites. The sites are ninety degrees relative to the center of the colloid. This functionalization is used to form self-assembled trimers. Through this process, the ability to use other particles as masking agents in the particle lithography process is demonstrated. Also demonstrated is the ability to assemble particles composed of differing materials. Modeling aided in understanding how a lithographed and complementary particle might interact. Phase diagrams were constructed to show the critical coagulation concentration of salt needed for a lithographed particle to bind to its complement. This salt concentration is a function of patch size and potential, and particle size and potential. An effective patch size is defined and found to vary little as a function of system parameters. Defining a critical coagulation concentration suggests the ability to store lithographed precursor particles. This

  11. Dynamics of Colloidal Disorder-Order Transition

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Experiments with colloidal solutions of plastic microspheres suspended in a liquid serve as models of how molecules interact and form crystals. For the Dynamics of Colloidal Disorder-Order Transition (CDOT) experiment, Paul Chaikin of Princeton University has identified effects that are attributable to Earth's gravity and demonstrated that experiments are needed in the microgravity of orbit. Space experiments have produced unexpected dendritic (snowflake-like) structures. To date, the largest hard sphere crystal grown is a 3 mm single crystal grown at the cool end of a ground sample. At least two more additional flight experiments are plarned aboard the International Space Station. This image is from a video downlink.

  12. Partial rejuvenation of a colloidal glass.

    PubMed

    Ozon, F; Narita, T; Knaebel, A; Debrégeas, G; Hébraud, P; Munch, J-P

    2003-09-01

    We study the effect of shear on the aging dynamics of a colloidal suspension of synthetic clay particles. We find that a shear of amplitude gamma reduces the relaxation time measured just after the cessation of shear by a factor exp(-gamma/gamma(c)), with gamma(c) approximately 5%, and is independent of the duration and the frequency of the shear. This simple law for the rejuvenation effect shows that the energy involved in colloidal rearrangements is proportional to the shear amplitude gamma rather than gamma(2), leading to an Eyring-like description of the dynamics of our system. PMID:14524814

  13. Bidisperse colloids: nanoparticles and microemulsions in coexistence.

    PubMed

    Tabor, Rico F; Eastoe, Julian; Dowding, Peter J; Grillo, Isabelle; Rogers, Sarah E

    2010-04-15

    Mixed 'hard-soft' colloidal systems have been generated in which the 'hard' components (80 nm diameter silica nanoparticles) coexist with a population of 'soft' microemulsion droplets, both structures stabilised by the anionic surfactant sodium bis(ethylhexyl)sulfosuccinate (AOT) with toluene as solvent. The addition of water to swell the inverse micelles to form microemulsion droplets appears to increase attractive interactions between the silica particles (determined by DLS), possibly due to adsorption of some water at the silica-toluene interface; however, long-term stability of the dispersions is maintained. Small-angle neutron scattering was used to examine the structures present in these new colloidal systems. PMID:20144832

  14. Binary Colloidal Alloy Test-5: Compete

    NASA Technical Reports Server (NTRS)

    Frisken, Barbara J.; Bailey, Arthur E.; Weitz, David A.

    2008-01-01

    The Binary Colloidal Alloy Test - 5: Compete (BCAT-5-Compete) investigation will photograph andomized colloidal samples onboard the International Space Station (ISS) to determine their resulting structure over time. The use of EarthKAM software and hardware will allow the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-Compete will utilize samples 6 - 8 in the BCAT-5 hardware to study the competition between phase separation and crystallization, which is important in the manufacture of plastics and other materials.

  15. Self-assembly of colloidal surfactants

    NASA Astrophysics Data System (ADS)

    Kegel, Willem

    2012-02-01

    We developed colloidal dumbbells with a rough and a smooth part, based on a method reported in Ref. [1]. Specific attraction between the smooth parts occurs upon addition of non-adsorbing polymers of appropriate size. We present the first results in terms of the assemblies that emerge in these systems. [4pt] [1] D.J. Kraft, W.S. Vlug, C.M. van Kats, A. van Blaaderen, A. Imhof and W.K. Kegel, Self-assembly of colloids with liquid protrusions, J. Am. Chem. Soc. 131, 1182, (2009)

  16. Collective sliding states for colloidal molecular crystals

    SciTech Connect

    Reichhardt, Charles; Reichhardt, Cynthia

    2008-01-01

    We study the driving of colloidal molecular crystals over periodic substrates such as those created with optical traps. The n-merization that occurs in the colloidal molecular crystal states produces a remarkably rich variety of distinct dynamical behaviors, including polarization effects within the pinned phase and the formation of both ordered and disordered sliding phases. Using computer simulations, we map the dynamic phase diagrams as a function of substrate strength for dimers and trimers on a triangular substrate, and correlate features on the phase diagram with transport signatures.

  17. Binary Colloidal Alloy Test-5: Phase Separation

    NASA Technical Reports Server (NTRS)

    Lynch, Matthew; Weitz, David A.; Lu, Peter J.

    2008-01-01

    The Binary Colloidal Alloy Test - 5: Phase Separation (BCAT-5-PhaseSep) experiment will photograph initially randomized colloidal samples onboard the ISS to determine their resulting structure over time. This allows the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-PhaseSep studies collapse (phase separation rates that impact product shelf-life); in microgravity the physics of collapse is not masked by being reduced to a simple top and bottom phase as it is on Earth.

  18. Colloid mobilization and transport during capillary fringe fluctuations.

    PubMed

    Aramrak, Surachet; Flury, Markus; Harsh, James B; Zollars, Richard L

    2014-07-01

    Capillary fringe fluctuations due to changing water tables lead to displacement of air-water interfaces in soils and sediments. These moving air-water interfaces can mobilize colloids. We visualized colloids interacting with moving air-water interfaces during capillary fringe fluctuations by confocal microscopy. We simulated capillary fringe fluctuations in a glass-bead-filled column. We studied four specific conditions: (1) colloids suspended in the aqueous phase, (2) colloids attached to the glass beads in an initially wet porous medium, (3) colloids attached to the glass beads in an initially dry porous medium, and (4) colloids suspended in the aqueous phase with the presence of a static air bubble. Confocal images confirmed that the capillary fringe fluctuations affect colloid transport behavior. Hydrophilic negatively charged colloids initially suspended in the aqueous phase were deposited at the solid-water interface after a drainage passage, but then were removed by subsequent capillary fringe fluctuations. The colloids that were initially attached to the wet or dry glass bead surface were detached by moving air-water interfaces in the capillary fringe. Hydrophilic negatively charged colloids did not attach to static air-bubbles, but hydrophobic negatively charged and hydrophilic positively charged colloids did. Our results demonstrate that capillary fringe fluctuations are an effective means for colloid mobilization. PMID:24897130

  19. Fabrication of High Sensitive Immunochromato Kit Using Au Colloid

    NASA Astrophysics Data System (ADS)

    Okamoto, Koji

    Au colloid have characteristics of surface plasmon resonance with absorption at 500 nm~600 nm wavelength. Surface on the citric acid Au colloid can be conjugated with protein eg. antibody. Various particle size of Au colloid makes it high sensitive immunochromato as diagnostics. High sensitive immunochromato will be useful for application of cancer marker eg. prostate specific antigen and influenza early diagnosis.

  20. Ultrasound Propagation in Colloidal Dispersions.

    NASA Astrophysics Data System (ADS)

    Sherman, Nigel E.

    Available from UMI in association with The British Library. This thesis describes apparatus and techniques for making ultrasonic measurements in fluids and applications of them to measurements of ultrasonic parameters in colloidal dispersions. A brief description of the properties and uses of ultrasound propagation in dispersions is followed by an extensive review of theories which relate the particulate properties of the dispersions to the measurable ultrasonic parameters, velocity (c) and attenuation (alpha ). Measurement principles are outlined related to the design of near-field measurement methods and the development of three techniques is described. These are shown to give results which are both highly self-consistent and in excellent agreement with a far-field method. Measurements of alpha and c for model dispersions of glass spheres in Newtonian liquids are shown to be in good agreement with the relevant theory when particle polydispersity is taken into account. For structured fluids as the continuous phase, the alpha and c data for suspensions of spheres are used to obtain the continuous phase viscosity ( eta). The alpha data agree approximately with the macroscopic viscosity, but the velocity data requires the introduction of a shear elastic term and the revision of theory in order to obtain agreement. Attenuation as a function of barite concentration in Newtonian liquids was investigated and the ultrasonic particle radius was found to be systematically larger than expected. This is attributed to particle rugosity. Measurements of alpha and c using non-gelling aqueous kaolinite suspensions are shown to agree well with theory when the eccentricity and the interactions of particles are taken into account. For gelling aqueous bentonite suspensions, alpha and c were found to be time-dependent over a period of several days following initial dispersion. The observed increases in both alpha and c are interpreted in terms of a growth in gel fraction and shear

  1. Colloids in the River Inn

    NASA Astrophysics Data System (ADS)

    Ueckert, Martina; Niessner, Reinhard; Baumann, Thomas

    2015-04-01

    In the light of an increasing number of technical applications using nanoparticles and reports of adverse effects of engineered nanoparticles, research on the occurrence and stability of particles in all compartments has to be intensified. Colloids in river water represent the geologic setting, environmental conditions, and the anthropogenic use in its catchment. The river not only acts as a sink for nanoparticles but also as the source term due to exchange in the hyporheic zone and in bank filtration setups. The concentration, size distribution and elemental composition of particles in the River Inn were studied from the source in the Swiss Alps to the river mouth at Passau from 2008 to 2014. Samples were collected after each tributary from a sub-catchment and filtered on site using a new filtration device for gentle filtration. The elemental composition was determined after acid digestion with ICP/MS. SEM/EDX analysis provided morphological and elemental information for single particles. A complementary chemical analysis of the river water was performed to assess the geochemical stability of individual particles. As presented at EGU 2014, particles in the upper, rural parts mainly reveal changes in the geological setting of the tributary catchments. Not unexpectedly, particles originating from crystalline rocks, were more stable than particles originating from calcareous rocks. Anthropogenic and industrial influences increase in the lower parts. This went together with a change of the size distribution, an increase of the number of organic particles, and a decrease of the microfauna. Interestingly, specific leisure activities in a sub-catchment, like extensive downhill skiing, manifest itself in the particle composition. This general setting was validated in last year's sampling campaigns. An interesting change in on site parameters and hydrochemical composition was seen during all sampling campaigns at an inflow from the valley Kaunertal, Austria. Therefore

  2. Les plaies du tendon patellaire

    PubMed Central

    Mechchat, Atif; Elidrissi, Mohammed; Mardy, Abdelhak; Elayoubi, Abdelghni; Shimi, Mohammed; Elibrahimi, Abdelhalim; Elmrini, Abdelmajid

    2014-01-01

    Les plaies du tendon patellaire sont peu fréquentes et sont peu rapportés dans la littérature, contrairement aux ruptures sous cutanées. Les sections du tendon patellaire nécessitent une réparation immédiate afin de rétablir l'appareil extenseur et de permettre une récupération fonctionnelle précoce. A travers ce travail rétrospectif sur 13 cas, nous analysons les aspects épidémiologiques, thérapeutiques et pronostiques de ce type de pathologie en comparant différents scores. L’âge moyen est de 25 ans avec une prédominance masculine. Les étiologies sont dominées par les accidents de la voie publique (68%) et les agressions par agent tranchant (26%) et contendant (6 %). Tous nos patients ont bénéficié d'un parage chirurgical avec suture tendineuse direct protégée par un laçage au fils d'aciers en légère flexion. La rééducation est débutée après sédation des phénomènes inflammatoires. Au dernier recul les résultats sont excellents et bon à 92%. Nous n'avons pas noté de différence de force musculaire et d'amplitude articulaire entre le genou sain et le genou lésé. Les lésions ouvertes du tendon patellaire est relativement rare. La prise en charge chirurgicale rapide donne des résultats assez satisfaisants. La réparation est généralement renforcée par un semi-tendineux, synthétique ou métallique en forme de cadre de renfort pour faciliter la réadaptation et réduire le risque de récidive après la fin de l'immobilisation. PMID:25170379

  3. Pore water colloid properties in argillaceous sedimentary rocks.

    PubMed

    Degueldre, Claude; Cloet, Veerle

    2016-11-01

    The focus of this work is to evaluate the colloid nature, concentration and size distribution in the pore water of Opalinus Clay and other sedimentary host rocks identified for a potential radioactive waste repository in Switzerland. Because colloids could not be measured in representative undisturbed porewater of these host rocks, predictive modelling based on data from field and laboratory studies is applied. This approach allowed estimating the nature, concentration and size distributions of the colloids in the pore water of these host rocks. As a result of field campaigns, groundwater colloid concentrations are investigated on the basis of their size distribution quantified experimentally using single particle counting techniques. The colloid properties are estimated considering data gained from analogue hydrogeochemical systems ranging from mylonite features in crystalline fissures to sedimentary formations. The colloid concentrations were analysed as a function of the alkaline and alkaline earth element concentrations. Laboratory batch results on clay colloid generation from compacted pellets in quasi-stagnant water are also reported. Experiments with colloids in batch containers indicate that the size distribution of a colloidal suspension evolves toward a common particle size distribution independently of initial conditions. The final suspension size distribution was found to be a function of the attachment factor of the colloids. Finally, calculations were performed using a novel colloid distribution model based on colloid generation, aggregation and sedimentation rates to predict under in-situ conditions what makes colloid concentrations and size distributions batch- or fracture-size dependent. The data presented so far are compared with the field and laboratory data. The colloid occurrence, stability and mobility have been evaluated for the water of the considered potential host rocks. In the pore water of the considered sedimentary host rocks, the clay

  4. Prospects of Colloidal Copper Chalcogenide Nanocrystals.

    PubMed

    van der Stam, Ward; Berends, Anne C; de Mello Donega, Celso

    2016-03-01

    Over the past few years, colloidal copper chalcogenide nanocrystals (NCs) have emerged as promising alternatives to conventional Cd and Pb chalcogenide NCs. Owing to their wide size, shape, and composition tunability, Cu chalcogenide NCs hold great promise for several applications, such as photovoltaics, lighting and displays, and biomedical imaging. They also offer characteristics that are unparalleled by Cd and Pb chalcogenide NCs, such as plasmonic properties. Moreover, colloidal Cu chalcogenide NCs have low toxicity, potentially lower costs, and excellent colloidal stability. This makes them attractive materials for the large-scale deployment of inexpensive, sustainable, and environmentally benign solution-processed devices. Nevertheless, the synthesis of colloidal Cu chalcogenide NCs, especially that of ternary and quaternary compositions, has yet to reach the same level of mastery as that available for the prototypical Cd chalcogenide based NCs. This review provides a concise overview of this rapidly advancing field, sketching the state of the art and highlighting the key challenges. We discuss recent developments in the synthesis of size-, shape-, and composition-controlled NCs of Cu chalcogenides, with emphasis in strategies to circumvent the limitations arising from the need to precisely balance the reactivities of multiple precursors in synthesizing ternary and quaternary compositions. In this respect, we show that topotactic cation-exchange reactions are a promising alternative route to complex multinary Cu chalcogenide NCs and hetero-NCs, which are not attainable by conventional routes. The properties and potential applications of Cu chalcogenide NCs and hetero-NCs are also addressed. PMID:26684665

  5. Advanced Colloids Experiment (ACE-T1)

    NASA Technical Reports Server (NTRS)

    Meyer, William V.; Sicker, Ron; Brown, Dan; Eustace, John

    2015-01-01

    Increment 45 - 46 Science Symposium presentation of Advanced Colloids Experiment (ACE-T1) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.

  6. Colloid Formation at Waste Plume Fronts

    SciTech Connect

    Wan, Jiamin; Tokunaga, Tetsu K.; Saiz, Eduardo; Larsen, Joern T.; Zheng, Zuoping; Couture, Rex A.

    2004-05-22

    Highly saline and caustic tank waste solutions containing radionuclides and toxic metals have leaked into sediments at U. S. Department of Energy (DOE) facilities such as the Hanford Site (Washington State). Colloid transport is frequently invoked to explain migration of radionuclides and metals in the subsurface. To understand colloid formation during interactions between highly reactive fluids and sediments and its impact on contaminant transport, we simulated tank waste solution (TWS) leakage processes in laboratory columns at ambient and elevated (70 C) temperatures. We found that maximum formation of mobile colloids occurred at the plume fronts (hundreds to thousands times higher than within the plume bodies or during later leaching). Concentrations of suspended solids were as high as 3 mass%, and their particle-sizes ranged from tens of nm to a few {micro}m. Colloid chemical composition and mineralogy depended on temperature. During infiltration of the leaked high Na{sup +} waste solution, rapid and completed Na{sup +} replacement of exchangeable Ca{sup 2+} and Mg{sup 2+} from the sediment caused accumulation of these divalent cations at the moving plume front. Precipitation of supersaturated Ca{sup 2+}/Mg{sup 2+}-bearing minerals caused dramatic pH reduction at the plume front. In turn, the reduced pH caused precipitation of other minerals. This understanding can help predict the behavior of contaminant trace elements carried by the tank waste solutions, and could not have been obtained through conventional batch studies.

  7. Advanced Colloids Experiment (ACE-H-2)

    NASA Technical Reports Server (NTRS)

    Meyer, William V.; Sicker, Ron; Chmiel, Alan J.; Eustace, John; LaBarbera, Melissa

    2015-01-01

    Increment 43 - 44 Science Symposium presentation of Advanced Colloids Experiment (ACE-H-2) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.

  8. Colloidal crystal grain boundary formation and motion

    PubMed Central

    Edwards, Tara D.; Yang, Yuguang; Beltran-Villegas, Daniel J.; Bevan, Michael A.

    2014-01-01

    The ability to assemble nano- and micro- sized colloidal components into highly ordered configurations is often cited as the basis for developing advanced materials. However, the dynamics of stochastic grain boundary formation and motion have not been quantified, which limits the ability to control and anneal polycrystallinity in colloidal based materials. Here we use optical microscopy, Brownian Dynamic simulations, and a new dynamic analysis to study grain boundary motion in quasi-2D colloidal bicrystals formed within inhomogeneous AC electric fields. We introduce “low-dimensional” models using reaction coordinates for condensation and global order that capture first passage times between critical configurations at each applied voltage. The resulting models reveal that equal sized domains at a maximum misorientation angle show relaxation dominated by friction limited grain boundary diffusion; and in contrast, asymmetrically sized domains with less misorientation display much faster grain boundary migration due to significant thermodynamic driving forces. By quantifying such dynamics vs. compression (voltage), kinetic bottlenecks associated with slow grain boundary relaxation are understood, which can be used to guide the temporal assembly of defect-free single domain colloidal crystals. PMID:25139760

  9. Self assembly of anisotropic colloidal particles

    NASA Astrophysics Data System (ADS)

    Florea, Daniel; Wyss, Hans

    2012-02-01

    Colloidal particles have been successfully used as ''model atoms'', as their behavior can be more directly studied than that of atoms or molecules by direct imaging in a confocal microscope. Most studies have focussed on spherical particles with isotropic interactions. However, a range of interesting materials such as many supramolecular polymers or biopolymers exhibit highly directional interactions. To capture their behavior in colloidal model systems, particles with anisotropic interactions are clearly required. Here we use a colloidal system of nonspherical colloids, where highly directional interactions can be induced via depletion. By biaxially stretching spherical PMMA particles we create oblate spheroidal particles. We induce attractive interactions between these particles by adding a non-adsorbing polymer to the background liquid. The resulting depletion interaction is stronger along the minor axis of the oblate spheroids. We study the phase behavior of these materials as a function of the ellipsoid aspect ratio, the strength of the depletion interactions, and the particle concentration. The resulting morphologies are qualitatively different from those observed with spherical particles. This can be exploited for creating new materials with tailored structures.

  10. Practical colloidal processing of multication ceramics

    SciTech Connect

    Bell, Nelson S.; Monson, Todd C.; Diantonio, Christopher; Wu, Yiquan

    2015-09-07

    The use of colloidal processing principles in the formation of ceramic materials is well appreciated for developing homogeneous material properties in sintered products, enabling novel forming techniques for porous ceramics or 3D printing, and controlling microstructure to enable optimized material properties. The solution processing of electronic ceramic materials often involves multiple cationic elements or dopants to affect microstructure and properties. Material stability must be considered through the steps of colloidal processing to optimize desired component properties. This review provides strategies for preventing material degradation in particle synthesis, milling processes, and dispersion, with case studies of consolidation using spark plasma sintering of these systems. The prevention of multication corrosion in colloidal dispersions can be achieved by utilizing conditions similar to the synthesis environment or by the development of surface passivation layers. The choice of dispersing surfactants can be related to these surface states, which are of special importance for nanoparticle systems. A survey of dispersant chemistries related to some common synthesis conditions is provided for perovskite systems as an example. Furthermore, these principles can be applied to many colloidal systems related to electronic and optical applications.

  11. Practical colloidal processing of multication ceramics

    DOE PAGESBeta

    Bell, Nelson S.; Monson, Todd C.; Diantonio, Christopher; Wu, Yiquan

    2015-09-07

    The use of colloidal processing principles in the formation of ceramic materials is well appreciated for developing homogeneous material properties in sintered products, enabling novel forming techniques for porous ceramics or 3D printing, and controlling microstructure to enable optimized material properties. The solution processing of electronic ceramic materials often involves multiple cationic elements or dopants to affect microstructure and properties. Material stability must be considered through the steps of colloidal processing to optimize desired component properties. This review provides strategies for preventing material degradation in particle synthesis, milling processes, and dispersion, with case studies of consolidation using spark plasma sinteringmore » of these systems. The prevention of multication corrosion in colloidal dispersions can be achieved by utilizing conditions similar to the synthesis environment or by the development of surface passivation layers. The choice of dispersing surfactants can be related to these surface states, which are of special importance for nanoparticle systems. A survey of dispersant chemistries related to some common synthesis conditions is provided for perovskite systems as an example. Furthermore, these principles can be applied to many colloidal systems related to electronic and optical applications.« less

  12. Photoelectrochromism in Tungsten Trioxide Colloidal Solutions

    ERIC Educational Resources Information Center

    Chenthamarakshan, C. R.; Tacconi, N. R. de; Xu, Lucy; Rajeshwar, Krishnan

    2004-01-01

    Photophysical and photochemical properties of semiconductor metal oxide colloids are studied in the context of photoelectrochemical conversion and storage of solar energy. The experiment teaches the instrumental principles of UV-visible spectrophotometry, spectral acquisition and background subtraction strategies and diode array spectrometers.

  13. Cobalt-doped cadmium selenide colloidal nanowires.

    PubMed

    Li, Zhen; Du, Ai Jun; Sun, Qiao; Aljada, Muhsen; Cheng, Li Na; Riley, Mark J; Zhu, Zhong Hua; Cheng, Zhen Xiang; Wang, Xiao Lin; Hall, Jeremy; Krausz, Elmars; Qiao, Shi Zhang; Smith, Sean C; Lu, Gao Qing Max

    2011-11-21

    Co(2+)-doped CdSe colloidal nanowires with tunable size and dopant concentration have been prepared by a solution-liquid-solid (SLS) approach for the first time. These doped nanowires exhibit anomalous photoluminescence temperature dependence in comparison with undoped nanowires. PMID:21975534

  14. Solid colloids with surface-mobile linkers.

    PubMed

    van der Meulen, Stef A J; Helms, Gesa; Dogterom, Marileen

    2015-06-17

    In this report we review the possibilities of using colloids with surface mobile linkers for the study of colloidal self-assembly processes. A promising route to create systems with mobile linkers is the use of lipid (bi-)layers. These lipid layers can be either used in the form of vesicles or as coatings for hard colloids and emulsion droplets. Inside the lipid bilayers molecules can be inserted via membrane anchors. Due to the fluidity of the lipid bilayer, the anchored molecules remain mobile. The use of different lipid mixtures even allows creating Janus-like particles that exhibit directional bonding if linkers are used which have a preference for a certain lipid phase. In nature mobile linkers can be found e.g. as receptors in cells. Therefore, towards the end of the review, we also briefly address the possibility of using colloids with surface mobile linkers as model systems to mimic cell-cell interactions and cell adhesion processes. PMID:25993272

  15. Motile Fluids: Granular, Colloidal and Living

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Sriram

    2014-03-01

    My talk will present our recent results from theory, simulation and experiment on flocking, swarming and instabilities in diverse realizations of active systems. The findings I will report include: flocking at a distance in vibrated granular monolayers; the active hydrodynamics of self-propelled solids; clusters, asters and oscillations in colloidal chemotaxis. Supported by a J C Bose Fellowship.

  16. Collective dynamics of rotating colloidal particles

    NASA Astrophysics Data System (ADS)

    Magkiriadou, Sofia; Soni, Vishal; van Zuiden, Benny; Bartolo, Denis; Vitelli, Vincenzo; Irvine, William T. M.

    We study magnetic colloidal particles in suspension under the influence of a rotating magnetic field. When in aggregates, these particles show rich dynamics that are governed by magnetic and hydrodynamic interactions. By tuning these interactions, we probe the phase diagram of this system and study the emergent collective dynamics. Finally, we begin to investigate whether we can control this phase diagram with geometry.

  17. Grafting of oligosaccharides onto synthetic polymer colloids.

    PubMed

    Mange, Siyabonga; Dever, Cédric; De Bruyn, Hank; Gaborieau, Marianne; Castignolles, Patrice; Gilbert, Robert G

    2007-06-01

    A new method to form colloidally stable oligosaccharide-grafted synthetic polymer particles has been developed. The oligosaccharides, of weight-average degree of polymerization approximately 38, were obtained by enzymatic debranching of amylopectin. Through the use of a cerium(IV)-based redox initiation process, oligosaccharide chains are grafted onto a synthetic polymer colloid comprising electrostatically stabilized poly(methyl methacrylate) or polystyrene latex particles swollen with methyl methacrylate monomer. Ce(IV) creates a radical species on these oligosaccharides, which then propagates, initially with aqueous-phase monomer, then with the methyl methacrylate monomer inside the particles. Ultracentrifugation, NMR, and total starch analyses together prove that the grafting process has occurred, with at least 7.7 wt % starch grafted and a grafting efficiency of 33%. The surfactant used in latex preparation was removed by dialysis, resulting in particles colloidally stabilized with only linear starch as a steric stabilizer. The debranched starch that comprises these oligosaccharides is found to be a remarkably effective colloidal stabilizer, albeit at low electrolyte concentration, stabilizing particles with very sparse surface coverage. PMID:17497920

  18. The colloidal chemistry of ceramic clays

    NASA Technical Reports Server (NTRS)

    Phelps, G. W.

    1984-01-01

    The colloidal chemistry and mineralogy of two argil minerals were studied. Deposits of kaolin and of ceramic clays in the United States and England are discussed for the probable mechanism of formation. The structural modifications of the bed, original material associated with the clays and the proper use of flocculants are discussed.

  19. Colloidal nickel boride catalyst for hydrogenation of olefins

    SciTech Connect

    Nakao, Y.; Fujishige, S.

    1981-04-01

    Colloidal nickel boride was prepared from nickel(II) chloride by reduction with sodium borohydride in the presence of polyvinylpyrrolidone in ethanol. Hydrogenation of various olefins was examined over the colloidal catalyst at 30/sup 0/C and atmospheric pressure. The colloidal nickel boride was much more effective than the precipitated nickel boride prepared in the absence of polyvinylpyrrolidone as a hydrogenation catalyst, especially for isopropenyl compounds. Additional amines and sodium acetate were slightly inhibitive to the colloidal catalyst, while, being strongly promotive to the precipitated catalyst. The colloidal nickel boride was superior to the charcoal-supported metals of the platinum group in catalytic activity for ..cap alpha..-methylstyrene.

  20. Bonded boojum-colloids in nematic liquid crystals.

    PubMed

    Eskandari, Zahra; Silvestre, Nuno M; Telo da Gama, Margarida M

    2013-08-20

    We investigate bonded boojum-colloids in nematic liquid crystals, configurations where two colloids with planar degenerate anchoring are double-bonded through line defects connecting their surfaces. This bonded structure promotes the formation of linear chains aligned with the nematic director. We show that the bonded configuration is the global minimum in systems that favor twist deformations. In addition, we investigate the influence of confinement on the stability of bonded boojum-colloids. Although the unbonded colloid configuration, where the colloids bundle at oblique angles, is favored by confinement, the bonded configuration is again the global minimum for liquid crystals with sufficiently small twist elastic constants. PMID:23859624

  1. Validating LES for Jet Aeroacoustics

    NASA Technical Reports Server (NTRS)

    Bridges, James; Wernet, Mark P.

    2011-01-01

    Engineers charged with making jet aircraft quieter have long dreamed of being able to see exactly how turbulent eddies produce sound and this dream is now coming true with the advent of large eddy simulation (LES). Two obvious challenges remain: validating the LES codes at the resolution required to see the fluid-acoustic coupling, and the interpretation of the massive datasets that are produced. This paper addresses the former, the use of advanced experimental techniques such as particle image velocimetry (PIV) and Raman and Rayleigh scattering, to validate the computer codes and procedures used to create LES solutions. This paper argues that the issue of accuracy of the experimental measurements be addressed by cross-facility and cross-disciplinary examination of modern datasets along with increased reporting of internal quality checks in PIV analysis. Further, it argues that the appropriate validation metrics for aeroacoustic applications are increasingly complicated statistics that have been shown in aeroacoustic theory to be critical to flow-generated sound, such as two-point space-time velocity correlations. A brief review of data sources available is presented along with examples illustrating cross-facility and internal quality checks required of the data before it should be accepted for validation of LES.

  2. Validating LES for Jet Aeroacoustics

    NASA Technical Reports Server (NTRS)

    Bridges, James

    2011-01-01

    Engineers charged with making jet aircraft quieter have long dreamed of being able to see exactly how turbulent eddies produce sound and this dream is now coming true with the advent of large eddy simulation (LES). Two obvious challenges remain: validating the LES codes at the resolution required to see the fluid-acoustic coupling, and the interpretation of the massive datasets that result in having dreams come true. This paper primarily addresses the former, the use of advanced experimental techniques such as particle image velocimetry (PIV) and Raman and Rayleigh scattering, to validate the computer codes and procedures used to create LES solutions. It also addresses the latter problem in discussing what are relevant measures critical for aeroacoustics that should be used in validating LES codes. These new diagnostic techniques deliver measurements and flow statistics of increasing sophistication and capability, but what of their accuracy? And what are the measures to be used in validation? This paper argues that the issue of accuracy be addressed by cross-facility and cross-disciplinary examination of modern datasets along with increased reporting of internal quality checks in PIV analysis. Further, it is argued that the appropriate validation metrics for aeroacoustic applications are increasingly complicated statistics that have been shown in aeroacoustic theory to be critical to flow-generated sound.

  3. Assembly of Colloidal Materials Using Bioadhesive Interactions

    NASA Astrophysics Data System (ADS)

    Hammer, Daniel A.; Hiddessen, Amy L.; Tohver, Valeria; Crocker, John C.; Weitz, David A.

    2002-11-01

    We have pursued the use of biological crosslinking molecules of several types to make colloidal materials at relatively low volume fraction of colloidal particles. The objective is to make binary alloys of colloidal particles, made of two different colloidal particles coated with complementary biological lock-and-key binding molecules, which assemble due to the biological specificity. The long-term goal is to use low affinity lock-and-key biological interactions, so that the can anneal to form crystalline states. We have used a variety of different surface chemistries in order to make colloidal materials. Our first system involved using selectin-carbohydrate (sialyl-Lewis) interactions; this chemistry is derived from immune system. This chemical interaction is of relatively low affinity, with timescales for dissociation of several seconds. Furthermore, the adhesion mediated by these molecules can be reversed by the chelation of calcium atoms; thus assembled structures can be disassembled reversibly. Our second system employed avidin-biotin chemistry. This well-studied system is of high affinity, and is generally irreversible on a laboratory time-scale. Thus, we would expect selectin-carbohydrate interactions at high molecular density and avidin-biotin interactions to give kinetically-trapped structures; however, at low densities, we would expect significant differences in the structure and dynamics of the two materials, owing to their very different release rates. We have also begun to use a third chemistry - DNA hybridization. By attaching single stranded DNA oligonucleotide chains to beads, we can drive the assembly of colloidal materials by hybridization of complementary DNA chains. It is well known that DNA adenosine-thymine (A-T) and guanine-cytosine (G-C) bases hybridize pairwise with a Gibbs free energy change of 1.7 kcal/mol per base; thus, the energy of the assembly can be modulated by altering the number of complementary bases in the DNA chains. Using

  4. Assembly of Colloidal Materials Using Bioadhesive Interactions

    NASA Technical Reports Server (NTRS)

    Hammer, Daniel A.; Hiddessen, Amy L.; Tohver, Valeria; Crocker, John C.; Weitz, David A.

    2002-01-01

    We have pursued the use of biological crosslinking molecules of several types to make colloidal materials at relatively low volume fraction of colloidal particles. The objective is to make binary alloys of colloidal particles, made of two different colloidal particles coated with complementary biological lock-and-key binding molecules, which assemble due to the biological specificity. The long-term goal is to use low affinity lock-and-key biological interactions, so that the can anneal to form crystalline states. We have used a variety of different surface chemistries in order to make colloidal materials. Our first system involved using selectin-carbohydrate (sialyl-Lewis) interactions; this chemistry is derived from immune system. This chemical interaction is of relatively low affinity, with timescales for dissociation of several seconds. Furthermore, the adhesion mediated by these molecules can be reversed by the chelation of calcium atoms; thus assembled structures can be disassembled reversibly. Our second system employed avidin-biotin chemistry. This well-studied system is of high affinity, and is generally irreversible on a laboratory time-scale. Thus, we would expect selectin-carbohydrate interactions at high molecular density and avidin-biotin interactions to give kinetically-trapped structures; however, at low densities, we would expect significant differences in the structure and dynamics of the two materials, owing to their very different release rates. We have also begun to use a third chemistry - DNA hybridization. By attaching single stranded DNA oligonucleotide chains to beads, we can drive the assembly of colloidal materials by hybridization of complementary DNA chains. It is well known that DNA adenosine-thymine (A-T) and guanine-cytosine (G-C) bases hybridize pairwise with a Gibbs free energy change of 1.7 kcal/mol per base; thus, the energy of the assembly can be modulated by altering the number of complementary bases in the DNA chains. Using

  5. Colloid suspension stability and transport through unsaturated porous media

    SciTech Connect

    McGraw, M.A.; Kaplan, D.I.

    1997-04-01

    Contaminant transport is traditionally modeled in a two-phase system: a mobile aqueous phase and an immobile solid phase. Over the last 15 years, there has been an increasing awareness of a third, mobile solid phase. This mobile solid phase, or mobile colloids, are organic or inorganic submicron-sized particles that move with groundwater flow. When colloids are present, the net effect on radionuclide transport is that radionuclides can move faster through the system. It is not known whether mobile colloids exist in the subsurface environment of the Hanford Site. Furthermore, it is not known if mobile colloids would likely exist in a plume emanating from a Low Level Waste (LLW) disposal site. No attempt was made in this study to ascertain whether colloids would form. Instead, experiments and calculations were conducted to evaluate the likelihood that colloids, if formed, would remain in suspension and move through saturated and unsaturated sediments. The objectives of this study were to evaluate three aspects of colloid-facilitated transport of radionuclides as they specifically relate to the LLW Performance Assessment. These objectives were: (1) determine if the chemical conditions likely to exist in the near and far field of the proposed disposal site are prone to induce flocculation (settling of colloids from suspension) or dispersion of naturally occurring Hanford colloids, (2) identify the important mechanisms likely involved in the removal of colloids from a Hanford sediment, and (3) determine if colloids can move through unsaturated porous media.

  6. Analysis of colloids released from bentonite and crushed rock

    NASA Astrophysics Data System (ADS)

    Lahtinen, M.; Hölttä, P.; Riekkola, M.-L.; Yohannes, G.

    Inorganic colloids are present in natural groundwater but colloids can also be produced from degraded Engineered Barrier System (EBS) materials. The potential relevance of colloids for radionuclide transport is highly dependent on the release and stability of colloids in different chemical environments and their interaction with radionuclides. In this work, release and stability of inorganic colloids were determined from bentonite and crushed rock which will be used in the tunnel back-fill. In the batch dispersion experiments, MX-80 bentonite powder or crushed rock samples of mica gneiss, unaltered and two altered tonalites were added to Milli-Q water, saline OLSO, and low salinity Allard reference water with adjusted pH values 7-9. After 4 months, pH, particle size distribution, zeta potential, morphology, elemental composition, and colloid concentration were analyzed. The release and stability of colloids depended significantly on groundwater salinity, pH, and the degree of alteration of the rock. In saline OLSO, zeta potential values near zero, wide particle size range, and low colloid concentrations indicated particle aggregation and instable colloidal dispersion. In low salinity Allard and Milli-Q water, high or moderate negative zeta potential values, smaller particle sizes, and higher colloid concentrations than in OLSO indicated the existence of stable colloids.

  7. Colloid Bound Transport of Contaminats In The Unsaturated Zone

    NASA Astrophysics Data System (ADS)

    Hofmann, T.; Christ, A.

    Colloids can play a major role in the relocation of contaminants in the unsaturated zone. The amount of colloid driven transport is defined by soil chemistry, soil water chemistry and water flow velocity as well as colloid composition and formation. In a current research project we investigate the filtration and mobilization of colloids in unsaturated column studies. We use different soil types, chosen by a wide range of mean grain size and heterogeneity. Particle tracers are polystyrene solids with a de- fined negative surface charge and defined size from 50 nm to 10 µm. In addition, we use natural colloids extracted from a wide range of contaminated and uncontaminated land. Experimental conditions are exactly controlled throughout all the time. We alter mainly flow velocity ionic strength in order to study the filtration behaviour of the soils. In addition, Pyrene and Lead are are used as model contaminants. First results show the colloids are not retarded in many coarse structured soil types. Preferential colloid flow shows a major impact in breakthrough behaviour. Colloid bound lead is relocated significant through the unsaturated zone, whereas non colloid bound lead species are strongly retarded. In the presentation we will show results of contami- nant processes and present new results on the filtration behaviour of colloids in the unsaturated zone depending on flow velocity, soil type and colloid size.

  8. Scattering from correlations in colloidal systems

    SciTech Connect

    Hayter, J.B.

    1984-01-01

    Colloidal suspensions typically exhibit spatial correlations over distances of order 10-10/sup 4/ A, corresponding either to the size of individual particles (e.g., polymer chains, surfactant micelles) or to the range of interaction between particles (e.g., charged polymer lattices at low ionic strength). Apart from having fundamental intrinsic interest, such systems are also extremely useful as model systems with which to study, for example, non-Newtonian hydrodynamics, since temporal correlations are generally much longer lived (10/sup -8/-10/sup -3/ sec) than those found in simple atomic or small molecular systems (10/sup -13/-10/sup -10/ sec). Colloids have long been the subject of macroscopic phenomenological research (on rheological properties, for example), but it is only recently that microscopic light, x-ray and neutron scattering techniques have been applied to their study, in large part because of theoretical difficulties in understanding the scattering from dense liquid-like systems of interacting particles. For spherical colloids, such theoretical problems have now been largely overcome, and for anisotropic colloids experimental techniques are being developed which circumvent the intractable theoretical areas. This paper will first review some static light and small-angle neutron scattering (SANS) results on colloidal suspensions, both at equilibrium and in steady-state non-equilibrium situations, and will then discuss some dynamic measurements on polymer solutions and melts made using the neutron spin-echo (NSE) technique. Emphasis is placed on experiments which have a possible counterpart in synchrotron radiation studies. In particular, NSE extends the results of photon correlation spectroscopy (PCS) to larger momentum transfers and shorter time-scales than are available with visible light, and the extension of PCS to short wavelength on a synchrotron source would be of similar fundamental interest.

  9. [Preliminary study of colloid osmotic pressure for cardiopulmonary bypass].

    PubMed

    Wang, D; Xiang, L; Luo, J

    1996-12-01

    The ideal colloid osmotic pressure is beneficial to decrease the fluid accumulated in the pulmonary and other tissue during cardiopulmonary bypass. Schupbach reported the proper colloidosmotic pressure for cardiopulmonary bypass was 2.1 kPa (16 mmHg). Colloid osmotic pressures of blood and priming fluid during cardiopulmonary bypass were measured in 28 patients with heart disease by using colloid osmotic pressure detection apparatus. The value of colloid osmotic pressure suitable for the designed standard was apparently different among the Gelofusine group and other groups. P value was 0.005. Priming fluid for cardiopulmonary bypass needs to satisfy the quality and the quantity of colloid osmotic pressure. Using Albumin isn't economical. Whole blood and plazma are not suitable for increasing colloid osmotic pressure. Hydroxyethyl starch or Gelofusine is best choice in priming to get designed standard of colloid osmotic pressure. The ratio of hydroxyethyl starch or Gelofusine in priming fluid should beyond 1/2. PMID:9590779

  10. Tracking liquid in drying colloidal fluids with polarized light microscopy

    NASA Astrophysics Data System (ADS)

    Cho, Kun; Park, Jung Soo; Kim, Joon Heon; Weon, Byung Mook

    2014-11-01

    When colloidal fluids dry, tracking liquid surfaces around colloids is difficult with conventional imaging techniques. Here we show that polarized light microscopy (PM) is very useful in tracking liquid surfaces during drying processes of colloidal fluids. In particular, the PM mode is not a new or difficult way but is able to visualize liquid films above colloids in real time. We demonstrate that when liquid films above colloidal particles are broken, the PM patterns appear clearly: this feature is useful to identify the moment of liquid film rupture above colloids in drying colloidal fluids. This result is helpful to improve relevant processes such as inkjet printing, painting, and nanoparticle patterning (K.C. and J.S.P. equally contributed). This work (NRF-2013R1A22A04008115) was supported by Mid-career Researcher Program through NRF grant funded by the MEST.

