Science.gov

Sample records for active colloidal suspensions

  1. Nonequilibrium Equation of State in Suspensions of Active Colloids

    NASA Astrophysics Data System (ADS)

    Ginot, Félix; Theurkauff, Isaac; Levis, Demian; Ybert, Christophe; Bocquet, Lydéric; Berthier, Ludovic; Cottin-Bizonne, Cécile

    2015-01-01

    Active colloids constitute a novel class of materials composed of colloidal-scale particles locally converting chemical energy into motility, mimicking micro-organisms. Evolving far from equilibrium, these systems display structural organizations and dynamical properties distinct from thermalized colloidal assemblies. Harvesting the potential of this new class of systems requires the development of a conceptual framework to describe these intrinsically nonequilibrium systems. We use sedimentation experiments to probe the nonequilibrium equation of state of a bidimensional assembly of active Janus microspheres and conduct computer simulations of a model of self-propelled hard disks. Self-propulsion profoundly affects the equation of state, but these changes can be rationalized using equilibrium concepts. We show that active colloids behave, in the dilute limit, as an ideal gas with an activity-dependent effective temperature. At finite density, increasing the activity is similar to increasing adhesion between equilibrium particles. We quantify this effective adhesion and obtain a unique scaling law relating activity and effective adhesion in both experiments and simulations. Our results provide a new and efficient way to understand the emergence of novel phases of matter in active colloidal suspensions.

  2. Active colloidal suspensions exhibit polar order under gravity.

    PubMed

    Enculescu, Mihaela; Stark, Holger

    2011-07-29

    Recently, the steady sedimentation profile of a dilute suspension of chemically powered colloids was studied experimentally [J. Palacci et al., Phys. Rev. Lett. 105, 088304 (2010)]. It was found that the sedimentation length increases quadratically with the swimming speed of the active Brownian particles. Here we investigate theoretically the sedimentation of self-propelled particles undergoing translational and rotational diffusion. We find that the measured increase of the sedimentation length is coupled to a partial alignment of the suspension with the mean swimming direction oriented against the gravitational field. We suggest realistic parameter values to observe this polar order. Furthermore, we find that the dynamics of the active suspension can be derived from a generalized free energy functional.

  3. 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

  4. 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

  5. Gold enrichment in active geothermal systems by accumulating colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Hannington, Mark; Harðardóttir, Vigdis; Garbe-Schönberg, Dieter; Brown, Kevin L.

    2016-04-01

    The origins of high-grade hydrothermal ore deposits are debated, but active geothermal systems provide important clues to their formation. The highest concentrations of gold are found in geothermal systems with direct links to island arc magmatism. Yet, similar concentrations have also been found in the absence of any input from arc magmas, for example, in the Reykjanes geothermal field, Iceland. Here we analyse brine samples taken from deep wells at Reykjanes and find that gold concentrations in the reservoir zone have increased over the past seven years from an average of 3 ppb to 14 ppb. The metal concentrations greatly exceed the maximum solubility of gold in the reservoir under saturated conditions and are now nearly two orders of magnitude higher than in mid-ocean ridge black smoker fluids--the direct analogues of Reykjanes deep liquids. We suggest that ongoing extraction of brine, the resulting pressure drop, and increased boiling have caused gold to drop out of solution and become trapped in the reservoir as a colloidal suspension. This process may explain how the stock of metal in the reservoirs of fossil geothermal systems could have increased over time and thus become available for the formation of gold-rich ore deposits.

  6. 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.

  7. Consolidation of colloidal suspensions

    SciTech Connect

    Shih, Wei-Heng; Kim, Seong Il; Shih, Wan Y.; Aksay, I.A. ); Schilling, C.H. Pacific Northwest Lab., Richland, WA )

    1990-08-01

    A key step in the processing of ceramics is the consolidation of powders into engineered shapes. Colloidal processing uses solvents (usually water) and dispersants to break up powder agglomerates in suspension and thereby reduce the pore size in a consolidated compact. However, agglomeration and particle rearrangement leading to pore enlargement can still occur during drying. Therefore, it is beneficial to consolidate the compact as densely as possible during the suspension stage. The consolidation techniques of pressure filtration and centrifugation were studied and the results are reported in this paper. In particular, the steady-state pressure- density relationship was studied, and information was obtained regarding the consolidation process, the microstructure, and the average density profile of consolidated cakes. Recently, we performed Monte Carlo simulations on a cluster-cluster aggregation model with restructuring, and found the exponential relationship between pressure and density is indeed the result of the breaking up of the fractal structural units. Furthermore, we calculated density profiles from the bottom to the top of the consolidated cakes by solving the local static force balance equation in the continuum particulate network. 11 refs., 3 figs.

  8. Living Clusters and Crystals from Low-Density Suspensions of Active Colloids

    NASA Astrophysics Data System (ADS)

    Mognetti, B. M.; Šarić, A.; Angioletti-Uberti, S.; Cacciuto, A.; Valeriani, C.; Frenkel, D.

    2013-12-01

    Recent studies aimed at investigating artificial analogs of bacterial colonies have shown that low-density suspensions of self-propelled particles confined in two dimensions can assemble into finite aggregates that merge and split, but have a typical size that remains constant (living clusters). In this Letter, we address the problem of the formation of living clusters and crystals of active particles in three dimensions. We study two systems: self-propelled particles interacting via a generic attractive potential and colloids that can move toward each other as a result of active agents (e.g., by molecular motors). In both cases, fluidlike “living” clusters form. We explain this general feature in terms of the balance between active forces and regression to thermodynamic equilibrium. This balance can be quantified in terms of a dimensionless number that allows us to collapse the observed clustering behavior onto a universal curve. We also discuss how active motion affects the kinetics of crystal formation.

  9. 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.

  10. 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.

  11. CGEL-2: Structural Studies of Colloidal Suspensions

    NASA Technical Reports Server (NTRS)

    2004-01-01

    These are images of CGEL-2 samples taken during STS-95. They show binary colloidal suspensions that have formed ordered crystalline structures in microgravity. In sample 5, there are more particles therefore, many, many crystallites (small crystals) form. In sample 6, there are less particles therefore, the particles are far apart and few, much larger crystallites form. The white object in the right corner of sample 5 is the stir bar used to mix the sample at the begirning of the mission.

  12. 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)

  13. Structural properties of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Méndez-Alcaraz, J. M.; Chávez-Páez, M.; D'Aguanno, B.; Klein, R.

    1995-02-01

    Structural properties of three- and two-dimensional colloids composed by hard spheres and/or by Yukawa particles, which can have different diameters and charges, are studied by solving the Ornstein-Zernike equation, together with Percus-Yevick, hypernetted chain and Rogers-Young approximations. From the partial radial distribution functions gij( r) the partial structure factors Sij( k) are determined, and with them the compressibility structure factor Sx( k), the measured structure factor SM( k) and the Bhatia-Thornton structure factors SNN( k), SNQ( k) and SQQ( k). As an effect of diameter and/or charge polydispersity on the structure of binary mixtures, the position and height of the main peak of SM( k), and its value at k = 0, change non-monotonously with the composition. In the case of binary mixtures of hard and Yukawa spheres the structure is given by two different scales. A liquid-solid phase transition induced by a change in the dimensionality was found for monodisperse systems.

  14. 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.

  15. Theory of activated penetrant diffusion in viscous fluids and colloidal suspensions

    SciTech Connect

    Zhang, Rui; Schweizer, Kenneth S.

    2015-10-14

    We heuristically formulate a microscopic, force level, self-consistent nonlinear Langevin equation theory for activated barrier hopping and non-hydrodynamic diffusion of a hard sphere penetrant in very dense hard sphere fluid matrices. Penetrant dynamics is controlled by a rich competition between force relaxation due to penetrant self-motion and collective matrix structural (alpha) relaxation. In the absence of penetrant-matrix attraction, three activated dynamical regimes are predicted as a function of penetrant-matrix size ratio which are physically distinguished by penetrant jump distance and the nature of matrix motion required to facilitate its hopping. The penetrant diffusion constant decreases the fastest with size ratio for relatively small penetrants where the matrix effectively acts as a vibrating amorphous solid. Increasing penetrant-matrix attraction strength reduces penetrant diffusivity due to physical bonding. For size ratios approaching unity, a distinct dynamical regime emerges associated with strong slaving of penetrant hopping to matrix structural relaxation. A crossover regime at intermediate penetrant-matrix size ratio connects the two limiting behaviors for hard penetrants, but essentially disappears if there are strong attractions with the matrix. Activated penetrant diffusivity decreases strongly with matrix volume fraction in a manner that intensifies as the size ratio increases. We propose and implement a quasi-universal approach for activated diffusion of a rigid atomic/molecular penetrant in a supercooled liquid based on a mapping between the hard sphere system and thermal liquids. Calculations for specific systems agree reasonably well with experiments over a wide range of temperature, covering more than 10 orders of magnitude of variation of the penetrant diffusion constant.

  16. Theory of activated penetrant diffusion in viscous fluids and colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Schweizer, Kenneth S.

    2015-10-01

    We heuristically formulate a microscopic, force level, self-consistent nonlinear Langevin equation theory for activated barrier hopping and non-hydrodynamic diffusion of a hard sphere penetrant in very dense hard sphere fluid matrices. Penetrant dynamics is controlled by a rich competition between force relaxation due to penetrant self-motion and collective matrix structural (alpha) relaxation. In the absence of penetrant-matrix attraction, three activated dynamical regimes are predicted as a function of penetrant-matrix size ratio which are physically distinguished by penetrant jump distance and the nature of matrix motion required to facilitate its hopping. The penetrant diffusion constant decreases the fastest with size ratio for relatively small penetrants where the matrix effectively acts as a vibrating amorphous solid. Increasing penetrant-matrix attraction strength reduces penetrant diffusivity due to physical bonding. For size ratios approaching unity, a distinct dynamical regime emerges associated with strong slaving of penetrant hopping to matrix structural relaxation. A crossover regime at intermediate penetrant-matrix size ratio connects the two limiting behaviors for hard penetrants, but essentially disappears if there are strong attractions with the matrix. Activated penetrant diffusivity decreases strongly with matrix volume fraction in a manner that intensifies as the size ratio increases. We propose and implement a quasi-universal approach for activated diffusion of a rigid atomic/molecular penetrant in a supercooled liquid based on a mapping between the hard sphere system and thermal liquids. Calculations for specific systems agree reasonably well with experiments over a wide range of temperature, covering more than 10 orders of magnitude of variation of the penetrant diffusion constant.

  17. Nucleation of flocs in dilute colloidal suspensions

    SciTech Connect

    Agrawal, D.C.; Raj, R.; Cohen, C. )

    1989-11-01

    In contrast to earlier theories which assume that coagulation of particles in dilute colloidal suspensions occurs by random collisions, the authors present evidence that coagulation is limited by a nucleation and growth phenomenon, typical of a phase transformation. They show that suspensions of well-dispersed particles, which are almost indefinitely stable, flocculate rapidly when seeded with pregrown flocs. The nucleation argument is supported further by the observation that flocs which are grown at low {zeta} potential, where the particles strongly attract, do not peptize when the pH is changed to high {zeta} potential, where the attraction is weak. The experiments were carried out with aqueous dispersions of alumina particles. The timedependent change in cluster sizes was measured by in situ photon correlation spectroscopy. The observations raise the question of agglomeration as a phase transformation, involving a change in entropy, when the system moves from a dispersed to a flocculated state.