  11. Colloid Mobilization and Transport during Capillary Fringe Fluctuations

    NASA Astrophysics Data System (ADS)

    Aramrak, Surachet; Flury, Markus

    2016-04-01

    Capillary fringe fluctuations due to changing water tables lead to displacement of air-water interfaces in soils and sediments. These moving air-water interfaces can mobilize colloids. We visualized colloids interacting with moving air-water interfaces during capillary fringe fluctuations by confocal microscopy. We simulated capillary fringe fluctuations in a glass-bead filled column. Confocal images showed that the capillary fringe fluctuations affect colloid transport behavior. Hydrophilic negatively-charged colloids initially suspended in the aqueous phase were deposited at the solid-water interface after a drainage passage, but then were removed by subsequent capillary fringe fluctuations. The colloids that were initially attached to the wet or dry glass bead surface were detached by moving air-water interfaces in the capillary fringe. Hydrophilic negatively-charged colloids did not attach to static air-bubbles, but hydrophobic negatively-charged and hydrophilic positively-charged colloids did.

  12. Modeling of Hydrodynamic Chromatography for Colloid Migration in Fractured Rock

    SciTech Connect

    Li Shihhai; Jen, C.-P

    2001-02-15

    The role of colloids in the migration of radionuclides in the geosphere has been emphasized in the performance assessment of high-level radioactive waste disposal. The literature indicates that the colloid velocity may not be equal to the velocity of groundwater owing to hydrodynamic chromatography. A theoretical model for hydrodynamic chromatography of colloid migration in the fracture is proposed in the present work. In this model, the colloids are treated as nonreactive and the external forces acting on colloidal particles are considered including the inertial force, the van der Waals attractive force, and the electrical double-layer repulsive force, as well as the gravitational force. A fully developed concentration profile for colloids is obtained to elucidate migration behavior for colloids in the fracture. The effects of parameters governing these forces and the aperture of the fracture are determined using a theoretical model.

  13. LONG-TERM COLLOID MOBILIZATION AND COLLOID-FACILITATED TRANSPORT OF RADIONUCLIDES IN A SEMI-ARID VADOSE ZONE

    SciTech Connect

    Markus Flury; James B. Harsh; Fred Zhang; Glendon W. Gee; Earl D. Mattson; Peter C. L

    2012-08-01

    The main purpose of this project was to improve the fundamental mechanistic understanding and quantification of long-term colloid mobilization and colloid-facilitated transport of radionuclides in the vadose zone, with special emphasis on the semi-arid Hanford site. While we focused some of the experiments on hydrogeological and geochemical conditions of the Hanford site, many of our results apply to colloid and colloid-facilitated transport in general. Specific objectives were (1) to determine the mechanisms of colloid mobilization and colloid-facilitated radionuclide transport in undisturbed Hanford sediments under unsaturated flow, (2) to quantify in situ colloid mobilization and colloid-facilitated radionuclidetransport from Hanford sediments under field conditions, and (3) to develop a field-scale conceptual and numerical model for colloid mobilization and transport at the Hanford vadose zone, and use that model to predict long-term colloid and colloid- facilitated radionuclide transport. To achieve these goals and objectives, we have used a combination of experimental, theoretical, and numerical methods at different spatial scales, ranging from microscopic investigationsof single particle attachment and detachment to larger-scale field experiments using outdoor lysimeters at the Hanford site. Microscopic and single particle investigations provided fundamental insight into mechanisms of colloid interactions with the air-water interface. We could show that a moving air water interface (such as a moving water front during infiltration and drainage) is very effective in removing and mobilizing particles from a stationary surface. We further demonstrated that it is particularly the advancing air-water interface which is mainly responsible for colloid mobilization. Forces acting on the colloids calculated from theory corroborated our experimental results, and confirm that the detachment forces (surface tension forces) during the advancing air-water interface

  14. Quantitative uptake of colloidal particles by cell cultures.

    PubMed

    Feliu, Neus; Hühn, Jonas; Zyuzin, Mikhail V; Ashraf, Sumaira; Valdeperez, Daniel; Masood, Atif; Said, Alaa Hassan; Escudero, Alberto; Pelaz, Beatriz; Gonzalez, Elena; Duarte, Miguel A Correa; Roy, Sathi; Chakraborty, Indranath; Lim, Mei L; Sjöqvist, Sebastian; Jungebluth, Philipp; Parak, Wolfgang J

    2016-10-15

    The use of nanotechnologies involving nano- and microparticles has increased tremendously in the recent past. There are various beneficial characteristics that make particles attractive for a wide range of technologies. However, colloidal particles on the other hand can potentially be harmful for humans and environment. Today, complete understanding of the interaction of colloidal particles with biological systems still remains a challenge. Indeed, their uptake, effects, and final cell cycle including their life span fate and degradation in biological systems are not fully understood. This is mainly due to the complexity of multiple parameters which need to be taken in consideration to perform the nanosafety research. Therefore, we will provide an overview of the common denominators and ideas to achieve universal metrics to assess their safety. The review discusses aspects including how biological media could change the physicochemical properties of colloids, how colloids are endocytosed by cells, how to distinguish between internalized versus membrane-attached colloids, possible correlation of cellular uptake of colloids with their physicochemical properties, and how the colloidal stability of colloids may vary upon cell internalization. In conclusion three main statements are given. First, in typically exposure scenarios only part of the colloids associated with cells are internalized while a significant part remain outside cells attached to their membrane. For quantitative uptake studies false positive counts in the form of only adherent but not internalized colloids have to be avoided. pH sensitive fluorophores attached to the colloids, which can discriminate between acidic endosomal/lysosomal and neutral extracellular environment around colloids offer a possible solution. Second, the metrics selected for uptake studies is of utmost importance. Counting the internalized colloids by number or by volume may lead to significantly different results. Third, colloids

  15. EDITORIAL: Colloidal dispersions in external fields Colloidal dispersions in external fields

    NASA Astrophysics Data System (ADS)

    Löwen, Hartmut

    2012-11-01

    Colloidal dispersions have long been proven as pivotal model systems for equilibrium phase transition such as crystallization, melting and liquid-gas phase transition. The last decades have revealed that this is also true for nonequilibrium phenomena. In fact, the fascinating possibility to track the individual trajectories of colloidal particles has greatly advanced our understanding of collective behaviour in classical many-body systems and has helped to reveal the underlying physical principles of glass transition, crystal nucleation, and interfacial dynamics (to name just a few typical nonequilibrium effects). External fields can be used to bring colloids out of equilibrium in a controlled way. Different kinds of external fields can be applied to colloidal dispersions, namely shear flow, electric, magnetic and laser-optical fields, and confinement. Typical research areas can be sketched with the by now traditional complexity diagram (figure 1). The complexity of the colloidal system itself as embodied in statistical degrees of freedom is shown on the x-axis while the complexity of the problem posed, namely bulk, an inhomogeneity in equilibrium, steady state nonequilibrium and full time-dependent nonequilibrium are shown on the y-axis. The different external fields which can be imposed are indicated by the different hatched areas. figure1 Figure 1. Diagram of complexity for colloidal dispersions in external fields: while the x-axis shows the complexity of the system, the y-axis shows the complexity of the problem. Regions which can be accessed by different kinds of external fields are indicated. The arrows indicate recent research directions. Active particles are also indicated with a special complexity of internal degrees of freedom [1]. This collection of papers reflects the scientific programme of the International Conference on Colloidal Dispersions in External Fields III (CODEF III) which took place in Bonn-Bad Godesberg from 20-23 March 2012. This was the

  16. Hierarchical microstructures formed by bidisperse colloidal suspensions within colloid-in-liquid crystal gels.

    PubMed

    Diestra-Cruz, Heberth; Bukusoglu, Emre; Abbott, Nicholas L; Acevedo, Aldo

    2015-04-01

    Past studies have reported that colloids of a single size dispersed in the isotropic phase of a mesogenic solvent can form colloid-rich networks (and gels) upon thermal quenching of the system across the isotropic-nematic phase boundary of the mesogens. Herein we report the observation and characterization of complex hierarchical microstructures that form when bidisperse colloidal suspensions of nanoparticles (NPs; iron oxide with diameters of 188 ± 20 nm or poly(methyl methacrylate) with diameters of 150 ± 15 nm) and microparticles (MPs; polystyrene with diameters of 2.77 ± 0.20 μm) are dispersed in the isotropic phase of 4-pentyl-4'-cyanobiphenyl (5CB) and thermally quenched. Specifically, we document microstructuring that results from three sequential phase separation processes that occur at distinct temperatures during stepwise cooling of the ternary mixture from its miscibility region. The first phase transition demixes the system into coexisting MP-rich and NP-rich phases; the second promotes formation of a particle network within the MP-rich phase; and the third, which coincides with the isotropic-to-nematic phase transition of 5CB, produces a second colloidal network within the NP-rich phase. We quantified the dynamics of each demixing process by using optical microscopy and Fourier transform image analysis to establish that the phase transitions occur through (i) surface-directed spinodal decomposition, (ii) spinodal decomposition, and (iii) nucleation and growth, respectively. Significantly, the observed series of phase transitions leads to a hierarchical organization of cellular microstructures not observed in colloid-in-liquid crystal gels formed from monodisperse colloids. The results of this study suggest new routes to the synthesis of colloidal materials with hierarchical microstructures that combine large surface areas and organized porosity with potential applications in catalysis, separations, chemical sensing, or tissue engineering. PMID

  17. Approaches to separations using silica colloidal membranes

    NASA Astrophysics Data System (ADS)

    Ignacio-de Leon, Patricia Anne Argana

    This thesis describes the synthesis and properties of free-standing nanoporous silica colloidal membranes where the molecular transport is controlled on the basis of size, charge, and chiral selectivity. To achieve this, free-standing membranes were prepared from colloidal solutions of silica nanospheres and the nanopore size and surface functionality were varied. First, Au-coated membranes were prepared and the transport of neutral and charged small molecules through Au-coated silica colloidal membranes modified with poly(methacrylic acid) was studied. Polymer length was controlled by polymerization time to produce pH- and ion-responsive brushes inside the nanopores. By monitoring the flux of a diffusing species, it was demonstrated that the polyelectrolyte brush undergoes swelling and collapse when the pH is increased and decreased, respectively. We also observed an expansion and contraction in the absence and presence of counterions, respectively. We also studied the transport of enantiomers of a chiral dye molecule through silica colloidal membranes with attached chiral moieties. We used small molecules and polymers of amino acid derivatives and chiral calixarenes capable of chiral recognition as a result of stereochemically dependent noncovalent interactions with the diffusing molecule. We found that the selectivity remains approximately the same for membranes modified with small molecules and with polymers. This suggests that enantiopermselectivity depends primarily on the strength of noncovalent interactions rather than the availability of recognition sites. Next, the transport of various generations of dendrimers through silica colloidal membranes was studied in a proof-of-concept experiment to demonstrate the size-selectivity of our materials. Smaller dendrimers were found to diffuse faster and selectivity is improved by using smaller nanopores. Finally, the transport of proteins through silica colloidal membranes was studied as a function of nanopore size

  18. Advanced Colloids Experiment (ACE) Science Overview

    NASA Technical Reports Server (NTRS)

    Meyer, William V.; Sicker, Ronald J.; Chiaramonte, Francis P.; Luna, Unique J.; Chaiken, Paul M.; Hollingsworth, Andrew; Secanna, Stefano; Weitz, David; Lu, Peter; Yodh, Arjun; Yunker, Peter; Lohr, Matthew; Gratale, Matthew; Lynch, Matthew; Kodger, Thomas; Piazza, Roberto; Buzzaccaro, Stefano; Cipelletti, Luca; Schall, Peter; Veen, Sandra; Wegdam, Gerhard; Lee, Chand-Soo; Choi, Chang-Hyung; Paul, Anna-Lisa; Ferl, Robert J.; Cohen, Jacob

    2013-01-01

    The Advanced Colloids Experiment is being conducted on the International Space Station (ISS) using the Light Microscopy Module (LMM) in the Fluids Integrated Rack (FIR). Work to date will be discussed and future plans and opportunities will be highlighted. The LMM is a microscope facility designed to allow scientists to process, manipulate, and characterize colloidal samples in micro-gravity where the absence of gravitational settling and particle jamming enables scientists to study such things as:a.The role that disordered and ordered-packing of spheres play in the phase diagram and equation of state of hard sphere systems,b.crystal nucleation and growth, growth instabilities, and the glass transition, c.gelation and phase separation of colloid polymer mixtures,d.crystallization of colloidal binary alloys,e.competition between crystallization and phase separation,f.effects of anisotropy and specific interactions on packing, aggregation, frustration and crystallization,g.effects of specific reversible and irreversible interactions mediated in the first case by hybridization of complementary DNA strands attached to separate colloidal particles,h.Lock and key interactions between colloids with dimples and spheres which match the size and shape of the dimples,i.finding the phase diagrams of isotropic and interacting particles,j.new techniques for complex self-assembly including scenarios for self-replication, k.critical Casimir forces,l.biology (real and model systems) in microgravity,m.etc. By adding additional microscopy capabilities to the existing LMM, NASA will increase the tools available for scientists that fly experiments on the ISS enabling scientists to observe directly what is happening at the particle level. Presently, theories are needed to bridge the gap between what is being observed (at a macroscopic level when photographing samples) with what is happening at a particle (or microscopic) level. What is happening at a microscopic level will be directly

  19. Colloid Mobilization in Two Atlantic Coastal Plain Aquifers: Field Studies

    NASA Astrophysics Data System (ADS)

    Ryan, Joseph N.; Gschwend, Philip M.

    1990-02-01

    The geochemical mechanisms leading to the mobilization of colloids in groundwater were investigated in the Pine Barrens of New Jersey and in rural central Delaware by sampling pairs of wells screened in oxic and anoxic groundwaters in the same geologic formations. Samples were carefully taken at very low flow rates (˜100 mL min-1) to avoid suspending immobilized particles. The colloidal matter was characterized by light-scattering photometry, scanning electron microscopy, energy-dispersive X ray analysis, microelectrophoresis, and Fe, Al, Si, and organic carbon analyses. The colloids, composed primarily of clays, were observed at high concentrations (up to 60 mg colloids/L) in the anoxic groundwaters, while the oxic groundwaters exhibited ≤1 mg colloids/L. Colloidal organic carbon was present in all groundwaters; but under anoxic conditions, one-third to one-half of the total organic carbon was associated with the inorganic colloids. The field evidence indicates that anoxic conditions cause the mobilization of soil colloids by dissolving the ferric oxyhydroxide coatings cementing the clay particles to the aquifer solids. The depletion of oxidized iron on the surfaces of immobile particles and the addition of organic carbon coatings on the soil particles and colloids apparently stabilizes the colloidal suspension in the anoxic groundwaters.

  20. Colloidal mode of transport in the Potomac River watershed

    SciTech Connect

    Maher, I.L.; Foster, G.D.

    1995-12-31

    Similarly to the particulate phase the colloidal phase may play an important role in the organic contaminant transport downstream the river. The colloidal phase consisting of microparticles and micromolecules which are small enough to be mobile and large enough to attract pollutants can absorb nonpolar organic compounds similarly as do soil and sediment particles. To test the hypothesis three river water samples have been analyzed for PAH content in the dissolved, the colloidal, and the particulate phase. The first sample was collected at the Blue Ridge province of Potomac River watershed, at Point of Rocks, the second one in the Pidmont province, at Riverbend Park, and the third sample at Coastal Plane, at Dyke Marsh (Belle Heven marina). In the laboratory environment each water sample was prefiltered to separate the particulate phase form the dissolved and colloidal phase. One part of the prefiltered water sample was ultrafiltered to separate colloids while the second part of the water was Goulden extracted. The separated colloidal phase was liquid-liquid extracted (LLE) while filters containing the suspended solids were Soxhlet extracted. The extracts of the particulate phase, the colloidal phase, and the dissolved plus colloidal phase were analyzed for selected PAHs via GC/MS. It is planned that concentrations of selected PAHs in three phases will be used for calculations of the partition coefficients, the colloid/dissolved partition coefficient and the particle/dissolved partition coefficient. Both partition coefficients will be compared to define the significance of organic contaminant transport by aquatic colloids.

  1. Methods for colloid transport visualization in pore networks

    NASA Astrophysics Data System (ADS)

    Ochiai, Naoyuki; Kraft, Erika L.; Selker, John S.

    2006-12-01

    Prediction of colloid transport in the subsurface is relevant to researchers in a variety of fields such as contaminant transport, wastewater treatment, and bioremediation. Investigations have traditionally relied on column studies whereby mechanistic inferences must be drawn on the basis of colloid behavior at the outlet. Over the past decade, development of noninvasive visualization techniques based on visible light, magnetic resonance, and X rays have provided insight into a number of colloid transport mechanisms by enabling direct observation of individual colloids at the pore scale and colloid concentrations at longer length scales. As research focus shifts from transport of ideal colloids in ideal media such as glass beads to natural colloids in natural porous media, these noninvasive techniques will become increasingly useful for studying the collection of mechanisms at work in heterogeneous pore systems. It is useful at this juncture to review recent progress in colloid transport visualization as a starting point for further development of visualization tools to support investigation of colloids in natural systems. We briefly discuss characteristics of visualization systems currently used to study colloid transport in porous media and review representative microscale and mesoscale visualization studies conducted over the past decade, with additional attention given to two optical visualization systems being developed by the authors.

  2. Application of ESEM to environmental colloids. [Environmental Scanning Electron Microscopy

    SciTech Connect

    Nuttall, H.E.; Kale, R. . Dept. of Chemical/Nuclear Engineering)

    1993-08-01

    Environmental colloids are toxic or radioactive particles suspended in ground or surface water. These hazardous particles can facilitate and accelerate the transport of toxicants and enhance the threat to humans by exposure to pathogenic substances. The chemical and physical properties of hazardous colloids have not been well characterized nor are there standard colloid remediation technologies to prevent their deleterious effects. Colloid characterization requires measurement of their size distribution, zeta potential, chemical composition, adsorption capacity and morphology. The environmental scanning electron microscope (ESEM) by ElectroScan, Inc., analyzes particle sizes, composition, and morphology. It is also used in this study to identify the attachment of colloids onto packing or rock surfaces in the development of a colloid remediation process. The ESEM has confirmed the composition of groundwater colloids in these studies to be generally the same material as the surrounding rock. The morphology studies have generally shown that colloids are simply small pieces of the rock surface that have exfoliated into the surrounding water. However, in general, the source and chemical composition of groundwater colloids is site dependent. The authors have found that an ESEM works best as a valuable analysis tool within a suite of colloid characterization instruments.

  3. Cotransport of bismerthiazol and montmorillonite colloids in saturated porous media

    NASA Astrophysics Data System (ADS)

    Shen, Chongyang; Wang, Hong; Lazouskaya, Volha; Du, Yichun; Lu, Weilan; Wu, Junxue; Zhang, Hongyan; Huang, Yuanfang

    2015-06-01

    While bismerthiazol [N,N‧-methylene-bis-(2-amino-5-mercapto-1,3,4-thiadiazole)] is one of the most widely used bactericides, the transport of bismerthiazol in subsurface environments is unclear to date. Moreover, natural colloids are ubiquitous in the subsurface environments. The cotransport of bismerthiazol and natural colloids has not been investigated. This study conducted laboratory column experiments to examine the transport of bismerthiazol in saturated sand porous media both in the absence and presence of montmorillonite colloids. Results show that a fraction of bismerthiazol was retained in sand and the retention was higher at pH 7 than at pH 4 and 10. The retention did not change with ionic strength. The retention was attributed to the complex of bismerthiazol with metals/metal oxides on sand surfaces through ligand exchange. The transport of bismerthiazol was enhanced with montmorillonite colloids copresent in the solutions and, concurrently, the transport of montmorillonite colloids was facilitated by the bismerthiazol. The transport of montmorillonite colloids was enhanced likely because the bismerthiazol and the colloids competed for the attachment/adsorption sites on collector surfaces and the presence of bismerthiazol changed the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energies between colloids and collectors. The transport of bismerthiazol was inhibited if montmorillonite colloids were pre-deposited in sand because bismerthiazol could adsorb onto the colloid surfaces. The adsorbed bismerthiazol could be co-remobilized with the colloids from primary minima by decreasing ionic strength. Whereas colloid-facilitated transport of pesticides has been emphasized, our study implies that transport of colloids could also be facilitated by the presence of pesticides.

  4. Shape recognition of microbial cells by colloidal cell imprints

    NASA Astrophysics Data System (ADS)

    Borovička, Josef; Stoyanov, Simeon D.; Paunov, Vesselin N.

    2013-08-01

    We have engineered a class of colloids which can recognize the shape and size of targeted microbial cells and selectively bind to their surfaces. These imprinted colloid particles, which we called ``colloid antibodies'', were fabricated by partial fragmentation of silica shells obtained by templating the targeted microbial cells. We successfully demonstrated the shape and size recognition between such colloidal imprints and matching microbial cells. High percentage of binding events of colloidal imprints with the size matching target particles was achieved. We demonstrated selective binding of colloidal imprints to target microbial cells in a binary mixture of cells of different shapes and sizes, which also resulted in high binding selectivity. We explored the role of the electrostatic interactions between the target cells and their colloid imprints by pre-coating both of them with polyelectrolytes. Selective binding occurred predominantly in the case of opposite surface charges of the colloid cell imprint and the targeted cells. The mechanism of the recognition is based on the amplification of the surface adhesion in the case of shape and size match due to the increased contact area between the target cell and the colloidal imprint. We also tested the selective binding for colloid imprints of particles of fixed shape and varying sizes. The concept of cell recognition by colloid imprints could be used for development of colloid antibodies for shape-selective binding of microbes. Such colloid antibodies could be additionally functionalized with surface groups to enhance their binding efficiency to cells of specific shape and deliver a drug payload directly to their surface or allow them to be manipulated using external fields. They could benefit the pharmaceutical industry in developing selective antimicrobial therapies and formulations.

  5. Colloidal pseudocapacitor: Nanoscale aggregation of Mn colloids from MnCl2 under alkaline condition

    NASA Astrophysics Data System (ADS)

    Chen, Kunfeng; Xue, Dongfeng; Komarneni, Sridhar

    2015-04-01

    Novel colloidal pseudocapacitors are designed using commercially available MnCl2 salts as starting materials and KOH as electrolyte, where the colloids synthesis and subsequently integrating into practical electrode structures occur at the same spatial and temporal scale. Highly electroactive Mn7O13·5H2O colloids are formed in-situ by electric field assisted chemical coprecipitation in KOH solution. The highly efficient Faradaic redox reactions involving Mn3+ ↔ Mn4+ and Mn2+ ↔ Mn3+ are confirmed in electroactive Mn7O13·5H2O pseudocapacitors, which can deliver high specific capacitance of 2518 F/g based on active Mn cations at current density of 5 A/g. The present results show that instead of one-electron Faradaic reaction, Mn cations in our designed system can lead to two-electron Faradaic reactions. The colloidal pseudocapacitor system involving Mn-based colloids is a novel route to engineer electrochemical performances of inorganic pseudocapacitors.

  6. SUSY Les Houches Accord 2

    SciTech Connect

    Allanach, B.; Balazs, C.; Belanger, G.; Bernhardt, M.; Boudjema, F.; Choudhury, D.; Desch, K.; Ellwanger, U.; Gambino, P.; Godbole, R.; Goto, T.; /Cambridge U., DAMTP /Monash U. /Annecy, LAPTH /Bonn U. /Harish-Chandra Res. Inst. /Orsay, LPT /Turin U. /INFN, Turin /Bangalore, Indian Inst. Sci. /KEK, Tsukuba /Barcelona U.

    2007-11-08

    The Supersymmetry Les Houches Accord (SLHA) [1] provides a universal set of conventions for conveying spectral and decay information for supersymmetry analysis problems in high energy physics. Here, we propose extensions of the conventions of the first SLHA to include various generalizations: the minimal supersymmetric standard model with violation of CP, R-parity, and flavor, as well as the simplest next-to-minimal model.

  7. SUSY Les Houches Accord 2

    SciTech Connect

    Allanach, B.; Balazs, C.; Belanger, G.; Bernhardt, M.; Boudjema, F.; Choudhury, D.; Desch, K.; Ellwanger, U.; Gambino, P.; Godbole, R.; Goto, T.; Guasch, J.; Guchait, M.; Hahn, T.; Heinemeyer, S.; Hugonie, C.; Hurth, T.; Kraml, S.; Kreiss, S.; Lykken, J.; Moortgat, F.; /Cambridge U., DAMTP /Monash U. /Annecy, LAPTH /Bonn U. /Harish-Chandra Res. Inst. /Orsay, LPT /Turin U. /INFN, Turin /Bangalore, Indian Inst. Sci. /KEK, Tsukuba /Barcelona U. /Tata Inst. /Munich, Max Planck Inst. /Cantabria Inst. of Phys. /Montpellier U. /CERN /SLAC /Edinburgh U. /Fermilab /Zurich, ETH /Southampton U.

    2007-11-08

    The Supersymmetry Les Houches Accord (SLHA) provides a universal set of conventions for conveying spectral and decay information for supersymmetry analysis problems in high energy physics. Here, we propose extensions of the conventions of the first SLHA to include various generalizations: the minimal supersymmetric standard model with violation of CP, R-parity, and flavor, as well as the simplest next-to-minimal model.

  8. Slab photonic crystals with dimer colloid bases

    SciTech Connect

    Riley, Erin K.; Liddell Watson, Chekesha M.

    2014-06-14

    The photonic band gap properties for centered rectangular monolayers of asymmetric dimers are reported. Colloids in suspension have been organized into the phase under confinement. The theoretical model is inspired by the range of asymmetric dimers synthesized via seeded emulsion polymerization and explores, in particular, the band structures as a function of degree of lobe symmetry and degree of lobe fusion. These parameters are varied incrementally from spheres to lobe-tangent dimers over morphologies yielding physically realizable particles. The work addresses the relative scarcity of theoretical studies on photonic crystal slabs with vertical variation that is consistent with colloidal self-assembly. Odd, even and polarization independent gaps in the guided modes are determined for direct slab structures. A wide range of lobe symmetry and degree of lobe fusion combinations having Brillouin zones with moderate to high isotropy support gaps between odd mode band indices 3-4 and even mode band indices 1-2 and 2-3.

  9. Microscopic dynamics of synchronization in driven colloids

    PubMed Central

    Juniper, Michael P.N.; Straube, Arthur V.; Besseling, Rut; Aarts, Dirk G.A.L.; Dullens, Roel P.A.

    2015-01-01

    Synchronization of coupled oscillators has been scrutinized for over three centuries, from Huygens' pendulum clocks to physiological rhythms. One such synchronization phenomenon, dynamic mode locking, occurs when naturally oscillating processes are driven by an externally imposed modulation. Typically only averaged or integrated properties are accessible, leaving underlying mechanisms unseen. Here, we visualize the microscopic dynamics underlying mode locking in a colloidal model system, by using particle trajectories to produce phase portraits. Furthermore, we use this approach to examine the enhancement of mode locking in a flexible chain of magnetically coupled particles, which we ascribe to breathing modes caused by mode-locked density waves. Finally, we demonstrate that an emergent density wave in a static colloidal chain mode locks as a quasi-particle, with microscopic dynamics analogous to those seen for a single particle. Our results indicate that understanding the intricate link between emergent behaviour and microscopic dynamics is key to controlling synchronization. PMID:25994921

  10. 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

  11. Glassy Spin Dynamics in Buckled Colloidal Crystal

    NASA Astrophysics Data System (ADS)

    Zhou, Di; Wang, Feng; Han, Yilong

    Geometric frustration arises when lattice structure prevents simultaneous minimization of local interaction energies. It leads to highly degenerate ground states and complex behaviors in frustrated magnetic materials. Here we experimentally studied buckled 1.5-layer colloidal NIPA microgel crystals confined between parallel plates. Spheres buckled up and down are analogous to antiferromagnetic Ising spins. These spins on the distorted triangular lattice exhibit glassy dynamics at low temperatures. In particular, a spin only has 13 nearest-neighbor configurations, which enables to reveal the correlation between structures and dynamical heterogeneity. Soft modes also localize at high-energy regions. Further, we compared the colloidal spin system with kinetic constrained models (KCMs) and observed dynamical facilitation behaviors including excitations lines in space-time. Similar structures and glassy dynamics are also observed in our simulation of Coulomb charges on a triangular lattice. The work was supported by Grant RGC-GRF601613.

  12. Structure and hydrodynamics of colloidal systems

    NASA Astrophysics Data System (ADS)

    Hayter, John B.

    1986-02-01

    Invited paperColloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to μsec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.

  13. Structure and hydrodynamics of colloidal systems

    NASA Astrophysics Data System (ADS)

    Hayter, J. B.

    1985-07-01

    Colloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to (MU) sec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.

  14. Functionalized patchy particles using colloidal lenses

    NASA Astrophysics Data System (ADS)

    Middleton, Christine

    2014-03-01

    Colloidal assembly had been limited by the isotropic, nonspecific nature of interactions between spherical colloidal particles. By giving particles patches functionalized with single stranded DNA, these interactions can be made both directional and specific. We create patchy particles by adding patches to spherical emulsion droplets using the depletion interaction. First we make polystyrene particles in the shape of contact lenses to be the patches. The lenses are functionalized with single stranded DNA on their convex side. Then we put the lenses on the surface of oil emulsion droplets using the depletion interaction, creating a patch (or multiple patches) on the surface of each emulsion droplet. The emulsion droplets can now interact with each other in a specific, directional way through DNA functionalized patches.

  15. Collective motion in populations of colloidal robots

    NASA Astrophysics Data System (ADS)

    Bartolo, Denis; Bricard, Antoine; Caussin, Jean-Baptiste; Dauchot, Olivier; Desreumaux, Nicolas

    2014-03-01

    Could the behavior of bacteria swarms, fish schools, and bird flocks be understood within a unified framework? Can one ignore the very details of the interaction mechanisms at the individual level to elucidate how strikingly similar collective motion emerges at the group level in this broad range of motile systems? These seemingly provocative questions have triggered significant advance in the physics and the biology, communities over the last decade. In the physics language these systems, made of motile individuals, can all be though as different realizations of ``active matter.'' In this talk, I will show how to gain more insight into this vivid field using self-propelled colloids as a proxy for motile organism. I will show how to motorize colloidal particles capable of sensing the orientation of their neighbors. Then, I will demonstrate that these archetypal populations display spontaneous transitions to swarming motion, and to global directed motion with very few density and orientation fluctuations.

  16. Knot theory realizations in nematic colloids.

    PubMed

    Čopar, Simon; Tkalec, Uroš; Muševič, Igor; Žumer, Slobodan

    2015-02-10

    Nematic braids are reconfigurable knots and links formed by the disclination loops that entangle colloidal particles dispersed in a nematic liquid crystal. We focus on entangled nematic disclinations in thin twisted nematic layers stabilized by 2D arrays of colloidal particles that can be controlled with laser tweezers. We take the experimentally assembled structures and demonstrate the correspondence of the knot invariants, constructed graphs, and surfaces associated with the disclination loop to the physically observable features specific to the geometry at hand. The nematic nature of the medium adds additional topological parameters to the conventional results of knot theory, which couple with the knot topology and introduce order into the phase diagram of possible structures. The crystalline order allows the simplified construction of the Jones polynomial and medial graphs, and the steps in the construction algorithm are mirrored in the physics of liquid crystals. PMID:25624467

  17. Colloidal cholesteric liquid crystal in spherical confinement.

    PubMed

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S; Lavrentovich, Oleg D; Kumacheva, Eugenia

    2016-01-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter. PMID:27561545

  18. The NASA GSFC MEMS Colloidal Thruster

    NASA Technical Reports Server (NTRS)

    Cardiff, Eric H.; Jamieson, Brian G.; Norgaard, Peter C.; Chepko, Ariane B.

    2004-01-01

    A number of upcoming missions require different thrust levels on the same spacecraft. A highly scaleable and efficient propulsion system would allow substantial mass savings. One type of thruster that can throttle from high to low thrust while maintaining a high specific impulse is a Micro-Electro-Mechanical System (MEMS) colloidal thruster. The NASA GSFC MEMS colloidal thruster has solved the problem of electrical breakdown to permit the integration of the electrode on top of the emitter by a novel MEMS fabrication technique. Devices have been successfully fabricated and the insulation properties have been tested to show they can support the required electric field. A computational finite element model was created and used to verify the voltage required to successfully operate the thruster. An experimental setup has been prepared to test the devices with both optical and Time-Of-Flight diagnostics.

  19. Colloidal cholesteric liquid crystal in spherical confinement

    PubMed Central

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M.; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S.; Lavrentovich, Oleg D.; Kumacheva, Eugenia

    2016-01-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter. PMID:27561545

  20. Particles with changeable topology in nematic colloids.

    PubMed

    Ravnik, Miha; Čopar, Simon; Žumer, Slobodan

    2015-09-01

    We show that nematic colloids can serve as a highly variable and controllable platform for studying inclusions with changeable topology and their effects on the surrounding ordering fields. We explore morphing of toroidal and knotted colloidal particles into effective spheres, distinctively changing their Euler characteristic and affecting the surrounding nematic field, including topological defect structures. With toroidal particles, the inner nematic defect eventually transitions from a wide loop to a point defect (a small loop). Trefoil particles become linked with two knotted defect loops, mutually forming a three component link, that upon tightening transform into a two-component particle-defect loop link. For more detailed topological analysis, Pontryagin-Thom surfaces are calculated and visualised, indicating an interesting cascade of defect rewirings caused by the shape morphing of the knotted particles. PMID:26291540

  1. Particles with changeable topology in nematic colloids

    NASA Astrophysics Data System (ADS)

    Ravnik, Miha; Čopar, Simon; Žumer, Slobodan

    2015-09-01

    We show that nematic colloids can serve as a highly variable and controllable platform for studying inclusions with changeable topology and their effects on the surrounding ordering fields. We explore morphing of toroidal and knotted colloidal particles into effective spheres, distinctively changing their Euler characteristic and affecting the surrounding nematic field, including topological defect structures. With toroidal particles, the inner nematic defect eventually transitions from a wide loop to a point defect (a small loop). Trefoil particles become linked with two knotted defect loops, mutually forming a three component link, that upon tightening transform into a two-component particle-defect loop link. For more detailed topological analysis, Pontryagin-Thom surfaces are calculated and visualised, indicating an interesting cascade of defect rewirings caused by the shape morphing of the knotted particles.

  2. Knot theory realizations in nematic colloids

    PubMed Central

    Čopar, Simon; Tkalec, Uroš; Muševič, Igor; Žumer, Slobodan

    2015-01-01

    Nematic braids are reconfigurable knots and links formed by the disclination loops that entangle colloidal particles dispersed in a nematic liquid crystal. We focus on entangled nematic disclinations in thin twisted nematic layers stabilized by 2D arrays of colloidal particles that can be controlled with laser tweezers. We take the experimentally assembled structures and demonstrate the correspondence of the knot invariants, constructed graphs, and surfaces associated with the disclination loop to the physically observable features specific to the geometry at hand. The nematic nature of the medium adds additional topological parameters to the conventional results of knot theory, which couple with the knot topology and introduce order into the phase diagram of possible structures. The crystalline order allows the simplified construction of the Jones polynomial and medial graphs, and the steps in the construction algorithm are mirrored in the physics of liquid crystals. PMID:25624467

  3. Magnetic Colloids By Pulsed Laser Ablation

    NASA Astrophysics Data System (ADS)

    Pandey, B. K.; Singh, M. K.; Agarwal, A.; Gopal, R.

    2011-06-01

    Colloidal magnetic nanoparticles have been successfully synthesized by nano second pules laser ablation of a cobalt slice immersed in liquid (distilled water) medium. The focused output of 1064 nm wavelength of pulsed Nd: YAG laser operating at 40 mJ/pulse is used for ablation. The liquid enviorment allows formation of colloids with nanoparticles in uniform particle diameter. Synchrotron X-ray powder diffraction (XRD) is used for the study of structural property of synthesized nanoparticles. The magnetic properties of cobalt nanoparticles are also investigated. The coercivity of is found to be 73 Oe. The optical properties have been determined by UV-visible absorption spectroscopy and band gap found to be 2.16 and 3.60 eV.

  4. Structure and hydrodynamics of colloidal systems

    SciTech Connect

    Hayter, J.B.

    1985-07-01

    Colloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to ..mu..sec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.

  5. Microscopic dynamics of synchronization in driven colloids.

    PubMed

    Juniper, Michael P N; Straube, Arthur V; Besseling, Rut; Aarts, Dirk G A L; Dullens, Roel P A

    2015-01-01

    Synchronization of coupled oscillators has been scrutinized for over three centuries, from Huygens' pendulum clocks to physiological rhythms. One such synchronization phenomenon, dynamic mode locking, occurs when naturally oscillating processes are driven by an externally imposed modulation. Typically only averaged or integrated properties are accessible, leaving underlying mechanisms unseen. Here, we visualize the microscopic dynamics underlying mode locking in a colloidal model system, by using particle trajectories to produce phase portraits. Furthermore, we use this approach to examine the enhancement of mode locking in a flexible chain of magnetically coupled particles, which we ascribe to breathing modes caused by mode-locked density waves. Finally, we demonstrate that an emergent density wave in a static colloidal chain mode locks as a quasi-particle, with microscopic dynamics analogous to those seen for a single particle. Our results indicate that understanding the intricate link between emergent behaviour and microscopic dynamics is key to controlling synchronization. PMID:25994921

  6. Appendicite chronique chez les enfants

    PubMed Central

    Kim, David; Butterworth, Sonia A.; Goldman, Ran D.

    2016-01-01

    Résumé Question Alors que le diagnostic d’appendicite aigu est relativement simple à poser, celui d’appendicite chronique peut être controversé et souvent mal posé. De quelle manière et à quel moment les cliniciens devraient-ils investiguer l’appendicite chronique comme la cause de douleurs abdominales chroniques et récidivantes dans la population pédiatrique? Réponse L’appendicite chronique est une inflammation ou fibrose de longue date de l’appendice dont le tableau clinique est une douleur abdominale prolongée ou intermittente. Son diagnostic est souvent difficile à poser et elle peut entraîner des complications telles que des infections intra-abdominales, ou l’occlusion ou la perforation de l’intestin. Le tableau clinique, de même que les études d’imagerie, peuvent aider le clinicien à écarter d’autres affections, et chez les patients qui reçoivent un diagnostic, dont de nombreux enfants, l’appendicectomie soulage partiellement ou complètement la douleur.

  7. Nanoparticle engineering of colloidal suspension behavior

    NASA Astrophysics Data System (ADS)

    Chan, Angel Thanda

    We investigate the effects of highly charged nanoparticles on the phase behavior, structure, and assembly of colloidal microsphere suspensions. Specifically, by selectively tuning the electrostatic interactions between silica microspheres and polystyrene nanoparticles, we study the behavior of four key systems: (i) strongly repulsive, (ii) haloing, (iii) weakly attractive, and (iv) strongly attractive systems. In each system, a combination of nanoparticle adsorption, zeta potential, and confocal microscopy measurements are carried out to systematically study the effects of nanoparticle volume fraction, microsphere/nanoparticle size ratios, and interparticle interactions on their behavior. Our observations indicate that minimal adsorption of highly charged nanoparticles occurs on like-charged and negligibly-charged microspheres, whereas their extent of association increases dramatically with increasing microsphere-nanoparticle attraction. A rich phase behavior emerges in these systems based on whether the nanoparticle species serve as depletants, haloing, or bridging species. The phase transitions in the haloing system occur at constant nanoparticle volume fractions, φnano, over a broad range of microsphere volume fractions, φmicro . By contrast, the observed transitions in the weakly and strongly attractive mixtures occur at a constant number ratio of nanoparticles per microsphere, Nnano/Nmicro. Important structural differences emerge, which can be exploited in the assembly of colloidal gels for direct ink writing and colloidal crystals on epitaxially patterned substrates. Finally, for the first time, we explore nanoparticle haloing as a new route for stabilizing hydrophobic colloidal drugs in aqueous suspensions media for preparation of injectable pharmaceuticals. These microsphere suspensions exhibit improved stability relative to their surfactant-stabilized counterparts after autoclaving, a critical processing step for this target applications. This research

  8. Colloidal Nanocrystals Fluoresced by Surface Coordination Complexes

    PubMed Central

    Wang, Guan; Ji, Jianwei; Zhang, Xinwen; Zhang, Yan; Wang, Qiangbin; You, Xiaozeng; Xu, Xiangxing

    2014-01-01

    Colloidal Nanocrystals (NCs) with fluorescence originating from surface complexes are successfully prepared. The components of these NCs range from insulator, semiconductor to metal, with either pure phase, doped or core/shell structures. The photoluminescence of these NCs can be reversibly tuned across the visible to infrared spectrum, and even allow multi-color emission. A light emitting device is fabricated and a new in vivo cell imaging method is performed to demonstrate the power of this technology for emerging applications. PMID:24970242

  9. Structure and dynamics of biphasic colloidal mixtures.

    PubMed

    Mohraz, Ali; Weeks, Eric R; Lewis, Jennifer A

    2008-06-01

    We investigate the structure and dynamics of biphasic colloidal mixtures composed of coexisting attractive and repulsive microspheres by confocal microscopy. Attractive gels formed in the presence of repulsive microspheres are more spatially homogeneous and, on average, are both more locally tenuous and have fewer large voids than their unary counterparts. The repulsive microspheres within these mixtures display heterogeneous dynamics, with some species exhibiting freely diffusive Brownian motion while others are trapped within the gel network during aggregation. PMID:18643205

  10. Dynamics of Polymers in Colloidal Flows

    NASA Astrophysics Data System (ADS)

    Chen, Hsieh; Alexander-Katz, Alfredo

    2011-03-01

    This research is motivated by recent studies on the von Willebrand factor (vWF), a large multimeric protein that plays an essential role in the initial stages of blood clotting in blood vessels. Recent experiments substantiated the hypothesis that the vWF is activated by shear stress in blood flow that causes its shape to transform from a compact globule to an extended state, and biological function is obtained only in the extended state. Simple simulations (which only consider a single polymer in bulk shear flow) have successfully reproduced the observed dynamics of the vWF. However, a more refined model is still demanding for the better understanding of the behaviors of this biomolecule in the physiological environments. Here we refine the existing model by adding the drifting colloids into the flows to mimic the presence of the blood cells in the bloodstream. Preliminary result shows that colloids greatly influence the dynamics of the polymers. It is observed that the average extensions of polymers along and perpendicular to the shear flow direction are both increased with the presence of the colloids.