  18. Source of cytotoxicity in a colloidal silver nanoparticle suspension

    NASA Astrophysics Data System (ADS)

    Kukut Hatipoglu, Manolya; Keleştemur, Seda; Altunbek, Mine; Culha, Mustafa

    2015-05-01

    Silver nanoparticles (AgNPs) are increasingly used in a variety of applications because of their potential antimicrobial activity and their plasmonic and conductivity properties. In this study, we investigated the source of cytotoxicity, genotoxicity, and reactive oxygen species (ROS) production on human dermal fibroblast and human lung cancer (A549) cell lines upon exposure to AgNP colloidal suspensions prepared with the simplest and most commonly used Lee-Meisel method with a variety of reaction times and the concentrations of the reducing agent. The AgNPs synthesized with shorter reaction times were more cytotoxic and genotoxic due to the presence of a few nanometer-sized AgNP seeds. The suspensions prepared with an increased citrate concentration were not cytotoxic, but they induced more ROS generation on A549 cells due to the high citrate concentration. The genotoxicity of the suspension decreased significantly at the higher citrate concentrations. The analysis of both transmission electron microscopy images from the dried droplet areas of the colloidal suspensions and toxicity data indicated that the AgNP seeds were the major source of toxicity. The completion of the nucleation step and the formation of larger AgNPs effectively decreased the toxicity.

  19. Source of cytotoxicity in a colloidal silver nanoparticle suspension.

    PubMed

    Hatipoglu, Manolya Kukut; Keleştemur, Seda; Altunbek, Mine; Culha, Mustafa

    2015-05-15

    Silver nanoparticles (AgNPs) are increasingly used in a variety of applications because of their potential antimicrobial activity and their plasmonic and conductivity properties. In this study, we investigated the source of cytotoxicity, genotoxicity, and reactive oxygen species (ROS) production on human dermal fibroblast and human lung cancer (A549) cell lines upon exposure to AgNP colloidal suspensions prepared with the simplest and most commonly used Lee–Meisel method with a variety of reaction times and the concentrations of the reducing agent. The AgNPs synthesized with shorter reaction times were more cytotoxic and genotoxic due to the presence of a few nanometer-sized AgNP seeds. The suspensions prepared with an increased citrate concentration were not cytotoxic, but they induced more ROS generation on A549 cells due to the high citrate concentration. The genotoxicity of the suspension decreased significantly at the higher citrate concentrations. The analysis of both transmission electron microscopy images from the dried droplet areas of the colloidal suspensions and toxicity data indicated that the AgNP seeds were the major source of toxicity. The completion of the nucleation step and the formation of larger AgNPs effectively decreased the toxicity.

  20. 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.

  1. Measuring colloidal osmotic compressibility of a polymer-crowded colloidal suspension by optical trapping

    NASA Astrophysics Data System (ADS)

    Fu, Jinxin; Kara, Vural; Ou-Yang, H. Daniel

    2013-03-01

    Particle interactions determine the stability of nanoparticle suspensions and the phase separation of particle-polymer mixtures. However, due to the small sizes of the dispersed nanoparticles, it is not easy to directly measure interaction forces between particles in a colloidal suspension. In this paper, we propose an ``Optical Bottle'' approach to quantify these particle interactions in a suspension by measuring the colloidal osmotic compressibility of the nanoparticles. Virial expansion of the colloidal osmotic compressibility yields virial coefficients of different orders. The second order virial coefficient of aqueous suspensions of colloidal polystyrene nanospheres in the presence of high-salt (KCl) and polyethylene glycol (PEG) is found to decrease with increasing PEG concentration, suggesting an attractive depletion interaction between the PEG-crowed polystyrene particles.

  2. Einstein's osmotic equilibrium of colloidal suspensions in conservative force fields

    NASA Astrophysics Data System (ADS)

    Fu, Jinxin; Ou-Yang, H. Daniel

    2014-09-01

    Predicted by Einstein in his 1905 paper on Brownian motion, colloidal particles in suspension reach osmotic equilibrium under gravity. The idea was demonstrated by J.B. Perrin to win Nobel Prize in Physics in 1926. We show Einstein's equation for osmotic equilibrium can be applied to colloids in a conservative force field generated by optical gradient forces. We measure the osmotic equation of state of 100nm Polystyrene latex particles in the presence of KCl salt and PEG polymer. We also obtain the osmotic compressibility, which is important for determining colloidal stability and the internal chemical potential, which is useful for predicting the phase transition of colloidal systems. This generalization allows for the use of any conservative force fields for systems ranging from colloidal systems to macromolecular solutions.

  3. Coarsening mechanics of a colloidal suspension in toggled fields.

    PubMed

    Bauer, Jonathan L; Liu, Yifei; Kurian, Martin J; Swan, James W; Furst, Eric M

    2015-08-21

    Suspensions of paramagnetic colloids are driven to phase separate and self-assemble in toggled magnetic fields. At field strengths above 575 A/m and toggle frequencies between 0.66 and 2 Hz, an initial gel-like, arrested network collapses into condensed, ellipsoidal aggregates. The evolution to this equilibrium structure occurs via a Rayleigh-Plateau instability. The toggle frequency ν determines the fluidity of the breakup process. At frequencies between 0.66 and 1.5 Hz, the suspension breaks up similar to a viscous, Newtonian fluid. At frequencies ν > 1.5 Hz, the network ruptures like a viscoplastic material. The field strength alters the onset time of the instability. A power law relationship emerges as the scaled frequency and field strength can be used to predict the onset of breakup. These results further aid in understanding the mechanics and dynamics of the phase separation process of suspensions of polarizable colloids in toggled external fields. PMID:26298150

  4. Coarsening mechanics of a colloidal suspension in toggled fields

    NASA Astrophysics Data System (ADS)

    Bauer, Jonathan L.; Liu, Yifei; Kurian, Martin J.; Swan, James W.; Furst, Eric M.

    2015-08-01

    Suspensions of paramagnetic colloids are driven to phase separate and self-assemble in toggled magnetic fields. At field strengths above 575 A/m and toggle frequencies between 0.66 and 2 Hz, an initial gel-like, arrested network collapses into condensed, ellipsoidal aggregates. The evolution to this equilibrium structure occurs via a Rayleigh-Plateau instability. The toggle frequency ν determines the fluidity of the breakup process. At frequencies between 0.66 and 1.5 Hz, the suspension breaks up similar to a viscous, Newtonian fluid. At frequencies ν > 1.5 Hz, the network ruptures like a viscoplastic material. The field strength alters the onset time of the instability. A power law relationship emerges as the scaled frequency and field strength can be used to predict the onset of breakup. These results further aid in understanding the mechanics and dynamics of the phase separation process of suspensions of polarizable colloids in toggled external fields.

  5. Coarsening mechanics of a colloidal suspension in toggled fields.

    PubMed

    Bauer, Jonathan L; Liu, Yifei; Kurian, Martin J; Swan, James W; Furst, Eric M

    2015-08-21

    Suspensions of paramagnetic colloids are driven to phase separate and self-assemble in toggled magnetic fields. At field strengths above 575 A/m and toggle frequencies between 0.66 and 2 Hz, an initial gel-like, arrested network collapses into condensed, ellipsoidal aggregates. The evolution to this equilibrium structure occurs via a Rayleigh-Plateau instability. The toggle frequency ν determines the fluidity of the breakup process. At frequencies between 0.66 and 1.5 Hz, the suspension breaks up similar to a viscous, Newtonian fluid. At frequencies ν > 1.5 Hz, the network ruptures like a viscoplastic material. The field strength alters the onset time of the instability. A power law relationship emerges as the scaled frequency and field strength can be used to predict the onset of breakup. These results further aid in understanding the mechanics and dynamics of the phase separation process of suspensions of polarizable colloids in toggled external fields.

  6. Constant Stress and Pressure Rheology of Colloidal Suspensions.

    PubMed

    Wang, Mu; Brady, John F

    2015-10-01

    We study the constant stress and pressure rheology of dense hard-sphere colloidal suspensions using Brownian dynamics simulation. Expressing the flow behavior in terms of the friction coefficient-the ratio of shear to normal stress-reveals a shear arrest point from the collapse of the rheological data in the non-Brownian limit. The flow curves agree quantitatively (when scaled) with the experiments of Boyer et al. [Phys. Rev. Lett. 107, 188301 (2011)]. Near suspension arrest, both the shear and the incremental normal viscosities display a universal power law divergence. This work shows the important role of jamming on the arrest of colloidal suspensions and illustrates the care needed when conducting and analyzing experiments and simulations near the flow-arrest transition. PMID:26550755

  7. 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.

  8. Reentrant phase transition in charged colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Arora, Akhilesh K.; Tata, B. V. R.; Sood, A. K.; Kesavamoorthy, R.

    1988-06-01

    We report the observation of a novel phase transition in dilute aqueous suspensions of polystyrene particles as a function of ionic impurity concentration C. The suspension phase separates into dense and rare phases only for a restricted range of C which depends on particle concentration n. The dense phase has liquidlike or crystalline order depending on n and C. Free energies of the homogeneous and the phase-separated states are calculated with an effective interparticle potential. The calculated phase diagram is in qualitative agreement with the present experimental results.

  9. 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

  10. Drying of a colloidal suspension in confined geometry

    NASA Astrophysics Data System (ADS)

    Leng, Jacques

    2010-08-01

    We describe experiments on drying of a hard-sphere colloidal suspension in confined geometry where a drop of the suspension is squeezed in between two circular transparent plates and allowed to dry. In this situation, the geometry controls the vapor removal rate and leads to a facilitated observation directly inside the drop. We monitor the drying kinetics of colloids of two sizes and several volume fractions; in most cases, the drying kinetics leads to the formation of a crust at the level of the meniscus which can be either crystalline or glassy, the transition between the two cases being triggered by the local deposition velocity, itself slaved to the evaporation rate. It yields a final dry state which is either polycrystalline or amorphous. The crust is also responsible for a shape instability of the quasi-two-dimensional drop shrinking upon evaporation but with a crust opposing mechanical and flow resistance, and possibly a partial adhesion on the substrate.

  11. Depletion-induced structure and dynamics in bimodal colloidal suspensions.

    SciTech Connect

    Sikorski, M.; Sandy, A. R.; Narayanan, S.

    2011-05-03

    Combined small angle x-ray scattering and x-ray photon correlation spectroscopy studies of moderately concentrated bimodal hard-sphere colloidal suspensions in the fluid phase show that depletion-induced demixing introduces spatially heterogeneous dynamics with two distinct time scales. The adhesive nature, as well as the mobility, of the large particles is determined by the level of interaction within the monomodal domains. This interaction is driven by osmotic forces, which are governed by the relative concentration of the constituents.

  12. Stress distributions in flowing aggregated colloidal suspensions

    SciTech Connect

    Silbert, L.E.; Farr, R.S.; Melrose, J.R.; Ball, R.C.

    1999-09-01

    Simulations of the flow of concentrated aggregated colloidal systems, at the particulate level, are used to investigate the distribution of stresses in the shear-thinning regime. It is found that the distribution of shear stress carried by interparticle bonds decays approximately exponentially at large stresses, but with a double-exponential distribution for values of positive stress. The microstructural mechanisms associated with large stresses are manifested in clusters which dominate the positive contribution to the stress in the system. Towards the end of shear thinning the highest forces occur along bonds defining rods of particles aligned approximately along the flow-compression direction. We propose that the rheology of such systems is determined by a rupture{endash}reformation process of these clusters of stress concentration during the flow. The aggregation forces play the role of enhancing such stress concentration by stabilizing clusters against buckling. {copyright} {ital 1999 American Institute of Physics.}

  13. On Determination of the Equation of State of Colloidal Suspensions

    NASA Astrophysics Data System (ADS)

    Sirorattanakul, Krittanon; Huang, Hao; Uhl, Christopher; Ou-Yang, Daniel

    Colloidal suspensions are the main ingredients for a variety of materials in our daily life, e.g., milk, salad dressing, skin lotions and paint for wall coatings. Material properties of these systems require an understanding of the equation of state of these materials. Our project aims to experimentally determine the equation of state of colloidal suspensions by microfluidics, dielectrophoresis (DEP) and optical imaging. We use fluorescent polystyrene latexes as a model system for this study. Placing semi-permeable membranes between microfluidics channels, which made from PDMS, we control the particle concentration and ionic strengths of the suspension. We use osmotic equilibrium equation to analyze the particle concentration distribution in a potential force field created by DEP. We use confocal optical imaging to measure the spatial distribution of the particle concentration. We compare the results of our experimental study with data obtained by computer simulation of osmotic equilibrium of interacting colloids. NSF DMR-0923299, Emulsion Polymer Institute, Department of Physics, Bioengineering Program of Lehigh University.