  11. Microfluidic Rheology of Soft Colloidal Suspensions

    NASA Astrophysics Data System (ADS)

    Nordstrom, Kerstin; Arratia, Paulo; Verneuil, Emilie; Gollub, Jerry; Durian, Douglas

    2008-11-01

    The rheology of a suspension of soft colloidal particles is investigated using a pressure-driven flow in a deep 25 μm wide microchannel. The system is composed of N-isopropylacrylamide (NIPA), colloidal microgel particles, suspended in aqueous solution. NIPA is temperature-sensitive in that the hydrodynamic radius of a particle decreases as temperature increases [1]. Therefore, colloidal suspensions of different packing fraction can be obtained simply by varying the temperature using a temperature-controlled stage. We determine the velocity profile and the local shear rate of the suspension using particle image velocimetry (PIV). We have developed methods to accurately infer the suspension shear viscosity and shear stress as a function of shear rate. The dynamical range of shear rates probed is approximately 5 orders of magnitude, ranging from 10-3 to 10^2 s-1. Results show that as the packing fraction is increased towards the jamming point, the velocity profiles are markedly non-Newtonian. Further, near the jamming point, the stress versus shear rate curves show yield stress behavior. [1] Alsayed, A.M., Islam, M.F., Zhang, J., Collings, P.J., Yodh, A.J., Science 309, 1207.-1210 (2005)

  12. Synthesis of metal colloids in inverse microemulsions

    NASA Astrophysics Data System (ADS)

    Barnickel, P.; Wokaun, A.

    Colloidal silver and gold particles have been prepared by reduction of aqueous metal salt solutions in inverse microemulsions. The sols are characterized by absorption spectroscopy and electron microscopy. Ultrasound treatment during reduction results in a narrower size distribution of the colloidal particles, as evidenced by a narrower absorption band. Photochemical silver and gold sol formation, without the addition of a reducing agent, has been observed for inverse microemulsions of metal salt solutions in a medium consisting of dodecyl-heptaethyleneglycol-ether and hexane. The particle sizes determined from electron microscopy have been used as input parameters for the simulation of absorption spectra, based on the electromagnetic theory of localized surface plasmon excitation. For the gold sols a quantitative agreement between experimental and simulated spectra is obtained. With the silver colloids, the observed red-shift of the absorption maximum points to the presence of an ionic layer on the surface of the particles. When this layer is included in the theoretical model, good agreement with the experiment is achieved.

  13. Colloidal particle deposition in turbulent flow

    SciTech Connect

    Morton, D.S.

    1994-05-01

    A theoretical analysis is presented which describes the initial deposition of monodispersed spherical colloidal particles from a steady fully developed turbulent flow onto conduit walls. When the net particle-conduit electrical interaction potential is attractive, particle deposition is shown to be often governed by turbulent hydrodynamics. When the net particle-conduit electrical interaction potential possess a repulsive maximum, particle deposition to first order is uniform and depends solely on electrical interaction effects. The developed theoretical model specialized to orifice deposition with the use of Harwell Flow3D turbulence modelling software qualitatively described the deposition of 0.5 {mu}m silica particles onto glass orifices from an aqueous suspension. The effect of the electrical double layer on the rate of colloidal particle deposition in laminar flow has been described by Spielman and Friedlander (1), Dahneke (2), Bowen et al. (3) and Bowen and Epstein (4). This article describes the extension of their work to colloidal particle deposition under steady fully developed turbulent flow conditions. This article also reports the results of orifice particle deposition experiments which were conducted to qualitatively investigate the developed theoretical model.

  14. Dense colloidal fluids form denser amorphous sediments

    PubMed Central

    Liber, Shir R.; Borohovich, Shai; Butenko, Alexander V.; Schofield, Andrew B.; Sloutskin, Eli

    2013-01-01

    We relate, by simple analytical centrifugation experiments, the density of colloidal fluids with the nature of their randomly packed solid sediments. We demonstrate that the most dilute fluids of colloidal hard spheres form loosely packed sediments, where the volume fraction of the particles approaches in frictional systems the random loose packing limit, φRLP = 0.55. The dense fluids of the same spheres form denser sediments, approaching the so-called random close packing limit, φRCP = 0.64. Our experiments, where particle sedimentation in a centrifuge is sufficiently rapid to avoid crystallization, demonstrate that the density of the sediments varies monotonically with the volume fraction of the initial suspension. We reproduce our experimental data by simple computer simulations, where structural reorganizations are prohibited, such that the rate of sedimentation is irrelevant. This suggests that in colloidal systems, where viscous forces dominate, the structure of randomly close-packed and randomly loose-packed sediments is determined by the well-known structure of the initial fluids of simple hard spheres, provided that the crystallization is fully suppressed. PMID:23530198

  15. An evaporation model of colloidal suspension droplets

    NASA Astrophysics Data System (ADS)

    Sartori, Silvana; Li\\ Nán, Amable; Lasheras, Juan C.

    2009-11-01

    Colloidal suspensions of polymers in water or other solvents are widely used in the pharmaceutical industry to coat tablets with different agents. These allow controlling the rate at which the drug is delivered, taste or physical appearance. The coating is performed by simultaneously spraying and drying the tablets with the colloidal suspension at moderately high temperatures. The spreading of the coating on the pills surface depends on the droplet Webber and Reynolds numbers, angle of impact, but more importantly on the rheological properties of the drop. We present a model for the evaporation of a colloidal suspension droplet in a hot air environment with temperatures substantially lower than the boiling temperature of the carrier fluid. As the liquid vaporizes from the surface, a compacting front advances into the droplet faster than the liquid surface regresses, forming a shell of a porous medium where the particles reach their maximum packing density. While the surface regresses, the evaporation rate is determined by both the rate at which heat is transported to the droplet surface and the rate at which liquid vapor is diffused away from it. This regime continues until the compacting front reaches the center of the droplet, at which point the evaporation rate is drastically reduced.

  16. Composition of estuarine colloidal material: organic components

    USGS Publications Warehouse

    Sigleo, A.C.; Hoering, T.C.; Helz, G.R.

    1982-01-01

    Colloidal material in the size range 1.2 nm to 0.4 ??m was isolated by ultrafiltration from Chesapeake Bay and Patuxent River waters (U.S.A.). Temperature controlled, stepwise pyrolysis of the freeze-dried material, followed by gas chromatographic-mass spectrometric analyses of the volatile products indicates that the primary organic components of this polymer are carbohydrates and peptides. The major pyrolysis products at the 450??C step are acetic acid, furaldehydes, furoic acid, furanmethanol, diones and lactones characteristic of carbohydrate thermal decomposition. Pyrroles, pyridines, amides and indole (protein derivatives) become more prevalent and dominate the product yield at the 600??C pyrolysis step. Olefins and saturated hydrocarbons, originating from fatty acids, are present only in minor amounts. These results are consistent with the composition of Chesapeake phytoplankton (approximately 50% protein, 30% carbohydrate, 10% lipid and 10% nucleotides by dry weight). The pyrolysis of a cultured phytoplankton and natural particulate samples produced similar oxygen and nitrogencontaining compounds, although the proportions of some components differ relative to the colloidal fraction. There were no lignin derivatives indicative of terrestrial plant detritus in any of these samples. The data suggest that aquatic microorganisms, rather than terrestrial plants, are the dominant source of colloidal organic material in these river and estuarine surface waters. ?? 1982.

  17. Equilibrium crystal phases of triblock Janus colloids.

    PubMed

    Reinhart, Wesley F; Panagiotopoulos, Athanassios Z

    2016-09-01

    Triblock Janus colloids, which are colloidal spheres decorated with attractive patches at each pole, have recently generated significant interest as potential building blocks for functional materials. Their inherent anisotropy is known to induce self-assembly into open structures at moderate temperatures and pressures, where they are stabilized over close-packed crystals by entropic effects. We present a numerical investigation of the equilibrium phases of triblock Janus particles with many different patch geometries in three dimensions, using Monte Carlo simulations combined with free energy calculations. In all cases, we find that the free energy difference between crystal polymorphs is less than 0.2 kBT per particle. By varying the patch fraction and interaction range, we show that large patches stabilize the formation of structures with four bonds per patch over those with three. This transition occurs abruptly above a patch fraction of 0.30 and has a strong dependence on the interaction range. Furthermore, we find that a short interaction range favors four bonds per patch, with longer range increasingly stabilizing structures with only three bonds per patch. By quantifying the effect of patch geometry on the stability of the equilibrium crystal structures, we provide insights into the fundamental design rules for constructing complex colloidal crystals. PMID:27609002

  18. Nanosized gismondine grown in colloidal precursor solutions.

    PubMed

    Kecht, J; Mihailova, B; Karaghiosoff, K; Mintova, S; Bein, T

    2004-06-22

    A colloidal molecular sieve with GIS-type structure was prepared from aged aluminosilicate precursor solutions containing tetramethylammonium (TMA) hydroxide under hydrothermal treatment at 100 degrees C. The nucleation and the development of the GIS zeolite structure were studied by dynamic light scattering, scanning electron microscopy, X-ray diffraction, Raman and infrared spectroscopies, and liquid-state NMR spectroscopy. It is shown that the aging at room temperature leads to the formation of subcolloidal particles that incorporate TMA cations and form larger aggregates. After an extended heating of 13 days, a complete transformation from amorphous precursor material to crystalline GIS-type colloidal particles is observed. The mean hydrodynamic radius of the crystalline GIS particles is in the range of 30-50 nm. The specific template-framework interactions influence the spectral features of the TMA cations incorporated in the zeolite structure, thus making possible the use of the corresponding Raman spectra and 13C NMR data for the examination of the crystallinity of GIS-type colloidal particles stabilized in water. PMID:15986662

  19. Theory of dynamic arrest in colloidal mixtures

    NASA Astrophysics Data System (ADS)

    Juárez-Maldonado, R.; Medina-Noyola, M.

    2008-05-01

    We present a first-principles theory of dynamic arrest in colloidal mixtures based on the multicomponent self-consistent generalized Langevin equation theory of colloid dynamics [M. A. Chávez-Rojo and M. Medina-Noyola, Phys. Rev. E 72, 031107 (2005); M. A. Chávez-Rojo and M. Medina-Noyola, Phys. Rev. E76, 039902 (2007)]. We illustrate its application with a description of dynamic arrest in two simple model colloidal mixtures: namely, hard-sphere and repulsive Yukawa binary mixtures. Our results include observation of the two patterns of dynamic arrest, one in which both species become simultaneously arrested and the other involving the sequential arrest of the two species. The latter case gives rise to mixed states in which one species is arrested while the other species remains mobile. We also derive the (”bifurcation” or fixed-point”) equations for the nonergodic parameters of the system, which takes the surprisingly simple form of a system of coupled equations for the localization length of the particles of each species. The solution of this system of equations indicates unambiguously which species is arrested (finite localization length) and which species remains ergodic (infinite localization length). As a result, we are able to draw the entire ergodic-nonergodic phase diagram of the binary hard-sphere mixture.

  20. Light-activated self-propelled colloids

    PubMed Central

    Palacci, J.; Sacanna, S.; Kim, S.-H.; Yi, G.-R.; Pine, D. J.; Chaikin, P. M.

    2014-01-01

    Light-activated self-propelled colloids are synthesized and their active motion is studied using optical microscopy. We propose a versatile route using different photoactive materials, and demonstrate a multiwavelength activation and propulsion. Thanks to the photoelectrochemical properties of two semiconductor materials (α-Fe2O3 and TiO2), a light with an energy higher than the bandgap triggers the reaction of decomposition of hydrogen peroxide and produces a chemical cloud around the particle. It induces a phoretic attraction with neighbouring colloids as well as an osmotic self-propulsion of the particle on the substrate. We use these mechanisms to form colloidal cargos as well as self-propelled particles where the light-activated component is embedded into a dielectric sphere. The particles are self-propelled along a direction otherwise randomized by thermal fluctuations, and exhibit a persistent random walk. For sufficient surface density, the particles spontaneously form ‘living crystals’ which are mobile, break apart and reform. Steering the particle with an external magnetic field, we show that the formation of the dense phase results from the collisions heads-on of the particles. This effect is intrinsically non-equilibrium and a novel principle of organization for systems without detailed balance. Engineering families of particles self-propelled by different wavelength demonstrate a good understanding of both the physics and the chemistry behind the system and points to a general route for designing new families of self-propelled particles. PMID:25332383

  1. Colloidal particle deposition in turbulent flow

    NASA Astrophysics Data System (ADS)

    Morton, D. S.

    1994-05-01

    A theoretical analysis is presented which describes the initial deposition of monodispersed spherical colloidal particles from a steady fully developed turbulent flow onto conduit walls. When the net particle-conduit electrical interaction potential is attractive, particle deposition is shown to be often governed by turbulent hydrodynamics. When the net particle-conduit electrical interaction potential possess a repulsive maximum, particle deposition to first order is uniform and depends solely on electrical interaction effects. The developed theoretical model specialized to orifice deposition with the use of Harwell Flow 3D turbulence modelling software qualitatively described the deposition of 0.5 (mu)m silica particles onto glass orifices from an aqueous suspension. The effect of the electrical double layer on the rate of colloidal particle deposition in laminar flow has been described by Spielman and Friedlander, Dahneke, Bowen et al. and Bowen and Epstein. This article describes the extension of their work to colloidal particle deposition under steady fully developed turbulent flow conditions. This article also reports the results of orifice particle deposition experiments which were conducted to qualitatively investigate the developed theoretical model.

  2. Remotely Controlled Mixers for Light Microscopy Module (LMM) Colloid Samples

    NASA Technical Reports Server (NTRS)

    Kurk, Michael A. (Andy)

    2015-01-01

    Developed by NASA Glenn Research Center, the LMM aboard the International Space Station (ISS) is enabling multiple biomedical science experiments. Techshot, Inc., has developed a series of colloid specialty cell systems (C-SPECS) for use in the colloid science experiment module on the LMM. These low-volume mixing devices will enable uniform particle density and remotely controlled repetition of LMM colloid experiments. By automating the experiment process, C-SPECS allow colloid samples to be processed more quickly. In addition, C-SPECS will minimize the time the crew will need to spend on colloid experiments as well as eliminate the need for multiple and costly colloid samples, which are expended after a single examination. This high-throughput capability will lead to more efficient and productive use of the LMM. As commercial launch vehicles begin routine visits to the ISS, C-SPECS could become a significant means to process larger quantities of high-value materials for commercial customers.

  3. Design and elaboration of colloidal molecules: an overview.

    PubMed

    Duguet, Etienne; Désert, Anthony; Perro, Adeline; Ravaine, Serge

    2011-02-01

    The concept of colloidal molecules was first evoked by van Blaaderen in 2003 for describing small non-spherical colloids made of the aggregation of a small number of particles. He predicted original properties to the complex assemblies of such colloids, in particular in optics. This critical review deals with the different strategies reported for creating robust clusters of spherical particles which could mimic the space-filling models of simple conventional molecules. These routes concern either the controlled clustering of preformed colloids directed by coalescence, physical routes, chemical routes, or 2-D/3-D geometrical confinement, or strategies starting from a single colloid which is decorated by satellite colloids by taking advantage of controlled phase separation or nucleation and growth phenomena. These routes are compared from the viewpoint of the accessible shapes, their tunability and scalability (146 references). PMID:21212874

  4. Spatially and temporally reconfigurable assembly of colloidal crystals

    NASA Astrophysics Data System (ADS)

    Kim, Youngri; Shah, Aayush A.; Solomon, Michael J.

    2014-04-01

    The self-assembly of colloidal crystals is important to the production of materials with functional optical, mechanical and conductive properties. Yet, self-assembly methods are limited by their slow kinetics and lack of structural control in space and time. Refinements such as templating and directed assembly partially address the problem, albeit by introducing fixed surface features such as templates or electrodes. A template-free method to reconfigure colloidal crystals simultaneously in three-dimensional space and time would better align work in colloidal assembly with materials applications. Here, we report a photo-induced assembly method that yields regions either filled with colloidal crystals or completely devoid of colloids. The origin of the effect is found to be electrophoresis of colloids generated by photochemistry at an indium tin oxide-coated substrate. Simple optical manipulations are applied to reconfigure these assembly and depletion regions. Thus, the method represents a new kind of template-free, reconfigurable three-dimensional photolithography.

  5. A colloidal singularity reveals the crucial role of colloidal stability for nanomaterials in-vitro toxicity testing: nZVI-microalgae colloidal system as a case study.

    PubMed

    Gonzalo, Soledad; Llaneza, Veronica; Pulido-Reyes, Gerardo; Fernández-Piñas, Francisca; Bonzongo, Jean Claude; Leganes, Francisco; Rosal, Roberto; García-Calvo, Eloy; Rodea-Palomares, Ismael

    2014-01-01

    Aggregation raises attention in Nanotoxicology due to its methodological implications. Aggregation is a physical symptom of a more general physicochemical condition of colloidal particles, namely, colloidal stability. Colloidal stability is a global indicator of the tendency of a system to reduce its net surface energy, which may be achieved by homo-aggregation or hetero-aggregation, including location at bio-interfaces. However, the role of colloidal stability as a driver of ENM bioactivity has received little consideration thus far. In the present work, which focuses on the toxicity of nanoscaled Fe° nanoparticles (nZVI) towards a model microalga, we demonstrate that colloidal stability is a fundamental driver of ENM bioactivity, comprehensively accounting for otherwise inexplicable differential biological effects. The present work throws light on basic aspects of Nanotoxicology, and reveals a key factor which may reconcile contradictory results on the influence of aggregation in bioactivity of ENMs. PMID:25340509

  6. A Colloidal Singularity Reveals the Crucial Role of Colloidal Stability for Nanomaterials In-Vitro Toxicity Testing: nZVI-Microalgae Colloidal System as a Case Study

    PubMed Central

    Fernández-Piñas, Francisca; Bonzongo, Jean Claude; Leganes, Francisco; Rosal, Roberto; García-Calvo, Eloy; Rodea-Palomares, Ismael

    2014-01-01

    Aggregation raises attention in Nanotoxicology due to its methodological implications. Aggregation is a physical symptom of a more general physicochemical condition of colloidal particles, namely, colloidal stability. Colloidal stability is a global indicator of the tendency of a system to reduce its net surface energy, which may be achieved by homo-aggregation or hetero-aggregation, including location at bio-interfaces. However, the role of colloidal stability as a driver of ENM bioactivity has received little consideration thus far. In the present work, which focuses on the toxicity of nanoscaled Fe° nanoparticles (nZVI) towards a model microalga, we demonstrate that colloidal stability is a fundamental driver of ENM bioactivity, comprehensively accounting for otherwise inexplicable differential biological effects. The present work throws light on basic aspects of Nanotoxicology, and reveals a key factor which may reconcile contradictory results on the influence of aggregation in bioactivity of ENMs. PMID:25340509

  7. Multiarm Star Polymers as Model Soft Colloids

    NASA Astrophysics Data System (ADS)

    Vlassopoulos, Dimitris

    2010-03-01

    Over the last decade, star polymers emerged as a useful model colloids that interpolate between polymers and hard sphere colloids. Together with microgels, they represent two benchmark soft colloidal systems, their internal structure being the key difference. Indeed, in the case of stars with open structure, the arms can interpenetrate in dense suspensions. The latter feature, that can be probed experimentally, is responsible for a number of interesting structural and dynamic properties of star polymers that set them apart from microgels. In this talk we present the basic properties of star polymers and focus on their extraordinary behavior in the highly concentrated regime, which is typically glassy. Our rheological and scattering experiments demonstrate unique features of the star glasses. Here we discuss two major ones: (i) Aging after pre-shear (the so-called rejuvenation) proceeds via a two-step process, associated with a fast arm engagement and a slow cooperative (cage) rearrangement. Remarkably, at extremely long times a steady state is observed and the terminal time in these systems can be experimentally accessible (and hence tailored at molecular level), as a consequence of the arms fluctuations. (ii) Multiple glassy states can be obtained when mixing stars with polymers or with other stars. Simultaneous theoretical and simulations work suggests that the softness is at the core of this unexpected behavior where depletion gives rise to glass melting and eventually re-entrant glasses are formed. Construction of a state diagram suggests kinetic pathways for tailoring the flow of soft colloids. These examples outline the importance of particle architecture on colloidal properties. Stars are a representative of a large class of hairy particles. The parallel important developments in mode coupling theory and its verses provide much needed predictive tools and rationalization for a number of phenomena such as those discussed here, as well as the complex

  8. Electric field mediated colloidal assembly and control

    NASA Astrophysics Data System (ADS)

    Juarez, Jaime Javier

    2011-12-01

    This dissertation presents video microscopy measurements and computer simulations of colloidal particle interactions in inhomogeneous, high-frequency AC electric fields. The interactions of particles with each other and inhomogeneous electric fields are quantified as a function of concentration, field amplitude, and frequency. Visual state diagrams show that these interactions in concentrated systems produce quasi-two dimensional microstructures including confined hard disk fluids, oriented dipolar chains, and oriented hexagonal close packed crystals. The interaction of a particle interacting with an electric field is directly measured with analyses of a single diffusing colloid within electric fields in the absence of many body effects. Concentrated systems are characterized in terms of density profiles across the electrode gap and angular pair distribution functions. An inverse Monte Carlo analysis extracted the induced dipole-induced dipole interaction from concentrated measurements. A single adjustable parameter consistently modified the induced dipole-field potential and the induced dipole-induced dipole potential to account for modification of the local electric field as the result of the local particle concentration, frequency and configuration. Confocal laser scanning microscopy (CLSM) perform sensitive measurements of internal three dimensional structure of crystals assembled in an interfacial quadrupole electrode device. Radial distributions as functions of elevation are used to characterize the equilibrium structure. A single adjustable parameter modified known potentials to match Monte Carlo simulations with experiment. The local density from experiment and simulation matched the expected density calculated from a balance of osmotic pressure and dielectrophoretic compression. Simulations qualitatively matched experimental observations of microstructure as a function of field amplitude. Programmable assembly for colloidal crystals is implemented in the

  9. Colloidal Particles at Fluid Interfaces and the Interface of Colloidal Fluids

    NASA Astrophysics Data System (ADS)

    McGorty, Ryan

    Holographic microscopy is a unifying theme in the different projects discussed in this thesis. The technique allows one to observe microscopic objects, like colloids and droplets, in a three-dimensional (3D) volume. Unlike scanning 3D optical techniques, holography captures a sample's 3D information in a single image: the hologram. Therefore, one can capture 3D information at video frame rates. The price for such speed is paid in computation time. The 3D information must be extracted from the image by methods such as reconstruction or fitting the hologram to scattering calculations. Using holography, we observe a single colloidal particle approach, penetrate and then slowly equilibrate at an oil--water interface. Because the particle moves along the optical axis (z-axis) and perpendicular to the interface holography is used to determine its position. We are able to locate the particle's z-position to within a few nanometers with a time resolution below a millisecond. We find that the capillary force pulling the particle into the interface is not balanced by a hydrodynamic force. Rather, a larger-than-viscous dissipation associated with the three-phase contact-line slipping over the particle's surface results in equilibration on time scales orders of magnitude longer than the minute time scales over which our setup allows us to examine. A separate project discussed here also examines colloidal particles and fluid-fluid interfaces. But the fluids involved are composed of colloids. With a colloid and polymer water-based mixture we study the phase separation of the colloid-rich (or liquid) and colloid-poor (or gas) region. In comparison to the oil--water interface in the previously mentioned project, the interface between the colloidal liquid and gas phases has a surface tension nearly six orders of magnitude smaller. So interfacial fluctuations are observable under microscopy. We also use holographic microscopy to study this system but not to track particles with

  10. Internal Dynamics of Equilibrium Colloidal Clusters

    NASA Astrophysics Data System (ADS)

    Perry, Rebecca Wood

    Colloidal clusters, aggregates of a few micrometer-sized spherical particles, are a model experimental system for understanding the physics of self-assembly and processes such as nucleation. Colloidal clusters are well suited for studies on these topics because they are the simplest colloidal system with internal degrees of freedom. Clusters made from particles that weakly attract one another continually rearrange between different structures. By characterizing these internal dynamics and the structures connected by the rearrangement pathways, we seek to understand the statistical physics underlying self-assembly and equilibration. In this thesis, we examine the rearrangement dynamics of colloidal clusters and analyze the equilibrium distributions of ground and excited states. We prepare clusters of up to ten microspheres bound by short-range depletion interactions that are tuned to allow equilibration between multiple isostatic arrangements. To study these clusters, we use bright-field and digital holographic microscopy paired with computational post-processing to amass ensemble-averaged and time-averaged probabilities. We study both two-dimensional (2D) and three-dimensional (3D) clusters composed of either one or two species of particles. To learn about geometrical nucleation barriers, we track rearrangements of particles within freely rotating and translating 3D clusters. We show that rearrangements occur on a timescale of seconds, consistent with diffusion-dominated internal dynamics. To better understand excited states and transition pathways, we track hundreds of rearrangements between degenerate ground states in 2D clusters. We show that the rearrangement rates can be understood using a model with two parameters, which account for the diffusion coefficient along the excited-state rearrangement pathways and the interaction potential. To explore new methods to control self-assembly, we analyze clusters of two species with different masses and different

  11. Oppositely charged colloids out of equilibrium

    NASA Astrophysics Data System (ADS)

    Vissers, T.

    2010-11-01

    Colloids are particles with a size in the range of a few nanometers up to several micrometers. Similar to atomic and molecular systems, they can form gases, liquids, solids, gels and glasses. Colloids can be used as model systems because, unlike molecules, they are sufficiently large to be studied directly with light microscopy and move sufficiently slow to study their dynamics. In this thesis, we study binary systems of polymethylmethacrylate (PMMA) colloidal particles suspended in low-polar solvent mixtures. Since the ions can still partially dissociate, a surface charge builds up which causes electrostatic interactions between the colloids. By carefully tuning the conditions inside the suspension, we make two kinds of particles oppositely charged. To study our samples, we use Confocal Laser Scanning Microscopy (CLSM). The positively and negatively charged particles can be distinguished by a different fluorescent dye. Colloids constantly experience a random motion resulting from random kicks of surrounding solvent molecules. When the attractions between the oppositely charged particles are weak, the particles can attach and detach many times and explore a lot of possible configurations and the system can reach thermodynamic equilibrium. For example, colloidal ‘ionic’ crystals consisting of thousands to millions of particles can form under the right conditions. When the attractions are strong, the system can become kinetically trapped inside a gel-like state. We observe that when the interactions change again, crystals can even emerge again from this gel-like phase. By using local order parameters, we quantitatively study the crystallization of colloidal particles and identify growth defects inside the crystals. We also study the effect of gravity on the growth of ionic crystals by using a rotating stage. We find that sedimentation can completely inhibit crystal growth and plays an important role in crystallization from the gel-like state. The surface

  12. Study of the stability coated and uncoated nanosilver colloid

    NASA Astrophysics Data System (ADS)

    Harsojo, Respitaningrum, Afrianto, Toto; Sosiati, Harini

    2013-09-01

    The stability of nanosilver colloids made using electrochemical process and chemical process were investigated. In the process using a DC generator cell, two silver electrodes under a DC voltage were used to generate the colloid. In the chemical process the colloid was made using the dilution of AgNO3 in deionized water with the addition of sodium citrate. To increase the stability to this colloid was added polyvinyl alcohol. The stability In those three colloids were investigated using UV-Vis spectrometer. The size of the nano Ag was measured using transmission electron microscope (TEM). The study reveals that within period of two weeks the trend toward a stable colloid is shown by colloid using DC generator. The addition of PVA may stabilize the unstable colloid made using the chemichal process and reduce the size particle to significantly smaller particle compared to the one made using DC generator cell. The condition of obtaining the stable nano colloid silver with smaller particle size was discussed.

  13. Colloid mobilization by fluid displacement fronts in channels.

    PubMed

    Lazouskaya, Volha; Wang, Lian-Ping; Or, Dani; Wang, Gang; Caplan, Jeffrey L; Jin, Yan

    2013-09-15

    Understanding colloid mobilization during transient flow in soil is important for addressing colloid and contaminant transport issues. While theoretical descriptions of colloid detachment exist for saturated systems, corresponding mechanisms of colloid mobilization during drainage and imbibition have not been considered in detail. In this work, theoretical force and torque analyses were performed to examine the interactive effects of adhesion, drag, friction, and surface tension forces on colloid mobilization and to outline conditions corresponding to the mobilization mechanisms such as lifting, sliding, and rolling. Colloid and substrate contact angles were used as variables to determine theoretical criteria for colloid mobilization mechanisms during drainage and imbibition. Experimental mobilization of hydrophilic and hydrophobic microspheres with drainage and imbibition fronts was investigated in hydrophilic and hydrophobic channels using a confocal microscope. Colloid mobilization differed between drainage and imbibition due to different dynamic contact angles and interfacial geometries on the contact line. Experimental results did not fully follow the theoretical criteria in all cases, which was explained with additional factors not included in the theory such as presence of aggregates and trailing films. Theoretical force and torque analyses resulted in similar mobilization predictions and suggested that all mobilization mechanisms contributed to the observed colloid mobilization. PMID:23800372

  14. Statics and dynamics of colloidal particles on optical tray arrays

    SciTech Connect

    Reichardt, Charles; Reichhardt, Cynthia J

    2009-01-01

    We examine the statics and dynamics of charged colloids interacting with periodic optical trap arrays. In particular we study the regime where more than one colloid is confined in each trap, creating effective dimer, trimer, and higher order states called colloidal molecular crystals. The n-mer states have all effective orientational degree of freedom which can be controlled with an external driving field. In general, the external field causes a polarization effect where the orientation of the n-mers aligns with the external field, similar to liquid crystal systems. Additionally, under a rotating external drive the n-mers can rotate with the drive. In some cases a series of structural transitions in the colloidal crystal states occur in the rotating field due to a competition between the ordering of the colloidal molecular crystals and the polarization effect which orients the n-mers in the direction of the drive. We also show that for some parameters, the n-mers continuously rotate with the drive without witching, that depinning transitions can occur where the colloids jump from well to well, and that there are a number of distinct dynamical transitions between the phases. Finally, we illustrate colloidal orderings at fillings of more than four colloids per trap, indicating that it is possible to create higher order colloidal crystal cluster phases.

  15. Sodium meta-autunite colloids: Synthesis, characterization,stability

    SciTech Connect

    zzuoping@lbl.gov

    2004-04-10

    Waste forms of U such as those in the United States Department of Energy's Hanford Site often contain high concentrations of Na and P. Low solubility sodium uranyl phosphates such as sodium meta-autunite have the potential to form mobile colloids that can facilitate transport of this radionuclide. In order to understand the geochemical behavior of uranyl phosphate colloids, we synthesized sodiummeta-autunite colloids, and characterized their morphology, chemical composition, structure, dehydration, and surface charge. The stability of these synthetic plate-shaped colloids was tested with respect to time and pH. The highest aggregation rate was observed at pH 3, and the rate decreases as pH increases, indicating that higher stability of colloid dispersion under neutral and alkaline pH conditions. The synthetic colloids are all negatively charged and no isoelectric points were found over a pH range of 3 to 9. The zeta-potentials of the colloids in the phosphate solution show a strong pH-dependence in the more acidic range over time, but are relatively constant in the neutral and alkaline pH range. The geochemical behavior of the synthetic colloids can be interpreted using DLVO theory. The results suggest that formation of mobile sodium meta-autunite colloids can enhance the transport of U in some contaminated sediments.

  16. Tuning Colloid-Interface Interactions by Salt Partitioning.

    PubMed

    Everts, J C; Samin, S; van Roij, R

    2016-08-26

    We show that the interaction of an oil-dispersed colloidal particle with an oil-water interface is highly tunable from attractive to repulsive, either by varying the sign of the colloidal charge via charge regulation or by varying the difference in hydrophilicity between the dissolved cations and anions. In addition, we investigate the yet unexplored interplay between the self-regulated colloidal surface charge distribution with the planar double layer across the oil-water interface and the spherical one around the colloid. Our findings explain recent experiments and have direct relevance for tunable Pickering emulsions. PMID:27610887

  17. Analysis of colloidal phases in urban stormwater runoff

    SciTech Connect

    Grout, H.; Wiesner, M.R.; Bottero, J.Y.

    1999-03-15

    The composition and morphology of colloidal materials entering an urban waterway (Brays Bayou, Houston, USA) during a storm event was investigated. Analyses of organic carbon, Si, Al, Fe, Cr, Cu, Mn, Zn, Ca, Mg, and Ba were performed on the fraction of materials passing through a 0.45 {micro}m filter. This fraction, traditionally defined as dissolved, was further fractionated by ultracentrifugation into colloidal and dissolved fractions. Colloids, operationally defined by this procedure, accounted for 17% of the carbon, 32% of the silica, 79% of the Al, 85% of the Fe, 52% of the Cr, 43% of the Mn, and 29% of the Zn present in filtrates when averaged over the storm event. However, the composition of colloidal material was observed to change over time. For example, colloids were predominantly composed of silica during periods of dry weather flow and at the maximum of the stormwater flow, while carbon dominated the colloidal fraction at the beginning and declining stages of the storm event. These changes in colloidal composition were accompanied by changes in colloidal morphologies, varying from organic aggregates to diffuse gel-like structures rich in Si, Al, and Fe. The colloidal phase largely determined the variability of elements in the 0.45 {micro}m filtrate.

  18. Zero-valent iron colloid emplacement in sand columns

    SciTech Connect

    Cantrell, K.J.; Kaplan, D.I.

    1997-05-01

    Application of chemically reactive barriers to mitigate contaminant migration is an active area of research and development. Studies were conducted to evaluate a novel approach of emplacing chemically reactive barriers composed of zero-valent iron (Fe{sup 0}) by injecting suspensions of colloidal-size Fe{sup 0} particles into porous media. The specific objective of this study was to evaluate the effect of influent colloid concentration, rate, and volume of colloidal suspensions on Fe{sup 0} colloid emplacement in sand columns. Relatively even distributions of Fe{sup 0} throughout a sand column were obtained at low influent colloid concentrations and high injection rates. As the concentration of influent suspensions was increased, a point was reached beyond which a significant increase in the filtration of Fe{sup 0} particles near the front of the column was observed. This point was also found to occur at lower influent colloid concentrations as the injection rate was decreased, i.e., there was an interactive effect of influent colloid concentration and injection rate on the extent of filtration that occurred near the front of the column. As the volume of the colloidal suspension injected into the column was increased, the distribution of Fe{sup 0} colloids within the column became increasingly even.

  19. Three-dimensional colloidal crystals in liquid crystalline blue phases

    PubMed Central

    Ravnik, Miha; Alexander, Gareth P.; Yeomans, Julia M.; Žumer, Slobodan

    2011-01-01

    Applications for photonic crystals and metamaterials put stringent requirements on the characteristics of advanced optical materials, demanding tunability, high Q factors, applicability in visible range, and large-scale self-assembly. Exploiting the interplay between structural and optical properties, colloidal lattices embedded in liquid crystals (LCs) are promising candidates for such materials. Recently, stable two-dimensional colloidal configurations were demonstrated in nematic LCs. However, the question as to whether stable 3D colloidal structures can exist in an LC had remained unanswered. We show, by means of computer modeling, that colloidal particles can self-assemble into stable, 3D, periodic structures in blue phase LCs. The assembly is based on blue phases providing a 3D template of trapping sites for colloidal particles. The particle configuration is determined by the orientational order of the LC molecules: Specifically, face-centered cubic colloidal crystals form in type-I blue phases, whereas body-centered crystals form in type-II blue phases. For typical particle diameters (approximately 100 nm) the effective binding energy can reach up to a few 100 kBT, implying robustness against mechanical stress and temperature fluctuations. Moreover, the colloidal particles substantially increase the thermal stability range of the blue phases, for a factor of two and more. The LC-supported colloidal structure is one or two orders of magnitude stronger bound than, e.g., water-based colloidal crystals. PMID:21368186

  20. Electrochromism with colloidal WO3 and IrO2

    NASA Astrophysics Data System (ADS)

    Michalak, Franck; Rault, L.; Aldebert, Pierre

    1992-11-01

    Colloidal particles of WO3 and IrO2 are synthesized and dispersed within a gelatinous perfluorinated ionomer matrix. Experimental procedures are established in order to obtain percolation between the electrochromic particles. Colloidal particle sizes are measured by quasi elastic light scattering. Electrochemical properties of the mixed colloid electrodes are determined by cyclic voltammetry and impedance spectroscopy. Preliminary optical tests are performed in order to measure transmission and contrast of electrochromic half cells with a mixed colloid electrode, and also a sputtered oxide electrode.

  1. Infrared colloidal lead chalcogenide nanocrystals: synthesis, properties, and photovoltaic applications.

    PubMed

    Fu, Huiying; Tsang, Sai-Wing

    2012-04-01

    Simple solution phase, catalyst-free synthetic approaches that offer monodispersed, well passivated, and non-aggregated colloidal semiconductor nanocrystals have presented many research opportunities not only for fundamental science but also for technological applications. The ability to tune the electrical and optical properties of semiconductor nanocrystals by manipulating the size and shape of the crystals during the colloidal synthesis provides potential benefits to a variety of applications including photovoltaic devices, light-emitting diodes, field effect transistors, biological imaging/labeling, and more. Recent advances in the synthesis and characterization of colloidal lead chalcogenide nanocrystals and the achievements in colloidal PbS or PbSe nanocrystals solar cells have demonstrated the promising application of infrared-emitting colloidal lead chalcogenide nanocrystals in photovoltaic devices. Here, we review recent progress in the synthesis and optical properties of colloidal lead chalcogenide nanocrystals. We focus in particular upon the size- and shape-controlled synthesis of PbS, PbSe, and PbTe nanocrystals by using different precursors and various stabilizing surfactants for the growth of the colloidal nanocrystals. We also summarize recent advancements in the field of colloidal nanocrystals solar cells based on colloidal PbS and PbSe nanocrystals. PMID:22382898

  2. Colloid formation and laser-induced bleaching in fluorite

    SciTech Connect

    LeBret, Joel B.; Cramer, Loren P.; Norton, M. Grant; Dickinson, J. T.

    2004-11-08

    Colloid formation and subsequent laser-induced bleaching in fluorite has been studied by transmission electron microscopy and electron diffraction. At high incident electron-beam (e-beam) energies, Ca colloids with diameter {approx}10 nm form a simple cubic superlattice with lattice parameter a{approx}18 nm. The colloids themselves are topotactic with the fluorite matrix forming low-energy interfaces close to a {sigma}=21 special grain boundary in cubic materials. Laser irradiation using {lambda}=532 nm has been shown to effectively bleach the e-beam-irradiated samples returning the fluorite to its monocrystalline state. The bleached samples appear more resistant to further colloid formation.

  3. Fabrication and characterization of colloidal crystal thin films

    NASA Astrophysics Data System (ADS)

    Rodríguez, I.; Ramiro-Manzano, F.; Meseguer, F.; Bonet, E.

    2011-03-01

    We present a laboratory experiment that allows undergraduate or graduate students to get introduced to colloidal crystal research concepts in an interesting way. Moreover, such experiments and studies can also be useful in the field of crystallography or solid-state physics. The work concerns the growth of colloidal crystal thin films obtained from the crystallization of a latex colloidal solution in a wedge cell. Depending on the thickness of the sample, microcrystals with different structures and orientation are obtained. Colloidal arrangements are studied by scanning electronic microscopy images of the top and edge views of several areas of the crystals.

  4. Switching light with light - advanced functional colloidal monolayers

    NASA Astrophysics Data System (ADS)

    Bley, K.; Sinatra, N.; Vogel, N.; Landfester, K.; Weiss, C. K.

    2013-12-01

    Colloidal monolayers comprising of highly ordered two dimensional crystals are of high interest to generate surface patterns for a variety of different applications. Mostly, unfunctionalized polymer or silica colloids are assembled into monolayers. However, the incorporation of functional molecules into such colloids offers a convenient possibility of implementing additional properties to the two-dimensional crystal. Here, we present the formation of novel functional colloidal monolayers with photoswitchable fluorescence. The miniemulsion polymerization technique was used to incorporate an appropriate dye system of a perylene-based fluorophore and a bis-arylethene as a photochrome in polymeric colloids in defined ratios. Upon irradiation with UV or visible light the photochrome reversibly isomerizes from the ring-closed form, which is able to absorb light of the emission wavelength of the fluorescent dye and the ring-open form, which is not. The fluorescence emission of the dye can thus be reversibly switched on and off with light even when embedded in colloids. The colloids were self-assembled at the air-water interface to produce hexagonally ordered functional monolayers and more complex binary crystals. We investigate in detail the influence of the polymeric matrix on the switching properties of the fluorophore/photochrome system and find that the rate constants for the photoswitching, which all lie in the same range, are less influenced by the polymeric environment than expected. We demonstrate the reversible switching of the fluorescence emission in self-assembled colloidal monolayers. The arrangement of broadly distributed functional colloids into ordered monolayers with high addressability was obtained by the formation of binary colloidal monolayers.Colloidal monolayers comprising of highly ordered two dimensional crystals are of high interest to generate surface patterns for a variety of different applications. Mostly, unfunctionalized polymer or silica

  5. Les etoiles qui ne veulent pas vieillir

    NASA Astrophysics Data System (ADS)

    Bonnet-Bidaud, J. M.

    1995-12-01

    Qu'est-ce qui fait courir Jean-Claude Pecker ? Ses travaux sur les atmospheres stellaires qu'il poursuit aujourd'hui ? Son combat pour les droits de l'homme, ou contre le sceau du secret qui pese encore sur la recherche fondamentale ? Tout a la fois. Pour cette figure emblematique de l'astrophysique francaise, aujourd'hui a la retraite, pas question de raccrocher les armes...

  6. Switching light with light - advanced functional colloidal monolayers

    NASA Astrophysics Data System (ADS)

    Bley, K.; Sinatra, N.; Vogel, N.; Landfester, K.; Weiss, C. K.