  14. Aggregation and colloidal stability of fine-particle coal suspensions

    SciTech Connect

    Schroeder, P.R.; Rubin, A.J.

    1984-01-01

    The aggregation and colloidal stability of colloidal coal suspensions in the presence of varying concentrations of hydrogen ions, neutral salts, and aluminum sulfate were investigated. Critical concentration and critical pH values for coagulation and stabilization were determined from turbidity changes during settling following aggregation. Two colloidal suspensions of a bituminous coal representing stability extremes due to oxidation were compared. In the absence of other coagulants, vigorous oxidation lowered the isoelectric point of the coal sol from pH 5.1 to pH 1.1 and the pH for stabilization from 7.5 to 2.6. The coagulation of the suspensions followed the Schulze-Hardy rule as hydrophobic sols although the oxidized coal sol was slightly less sensitive to neutral salts. The entire log aluminum sulfate concentration-pH stability limit diagram for the oxidized coal sol was established. The boundaries of settling of the coal in the presence of aluminum sulfate were similar to other hydrophobic sols except for small differences in alkaline solution. Regions of ionic coagulation, rapid coagulation due to enmeshment in aluminum hydroxide precipitate, and restabilization were also observed and delineated.

  15. Forced spreading of films and droplets of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Espin, Leonardo; Kumar, Satish

    2014-11-01

    When a thin film of a colloidal suspension flows over a substrate, uneven distribution of the suspended particles can lead to an uneven coating. Motivated by this phenomenon, we analyse the flow of perfectly wetting films and droplets of colloidal suspensions down an inclined plane. Lubrication theory and the rapid-vertical-diffusion approximation are used to derive a coupled pair of one-dimensional partial differential equations describing the evolution of the interface height and particle concentration. Precursor films are assumed to be present, the colloidal particles are taken to be hard spheres, and particle and liquid dynamics are coupled through a concentration-dependent viscosity and diffusivity. We find that for sufficiently high Péclet numbers, even small initial concentration inhomogeneities produce viscosity gradients that cause the film or droplet front to evolve continuously in time instead of travelling without changing shape as happens in the absence of colloidal particles. Our results suggest that particle concentration gradients can have a dramatic influence on interface evolution in flowing films and droplets, a finding which may be relevant for understanding the onset of patterns that are observed experimentally.

  16. Mechanism of cake buildup in crossflow filtration of colloidal suspensions

    SciTech Connect

    Jiao, D.; Sharma, M.M. )

    1994-02-01

    Experimental results are presented for the crossflow filtration of concentrated bentonite suspensions. It is proposed that the hydrodynamic forces acting on the suspended colloids determine the rate of cake buildup and, therefore, the fluid loss rate. A simple model is proposed that predicts a power law relationship between the filtration rate and the shear stress at the cake surface. This is found to be consistent with experimental data at different filtration times at various suspension flow rates using three different suspensions. The mode shows that the cake formed will be inhomogeneous with smaller and smaller particles being deposited as filtration proceeds. An equilibrium cake thickness is achieved when no particles small enough to be deposited are available in the suspension. The cake thickness as a function of time can be computed form the model. It is also shown that for a given suspension rheology and flow rate there exists a critical permeability of the filter below which no cake will be formed. This critical permeability has been computed for these experiments. The model suggests that the equilibrium cake thickness can be precisely controlled by an appropriate choice of suspension flow rate and filter permeability. These observations have important implications in cross-flow filtration and in slip-casting of inorganic membranes.

  17. The renormalized Jellium model of colloidal suspensions with multivalent counterions

    NASA Astrophysics Data System (ADS)

    Colla, Thiago E.; Levin, Yan

    2010-12-01

    An extension of the renormalized Jellium model which allows to study colloidal suspensions containing trivalent counterions is proposed. The theory is based on a modified Poisson-Boltzmann equation which incorporates the effects of counterion correlations near the colloidal surfaces using a new boundary condition. The renormalized charges, the counterion density profiles, and osmotic pressures can be easily calculated using the modified renormalized Jellium model. The results are compared with the ones obtained using the traditional Wigner-Seitz (WS) cell approximation also with a new boundary condition. We find that while the thermodynamic functions obtained within the renormalized Jellium model are in a good agreement with their WS counterpart, the effective charges predicted by the two theories can be significantly different.

  18. Convection in colloidal suspensions with particle-concentration-dependent viscosity.

    PubMed

    Glässl, M; Hilt, M; Zimmermann, W

    2010-07-01

    The onset of thermal convection in a horizontal layer of a colloidal suspension is investigated in terms of a continuum model for binary-fluid mixtures where the viscosity depends on the local concentration of colloidal particles. With an increasing difference between the viscosity at the warmer and the colder boundary the threshold of convection is reduced in the range of positive values of the separation ratio psi with the onset of stationary convection as well as in the range of negative values of psi with an oscillatory Hopf bifurcation. Additionally the convection rolls are shifted downwards with respect to the center of the horizontal layer for stationary convection psi>0 and upwards for the Hopf bifurcation (psi<0.

  19. Dynamics of a model colloidal suspension from dilute to freezing.

    PubMed

    Hannam, S D W; Daivis, P J; Bryant, G

    2016-07-01

    Molecular dynamics simulation was used to study a model colloidal suspension at a range of packing fractions from the dilute limit up to the freezing point. This study builds on previous work by the authors which modeled the colloidal particles with a hard core surrounded by a Weeks-Chandler-Anderson potential with modified interaction parameters, and included an explicit solvent. In this work, we study dynamical properties of the model by first calculating the velocity autocorrelation function, the self-diffusion coefficient, and the mutual diffusion coefficient. We also perform detailed calculations of the colloidal particle intermediate scattering function to study the change in dynamics leading up to the freezing point, and to determine whether the current model can be used to interpret light scattering experiments. We then perform a multiexponential analysis on the intermediate scattering function results and find that the data are fitted well by the sum of two exponentials, which is in line with previous analysis of experimental colloidal suspensions. The amplitudes and decay coefficients of the two modes are determined over a large range of wave vectors at packing fractions leading up to the freezing point. We found that the maximum wave vector at which macroscopic diffusive behavior was observed decreased as the packing fraction increased, and a simple extrapolation shows the maximum wave vector going to zero at the melting point. Lastly, the ratio of the two decay coefficients is compared to the scaling law proposed by Segrè and Pusey [Phys. Rev. Lett. 77, 771 (1996)PRLTAO0031-900710.1103/PhysRevLett.77.771]. It was found that the ratio was not constant, but instead was wave vector dependent. PMID:27575191

  20. Dynamics of a model colloidal suspension from dilute to freezing

    NASA Astrophysics Data System (ADS)

    Hannam, S. D. W.; Daivis, P. J.; Bryant, G.

    2016-07-01

    Molecular dynamics simulation was used to study a model colloidal suspension at a range of packing fractions from the dilute limit up to the freezing point. This study builds on previous work by the authors which modeled the colloidal particles with a hard core surrounded by a Weeks-Chandler-Anderson potential with modified interaction parameters, and included an explicit solvent. In this work, we study dynamical properties of the model by first calculating the velocity autocorrelation function, the self-diffusion coefficient, and the mutual diffusion coefficient. We also perform detailed calculations of the colloidal particle intermediate scattering function to study the change in dynamics leading up to the freezing point, and to determine whether the current model can be used to interpret light scattering experiments. We then perform a multiexponential analysis on the intermediate scattering function results and find that the data are fitted well by the sum of two exponentials, which is in line with previous analysis of experimental colloidal suspensions. The amplitudes and decay coefficients of the two modes are determined over a large range of wave vectors at packing fractions leading up to the freezing point. We found that the maximum wave vector at which macroscopic diffusive behavior was observed decreased as the packing fraction increased, and a simple extrapolation shows the maximum wave vector going to zero at the melting point. Lastly, the ratio of the two decay coefficients is compared to the scaling law proposed by Segrè and Pusey [Phys. Rev. Lett. 77, 771 (1996), 10.1103/PhysRevLett.77.771]. It was found that the ratio was not constant, but instead was wave vector dependent.

  1. Dynamics of a model colloidal suspension from dilute to freezing.

    PubMed

    Hannam, S D W; Daivis, P J; Bryant, G

    2016-07-01

    Molecular dynamics simulation was used to study a model colloidal suspension at a range of packing fractions from the dilute limit up to the freezing point. This study builds on previous work by the authors which modeled the colloidal particles with a hard core surrounded by a Weeks-Chandler-Anderson potential with modified interaction parameters, and included an explicit solvent. In this work, we study dynamical properties of the model by first calculating the velocity autocorrelation function, the self-diffusion coefficient, and the mutual diffusion coefficient. We also perform detailed calculations of the colloidal particle intermediate scattering function to study the change in dynamics leading up to the freezing point, and to determine whether the current model can be used to interpret light scattering experiments. We then perform a multiexponential analysis on the intermediate scattering function results and find that the data are fitted well by the sum of two exponentials, which is in line with previous analysis of experimental colloidal suspensions. The amplitudes and decay coefficients of the two modes are determined over a large range of wave vectors at packing fractions leading up to the freezing point. We found that the maximum wave vector at which macroscopic diffusive behavior was observed decreased as the packing fraction increased, and a simple extrapolation shows the maximum wave vector going to zero at the melting point. Lastly, the ratio of the two decay coefficients is compared to the scaling law proposed by Segrè and Pusey [Phys. Rev. Lett. 77, 771 (1996)PRLTAO0031-900710.1103/PhysRevLett.77.771]. It was found that the ratio was not constant, but instead was wave vector dependent.

  2. Colloidal Suspensions in Shear Flow : a Real Space Study

    NASA Astrophysics Data System (ADS)

    Derks, D.

    2006-09-01

    We investigate the effect of shear flow on the microstructure of colloidal suspensions by means of microscopy. Systems of nearly equally sized particles are used, whose interactions and phase behavior are predominantly determined by their size and shape, and can further be tuned by the addition of polymers. Recently, a new type of shear cell was developed to study flowing suspensions in real space. The key property of this setup is the counter-rotating principle of the cone and plate, opening up the possibility to create a stationary layer in the bulk of the cell. In Chapter 2, we elaborate on the details of this setup and its performance. Fluorescence confocal microscopy is used to visualize the sheared suspension, and allows imaging of individual particles in the bulk in the stationary plane for a prolonged time. This way, the particle positions in a layer of, for example, a sheared colloidal crystal can be tracked. The particle dynamics in colloidal crystals in shear flow are the subject of Chapter 3. Here, the particles interact through a (nearly) hard sphere potential. Apart from the alignment of the crystal in the shear field and the collective zigzag motion, which had also been deduced from early scattering experiments, we find that random particle displacements increase with shear rate. Those increased fluctuations result in shear induced melting when their mean square displacement has reached about 13 % of the particle separation. Apart from hard spheres, we investigate mixtures of colloids and polymers in shear flow. The polymers cause an effective attraction between the spheres, leading to phase separation into a colloid rich (polymer poor) and a colloid poor (polymer rich) phase at sufficiently high colloid and polymer concentration. In Chapter 4, we study the demixing process in the (spinodal) two-phase region of the phase diagram. The system is quenched from an initially almost homogeneous state at very high shear rate to a low shear rate. A spinodal

  3. Lack of Syneresis during Gelation of Dense Colloidal Suspensions.

    PubMed

    Helbig; Hütter; Schönholzer

    2000-02-01

    This study reports experimental results about the shrinkage of particle networks produced by pH-induced destabilization of dense colloidal suspensions. The resulting solid networks exhibit no syneresis effects, at least prior to aging of the gel. From this lack of syneresis it is concluded that the solidification in wet particle systems either is not purely determined by energy (but is also influenced by entropic effects) or cannot be explained within the framework of (static) equilibrium thermodynamics at all. Copyright 2000 Academic Press.

  4. Convection in a colloidal suspension in a closed horizontal cell

    SciTech Connect

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

    2015-02-15

    The experimentally detected [1] oscillatory regimes of convection in a colloidal suspension of nanoparticles with a large anomalous thermal diffusivity in a closed horizontal cell heated from below have been simulated numerically. The concentration inhomogeneity near the vertical cavity boundaries arising from the interaction of thermal-diffusion separation and convective mixing has been proven to serve as a source of oscillatory regimes (traveling waves). The dependence of the Rayleigh number at the boundary of existence of the traveling-wave regime on the aspect ratio of the closed cavity has been established. The spatial characteristics of the emerging traveling waves have been determined.

  5. Convection of colloidal suspensions stratified by thermodiffusion and gravity.

    PubMed

    Smorodin, B L; Cherepanov, I N

    2014-11-01

    The convective stability thresholds and nonlinear evolution of convective rolls are numerically investigated in a plane horizontal layer of a colloidal suspension with positive separation ratio in the case of no-slip, impermeable horizontal boundaries. The characteristics of the steady and oscillatory patterns are analyzed under heating and gravity stratification. The standing and traveling waves are found as stable solutions within certain domains of parameters (on the plane of the Rayleigh and the Boltzmann numbers). Complex bifurcation and spatiotemporal properties are caused by the interaction of gravity sedimentation, Soret-induced gradients, and convective mixing of the fluid. PMID:25416242

  6. Convection of colloidal suspensions stratified by thermodiffusion and gravity.

    PubMed

    Smorodin, B L; Cherepanov, I N

    2014-11-01

    The convective stability thresholds and nonlinear evolution of convective rolls are numerically investigated in a plane horizontal layer of a colloidal suspension with positive separation ratio in the case of no-slip, impermeable horizontal boundaries. The characteristics of the steady and oscillatory patterns are analyzed under heating and gravity stratification. The standing and traveling waves are found as stable solutions within certain domains of parameters (on the plane of the Rayleigh and the Boltzmann numbers). Complex bifurcation and spatiotemporal properties are caused by the interaction of gravity sedimentation, Soret-induced gradients, and convective mixing of the fluid.

  7. Colloidal suspensions of C-particles: Entanglement, percolation and microrheology.

    PubMed

    Hoell, Christian; Löwen, Hartmut

    2016-05-01

    We explore structural and dynamical behavior of concentrated colloidal suspensions made up by C-shape particles using Brownian dynamics computer simulations and theory. In particular, we focus on the entanglement process between nearby particles for almost closed C-shapes with a small opening angle. Depending on the opening angle and the particle concentration, there is a percolation transition for the cluster of entangled particles which shows the classical scaling characteristics. In a broad density range below the percolation threshold, we find a stretched exponential function for the dynamical decorrelation of the entanglement process. Finally, we study a setup typical in microrheology by dragging a single tagged particle with constant speed through the suspension. We measure the cluster connected to and dragged with this tagged particle. In agreement with a phenomenological theory, the size of the dragged cluster depends on the dragging direction and increases markedly with the dragging speed.

  8. Colloidal suspensions of C-particles: Entanglement, percolation and microrheology

    NASA Astrophysics Data System (ADS)

    Hoell, Christian; Löwen, Hartmut

    2016-05-01

    We explore structural and dynamical behavior of concentrated colloidal suspensions made up by C-shape particles using Brownian dynamics computer simulations and theory. In particular, we focus on the entanglement process between nearby particles for almost closed C-shapes with a small opening angle. Depending on the opening angle and the particle concentration, there is a percolation transition for the cluster of entangled particles which shows the classical scaling characteristics. In a broad density range below the percolation threshold, we find a stretched exponential function for the dynamical decorrelation of the entanglement process. Finally, we study a setup typical in microrheology by dragging a single tagged particle with constant speed through the suspension. We measure the cluster connected to and dragged with this tagged particle. In agreement with a phenomenological theory, the size of the dragged cluster depends on the dragging direction and increases markedly with the dragging speed.

  9. 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

  10. 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.

  11. Probing Dynamical Heterogeneity in Dense Colloidal Suspensions with Depletion Attraction

    NASA Astrophysics Data System (ADS)

    Brown, Zachery; Hogan, Gregory; Gratale, Matthew; Yodh, Arjun G.; Habdas, Piotr

    We directly observe the particle dynamics in dense colloidal suspensions. Using depletion attraction, we vary inter particle potential to study the reentrant glass transition. Confocal microscopy and particle tracking allow us to follow particle trajectories over time. By varying inter particle attraction strength for a fixed volume fraction of colloidal suspensions, we observe three qualitatively different states. Mean square displacement and long time diffusion constant vary with the depletant concentration and indicate a glass state for low attraction strengths, ergodic liquid state for moderate attraction strengths, and attractive arrested state for the highest attraction strengths. Variance in the self overlap function gives the four point susceptibility, a measure of dynamical heterogeneity over a range of length scales and lag times. Results show that the lag times corresponding to the most heterogeneous dynamics are longer for arrested states than for fluid states. The length scale that maximizes four point susceptibility across a range of attraction strengths exhibits a reentrant glass behavior similar to that of the long time diffusion constant. Z.B., G.H., and P.H. acknowledge financial support of the NSF RUI-1306990. M.G. and A.G.Y. acknowledge financial support of the NSF Grant DMR-1205463, NSF MRSEC Grant DMR-1120901, and NASA Grant NNX08AO0G.

  12. Mean-field microrheology of a very soft colloidal suspension: Inertia induces shear thickening.

    PubMed

    Démery, Vincent

    2015-06-01

    Colloidal suspensions have a rich rheology and can exhibit shear thinning as well as shear thickening. Numerical simulations recently suggested that shear-thickening may be attributed to the inertia of the colloids, besides the hydrodynamic interactions between them. Here, we consider the ideal limit of a dense bath of soft colloids following an underdamped Langevin dynamics. We use a mean-field equation for the colloidal density to get an analytical expression of the drag force felt by a probe pulled at constant velocity through the suspension. Our results show that inertia can indeed induce shear thickening by allowing density waves to propagate through the suspension.

  13. Colloidal Brazil-nut effect in sediments of binary charged suspensions

    NASA Astrophysics Data System (ADS)

    Esztermann, A.; Löwen, H.

    2004-10-01

    Equilibrium sedimentation density profiles of charged binary colloidal suspensions are calculated by computer simulations and density-functional theory. For deionized samples, we predict a colloidal "Brazil nut" effect: heavy colloidal particles sediment on top of the lighter ones provided that their mass per charge is smaller than that of the lighter ones. This effect is verifiable in settling experiments.

  14. Modified Mason number for charged paramagnetic colloidal suspensions.

    PubMed

    Du, Di; Hilou, Elaa; Biswal, Sibani Lisa

    2016-06-01

    The dynamics of magnetorheological fluids have typically been described by the Mason number, a governing parameter defined as the ratio between viscous and magnetic forces in the fluid. For most experimental suspensions of magnetic particles, surface forces, such as steric and electrostatic interactions, can significantly influence the dynamics. Here we propose a theory of a modified Mason number that accounts for surface forces and show that this modified Mason number is a function of interparticle distance. We demonstrate that this modified Mason number is accurate in describing the dynamics of a rotating pair of paramagnetic colloids of identical or mismatched sizes in either high or low salt solutions. The modified Mason number is confirmed to be pseudoconstant for particle pairs and particle chains undergoing a stable-metastable transition during rotation. The interparticle distance term can be calculated using theory or can be measured experimentally. This modified Mason number is more applicable to magnetorheological systems where surface forces are not negligible. PMID:27415316

  15. Modified Mason number for charged paramagnetic colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Du, Di; Hilou, Elaa; Biswal, Sibani Lisa

    2016-06-01

    The dynamics of magnetorheological fluids have typically been described by the Mason number, a governing parameter defined as the ratio between viscous and magnetic forces in the fluid. For most experimental suspensions of magnetic particles, surface forces, such as steric and electrostatic interactions, can significantly influence the dynamics. Here we propose a theory of a modified Mason number that accounts for surface forces and show that this modified Mason number is a function of interparticle distance. We demonstrate that this modified Mason number is accurate in describing the dynamics of a rotating pair of paramagnetic colloids of identical or mismatched sizes in either high or low salt solutions. The modified Mason number is confirmed to be pseudoconstant for particle pairs and particle chains undergoing a stable-metastable transition during rotation. The interparticle distance term can be calculated using theory or can be measured experimentally. This modified Mason number is more applicable to magnetorheological systems where surface forces are not negligible.

  16. Computation of shear viscosity of colloidal suspensions by SRD-MD.

    PubMed

    Laganapan, A M K; Videcoq, A; Bienia, M; Ala-Nissila, T; Bochicchio, D; Ferrando, R

    2015-04-14

    The behaviour of sheared colloidal suspensions with full hydrodynamic interactions (HIs) is numerically studied. To this end, we use the hybrid stochastic rotation dynamics-molecular dynamics (SRD-MD) method. The shear viscosity of colloidal suspensions is computed for different volume fractions, both for dilute and concentrated cases. We verify that HIs help in the collisions and the streaming of colloidal particles, thereby increasing the overall shear viscosity of the suspension. Our results show a good agreement with known experimental, theoretical, and numerical studies. This work demonstrates the ability of SRD-MD to successfully simulate transport coefficients that require correct modelling of HIs.

  17. Computation of shear viscosity of colloidal suspensions by SRD-MD

    SciTech Connect

    Laganapan, A. M. K.; Videcoq, A. Bienia, M.; Ala-Nissila, T.; Bochicchio, D.; Ferrando, R.

    2015-04-14

    The behaviour of sheared colloidal suspensions with full hydrodynamic interactions (HIs) is numerically studied. To this end, we use the hybrid stochastic rotation dynamics-molecular dynamics (SRD-MD) method. The shear viscosity of colloidal suspensions is computed for different volume fractions, both for dilute and concentrated cases. We verify that HIs help in the collisions and the streaming of colloidal particles, thereby increasing the overall shear viscosity of the suspension. Our results show a good agreement with known experimental, theoretical, and numerical studies. This work demonstrates the ability of SRD-MD to successfully simulate transport coefficients that require correct modelling of HIs.

  18. Characterizations and Stability of Colloidal Coal-Measure Kaolinite in Aqueous Suspensions: a Review

    NASA Astrophysics Data System (ADS)

    Liu, Lingyun; Hu, Yang; Min, Fanfei; Zhang, Mingxu; Song, Shaoxian

    2013-03-01

    Coal-measure kaolinite is a main gangue mineral in coal deposits. Because of the colloidal particle size, the kaolinite is very stable in coal tailing slurries, leading to a high turbidity of recycled water in coal washing plants. The coagulation of colloidal kaolinite in aqueous suspensions is an essential problem in many coal washing plants. This review highlights the characterizations and stability of colloidal coal-measure kaolinite in aqueous suspensions. The characterizations include mineralogy, electrokinetics and hydration layers on kaolinite surfaces. The coagulation of colloidal kaolinite in aqueous suspensions is reviewed and discussed on the basis of the DLVO theory and the characterization. In addition,the main parameters of affecting the coagulation, such as suspension pH, electrolytic ions and temperature, are summarized.