    2013-12-01

    Colloidal monolayers comprising of highly ordered two dimensional crystals are of high interest to generate surface patterns for a variety of different applications. Mostly, unfunctionalized polymer or silica colloids are assembled into monolayers. However, the incorporation of functional molecules into such colloids offers a convenient possibility of implementing additional properties to the two-dimensional crystal. Here, we present the formation of novel functional colloidal monolayers with photoswitchable fluorescence. The miniemulsion polymerization technique was used to incorporate an appropriate dye system of a perylene-based fluorophore and a bis-arylethene as a photochrome in polymeric colloids in defined ratios. Upon irradiation with UV or visible light the photochrome reversibly isomerizes from the ring-closed form, which is able to absorb light of the emission wavelength of the fluorescent dye and the ring-open form, which is not. The fluorescence emission of the dye can thus be reversibly switched on and off with light even when embedded in colloids. The colloids were self-assembled at the air-water interface to produce hexagonally ordered functional monolayers and more complex binary crystals. We investigate in detail the influence of the polymeric matrix on the switching properties of the fluorophore/photochrome system and find that the rate constants for the photoswitching, which all lie in the same range, are less influenced by the polymeric environment than expected. We demonstrate the reversible switching of the fluorescence emission in self-assembled colloidal monolayers. The arrangement of broadly distributed functional colloids into ordered monolayers with high addressability was obtained by the formation of binary colloidal monolayers.Colloidal monolayers comprising of highly ordered two dimensional crystals are of high interest to generate surface patterns for a variety of different applications. Mostly, unfunctionalized polymer or silica

  7. Fast microbial reduction of ferrihydrite colloids from a soil effluent

    NASA Astrophysics Data System (ADS)

    Fritzsche, Andreas; Bosch, Julian; Rennert, Thilo; Heister, Katja; Braunschweig, Juliane; Meckenstock, Rainer U.; Totsche, Kai U.

    2012-01-01

    Recent studies on the microbial reduction of synthetic iron oxide colloids showed their superior electron accepting property in comparison to bulk iron oxides. However, natural colloidal iron oxides differ in composition from their synthetic counterparts. Besides a potential effect of colloid size, microbial iron reduction may be accelerated by electron-shuttling dissolved organic matter (DOM) as well as slowed down by inhibitors such as arsenic. We examined the microbial reduction of OM- and arsenic-containing ferrihydrite colloids. Four effluent fractions were collected from a soil column experiment run under water-saturated conditions. Ferrihydrite colloids precipitated from the soil effluent and exhibited stable hydrodynamic diameters ranging from 281 (±146) nm in the effluent fraction that was collected first and 100 (±43) nm in a subsequently obtained effluent fraction. Aliquots of these oxic effluent fractions were added to anoxic low salt medium containing diluted suspensions of Geobacter sulfurreducens. Independent of the initial colloid size, the soil effluent ferrihydrite colloids were quickly and completely reduced. The rates of Fe2+ formation ranged between 1.9 and 3.3 fmol h-1 cell-1, and are in the range of or slightly exceeding previously reported rates of synthetic ferrihydrite colloids (1.3 fmol h-1 cell-1), but greatly exceeding previously known rates of macroaggregate-ferrihydrite reduction (0.07 fmol h-1 cell-1). The inhibition of microbial Fe(III) reduction by arsenic is unlikely or overridden by the concurrent enhancement induced by soil effluent DOM. These organic species may have increased the already high intrinsic reducibility of colloidal ferrihydrite owing to quinone-mediated electron shuttling. Additionally, OM, which is structurally associated with the soil effluent ferrihydrite colloids, may also contribute to the higher reactivity due to increasing solubility and specific surface area of ferrihydrite. In conclusion, ferrihydrite

  8. Physics of Colloids in Space (PCS): Microgravity Experiment Completed Operations on the International Space Station

    NASA Technical Reports Server (NTRS)

    Doherty, Michael P.; Sankaran, Subramanian

    2003-01-01

    Immediately after mixing, the two-phase-like colloid-polymer critical point sample begins to phase separate, or de-mix, into two phases-one that resembles a gas and one that resembles a liquid, except that the particles are colloids and not atoms. The colloid-poor black regions (colloidal gas) grow bigger, and the colloid-rich white regions (colloidal liquid) become whiter as the domains further coarsen. Finally, complete phase separation is achieved, that is, just one region of each colloid-rich (white) and colloid-poor (black) phase. This process was studied over four decades of length scale, from 1 micrometer to 1 centimeter.

  9. DNA hybridization and ligation for directed colloidal assembly

    NASA Astrophysics Data System (ADS)

    Shyr, Margaret

    Colloidal assembly using DNA hybridization has been pursued as a means assemble non-conventional ordered colloidal structures. However, to date it is undetermined whether DNA hybridization can be used to achieve non-FCC colloidal crystals. Using microcontact printing techniques, we have fabricated covalently bound single stranded DNA (ssDNA) two-dimensional arrays on glass surfaces, which were used to direct the assembly of complementary DNA functionalized polystyrene colloids. Two of the hallmarks of DNA hybridization, sequence specificity and thermal reversibility, were demonstrated. Due to the periodicity of these arrays, laser diffraction was used to directly monitor these structures during assembly. To demonstrate the versatility of the 2D colloidal array assembled via DNA hybridization, a catalytic DNA sequence or DNAzyme was incorporated into the colloidal array system. By tethering the enzymatic strand to the patterned glass surface and the substrate strand to polystyrene colloids, we showed that the DNAzyme could prevent the assembly of the arrays when the required Pb2+ cofactor was provided. Attempts to assemble the colloid arrays and disassemble via the Pb2+-DNAzyme induced cleavage were unsuccessful, likely due to the incomplete cleavage of the multitude of hybridized linkages between each colloid and the surface. Since DNA is not only capable of catalyzing reactions, but also capable of being reacted upon by a variety of biological enzymes, we examined the use of DNA ligase as a means to control the assembly of DNA-functionalized colloids. A three-sequence linker system was used for the hybridization mediated assembly of colloids: one sequence was tethered to the surface of the glass slide or colloids, one was tethered to another colloid surface, and the linker sequence hybridizes simultaneously to both tethered sequences. Once hybridized, the two tethered fragments can be ligated using DNA ligase, resulting in a continuous sequence tethered on one end

  10. Duration test of an annular colloid thruster.

    NASA Technical Reports Server (NTRS)

    Perel, J.; Mahoney, J. F.; Daley, H. L.

    1972-01-01

    An annular colloid thruster was continuously operated for 1023 hours. Performance was stable with no sparking and negligible drain currents observed. An average thrust of 25.1 micropounds and an average specific impulse of 1160 seconds were obtained at an accelerating voltage of 15 k he thruster exhaust beam was continuously neutralized using electrons and electrostatic vectoring was demonstrated periodically. The only clear trend with time was an increase in specific impulse during the last third of the test period. From these results the thruster lifetime was estimated to be over an order of magnitude greater than the test duration.

  11. Thermoelectricity and thermodiffusion in charged colloids

    NASA Astrophysics Data System (ADS)

    Huang, B. T.; Roger, M.; Bonetti, M.; Salez, T. J.; Wiertel-Gasquet, C.; Dubois, E.; Cabreira Gomes, R.; Demouchy, G.; Mériguet, G.; Peyre, V.; Kouyaté, M.; Filomeno, C. L.; Depeyrot, J.; Tourinho, F. A.; Perzynski, R.; Nakamae, S.

    2015-08-01

    The Seebeck and Soret coefficients of ionically stabilized suspension of maghemite nanoparticles in dimethyl sulfoxide are experimentally studied as a function of nanoparticle volume fraction. In the presence of a temperature gradient, the charged colloidal nanoparticles experience both thermal drift due to their interactions with the solvent and electric forces proportional to the internal thermoelectric field. The resulting thermodiffusion of nanoparticles is observed through forced Rayleigh scattering measurements, while the thermoelectric field is accessed through voltage measurements in a thermocell. Both techniques provide independent estimates of nanoparticle's entropy of transfer as high as 82 meV K-1. Such a property may be used to improve the thermoelectric coefficients in liquid thermocells.

  12. Colloidal solutions of organic conductive nanoparticles.

    PubMed

    de Caro, Dominique; Souque, Matthieu; Faulmann, Christophe; Coppel, Yannick; Valade, Lydie; Fraxedas, Jordi; Vendier, Olivier; Courtade, Frédéric

    2013-07-16

    Although molecular metals have been known for decades, their insolubility, low vapor pressure, and synthesis routes have prevented them from being integrated into electronic devices. We have prepared stable colloidal solutions of the organic metal TTF-TCNQ that overcome such difficulties. The solutions contain well-dispersed nanoparticles stabilized by long alkyl chain amines. They afford soluble powders by evaporation and homogeneous thin films by drop-casting. Powders and films show room temperature conductivities in the 0.01-0.1 S cm(-1) range. PMID:23772890

  13. Fractal-like structures in colloid science.

    PubMed

    Lazzari, S; Nicoud, L; Jaquet, B; Lattuada, M; Morbidelli, M

    2016-09-01

    The present work aims at reviewing our current understanding of fractal structures in the frame of colloid aggregation as well as the possibility they offer to produce novel structured materials. In particular, the existing techniques to measure and compute the fractal dimension df are critically discussed based on the cases of organic/inorganic particles and proteins. Then the aggregation conditions affecting df are thoroughly analyzed, pointing out the most recent literature findings and the limitations of our current understanding. Finally, the importance of the fractal dimension in applications is discussed along with possible directions for the production of new structured materials. PMID:27233526

  14. Crystalline Colloidal Arrays in Polymer Matrices

    NASA Technical Reports Server (NTRS)

    Sunkara, Hari B.; Penn, B. G.; Frazier, D. O.; Ramachandran, N.

    1997-01-01

    Crystalline Colloidal Arrays (CCA, also known as colloidal crystals), composed of aqueous or nonaqueous dispersions of self-assembled nanosized polymer colloidal spheres, are emerging toward the development of advanced optical devices for technological applications. The spontaneous self assembly of polymer spheres in a dielectric medium results from the electrostatic repulsive interaction between particles of uniform size and charge distribution. In a way similar to atomic crystals that diffract X-rays, CCA dispersions in thin quartz cells selectively and efficiently Bragg diffract the incident visible light. The reason for this diffraction is because the lattice (body or face centered cubic) spacing is on the order of the wavelength of visible light. Unlike the atomic crystals that diffract a fixed wavelength, colloidal crystals in principle, depending on the particle size, particle number and charge density, can diffract W, Vis or IR light. Therefore, the CCA dispersions can be used as laser filters. Besides, the diffraction intensity depends on the refractive index mismatch between polymer spheres and dielectric medium; therefore, it is possible to modulate incident light intensities by manipulating the index of either the spheres or the medium. Our interest in CCA is in the fabrication of all-optical devices such as optical switches, limiters, and spatial light modulators for optical signal processing. The two major requirements from a materials standpoint are the incorporation of suitable nonlinear optical materials (NLO) into polymer spheres which will allow us to alter the refractive index of the spheres by intense laser radiation, and preparation of solid CCA filters which can resist laser damage. The fabrication of solid composite filters not only has the advantage that the films are easier to handle, but also the arrays in solid films are more robust than in liquid media. In this paper, we report the photopolymerization process used to trap CCA in polymer

  15. Deterministic aggregation kinetics of superparamagnetic colloidal particles

    NASA Astrophysics Data System (ADS)

    Reynolds, Colin P.; Klop, Kira E.; Lavergne, François A.; Morrow, Sarah M.; Aarts, Dirk G. A. L.; Dullens, Roel P. A.

    2015-12-01

    We study the irreversible aggregation kinetics of superparamagnetic colloidal particles in two dimensions in the presence of an in-plane magnetic field at low packing fractions. Optical microscopy and image analysis techniques are used to follow the aggregation process and in particular study the packing fraction and field dependence of the mean cluster size. We compare these to the theoretically predicted scalings for diffusion limited and deterministic aggregation. It is shown that the aggregation kinetics for our experimental system is consistent with a deterministic mechanism, which thus shows that the contribution of diffusion is negligible.

  16. The promise of next generation colloids

    PubMed Central

    Creagh-Brown, Ben C; Evans, Timothy W

    2008-01-01

    The aim of perioperative haemodilution is to reduce loss of red blood cells during elective surgery. The oncotic and molecular characteristics of the various plasma substitutes employed determine how effectively normovolaemia is maintained, and their non-oncotic effects include alterations in microvascular perfusion. In the previous issue of Critical Care, Martini and colleagues assessed the effects of haemodilution with either polyethylene glycol (PEG)ylated albumin or a commercially available hydroxyethyl starch-based colloid in a hamster haemorrhage model. PEGylated albumin was superior to hydroxyethyl starch, as reflected by survival, haemodynamic parameters and assessment of the microcirculation using intravital microscopy. PMID:18492220

  17. Antibacterial Fluorinated Silica Colloid Superhydrophobic Surfaces

    PubMed Central

    Privett, Benjamin J.; Youn, Jonghae; Hong, Sung A; Lee, Jiyeon; Han, Junhee

    2011-01-01

    A superhydrophobic xerogel coating synthesized from a mixture of nanostructured fluorinated silica colloids, fluoroalkoxysilane, and a backbone silane is reported. The resulting fluorinated surface was characterized using contact angle goniometry, SEM, and AFM. Quantitative bacterial adhesion studies performed using a parallel plate flow cell demonstrated that the adhesion of Staphylococcus aureus and Pseudomonas aeruginosa were reduced by 2.08 ± 0.25 and 1.76 ± 0.12 log over controls, respectively. This simple superhydrophobic coating synthesis may be applied to any surface regardless of geometry and does not require harsh synthesis or processing conditions, making it an ideal candidate as a biopassivation strategy. PMID:21718023

  18. Colloidally deposited nanoparticle wires for biophysical detection

    NASA Astrophysics Data System (ADS)

    Shen, Sophie C.; Liu, Wen-Tao; Diao, Jia-Jie

    2015-12-01

    Among the techniques developed to prepare nanoparticle wires for multiple applications, the colloidal deposition method at interface has been regarded as cost-efficient and eco-friendly, and hence has attracted an increasing amount of research attention. In this report, the recent developments in preparing nanoparticle wires and integrated nanoparticle wire arrays using this technique have been reviewed. Furthermore, we have also discussed the application of these nanoparticle structures in detecting chemical and biological molecules. Project supported by the Fundamental Research Funds for the Central Universities through Xi’an Jiaotong University and the National Key Basic Research Program of China (Grant No. 2015CB856304).

  19. Lead removal with adsorbing colloid flotation

    SciTech Connect

    Thackston, E.L.; Wilson, D.J.; Hanson, J.S.; Miller, D.L. Jr.

    1980-02-01

    A process that removes lead from industrial waste by adsorbing colloid foam flotation has been designed and demonstrated. A system of ferric chloride and sodium lauryl sulfate, both relatively inexpensive chemicals, gave good performance with optimum dosages of sodium lauryl sulfate at 40 mg/l and trivalent iron at 150 mg/l. With optimum chemical and hydraulic conditions, the pilot plant was able to produce effluents with lead concentrations of less than 0.5 mg/l. The process may be especially attractive where space for heavy metals removal equipment is extremely limited.

  20. Stable monodisperse nanomagnetic colloidal suspensions: An overview.

    PubMed

    Ramimoghadam, Donya; Bagheri, Samira; Abd Hamid, Sharifah Bee

    2015-09-01

    Magnetic iron oxide nanoparticles (MNPs) have emerged as highly desirable nanomaterials in the context of many research works, due to their extensive industrial applications. However, they are prone to agglomerate on account of the anisotropic dipolar attraction, and therefore misled the particular properties related to single-domain magnetic nanostructures. The surface modification of MNPs is quite challenging for many applications, as it involves surfactant-coating for steric stability, or surface modifications that results in repulsive electrostatic force. Hereby, we focus on the dispersion of MNPs and colloidal stability. PMID:26073507

  1. Foam analogy in charged colloidal crystals.

    PubMed

    Kung, William; Ziherl, P; Kamien, Randall D

    2002-05-01

    We model charged colloidal suspensions using an analogy with foams. We study the solid-solid phase transitions of these systems as a function of particle volume fraction and ionic strength. The screened-Coulomb interaction is replaced by an interaction between walls of the Voronoi cells around each particle. We fit the surface charge to reproduce the phase diagram for the charged suspension studied by Sirota et al. [Phys. Rev. Lett. 62, 1524 (1989)]. With this fit parameter we are able to calculate the elastic moduli of the system and find good agreement with the available data. PMID:12059512

  2. Three-dimensional lock and key colloids.

    PubMed

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Yi, Gi-Ra; Sacanna, Stefano; Pine, David J; Weck, Marcus

    2014-05-14

    Colloids with well-defined multicavities are synthesized through the hydrolytic removal of silica cluster templates from organo-silica hybrid patchy particles. The geometry of the cavities stems from the originally assembled cluster templates, displaying well-defined three-dimensional symmetries, ranging from spherical, linear, triangular, tetrahedral, trigonal dipyramidal, octahedral, to pentagonal dipyramidal. The concave surface of the cavities is smooth, and the cavity shallowness and size can be varied. These particles with multicavities can act as "lock" particles with multiple "key holes". Up to n "key" particles can self-assemble into the lock particles via depletion interaction, resulting in multivalent, site-specific, reversible, and flexible bonding. PMID:24785203

  3. Steering trajectories in magnetically actuated colloidal propellers.

    PubMed

    Tierno, P; Sagués, F

    2012-08-01

    Microscale colloidal doublets composed of DNA-linked paramagnetic particles and floating close to a surface are able to propel in viscous fluids when subjected to external precessing magnetic fields. We show here that for certain values of the precession angle, the composite particles can be steered into tilted rather than linear trajectories characterized by a non-vanishing lateral velocity during motion. We extend the original model developed in Phys. Rev. Lett. 101, 218304 (2008) in order to explain this phenomenon, by including high-order corrections in the expansion of the director field and demonstrate the validity of this approach by comparing the analytical results with the experimental data. PMID:22872443

  4. Measurement of Diffraction Properties of Colloidal Crystals

    NASA Astrophysics Data System (ADS)

    Selan, Nicholas; Blades, Michael; Joy, Midhun; Gilchrist, James; Rotkin, Slava

    Close-packed, self-assembled arrays of micrometer polystyrene or silica spheres are high quality artificial crystals that generate well-defined diffraction patterns in the visible range. Such crystals are explored as possible substrates for deposition of nanomaterials such as graphene. Quasi-monochromatic visible light diffraction microscopy is used to characterize effective refractive index and crystal structure, specifically grain size, orientation, and lattice parameters. These parameters can be used to monitor deformations of the colloidal crystal lattice during transfer of nanomaterials. NSF ECCS-1509786, N.S. acknowledges RET supplement to NSF ECCS-1202398.

  5. Avalanches, plasticity, and ordering in colloidal crystals under compression

    NASA Astrophysics Data System (ADS)

    McDermott, D.; Reichhardt, C. J. Olson; Reichhardt, C.

    2016-06-01

    Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.

  6. Avalanches, plasticity, and ordering in colloidal crystals under compression.

    PubMed

    McDermott, D; Reichhardt, C J Olson; Reichhardt, C

    2016-06-01

    Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events. PMID:27415320

  7. Recent Results from the Physics of Colloids in Space

    NASA Technical Reports Server (NTRS)

    Weitz, David A.; Bailey, A.; Christianson, R.; Manley, S.; Prasad, V.; Segre, P.; Gasser, U.; Cipelletti, L.; Schoefield, A.; Pusey, P.

    2002-01-01

    The Physics of Colloids in Space is an experiment which flew in the ISS. Data on several different samples of colloidal particles were obtained. They provided unexpected information about the behavior of the samples in microgravity. The data are currently being analyzed. The most recent findings will be discussed in this talk.

  8. Feasibility of colloidal silver SERS for rapid bacterial screening

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Citrate-reduced silver colloids have been used extensively for surface-enhanced Raman scattering (SERS) study and are commonly characterized by UV-visible spectroscopy. In this work, relative standard deviation (RSD) of SERS spectra from silver colloidal suspensions and ratios of SERS peaks from sma...

  9. Fabrication and Characterization of Colloidal Crystal Thin Films

    ERIC Educational Resources Information Center

    Rodriguez, I.; Ramiro-Manzano, F.; Meseguer, F.; Bonet, E.

    2011-01-01

    We present a laboratory experiment that allows undergraduate or graduate students to get introduced to colloidal crystal research concepts in an interesting way. Moreover, such experiments and studies can also be useful in the field of crystallography or solid-state physics. The work concerns the growth of colloidal crystal thin films obtained…

  10. Stable Colloidal Drug Aggregates Catch and Release Active Enzymes.

    PubMed

    McLaughlin, Christopher K; Duan, Da; Ganesh, Ahil N; Torosyan, Hayarpi; Shoichet, Brian K; Shoichet, Molly S

    2016-04-15

    Small molecule aggregates are considered nuisance compounds in drug discovery, but their unusual properties as colloids could be exploited to form stable vehicles to preserve protein activity. We investigated the coaggregation of seven molecules chosen because they had been previously intensely studied as colloidal aggregators, coformulating them with bis-azo dyes. The coformulation reduced colloid sizes to <100 nm and improved uniformity of the particle size distribution. The new colloid formulations are more stable than previous aggregator particles. Specifically, coaggregation of Congo Red with sorafenib, tetraiodophenolphthalein (TIPT), or vemurafenib produced particles that are stable in solutions of high ionic strength and high protein concentrations. Like traditional, single compound colloidal aggregates, the stabilized colloids adsorbed and inhibited enzymes like β-lactamase, malate dehydrogenase, and trypsin. Unlike traditional aggregates, the coformulated colloid-protein particles could be centrifuged and resuspended multiple times, and from resuspended particles, active trypsin could be released up to 72 h after adsorption. Unexpectedly, the stable colloidal formulations can sequester, stabilize, and isolate enzymes by spin-down, resuspension, and release. PMID:26741163

  11. A Stochastic Model for Colloid Transport and Deposition

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Profiles of retained colloids in porous media have frequently been observed to be hyper-exponential or nonmonotonic with transport depth under unfavorable attachment conditions, whereas filtration theory predicts an exponential profile. In this work we present a stochastic model for colloid transpo...

  12. Colloidal deposition and aggregation in the presence of charged collectors

    NASA Astrophysics Data System (ADS)

    Sadri, Behnam; Rajendran, Arvind; Bhattacharjee, Subir; Colloids; complex fluid laboratory Team

    2014-11-01

    The transport of colloidal particles in porous media is of great importance in sub-surface environments. These colloidal particles facilitate transport of contaminants, low-soluble compounds and metals in groundwater. Here, we have studied transport dynamics of colloids inside porous medium using a combination of column experiments and batch studies. Polystyrene latex beads (100 nm), as colloidal agents, and soda lime glass beads, as porous medium, are employed in this work. On the one hand, batch experiments are undertaken to better understand concurrent aggregation and deposition of particles. On the other hand, column experiments are performed to understand the flow induced deposition of colloidal particles in the interstitial voids. Effect of collector surface preparation, pH, colloidal suspension concentration and collector beads mass is studied. Chemical release and shear field are revealed as two significant factors lying behind the coagulation of colloidal particles. These findings help us to better distinguish mechanisms responsible for the transport of colloids inside porous medium. We are collaborators. Behnam Sadri is master of science student while two other professor are supervising his research work.

  13. Reentrant phase transitions from depletion: colloidal crystals to flocculation

    NASA Astrophysics Data System (ADS)

    Feng, Lang; Laderman, Bezia; Sacanna, Stefano; Chaikin, Paul

    2014-03-01

    Conventional depletion is supposed to be temperature independent. However, we find that many typical colloid-depletion systems show remarkable phenomena as temperature is varied. 1 μm polystyrene spheres in water are known to form colloidal crystals when PEO is added as a depletant. When this system is heated the crystal melts at a first critical temperature T1 ~ 60 C , and then at higher temperature T2 ~ 70 C the colloids flocculate. We argue that a weak temperature-dependent interaction between polymer and colloid is responsible for the observed phenomena: crystals form when the colloid-polymer interaction is repulsive, flocculation occurs when the interaction is attractive, and melting occurs in between when both phases are frustrated. The melted phase occurs due to an unexpected cancelation when combining both entropic and enthalpic attractions. We propose a simple statistical model to map out the observed transitions and fill the theoretical gap between the two established scenarios for colloid-polymer systems, namely depletion and flocculation. We have seen the same temperature dependent phenomena for TPM, PS and silica spheres with PEO and dextran as depletants. Our discovery provides a fundamental understanding of the polymer-colloid system and opens new possibilities for colloidal self-assembly and temperature-controlled viscoelastic materials.

  14. STABILITY AND TRANSPORT OF INORGANIC COLLOIDS THROUGH CONTAMINATED AQUIFER MATERIAL

    EPA Science Inventory

    Laboratory columns using contaminated natural aquifer material from Globe, Arizona, were used to investigate the transport of inorganic colloids under saturated flow conditions. e2O3 radio-labeled spherical colloids of various diameters were synthesized and introduced into the co...

  15. Physics of Colloids in Space: Flight Hardware Operations on ISS

    NASA Technical Reports Server (NTRS)

    Doherty, Michael P.; Bailey, Arthur E.; Jankovsky, Amy L.; Lorik, Tibor

    2002-01-01

    The Physics of Colloids in Space (PCS) experiment was launched on Space Shuttle STS-100 in April 2001 and integrated into EXpedite the PRocess of Experiments to Space Station Rack 2 on the International Space Station (ISS). This microgravity fluid physics investigation is being conducted in the ISS U.S. Lab 'Destiny' Module over a period of approximately thirteen months during the ISS assembly period from flight 6A through flight 9A. PCS is gathering data on the basic physical properties of simple colloidal suspensions by studying the structures that form. A colloid is a micron or submicron particle, be it solid, liquid, or gas. A colloidal suspension consists of these fine particles suspended in another medium. Common colloidal suspensions include paints, milk, salad dressings, cosmetics, and aerosols. Though these products are routinely produced and used, we still have much to learn about their behavior as well as the underlying properties of colloids in general. The long-term goal of the PCS investigation is to learn how to steer the growth of colloidal structures to create new materials. This experiment is the first part of a two-stage investigation conceived by Professor David Weitz of Harvard University (the Principal Investigator) along with Professor Peter Pusey of the University of Edinburgh (the Co-Investigator). This paper describes the flight hardware, experiment operations, and initial science findings of the first fluid physics payload to be conducted on ISS: The Physics of Colloids in Space.

  16. Spontaneous resolution of a colloid cyst of the third ventricle.

    PubMed

    Annamalai, G; Lindsay, K W; Bhattacharya, J J

    2008-01-01

    We report a case of an asymptomatic colloid cyst of the third ventricle in a 35-year-old male, which on follow-up MRI at 15 months appears to have spontaneously resolved. To our knowledge, this is the first such case reported and supports the role of conservative management of small asymptomatic colloid cysts. PMID:18079347

  17. Colloid adhesive parameters for chemical heterogeneous porous media

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A simple modeling approach was developed to calculate colloid adhesive parameters for chemically heterogeneous porous media. The area of the zone of electrostatic influence between a colloid and solid-water interface (Az) was discretized into a number of equally sized grid cells to capture chemical...

  18. Coherent Acoustic Phonons in Colloidal Semiconductor Nanocrystal Superlattices.

    PubMed

    Poyser, Caroline L; Czerniuk, Thomas; Akimov, Andrey; Diroll, Benjamin T; Gaulding, E Ashley; Salasyuk, Alexey S; Kent, Anthony J; Yakovlev, Dmitri R; Bayer, Manfred; Murray, Christopher B

    2016-01-26

    The phonon properties of films fabricated from colloidal semiconductor nanocrystals play a major role in thermal conductance and electron scattering, which govern the principles for building colloidal-based electronics and optics including thermoelectric devices with a high ZT factor. The key point in understanding the phonon properties is to obtain the strength of the elastic bonds formed by organic ligands connecting the individual nanocrystallites. In the case of very weak bonding, the ligands become the bottleneck for phonon transport between infinitively rigid nanocrystals. In the opposite case of strong bonding, the colloids cannot be considered as infinitively rigid beads and the distortion of the superlattice caused by phonons includes the distortion of the colloids themselves. We use the picosecond acoustics technique to study the acoustic coherent phonons in superlattices of nanometer crystalline CdSe colloids. We observe the quantization of phonons with frequencies up to 30 GHz. The frequencies of quantized phonons depend on the thickness of the colloidal films and possess linear phonon dispersion. The measured speed of sound and corresponding wave modulus in the colloidal films point on the strong elastic coupling provided by organic ligands between colloidal nanocrystals. PMID:26696021

  19. Predicting colloid transport through saturated porous media: A critical review

    NASA Astrophysics Data System (ADS)

    Molnar, Ian L.; Johnson, William P.; Gerhard, Jason I.; Willson, Clinton S.; O'Carroll, Denis M.

    2015-09-01

    Understanding and predicting colloid transport and retention in water-saturated porous media is important for the protection of human and ecological health. Early applications of colloid transport research before the 1990s included the removal of pathogens in granular drinking water filters. Since then, interest has expanded significantly to include such areas as source zone protection of drinking water systems and injection of nanometals for contaminated site remediation. This review summarizes predictive tools for colloid transport from the pore to field scales. First, we review experimental breakthrough and retention of colloids under favorable and unfavorable colloid/collector interactions (i.e., no significant and significant colloid-surface repulsion, respectively). Second, we review the continuum-scale modeling strategies used to describe observed transport behavior. Third, we review the following two components of colloid filtration theory: (i) mechanistic force/torque balance models of pore-scale colloid trajectories and (ii) approximating correlation equations used to predict colloid retention. The successes and limitations of these approaches for favorable conditions are summarized, as are recent developments to predict colloid retention under the unfavorable conditions particularly relevant to environmental applications. Fourth, we summarize the influences of physical and chemical heterogeneities on colloid transport and avenues for their prediction. Fifth, we review the upscaling of mechanistic model results to rate constants for use in continuum models of colloid behavior at the column and field scales. Overall, this paper clarifies the foundation for existing knowledge of colloid transport and retention, features recent advances in the field, critically assesses where existing approaches are successful and the limits of their application, and highlights outstanding challenges and future research opportunities. These challenges and opportunities

  20. Humic colloid-borne natural polyvalent metal ions: dissociation experiment.

    PubMed

    Geckeis, H; Rabung, Th; Ngo Manh, T; Kim, J I; Beck, H P

    2002-07-01

    The natural association nature of the humic colloid-borne trace elements is investigated. Rare earth elements (REE) Th and U are chosen as naturally occurring representatives and chemical homologues for actinides of different oxidation states present in nuclear waste. Tri- and tetravalent elements in two investigated Gorleben groundwaters (Gohy-532 and -2227) almost exclusively occur as humic or fulvic colloid-borne species. Their desorption behavior from colloids is examined in the unperturbed groundwater (pH approximately 8) under anaerobic conditions (Ar/1% CO2) by addition of a chelating cation exchanger resin. Particularly, the dissociation process of naturally occurring Eu(III) in the groundwater is compared with the Eu(III) desorption from its humate complex prepared with purified Aldrich humic acid in a buffered aqueous solution at pH approximately 8. The Eu(III) dissociation from the groundwater colloids is found to be considerably slower than found for the humate complex synthesized in the laboratory. This suggests that under natural aquatic conditions the Eu(III) binding in colloids is chemically different from the simple humate complexation as observed in the laboratory experiment. The colloid characterization bythe size exclusion chromatography (SEC) and the flow field-flow fractionation (FFFF) indicates that natural colloid-borne trace elements are found predominantly in colloids of larger size (>15 nm in size), while Eu(III) in its humate complex is found mainly in colloids of hydrodynamic diameters <5 nm. The slower desorption kinetics and the larger colloid size suggest that the polyvalent metal ion binding in natural humic colloids is associated to polynucleation with other co-present trace metal ions. Radiotracer experiments reveal that isotopic equilibria with the naturally colloid-borne trace elements are not attained within a period of more than 100 days, indicating irreversible binding of at least a part of colloid-borne polyvalent trace

  1. Colloidal characterization of silicon nitride and silicon carbide

    NASA Technical Reports Server (NTRS)

    Feke, Donald L.

    1986-01-01

    The colloidal behavior of aqueous ceramic slips strongly affects the forming and sintering behavior and the ultimate mechanical strength of the final ceramic product. The colloidal behavior of these materials, which is dominated by electrical interactions between the particles, is complex due to the strong interaction of the solids with the processing fluids. A surface titration methodology, modified to account for this interaction, was developed and used to provide fundamental insights into the interfacial chemistry of these systems. Various powder pretreatment strategies were explored to differentiate between true surface chemistry and artifacts due to exposure history. The colloidal behavior of both silicon nitride and carbide is dominated by silanol groups on the powder surfaces. However, the colloid chemistry of silicon nitride is apparently influenced by an additional amine group. With the proper powder treatments, silicon nitride and carbide powder can be made to appear colloidally equivalent. The impact of these results on processing control will be discussed.

  2. Dielectric effects on the ion distribution near a Janus colloid

    NASA Astrophysics Data System (ADS)

    Wu, Huanxin; Han, Ming; Luijten, Erik

    Spherical Janus colloids, particles with two domains of different materials, are typically heterogeneous in permittivity. This dielectric heterogeneity will influence their behavior in electrolytes, ranging from their aggregation to their electrokinetics in external fields. We investigate the structure of the electric double layer around spherical Janus colloids immersed in solution via molecular dynamics simulations. Polarization of the colloidal surfaces by the surrounding ions is calculated dynamically with a boundary-element method based Poisson solver. One observation is that even neutral Janus colloids may carry a net dipole moment in the presence of asymmetric salts. Moreover, we extend this study to incorporate a spatially varying permittivity of the solvent near a charged Janus colloid, and demonstrate the effect of this dielectric variation on the electric double layer.

  3. SUBSURFACE MOBILE PLUTONIUM SPECIATION: SAMPLING ARTIFACTS FOR GROUNDWATER COLLOIDS

    SciTech Connect

    Kaplan, D.; Buesseler, K.

    2010-06-29

    A recent review found several conflicting conclusions regarding colloid-facilitated transport of radionuclides in groundwater and noted that colloids can both facilitate and retard transport. Given these contrasting conclusions and the profound implications even trace concentrations of plutonium (Pu) have on the calculated risk posed to human health, it is important that the methodology used to sample groundwater colloids be free of artifacts. The objective of this study was: (1) to conduct a field study and measure Pu speciation, ({sup 239}Pu and {sup 240}Pu for reduced-Pu{sub aq}, oxidized-Pu{sub aq}, reduced-Pu{sub colloid}, and oxidized-Pu{sub colloid}), in a Savannah River Site (SRS) aquifer along a pH gradient in F-Area, (2) to determine the impact of pumping rate on Pu concentration, Pu speciation, and Pu isotopic ratios, (3) determine the impact of delayed sample processing (as opposed to processing directly from the well).

  4. Using depletion to control colloidal crystal assemblies of hard cuboctahedra.

    PubMed

    Karas, Andrew S; Glaser, Jens; Glotzer, Sharon C

    2016-06-21

    Depletion interactions arise from entropic forces, and their ability to induce aggregation and even ordering of colloidal particles through self-assembly is well established, especially for spherical colloids. We vary the size and concentration of penetrable hard sphere depletants in a system of cuboctahedra, and we show how depletion changes the preferential facet alignment of the colloids and thereby selects different crystal structures. Moreover, we explain the cuboctahedra phase behavior using perturbative free energy calculations. We find that cuboctahedra can form a stable simple cubic phase, and, remarkably, that the stability of this phase can be rationalized only by considering the effects of both the colloid and depletant entropy. We corroborate our results by analyzing how the depletant concentration and size affect the emergent directional entropic forces and hence the effective particle shape. We propose the use of depletants as a means of easily changing the effective shape of self-assembling anisotropic colloids. PMID:27194463

  5. Reconfigurable multi-scale colloidal assembly on excluded volume patterns

    NASA Astrophysics Data System (ADS)

    Edwards, Tara D.; Yang, Yuguang; Everett, W. Neil; Bevan, Michael A.

    2015-09-01

    The ability to create multi-scale, periodic colloidal assemblies with unique properties is important to emerging applications. Dynamically manipulating colloidal structures via tunable kT-scale attraction can provide the opportunity to create particle-based nano- and microstructured materials that are reconfigurable. Here, we report a novel tactic to obtain reconfigurable, multi-scale, periodic colloidal assemblies by combining thermoresponsive depletant particles and patterned topographical features that, together, reversibly mediate local kT-scale depletion interactions. This method is demonstrated in optical microscopy experiments to produce colloidal microstructures that reconfigure between well-defined ordered structures and disordered fluid states as a function of temperature and pattern feature depth. These results are well described by Monte Carlo simulations using theoretical depletion potentials that include patterned excluded volume. Ultimately, the approach reported here can be extended to control the size, shape, orientation, and microstructure of colloidal assemblies on multiple lengths scales and on arbitrary pre-defined pattern templates.

  6. Laser speckle reduction via colloidal-dispersion-filled projection screens.

    PubMed

    Riechert, Falko; Bastian, Georg; Lemmer, Uli

    2009-07-01

    We use projection screens filled with colloidal dispersions to reduce laser speckle in laser projection systems. Laser light is multiply scattered at the globules of the colloidal dispersion's internal phase, which do Brownian movement. The integration time of the human eye causes a perception of a reduced laser speckle contrast because of temporal averaging. As a counteracting effect, blurring of projected images occurs in the colloidal dispersion, which degrades image quality. We measure and compare speckle reduction and blurring of three different colloidal dispersions filled into transmission screens of different thicknesses. We realized a high speckle contrast reduction at simultaneously low blurring with a thin screen filled with a highly scattering colloidal dispersion with forward-peaked scattering. We realize speckle contrast values below 3% at acceptable blurring. PMID:19571932

  7. Nonlinear machine learning and design of reconfigurable digital colloids.

    PubMed

    Long, Andrew W; Phillips, Carolyn L; Jankowksi, Eric; Ferguson, Andrew L

    2016-09-14

    Digital colloids, a cluster of freely rotating "halo" particles tethered to the surface of a central particle, were recently proposed as ultra-high density memory elements for information storage. Rational design of these digital colloids for memory storage applications requires a quantitative understanding of the thermodynamic and kinetic stability of the configurational states within which information is stored. We apply nonlinear machine learning to Brownian dynamics simulations of these digital colloids to extract the low-dimensional intrinsic manifold governing digital colloid morphology, thermodynamics, and kinetics. By modulating the relative size ratio between halo particles and central particles, we investigate the size-dependent configurational stability and transition kinetics for the 2-state tetrahedral (N = 4) and 30-state octahedral (N = 6) digital colloids. We demonstrate the use of this framework to guide the rational design of a memory storage element to hold a block of text that trades off the competing design criteria of memory addressability and volatility. PMID:27498992

  8. Glassy dislocation dynamics in colloidal dimer crystals

    NASA Astrophysics Data System (ADS)

    Gerbode, Sharon

    2012-02-01

    Dislocation mobility is central to both the mechanical response and the relaxation mechanisms of crystalline materials. Recent experiments have explored the role of novel particle anisotropies in affecting the rules of defect motion in crystals. ``Peanut-shaped'' colloidal dimer particles consisting of two connected spherical lobes form densely packed crystals in 2D. In these ``degenerate crystals,'' the particle lobes occupy triangular lattice sites while the particle axes are randomly oriented among the three crystalline directions. One consequence of the random orientations of the dimers is that dislocation glide is severely limited by certain particle arrangements in the degenerate crystals. Using optical tweezers to manipulate single lobe-sized spherical intruder particles, we locally deform the crystal, creating defects. During subsequent relaxation, the dislocations formed during the deformation leave the crystal grain, either via annihilation with other dislocations or by moving to a grain boundary. Interestingly, in large crystalline grains this dislocation relaxation occurs through a two-stage process reminiscent of slow relaxations in glassy systems, suggesting the novel concept that glassy phenomena may be introduced to certain kinds of colloidal crystals via simple anisotropic constituents.