  19. Dipolar colloids in apolar media: direct microscopy of two-dimensional suspensions

    PubMed Central

    Janai, Erez; Cohen, Avner P.; Butenko, Alexander V.; Schofield, Andrew B.; Schultz, Moty; Sloutskin, Eli

    2016-01-01

    Spherical colloids, in an absence of external fields, are commonly assumed to interact solely through rotationally-invariant potentials, u(r). While the presence of permanent dipoles in aqueous suspensions has been previously suggested by some experiments, the rotational degrees of freedom of spherical colloids are typically neglected. We prove, by direct experiments, the presence of permanent dipoles in commonly used spherical poly(methyl methacrylate) (PMMA) colloids, suspended in an apolar organic medium. We study, by a combination of direct confocal microscopy, computer simulations, and theory, the structure and other thermodynamical properties of organic suspensions of colloidal spheres, confined to a two-dimensional (2D) monolayer. Our studies reveal the effects of the dipolar interactions on the structure and the osmotic pressure of these fluids. These observations have far-reaching consequences for the fundamental colloidal science, opening new directions in self-assembly of complex colloidal clusters. PMID:27346611

  20. Dipolar colloids in apolar media: direct microscopy of two-dimensional suspensions

    NASA Astrophysics Data System (ADS)

    Janai, Erez; Cohen, Avner P.; Butenko, Alexander V.; Schofield, Andrew B.; Schultz, Moty; Sloutskin, Eli

    2016-06-01

    Spherical colloids, in an absence of external fields, are commonly assumed to interact solely through rotationally-invariant potentials, u(r). While the presence of permanent dipoles in aqueous suspensions has been previously suggested by some experiments, the rotational degrees of freedom of spherical colloids are typically neglected. We prove, by direct experiments, the presence of permanent dipoles in commonly used spherical poly(methyl methacrylate) (PMMA) colloids, suspended in an apolar organic medium. We study, by a combination of direct confocal microscopy, computer simulations, and theory, the structure and other thermodynamical properties of organic suspensions of colloidal spheres, confined to a two-dimensional (2D) monolayer. Our studies reveal the effects of the dipolar interactions on the structure and the osmotic pressure of these fluids. These observations have far-reaching consequences for the fundamental colloidal science, opening new directions in self-assembly of complex colloidal clusters.

  1. Kinetics of the glass transition of fragile soft colloidal suspensions.

    PubMed

    Saha, Debasish; Joshi, Yogesh M; Bandyopadhyay, Ranjini

    2015-12-01

    Microscopic relaxation time scales are estimated from the autocorrelation functions obtained by dynamic light scattering experiments for Laponite suspensions with different concentrations (CL), added salt concentrations (CS), and temperatures (T). It has been shown in an earlier work [D. Saha, Y. M. Joshi, and R. Bandyopadhyay, Soft Matter 10, 3292 (2014)] that the evolutions of relaxation time scales of colloidal glasses can be compared with molecular glass formers by mapping the waiting time (tw) of the former with the inverse of thermodynamic temperature (1/T) of the latter. In this work, the fragility parameter D, which signifies the deviation from Arrhenius behavior, is obtained from fits to the time evolutions of the structural relaxation time scales. For the Laponite suspensions studied in this work, D is seen to be independent of CL and CS but is weakly dependent on T. Interestingly, the behavior of D corroborates the behavior of fragility in molecular glass formers with respect to equivalent variables. Furthermore, the stretching exponent β, which quantifies the width w of the spectrum of structural relaxation time scales, is seen to depend on tw. A hypothetical Kauzmann time tk, analogous to the Kauzmann temperature for molecular glasses, is defined as the time scale at which w diverges. Corresponding to the Vogel temperature defined for molecular glasses, a hypothetical Vogel time tα (∞) is also defined as the time at which the structural relaxation time diverges. Interestingly, a correlation is observed between tk and tα (∞), which is remarkably similar to that known for fragile molecular glass formers. A coupling model that accounts for the tw-dependence of the stretching exponent is used to analyse and explain the observed correlation between tk and tα (∞). PMID:26646885

  2. Kinetics of the glass transition of fragile soft colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Saha, Debasish; Joshi, Yogesh M.; Bandyopadhyay, Ranjini

    2015-12-01

    Microscopic relaxation time scales are estimated from the autocorrelation functions obtained by dynamic light scattering experiments for Laponite suspensions with different concentrations (CL), added salt concentrations (CS), and temperatures (T). It has been shown in an earlier work [D. Saha, Y. M. Joshi, and R. Bandyopadhyay, Soft Matter 10, 3292 (2014)] that the evolutions of relaxation time scales of colloidal glasses can be compared with molecular glass formers by mapping the waiting time (tw) of the former with the inverse of thermodynamic temperature (1/T) of the latter. In this work, the fragility parameter D, which signifies the deviation from Arrhenius behavior, is obtained from fits to the time evolutions of the structural relaxation time scales. For the Laponite suspensions studied in this work, D is seen to be independent of CL and CS but is weakly dependent on T. Interestingly, the behavior of D corroborates the behavior of fragility in molecular glass formers with respect to equivalent variables. Furthermore, the stretching exponent β, which quantifies the width w of the spectrum of structural relaxation time scales, is seen to depend on tw. A hypothetical Kauzmann time tk, analogous to the Kauzmann temperature for molecular glasses, is defined as the time scale at which w diverges. Corresponding to the Vogel temperature defined for molecular glasses, a hypothetical Vogel time tα ∞ is also defined as the time at which the structural relaxation time diverges. Interestingly, a correlation is observed between tk and tα ∞ , which is remarkably similar to that known for fragile molecular glass formers. A coupling model that accounts for the tw-dependence of the stretching exponent is used to analyse and explain the observed correlation between tk and tα ∞ .

  3. 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.

  4. 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

  5. Coupling between bulk- and surface chemistry in suspensions of charged colloids

    NASA Astrophysics Data System (ADS)

    Heinen, M.; Palberg, T.; Löwen, H.

    2014-03-01

    The ionic composition and pair correlations in fluid phases of realistically salt-free charged colloidal sphere suspensions are calculated in the primitive model. We obtain the number densities of all ionic species in suspension, including low-molecular weight microions, and colloidal macroions with acidic surface groups, from a self-consistent solution of a coupled physicochemical set of nonlinear algebraic equations and non-mean-field liquid integral equations. Here, we study suspensions of colloidal spheres with sulfonate or silanol surface groups, suspended in demineralized water that is saturated with carbon dioxide under standard atmosphere. The only input required for our theoretical scheme are the acidic dissociation constants pKa, and effective sphere diameters of all involved ions. Our method allows for an ab initio calculation of colloidal bare and effective charges, at high numerical efficiency.

  6. Surface freezing and surface coverage as key factors for spontaneous formation of colloidal fibers in vacuum drying of colloidal suspensions.

    PubMed

    Inasawa, S; Katayama, T; Yamaguchi, Y

    2016-09-28

    In this study, we investigated vacuum drying of droplets of colloidal suspension. Because of the loss of the latent heat of vaporization, the drying droplet was cooled and then formed ice. Colloidal fibers consisting of packed particles spontaneously formed when the droplet froze from the gas-liquid interface. Conversely, we observed formation of sponge-like porous structures of particles when the whole droplet almost simultaneously froze. However, the freezing mode was not the only factor for formation of colloidal fibers. We found that the surface coverage of particles on the gas-liquid interface was also important. Owing to drying, some particles accumulated at the interface before freezing. When the surface coverage was higher than a threshold value, formation of fibers was severely restricted even in the surface freezing mode. Our results clearly show the important roles of surface freezing and the surface coverage of particles on the gas-liquid interface in formation of colloidal fibers. PMID:27550740

  7. Active microrheology of Brownian suspensions via Accelerated Stokesian Dynamics simulations

    NASA Astrophysics Data System (ADS)

    Chu, Henry; Su, Yu; Gu, Kevin; Hoh, Nicholas; Zia, Roseanna

    2015-11-01

    The non-equilibrium rheological response of colloidal suspensions is studied via active microrheology utilizing Accelerated Stokesian Dynamics simulations. In our recent work, we derived the theory for micro-diffusivity and suspension stress in dilute suspensions of hydrodynamically interacting colloids. This work revealed that force-induced diffusion is anisotropic, with qualitative differences between diffusion along the line of the external force and that transverse to it, and connected these effects to the role of hydrodynamic, interparticle, and Brownian forces. This work also revealed that these forces play a similar qualitative role in the anisotropy of the stress and in the evolution of the non-equilibrium osmotic pressure. Here, we show that theoretical predictions hold for suspensions ranging from dilute to near maximum packing, and for a range of flow strengths from near-equilibrium to the pure-hydrodynamic limit.

  8. Interface instability modes in freezing colloidal suspensions: revealed from onset of planar instability

    PubMed Central

    Wang, Lilin; You, Jiaxue; Wang, Zhijun; Wang, Jincheng; Lin, Xin

    2016-01-01

    Freezing colloidal suspensions widely exists in nature and industry. Interface instability has attracted much attention for the understandings of the pattern formation in freezing colloidal suspensions. However, the interface instability modes, the origin of the ice banding or ice lamellae, are still unclear. In-situ experimental observation of the onset of interface instability remains absent up to now. Here, by directly imaging the initial transient stage of planar interface instability in directional freezing colloidal suspensions, we proposed three interface instability modes, Mullins-Sekerka instability, global split instability and local split instability. The intrinsic mechanism of the instability modes comes from the competition of the solute boundary layer and the particle boundary layer, which only can be revealed from the initial transient stage of planar instability in directional freezing. PMID:26996630

  9. Onsager’s reciprocal relations for electroacoustic and sedimentation: Application to (concentrated) colloidal suspensions

    SciTech Connect

    Gourdin-Bertin, S.; Chassagne, C.

    2015-05-21

    In this article, the relations for electroacoustic phenomena, such as sedimentation potential, sedimentation intensity, colloid vibration potential, colloid vibration intensity/current, or electric sonic amplitude, are given, on the basis of irreversible thermodynamics. This formalism allows in particular to discuss the different expressions for concentrated suspensions found by various authors, which are of great practical interest. It was found that some existing expressions have to be corrected. Relations between the electrophoretic mobilities assessed by the different experiments are derived.

  10. Interfacial undercooling in solidification of colloidal suspensions: analyses with quantitative measurements

    PubMed Central

    You, Jiaxue; Wang, Lilin; Wang, Zhijun; Li, Junjie; Wang, Jincheng; Lin, Xin; Huang, Weidong

    2016-01-01

    Interfacial undercooling in the complex solidification of colloidal suspensions is of significance and remains a puzzling problem. Two types of interfacial undercooling are supposed to be involved in the freezing of colloidal suspensions, i.e., solute constitutional supercooling (SCS) caused by additives in the solvent and particulate constitutional supercooling (PCS) caused by particles. However, quantitative identification of the interfacial undercooling in the solidification of colloidal suspensions, is still absent; thus, the question of which type of undercooling is dominant in this complex system remains unanswered. Here, we quantitatively measured the static and dynamic interface undercoolings of SCS and PCS in ideal and practical colloidal systems. We show that the interfacial undercooling primarily comes from SCS caused by the additives in the solvent, while PCS is minor. This finding implies that the thermodynamic effect of particles from the PCS is not the fundamental physical mechanism for pattern formation of cellular growth and lamellar structure in the solidification of colloidal suspensions, a general case of ice-templating method. Instead, the patterns in the ice-templating method can be controlled effectively by adjusting the additives. PMID:27329394

  11. Interfacial undercooling in solidification of colloidal suspensions: analyses with quantitative measurements.

    PubMed

    You, Jiaxue; Wang, Lilin; Wang, Zhijun; Li, Junjie; Wang, Jincheng; Lin, Xin; Huang, Weidong

    2016-01-01

    Interfacial undercooling in the complex solidification of colloidal suspensions is of significance and remains a puzzling problem. Two types of interfacial undercooling are supposed to be involved in the freezing of colloidal suspensions, i.e., solute constitutional supercooling (SCS) caused by additives in the solvent and particulate constitutional supercooling (PCS) caused by particles. However, quantitative identification of the interfacial undercooling in the solidification of colloidal suspensions, is still absent; thus, the question of which type of undercooling is dominant in this complex system remains unanswered. Here, we quantitatively measured the static and dynamic interface undercoolings of SCS and PCS in ideal and practical colloidal systems. We show that the interfacial undercooling primarily comes from SCS caused by the additives in the solvent, while PCS is minor. This finding implies that the thermodynamic effect of particles from the PCS is not the fundamental physical mechanism for pattern formation of cellular growth and lamellar structure in the solidification of colloidal suspensions, a general case of ice-templating method. Instead, the patterns in the ice-templating method can be controlled effectively by adjusting the additives. PMID:27329394

  12. A new way to apply ultrasound in cross-flow ultrafiltration: application to colloidal suspensions.

    PubMed

    Hengl, N; Jin, Y; Pignon, F; Baup, S; Mollard, R; Gondrexon, N; Magnin, A; Michot, L; Paineau, E

    2014-05-01

    A new coupling of ultrasound device with membrane process has been developed in order to enhance cross-flow ultrafiltration of colloidal suspensions usually involved in several industrial applications included bio and agro industries, water and sludge treatment. In order to reduce mass transfer resistances induced by fouling and concentration polarization, which both are main limitations in membrane separation process continuous ultrasound is applied with the help of a vibrating blade (20 kHz) located in the feed channel all over the membrane surface (8mm between membrane surface and the blade). Hydrodynamic aspects were also taking into account by the control of the rectangular geometry of the feed channel. Three colloidal suspensions with different kinds of colloidal interaction (attractive, repulsive) were chosen to evaluate the effect of their physico-chemical properties on the filtration. For a 90 W power (20.5 W cm(-2)) and a continuous flow rate, permeation fluxes are increased for each studied colloidal suspension, without damaging the membrane. The results show that the flux increase depends on the initial structural properties of filtered dispersion in terms of colloidal interaction and spatial organizations. For instance, a Montmorillonite Wyoming-Na clay suspension was filtered at 1.5 × 10(5)Pa transmembrane pressure. Its permeation flux is increased by a factor 7.1, from 13.6 L m(-2)h(-1) without ultrasound to 97 L m(-2)h(-1) with ultrasound.

  13. Effect of Salt Concentration on the Pattern Formation of Colloidal Suspension

    NASA Astrophysics Data System (ADS)

    Ma, Wenjie; Wang, Yuren

    We study the effect of salt concentration on the drying process and pattern of thin liquid layer colloidal suspension. Panasonic camera is used to capture the drying process and macroscopic pattern. Microscopic patterns are analyzed by optical microscopy. It is shown that broad-ring pattern is avoided by adding little amount of sodium chloide into colloidal suspension. with the increase of salt concentraion, convection strength and interface instability are weakened, thus the edge of film becomes smooth and more homogeneous film forms. Beautiful microscopic patterns demonstrate that the cooperative interaction between sodium chloide and silica spheres has important influence on the pattern formation.

  14. Clogging by sieving in microchannels: Application to the detection of contaminants in colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Sauret, Alban; Barney, Erin C.; Perro, Adeline; Villermaux, Emmanuel; Stone, Howard A.; Dressaire, Emilie

    2014-08-01

    We report on a microfluidic method that allows measurement of a small concentration of large contaminants in suspensions of solid micrometer-scale particles. To perform the measurement, we flow the colloidal suspension through a series of constrictions, i.e., a microchannel of varying cross-section. We show and quantify the role of large contaminants in the formation of clogs at a constriction and the growth of the resulting filter cake. By measuring the time interval between two clogging events in an array of parallel microchannels, we are able to estimate the concentration of contaminants whose size is selected by the geometry of the microfluidic device. This technique for characterizing colloidal suspensions offers a versatile and rapid tool to explore the role of contaminants on the properties of the suspensions.

  15. Investigation of particles size effects in Dissipative Particle Dynamics (DPD) modelling of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Mai-Duy, N.; Phan-Thien, N.; Khoo, B. C.

    2015-04-01

    In the Dissipative Particle Dynamics (DPD) simulation of suspension, the fluid (solvent) and colloidal particles are replaced by a set of DPD particles and therefore their relative sizes (as measured by their exclusion zones) can affect the maximal packing fraction of the colloidal particles. In this study, we investigate roles of the conservative, dissipative and random forces in this relative size ratio (colloidal/solvent). We propose a mechanism of adjusting the DPD parameters to properly model the solvent phase (the solvent here is supposed to have the same isothermal compressibility to that of water).

  16. A Navier-Stokes phase-field crystal model for colloidal suspensions

    SciTech Connect

    Praetorius, Simon Voigt, Axel

    2015-04-21

    We develop a fully continuous model for colloidal suspensions with hydrodynamic interactions. The Navier-Stokes Phase-Field Crystal model combines ideas of dynamic density functional theory with particulate flow approaches and is derived in detail and related to other dynamic density functional theory approaches with hydrodynamic interactions. The derived system is numerically solved using adaptive finite elements and is used to analyze colloidal crystallization in flowing environments demonstrating a strong coupling in both directions between the crystal shape and the flow field. We further validate the model against other computational approaches for particulate flow systems for various colloidal sedimentation problems.

  17. The Influence of Gravity on Nucleation, Growth, Stability and Structure in Crystallizing Colloidal Suspensions

    NASA Technical Reports Server (NTRS)

    Gast, Alice P.

    1996-01-01

    Our goal is to understand the dynamics of particles within colloidal crystals. In particular, we focus on the influence of the cell walls and gravity on the particle dynamics. In this study, we will use a novel light scattering experiment, known as diffusing wave spectroscopy, to probe particle motions in turbid suspensions. This is a noninvasive experimental probe of interparticle dynamics.

  18. Effect of three-body interactions on the phase behavior of charge-stabilized colloidal suspensions.

    PubMed

    Hynninen, A-P; Dijkstra, M; van Roij, R

    2004-06-01

    We study numerically the effect of attractive triplet interactions on the phase behavior of suspensions of highly charged colloidal particles at low salinity. In our computer simulations, we employ the pair and triplet potentials that were obtained from a numerical Poisson-Boltzmann study [Phys. Rev. E 66, 011402 (2002)

  19. Brownian-dynamics simulation studies of a charge-stabilized colloidal suspension under shear flow

    SciTech Connect

    Chakrabarti, J. ); Sood, A.K.; Krishnamurthy, H.R. Jawaharlal Nehru Center for Advanced Scientific Research, Indian Institute of Science campus, Bangalore 560012 )

    1994-11-01

    We have carried out Brownian-dynamics simulations of a charged colloidal suspension under oscillatory shear flow with both Couette and Poiseuille velocity profiles. We show that in the steady-shear'' limit, for both of the velocity profiles, the enhancement of the self-diffusion coefficient in directions transverse to the flow shows a crossover from a [dot [gamma

  20. An Automatic Phase-Change Detection Technique for Colloidal Hard Sphere Suspensions

    NASA Technical Reports Server (NTRS)

    McDowell, Mark; Gray, Elizabeth; Rogers, Richard B.

    2005-01-01

    Colloidal suspensions of monodisperse spheres are used as physical models of thermodynamic phase transitions and as precursors to photonic band gap materials. However, current image analysis techniques are not able to distinguish between densely packed phases within conventional microscope images, which are mainly characterized by degrees of randomness or order with similar grayscale value properties. Current techniques for identifying the phase boundaries involve manually identifying the phase transitions, which is very tedious and time consuming. We have developed an intelligent machine vision technique that automatically identifies colloidal phase boundaries. The algorithm utilizes intelligent image processing techniques that accurately identify and track phase changes vertically or horizontally for a sequence of colloidal hard sphere suspension images. This technique is readily adaptable to any imaging application where regions of interest are distinguished from the background by differing patterns of motion over time.

  1. In situ observation the interface undercooling of freezing colloidal suspensions with differential visualization method

    NASA Astrophysics Data System (ADS)

    You, Jiaxue; Wang, Lilin; Wang, Zhijun; Li, Junjie; Wang, Jincheng; Lin, Xin; Huang, Weidong

    2015-08-01

    Interface undercooling is one of the most significant parameters in the solidification of colloidal suspensions. However, quantitative measurement of interface undercooling of colloidal suspensions is still a challenge. Here, a new experimental facility and gauging method are designed to directly reveal the interface undercooling on both static and dynamic cases. The interface undercooling is visualized through the discrepancy of solid/liquid interface positions between the suspensions and its solvent in a thermal gradient apparatus. The resolutions of the experimental facility and gauging method are proved to be 0.01 K. The high precision of the method comes from the principle of converting temperature measurement into distance measurement in the thermal gradient platform. Moreover, both static and dynamic interface undercoolings can be quantitatively measured.

  2. Photoluminescence quantum yield of PbS nanocrystals in colloidal suspensions

    SciTech Connect

    Greben, M.; Fucikova, A.; Valenta, J.

    2015-04-14

    The absolute photoluminescence (PL) quantum yield (QY) of oleic acid-capped colloidal PbS quantum dots (QDs) in toluene is thoroughly investigated as function of QD size, concentration, excitation photon energy, and conditions of storage. We observed anomalous decrease of QY with decreasing concentration for highly diluted suspensions. The ligand desorption and QD-oxidation are demonstrated to be responsible for this phenomenon. Excess of oleic acid in suspensions makes the QY values concentration-independent over the entire reabsorption-free range. The PL emission is shown to be dominated by surface-related recombinations with some contribution from QD-core transitions. We demonstrate that QD colloidal suspension stability improves with increasing the concentration and size of PbS QDs.

  3. Active motion induced break-up of colloidal gels

    NASA Astrophysics Data System (ADS)

    Szakasits, Megan; Solomon, Michael

    2015-03-01

    We found that fractal gel networks of polystyrene colloids can be broken up by active motion of Janus colloids that have been incorporated into them. Janus particles were synthesized by electron beam deposition of platinum onto one micron carboxylate modified polystyrene particles. Through addition of the divalent salt magnesium chloride, an initially stable suspension of Janus and polystyrene colloids, present in equal proportion, underwent aggregation to yield a fractal gel. The Janus colloids were activated by addition of 30% v/v hydrogen peroxide through a porous hydrogel membrane. Changes in structure and dynamics were visualized by two channel confocal laser scanning microscopy (CLSM). By means of image analysis, we calculated the mean squared displacement (MSD) and radial distribution function (RDF) for gel samples before and after addition of hydrogen peroxide. The MSD confirmed the Janus particles we synthesized undergo active motion. The RDF and cluster size distribution of gel samples before and after addition of peroxide demonstrate how active motion broke apart the gel network into smaller clusters.

  4. Role of particle dissolution in the stability of binary yttria-silica colloidal suspensions

    SciTech Connect

    Yasrebi, M.; Kemp, W.; Sturgis, D.H.; Ziomek-Moroz, M.

    1996-05-01

    The stability of yttria-silica binary aqueous colloidal suspensions is examined as a function of time. It has been observed that initially stable silica particles go through a flocculation period and then restabilize. This phenomenon is attributed to slow dissolution and the specific adsorption of trivalent yttrium cation and its hydroxo complexes on the surface of silica. Furthermore, it is shown that the kinetics of flocculation and restabilization can be controlled by pH adjustment.

  5. Rheology of dense suspensions of non colloidal spheres in yield-stress fluids

    NASA Astrophysics Data System (ADS)

    Guazzelli, Elisabeth; Dagois-Bohy, Simon; Hormozi, Sarah; Pouliquen, Olivier; Aix-Marseille Université, Cnrs, Iusti Umr 7343 Team; Department Of Mechanical Engineering, Ohio University Team

    2015-11-01

    Pressure-imposed rheometry is used to study the rheological properties of suspensions of non colloidal spheres in yield stress fluids. Accurate measurements for both the shear stress and particle normal stress are obtained in the dense regime. The rheological measurements are favourably compared to a model based on scaling arguments and homogenisation methods. The detailed account of this study can be found in. ANR-13-IS09-0005-01, Etudes et Productions Schlumberger, NSERC Postdoctoral Fellowships Program PDF-439036-2013.