  9. Critical Casimir forces for colloidal assembly.

    PubMed

    Nguyen, V D; Dang, M T; Nguyen, T A; Schall, P

    2016-02-01

    Critical Casimir forces attract increasing interest due to their opportunities for reversible particle assembly in soft matter and nano science. These forces provide a thermodynamic analogue of the celebrated quantum mechanical Casimir force that arises from the confinement of vacuum fluctuations of the electromagnetic field. In its thermodynamic analogue, solvent fluctuations, confined between suspended particles, give rise to an attractive or repulsive force between the particles. Due to its unique temperature dependence, this effect allows in situ control of reversible assembly. Both the force magnitude and range vary with the solvent correlation length in a universal manner, adjusting with temperature from fractions of the thermal energy, k B T, and nanometre range to several ten kT and micrometer length scale. Combined with recent breakthroughs in the synthesis of complex particles, critical Casimir forces promise the design and assembly of complex colloidal structures, for fundamental studies of equilibrium and out-of-equilibrium phase behaviour. This review highlights recent developments in this evolving field, with special emphasis on the dynamic interaction control to assemble colloidal structures, in and out of equilibrium. PMID:26750980

  10. Removal of colloidal biogenic selenium from wastewater.

    PubMed

    Staicu, Lucian C; van Hullebusch, Eric D; Oturan, Mehmet A; Ackerson, Christopher J; Lens, Piet N L

    2015-04-01

    Biogenic selenium, Se(0), has colloidal properties and thus poses solid-liquid separation problems, such as poor settling and membrane fouling. The separation of Se(0) from the bulk liquid was assessed by centrifugation, filtration, and coagulation-flocculation. Se(0) particles produced by an anaerobic granular sludge are normally distributed, ranging from 50 nm to 250 nm, with an average size of 166±29 nm and a polydispersity index of 0.18. Due to its nanosize range and protein coating-associated negative zeta potential (-15 mV to -23 mV) between pH 2 and 12, biogenic Se(0) exhibits colloidal properties, hampering its removal from suspension. Centrifugation at different centrifugal speeds achieved 22±3% (1500 rpm), 73±2% (3000 rpm) and 91±2% (4500 rpm) removal. Separation by filtration through 0.45 μm filters resulted in 87±1% Se(0) removal. Ferric chloride and aluminum sulfate were used as coagulants in coagulation-flocculation experiments. Aluminum sulfate achieved the highest turbidity removal (92±2%) at a dose of 10(-3) M, whereas ferric chloride achieved a maximum turbidity removal efficiency of only 43±4% at 2.7×10(-4) M. Charge repression plays a minor role in particle neutralization. The sediment volume resulting from Al2(SO3)4 treatment is three times larger than that produced by FeCl3. PMID:25559175

  11. Visualization of dislocation dynamics in colloidal crystals.

    PubMed

    Schall, Peter; Cohen, Itai; Weitz, David A; Spaepen, Frans

    2004-09-24

    The dominant mechanism for creating large irreversible strain in atomic crystals is the motion of dislocations, a class of line defects in the crystalline lattice. Here we show that the motion of dislocations can also be observed in strained colloidal crystals, allowing detailed investigation of their topology and propagation. We describe a laser diffraction microscopy setup used to study the growth and structure of misfit dislocations in colloidal crystalline films. Complementary microscopic information at the single-particle level is obtained with a laser scanning confocal microscope. The combination of these two techniques enables us to study dislocations over a range of length scales, allowing us to determine important parameters of misfit dislocations such as critical film thickness, dislocation density, Burgers vector, and lattice resistance to dislocation motion. We identify the observed dislocations as Shockley partials that bound stacking faults of vanishing energy. Remarkably, we find that even on the scale of a few lattice vectors, the dislocation behavior is well described by the continuum approach commonly used to describe dislocations in atomic crystals. PMID:15448265

  12. Magnetically Driven Swimming of Nanoscale Colloidal Assemblies

    NASA Astrophysics Data System (ADS)

    Breidenich, Jennifer; Benkoski, Jason; Baird, Lance; Deacon, Ryan; Land, H. Bruce; Hayes, Allen; Keng, Pei; Pyun, Jeffrey

    2009-03-01

    At microscopic length scales, locomotion can only be generated through asymmetric conformation changes, such as the undulating flagellum employed by protozoa. This simple yet elegant design is optimized according to the dueling needs of miniaturization and the fluid dynamics of the low Reynolds number environment. In this study, we fabricate nanoscale colloidal assemblies that mimic the head + tail structure of flagellates. The assemblies consist of two types of magnetic colloids: 25 nm polystyrene-coated Co nanoparticles, and 250 nm polyethylene glycol coated magnetite nanoparticles. When mixed together in N-dimethylformamide, the Co nanoparticles assemble into flexible, segmented chains ranging in length from 1 - 5 μm. These chains then attach at one end to the larger magnetic beads due to magnetic attraction. This head + tail structure aligns with an external uniform magnetic field and is actuated by an oscillating transverse field. We examine the effects of Co nanoparticle concentration, magnetite bead concentration, magnetic field strength, and oscillation frequency on the formation of swimmers and the speed of locomotion.

  13. Two-dimensional magnetic colloids under shear.

    PubMed

    Mohorič, Tomaž; Dobnikar, Jure; Horbach, Jürgen

    2016-04-01

    Complex rheological properties of soft disordered solids, such as colloidal gels or glasses, inspire a range of novel applications. However, the microscopic mechanisms of their response to mechanical loading are not well understood. Here, we elucidate some aspects of these mechanisms by studying a versatile model system, i.e. two-dimensional superparamagnetic colloids in a precessing magnetic field, whose structure can be tuned from a hexagonal crystal to a disordered gel network by varying the external field opening angle θ. We perform Langevin dynamics simulations subjecting these structures to a constant shear rate and observe three qualitatively different types of material response. In hexagonal crystals (θ = 0°), at a sufficiently low shear rate, plastic flow occurs via successive stress drops at which the stress releases due to the formation of dislocation defects. The gel network at θ = 48°, on the contrary, via bond rearrangement and transient shear banding evolves into a homogeneously stretched network at large strains. The latter structure remains metastable after switching off of the shear. At θ = 50°, the external shear makes the system unstable against phase separation and causes a failure of the network structure leading to the formation of hexagonal close packed clusters interconnected by particle chains. At a microcopic level, our simulations provide insight into some of the mechanisms by which strain localization as well as material failure occur in a simple gel-like network. Furthermore, we demonstrate that new stretched network structures can be generated by the application of shear. PMID:26877059

  14. Adhesion of colloidal particles on modified electrodes.

    PubMed

    Kuznetsov, Volodymyr; Papastavrou, Georg

    2012-12-01

    The adhesion between colloidal silica particles and modified electrodes has been studied by direct force measurements with the colloidal probe technique based on the atomic force microscope (AFM). The combination of potentiostatic control of gold electrodes and chemical modification of their surface with self-assembled monolayers (SAMs) allows for the decoupling of forces due to the electrical double layers and functional groups at the solid/liquid interface. Adhesion on such electrodes can be tuned over a large range using the externally applied potential and the aqueous solution's ionic strength. By utilizing cantilevers with a high force constant, it is possible to separate the various contributions to adhesion in an unambiguous manner. These contributions comprise diffuse-layer overlap, van der Waals forces, solvent exclusion, and electrocapillarity. A quantitative description of the observed adhesion forces is obtained by taking into account the surface roughness of the silica particle. The main component of the adhesion forces originates from the overlap of the electrical double layers, which is tuned by the external potential. By contrast, effects due to electrocapillarity are of only minor importance. Based on our quantitative analysis, a new approach is proposed that allows tuning of the adhesion force as a function of the externally applied potential. We expect this approach to have important applications for the design of microelectromechanical systems (MEMS), the development of electrochemical sensors, and the application of micro- and nanomanipulation. PMID:23072548

  15. Colloidal analogs of molecular chain stoppers

    PubMed Central

    Klinkova, Anna; Thérien-Aubin, Héloïse; Choueiri, Rachelle M.; Rubinstein, Michael; Kumacheva, Eugenia

    2013-01-01

    A similarity between chemical reactions and self-assembly of nanoparticles offers a strategy that can enrich both the synthetic chemistry and the nanoscience fields. Synthetic methods should enable quantitative control of the structural characteristics of nanoparticle ensembles such as their aggregation number or directionality, whereas the capability to visualize and analyze emerging nanostructures using characterization tools can provide insight into intelligent molecular design and mechanisms of chemical reactions. We explored this twofold concept for an exemplary system including the polymerization of bifunctional nanoparticles in the presence of monofunctional colloidal chain stoppers. Using reaction-specific design rules, we synthesized chain stoppers with controlled reactivity and achieved quantitative fine-tuning of the self-assembled structures. Analysis of the nanostructures provided information about polymerization kinetics, side reactions, and the distribution of all of the species in the reaction system. A quantitative model was developed to account for the reactivity, kinetics, and side reactions of nanoparticles, all governed by the design of colloidal chain stoppers. This work provided the ability to test theoretical models developed for molecular polymerization. PMID:24190993

  16. Hierarchical Fast Multipole Simulation of Magnetic Colloids

    NASA Astrophysics Data System (ADS)

    Günal, Yüksel; Visscher, Pieter

    1997-03-01

    We have extended the well-known "fast multipole"footnote L. F. Greengard and V. Rokhlin, J. Comp. Phys. 73 p. 325, 1987. methods for molecular-dynamics simulation of large systems of point charges to continuum systems, such as magnetic films or colloids/march.html>particulate suspensions. (These methods reduce the computational labor from O(N^2) to O(N log N) or O(N), the number of particles). We apply the method to the particular case of a colloidal dispersion of magnetized cylindrical particles. Our method is fully hierarchical, both upward and downward from the particle size scale. The force on each particle is calculated by grouping distant particles into large clusters, nearer particles into smaller clusters, and dividing the nearest particles into segments. The fineness with which the particles are divided is controlled by an error tolerance parameter. The field of each cluster or segment is computed from a multipole expansion. Distant periodic images are also treated as multipoles - this is much faster than standard Fourier-transform or Ewald summation techniques.

  17. Critical Casimir forces for colloidal assembly

    NASA Astrophysics Data System (ADS)

    Nguyen, V. D.; Dang, M. T.; Nguyen, T. A.; Schall, P.

    2016-02-01

    Critical Casimir forces attract increasing interest due to their opportunities for reversible particle assembly in soft matter and nano science. These forces provide a thermodynamic analogue of the celebrated quantum mechanical Casimir force that arises from the confinement of vacuum fluctuations of the electromagnetic field. In its thermodynamic analogue, solvent fluctuations, confined between suspended particles, give rise to an attractive or repulsive force between the particles. Due to its unique temperature dependence, this effect allows in situ control of reversible assembly. Both the force magnitude and range vary with the solvent correlation length in a universal manner, adjusting with temperature from fractions of the thermal energy, k B T, and nanometre range to several ten kT and micrometer length scale. Combined with recent breakthroughs in the synthesis of complex particles, critical Casimir forces promise the design and assembly of complex colloidal structures, for fundamental studies of equilibrium and out-of-equilibrium phase behaviour. This review highlights recent developments in this evolving field, with special emphasis on the dynamic interaction control to assemble colloidal structures, in and out of equilibrium.

  18. Colloidal aggregation and dynamics in anisotropic fluids

    PubMed Central

    Mondiot, Frédéric; Botet, Robert; Snabre, Patrick; Mondain-Monval, Olivier; Loudet, Jean-Christophe

    2014-01-01

    We present experiments and numerical simulations to investigate the collective behavior of submicrometer-sized particles immersed in a nematic micellar solution. We use latex spheres with diameters ranging from 190 to 780 nm and study their aggregation properties due to the interplay of the various colloidal forces at work in the system. We found that the morphology of aggregates strongly depends on the particle size, with evidence for two distinct regimes: the biggest inclusions clump together within minutes into either compact clusters or V-like structures that are completely consistent with attractive elastic interactions. On the contrary, the smallest particles form chains elongated along the nematic axis, within comparable timescales. In this regime, Monte Carlo simulations, based on a modified diffusion-limited cluster aggregation model, strongly suggest that the anisotropic rotational Brownian motion of the clusters combined with short-range depletion interactions dominate the system coarsening; elastic interactions no longer prevail. The simulations reproduce the sharp transition between the two regimes on increasing the particle size. We provide reasonable estimates to interpret our data and propose a likely scenario for colloidal aggregation. These results emphasize the growing importance of the diffusion of species at suboptical-wavelength scales and raise a number of fundamental issues. PMID:24715727

  19. Dynamics of colloidal particles in ice

    NASA Astrophysics Data System (ADS)

    Spannuth, Melissa; Mochrie, S. G. J.; Peppin, S. S. L.; Wettlaufer, J. S.

    2011-03-01

    Solidification of the solvent phase of a colloidal suspension occurs in many natural and technological settings and is becoming a popular technique for creating microporous structures and composite materials. During freezing, regions of high particle density can form as particles are rejected from the growing solid and guided into a variety of macroscopic morphologies. The particles in the high density regions form an amorphous colloidal solid that deforms in response to internal and external stresses. Using X-ray Photon Correlation Spectroscopy, we studied this deformation for silica particles in polycrystalline ice. We found that the particles in the high density regions underwent ballistic motion coupled with a non-exponential decay of the intensity autocorrelation function (ACF) that transitions from a stretched to a compressed exponential with increasing scattering vector q. While ballistic motion and a compressed exponential decay of the ACF is common, the coupling with a stretched exponential decay is very rare and a transition with increasing q has not previously been reported. We explain this behavior in terms of ice grain boundary migration.

  20. Liquid-vapor interfaces of patchy colloids.

    PubMed

    Oleksy, A; Teixeira, P I C

    2015-01-01

    We investigate the liquid-vapor interface of a model of patchy colloids. This model consists of hard spheres decorated with short-ranged attractive sites ("patches") of different types on their surfaces. We focus on a one-component fluid with two patches of type A and nine patches of type B (2A9B colloids), which has been found to exhibit reentrant liquid-vapor coexistence curves and very low-density liquid phases. We have used the density-functional theory form of Wertheim's first-order perturbation theory of association, as implemented by Yu and Wu [J. Chem. Phys. 116, 7094 (2002)], to calculate the surface tension, and the density and degree of association profiles, at the liquid-vapor interface of our model. In reentrant systems, where AB bonds dominate, an unusual thickening of the interface is observed at low temperatures. Furthermore, the surface tension versus temperature curve reaches a maximum, in agreement with Bernardino and Telo da Gama's mesoscopic Landau-Safran theory [Phys. Rev. Lett. 109, 116103 (2012)]. If BB attractions are also present, competition between AB and BB bonds gradually restores the monotonic temperature dependence of the surface tension. Lastly, the interface is "hairy," i.e., it contains a region where the average chain length is close to that in the bulk liquid, but where the density is that of the vapor. Sufficiently strong BB attractions remove these features, and the system reverts to the behavior seen in atomic fluids. PMID:25679617

  1. Phase transformations in binary colloidal monolayers.

    PubMed

    Yang, Ye; Fu, Lin; Marcoux, Catherine; Socolar, Joshua E S; Charbonneau, Patrick; Yellen, Benjamin B

    2015-03-28

    Phase transformations can be difficult to characterize at the microscopic level due to the inability to directly observe individual atomic motions. Model colloidal systems, by contrast, permit the direct observation of individual particle dynamics and of collective rearrangements, which allows for real-space characterization of phase transitions. Here, we study a quasi-two-dimensional, binary colloidal alloy that exhibits liquid-solid and solid-solid phase transitions, focusing on the kinetics of a diffusionless transformation between two crystal phases. Experiments are conducted on a monolayer of magnetic and nonmagnetic spheres suspended in a thin layer of ferrofluid and exposed to a tunable magnetic field. A theoretical model of hard spheres with point dipoles at their centers is used to guide the choice of experimental parameters and characterize the underlying materials physics. When the applied field is normal to the fluid layer, a checkerboard crystal forms; when the angle between the field and the normal is sufficiently large, a striped crystal assembles. As the field is slowly tilted away from the normal, we find that the transformation pathway between the two phases depends strongly on crystal orientation, field strength, and degree of confinement of the monolayer. In some cases, the pathway occurs by smooth magnetostrictive shear, while in others it involves the sudden formation of martensitic plates. PMID:25677504

  2. Colloidal motility and patterning by physical chemotaxis

    NASA Astrophysics Data System (ADS)

    Palacci, Jeremie; Abecassis, Benjamin; Cottin-Bizonne, Cecile; Ybert, Christophe; Bocquet, Lyderic

    2009-11-01

    We developped a microfluidic setup to show the motility of colloids or biomolecules under a controlled salt gradient thanks to the diffusiophoresis phenomenon [1,2]. We can therefore mimic chemotaxis on simple physical basis with thrilling analogies with the biological chemotaxis of E. Coli bacteria: salt dependance of the velocity [3] and log-sensing behavior [4]. In addition with a temporally tunable gradient we show we can generate an effective osmotic potential to trap colloids or DNA. These experimental observations are supported by numerical simulations and an asymptotic ratchet model. Finally, we use these traps to generate various patterns and because concentration gradients are ubiquitous in nature, we question for the role of such a mecanism in morphogenesis [5] or positioning perspectives in cells [6]. [4pt] [1] B. Abecassis, C. Cottin-Bizonne, C. Ybert, A. Ajdari, and L. Bocquet, Nat. Mat., 7(10):785--789, 2008. [2] Anderson, Ann. Rev. Fluid Mech, 21, 1989. [3] Y. L. Qi and J. Adler, PNAS, 86(21):8358--8362, 1989. [4] Y. V. Kalinin, L. L. Jiang, Y. H. Tu, and M. M. Wu, Biophys. J., 96(6):2439--2448, 2009. [4] J. B. Moseley, A. Mayeux, A. Paoletti, and P. Nurse, Nat., 459(7248):857--U8, 2009. [6] L. Wolpert, Dev., 107:3--12, 1989

  3. Switching light with light--advanced functional colloidal monolayers.

    PubMed

    Bley, K; Sinatra, N; Vogel, N; Landfester, K; Weiss, C K

    2014-01-01

    Colloidal monolayers comprising of highly ordered two dimensional crystals are of high interest to generate surface patterns for a variety of different applications. Mostly, unfunctionalized polymer or silica colloids are assembled into monolayers. However, the incorporation of functional molecules into such colloids offers a convenient possibility of implementing additional properties to the two-dimensional crystal. Here, we present the formation of novel functional colloidal monolayers with photoswitchable fluorescence. The miniemulsion polymerization technique was used to incorporate an appropriate dye system of a perylene-based fluorophore and a bis-arylethene as a photochrome in polymeric colloids in defined ratios. Upon irradiation with UV or visible light the photochrome reversibly isomerizes from the ring-closed form, which is able to absorb light of the emission wavelength of the fluorescent dye and the ring-open form, which is not. The fluorescence emission of the dye can thus be reversibly switched on and off with light even when embedded in colloids. The colloids were self-assembled at the air-water interface to produce hexagonally ordered functional monolayers and more complex binary crystals. We investigate in detail the influence of the polymeric matrix on the switching properties of the fluorophore/photochrome system and find that the rate constants for the photoswitching, which all lie in the same range, are less influenced by the polymeric environment than expected. We demonstrate the reversible switching of the fluorescence emission in self-assembled colloidal monolayers. The arrangement of broadly distributed functional colloids into ordered monolayers with high addressability was obtained by the formation of binary colloidal monolayers. PMID:24227011

  4. Large-scale assembly of colloidal particles

    NASA Astrophysics Data System (ADS)

    Yang, Hongta

    This study reports a simple, roll-to-roll compatible coating technology for producing three-dimensional highly ordered colloidal crystal-polymer composites, colloidal crystals, and macroporous polymer membranes. A vertically beveled doctor blade is utilized to shear align silica microsphere-monomer suspensions to form large-area composites in a single step. The polymer matrix and the silica microspheres can be selectively removed to create colloidal crystals and self-standing macroporous polymer membranes. The thickness of the shear-aligned crystal is correlated with the viscosity of the colloidal suspension and the coating speed, and the correlations can be qualitatively explained by adapting the mechanisms developed for conventional doctor blade coating. Five important research topics related to the application of large-scale three-dimensional highly ordered macroporous films by doctor blade coating are covered in this study. The first topic describes the invention in large area and low cost color reflective displays. This invention is inspired by the heat pipe technology. The self-standing macroporous polymer films exhibit brilliant colors which originate from the Bragg diffractive of visible light form the three-dimensional highly ordered air cavities. The colors can be easily changed by tuning the size of the air cavities to cover the whole visible spectrum. When the air cavities are filled with a solvent which has the same refractive index as that of the polymer, the macroporous polymer films become completely transparent due to the index matching. When the solvent trapped in the cavities is evaporated by in-situ heating, the sample color changes back to brilliant color. This process is highly reversible and reproducible for thousands of cycles. The second topic reports the achievement of rapid and reversible vapor detection by using 3-D macroporous photonic crystals. Capillary condensation of a condensable vapor in the interconnected macropores leads to the

  5. How colloid-colloid interactions and hydrodynamic effects influence the percolation threshold: A simulation study in alumina suspensions.

    PubMed

    Laganapan, Aleena Maria; Mouas, Mohamed; Videcoq, Arnaud; Cerbelaud, Manuella; Bienia, Marguerite; Bowen, Paul; Ferrando, Riccardo

    2015-11-15

    The percolation behavior of alumina suspensions is studied by computer simulations. The percolation threshold ϕc is calculated, determining the key factors that affect its magnitude: the strength of colloid-colloid attraction and the presence of hydrodynamic interactions (HIs). To isolate the effects of HIs, we compare the results of Brownian Dynamics, which do not include hydrodynamics, with those of Stochastic Rotation Dynamics-Molecular Dynamics, which include hydrodynamics. Our results show that ϕc decreases with the increase of the attraction between the colloids. The inclusion of HIs always leads to more elongated structures during the aggregation process, producing a sizable decrease of ϕc when the colloid-colloid attraction is not too strong. On the other hand, the effects of HIs on ϕc tend to become negligible with increasing attraction strength. Our ϕc values are in good agreement with those estimated by the yield stress model by Flatt and Bowen. PMID:26232284

  6. EDITORIAL: Colloidal dispersions in external fields Colloidal dispersions in external fields

    NASA Astrophysics Data System (ADS)

    Löwen, Hartmut

    2012-11-01

    Colloidal dispersions have long been proven as pivotal model systems for equilibrium phase transition such as crystallization, melting and liquid-gas phase transition. The last decades have revealed that this is also true for nonequilibrium phenomena. In fact, the fascinating possibility to track the individual trajectories of colloidal particles has greatly advanced our understanding of collective behaviour in classical many-body systems and has helped to reveal the underlying physical principles of glass transition, crystal nucleation, and interfacial dynamics (to name just a few typical nonequilibrium effects). External fields can be used to bring colloids out of equilibrium in a controlled way. Different kinds of external fields can be applied to colloidal dispersions, namely shear flow, electric, magnetic and laser-optical fields, and confinement. Typical research areas can be sketched with the by now traditional complexity diagram (figure 1). The complexity of the colloidal system itself as embodied in statistical degrees of freedom is shown on the x-axis while the complexity of the problem posed, namely bulk, an inhomogeneity in equilibrium, steady state nonequilibrium and full time-dependent nonequilibrium are shown on the y-axis. The different external fields which can be imposed are indicated by the different hatched areas. figure1 Figure 1. Diagram of complexity for colloidal dispersions in external fields: while the x-axis shows the complexity of the system, the y-axis shows the complexity of the problem. Regions which can be accessed by different kinds of external fields are indicated. The arrows indicate recent research directions. Active particles are also indicated with a special complexity of internal degrees of freedom [1]. This collection of papers reflects the scientific programme of the International Conference on Colloidal Dispersions in External Fields III (CODEF III) which took place in Bonn-Bad Godesberg from 20-23 March 2012. This was the

  7. Regard sur les lazarets en terre canadienne

    PubMed Central

    Milot, Jean

    2008-01-01

    Puisant dans les nombreuses références qu’offrent les publications médicales canadiennes du milieu du XIXe siècle à nos jours, l’auteur fait découvrir l’existence de lazarets en terre canadienne, décrit l’impact de la maladie sur les conditions vie des lépreux qui y étaient confinés et en souligne les contrecoups tant sur le plan physique et psychologique que social. Il présente un bref aperçu de la maladie, ses symptômes, ses signes ainsi que ses complications oculaires et rappelle les premiers moyens thérapeutiques à base d’huile de chaulmoogra introduits dans la colonie de Tracadie vers 1901. Il illustre son propos en évoquant la vie dans les lazarets de l’île de Sheldrake (1844–1848) et de Tracadie (1848–1965) au Nouveau-Brunswick, puis dans ceux des îles D’Arcy (1891–1924) et de Bentinck (1924–1957) en Colombie-Britannique. PMID:19352451

  8. Engineering colloidal assembly via biological adhesion

    NASA Astrophysics Data System (ADS)

    Hiddessen, Amy Lynn

    Due to highly specialized recognition properties, biological receptor-ligand interactions offer valuable tools for engineering the assembly of novel colloidal materials. A unique sub-class of these macromolecules, called selectins, was exploited to develop binary suspensions where particles are programmed to associate reversibly or irreversibly via specific biomolecular cross-linking. Flow cytometry and videomicroscopy were used to examine factors controlling suspension assembly and structure, including biomolecular affinity and density, and individual and total particle volume fractions. By functionalizing small (RA = 0.47 mum) and larger (RB = 2.75 mum) particles with high surface densities of complementary E-selectin/sialyl Lewis X (sLeX) carbohydrate chemistry, a series of structures, from colloidal micelles (large particle coated with smaller particles) and clusters, to rings and elongated chains, was synthesized by decreasing the number ratio, NA/NB, of small (A) to large (B) particles (2 ≤ NA/NB ≤ 200) at low total volume fraction (10-4 ≤ φT ≤ 10-3 ). Using significantly lower surface densities, the low affinity binding between E-selectin and sLeX was exploited to create particles that interact reversibly, and average particle interaction lifetimes were tuned from minutes down to single selectin-carbohydrate bond lifetimes (≈1 s) by reducing sLeX density, a significant step toward assembling ordered microstructures. Particle binding lifetimes were analyzed with a receptor-ligand binding model, yielding estimates for molecular parameters, including on rate, 10-2 s-1 < kon < 10-1 s-1, and unstressed off rate, 0.25 s-1 ≤ kor ≤ 1.0 s-1, that characterize the docking dynamics of particles. Finally, at significantly higher volume fraction (φ T ≥ 10-1) and low number ratio, the rheology of space-filling networks crosslinked by high affinity streptavidin-biotin chemistry was probed to acquire knowledge on bulk properties of biocolloidal suspensions

  9. Colloid Facilitated Transport of Plutonium in Fractured Volcanic Tuff

    NASA Astrophysics Data System (ADS)

    Kersting, A. B.; Zhao, P.; Walensky, J. R.; Roberts, S. K.; Johnson, M. R.; Zavarin, M.; Ramon, E. C.

    2004-12-01

    The transport of low-solubility radionuclides in a colloidal- or colloidal bound state is frequently suspected or observed. Groundwater contaminated with radionuclides associated with underground nuclear tests was collected from several different well locations at the Nevada Test Site (NTS). In each case, the low-levels of plutonium detected in the groundwater were overwhelmingly (>95percent) associated with the colloidal and not the dissolved fraction of the groundwater. The colloidal fractions consisted of secondary minerals such as clays and zeolites. To better understand the mechanisms controlling the potential colloidal transport of plutonium, colloid-facilitated fracture flow laboratory experiments are being conducted. Pseudocolloids consisting of Pu(IV) sorbed to clinoptilolite were combined with a radionuclide solution cocktail consisting of Np, U, Cs, Sr, Sm and 3H and Re (analog to Tc) tracers in NTS-type synthetic groundwater (4.5mM NaHCO3-). The cocktail was injected into a smooth fracture in a volcanic tuff rock core from the NTS and the effluent analyzed. Autoradiography and secondary ion mass spectrometry will be used to understand the mineral -colloid-radionuclide interactions in the fracture volcanic tuff.

  10. Chiral Colloidal Molecules And Observation of The Propeller Effect

    PubMed Central

    2013-01-01

    Chiral molecules play an important role in biological and chemical processes, but physical effects due to their symmetry-breaking are generally weak. Several physical chiral separation schemes which could potentially be useful, including the propeller effect, have therefore not yet been demonstrated at the molecular scale. However, it has been proposed that complex nonspherical colloidal particles could act as “colloidal molecules” in mesoscopic model systems to permit the visualization of molecular phenomena that are otherwise difficult to observe. Unfortunately, it is difficult to synthesize such colloids because surface minimization generally favors the growth of symmetric particles. Here we demonstrate the production of large numbers of complex colloids with glancing angle physical vapor deposition. We use chiral colloids to demonstrate the Baranova and Zel’dovich (BaranovaN. B.Zel’dovichB. Y.Chem. Phys. Lett.1978, 57, 435) propeller effect: the separation of a racemic mixture by application of a rotating field that couples to the dipole moment of the enantiomers and screw propels them in opposite directions. The handedness of the colloidal suspensions is monitored with circular differential light scattering. An exact solution for the colloid’s propulsion is derived, and comparisons between the colloidal system and the corresponding effect at the molecular scale are made. PMID:23883328

  11. Characteristics of colloids generated during the corrosion of nuclear waste glasses in groundwater

    SciTech Connect

    Feng, X.; Buck, E.C.; Mertz, C.; Bates, J.K.; Cunnane, J.C.; Chaiko, D.

    1993-10-01

    Aqueous colloidal suspensions were generated by reacting nuclear waste glasses with groundwater at 90{degrees}C at different ratios of the glass surface area to solution volume (S/V). The colloids have been characterized in terms of size, charge, identity, and stability with respect to salt concentration, pH, and time, by examination using dynamic light scattering, electrophoretic mobility, and transmission electron microscopy. The colloids are predominately produced by precipitation from solution, possibly with contribution from reacted layers that have spallated from the glass. These colloids are silicon-rich minerals. The colloidal suspensions agglomerate when the salinity of the solutions increase. The following implications for modeling the colloidal transport of contaminants have been derived from this study: (1) The sources of the colloids are not only solubility-limited real colloids and the pseudo colloids formed by adsorption of radionuclides onto a groundwater colloid, but also from the spalled surface layers of reacted waste glasses. (2) In a repository, the local environment is likely to be glass-reaction dominated and the salt concentration is likely to be high, leading to rapid colloid agglomeration and settling; thus, colloid transport may be insignificant. (3) If large volumes of groundwater contact the glass reaction site, the precipitated colloids may become resuspended, and colloid transport may become important. (4) Under most conditions, the colloids are negatively charged and will deposit readily on positively charged surfaces. Negatively charged surfaces will, in general, facilitate colloid stability and transport.

  12. Study on Colloidal Model of Petroleum Residues through the Attraction Potential between Colloids

    PubMed Central

    Zhang, Long-li; Yang, Guo-hua; Yang, Chao-he; Que, Guo-he

    2016-01-01

    The samples of DaGang atmospheric residue (DG-AR), Middle East atmospheric residue (ME-AR), TaHe atmospheric residue (TH-AR), and their thermal reaction samples were chosen for study. All the samples were fractioned into six components separately, including saturates plus light aromatics, heavy aromatics, light resins, middle resins, heavy resins, and asphaltenes. The dielectric permittivity of the solutions of these components was measured, and the dielectric permittivity values of the components can be determined by extrapolation, which increased steadily from saturates plus light aromatics to asphaltenes. Moreover, the Hamaker constants of the components were calculated from their dielectric permittivity values. The Van der Waals attractive potential energy between colloids corresponding to various models could be calculated from the fractional composition and the Hamaker constants of every component. It was assumed that the cores of colloidal particles were formed by asphaltenes and heavy resins mainly; the other fractions acted as dispersion medium. For the three serials of thermal reaction samples, the Van der Waals attraction potential energy between colloids for this kind of model was calculated. For TH-AR thermal reaction samples, the Van der Waals attraction potential energy presented the maximum as thermal reaction is going on, which was near to the end of coke induction period. PMID:27274729

  13. Study on Colloidal Model of Petroleum Residues through the Attraction Potential between Colloids.

    PubMed

    Zhang, Long-Li; Yang, Guo-Hua; Yang, Chao-He; Que, Guo-He

    2016-01-01

    The samples of DaGang atmospheric residue (DG-AR), Middle East atmospheric residue (ME-AR), TaHe atmospheric residue (TH-AR), and their thermal reaction samples were chosen for study. All the samples were fractioned into six components separately, including saturates plus light aromatics, heavy aromatics, light resins, middle resins, heavy resins, and asphaltenes. The dielectric permittivity of the solutions of these components was measured, and the dielectric permittivity values of the components can be determined by extrapolation, which increased steadily from saturates plus light aromatics to asphaltenes. Moreover, the Hamaker constants of the components were calculated from their dielectric permittivity values. The Van der Waals attractive potential energy between colloids corresponding to various models could be calculated from the fractional composition and the Hamaker constants of every component. It was assumed that the cores of colloidal particles were formed by asphaltenes and heavy resins mainly; the other fractions acted as dispersion medium. For the three serials of thermal reaction samples, the Van der Waals attraction potential energy between colloids for this kind of model was calculated. For TH-AR thermal reaction samples, the Van der Waals attraction potential energy presented the maximum as thermal reaction is going on, which was near to the end of coke induction period. PMID:27274729

  14. Solvent wrapped metastable colloidal crystals: highly mutable colloidal assemblies sensitive to weak external disturbance.

    PubMed

    Yang, Dongpeng; Ye, Siyun; Ge, Jianping

    2013-12-11

    Solvent wrapped "metastable" crystalline colloidal arrays (CCAs) have been prepared by supersaturation induced precipitation and self-assembly of monodisperse particles in polar/nonpolar organic solvents. These metastable CCAs possess ordered structures but with less stability comparing with traditionally fixed colloidal crystal systems. They are stabilized by the balance between long-range attraction and electrostatic repulsion of neighboring like-charged particles. Monitoring the reflection intensity during evaporation suggests that these crystals can exist for several hours at 90 °C and even longer at room temperature. Based on the evolution of particle volume fraction in whole suspension (φ(SiO2)), crystal phase (φ(crystal)), and liquid phase (φ(liquid)), the formation of metastable CCAs can be understood as a microscopic phase separation process, where the homogeneous dispersion will separate into a "crystal phase" with orderly stacked particles and a "liquid phase" with randomly dispersed particles. Further calculation of the volume fraction of crystal phase (V(crystal)/V(total)) and the ratio of particles in crystal phase (f(crystal)) shows that with the increase of designed Φ(SiO2), more particles precipitate to form colloidal crystals with larger sizes but the lattice spacing of the microcrystals remains constant. Unlike fixed or traditional responsive CCAs, these metastable CCAs can reversibly assemble and disassemble with great ease, because little energy is involved or required in this transformation. Therefore, they can sense weak external disturbances, including subtle motion and slight friction or shearing forces. PMID:24266836

  15. Colloidal stability and chemical reactivity of complex colloids containing Fe³⁺.

    PubMed

    van Leeuwen, Y M; Velikov, K P; Kegel, W K

    2014-07-15

    The reactivity of iron contained within insoluble colloidal metal-pyrophosphate salts was determined and compared to the reactivity of a soluble iron salt (FeCl3). As a model system for the reactivity of iron in food products, the formation of an iron-polyphenol complex was followed with spectrophotometry. Three types of systems were prepared and their colloidal stability and reactivity studied: Fe(3+) pyrophosphate, protein-coated Fe(3+) pyrophosphate and mixed-metal pyrophosphates containing Fe(3+) and a second cation M. The additional cation used was either monovalent (sodium) or divalent (M(2+)). It was found that: (i) incorporating iron in a colloidal salt reduced its reactivity compared to free Fe(3+) ions; (ii) coating the particles with a layer of hydrophobic protein (zein) increased stability and further decreased the reactivity. Finally, the most surprising result was that (iii) a mixed system containing more Fe(3+) than M actually increased the reactivity of the contained iron, while the reverse, a system containing excess M, inhibited the reactivity completely. PMID:24594169

  16. Colloidal Nanoantennas for Hyperspectral Chemical Mapping.

    PubMed

    Dill, Tyler J; Rozin, Matthew J; Palani, Stephen; Tao, Andrea R

    2016-08-23

    Tip-enhanced Raman spectroscopy enables access to chemical information with nanoscale spatial resolution and single-molecule sensitivities by utilizing optical probes that are capable of confining light to subwavelength dimensions. Because the probes themselves possess nanoscale features, they are notoriously difficult to fabricate, and more critically, can result in poor reproducibility. Here, we demonstrate high-performance, predictable, and readily tunable nanospectroscopy probes that are fabricated by self-assembly. Shaped metal nanoparticles are organized into dense layers and deposited onto scanning probe tips. When coupled to a metal surface, these probes behave like nanoantenna by supporting a strong optical resonance, producing dramatic Raman field enhancements in the range of 10(8)-10(9) with sub-50 nm spatial resolution. In contrast to other nanospectroscopy probes, our colloidal probes can be fabricated in a scalable fashion with a batch-to-batch reproducibility of ∼80% and serve as an important demonstration of bottom-up engineering. PMID:27454680

  17. Emergent vortices in populations of colloidal rollers

    PubMed Central

    Bricard, Antoine; Caussin, Jean-Baptiste; Das, Debasish; Savoie, Charles; Chikkadi, Vijayakumar; Shitara, Kyohei; Chepizhko, Oleksandr; Peruani, Fernando; Saintillan, David; Bartolo, Denis

    2015-01-01

    Coherent vortical motion has been reported in a wide variety of populations including living organisms (bacteria, fishes, human crowds) and synthetic active matter (shaken grains, mixtures of biopolymers), yet a unified description of the formation and structure of this pattern remains lacking. Here we report the self-organization of motile colloids into a macroscopic steadily rotating vortex. Combining physical experiments and numerical simulations, we elucidate this collective behaviour. We demonstrate that the emergent-vortex structure lives on the verge of a phase separation, and single out the very constituents responsible for this state of polar active matter. Building on this observation, we establish a continuum theory and lay out a strong foundation for the description of vortical collective motion in a broad class of motile populations constrained by geometrical boundaries. PMID:26088835

  18. MOLECULAR DESIGN OF COLLOIDS IN SUPERCRITICAL FLUIDS

    SciTech Connect

    Keith P. Johnston

    2009-04-06

    The environmentally benign, non-toxic, non-flammable fluids water and carbon dioxide (CO2) are the two most abundant and inexpensive solvents on earth. Emulsions of these fluids are of interest in many industrial processes, as well as CO2 sequestration and enhanced oil recovery. Until recently, formation of these emulsions required stabilization with fluorinated surfactants, which are expensive and often not environmentally friendly. In this work we overcame this severe limitation by developing a fundamental understanding of the properties of surfactants the CO2-water interface and using this knowledge to design and characterize emulsions stabilized with either hydrocarbon-based surfactants or nanoparticle stabilizers. We also discovered a new concept of electrostatic stabilization for CO2-based emulsions and colloids. Finally, we were able to translate our earlier work on the synthesis of silicon and germanium nanocrystals and nanowires from high temperatures and pressures to lower temperatures and ambient pressure to make the chemistry much more accessible.

  19. Dips and rims in dried colloidal films.

    PubMed

    Parneix, C; Vandoolaeghe, P; Nikolayev, V S; Quéré, D; Li, J; Cabane, B

    2010-12-31

    We describe a spatial pattern arising from the nonuniform evaporation of a colloidal film. Immediately after the film deposition, an obstacle is positioned above its free surface, minimizing evaporation at this location. In a first stage, the film dries everywhere but under the obstacle, where a liquid region remains. Subsequently, this liquid region evaporates near its boundaries with the dry film. This loss of water causes a flow of liquid and particles from the center of the obstructed region to its periphery. The final film has a dip surrounded by a rim whose diameter is set by the obstacle. This turns out to be a simple technique for structuring films of nanometric thickness. PMID:21231686

  20. Aqueous Black Colloids of Reticular Nanostructured Gold

    NASA Astrophysics Data System (ADS)

    Stanca, S. E.; Fritzsche, W.; Dellith, J.; Froehlich, F.; Undisz, A.; Deckert, V.; Krafft, C.; Popp, J.

    2015-01-01

    Since ancient times, noble gold has continuously contributed to several aspects of life from medicine to electronics. It perpetually reveals its new features. We report the finding of a unique form of gold, reticular nanostructured gold (RNG), as an aqueous black colloid, for which we present a one-step synthesis. The reticules consist of gold crystals that interconnect to form compact strands. RNG exhibits high conductivity and low reflection, and these features, coupled with the high specific surface area of the material, could prove valuable for applications in electronics and catalysis. Due to high absorption throughout the visible and infrared domain, RNG has the potential to be applied in the construction of sensitive solar cells or as a substrate for Raman spectroscopy.

  1. Hardening and yielding in colloidal gels

    NASA Astrophysics Data System (ADS)

    Del Gado, Emanuela; Colombo, Jader; Bouzid, Mehdi

    Attractive colloidal gel networks are disordered elastic solids that can form even in extremely dilute particle suspensions. With interaction strengths comparable to the thermal energy, their stress-bearing network can locally restructure via breaking and reforming inter-particle bonds. We use molecular dynamics simulations of a model system to investigate the strain hardening and the yielding process. During shear start up protocol, the system exhibits strong localization of tensile stresses that may be released through the breaking and formation of new bonds. In this regime, the small amplitude oscillatory shear analysis shows that the storage and the loss modulus follow a power law behavior that are closely reminiscent of experimental observations. At large accumulated strains, the strain-induced reorganization of the gel may trigger flow heterogeneities and eventually lead to the yielding of the gel via a quasi brittle damage of its structure.

  2. Binding kinetics of lock and key colloids.

    PubMed

    Colón-Meléndez, Laura; Beltran-Villegas, Daniel J; van Anders, Greg; Liu, Jun; Spellings, Matthew; Sacanna, Stefano; Pine, David J; Glotzer, Sharon C; Larson, Ronald G; Solomon, Michael J

    2015-05-01

    Using confocal microscopy and first passage time analysis, we measure and predict the rates of formation and breakage of polymer-depletion-induced bonds between lock-and-key colloidal particles and find that an indirect route to bond formation is accessed at a rate comparable to that of the direct formation of these bonds. In the indirect route, the pocket of the lock particle is accessed by nonspecific bonding of the key particle with the lock surface, followed by surface diffusion leading to specific binding in the pocket of the lock. The surprisingly high rate of indirect binding is facilitated by its high entropy relative to that of the pocket. Rate constants for forward and reverse transitions among free, nonspecific, and specific bonds are reported, compared to theoretical values, and used to determine the free energy difference between the nonspecific and specific binding states. PMID:25956122

  3. Magnetic Separation Dynamics of Colloidal Magnetic Nanoparticles

    SciTech Connect

    Kaur, M.; Huijin Zhang,; You Qiang,

    2013-01-01

    Surface functionalized magnetic nanoparticles (MNPs) are appealing candidates for analytical separation of heavy metal ions from waste water and separation of actinides from spent nuclear fuel. This work studies the separation dynamics and investigates the appropriate magnetic-field gradients. A dynamic study of colloidal MNPs was performed for steady-state flow. Measurements were conducted to record the separation time of particles as a function of magnetic field gradient. The drag and magnetic forces play a significant role on the separation time. A drop in saturation magnetization and variation of particle size occurs after surface functionalization of the MNPs; these are the primary factors that affect the separation time and velocity of the MNPs. The experimental results are correlated to a theoretical one-dimensional model.

  4. Emergent vortices in populations of colloidal rollers.

    PubMed

    Bricard, Antoine; Caussin, Jean-Baptiste; Das, Debasish; Savoie, Charles; Chikkadi, Vijayakumar; Shitara, Kyohei; Chepizhko, Oleksandr; Peruani, Fernando; Saintillan, David; Bartolo, Denis

    2015-01-01

    Coherent vortical motion has been reported in a wide variety of populations including living organisms (bacteria, fishes, human crowds) and synthetic active matter (shaken grains, mixtures of biopolymers), yet a unified description of the formation and structure of this pattern remains lacking. Here we report the self-organization of motile colloids into a macroscopic steadily rotating vortex. Combining physical experiments and numerical simulations, we elucidate this collective behaviour. We demonstrate that the emergent-vortex structure lives on the verge of a phase separation, and single out the very constituents responsible for this state of polar active matter. Building on this observation, we establish a continuum theory and lay out a strong foundation for the description of vortical collective motion in a broad class of motile populations constrained by geometrical boundaries. PMID:26088835

  5. 'Thermal forces': colloids in temperature gradients

    NASA Astrophysics Data System (ADS)

    Piazza, Roberto

    2004-09-01

    In the presence of a thermal gradient, macromolecular solutes or dispersed particles drift to the cold or to the hot side: this effect is known as thermophoresis, and is the counterpart of particle suspensions of the Soret effect (or thermal diffusion) in simple fluid mixtures. Here I review recent experimental results on colloid thermophoresis and present new data suggesting a universal nature for the temperature dependence of thermophoresis in aqueous systems. There are strong analogies between thermophoresis in liquids and other thermally induced flow processes like gas thermal creep and membrane thermo-osmosis; starting from these, I present some guidelines for a general model of thermophoresis in disperse systems, accounting both for single-particle and collective effects.

  6. Brownian diffusion of a partially wetted colloid

    NASA Astrophysics Data System (ADS)

    Boniello, Giuseppe; Blanc, Christophe; Fedorenko, Denys; Medfai, Mayssa; Mbarek, Nadia Ben; in, Martin; Gross, Michel; Stocco, Antonio; Nobili, Maurizio

    2015-09-01

    The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories suggests that such dynamics is governed by a viscous force lower than that observed in the more viscous fluid. Here, we show experimentally that a particle straddling an air/water interface feels a large viscous drag that is unexpectedly larger than that measured in the bulk. We suggest that such a result arises from thermally activated fluctuations of the interface at the solid/air/liquid triple line and their coupling to the particle drag through the fluctuation-dissipation theorem. Our findings should inform approaches for improved control of the kinetically driven assembly of anisotropic particles with a large triple-line-length/particle-size ratio, and help to understand the formation and structure of such arrested materials.

  7. Brownian diffusion of a partially wetted colloid.

    PubMed

    Boniello, Giuseppe; Blanc, Christophe; Fedorenko, Denys; Medfai, Mayssa; Mbarek, Nadia Ben; In, Martin; Gross, Michel; Stocco, Antonio; Nobili, Maurizio

    2015-09-01

    The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories suggests that such dynamics is governed by a viscous force lower than that observed in the more viscous fluid. Here, we show experimentally that a particle straddling an air/water interface feels a large viscous drag that is unexpectedly larger than that measured in the bulk. We suggest that such a result arises from thermally activated fluctuations of the interface at the solid/air/liquid triple line and their coupling to the particle drag through the fluctuation-dissipation theorem. Our findings should inform approaches for improved control of the kinetically driven assembly of anisotropic particles with a large triple-line-length/particle-size ratio, and help to understand the formation and structure of such arrested materials. PMID:26147846

  8. Cooperative polymerization of one-patch colloids

    SciTech Connect

    Vissers, Teun; Smallenburg, Frank; Munaò, Gianmarco; Preisler, Zdeněk; Sciortino, Francesco

    2014-04-14

    We numerically investigate cooperative polymerization in an off-lattice model based on a pairwise additive potential using particles with a single attractive patch that covers 30% of the colloid surface. Upon cooling, these particles self-assemble into small clusters which, below a density-dependent temperature, spontaneously reorganize into long straight tubes. We evaluate the partition functions of clusters of all sizes to provide an accurate description of the chemical reaction constants governing this process. Our calculations show that, for intermediate sizes, the partition functions retain contributions from two different structures, differing in both energy and entropy. We illustrate the microscopic mechanism behind the complex polymerization process in this system and provide a detailed evaluation of its thermodynamics.

  9. Imbibition kinetics of spherical colloidal aggregates.

    PubMed

    Debacker, A; Makarchuk, S; Lootens, D; Hébraud, P

    2014-07-11

    The imbibition kinetics of a millimeter-sized aggregate of 300 nm diameter colloidal particles by a wetting pure solvent is studied. Three successive regimes are observed. First, the imbibition proceeds by compressing the air inside the aggregate. Next, the solvent stops when the pressure of the compressed air is equal to the excess of capillary pressure at the meniscus of the wetting solvent in the porous aggregate. The interface is pinned and the aggregate slowly degases up to the point where the pressure of the entrapped air stops decreasing and is controlled by the capillary pressure. Finally, the imbibition starts again at a constant excess of pressure, smaller than the capillary pressure but larger than the one of the atmosphere. This last stage leads to the complete infiltration of the aggregate. PMID:25062241

  10. Thermoelectricity and thermodiffusion in charged colloids.

    PubMed

    Huang, B T; Roger, M; Bonetti, M; Salez, T J; Wiertel-Gasquet, C; Dubois, E; Cabreira Gomes, R; Demouchy, G; Mériguet, G; Peyre, V; Kouyaté, M; Filomeno, C L; Depeyrot, J; Tourinho, F A; Perzynski, R; Nakamae, S

    2015-08-01

    The Seebeck and Soret coefficients of ionically stabilized suspension of maghemite nanoparticles in dimethyl sulfoxide are experimentally studied as a function of nanoparticle volume fraction. In the presence of a temperature gradient, the charged colloidal nanoparticles experience both thermal drift due to their interactions with the solvent and electric forces proportional to the internal thermoelectric field. The resulting thermodiffusion of nanoparticles is observed through forced Rayleigh scattering measurements, while the thermoelectric field is accessed through voltage measurements in a thermocell. Both techniques provide independent estimates of nanoparticle's entropy of transfer as high as 82 meV K(-1). Such a property may be used to improve the thermoelectric coefficients in liquid thermocells. PMID:26254665

  11. Aqueous Black Colloids of Reticular Nanostructured Gold

    PubMed Central

    Stanca, S. E.; Fritzsche, W.; Dellith, J.; Froehlich, F.; Undisz, A.; Deckert, V.; Krafft, C.; Popp, J.

    2015-01-01

    Since ancient times, noble gold has continuously contributed to several aspects of life from medicine to electronics. It perpetually reveals its new features. We report the finding of a unique form of gold, reticular nanostructured gold (RNG), as an aqueous black colloid, for which we present a one-step synthesis. The reticules consist of gold crystals that interconnect to form compact strands. RNG exhibits high conductivity and low reflection, and these features, coupled with the high specific surface area of the material, could prove valuable for applications in electronics and catalysis. Due to high absorption throughout the visible and infrared domain, RNG has the potential to be applied in the construction of sensitive solar cells or as a substrate for Raman spectroscopy. PMID:25600497

  12. Synthesis of colloidal uranium-dioxide nanocrystals.

    PubMed

    Wu, Huimeng; Yang, Yongan; Cao, Y Charles

    2006-12-27

    In this paper, we have developed an organic-phase synthesis method for producing size-controlled, nearly monodispersed, colloidal uranium-dioxide nanocrystals. These UO2 nanocrystals are potentially important to applications such as nuclear fuel materials, catalysts, and thermopower materials. In addition, we have systematically mapped out the functions of the solvents (oleic acid, oleylamine, and 1-octadecene) in the synthesis, and we found that N-(cis-9-octadecenyl)oleamide-a product of the condensation of oleic acid and oleylamine-can substantially affect the formation of UO2 nanocrystals. Importantly, these results provide fundamental insight into the mechanisms of UO2 nanocrystal synthesis. Moreover, because a mixture of oleic acid and oleylamine has been widely used in synthesizing a variety of high-quality metal or metal-oxide nanocrystals, the results herein should also be important for understanding the detailed mechanisms of these syntheses. PMID:17177400

  13. Active colloids that slosh through passive matrices

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Granick, Steve

    Studies of natural and artificial active matter have focused on systems with a large mismatch of the time and length scales for active and passive elements, but in a variety of non-equilibrium condensed matter systems, including numerous biological processes, actively driven elements have a crowded environment of surrounding passive ``solvent'' elements of comparable size. Here we study self-propelled colloidal particles in a passive matrix of comparable size. Particles with high activity take straight lines and sharp turns through the soft 2-D crystal matrix to ensure rapid healing of the crystal structure. Effective attraction between active particles arises when the concentration of active particles or the hardness of the matrix increases; active particles tend to segregate in the grain boundaries of the crystal matrix.

  14. Multimodal Plasmonics in Fused Colloidal Networks

    PubMed Central

    Teulle, Alexandre; Bosman, Michel; Girard, Christian; Gurunatha, Kargal L.; Li, Mei; Mann, Stephen; Dujardin, Erik

    2014-01-01

    Harnessing the optical properties of noble metals down to the nanometer-scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon (SP) properties must be controlled with a challenging high level of precision. Here, we demonstrate that ultimate lateral confinement and delocalization of SP modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the SP modes associated with the colloidal superstructures are evidenced by performing monochromated electron energy loss spectroscopy with a nanometer-sized electron probe. We prepare the metallic bead strings by electron beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphology and crystallinity but develop very low energy SP modes that are capable of supporting long range and spectrally tunable propagation in nanoscale waveguides. PMID:25344783

  15. Metastable orientational order of colloidal discoids

    PubMed Central

    Hsiao, Lilian C.; Schultz, Benjamin A.; Glaser, Jens; Engel, Michael; Szakasits, Megan E.; Glotzer, Sharon C.; Solomon, Michael J.

    2015-01-01

    The interplay between phase separation and kinetic arrest is important in supramolecular self-assembly, but their effects on emergent orientational order are not well understood when anisotropic building blocks are used. Contrary to the typical progression from disorder to order in isotropic systems, here we report that colloidal oblate discoids initially self-assemble into short, metastable strands with orientational order—regardless of the final structure. The model discoids are suspended in a refractive index and density-matched solvent. Then, we use confocal microscopy experiments and Monte Carlo simulations spanning a broad range of volume fractions and attraction strengths to show that disordered clusters form near coexistence boundaries, whereas oriented strands persist with strong attractions. We rationalize this unusual observation in light of the interaction anisotropy imparted by the discoids. These findings may guide self-assembly for anisotropic systems in which orientational order is desired, such as when tailored mechanical properties are sought. PMID:26443082

  16. Building devices from colloidal quantum dots.

    PubMed

    Kagan, Cherie R; Lifshitz, Efrat; Sargent, Edward H; Talapin, Dmitri V

    2016-08-26

    The continued growth of mobile and interactive computing requires devices manufactured with low-cost processes, compatible with large-area and flexible form factors, and with additional functionality. We review recent advances in the design of electronic and optoelectronic devices that use colloidal semiconductor quantum dots (QDs). The properties of materials assembled of QDs may be tailored not only by the atomic composition but also by the size, shape, and surface functionalization of the individual QDs and by the communication among these QDs. The chemical and physical properties of QD surfaces and the interfaces in QD devices are of particular importance, and these enable the solution-based fabrication of low-cost, large-area, flexible, and functional devices. We discuss challenges that must be addressed in the move to solution-processed functional optoelectronic nanomaterials. PMID:27563099

  17. Aging dynamics of colloidal hard sphere glasses.

    PubMed

    Martinez, V A; Bryant, G; van Megen, W

    2010-09-21

    We report the results of dynamic light scattering measurements of the coherent intermediate scattering function (ISF) of glasses of colloidal hard spheres for several volume fractions and a range of scattering vectors around the primary peak of the static structure factor. The ISF shows a clear crossover from an initial fast decay to a slower nonstationary decay. Aging is quantified in several different ways. However, regardless of the method chosen, the perfect "aged" glass is approached in a power law fashion. In particular the coupling between the fast and slow decays, as measured by the degree of stretching of the ISF at the crossover, also decreases algebraically with waiting time. The nonstationarity of this coupling implies that even the fastest detectable processes are themselves nonstationary. PMID:20866156

  18. Luminescence upconversion in colloidal double quantum dots.

    PubMed

    Deutsch, Zvicka; Neeman, Lior; Oron, Dan

    2013-09-01

    Luminescence upconversion nanocrystals capable of converting two low-energy photons into a single photon at a higher energy are sought-after for a variety of applications, including bioimaging and photovoltaic light harvesting. Currently available systems, based on rare-earth-doped dielectrics, are limited in both tunability and absorption cross-section. Here we present colloidal double quantum dots as an alternative nanocrystalline upconversion system, combining the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. By tailoring its composition and morphology, we form a semiconducting nanostructure in which excited electrons are delocalized over the entire structure, but a double potential well is formed for holes. Upconversion occurs by excitation of an electron in the lower energy transition, followed by intraband absorption of the hole, allowing it to cross the barrier to a higher energy state. An overall conversion efficiency of 0.1% per double excitation event is achieved. PMID:23912060

  19. Reentrant network formation in patchy colloidal mixtures under gravity

    NASA Astrophysics Data System (ADS)

    de las Heras, Daniel; Treffenstädt, Lucas L.; Schmidt, Matthias

    2016-03-01

    We study a two-dimensional binary mixture of patchy colloids in sedimentation-diffusion equilibrium using Monte Carlo simulation and Wertheim's theory. By tuning the buoyant masses of the colloids we can control the gravity-induced sequence of fluid stacks of differing density and percolation properties. We find complex stacking sequences with up to four layers and reentrant network formation, consistently in simulations and theoretically using only the bulk phase diagram as input. Our theory applies to general patchy colloidal mixtures and is relevant to understanding experiments under gravity.

  20. Electric double layer of anisotropic dielectric colloids under electric fields

    NASA Astrophysics Data System (ADS)

    Han, M.; Wu, H.; Luijten, E.

    2016-07-01

    Anisotropic colloidal particles constitute an important class of building blocks for self-assembly directed by electrical fields. The aggregation of these building blocks is driven by induced dipole moments, which arise from an interplay between dielectric effects and the electric double layer. For particles that are anisotropic in shape, charge distribution, and dielectric properties, calculation of the electric double layer requires coupling of the ionic dynamics to a Poisson solver. We apply recently proposed methods to solve this problem for experimentally employed colloids in static and time-dependent electric fields. This allows us to predict the effects of field strength and frequency on the colloidal properties.

  1. Colloid-in-Liquid Crystal Gels Formed via Spinodal Decomposition

    PubMed Central

    Pal, Santanu Kumar; de Pablo, Juan J.

    2014-01-01

    We report that colloid-in-liquid crystal (CLC) gels can be formed via a two-step process that involves spinodal decomposition of a dispersion of colloidal particles in an isotropic phase of mesogens followed by nucleation of nematic domains within the colloidal network defined by the spinodal process. This pathway contrasts to previously reported routes leading to the formation of CLC gels, which have involved entanglement of defects or exclusion of particles from growing nematic domains. The new route provides the basis of simple design rules that enable control of the microstructure and dynamic mechanical properties of the gels. PMID:24651134

  2. Swelling-based method for preparing stable, functionalized polymer colloids.

    PubMed

    Kim, Anthony J; Manoharan, Vinothan N; Crocker, John C

    2005-02-16

    We describe a swelling-based method to prepare sterically stabilized polymer colloids with different functional groups or biomolecules attached to their surface. It should be applicable to a variety of polymeric colloids, including magnetic particles, fluorescent particles, polystyrene particles, PMMA particles, and so forth. The resulting particles are more stable in the presence of monovalent and divalent salt than existing functionalized colloids, even in the absence of any surfactant or protein blocker. While we use a PEG polymer brush here, the method should enable the use of a variety of polymer chemistries and molecular weights. PMID:15700965

  3. Photophysics and photochemistry of quantized ZnO colloids

    SciTech Connect

    Kamat, P.V.; Patrick, B.

    1992-08-06

    The photophysical and photochemical behavior of quantized ZnO colloids in ethanol has been investigated by time-resolved transient absorption and emission measurements. Trapping of electrons at the ZnO surface resulted in broad absorption in the red region. The green emission of ZnO colloids was readily quenched by hole scavengers such as SCN{sup -} and I{sup -}. The photoinduced charge transfer to these hole scavengers was studied by laser flash photolysis. The yield of oxidized product increased considerably when ZnO colloids were coupled with ZnSe. 36 refs., 11 figs., 1 tab.

  4. Does Shining Light on Gold Colloids Influence Aggregation?

    PubMed Central

    Bhattacharya, Susmita; Narasimha, Suda; Roy, Anushree; Banerjee, Soumitro

    2014-01-01

    In this article we revisit the much-studied behavior of self-assembled aggregates of gold colloidal particles. In the literature, the electrostatic interactions, van der Waals interactions, and the change in free energy due to ligand-ligand or ligand-solvent interactions are mainly considered to be the dominating factors in determining the characteristics of the gold aggregates. However, our light scattering and imaging experiments clearly indicate a distinct effect of light in the growth structure of the gold colloidal particles. We attribute this to the effect of a non-uniform distribution of the electric field in aggregated gold colloids under the influence of light. PMID:24909824

  5. Binary Colloidal Alloy Test-5: Three-Dimensional Melt

    NASA Technical Reports Server (NTRS)

    Yodh, Arjun G.

    2008-01-01

    Binary Colloidal Alloy Test - 5: Three-Dimensional Melt (BCAT-5-3DMelt) photographs initially randomized colloidal samples in microgravity to determine their resulting structure over time. BCAT-5-3D-Melt will allow the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-3D-Melt will look at the mechanisms of melting using three-dimensional temperature sensitive colloidal crystals. Results will help scientists develop fundamental physics concepts previously shadowed by the effects of gravity.

  6. The dynamical crossover in attractive colloidal systems

    SciTech Connect

    Mallamace, Francesco; Corsaro, Carmelo; Stanley, H. Eugene; Mallamace, Domenico; Chen, Sow-Hsin

    2013-12-07

    We study the dynamical arrest in an adhesive hard-sphere colloidal system. We examine a micellar suspension of the Pluronic-L64 surfactant in the temperature (T) and volume fraction (ϕ) phase diagram. According to mode-coupling theory (MCT), this system is characterized by a cusp-like singularity and two glassy phases: an attractive glass (AG) phase and a repulsive glass (RG) phase. The T − ϕ phase diagram of this system as confirmed by a previous series of scattering data also exhibits a Percolation Threshold (PT) line, a reentrant behavior (AG-liquid-RG), and a glass-to-glass transition. The AG phase can be generated out of the liquid phase by using T and ϕ as control parameters. We utilize viscosity and nuclear magnetic resonance (NMR) techniques. NMR data confirm all the characteristic properties of the colloidal system phase diagram and give evidence of the onset of a fractal-like percolating structure at a precise threshold. The MCT scaling laws used to study the shear viscosity as a function of ϕ and T show in both cases a fragile-to-strong liquid glass-forming dynamic crossover (FSC) located near the percolation threshold where the clustering process is fully developed. These results suggest a larger thermodynamic generality for this phenomenon, which is usually studied only as a function of the temperature. We also find that the critical values of the control parameters, coincident with the PT line, define the locus of the FSC. In the region between the FSC and the glass transition lines the system dynamics are dominated by clustering effects. We thus demonstrate that it is possible, using the conceptual framework provided by extended mode-coupling theory, to describe the way a system approaches dynamic arrest, taking into account both cage and hopping effects.

  7. The dynamical crossover in attractive colloidal systems

    NASA Astrophysics Data System (ADS)

    Mallamace, Francesco; Corsaro, Carmelo; Stanley, H. Eugene; Mallamace, Domenico; Chen, Sow-Hsin

    2013-12-01

    We study the dynamical arrest in an adhesive hard-sphere colloidal system. We examine a micellar suspension of the Pluronic-L64 surfactant in the temperature (T) and volume fraction (ϕ) phase diagram. According to mode-coupling theory (MCT), this system is characterized by a cusp-like singularity and two glassy phases: an attractive glass (AG) phase and a repulsive glass (RG) phase. The T - ϕ phase diagram of this system as confirmed by a previous series of scattering data also exhibits a Percolation Threshold (PT) line, a reentrant behavior (AG-liquid-RG), and a glass-to-glass transition. The AG phase can be generated out of the liquid phase by using T and ϕ as control parameters. We utilize viscosity and nuclear magnetic resonance (NMR) techniques. NMR data confirm all the characteristic properties of the colloidal system phase diagram and give evidence of the onset of a fractal-like percolating structure at a precise threshold. The MCT scaling laws used to study the shear viscosity as a function of ϕ and T show in both cases a fragile-to-strong liquid glass-forming dynamic crossover (FSC) located near the percolation threshold where the clustering process is fully developed. These results suggest a larger thermodynamic generality for this phenomenon, which is usually studied only as a function of the temperature. We also find that the critical values of the control parameters, coincident with the PT line, define the locus of the FSC. In the region between the FSC and the glass transition lines the system dynamics are dominated by clustering effects. We thus demonstrate that it is possible, using the conceptual framework provided by extended mode-coupling theory, to describe the way a system approaches dynamic arrest, taking into account both cage and hopping effects.

  8. The dynamical crossover in attractive colloidal systems.

    PubMed

    Mallamace, Francesco; Corsaro, Carmelo; Stanley, H Eugene; Mallamace, Domenico; Chen, Sow-Hsin

    2013-12-01

    We study the dynamical arrest in an adhesive hard-sphere colloidal system. We examine a micellar suspension of the Pluronic-L64 surfactant in the temperature (T) and volume fraction (φ) phase diagram. According to mode-coupling theory (MCT), this system is characterized by a cusp-like singularity and two glassy phases: an attractive glass (AG) phase and a repulsive glass (RG) phase. The T - φ phase diagram of this system as confirmed by a previous series of scattering data also exhibits a Percolation Threshold (PT) line, a reentrant behavior (AG-liquid-RG), and a glass-to-glass transition. The AG phase can be generated out of the liquid phase by using T and φ as control parameters. We utilize viscosity and nuclear magnetic resonance (NMR) techniques. NMR data confirm all the characteristic properties of the colloidal system phase diagram and give evidence of the onset of a fractal-like percolating structure at a precise threshold. The MCT scaling laws used to study the shear viscosity as a function of φ and T show in both cases a fragile-to-strong liquid glass-forming dynamic crossover (FSC) located near the percolation threshold where the clustering process is fully developed. These results suggest a larger thermodynamic generality for this phenomenon, which is usually studied only as a function of the temperature. We also find that the critical values of the control parameters, coincident with the PT line, define the locus of the FSC. In the region between the FSC and the glass transition lines the system dynamics are dominated by clustering effects. We thus demonstrate that it is possible, using the conceptual framework provided by extended mode-coupling theory, to describe the way a system approaches dynamic arrest, taking into account both cage and hopping effects. PMID:24320386

  9. Anomalous columnar order of charged colloidal platelets.

    PubMed

    Morales-Anda, L; Wensink, H H; Galindo, A; Gil-Villegas, A

    2012-01-21

    Monte Carlo computer simulations are carried out for a model system of like-charged colloidal platelets in the isothermal-isobaric ensemble (NpT). The aim is to elucidate the role of electrostatic interactions on the structure of synthetic clay systems at high particle densities. Short-range repulsions between particles are described by a suitable hard-core model representing a discotic particle. This potential is supplemented with an electrostatic potential based on a Yukawa model for the screened Coulombic potential between infinitely thin disklike macro-ions. The particle aspect-ratio and electrostatic parameters were chosen to mimic an aqueous dispersion of thin, like-charged, rigid colloidal platelets at finite salt concentration. An examination of the fluid phase diagram reveals a marked shift in the isotropic-nematic transition compared to the hard cut-sphere reference system. Several statistical functions, such as the pair correlation function for the center-of-mass coordinates and structure factor, are obtained to characterize the structural organization of the platelets phases. At low salinity and high osmotic pressure we observe anomalous hexagonal columnar structures characterized by interpenetrating columns with a typical intercolumnar distance corresponding to about half of that of a regular columnar phase. Increasing the ionic strength leads to the formation of glassy, disordered structures consisting of compact clusters of platelets stacked into finite-sized columns. These so-called "nematic columnar" structures have been recently observed in systems of charge-stabilized gibbsite platelets. Our findings are corroborated by an analysis of the static structure factor from a simple density functional theory. PMID:22280777

  10. Liquid-vapor interfaces of patchy colloids

    NASA Astrophysics Data System (ADS)

    Oleksy, A.; Teixeira, P. I. C.

    2015-01-01

    We investigate the liquid-vapor interface of a model of patchy colloids. This model consists of hard spheres decorated with short-ranged attractive sites ("patches") of different types on their surfaces. We focus on a one-component fluid with two patches of type A and nine patches of type B (2 A 9 B colloids), which has been found to exhibit reentrant liquid-vapor coexistence curves and very low-density liquid phases. We have used the density-functional theory form of Wertheim's first-order perturbation theory of association, as implemented by Yu and Wu [J. Chem. Phys. 116, 7094 (2002), 10.1063/1.1463435], to calculate the surface tension, and the density and degree of association profiles, at the liquid-vapor interface of our model. In reentrant systems, where A B bonds dominate, an unusual thickening of the interface is observed at low temperatures. Furthermore, the surface tension versus temperature curve reaches a maximum, in agreement with Bernardino and Telo da Gama's mesoscopic Landau-Safran theory [Phys. Rev. Lett. 109, 116103 (2012), 10.1103/PhysRevLett.109.116103]. If B B attractions are also present, competition between A B and B B bonds gradually restores the monotonic temperature dependence of the surface tension. Lastly, the interface is "hairy," i.e., it contains a region where the average chain length is close to that in the bulk liquid, but where the density is that of the vapor. Sufficiently strong B B attractions remove these features, and the system reverts to the behavior seen in atomic fluids.

  11. LES versus DNS: A comparative study

    NASA Technical Reports Server (NTRS)

    Shtilman, L.; Chasnov, J. R.

    1992-01-01

    We have performed Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) of forced isotropic turbulence at moderate Reynolds numbers. The subgrid scale model used in the LES is based on an eddy viscosity which adjusts instantaneously the energy spectrum of the LES to that of the DNS. The statistics of the large scales of the DNS (filtered DNS field or fDNS) are compared to that of the LES. We present results for the transfer spectra, the skewness and flatness factors of the velocity components, the PDF's of the angle between the vorticity and the eigenvectors of the rate of strain, and that between the vorticity and the vorticity stretching tensor. The above LES statistics are found to be in good agreement with those measured in the fDNS field. We further observe that in all the numerical measurements, the trend was for the LES field to be more gaussian than the fDNS field. Future research on this point is planned.

  12. Controlling colloidal phase transitions with critical Casimir forces.

    PubMed

    Nguyen, Van Duc; Faber, Suzanne; Hu, Zhibing; Wegdam, Gerard H; Schall, Peter

    2013-01-01

    The critical Casimir force provides a thermodynamic analogue of the quantum mechanical Casimir force that arises from the confinement of electromagnetic field fluctuations. In its thermodynamic analogue, two surfaces immersed in a critical solvent mixture attract each other due to confinement of solvent concentration fluctuations. Here, we demonstrate the active assembly control of colloidal equilibrium phases using critical Casimir forces. We guide colloidal particles into analogues of molecular liquid and solid phases via exquisite control over their interactions. By measuring the critical Casimir pair potential directly from density fluctuations in the colloidal gas, we obtain insight into liquefaction at small scales. We apply the van der Waals model of molecular liquefaction and show that the colloidal gas-liquid condensation is accurately described by the van der Waals theory, even on the scale of a few particles. These results open up new possibilities in the active assembly control of micro and nanostructures. PMID:23481392

  13. Active colloids propelled by induced-charge electrophoresis

    NASA Astrophysics Data System (ADS)

    Han, Ming; Luijten, Erik

    Populations of motile organisms exhibit a variety of collective behaviors, ranging from bacterial colony formation to the flocking of birds. Current understanding of these active motions, which are typically far from equilibrium and based on the collective behavior of self-propelled entities, is far from complete. One approach is to reproduce these observations in systems of synthetic active colloids. However, one of the standard self-propulsion mechanisms, induced-charge electrophoresis (ICEP) of a dielectric Janus colloid remains not fully understood by itself, especially the strong dependence of the resultant particle motion on the frequency of the external field. Resolution of this outstanding problem requires detailed study of the time-resolved dielectric response of the colloid and the dynamics of the electric double layer. Through molecular dynamics simulations coupled with an efficient dielectric solver, we elucidate the underlying mechanism of the frequency dependence of ICEP and the polarization of a metallodielectric Janus colloid.

  14. PCR detection of groundwater bacteria associated with colloidal transport

    SciTech Connect

    Cruz-Perez, P.; Stetzenbach, L.D.; Alvarez, A.J.

    1996-02-29

    Colloidal transport may increase the amount of contaminant material than that which could be transported by water flow alone. The role of colloids in groundwater contaminant transport is complicated and may involve many different processes, including sorption of elements onto colloidal particles, coagulation/dissolution, adsorption onto solid surfaces, filtration, and migration. Bacteria are known to concentrate minerals and influence the transport of compounds in aqueous environments and may also serve as organic colloids, thereby influencing subsurface transport of radionuclides and other contaminants. The initial phase of the project consisted of assembling a list of bacteria capable of sequestering or facilitating mineral transport. The development and optimization of the PCR amplification assay for the detection of the organisms of interest, and the examination of regional groundwaters for those organisms, are presented for subsequent research.

  15. Synthetic Strategies Toward DNA-Coated Colloids that Crystallize.

    PubMed

    Wang, Yufeng; Wang, Yu; Zheng, Xiaolong; Ducrot, Étienne; Lee, Myung-Goo; Yi, Gi-Ra; Weck, Marcus; Pine, David J

    2015-08-26

    We report on synthetic strategies to fabricate DNA-coated micrometer-sized colloids that, upon thermal annealing, self-assemble into various crystal structures. Colloids of a wide range of chemical compositions, including poly(styrene), poly(methyl methacrylate), titania, silica, and a silica-methacrylate hybrid material, are fabricated with smooth particle surfaces and a dense layer of surface functional anchors. Single-stranded oligonucleotides with a short sticky end are covalently grafted onto particle surfaces employing a strain-promoted alkyne-azide cycloaddition reaction resulting in DNA coatings with areal densities an order of magnitude higher than previously reported. Our approach allows the DNA-coated colloids not only to aggregate upon cooling but also to anneal and rearrange while still bound together, leading to the formation of colloidal crystal compounds when particles of different sizes or different materials are combined. PMID:26192470

  16. Bulk synthesis of polymer-inorganic colloidal clusters.

    PubMed

    Perro, Adeline; Manoharan, Vinothan N

    2010-12-21

    We describe a procedure to synthesize colloidal clusters with polyhedral morphologies in high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. We show that the synthesis initially used for silica-polystyrene hybrid clusters can be generalized to create clusters from other inorganic and polymer particles. We also show that high yields of particular morphologies can be obtained by precise control of the inorganic seed particle size, a finding that can be explained using a hard-sphere packing model. These clusters can be further chemically modified for a variety of applications. Introducing a cross-linker leads to colloidal clusters that can be index matched in an appropriate solvent, allowing them to be used for particle tracking or optical studies of colloidal self-assembly. Also, depositing a thin silica layer on these colloids allows the surface properties to be controlled using silane chemistry. PMID:21080658

  17. COUPLING OF PHYSICAL AND CHEMICAL MECHANISMS OF COLLOID DEPOSITION

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Considerable research suggests that colloid deposition is frequently not consistent with filtration theory predictions under unfavorable attachment conditions. Filtration theory does not include the potential influence of pore structure on straining deposition. Conversely, previous research on strai...

  18. A Simple Experiment Illustrating the Structure of Association Colloids.

    ERIC Educational Resources Information Center

    Friberg, Stig. E.; Bendiksen, Beverly

    1979-01-01

    The experiment described is intended to illustrate the intermolecular phenomena involved in association colloids. These are normal and inverse micelles and lyotropic liquid crystals. Solubilization, microemulsion and emulsion are discussed. (Author/SA)

  19. MANIPULATING SUBSURFACE COLLOIDS TO ENHANCE CLEANUPS OF DOE WASTE SITES

    EPA Science Inventory

    Colloidal phases, such as submicrometer iron oxyhydroxides, aluminosilicate clays, and humic macromolecules, are important subsurface sorbents for the low-solubility chemicals in DOE wastes. Recent research we have performed as part of DOE's Subsurface Science Program has demonst...

  20. Guided colloidal crystallization in a galvanic micro reactor

    NASA Astrophysics Data System (ADS)

    Punckt, Christian; Jan, Linda; Khusid, Boris; Aksay, Ilhan A.

    2009-11-01

    We present a novel method for assembling colloidal particles into an ordered coplanar array of two-dimensional crystals. This technique utilizes an autonomous galvanic micro reactor to control the location and morphology of colloidal crystals. Coplanar arrays of copper and gold microelectrodes are placed into a dilute water solution of hydrochloric acid to form a galvanic couple between the copper acting as an anode and the gold as a cathode. Under appropriate conditions, colloidal particles suspended in the solution assemble into two-dimensional colloidal crystals adherent to the anodic copper. Polystyrene and silica particles having similar sizes and zeta potentials but different densities were employed to study the fluid flow in the galvanic reactor. Spatially resolved, optical analysis of the reaction rate was used to estimate the magnitude and distribution of the electric current over the copper electrodes. Physical mechanisms governing the particle motion and aggregation will be discussed.

  1. Stable liquid crystalline phases of colloidally dispersed exfoliated layered niobates.

    PubMed

    Nakato, Teruyuki; Miyamoto, Nobuyoshi; Harada, Akiko

    2004-01-01

    Colloidally dispersed niobium oxide nanosheets obtained by exfoliation of layered niobates HNb(3)O(8) and HTiNbO(5) formed stable liquid crystalline phases; their liquid crystallinity was dependent on the niobate species exfoliated. PMID:14737341

  2. Colloidal structural evolution of asphaltene studied by confocal microscopy

    NASA Astrophysics Data System (ADS)

    Hung, Jannett; Castillo, Jimmy A.; Reyes, A.

    2004-10-01

    In this work, a detail analysis of the flocculation kinetic of asphaltenes colloidal particles has been carried out usng confocal microscopy. The colloidal structural evolution of the asphaltene flocculated has had varies postulated; however, the aggregation process of asphaltene is still not fully understood. In a recent paper, using Confocal microscope (homemade), we reported high-resolution micrographic images of asphaltenes flocculated and the correlation between crude oil stability and flocculation process. This technique permitted visualizes directly the physical nature of asphaltene flocculated. In this work, a detail analysis of the flocculation kinetic of asphaltene colloidal particles has been carried out using confocal microscopy. The physical nature of asphaltene flocculated from different crude oils is showed through of high-resolution image micrographies and its colloidal structural evolution.

  3. Colloid Formation by Drugs in Simulated Intestinal Fluid

    PubMed Central

    2010-01-01

    Many organic molecules form colloidal aggregates in aqueous solution at micromolar concentrations. These aggregates promiscuously inhibit soluble proteins and are a major source of false positives in high-throughput screening. Several drugs also form colloidal aggregates, and there has been speculation that this may affect the absorption and distribution of at least one drug in vivo. Here we investigate the ability of drugs to form aggregates in simulated intestinal fluid. Thirty-three Biopharmaceutics Classification System (BCS) class II and class IV drugs, spanning multiple pharmacological activities, were tested for promiscuous aggregation in biochemical buffers. The 22 that behaved as aggregators were then tested for colloid formation in simulated intestinal fluid, a buffer mimicking conditions in the small intestine. Six formed colloids at concentrations equal to or lower than the concentrations reached in the gut, suggesting that aggregation may have an effect on the absorption and distribution of these drugs, and potentially others, in vivo. PMID:20426472

  4. Characterization of uranium corrosion product colloids by dynamic light scattering.

    SciTech Connect

    Mertz, C.; Bowers, D.; Goldberg, M.; Shelton-Davis, C.

    2000-11-16

    The Department of Energy plans to dispose of approximately 2100 metric tons of spent metallic uranium fuel in the mined repository at Yucca Mountain. Laboratory studies at Argonne National Laboratory have shown that corrosion of metallic uranium fuel with groundwater generates significant quantities of stable colloids. This finding is considered very important in light of the recent report (1) of rapid subsurface transport of radionuclides at the Nevada Test Site via colloids. Thus, sparingly soluble radionuclides can be transported with the colloids through the subsurface aqueous environment to much greater distances than is predicted based on the aqueous volubility of the radionuclides alone. Accordingly, characterization of colloids generated by fuel corrosion is necessary for assessing the long-term fate and transport of radionuclides in the repository environment.

  5. COLLOIDAL AGGLOMERATES IN TANK SLUDGE: IMPACT ON WASTE PROCESSING

    EPA Science Inventory

    During processing of radioactive wastes, insoluble sludges consisting of submicron colloidal particles can clog transfer lines or interfere with solid-liquid separations. The wide range of properties observed for tank wastes can be rationalized by understanding how solution condi...

  6. 1. LOOKING EAST FROM 127125 JACKSON AVENUE (INDUSTRIAL COLLOIDS AND ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. LOOKING EAST FROM 127-125 JACKSON AVENUE (INDUSTRIAL COLLOIDS AND CHEMICALS, INC.) TO SULLIVAN'S SALOON (in background, with domed roof) - Jackson Avenue Warehouse District, 101-131 & 120-122 Jackson Avenue, Knoxville, Knox County, TN

  7. Collective behavior of chemotactic colloids: clusters, asters and oscillations

    NASA Astrophysics Data System (ADS)

    Saha, Suropriya; Golestanian, Ramin; Ramaswamy, Sriram

    2014-03-01

    Catalytic colloidal swimmers are a particularly promising example of systems that emulate properties of living matter, such as motility, gradient-sensing, signaling and replication. Here we present a comprehensive theoretical description of dynamics of an individual patterned catalytic colloid, leading controllably to chemotactic or anti-chemotactic behavior. We find that both the positional and the orientational degrees of freedom of the active colloids can exhibit condensation, signaling formation of clusters and asters. The kinetics of catalysis introduces a natural control parameter for the range of the interaction mediated by the diffusing chemical species. For various regimes in parameter space in the long-ranged limit our system displays precise analogs to gravitational collapse, plasma oscillations and electrostatic screening. We present prescriptions for how to tune the surface properties of the colloids during fabrication to achieve each type of behavior.

  8. Preparation of stable colloidal dispersions in fluorinated liquids

    NASA Technical Reports Server (NTRS)

    Kaiser, R.

    1972-01-01

    Chemical method for separating oil from water by liquid barrier which can be positioned magnetically is described. Fluorocarbon liquids containing colloidal suspension of magnetite is proposed. Chemical composition of magnetite and fluorinated ether polymer are presented.

  9. DEMONSTRATION BULLETIN: COLLOID POLISHING FILTER METHOD - FILTER FLOW TECHNOLOGY, INC.

    EPA Science Inventory

    The Filter Flow Technology, Inc. (FFT) Colloid Polishing Filter Method (CPFM) was tested as a transportable, trailer mounted, system that uses sorption and chemical complexing phenomena to remove heavy metals and nontritium radionuclides from water. Contaminated waters can be pro...

  10. Digital colloids: reconfigurable clusters as high information density elements.

    PubMed

    Phillips, Carolyn L; Jankowski, Eric; Krishnatreya, Bhaskar Jyoti; Edmond, Kazem V; Sacanna, Stefano; Grier, David G; Pine, David J; Glotzer, Sharon C

    2014-10-14

    Through the design and manipulation of discrete, nanoscale systems capable of encoding massive amounts of information, the basic components of computation are open to reinvention. These components will enable tagging, memory storage, and sensing in unusual environments - elementary functions crucial for soft robotics and "wet computing". Here we show how reconfigurable clusters made of N colloidal particles bound flexibly to a central colloidal sphere have the capacity to store an amount of information that increases as O(N ln(N)). Using Brownian dynamics simulations, we predict dynamical regimes that allow for information to be written, saved, and erased. We experimentally assemble an N = 4 reconfigurable cluster from chemically synthesized colloidal building blocks, and monitor its equilibrium dynamics. We observe state switching in agreement with simulations. This cluster can store one bit of information, and represents the simplest digital colloid. PMID:25034966

  11. Hydrogen emission under laser exposure of colloidal solutions of nanoparticles

    NASA Astrophysics Data System (ADS)

    Barmina, E. V.; Simakin, A. V.; Shafeev, G. A.

    2016-07-01

    We report the generation of molecular hydrogen from water by laser irradiation, without any electrodes and photocatalysts. A near infrared pulsed nanosecond laser is used for exposure of colloidal solution of Au nanoparticles suspended in water. Laser exposure of the colloidal solution results in formation of breakdown plasma in liquid and emission of H2. The rate of H2 emission depends critically on the energy of laser pulses. There is a certain threshold in laser fluence in liquid (around 50 J/cm2) below which plasma disappears and H2 emission stops. H2 emission from colloidal solution of Au nanoparticles in ethanol is higher than that from similar water colloid. It is found that formation of plasma and emission of H2 or D2 can be induced by laser exposure of pure liquids, either H2O or D2O, respectively. The results are interpreted as water molecules splitting by direct electron impact from breakdown plasma.

  12. 99M-Technetium labeled tin colloid radiopharmaceuticals

    DOEpatents

    Winchell, Harry S.; Barak, Morton; Van Fleet, III, Parmer

    1976-07-06

    An improved 99m-technetium labeled tin(II) colloid, size-stabilized for reticuloendothelial organ imaging without the use of macromolecular stabilizers and a packaged tin base reagent and an improved method for making it are disclosed.