  6. The structure of binary mixtures of charged colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Méndez-Alcaraz, J. M.; D'Aguanno, B.; Klein, R.

    1991-11-01

    Structural properties of mixtures of charged colloidal particles are studied by solving the Ornstein-Zernike equation together with the Rogers-Young closure relation. The partial radial distribution functions g ij( r) are found to agree very well with results obtained from molecular dynamics simulations. From g ij( r) partial structure factors S ij( k) are determined. They are used to obtain results for the experimentally accessible structure factor SM( k) and for the Bhatia-Thornton structure factors SNN( k), SCC( k) and SCC( k). The latter describe concentration ordering, charge ordering and their coupling. A systematic study of these quantities is presented as a function of relative composition of the two components. It is found that various features of SM( k), such as position and height of the main peak and its value at k = 0, change non-monotonously as a function of composition.

  7. Accelerated lattice Boltzmann model for colloidal suspensions rheology and interface morphology

    NASA Astrophysics Data System (ADS)

    Farhat, Hassan

    Colloids are ubiquitous in the food, medical, cosmetic, polymer, water purification and pharmaceutical industries. Colloids thermal, mechanical and storage properties are highly dependent on their interface morphology and their rheological behavior. Numerical methods provide a cheap and reliable virtual laboratory for the study of colloids. However efficiency is a major concern to address when using numerical methods for practical applications. This work introduces the main building-blocks for an improved lattice Boltzmann-based numerical tool designed for the study of colloidal rheology and interface morphology. The efficiency of the proposed model is enhanced by using the recently developed and validated migrating multi-block algorithms for the lattice Boltzmann method (LBM). The migrating multi-block was used to simulate single component, multi-component, multiphase and single component multiphase flows. Results were validated by experimental, numerical and analytical solutions. The contamination of the fluid-fluid interface influences the colloids morphology. This issue was addressed by the introduction of the hybrid LBM for surfactant-covered droplets. The module was used for the simulation of surfactant-covered droplet deformation under shear and uniaxial extensional flows respectively and under buoyancy. Validation with experimental and theoretical results was provided. Colloids are non-Newtonian fluids which exhibit rich rheological behavior. The suppression of coalescence module is the part of the proposed model which facilitates the study of colloids rheology. The model results for the relative viscosity were in agreement with some theoretical results. Biological suspensions such as blood are macro-colloids by nature. The study of the blood flow in the microvasculature was heuristically approached by assuming the red blood cells as surfactant covered droplets. The effects of interfacial tension on the flow velocity and the droplet exclusion from the walls

  8. Swarming of active colloidal Janus particles: Polar waves and vortices

    NASA Astrophysics Data System (ADS)

    Xu, Cong; Yan, Jing; Han, Ming; Luijten, Erik; Granick, Steve

    2015-03-01

    The synthesis of artificial ``swarming'' particles with tunable interaction represents a strong interest of the soft active matter community. Here, we demonstrate a straightforward design of swarming Janus colloids that exhibit transient mutual alignment within a certain frequency range of an applied AC electric field. In a dense two-dimensional suspension of these Janus colloids, we observe that coherent polar waves emerge at first, which then collide and merge into stable discrete vortices. Based upon a careful analysis of the pair interaction, we propose a simple mechanism that explains the formation of the polar waves, with agreement between experiment and simulation. A rich spectrum of phenomena, including dimer swarming, chain formation, and particle clustering, can be further achieved by changing the frequency of the AC electric field. Currently working as a postdoctoral researcher in Princeton University.

  9. Colloidal stability of coal-simulated suspensions in selective agglomeration

    SciTech Connect

    Schurger, M.L.

    1989-01-01

    A coal suspension was simulated by using graphite to simulate the carbonaceous fraction and kaolinite clay to simulate the ash fraction. Separate studies on each material established their response to additions of oxidized pyrite (ferrous sulfate) and a humic acid simulate (salicylic acid) in terms of zeta potentials profiles with pH and Ionic strength. Concentrations of iron and salicylic acid evaluated were 4.5 {times} 10{sup {minus}3} M and 2.0 {times} 10{sup {minus}4} M, respectively. The zeta potentials profiles of graphite, clay and hexadecane were negative throughout the pH ranges studied. The addition of iron lowered the zeta potentials all of the suspensions under all pH and ionic strength conditions. Salicylic acid decreased the graphite and hexadecane zeta potentials but had no effect on the clay zeta potential profiles. Agglomeration of graphite with bridging liquid shows distinct time dependent rate mechanisms, a initial growth of graphite agglomerates followed by consolidation phase. Graphite agglomeration was rapid with the maximum amount of agglomerate volume growth occurring in under 2-4 minutes. Agglomeration in the first two minutes was characterized by a 1st order rate mechanism. The presence of either Iron and salicylic acid generally improved the first order rates. The addition of clay also improved the first order rates except in the presence of salicylic acid. Heteroagglomeration of graphite with clay was found by hydrodynamic arguments to be unfavored. A multicomponent population balance model which had been developed for evaluating collision efficiencies of coal, ash and pyrite selective agglomeration was evaluated to explain these results. The growth and consolidation characteristics of graphite agglomeration for the experimental conditions examined herein revealed the limitations of such as model for this application.

  10. Segregated Ice Growth in a Suspension of Colloidal Particles.

    PubMed

    Schollick, Julia M H; Style, Robert W; Curran, Arran; Wettlaufer, John S; Dufresne, Eric R; Warren, Patrick B; Velikov, Krassimir P; Dullens, Roel P A; Aarts, Dirk G A L

    2016-04-28

    We study the freezing of a dispersion of colloidal silica particles in water, focusing on the formation of segregated ice in the form of ice lenses. Local temperature measurements in combination with video microscopy give insight into the rich variety of factors that control ice lens formation. We observe the initiation of the lenses, their growth morphology, and their final thickness and spacing over a range of conditions, in particular the effect of the particle packing and the cooling rate. We find that increasing the particle density drastically reduces the thickness of lenses but has little effect on the lens spacing. Therefore, the fraction of segregated ice formed reduces. The effect of the cooling rate, which is the product of the temperature gradient and the pulling speed across the temperature gradient, depends on which parameter is varied. A larger temperature gradient causes ice lenses to be initiated more frequently, while a lower pulling speed allows for more time for ice lenses to grow: both increase the fraction of segregated ice. Surprisingly, we find that the growth rate of a lens does not depend on its undercooling. Finally, we have indications of pore ice in front of the warmest ice lens, which has important consequences for the interpretation of the measured trends. Our findings are relevant for ice segregation occurring in a wide range of situations, ranging from model lab experiments and theories to geological and industrial processes, like frost heave and frozen food production. PMID:27046043

  11. Photodegradation of dispersants in colloidal suspensions of pristine graphene.

    PubMed

    Hansen, Matthew J; Rountree, Kyler S; Irin, Fahmida; Sweeney, Charles B; Klaassen, Christopher D; Green, Micah J

    2016-03-15

    We demonstrate that UV degradation can remove polymeric dispersants from the surface of colloidal pristine graphene. In particular, we investigated the irradiation of polyvinylpyrrolidone (PVP)-dispersed graphene in water; this polymer has been established as a versatile nanosheet dispersant for a range of solvents, and it undergoes photo-oxidative degradation when exposed to UV light. We find that the molecular weight of PVP decreases with irradiation time and subsequently desorbs from the graphene surface. This causes gradual destabilization of graphene and agglomeration in water. The amount of adsorbed PVP decreases by approximately 45% after 4 h of irradiation in comparison with the non-irradiated dispersion. At this point, the majority of the stable graphene nanosheets flocculate, likely because of insufficient surface coverage as indicated by thermogravimetric analysis. Graphene aggregates were characterized as a function of irradiation time by optical microscopy, UV-vis spectroscopy, Raman spectroscopy, and conductivity measurements; the data suggest that the agglomerates maintain a graphene-like (rather than graphite-like) structure. The effect is also observed for another graphene dispersant (sapogenin), which suggests that our findings can be generalized to the broader class of photodegradable dispersants. PMID:26771505

  12. Dynamical facilitation governs glassy dynamics in suspensions of colloidal ellipsoids

    PubMed Central

    Mishra, Chandan K.; Hima Nagamanasa, K.; Ganapathy, Rajesh; Sood, A. K.; Gokhale, Shreyas

    2014-01-01

    One of the greatest challenges in contemporary condensed matter physics is to ascertain whether the formation of glasses from liquids is fundamentally thermodynamic or dynamic in origin. Although the thermodynamic paradigm has dominated theoretical research for decades, the purely kinetic perspective of the dynamical facilitation (DF) theory has attained prominence in recent times. In particular, recent experiments and simulations have highlighted the importance of facilitation using simple model systems composed of spherical particles. However, an overwhelming majority of liquids possess anisotropy in particle shape and interactions, and it is therefore imperative to examine facilitation in complex glass formers. Here, we apply the DF theory to systems with orientational degrees of freedom as well as anisotropic attractive interactions. By analyzing data from experiments on colloidal ellipsoids, we show that facilitation plays a pivotal role in translational as well as orientational relaxation. Furthermore, we demonstrate that the introduction of attractive interactions leads to spatial decoupling of translational and rotational facilitation, which subsequently results in the decoupling of dynamical heterogeneities. Most strikingly, the DF theory can predict the existence of reentrant glass transitions based on the statistics of localized dynamical events, called excitations, whose duration is substantially smaller than the structural relaxation time. Our findings pave the way for systematically testing the DF approach in complex glass formers and also establish the significance of facilitation in governing structural relaxation in supercooled liquids. PMID:25313030

  13. Experimental data and theoretical predictions for the rate of electrophoretic clarification of colloidal suspensions

    SciTech Connect

    Johnson, T.J.; Davis, E.J.

    2000-05-01

    An experimental and theoretical investigation of the electrophoretic clarification rate of colloidal suspensions was conducted. The suspensions included a coal-washing effluent and a model system of TiO{sub 2} particles. A parametric study of TiO{sub 2} suspensions was performed to validate and analysis of the electrophoretic motion of the clarification front formed between a clear zone and the suspension. To measure the electric field strength needed in the prediction of the location of the front, a moveable probe and salt bridge were connected to a reference electrode. Using the measured electric field strengths, it was found that the numerical solution to the unit cell electrophoresis model agrees with the measured clarification rates. For suspensions with moderately thick electric double layers and high particle volume fractions the deviations from classical Smoluchowski theory are substantial, and the numerical analysis is in somewhat better agreement with the data than a prior solution of the problem. The numerical model reduces to the predictions of previous theories as the thickness of the electric double layer decreases, and it is in good agreement with the clarification rate measured for a coal-washing effluent suspension with thin electric double layers.

  14. Aging and Yielding of Colloidal Suspension by MRI Velocimetry

    NASA Astrophysics Data System (ADS)

    Ragouilliaux, A.; Herzhaft, B.; Ovarlez, G.; Coussot, P.