  13. Controlled assembly of jammed colloidal shells on fluid droplets.

    PubMed

    Subramaniam, Anand Bala; Abkarian, Manouk; Stone, Howard A

    2005-07-01

    Assembly of colloidal particles on fluid interfaces is a promising technique for synthesizing two-dimensional microcrystalline materials useful in fields as diverse as biomedicine, materials science, mineral flotation and food processing. Current approaches rely on bulk emulsification methods, require further chemical and thermal treatments, and are restrictive with respect to the materials used. The development of methods that exploit the great potential of interfacial assembly for producing tailored materials have been hampered by the lack of understanding of the assembly process. Here we report a microfluidic method that allows direct visualization and understanding of the dynamics of colloidal crystal growth on curved interfaces. The crystals are periodically ejected to form stable jammed shells, which we refer to as colloidal armour. We propose that the energetic barriers to interfacial crystal growth and organization can be overcome by targeted delivery of colloidal particles through hydrodynamic flows. Our method allows an unprecedented degree of control over armour composition, size and stability. PMID:15937488

  14. Designed Assembly and Integration of Colloidal Nanocrystals for Device Applications.

    PubMed

    Yang, Jiwoong; Choi, Moon Kee; Kim, Dae-Hyeong; Hyeon, Taeghwan

    2016-02-10

    Colloidal nanocrystals have been intensively studied over the past three decades due to their unique properties that originate, in large part, from their nanometer-scale sizes. For applications in electronic and optoelectronic devices, colloidal nanoparticles are generally employed as assembled nanocrystal solids, rather than as individual particles. Consequently, tailoring 2D patterns as well as 3D architectures of assembled nanocrystals is critical for their various applications to micro- and nanoscale devices. Here, recent advances in the designed assembly, film fabrication, and printing/integration methods for colloidal nanocrystals are presented. The advantages and drawbacks of these methods are compared, and various device applications of assembled/integrated colloidal nanocrystal solids are discussed. PMID:26707709

  15. The viscosity of colloidal spheres in deionized suspensions

    NASA Astrophysics Data System (ADS)

    Okubo, Tsuneo

    1987-12-01

    Viscosities of colloidal spheres, i.e., colloidal silica (diameter 8 and 45 nm) and monodisperse polystyrene latices (diameter 85 to 780 nm), are measured in deionized (``salt-free'') suspensions and in the presence of a small amount of NaCl. The reduced viscosities (specific viscosity divided by concentration) of deionized silica (diameter 8 nm) are much higher than would be expected by Einstein's prediction and decrease sharply with increasing concentration. A sharp peak is observed in the reduced viscosity vs concentration curves of deionized colloidal silica of 45 nm diameter and the deionized latex spheres. The peak corresponds to the transition between ``liquid-like'' and ``crystal-like'' structures. These results show that electrostatic intersphere repulsion and the elongated Debye-screening length around the colloidal spheres are essential to explain the extraordinary properties.

  16. On the Absence of Red Structural Color in Colloidal Glasses

    NASA Astrophysics Data System (ADS)

    Magkiriadou, Sofia; Park, Jin-Gyu; Kim, Young-Seok; Yi, Gi-Ra; Manoharan, Vinothan N.

    2013-03-01

    When a colloidal glass is illuminated, the short-ranged spatial correlations between neighboring particles can give rise to constructive interference for a particular wavelength. Unlike the structural colors arising from Bragg diffraction in colloidal crystals, the colors of these colloidal glasses are independent of angle due to the disordered, isotropic microstructure. We therefore call them ``photonic glasses.'' A similar coloration mechanism is found in the feathers of certain birds. However, there are few examples of red photonic glasses either in nature or in colloidal systems. Using scattering theory, we show that the absence of red photonic glasses can be explained by the wavelength-dependence of the single-particle scattering cross-section, which can override the interference condition set by the structure. We propose ways to overcome this obstacle, and we report on experimental methods to make non-iridescent, structural red color.

  17. Colloidal stability of iron oxide nanoparticles with multivalent polymer surfactants.

    PubMed

    Choi, Young-Wook; Lee, Hoik; Song, Youngjun; Sohn, Daewon

    2015-04-01

    This paper introduces a new approach for preparing magnetic colloidal suspensions with electrostatic repulsion between particles and polyelectrolyte surfactants. The surface charge of the iron oxide particles was positive in acidic aqueous conditions; however the surface charge of the colloid was negative in basic aqueous conditions due to the amphoteric property of Fe2O3. The long-term colloidal stability and particle distribution of the multivalent charged polymers, Poly(4-vinylbenzenesulfonate sodium salt) (PSS), Poly(acrylic acid) (PAA), and Poly(allylamine hydrochloride) (PAH) were compared with the monovalent surfactant sodium dodecyl sulfate (SDS). Both mono- and multivalent surfactant molecules showed good colloidal stability for extended periods of time. However, the particle distribution was dependent on the hydrophobicity of the surfactants' functional groups. Polyelectrolytes with a negatively charged functional group showed good long-term stability of particles and a narrow particle distribution regardless of the acid dissociation constant (pKa) of the polymer. PMID:25526296

  18. Les Elements Legers: Diffusion dans les Enveloppes Stellaires et Implications Cosmologiques

    NASA Astrophysics Data System (ADS)

    Richer, Jacques

    1992-01-01

    Les observations des abondances des elements legers (Z <= 5) sont utilisees pour estimer la quantitie de lithium qui a ete produite lors du Big -Bang, et obtenir simultanement des contraintes sur la nature des inhomogeneites qui ont pu exister durant la nucleosynthese primordiale. Nous utilisons un modele simple capable de simuler approximativement la diffusion et la retro-diffusion des neutrons a travers la matiere inhomogene durant les premieres minutes de l'expansion de l'Univers. Nous tenons compte de la difference possible entre l'abondance primordiale de Li et les abondances observees dans les plus vieilles etoiles. Cette difference (un facteur 2, environ) est estimee en construisant des modeles evolutifs d'etoiles peu massives de Population II, incluant la sedimentation gravitationnelle du lithium et de l'helium. Ces modeles montrent egalement que les ages des vieux amas stellaires sont grandement surestimes lorsqu'ils sont determines a partir de modeles stellaires n'incluant pas l'effet de la diffusion de He. Nous calculons ensuite comment evoluent les abondances de Li et Be dans des etoiles plus massives et plus jeunes, de la pre-sequence principale ou de la ZAMS, jusqu'a l'epuisement de leur hydrogene central. Les modeles incluent la sedimentation simultanee de l'helium a travers l'enveloppe. Une approche hierarchique (evolution du coeur--evolution de l'enveloppe --tri des elements traces) est utilisee pour simuler efficacement le grand nombre d'etoiles necessaire pour la construction d'isochrones. Une attention particuliere est portee aux consequences de la sedimentation de He sur l'etendue des zones convectives, et sur la diffusion de Li et Be. Les forces radiatives agissant sur ces deux elements sont calculees en detail a partir des donnees atomiques. Les etoiles simulees correspondent approximativement aux types spectraux A, F, et AmFm. Les abondances de Li et Be observees dans les etoiles jeunes de ces types sont comparees a nos predictions dans le

  19. Linking Colloid Deposit Morphology and Clogging in Porous Media

    NASA Astrophysics Data System (ADS)

    Roth, E. J.; Mont-eton, M. E.; Mays, D. C.

    2012-12-01

    Innovations in the field of groundwater remediation have been hampered by delivery limitations in the porous media. For example, colloid deposits (comprising clays or silts) can cause a detrimental reduction in permeability, or clogging, which is problematic for groundwater remediation as well as granular media filtration and aquifer storage and recovery. During remediation, clogging creates preferential pathways in the media, leading to localized rather than spatially extensive contaminant treatment. Consequentially, remediation efforts become more expensive, less effective, and take a very long time. This presentation describes ongoing research investigating the link between colloid deposit morphology and clogging in porous media. As described by Darcy's Law, the velocity of fluid flow through porous media is proportional to permeability, which depends, in part, on porosity. However, changes in permeability are not in accord with changes in porosity as predicted by the Kozeny-Carman equation. It is hypothesized that unmeasured aspects of colloid deposit morphology could be the cause of this anomaly. Colloidal phenomena have important and dynamic effects on the permeability of natural porous media, and several lines of evidence suggest a correlation between clogging in porous media and the fractal dimension of colloid deposits. Here, a custom-built static light scattering apparatus is used to measure the fractal dimension of colloid deposits in refractive index matched porous media within a flow column. The media in our flow column is Nafion, which becomes essentially invisible when saturated by a solution of isopropanol and water. Polystyrene microspheres are then added to the influent through the column as a surrogate for natural colloids. Light from a laser is passed through the column, scattering from the deposited colloids, but not from the index matched Nafion. The resulting intensity of scattered light is measured as a function of scattering angle, and then

  20. Fourier-transform light scattering of individual colloidal clusters.

    PubMed

    Yu, HyeonSeung; Park, HyunJoo; Kim, Youngchan; Kim, Mahn Won; Park, YongKeun

    2012-07-01

    We present measurements of the scalar-field light scattering of individual dimer, trimer, and tetrahedron shapes among colloidal clusters. By measuring the electric field with quantitative phase imaging at the sample plane and then numerically propagating to the far-field scattering plane, the two-dimensional light-scattering patterns from individual colloidal clusters are effectively and precisely retrieved. The measured scattering patterns are consistent with simulated patterns calculated from the generalized multiparticle Mie solution. PMID:22743460

  1. SANS (small-angle neutron scattering) from polymers and colloids

    SciTech Connect

    Hayter, J.B.

    1987-01-01

    Small-angle neutron scattering (SANS) has been remarkably successful in providing detailed quantitative structural information on complex everyday materials, such as polymers and colloids, which are often of considerable industrial as well as academic interest. This paper reviews some recent SANS experiments on polymers and colloids, including ferrofluids, and discusses the use of these apparently complex systems as general physical models of the liquid or solid state.

  2. Binary Colloidal Alloy Test-3 and 4: Critical Point

    NASA Technical Reports Server (NTRS)

    Weitz, David A.; Lu, Peter J.

    2007-01-01

    Binary Colloidal Alloy Test - 3 and 4: Critical Point (BCAT-3-4-CP) will determine phase separation rates and add needed points to the phase diagram of a model critical fluid system. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.

  3. Synthesis of colloidal solutions with silicon nanocrystals from porous silicon

    PubMed Central

    2014-01-01

    In this work, we have obtained colloidal solutions of Si nanocrystals (Si-ncs), starting from free-standing porous silicon (PSi) layers. PSi layers were synthesized using a two-electrode Teflon electrochemical cell; the etching solution contained hydrogen peroxide 30%, hydrofluoric acid 40% (HF), and methanol. The anodizing current density was varied to 250 mA cm-2, 1 A cm-2, and 1.2 A cm-2. Thus obtained, PSi was mechanically pulverized in a mortar agate; then, the PSi powders were poured into different solutions to get the final Si-ncs colloidal solutions. The different optical, morphological, and structural characteristics of the colloidal solutions with Si-ncs were measured and studied. These Si-ncs colloidal solutions, measured by photoluminescence (PL), revealed efficient blue-green or violet emission intensities. The results of X-ray diffraction (XRD) indicate that the colloidal solutions are mainly composed of silicon nanocrystallites. The result of UV–vis transmittance indicates that the optical bandgap energies of the colloidal solutions varied from 2.3 to 3.5 eV for colloids prepared in methanol, ethanol, and acetone. The transmission electron microscopy (TEM) images showed the size of the nanocrystals in the colloidal solutions. Fourier transform infrared spectroscopy (FTIR) spectra showed different types of chemical bonds such as Si-O-Si, Si-CH2, and SiH x , as well as some kind of defects. PACS 61.46Df.-a; 61.43.Gt; 61.05.cp; 78.55.-m; 81.15.Gh PMID:25324709

  4. Colloidal Stability of Graphene Oxide: Aggregation in Two Dimensions.

    PubMed

    Gudarzi, Mohsen Moazzami

    2016-05-24

    Colloidal stability of graphene oxide (GO) is studied in aqueous and organic media accompanied by an improved aggregation model based on Derjaguin-Landau-Verwey- Overbeek (DLVO) theory for ultrathin colloidal flakes. It is found that both magnitude and scaling laws for the van der Waals forces are affected significantly by the two-dimensional (2D) nature of GO. Experimental critical coagulation concentrations (CCC) of GO in monovalent salt solutions concur with DLVO theory prediction. The surface charge density of GO is largely affected by pH. However, theoretical calculations and experimental observations show that the colloidal stability of the 2D colloids is less sensitive to the changes in the surface charge density compared to the classical picture of 3D colloids. The DLVO theory also quantitatively predicts the colloidal stability of reduced GO (rGO). The origin of lower stability of rGO compared to GO is rooted in the higher van der Waals forces among rGO sheets, and particularly, in the removal of negatively charged groups, and possibly formation of some cationic groups during reduction. GO also exfoliates in the polar organic solvents and results in stable dispersions. However, addition of nonpolar solvents perturbs the colloidal stability at a critical volume fraction. Analyzing the aggregation of GO in mixtures of different nonpolar solvents and N-methyl-2-pyrrolidone proposed that the solvents with dielectric constants of less than 24 are not able to host stable colloids of GO. However, dispersions of GO in very polar solvents shows unexpected stability at high concentration (>1 M) of salts and acids. The origin of this stability is most probably solvation forces. A crucial parameter affecting the ability of polar solvents to impart high stability to GO is their molecular size: the bigger they are, the higher the chance for stabilization. PMID:27143102

  5. Generation of colloidal granules and capsules from double emulsion drops

    NASA Astrophysics Data System (ADS)

    Hess, Kathryn S.

    Assemblies of colloidal particles are extensively used in ceramic processing, pharmaceuticals, inks and coatings. In this project, the aim was to develop a new technique to fabricate monodispersed colloidal assemblies. The use of microfluidic devices and emulsion processing allows for the fabrication of complex materials that can be used in a variety of applications. A microfluidic device is used to create monodispersed water/oil/water (w/o/w) double emulsions with interior droplets of colloidal silica suspension ranging in size from tens to hundreds of microns. By tailoring the osmotic pressure using glycerol as a solute in the continuous and inner phases of the emulsion, we can control the final volume size of the monodispersed silica colloidal crystals that form in the inner droplets of the double emulsion. Modifying the ionic strength in the colloidal dispersion can be used to affect the particle-particle interactions and crystal formation of the final colloidal particle. This w/o/w technique has been used with other systems of metal oxide colloids and cellulose nanocrystals. Encapsulation of the colloidal suspension in a polymer shell for the generation of ceramic-polymer core-shell particles has also been developed. These core-shell particles have spawned new research in the field of locally resonant acoustic metamaterials. Systems and chemistries for creating cellulose hydrogels within the double emulsions have also been researched. Water in oil single emulsions and double emulsions have been used to create cellulose hydrogel spheres in the sub-100 micron diameter range. Oil/water/oil double emulsions allow us to create stable cellulose capsules. The addition of a second hydrogel polymer, such as acrylate or alginate, further strengthens the cellulose gel network and can also be processed into capsules and particles using the microfluidic device. This work could have promising applications in acoustic metamaterials, personal care products, pharmaceuticals

  6. Self-assembly of active colloidal molecules with dynamic function

    NASA Astrophysics Data System (ADS)

    Soto, Rodrigo; Golestanian, Ramin

    Catalytically active colloids maintain non-equilibrium conditions in which they produce and deplete chemicals at their surface. While individual colloids that are symmetrically coated do not exhibit dynamical activity, the concentration fields resulting from their chemical activity decay as 1/r and produce gradients that attract or repel other colloids depending on their surface chemistry and ambient variables. This results in a non-equilibrium analogue of ionic systems, but with the remarkable novel feature of action-reaction symmetry breaking. In dilute conditions these active colloids join up to form molecules via generalized ionic bonds. Colloids are found to join up to form self-assembled molecules that could be inert or have spontaneous activity in the form of net translational velocity and spin depending on their symmetry properties and their constituents. As the interactions do not satisfy detailed-balance, it is possible to achieve structures with time dependent functionality. We study a molecule that adopts spontaneous oscillations and another that exhibits a run-and-tumble dynamics similar to bacteria. Our study shows that catalytically active colloids could be used for designing self-assembled structures that posses dynamical functionalities.

  7. Colloid-Facilitated Transport of Radionuclides through the Vadose Zone

    SciTech Connect

    Flury, Markus; Harsh, James B.; Zachara, John M.; Jin, Yan

    2002-06-01

    This project seeks to improve the basic understanding of colloid and colloid-facilitated transport of Cs in the vadose zone. The specific objectives are: (1) Determine the structure, composition, and surface charge characteristics of colloidal particles formed under conditions similar to those occurring during leakage of waste typical of Hanford tank supernatants into soils and sediments surrounding the tanks. (2) Characterize the mutual interactions between colloids, contaminant, and soil matrix in batch experiments under various ionic strength and pH conditions. We will investigate the nature of the solid-liquid interactions and the kinetics of the reactions. (3) Evaluate mobility of colloids through soil under different degrees of water saturation and solution chemistry (ionic strength and pH). (4) Determine the potential of colloids to act as carriers to transport the contaminant through the vadose zone and verify the results through comparison with field samples collected under leaking tanks. Results of this project will help to understand the fundamental mechanisms of Cs transport under the leaking Hanford tanks, and thus contribute to the long-term clean-up strategies at the Hanford site.

  8. Radiologic manifestations of colloid cysts: a pictorial essay.

    PubMed

    Algin, Oktay; Ozmen, Evrim; Arslan, Halil

    2013-02-01

    Colloid cysts are among rare benign tumours of the third ventricle. Although the most frequent symptoms are headache and syncope, arrest hydrocephalus or sudden death could appear with colloid cysts. The aim of this pictorial essay was to increase awareness of the clinical presentation, computed tomography (CT) and magnetic resonance (MR) imaging spectrum, and treatment options of the colloid cysts. The data of 11 patients with histopathologically and/or clinically proven colloid cyst were analysed, retrospectively; and the neuroradiologic appearances of the cysts were evaluated. The CT and MR appearance of colloid cysts may change, depending on the viscosity or the cholesterol content of the cysts. However, the cystic content is the most important factor that could affect the success of treatment. Cysts that are especially rich in protein and cholesterol tend to be hyperdense on CT, hypointense on T2-weighted sequences and hyperintense on T1-weighted sequences. These cysts are viscous, and the success of aspiration is significantly low. In the diagnosis and evaluation of small-sized cysts that have an ingredient similar to cerebrospinal fluid, 3-dimensional sequences might be useful. The radiologic appearances of colloid cysts could play an important role in directing these patients to alternative surgical modalities, including resection. PMID:22575594

  9. Assembly of colloidal strings in a simple fluid flow

    NASA Astrophysics Data System (ADS)

    Abe, Yu; Francis, Lorraine; Cheng, Xiang

    Colloidal particles self-assemble into ordered structures ranging from face- and body-centered cubic crystals to binary ionic crystals and to kagome lattices. Such diverse micron-scale structures are of practical importance for creating photonic materials and also of fundamental interest for probing equilibrium and non-equilibrium statistical mechanics. As a particularly interesting example, 1D colloidal strings provide a unique system for investigating non-equilibrium dynamics of crystal lattices. Here, we report a simple experimental method for constructing 1D colloidal crystals, where colloidal particles self-assemble into flow-aligned string structures near solid boundary under unidirectional flows. Using fast confocal microscopy, we explore the degree of particle alignment as functions of flow rate, particle concentrations, wetting properties of solid boundary and ionic strength of solvent. Through our systematic experiments, we show that these colloidal strings arise from hydrodynamic coupling, facilitated by electrostatic attractions between particles and the boundary. Compared with previous methods, our work provides a much simpler experimental procedure for assembling a large number of colloidal strings.

  10. Using colloids to model atomic thin film growth

    NASA Astrophysics Data System (ADS)

    Ganapathy, Rajesh; Buckley, Mark; Cohen, Itai

    2009-03-01

    We epitaxially grow colloidal thin films by sedimenting micron sized colloidal particles on a microfabricated substrate. The attractive interaction between the colloids, induced by a depletant polymer, leads to the nucleation of islands that grow and coalesce with one another. We use confocal microscopy and particle tracking to study the dynamics of the colloidal particles as they diffuse, aggregate and rearrange configurations during deposition. The saturation island density is estimated as a function of the deposition rate and depletant concentration. We find that our results are in excellent agreement with those obtained from atomic deposition experiments suggesting that our system can be used to model various phenomena that occur in atomic thin film growth. Furthermore, we quantify the Ehrlich-Schwoebel step edge barrier by using holographic optical tweezers to create artificial islands and study the dynamics of colloidal monomers placed on the edge of these islands. Owing to the short-range of the attractive interaction in our system, the origin of the step edge barrier in colloids is strikingly different from atoms.

  11. Patterning symmetry in the rational design of colloidal crystals.

    PubMed

    Romano, Flavio; Sciortino, Francesco

    2012-01-01

    Colloidal particles have the right size to form ordered structures with periodicities comparable to the wavelength of visible light. The tantalizing colours of precious opals and the colour of some species of birds are examples of polycrystalline colloidal structures found in nature. Driven by the demands of several emergent technologies, efforts have been made to develop efficient, self-assembly-based methodologies for generating colloidal single crystals with well-defined morphologies. Somewhat unfortunately, these efforts are often frustrated by the formation of structures lacking long-range order. Here we show that the rational design of patch shape and symmetry can drive patchy colloids to crystallize in a single, selected morphology by structurally eliminating undesired polymorphs. We provide a proof of this concept through the numerical investigation of triblock Janus colloids. One particular choice of patch symmetry yields, via spontaneous crystallization, a pure tetrastack lattice, a structure with attractive photonic properties, whereas another one results in a colloidal clathrate-like structure, in both cases without any interfering polymorphs. PMID:22828635

  12. Method and mechanism of colloidal assembly for surface patterning

    NASA Astrophysics Data System (ADS)

    Das, Sayantan

    In the field of self-assembly of colloids, there are a number of unanswered questions; can creation of surface patterns be merely achieved by the design of the process? What is the mechanism behind the formation of spontaneous surface patterns? In addition, how to control these patterns? These questions were answered in this work. In particular, we study the self --assembly of nanoparticles into monolayers as a means to build hierarchical structures that will exhibit new functionality. The techniques utilized include convective self-assembly and DOD inkjet printers. For uniform and controlled colloidal monolayers with reduced defects, we present a study on different solvent compositions and use of external modifiers such as vibration and surface coatings during the self-assembly process. These monolayers can be used in colloidal lithography, to prepare high quality metallic nanostructures. Moreover, the live view of particles during self-assembly and modelling of capillary interaction between the colloids, helps to unravel the mechanism behind colloidal phase segregation. This work has produced novel surface patterning using simple scalable methods, which can be used for various applications. One of the promising applications includes use of phase segregated stripe pattern array of mixed colloids as color filters for display devices.

  13. Subharmonic Shapiro steps of sliding colloidal monolayers in optical lattices.

    PubMed

    Paronuzzi Ticco, Stella V; Fornasier, Gabriele; Manini, Nicola; Santoro, Giuseppe E; Tosatti, Erio; Vanossi, Andrea

    2016-04-01

    We investigate theoretically the possibility to observe dynamical mode locking, in the form of Shapiro steps, when a time-periodic potential or force modulation is applied to a two-dimensional (2D) lattice of colloidal particles that are dragged by an external force over an optically generated periodic potential. Here we present realistic molecular dynamics simulations of a 2D experimental setup, where the colloid sliding is realized through the motion of soliton lines between locally commensurate patches or domains, and where the Shapiro steps are predicted and analyzed. Interestingly, the jump between one step and the next is seen to correspond to a fixed number of colloids jumping from one patch to the next, across the soliton line boundary, during each ac cycle. In addition to ordinary 'integer' steps, coinciding here with the synchronous rigid advancement of the whole colloid monolayer, our main prediction is the existence of additional smaller 'subharmonic' steps due to localized solitonic regions of incommensurate layers executing synchronized slips, while the majority of the colloids remains pinned to a potential minimum. The current availability and wide parameter tunability of colloid monolayers makes these predictions potentially easy to access in an experimentally rich 2D geometrical configuration. PMID:26933976

  14. Physics of Colloids in Space-2 (PCS-2)

    NASA Technical Reports Server (NTRS)

    Sankaran, Subramanian; Gasser, Urs; Manley, Suliana; Valentine, Megan; Prasad, Vikram; Rudhardt, Daniel; Bailey, Arthur; Dinsmore, Anthony; Segre, Phil; Doherty, Michael P.

    2001-01-01

    The Physics of Colloids-2 (PCS-2) experiment is aimed at investigating the basic physical properties of several types of colloidal suspensions. The three broad classes of colloidal systems of interest are binary colloids, colloid-polymer mixtures, and fractal gels. The objective is to understand their phase behavior as well as the kinetics of the phase transitions in the absence of gravity. The nucleation, growth, and morphology characteristics of the crystals and gels that form would be studied using confocal microscopy. These will be observed directly with excellent time resolution, and therefore extensive information about the different phases and their growth mechanisms will be gained. With the laser tweezers, it will be possible to measure the strength of these structures and to modify them in a controlled way, and the spectrophotometer will provide the possibility to probe their optical properties. We believe that this experiment will provide the basis for future 'colloid engineering' in which complicated structures with novel properties (e.g., photonic crystals) will be grown by controlled self-assembly.

  15. Current problems in the study of colloidal transport in soil

    NASA Astrophysics Data System (ADS)

    Shein, E. V.; Devin, B. A.

    2007-04-01

    A review of recent literature on the transport of organic and mineral colloids in soils demonstrated the role of such factors as the extrema of water flow velocities, the anisotropy of physical properties, and the presence of preferential water flows in macropores and fissures. In unsaturated soils, the concentration of colloids at the gas-water interphace and the amphiphilicity of their surface are of great importance. The transfer of “living collids” (bacteria and viruses) is mainly due to the convection mechanism; however, of great importance are the entrapping of microorganisms in fine pores, their adsorption (adhesion), their concentration on the gas-water interphace, their sedimentation, and the affecting chemical factors, such as the ionic strength and the pH of the solution. The effect of biological factors is related to the size of cells, chemotaxic mobility, and the growth and reproduction of the microbial biomass. The focal points of recent studies on colloid transport are considered: the study of mechanisms of colloid mobilization under different conditions, the improvement of methods for the direct observation of colloid migration (micromodels, computer tomography, etc.), and the possibility of quantitative description of the entrapping of colloidal particles in soil pores.

  16. Subharmonic Shapiro steps of sliding colloidal monolayers in optical lattices

    NASA Astrophysics Data System (ADS)

    Paronuzzi Ticco, Stella V.; Fornasier, Gabriele; Manini, Nicola; Santoro, Giuseppe E.; Tosatti, Erio; Vanossi, Andrea

    2016-04-01

    We investigate theoretically the possibility to observe dynamical mode locking, in the form of Shapiro steps, when a time-periodic potential or force modulation is applied to a two-dimensional (2D) lattice of colloidal particles that are dragged by an external force over an optically generated periodic potential. Here we present realistic molecular dynamics simulations of a 2D experimental setup, where the colloid sliding is realized through the motion of soliton lines between locally commensurate patches or domains, and where the Shapiro steps are predicted and analyzed. Interestingly, the jump between one step and the next is seen to correspond to a fixed number of colloids jumping from one patch to the next, across the soliton line boundary, during each ac cycle. In addition to ordinary ‘integer’ steps, coinciding here with the synchronous rigid advancement of the whole colloid monolayer, our main prediction is the existence of additional smaller ‘subharmonic’ steps due to localized solitonic regions of incommensurate layers executing synchronized slips, while the majority of the colloids remains pinned to a potential minimum. The current availability and wide parameter tunability of colloid monolayers makes these predictions potentially easy to access in an experimentally rich 2D geometrical configuration.

  17. Non-equilibrium phenomena in disordered colloidal solids

    NASA Astrophysics Data System (ADS)

    Yunker, Peter

    Colloidal particles are a convenient tool for studying a variety of non-equilibrium phenomena. I will discuss experiments that investigate the aging and non-equilibrium growth of disordered solids. In the first set of experiments, colloidal glasses are rapidly formed to study aging in jammed packings. A colloidal fluid, composed of micron-sized temperature-sensitive pNIPAM particles, is rapidly quenched into a colloidal glass. After the glass is formed, collective rearrangements occur as the glass ages. Particles that undergo irreversible rearrangements, which break nearest-neighbor pairings and allow the glass to relax, are identified. These irreversible rearrangements are accompanied by large clusters of fast moving particles; the number of particles involved in these clusters increases as the glass ages, leading to the slowing of dynamics that is characteristic of aging. In the second set of experiments, we study the role particle shape, and thus, interparticle interaction, plays in the formation of disordered solids with different structural and mechanical properties. Aqueous suspensions of colloidal particles with different shapes evaporate on glass slides. Convective flows during evaporation carry particles from drop center to drop edge, where they accumulate. The resulting particle deposits grow heterogeneously from the edge on the air-water interface. Three distinct growth processes were discovered in the evaporating colloidal suspensions by tuning particle shape-dependent capillary interactions and thus varying the microscopic rules of deposition. Mechanical testing of these particulate deposits reveals that the deposit bending rigidity increases as particles become more anisotropic in shape.

  18. Solidification of a Charged Colloidal Dispersion Investigated Using Microfluidic Pervaporation.

    PubMed

    Ziane, Nadia; Salmon, Jean-Baptiste

    2015-07-28

    We investigate the dynamics of solidification of a charged colloidal dispersion using an original microfluidic technique referred to as micropervaporation. This technique exploits pervaporation within a microfluidic channel to extract the solvent of a dilute colloidal dispersion. Pervaporation concentrates the colloids in a controlled way up to the tip of the channel until a wet solid made of closely packed colloids grows and invades the microfluidic channel. For the charged dispersion under study, we however evidence a liquid to solid transition (LST) preceding the formation of the solid, owing to the presence of long-range electrostatic interactions. This LST is associated with the nucleation and growth of domains confined in the channel. These domains are then compacted anisotropically up to forming a wet solid of closely packed colloids. This solid then invades the whole channel as in directional drying with a growth rate which depends on the microfluidic geometry. In the final steps of the solidification, we observed the occurrence of cracks and shear bands, the delamination of the wet solid from the channel walls, and its invasion by a receding air front. Interestingly, this air front follows specific patterns within the solid which reveal different microscopic colloidal organizations. PMID:26131999

  19. Electric Field Driven Self-Assembly of Colloidal Rods

    NASA Astrophysics Data System (ADS)

    Juarez, Jaime; Chaudhary, Kundan; Chen, Qian; Granick, Steve; Lewis, Jennifer

    2012-02-01

    The ability to assemble anisotropic colloidal building blocks into ordered configurations is of both scientific and technological importance. We are studying how electric field-induced interactions guide the self-assembly of these blocks into well aligned microstructures. Specifically, we present observations of the assembly of colloidal silica rods (L/D ˜ 4) within planar electrode cells as a function of different electric field parameters. Results from video microscopy and image analysis demonstrate that aligned microstructures form due to the competition between equilibrium interactions of induced dipoles and non-equilibrium processes (i.e., electro-osmosis). Under the appropriate electric field conditions (˜ kHZ AC fields), aligned colloidal rod fluids form over large areas on the electrode surface. The superposition of a DC electric field to this aligned colloidal rod fluid initiates their condensation into a vertically oriented crystalline phase. Ongoing work is now focused on exploring how temporal changes to electric fields influence colloidal rod dynamics and, hence, the assembly kinetics of aligned colloidal monolayers.

  20. Stratification of colloidal aggregation coupled with sedimentation.

    PubMed

    González, Agustín E

    2006-12-01

    One of the consequences of sedimentation in colloidal aggregation is the stratification of the system in the sense that, after a sufficiently long elapsed time, the large clusters lie preferentially at the bottom zones of the confinement prism, and the structural and dynamical quantities describing the aggregates depend on the depth at which they are measured. A few years ago a computer simulation using particles for colloidal aggregation coupled with sedimentation was proposed by the author [A. E. González, Phys. Rev. Lett. 86, 1243 (2001)]. In that simulation, due to computational limitations, the mentioned quantities were averaged over all clusters in the prism, independently of the depth at which they were located, in order to have good statistics for the evaluation of the cluster fractal dimension and the cluster size distribution function. In this work we present a computer simulation using particles of colloidal aggregation coupled with sedimentation, for which the clusters in the simulation box represent those clusters inside a layer at a fixed depth and of arbitrary thickness in the prism. It would then be possible to compare the results with an eventual validation experiment, in which an aggregating sample is sipped out with a pipette at a fixed depth in the prism and subjected to further studies, or with a light scattering study in which the laser beam is focused at a fixed depth in the system. We confirm the acceleration of the aggregation rate, followed by a slowing down, compared with an aggregating system driven purely by diffusion (DLCA). In the present system, the large clusters when drifting downwards sweep smaller ones, which in turn occlude the holes and cavities of these large clusters, increasing in this way their compacticity. We also confirm that (i) in some cases of sedimentation strengths and layer depths, the mean width (perpendicular to the gravitational field direction) and the mean height of the large settling clusters scale with the

  1. Influence of colloidal particle transfer on the quality of self-assembling colloidal photonic crystal under confined condition

    NASA Astrophysics Data System (ADS)

    Zhao, Yong-Qiang; Li, Juan; Liu, Qiu-Yan; Dong, Wen-Jun; Chen, Ben-Yong; Li, Chao-Rong

    2015-02-01

    The relationship between colloidal particle transfer and the quality of colloidal photonic crystal (CPC) is investigated by comparing colloidal particle self-assembling under the vertical channel (VC) and horizontal channel (HC) conditions. Both the theoretical analyses and the experimental measurements indicate that crystal quality depends on the stability of mass transfer. For the VC, colloidal particle transfer takes place in a stable laminar flow, which is conducive to forming high-quality crystal. In contrast, it happens in an unstable turbulent flow for the HC. Crystals with cracks and an uneven surface formed under the HC condition can be seen from the images of a field emission scanning electron microscope (SEM) and a three-dimensional (3D) laser scanning microscope (LSM), respectively. Project supported by the National Natural Science Foundation of China (Grant Nos. 91122022 and 51172209) and the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT), China (Grant No. IRT13097).

  2. Equation of State and Structure of Electrostatic Colloidal Crystals: Osmotic Pressure and Scattering Study

    NASA Astrophysics Data System (ADS)

    Reus, V.; Belloni, L.; Zemb, T.; Lutterbach, N.; Versmold, H.

    1997-04-01

    structure et les interactions interparticulaires en fonction de la fraction volumique à salinité constante de l'ordre de la micromole/l. Lorsque la cristallisation est lente, nous observons des cristaux parfaits cubiques centrés par diffusion de lumière pour des fractions volumiques comprises entre 0,04 et 0,7 % et cubiques faces centrées pax diffusion de rayons X aux petits angles pour des fractions volumiques plus élevées (2 12 %). Après cisaillement, des défauts apparaissent dans les cristaux ; ils sont caractérisés par la disparition de certaines raies de Bragg en diffusion de lumière pour des échantillons de fraction volumique comprise entre 0,1 et 0,3 % et par la présence d'un pré pic observé par diffusion de rayons X aux petits angles avant le premier pic de Bragg, pour des échantillons plus concentrés (2 12 %). Les pressions osmotiques ont été mesurées par différence de pression hydrostatique entre la solution et le réservoir séparés par une membrane hémiperméable. Les données expérimentales sont bien reproduites par la théorie Poisson Boltzmann Réseau (PBR) qui montre que les interactions sont purement répulsives. Aucune force attractive faible de longue portée n'a été détectée expérimentalement. En calculant le déplacement moyen d'une particule à l'intérieur de sa cage à l'aide du modèle PBR "excentré", nous avons vérifié que le critère de Lindemann était satisfait pour tous les cristaux observés. Cette étude a permis de déterminer l'équation d'état d'un cristal colloidal électrostatique. Les résultats sont équivalents à une mesure de force ultraprécise puisque les forces d'interaction mesurées entre particules sont de l'ordre de 10^{-12} N pour des distances centre à centre de l'ordre de 4000 Å.

  3. Chancellor Water Colloids: Characterization and Radionuclide Associated Transport

    SciTech Connect

    Reimus, Paul William; Boukhalfa, Hakim

    2014-09-26

    Column transport experiments were conducted in which water from the Chancellor nuclear test cavity was transported through crushed volcanic tuff from Pahute Mesa. In one experiment, the cavity water was spiked with solute 137Cs, and in another it was spiked with 239/240Pu(IV) nanocolloids. A third column experiment was conducted with no radionuclide spike at all, although the 137Cs concentrations in the water were still high enough to quantify in the column effluent. The radionuclides strongly partitioned to natural colloids present in the water, which were characterized for size distribution, mass concentration, zeta potential/surface charge, critical coagulation concentration, and qualitative mineralogy. In the spiked water experiments, the unanalyzed portion of the high-concentration column effluent samples were combined and re-injected into the respective columns as a second pulse. This procedure was repeated again for a third injection. Measurable filtration of the colloids was observed after each initial injection of the Chancellor water into the columns, but the subsequent injections (spiked water experiments only) exhibited no apparent filtration, suggesting that the colloids that remained mobile after relatively short transport distances were more resistant to filtration than the initial population of colloids. It was also observed that while significant desorption of 137Cs from the colloids occurred after the first injection in both the spiked and unspiked waters, subsequent injections of the spiked water exhibited much less 137Cs desorption (much greater 137Cs colloid-associated transport). This result suggests that the 137Cs that remained associated with colloids during the first injection represented a fraction that was more strongly adsorbed to the mobile colloids than the initial 137Cs associated with the colloids. A greater amount of the 239/240

  4. Chemical Routes to Colloidal Chalcogenide Nanosheets

    SciTech Connect

    Schaak, Raymond

    2015-02-19

    This project sought to develop new low-temperature synthetic pathways to intermetallic and chalcogenide nanostructures and powders, with an emphasis on systems that are relevant to advancing the synthesis, processing, and discovery of superconducting materials. The primary synthetic routes involved solution chemistry methods, and several fundamental synthetic challenges that underpinned the formation of these materials were identified and investigated. Methods for incorporating early transition metals and post transition metals into nanoscale and bulk crystals using low-temperature solution chemistry methods were developed and studied, leading to colloidal nanocrystals of elemental indium, manganese, and germanium, as well as nanocrystalline and bulk intermetallic compounds containing germanium, gallium, tin, indium, zinc, bismuth, and lithium. New chemical tools were developed to help target desired phases in complex binary intermetallic and metal chalcogenide systems that contain multiple stable phases, including direct synthesis methods and chemical routes that permit post-synthetic modification. Several phases that are metastable in bulk systems were targeted, synthesized, and characterized as nanocrystalline solids and bulk powders, including the L12-type intermetallic compounds Au3Fe, Au3Ni, and Au3Co, as well as wurtzite-type MnSe. Methods for accessing crystalline metal borides and carbides using direct solution chemistry methods were also developed, with an emphasis on Ni3B and Ni3C, which revealed useful correlations of composition and magnetic properties. Methods for scale-up and nanoparticle purification were explored, providing access to centimeter-scale pressed pellets of polyol-synthesized nanopowders and a bacteriophage-mediated method for separating impure nanoparticle mixtures into their components. Several advances were made in the synthesis of iron selenide and related superconducting materials, including the production of colloidal Fe

  5. Analysis report for WIPP colloid model constraints and performance assessment parameters

    SciTech Connect

    Mariner, Paul E.; Sassani, David Carl

    2014-03-01

    An analysis of the Waste Isolation Pilot Plant (WIPP) colloid model constraints and parameter values was performed. The focus of this work was primarily on intrinsic colloids, mineral fragment colloids, and humic substance colloids, with a lesser focus on microbial colloids. Comments by the US Environmental Protection Agency (EPA) concerning intrinsic Th(IV) colloids and Mg-Cl-OH mineral fragment colloids were addressed in detail, assumptions and data used to constrain colloid model calculations were evaluated, and inconsistencies between data and model parameter values were identified. This work resulted in a list of specific conclusions regarding model integrity, model conservatism, and opportunities for improvement related to each of the four colloid types included in the WIPP performance assessment.

  6. Chemical colloids versus biological colloids: a comparative study for the elucidation of the mechanism of protein fiber formation

    NASA Technical Reports Server (NTRS)

    Xu, Shaohua; Wu, David; Arnsdorf, Morton; Johnson, Robert; Getz, Godfrey S.; Cabana, Veneracion G.

    2005-01-01

    Fiber formation from murine serum amyloid A1 (SAA) was compared to the linear aggregation and fiber formation of colloidal gold particles. Here we report the similarities of these processes. Upon incubation with acetic acid, SAA misfolds and adopts a new conformation, which we termed saa. saa apparently is less soluble than SAA in aqueous solution; it aggregates and forms nucleation units and then fibers. The fibers appear as a string of the nucleation units. Additionally, an external electric field promotes saa fiber formation. These properties of saa are reminiscent of colloidal gold formation from gold ions and one-dimensional aggregation of the gold colloids. Colloidal gold particles were also found to be capable of aggregating one-dimensionally under an electric field or in the presence of polylysine. These gold fibers resembled in structure that of saa fibers. In summary, protein aggregation and formation of fibers appear to follow the generalized principles derived in colloidal science for the aggregation of atoms and molecules, including polymers such as polypeptides. The analysis of colloidal gold formation and of one-dimensional aggregation provides a simple model system for the elucidation of some aspects of protein fiber formation.

  7. Tracking colloid transport in porous media using discrete flow fields and sensitivity of simulated colloid deposition to space discretization.

    PubMed

    Li, Zhelong; Zhang, Dongxiao; Li, Xiqing

    2010-02-15

    Advances in pore structure characterization and lattice-Boltzmann (LB) simulations of flow fields in pore spaces are making mechanistic simulations of colloid transport in real porous media a realistic goal. The primary challenge to reach this goal may be the computational demand of LB flow simulations in discretized porous medium domains at an assemblage scale. In this work, flow fields in simple cubic and dense packing systems were simulated at different discretization resolutions using the LB method. The simulated flow fields were incorporated into to a three-dimensional particle tracking model to simulate colloid transport in the two systems. The simulated colloid deposition tended to become asymptotic at a critical discretization resolution (voxel-grain size ratio = 0.01) at groundwater flow regimes for colloids down to submicrometer level under favorable conditions and down to around 1 microm under unfavorable conditions. The average simulated fluid velocities near grain surfaces were extracted to explain the sensitivities of simulated depositions to space discretization under both conditions. At the critical discretization resolution, current computation capacity would allow flow simulations and particle tracking in assemblage porous medium domains. In addition, particle tracking simulations revealed that colloids may be retained in flow vortices under conditions both favorable and unfavorable for deposition. Colloid retention in flow vortices has been proposed only very recently. Here we provide a mechanistic confirmation to this novel retention process. PMID:20088544

  8. Fractures as Carriers for Colloid and Nano-Particles

    NASA Astrophysics Data System (ADS)

    Weisbrod, N.; Cohen, M.; Tang, X.; Zvikelsky, O.; Meron, H.

    2013-12-01

    One of the major questions in studies in which transport of colloids and nano particles (NPs) is being explored is whether or not they will be mobile on large scales and in large conduits such as fractures and cracks. While many studies explore the migration on a small scale and mostly in ideal porous media, less is known about this topic on larger scales and in fractured rocks or cracked soils. Fractures are likely to be favorable carriers for colloids and NPs due to their large aperture, enabling relatively high flow velocity and smaller tortuosity of the flow path. Transport of various colloids including microspheres, clay particles and viruses, as well as colloid-facilitated transport of lead and cesium was explored in a naturally discrete fractured chalk cores. Preliminary work exploring the transport of NZVIs and TiO2 NPs is being carried out through these cores as well. Our results indicate very high recovery of large microspheres (0.2 and 1 micron) and lower recovery of the small spheres (0.02 micron). It was observed that clay particles, with similar surface properties and sizes to that of the microspheres, show significantly lower recoveries (50 vs over 90%), probably due to the high density of clay particles in respect to the microspheres (2.65 vs. 1.05 g/cm3). High recovery of bacteriophages was also observed, but they exhibit some differences in respect to microspheres with similar properties. In all cases, including the 0.02 micron colloids exhibiting lower recovery rates, arrival times were earlier than that of the bromide that was used as a reference. It was found that colloid-facilitated transport played a major role in the migration of lead and cesium through the fracture. In practice, lead was found to be mobile only in a colloidal form. The on-going work on NP transport through fractures is still in a preliminary phase. Nevertheless, TiO2 recovery was found to be very low. In conclusion, it was observed that in many cases fractures are favorable

  9. Prise en charge de l’infection gonococcique chez les adultes et les jeunes

    PubMed Central

    Pogany, Lisa; Romanowski, Barbara; Robinson, Joan; Gale-Rowe, Margaret; Latham-Carmanico, Cathy; Weir, Christine; Wong, Tom

    2015-01-01

    Résumé Objectif Présenter des recommandations sur la prise en charge de l’infection gonococcique chez les adultes et les jeunes. Qualité des données Les recommandations thérapeutiques des lignes directrices canadiennes sur les infections transmissibles sexuellement reposent sur une recherche documentaire de même que sur des catégories de recommandations et des niveaux de qualité de données déterminés par au moins 2 évaluateurs. Les recommandations ont été revues par des pairs et sont en instance d’approbation par le groupe de travail d’experts. Message principal Les nouvelles recommandations portant sur la prise en charge de l’infection gonococcique chez les adultes et les jeunes préconisent les cultures à titre d’outil diagnostique lorsqu’elles sont pratiques, le traitement par antibiothérapie combinée (ceftriaxone associée à l’azithromycine) et le signalement sans délai de tous les cas dont le traitement a échoué aux autorités de santé publique. Conclusion Si elles sont suivies, ces nouvelles recommandations pourraient réduire l’échec thérapeutique, contribuer à une surveillance plus étroite des tendances à la résistance de Neisseria gonorrhoeae aux antibiotiques et contribuer à prévenir la transmission de gonorrhée résistante à plusieurs médicaments.

  10. Colloidal Wormlike Micelles with Highly Ferromagnetic Properties.

    PubMed

    Zhao, Wenrong; Dong, Shuli; Hao, Jingcheng

    2015-10-20

    For the first time, a new fabrication method for manipulating the ferromagnetic property of molecular magnets by forming wormlike micelles in magnetic-ionic-liquid (mag-IL) complexes is reported. The ferromagnetism of the mag-IL complexes was enhanced 4-fold because of the formation of wormlike micelles, presenting new evidence for the essence of magnetism generation at a molecular level. Characteristics such as morphology and magnetic properties of the wormlike micelle gel were investigated in detail by cryogenic transmission electron microscopy (Cryo-TEM), rheological measurements, circular dichroism (CD), FT-IR spectra, and the superconducting quantum interference device method (SQUID). An explanation of ferromagnetism elevation from the view of the molecular (ionic) distribution is also given. For the changes of magnetic properties (ferromagnetism elevation) in the wormlike micelle systems, the ability of CTAFe in magnetizing AzoNa4 (or AzoH4) can be ascribed to an interplay of the magnetic [FeCl3Br](-) ions both in the Stern layer and in the cores of the wormlike micelles. Formation of colloidal aggregates, i.e., wormlike micelles, provides a new strategy to tune the magnetic properties of novel molecular magnets. PMID:26411638

  11. Maximizing exosome colloidal stability following electroporation.

    PubMed

    Hood, Joshua L; Scott, Michael J; Wickline, Samuel A

    2014-03-01

    Development of exosome-based semisynthetic nanovesicles for diagnostic and therapeutic purposes requires novel approaches to load exosomes with cargo. Electroporation has previously been used to load exosomes with RNA. However, investigations into exosome colloidal stability following electroporation have not been considered. Herein, we report the development of a unique trehalose pulse media (TPM) that minimizes exosome aggregation following electroporation. Dynamic light scattering (DLS) and RNA absorbance were employed to determine the extent of exosome aggregation and electroextraction post electroporation in TPM compared to common PBS pulse media or sucrose pulse media (SPM). Use of TPM to disaggregate melanoma exosomes post electroporation was dependent on both exosome concentration and electric field strength. TPM maximized exosome dispersal post electroporation for both homogenous B16 melanoma and heterogeneous human serum-derived populations of exosomes. Moreover, TPM enabled heavy cargo loading of melanoma exosomes with 5nm superparamagnetic iron oxide nanoparticles (SPION5) while maintaining original exosome size and minimizing exosome aggregation as evidenced by transmission electron microscopy. Loading exosomes with SPION5 increased exosome density on sucrose gradients. This provides a simple, label-free means of enriching exogenously modified exosomes and introduces the potential for MRI-driven theranostic exosome investigations in vivo. PMID:24333249

  12. Kibble-Zurek mechanism in colloidal monolayers.

    PubMed

    Deutschländer, Sven; Dillmann, Patrick; Maret, Georg; Keim, Peter

    2015-06-01

    The Kibble-Zurek mechanism describes the evolution of topological defect structures like domain walls, strings, and monopoles when a system is driven through a second-order phase transition. The model is used on very different scales like the Higgs field in the early universe or quantum fluids in condensed matter systems. A defect structure naturally arises during cooling if separated regions are too far apart to communicate (e.g., about their orientation or phase) due to finite signal velocity. This lack of causality results in separated domains with different (degenerated) locally broken symmetry. Within this picture, we investigate the nonequilibrium dynamics in a condensed matter analog, a 2D ensemble of colloidal particles. In equilibrium, it obeys the so-called Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) melting scenario with continuous (second order-like) phase transitions. The ensemble is exposed to a set of finite cooling rates covering roughly three orders of magnitude. Along this process, we analyze the defect and domain structure quantitatively via video microscopy and determine the scaling of the corresponding length scales as a function of the cooling rate. We indeed observe the scaling predicted by the Kibble-Zurek mechanism for the KTHNY universality class. PMID:25902492

  13. Small bright charged colloidal quantum dots.

    PubMed

    Qin, Wei; Liu, Heng; Guyot-Sionnest, Philippe

    2014-01-28

    Using electrochemical charge injection, the fluorescence lifetimes of negatively charged core/shell CdTe/CdSe QDs are measured as a function of core size and shell thickness. It is found that the ensemble negative trion lifetimes reach a maximum (∼4.5 ns) for an intermediate shell thickness. This leads to the smallest particles (∼4.5 nm) with the brightest trion to date. Single dot measurements show that the negative charge suppresses blinking and that the trion can be as bright as the exciton at room temperature. In contrast, the biexciton lifetimes remain short and exhibit only a monotonous increase with shell thickness, showing no correlation with the negative trion decays. The suppression of the Auger process in small negatively charged CdTe/CdSe quantum dots is unprecedented and a significant departure from prior results with ultrathick CdSe/CdS core/shell or dot-in-rod structures. The proposed reason for the optimum shell thickness is that the electron-hole overlap is restricted to the CdTe core while the electron is tuned to have zero kinetic energy in the core for that optimum shell thickness. The different trend of the biexciton lifetime is not explained but tentatively attributed to shorter-lived positive trions at smaller sizes. These results improve our understanding of multiexciton recombination in colloidal quantum dots and may lead to the design of bright charged QDs for more efficient light-emitting devices. PMID:24350673

  14. Multiple Exciton Generation in Colloidal Silicon Nanocrystals

    SciTech Connect

    Beard, M. C.; Knutsen, K. P.; Yu, P.; Luther, J. M.; Song, Q.; Metzger, W. K.; Ellingson, R. J.; Nozik, A. M.

    2007-01-01

    Multiple exciton generation (MEG) is a process whereby multiple electron-hole pairs, or excitons, are produced upon absorption of a single photon in semiconductor nanocrystals (NCs) and represents a promising route to increased solar conversion efficiencies in single-junction photovoltaic cells. We report for the first time MEG yields in colloidal Si NCs using ultrafast transient absorption spectroscopy. We find the threshold photon energy for MEG in 9.5 nm diameter Si NCs (effective band gap {identical_to} Eg = 1.20 eV) to be 2.4 {+-} 0.1E{sub g} and find an exciton-production quantum yield of 2.6 {+-} 0.2 excitons per absorbed photon at 3.4E{sub g}. While MEG has been previously reported in direct-gap semiconductor NCs of PbSe, PbS, PbTe, CdSe, and InAs, this represents the first report of MEG within indirect-gap semiconductor NCs. Furthermore, MEG is found in relatively large Si NCs (diameter equal to about twice the Bohr radius) such that the confinement energy is not large enough to produce a large blue-shift of the band gap (only 80 meV), but the Coulomb interaction is sufficiently enhanced to produce efficient MEG. Our findings are of particular importance because Si dominates the photovoltaic solar cell industry, presents no problems regarding abundance and accessibility within the Earth's crust, and poses no significant environmental problems regarding toxicity.

  15. Chemisorption effects on colloidal lead nanoparticles

    SciTech Connect

    Henglein, A.

    1999-10-28

    A stable aqueous lead sol (10 nm particles) is formed upon the {gamma}-irradiation of Pb(ClO{sub 4}){sub 2} in the presence of (poly)ethyleneimine. Lead nanoparticles have an absorption band at 218 nm with {epsilon} = 3.2 x 10{sup 4} M{sup {minus}1} cm{sup {minus}1}; the band appears at the wavelength that is expected for a surface plasmon oscillation. The changes in the shape of the absorption band, which occur upon the interaction of the nanoparticles with various solutes, are described and interpreted. Oxygen, nitrous oxide, carbon tetrachloride, and chloroform oxidize colloidal lead particles to Pb{sup 2+}. Carbon disulfide oxidizes only surface lead atoms to yield a layer of PbS precursor. The oxidation of lead particles by the ions of noble metals is investigated for Ag{sup +} and Cu{sup 2+}. Silver ions oxidize lead nanoparticles incompletely, which is explained by the formation of mixed Ag-Pb structures. Cu{sup 2+} ions also do not completely oxidize lead particles, although Cu particles with a low Pb content can be obtained.

  16. Force vs. extension of colloidal membranes

    NASA Astrophysics Data System (ADS)

    Jia, Leroy; Pelcovits, Robert; Powers, Thomas; Zakhary, Mark; Dogic, Zvonimir

    In experiments, disk-shaped colloidal membranes composed of long rod-like viruses will take on a twisted ribbon shape under the application of a diametric stretching force. We use an effective model valid for membranes with small twist penetration to study this phase transition and calculate the force necessary to stretch the membrane to a given extension. The model predicts that for small deformations, the force is linear with spring constant depending on the effective edge bending stiffness of the membrane, while for large extensions, the force is found to saturate to a constant value. Surprisingly, the force is not a monotonic function of the extension. Finally, we use simple numerical calculations to find a power law that accurately describes the critical stretch at which the membrane starts to twist, which may be used to estimate the value of unknown parameters by comparison with experimental data. We are grateful for support from the Brandeis Center for Bioinspired Soft Materials, NSF MRSEC, DMR-1420382.

  17. Colloidal quantum dot light-emitting devices.

    PubMed

    Wood, Vanessa; Bulović, Vladimir

    2010-01-01

    Colloidal quantum dot light-emitting devices (QD-LEDs) have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI). We review the key advantages of using quantum dots (QDs) in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs - optical excitation, Förster energy transfer, and direct charge injection - that have been leveraged to create QD-LEDs. We outline the challenges facing QD-LED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desirable color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (>65 lumens per Watt). We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs. PMID:22110863

  18. Dynamics of hard sphere colloidal dispersions

    NASA Technical Reports Server (NTRS)

    Zhu, J. X.; Chaikin, Paul M.; Phan, S.-E.; Russel, W. B.

    1994-01-01

    Our objective is to perform on homogeneous, fully equilibrated dispersions the full set of experiments characterizing the transition from fluid to solid and the properties of the crystalline and glassy solid. These include measurements quantifying the nucleation and growth of crystallites, the structure of the initial fluid and the fully crystalline solid, and Brownian motion of particles within the crystal, and the elasticity of the crystal and the glass. Experiments are being built and tested for ideal microgravity environment. Here we describe the ground based effort, which exploits a fluidized bed to create a homogeneous, steady dispersion for the studies. The differences between the microgravity environment and the fluidized bed is gauged by the Peclet number Pe, which measures the rate of convection/sedimentation relative to Brownian motion. We have designed our experiment to accomplish three types of measurements on hard sphere suspensions in a fluidized bed: the static scattering intensity as a function of angle to determine the structure factor, the temporal autocorrelation function at all scattering angles to probe the dynamics, and the amplitude of the response to an oscillatory forcing to deduce the low frequency viscoelasticity. Thus the scattering instrument and the colloidal dispersion were chosen such as that the important features of each physical property lie within the detectable range for each measurement.

  19. Nonvolatile optically-erased colloidal memristors

    NASA Astrophysics Data System (ADS)

    Huebner, Christopher F.; Tsyalkovsky, Volodymyr; Bandera, Yuriy; Burdette, Mary K.; Shetzline, Jamie A.; Tonkin, Charles; Creager, Stephen E.; Foulger, Stephen H.

    2015-01-01

    A nonconjugated methacrylate terpolymer containing carbazole moieties (electron donors), 1,3,4-oxadiazole moieties (electron acceptors), and Coumarin-6 in the pendant groups was synthesized via free radical copolymerization of methacrylate monomers containing the respective functional groups. The terpolymer was formed into 57 nm particles through a mini-emulsion route. For a thin 100 nm film of the fused particles sandwiched between an indium-tin oxide (ITO) electrode and an Al electrode, the structure behaved as a nonvolatile flash (rewritable) memory with accessible electronic states that could be written, read, and optically erased. The device exhibited a turn-on voltage of ca. -4.5 VDC and a 106 current ratio. A device in the ON high conductance state could be reverted to the OFF state with a short exposure to a 360 nm light source. The development of semiconducting colloidal inks that can be converted into electroactive devices through a continuous processing method is a critical step in the widespread adoption of these 2D manufacturing technologies for printed electronics.

  20. Colloidal diffusion over a random landscape

    NASA Astrophysics Data System (ADS)

    Su, Yun; Ma, Xiao-Guang; Lai, Pik-Yin; Tong, Penger

    2015-03-01

    A two-dimensional quenched random energy landscape is generated by using a randomly packed layer of colloidal spheres of two different sizes fixed on a glass substrate. A number of monodisperse particles diffuse on the top of the first layer particles. The diffusing particles in water feel the gravitational energy landscape U(x,y) generated by the modulated surface of the first layer particles. The trajectories of the particles are obtained by optical microscopy and particle tracking. The energy landscape U(x,y) is obtained from the measured population histogram P(x,y) of the diffusing particles via the Boltzmann distribution, P(x,y) =exp[-U(x,y)/ k_BT], where k_B T is the thermal energy of the particles. The distribution of the energy barrier heights is obtained from the measured U(x,y). From the particle's trajectories, we obtain the dynamical properties of the diffusing particles over the random energy landscape, such as the mean square displacement and distribution of the escape time across the energy barriers. A quantitative relationship between the long-time diffusion coefficient and the random energy landscape is found experimentally, which is in good agreement with the theoretical prediction. *Work supported in part by the Research Grants Council of Hong Kong SAR.

  1. Elastic properties of hollow colloidal particles

    NASA Astrophysics Data System (ADS)

    Zoldesi, C. I.; Ivanovska, I. L.; Quilliet, C.; Wuite, G. J. L.; Imhof, A.

    2008-11-01

    The elastic properties of micrometer-sized hollow colloidal particles obtained by emulsion templating are probed by nanoindentation measurements in which point forces are applied to solvent-filled particles supported on a flat substrate. We show that the shells respond linearly up to forces of 7-21nN , where the indentation becomes of the order of the shell thickness (20-40nm) . In the linear region, the particle deformation is reversible. The measured Young’s modulus (˜200MPa) is comparable to values for stiff rubbers or soft polymers. At larger applied force, we observe a crossover into a nonlinear regime, where the shells assume a buckled shape. Here, the force increases approximately as the square root of the indentation, in agreement with the theory of elasticity of thin shells. We also observe permanent deformation of the shells after probing them repetitively beyond the linear regime. Finally, the measured elastic properties of the shells nicely explain their spontaneous buckling in solution and due to drying.

  2. Behaviour of magnetic Janus-like colloids

    NASA Astrophysics Data System (ADS)

    Novak, Ekaterina V.; Pyanzina, Elena S.; Kantorovich, Sofia S.

    2015-06-01

    We present a theoretical study of Janus-like magnetic particles at low temperature. To describe the basic features of the Janus-type magnetic colloids, we put forward a simple model of a spherical particle with a dipole moment shifted outwards from the centre and oriented perpendicular to the particle radius. Using direct calculations and molecular dynamics computer simulations, we investigate the ground states of small clusters and the behaviour of bigger systems at low temperature. In both cases the important parameter is the dipolar shift, which leads to different ground states and, as a consequence, to a different microscopic behaviour in the situation when the thermal fluctuations are finite. We show that the head-to-tail orientation of dipoles provides a two-particle energy minima only if the dipoles are not shifted from the particle centres. This is one of the key differences from the system of shifted dipolar particles (sd-particles), in which the dipole was shifted outwards radially, studied earlier (Kantorovich et al 2011 Soft Matter 7 5217-27). For sd-particles the dipole could be shifted out of the centre for almost 40% before the head-to-tail orientation was losing its energetic advantage. This peculiarity manifests itself in the topology of the small clusters in the ground state and in the response of the Janus-like particle systems to an external magnetic field at finite temperatures.

  3. Gelation and phase separation of attractive colloids

    NASA Astrophysics Data System (ADS)

    Lu, Peter James

    2008-07-01

    I present several scientific and technical contributions in this thesis. I demonstrate that the gelation of spherical particles with isotropic, short-range attractive interactions is initiated by spinodal decomposition, a thermodynamic instability that triggers the formation of clusters that span and dynamically arrest to create a gel. This simple, universal gelation picture does not depend on microscopic system-specific details---thus broadly describing any particle system with short-range attractions---and suggests that gelation, often considered a purely kinetic phenomenon, is in fact a direct consequence of equilibrium liquid-gas phase separation. I also demonstrate that spherical particles with isotropic attractive interactions exhibit a stable phase---a fluid of particle clusters---that persists on experimental timescales even in the absence of any long-range Coulombic charge repulsion; this contrasts some expectations based on simulation and theory. I describe a new capability I created by integrating accelerated image processing software that I wrote into a high-speed confocal microscope system that I developed: active target-locking, the ability to follow freely-moving complex objects within a microscope sample, even as they change size, shape, and orientation---in real time. Finally, I report continuous, month-long observations of near-critical spinodal decomposition of colloids with isotropic attractions, aboard the International Space Station. I also include detailed descriptions, with examples and illustrations, of the tools and techniques that I have developed to produce these results.

  4. Hydrodynamically Driven Colloidal Assembly in Dip Coating

    NASA Astrophysics Data System (ADS)

    Colosqui, Carlos E.; Morris, Jeffrey F.; Stone, Howard A.

    2013-05-01

    We study the hydrodynamics of dip coating from a suspension and report a mechanism for colloidal assembly and pattern formation on smooth substrates. Below a critical withdrawal speed where the coating film is thinner than the particle diameter, capillary forces induced by deformation of the free surface prevent the convective transport of single particles through the meniscus beneath the film. Capillary-induced forces are balanced by hydrodynamic drag only after a minimum number of particles assemble within the meniscus. The particle assembly can thus enter the thin film where it moves at nearly the withdrawal speed and rapidly separates from the next assembly. The interplay between hydrodynamic and capillary forces produces periodic and regular structures below a critical ratio Ca2/3/Bo<0.7, where Ca and Bo are the capillary and Bond numbers, respectively. An analytical model and numerical simulations are presented for the case of two-dimensional flow with circular particles in suspension. The hydrodynamically driven assembly documented here is consistent with stripe pattern formations observed experimentally in dip coating.

  5. Colloidal quantum dot materials for infrared optoelectronics

    NASA Astrophysics Data System (ADS)

    Arinze, Ebuka S.; Nyirjesy, Gabrielle; Cheng, Yan; Palmquist, Nathan; Thon, Susanna M.

    2015-09-01

    Colloidal quantum dots (CQDs) are an attractive material for optoelectronic applications because they combine flexible, low-cost solution-phase synthesis and processing with the potential for novel functionality arising from their nanostructure. Specifically, the bandgap of films composed of arrays of CQDs can be tuned via the quantum confinement effect for tailored spectral utilization. PbS-based CQDs can be tuned throughout the near and mid-infrared wavelengths and are a promising materials system for photovoltaic devices that harvest non-visible solar radiation. The performance of CQD solar cells is currently limited by an absorption-extraction compromise, whereby photon absorption lengths in the near infrared spectral regime exceed minority carrier diffusion lengths in the bulk films. Several light trapping strategies for overcoming this compromise and increasing the efficiency of infrared energy harvesting will be reviewed. A thin-film interference technique for creating multi-colored and transparent solar cells will be presented, and a discussion of designing plasmonic nanomaterials based on earth-abundant materials for integration into CQD solar cells is developed. The results indicate that it should be possible to achieve high absorption and color-tunability in a scalable nanomaterials system.

  6. Core/shell colloidal semiconductor nanoplatelets.

    PubMed

    Mahler, Benoit; Nadal, Brice; Bouet, Cecile; Patriarche, Gilles; Dubertret, Benoit

    2012-11-14

    We have recently synthesized atomically flat semiconductor colloidal nanoplatelets with quasi 2D geometry. Here, we show that core/shell nanoplatelets can be obtained with a 2D geometry that is conserved. The epitaxial growth of the shell semiconductor is performed at room temperature. We report the detailed synthesis of CdSe/CdS and CdSe/CdZnS structures with different shell thicknesses. The shell growth is characterized both spectroscopically and structurally. In particular, the core/shell structure appears very clearly on high-resolution, high-angle annular dark-field transmission electron microscope images, thanks to the difference of atomic density between the core and the shell. When the nanoplatelets stand on their edge, we can precisely count the number of atomic planes forming the core and the shell. This provides a direct measurement, with atomic precision, of the core nanoplatelets thickness. The constraints exerted by the shell growth on the core is analyzed using global phase analysis. The core/shell nanoplatelets we obtained have narrow emission spectra with full-width at half-maximum close to 20 nm, and quantum yield that can reach 60%. PMID:23057684

  7. Seeded Growth of Colloidal Silica Particles

    NASA Technical Reports Server (NTRS)

    Wurm, David B.

    1999-01-01

    The method of seeded growth was studied for producing mondisperse colloidal silica particles. It was shown that particle size as well as weight percent solids could be controlled by using this method. The particles were characterized by transmission electron microscopy (TEM) and quasielastic light scattering (QELS). The particles were found to have a bimodal size distribution when examined by TEM. The particle size as determined by QELS was found to be roughly 10-20% larger than the particle size as determined by TEM. Furthermore, the polydispersity (standard deviation/mean particle size) as determined by QELS was found to be significantly lower than the polydispersity as determined by TEM. This underscores the importance of using TEM as a characterization technique for determining particle monodispersity. It was also noted that there was an increase in particle roughness as the weight percent of the silica particles increased and a new nucleation of particles was observed as the weight percent approached 13%. A recipe for producing monodisperse silica particles in the 150 nm size range is presented.

  8. Kibble–Zurek mechanism in colloidal monolayers

    PubMed Central

    Deutschländer, Sven; Dillmann, Patrick; Maret, Georg; Keim, Peter

    2015-01-01

    The Kibble–Zurek mechanism describes the evolution of topological defect structures like domain walls, strings, and monopoles when a system is driven through a second-order phase transition. The model is used on very different scales like the Higgs field in the early universe or quantum fluids in condensed matter systems. A defect structure naturally arises during cooling if separated regions are too far apart to communicate (e.g., about their orientation or phase) due to finite signal velocity. This lack of causality results in separated domains with different (degenerated) locally broken symmetry. Within this picture, we investigate the nonequilibrium dynamics in a condensed matter analog, a 2D ensemble of colloidal particles. In equilibrium, it obeys the so-called Kosterlitz–Thouless–Halperin–Nelson–Young (KTHNY) melting scenario with continuous (second order-like) phase transitions. The ensemble is exposed to a set of finite cooling rates covering roughly three orders of magnitude. Along this process, we analyze the defect and domain structure quantitatively via video microscopy and determine the scaling of the corresponding length scales as a function of the cooling rate. We indeed observe the scaling predicted by the Kibble–Zurek mechanism for the KTHNY universality class. PMID:25902492

  9. Colloidal nanocrystals of lithiated group 14 elements.

    PubMed

    Cloud, Jacqueline E; Wang, Yonglong; Yoder, Tara S; Taylor, Lauren W; Yang, Yongan

    2014-12-22

    The synthesis of colloidal nanocrystals (NCs) of lithiated group 14 elements (Z=Si, Ge, and Sn) is reported, which are Li4.4 Si, Li3.75 Si, Li4.4 Ge, and Li4.4 Sn. Lix Z compounds are highly reactive and cannot be synthesized by existing methods. The success relied on separating the surface protection from the crystal formation and using a unique passivating ligand. Bare Lix Z crystals were first produced by milling elemental Li and Z in an argon-filled jar. Then, under the assistance of additional milling, hexyllithium was added to passivate the freshly generated Lix Z NCs. This ball-milling-assisted surface protection method may be generalized to similar systems, such as Nax Z and Kx Z. Moreover, Li4.4 Si and Li4.4 Ge NCs were conformally encapsulated in carbon fibers, providing great opportunities for studying the potential of using Lix Z to mitigate the volume-fluctuation-induced poor cyclability problem confronted by Z anodes in lithium-ion batteries. PMID:25367697

  10. Dynamics of cracking in drying colloidal sheets.

    PubMed

    Sengupta, Rajarshi; Tirumkudulu, Mahesh S

    2016-04-01

    Colloidal dispersions are known to display a fascinating network of cracks on drying. We probe the fracture mechanics of free-standing films of aqueous polymer-particle dispersions. Thin films of the dispersion are cast between a pair of plain steel wires and allowed to dry under ambient conditions. The strain induced on the particle network during drying is relieved by cracking. The stress which causes the films to crack has been calculated by measuring the deflection of the wires. The critical cracking stress varied inversely to the two-thirds' power of the film thickness. We also measure the velocity of the tip of a moving crack. The motion of a crack has been modeled as a competition between the release of the elastic energy stored in the particle network, the increase in surface energy as a result of the growth of a crack, the rate of viscous dissipation of the interstitial fluid and the kinetic energy associated with a moving crack. There is fair agreement between the measured crack velocities and predictions. PMID:26924546

  11. When Colloidal Particles Become Polymer Coils.

    PubMed

    Mourran, Ahmed; Wu, Yaodong; Gumerov, Rustam A; Rudov, Andrey A; Potemkin, Igor I; Pich, Andrij; Möller, Martin

    2016-01-26

    This work concerns interfacial adsorption and attachment of swollen microgel with low- to medium-level cross-linking density. Compared to colloids that form a second, dispersed phase, the suspended swollen microgel particles are ultrahigh molecular weight molecules, which are dissolved like a linear polymer, so that solvent and solute constitute only one phase. In contrast to recent literature in which microgels are treated as particles with a distinct surface, we consider solvent-solute interaction as well as interfacial adsorption based on the chain segments that can form trains of adsorbed segments and loops protruding from the surface into the solvent. We point out experimental results that support this discrimination between particles and microgels. The time needed for swollen microgels to adsorb at the air/water interface can be 3 orders of magnitude shorter than that for dispersed particles and decreases with decreasing cross-linking density. Detailed analysis of the microgels deformation, in the dry state, at a solid surface enabled discrimination particle like microgel in which case spreading was controlled predominantly by the elasticity and molecule like adsorption characterized by a significant overstreching, ultimately leading to chain scission of microgel strands. Dissipative particle dynamics simulations confirms the experimental findings on the interfacial activity and spreading of microgel at liquid/air interface. PMID:26717422

  12. Advancing colloidal quantum dot photovoltaic technology

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Arinze, Ebuka S.; Palmquist, Nathan; Thon, Susanna M.

    2016-06-01

    Colloidal quantum dots (CQDs) are attractive materials for solar cells due to their low cost, ease of fabrication and spectral tunability. Progress in CQD photovoltaic technology over the past decade has resulted in power conversion efficiencies approaching 10%. In this review, we give an overview of this progress, and discuss limiting mechanisms and paths for future improvement in CQD solar cell technology.We briefly summarize nanoparticle synthesis and film processing methods and evaluate the optoelectronic properties of CQD films, including the crucial role that surface ligands play in materials performance. We give an overview of device architecture engineering in CQD solar cells. The compromise between carrier extraction and photon absorption in CQD photovoltaics is analyzed along with different strategies for overcoming this trade-off. We then focus on recent advances in absorption enhancement through innovative device design and the use of nanophotonics. Several light-trapping schemes, which have resulted in large increases in cell photocurrent, are described in detail. In particular, integrating plasmonic elements into CQD devices has emerged as a promising approach to enhance photon absorption through both near-field coupling and far-field scattering effects. We also discuss strategies for overcoming the single junction efficiency limits in CQD solar cells, including tandem architectures, multiple exciton generation and hybrid materials schemes. Finally, we offer a perspective on future directions for the field and the most promising paths for achieving higher device efficiencies.

  13. Towards high resolution ^1H NMR spectra of tannin colloidal aggregates

    NASA Astrophysics Data System (ADS)

    Mirabel, M.; Glories, Y.; Pianet, I.; Dufourc, E. J.

    1999-10-01

    The time dependent colloidal formation of tannins in hydro-alcoholic medium has been studied by 1H-NMR. Line broadening observed with time can be cancelled by making use of magic angle sample spinning (MASS) thus yielding sharp lines that allow structural studies. We used as an example catechin, a constitutive monomer of Bordeaux young red wine tannins. Chemical shift variations of polyphenol protons allow monitoring the time course of aggregation. La formation de tanins colloïdaux au cours du temps, en milieu hydroalcoolique, a été suivie par RMN-^1H. Un élargissement marqué des résonances est observé et peut être supprimé par la rotation de l'échantillon à l'angle magique ce qui ouvre tout un champ d'études structurales sur ces composés colloïdaux. L'exemple proposé est celui de la catéchine, monomère constitutif de tannins présents en grande quantité dans les vins rouges jeunes de Bordeaux. Des variations du déplacement chimique de certains protons polyphénoliques permettent de suivre l'évolution temporelle de l'agrégation.

  14. Colloidal microcapsules: Surface engineering of nanoparticles for interfacial assembly

    NASA Astrophysics Data System (ADS)

    Patra, Debabrata

    2011-12-01

    Colloidal Microcapsules (MCs), i.e. capsules stabilized by nano-/microparticle shells are highly modular inherently multi-scale constructs with applications in many areas of material and biological sciences e.g. drug delivery, encapsulation and microreactors. These MCs are fabricated by stabilizing emulsions via self-assembly of colloidal micro/nanoparticles at liquid-liquid interface. In these systems, colloidal particles serve as modular building blocks, allowing incorporation of the particle properties into the functional capabilities of the MCs. As an example, nanoparticles (NPs) can serve as appropriate antennae to induce response by external triggers (e.g. magnetic fields or laser) for controlled release of encapsulated materials. Additionally, the dynamic nature of the colloidal assembly at liquid-liquid interfaces result defects free organized nanostructures with unique electronic, magnetic and optical properties which can be tuned by their dimension and cooperative interactions. The physical properties of colloidal microcapsules such as permeability, mechanical strength, and biocompatibility can be precisely controlled through the proper choice of colloids and preparation conditions for their. This thesis illustrates the fabrication of stable and robust MCs through via chemical crosslinking of the surface engineered NPs at oil-water interface. The chemical crosslinking assists NPs to form a stable 2-D network structure at the emulsion interface, imparting robustness to the emulsions. In brief, we developed the strategies for altering the nature of chemical interaction between NPs at the emulsion interface and investigated their role during the self-assembly process. Recently, we have fabricated stable colloidal microcapsule (MCs) using covalent, dative as well as non-covalent interactions and demonstrated their potential applications including encapsulation, size selective release, functional devices and biocatalysts.

  15. Sorption of radionuclides at tracer level on mineral colloids

    SciTech Connect

    Hadem, N.; Fourest, B.; Guillaumont, R.

    1995-12-01

    Transport of radionuclides by colloids through the geosphere is an important issue in exercises aimed to assess the safety of an underground radwaste repository sited in a water saturated zone. The first problems to deal with are the characterization of the colloids and their capabilities to sorb, at trace level and even at tracer level, radionuclides. This study investigates the relationships between the sorption of short lived {sup 137}Cs{sup +}, {sup 223}Ra{sup 2+}, {sup 227}Th and {sup 131}I{sup -} and the zeta potential, {zeta}-potential, of well identified colloids, as a function of pH (2 to 11), ionic strength, I (10{sup -3} to 1 M), and colloid concentration (up to 2000 ppm). {xi}-potential is the essential parameter to be considered since it reflects both the stability and the surface charge of the colloid. SiO{sub 2}, TiO{sub 2}, A1{sub 2}O{sub 3} and Th{sub 3}(PO{sub 4}){sub 4} colloids have been chosen as `model colloids`. They are not really found in natural media, but are representative of particles with isoelectric points (i.e.p.) ranging between pH 2 to 9. In some cases the effect of the concentration of the elements has been studied as well, to check saturation effects (Cs and I from 10{sup -11} to 10{sup -2}M). Experimental data show that the distribution of radionuclides between the two phases considered depends mainly on zeta potential, but also on other identified factors.

  16. Colloid facilitated transport of lanthanides through discrete fractures in chalk

    NASA Astrophysics Data System (ADS)

    Tran, Emily; Klein Ben-David, Ofra; Teutsch, Nadya; Weisbrod, Noam

    2015-04-01

    Geological disposal of high-level radioactive waste is the internationally agreed-upon, long term solution for the disposal of long lived radionuclides and spent fuel. Eventually, corrosion of the waste canisters may lead to leakage of their hazardous contents, and the radionuclides can ultimately make their way into groundwater and pose a threat to the biosphere. Engineered bentonite barriers placed around nuclear waste repositories are generally considered sufficient to impede the transport of radionuclides from their storage location to the groundwater. However, colloidal-sized mobile bentonite particles eroding from these barriers have come under investigation as a potential transport vector for radionuclides sorbed to them. In addition, the presence of organic matter in groundwater has been shown to additionally facilitate the uptake of radionuclides by the clay colloids. This study aims to evaluate the transport behaviors of radionuclides in colloid-facilitated transport through a fractured chalk matrix and under geochemical conditions representative of the Negev desert, Israel. Lanthanides are considered an acceptable substitute to actinides for research on radionuclide transportation due to their similar chemical behavior. In this study, the migration of Ce both with and without colloidal particles was explored and compared to the migration of a conservative tracer (bromide). Tracer solutions containing known concentrations of Ce, bentonite colloids, humic acid and bromide were prepared in a matrix solution containing salt concentrations representative of that of the average rain water found in the Negev. These solutions were then injected into a flow system constructed around a naturally fractured chalk core. Samples were analyzed for Ce and Br using ICP-MS, and colloid concentrations were determined using spectrophotographic analysis. Breakthrough curves comparing the rates of transportation of each tracer were obtained, allowing for comparison of

  17. Size-dependent Turbidimatric Quantification of Mobile Colloids in Field Samples

    NASA Astrophysics Data System (ADS)

    Yan, J.; Meng, X.; Jin, Y.

    2015-12-01

    Natural colloids, often defined as entities with sizes < 1.0 μm, have attracted much research attention because of their ability to facilitate the transport of contaminants in the subsurface environment. However, due to their small size and generally low concentrations in field samples, quantification of mobile colloids, especially the smaller fractions (< 0.45 µm), which are operationally defined as dissolved, is largely impeded and hence the natural colloidal pool is greatly overlooked and underestimated. The main objectives of this study are to: (1) develop an experimentally and economically efficient methodology to quantify natural colloids in different size fractions (0.1-0.45 and 0.45-1 µm); (2) quantify mobile colloids including small colloids, < 0.45 µm particularly, in different natural aquatic samples. We measured and generated correlations between mass concentration and turbidity of colloid suspensions, made by extracting and fractionating water dispersible colloids in 37 soils from different areas in the U.S. and Denmark, for colloid size fractions 0.1-0.45 and 0.45-1 µm. Results show that the correlation between turbidity and colloid mass concentration is largely affected by colloid size and iron content, indicating the need to generate different correlations for colloids with constrained size range and iron content. This method enabled quick quantification of colloid concentrations in a large number of field samples collected from freshwater, wetland and estuaries in different size fractions. As a general trend, we observed high concentrations of colloids in the < 0.45 µm fraction, which constitutes a significant percentage of the total mobile colloidal pool (< 1 µm). This observation suggests that the operationally defined cut-off size for "dissolved" phase can greatly underestimate colloid concentration therefore the role that colloids play in the transport of associated contaminants or other elements.

  18. COLLOID-FACILITATED TRANSPORT OF RADIONUCLIDES THROUGH THE VADOSE ZONE

    SciTech Connect

    Flury, Markus

    2003-09-14

    Contaminants have leaked into the vadose zone at the USDOE Hanford reservation. It is important to understand the fate and transport of these contaminants to design remediation strategies and long-term waste management plans at the Hanford reservation. Colloids may play an important role in fate and transport of strongly sorbing contaminants, such as Cs or Pu. This project seeks to improve the basic understanding of colloid and colloid-facilitated transport of contaminants in the vadose zone. The specific objectives addressed are: (1) Determine the structure, composition, and surface charge characteristics of colloidal particles formed under conditions similar to those occurring during leakage of waste typical of Hanford tank supernatants into soils and sediments surrounding the tanks. (2) Characterize the mutual interactions between colloids, contaminant, and soil matrix in batch experiments under various ionic strength and pH conditions. We will investigate the nature of the solid-liquid interactions and the kinetics of the reactions. (3) Evaluate mobility of colloids through soil under different degrees of water saturation and solution chemistry (ionic strength and pH). (4) Determine the potential of colloids to act as carriers to transport the contaminant through the vadose zone and verify the results through comparison with field samples collected under leaking tanks. (5) Improve conceptual characterization of colloid-contaminant-soil interactions and colloid-facilitated transport for implementation into reactive chemical transport models. This project was in part supported by an NSF-IGERT grant to Washington State University. The IGERT grant provided funding for graduate student research and education, and two graduate students were involved in the EMSP project. The IGERT program also supported undergraduate internships. The project is part of a larger EMSP program to study fate and transport of contaminants under leaking Hanford waste tanks. The project has

  19. Does Water Content or Flow Rate Control Colloid Transport in Unsaturated Porous Media?

    SciTech Connect

    Thorsten Knappenberger; Markus Flury; Earl D. Mattson; James B. Harsh

    2014-03-01

    Mobile colloids can play an important role in contaminant transport in soils: many contaminants exist in colloidal form, and colloids can facilitate transport of otherwise immobile contaminants. In unsaturated soils, colloid transport is, among other factors, affected by water content and flow rate. Our objective was to determine whether water content or flow rate is more important for colloid transport. We passed negatively charged polystyrene colloids (220 nm diameter) through unsaturated sand-filled columns under steady-state flow at different water contents (effective water saturations Se ranging from 0.1 to 1.0, with Se = (? – ?r)/(?s – ?r)) and flow rates (pore water velocities v of 5 and 10 cm/min). Water content was the dominant factor in our experiments. Colloid transport decreased with decreasing water content, and below a critical water content (Se < 0.1), colloid transport was inhibited, and colloids were strained in water films. Pendular ring and water film thickness calculations indicated that colloids can move only when pendular rings are interconnected. The flow rate affected retention of colloids in the secondary energy minimum, with less colloids being trapped when the flow rate increased. These results confirm the importance of both water content and flow rate for colloid transport in unsaturated porous media and highlight the dominant role of water content.

  20. Pair interaction of catalytically active colloids: from assembly to escape

    NASA Astrophysics Data System (ADS)

    Sharifi-Mood, Nima; Mozaffari, Ali; Córdova-Figueroa, Ubaldo M.

    2016-07-01

    The dynamics and pair trajectory of two self-propelled colloids are reported. The autonomous motions of the colloids are due to a catalytic chemical reaction taking place asymmetrically on their surfaces that generates a concentration gradient of interactive solutes around the particles and actuate particle propulsion. We consider two spherical particles with symmetric catalytic caps extending over the local polar angles $\\theta^1_{cap}$ and $\\theta^2_{cap}$ from the centers of active sectors in an otherwise quiescent fluid. A combined analytical-numerical technique was developed to solve the coupled mass transfer equation and the hydrodynamics in the Stokes flow regime. The ensuing pair trajectory of the colloids is controlled by the reacting coverages $\\theta^j_{cap}$ and their initial relative orientation with respect to each other. Our analysis indicates two possible scenarios for pair trajectories of catalytic self-propelled particles: either the particles approach, come into contact and assemble or they interact and move away from each other (escape). For arbitrary motions of the colloids, it is found that the direction of particle rotations is the key factor in determining the escape or assembly scenario. Based on the analysis, a phase diagram is sketched for the pair trajectory of the catalytically active particles as a function of active coverages and their initial relative orientations. We believe this study has important implications in elucidation of collective behaviors of auotophoretically self-propelled colloids.