    2008-07-01

    We study a suspension of water droplets in oil which, due to organoclay particles links, exhibits a yielding and thixotropic behavior. The local rheological behavior in time is determined with the help of MRI velocimetry in a Couette flow. Under constant rotation velocity, in a first stage we observe a progressive displacement of the fluid/solid interface towards the inner cylinder, which is associated with the increase of a critical shear rate below which there is apparently no flow. During this stage our local measurements show that the constitutive equation of the liquid region does not vary in time: only the thickness of the sheared region and the critical shear rate vary. Then we focus on the behavior in the solid and liquid regimes as a function of the droplet concentration φ (from 20 to 70%). The solid regime is studied by measuring the evolution of the elastic modulus (G) in time. The initial level of G increases with φ but G also increases in time, witch is the hallmark of the thixotropy (aging) at rest. We find that the effect of time on the restructuring is much larger than the effect of concentration increase. In order to study the liquid regime, we build the local flow curves from MRI velocity profiles as a function of time for all the formulations. The effect of a significant increase in droplet concentration on the material behavior in the liquid regime is found to be minor, in contrast with its effect on the behavior in the solid regime. This is explained by the fact that the behavior in the solid regime is mainly controlled by the droplet aggregation, a process which plays a much smaller role as soon as the liquid regime is reached.

  15. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Self-Assembling of Colloidal Particles Dispersed in Mixture of Ethanol and Water at the Air-Liquid Interface of Colloidal Suspension at Room Temperature

    NASA Astrophysics Data System (ADS)

    Wang, Ai-Jun; Chen, Sheng-Li; Dong, Peng; Zhou, Qian; Yuan, Gui-Mei; Su, Gu-Cong

    2009-08-01

    Self-assembling of colloidal particles dispersed in a mixture of ethanol and water at the air-liquid interface of the colloidal suspension at room temperature is investigated, and a method of rapidly assembling colloidal particles is proposed. By this method, a uniform colloidal crystal thin film over ten square centimeters in area can be fabricated in 10 min without special facilities and heating the suspension. SEM images and a normal incidence transmission spectrum of the sample show that the colloidal crystal film fabricated by this method is of high quality. In addition, this method is very suitable for fabricating colloidal crystal heterostructures.

  16. Rheological and solid-liquid separation properties of bimodal suspensions of colloidal gibbsite and boehmite

    SciTech Connect

    Bruinsma, P.J.; Wang, Y.; Li, X.S.; Liu, J.; Smith, P.A.; Bunker, B.C.

    1997-08-01

    Bimodal suspensions of nanometer-sized boehmite particles and micron-sized gibbsite particles in 0.10 M NaNO{sub 3} are used as models to gain insight into the physical properties of agglomerating colloidal suspensions containing bimodal distributions of primary particles. Results on the gibbsite--boehmite mixtures show that the presence of small particles in a suspension can have a dramatic impact on the rheological, sedimentation, and filtration characteristics of suspensions of larger particles. Transmission electron micrographs show that boehmite forms a coating on the larger gibbsite particles. The coating provides steric repulsion and reduces the attractive interactions between the larger particles, leading to viscosity decreases and greater densification of sediments and filter cakes. A model has been developed to rationalize observed property changes based on the range of agglomerate structures that can form in mixtures of large and small particles. Results are discussed in the content of the processing of nuclear waste sludges, but are applicable to a wide range of bimodal suspensions.

  17. Dynamics of highly polydisperse colloidal suspensions as a model system for bacterial cytoplasm.

    PubMed

    Hwang, Jiye; Kim, Jeongmin; Sung, Bong June

    2016-08-01

    There are various kinds of macromolecules in bacterial cell cytoplasm. The size polydispersity of the macromolecules is so significant that the crystallization and the phase separation could be suppressed, thus stabilizing the liquid state of bacterial cytoplasm. On the other hand, recent experiments suggested that the macromolecules in bacterial cytoplasm should exhibit glassy dynamics, which should be also affected significantly by the size polydispersity of the macromolecules. In this work, we investigate the anomalous and slow dynamics of highly polydisperse colloidal suspensions, of which size distribution is chosen to mimic Escherichia coli cytoplasm. We find from our Langevin dynamics simulations that the diffusion coefficient (D_{tot}) and the displacement distribution functions (P(r,t)) averaged over all colloids of different sizes do not show anomalous and glassy dynamic behaviors until the system volume fraction ϕ is increased up to 0.82. This indicates that the intrinsic polydispersity of bacterial cytoplasm should suppress the glass transition and help maintain the liquid state of the cytoplasm. On the other hand, colloids of each kind show totally different dynamic behaviors depending on their size. The dynamics of colloids of different size becomes non-Gaussian at a different range of ϕ, which suggests that a multistep glass transition should occur. The largest colloids undergo the glass transition at ϕ=0.65, while the glass transition does not occur for smaller colloids in our simulations even at the highest value of ϕ. We also investigate the distribution (P(θ,t)) of the relative angles of displacement for macromolecules and find that macromolecules undergo directionally correlated motions in a sufficiently dense system. PMID:27627367

  18. Dynamics of highly polydisperse colloidal suspensions as a model system for bacterial cytoplasm

    NASA Astrophysics Data System (ADS)

    Hwang, Jiye; Kim, Jeongmin; Sung, Bong June

    2016-08-01

    There are various kinds of macromolecules in bacterial cell cytoplasm. The size polydispersity of the macromolecules is so significant that the crystallization and the phase separation could be suppressed, thus stabilizing the liquid state of bacterial cytoplasm. On the other hand, recent experiments suggested that the macromolecules in bacterial cytoplasm should exhibit glassy dynamics, which should be also affected significantly by the size polydispersity of the macromolecules. In this work, we investigate the anomalous and slow dynamics of highly polydisperse colloidal suspensions, of which size distribution is chosen to mimic Escherichia coli cytoplasm. We find from our Langevin dynamics simulations that the diffusion coefficient (Dtot) and the displacement distribution functions (P (r ,t ) ) averaged over all colloids of different sizes do not show anomalous and glassy dynamic behaviors until the system volume fraction ϕ is increased up to 0.82. This indicates that the intrinsic polydispersity of bacterial cytoplasm should suppress the glass transition and help maintain the liquid state of the cytoplasm. On the other hand, colloids of each kind show totally different dynamic behaviors depending on their size. The dynamics of colloids of different size becomes non-Gaussian at a different range of ϕ , which suggests that a multistep glass transition should occur. The largest colloids undergo the glass transition at ϕ =0.65 , while the glass transition does not occur for smaller colloids in our simulations even at the highest value of ϕ . We also investigate the distribution (P (θ ,t ) ) of the relative angles of displacement for macromolecules and find that macromolecules undergo directionally correlated motions in a sufficiently dense system.

  19. Compensating for Electrode Polarization in Dielectric Spectroscopy Studies of Colloidal Suspensions: Theoretical Assessment of Existing Methods.

    PubMed

    Chassagne, Claire; Dubois, Emmanuelle; Jiménez, María L; van der Ploeg, J P M; van Turnhout, Jan

    2016-01-01

    Dielectric spectroscopy can be used to determine the dipole moment of colloidal particles from which important interfacial electrokinetic properties, for instance their zeta potential, can be deduced. Unfortunately, dielectric spectroscopy measurements are hampered by electrode polarization (EP). In this article, we review several procedures to compensate for this effect. First EP in electrolyte solutions is described: the complex conductivity is derived as function of frequency, for two cell geometries (planar and cylindrical) with blocking electrodes. The corresponding equivalent circuit for the electrolyte solution is given for each geometry. This equivalent circuit model is extended to suspensions. The complex conductivity of a suspension, in the presence of EP, is then calculated from the impedance. Different methods for compensating for EP are critically assessed, with the help of the theoretical findings. Their limit of validity is given in terms of characteristic frequencies. We can identify with one of these frequencies the frequency range within which data uncorrected for EP may be used to assess the dipole moment of colloidal particles. In order to extract this dipole moment from the measured data, two methods are reviewed: one is based on the use of existing models for the complex conductivity of suspensions, the other is the logarithmic derivative method. An extension to multiple relaxations of the logarithmic derivative method is proposed. PMID:27486575

  20. Angle-resolved second harmonic light scattering from colloidal suspensions and second harmonic particle microscopy

    NASA Astrophysics Data System (ADS)

    Yang, Ningping

    2001-08-01

    We have carried out two nonlinear optical experiments with colloidal particles. Our first nonlinear optical experiment studied Second-Harmonic Generation (SHG) light scattering from colloidal suspension. In particular, we measured the angle-resolved second-harmonic generation light scattering from suspensions of centrosymmetric micron-size polystyrene spheres with surface-adsorbed dye (malachite green). The second-harmonic scattering angular profiles differ qualitatively from the linear light scattering angular profiles of the same particles. We have investigated these radiation patterns using several polarization configurations and particle diameters. We introduce a simple Rayleigh-Gans-Debye model to account for the SHG scattering anisotropy. The model compares favorably with our experimental data. Our measurements suggest scattering anisotropy may be used to isolate particle nonlinear optical effect from other bulk nonlinear optical effects in suspension. Our second nonlinear optical experiment studied the Second-Harmonic Generation (SHG) from single micron-size particles. We built a nonlinear optical microscope for this purpose. We report experimental observations of second harmonic generation from single micron-size polystyrene (PS), silica, and PolyMethylMethAcrylate (PMMA) spheres on flat substrates by SHG microscopy. At low input light intensities the SH signals depend quadratically on the intensity of the excitation beam, but at larger input intensities some of the SH signals increase exponentially with increasing input intensity. This exponential enhancement depends on particle size and sphere composition. We describe the experiments, report the observations and provide an approximate analytical framework for understanding our measurements.

  1. Compensating for electrode polarization in dielectric spectroscopy studies of colloidal suspensions: theoretical assessment of existing methods

    NASA Astrophysics Data System (ADS)

    Chassagne, Claire; Dubois, Emmanuelle; Jiménez, María Luisa; van der Ploeg, Jacques; Turnhout, Jan

    2016-07-01

    Dielectric spectroscopy can be used to determine the dipole moment of colloidal particles from which important interfacial electrokinetic properties, for instance their zeta potential, can be deduced. Unfortunately, dielectric spectroscopy measurements are hampered by electrode polarization (EP). In this article, we review several procedures to compensate for this effect. First EP in electrolyte solutions is described: the complex conductivity is derived as function of frequency, for two cell geometries (planar and cylindrical) with blocking electrodes. The corresponding equivalent circuit for the electrolyte solution is given for each geometry. This equivalent circuit model is extended to suspensions. The complex conductivity of a suspension, in the presence of EP, is then calculated from the impedance measured. Different methods for compensating for EP are critically assessed, with the help of the theoretical findings. Their limit of validity is given in terms of characteristic frequencies. We can identify with one of these frequencies the frequency range within which data uncorrected for EP may be used to assess the dipole moment of colloidal particles. In order to extract this dipole moment from the measured data, two methods are reviewed: one is based on the use of existing models for the complex conductivity of suspensions, the other is the logarithmic derivative method. An extension to multiple relaxations of the logarithmic derivative method is proposed.

  2. Compensating for Electrode Polarization in Dielectric Spectroscopy Studies of Colloidal Suspensions: Theoretical Assessment of Existing Methods

    PubMed Central

    Chassagne, Claire; Dubois, Emmanuelle; Jiménez, María L.; van der Ploeg, J. P. M; van Turnhout, Jan

    2016-01-01

    Dielectric spectroscopy can be used to determine the dipole moment of colloidal particles from which important interfacial electrokinetic properties, for instance their zeta potential, can be deduced. Unfortunately, dielectric spectroscopy measurements are hampered by electrode polarization (EP). In this article, we review several procedures to compensate for this effect. First EP in electrolyte solutions is described: the complex conductivity is derived as function of frequency, for two cell geometries (planar and cylindrical) with blocking electrodes. The corresponding equivalent circuit for the electrolyte solution is given for each geometry. This equivalent circuit model is extended to suspensions. The complex conductivity of a suspension, in the presence of EP, is then calculated from the impedance. Different methods for compensating for EP are critically assessed, with the help of the theoretical findings. Their limit of validity is given in terms of characteristic frequencies. We can identify with one of these frequencies the frequency range within which data uncorrected for EP may be used to assess the dipole moment of colloidal particles. In order to extract this dipole moment from the measured data, two methods are reviewed: one is based on the use of existing models for the complex conductivity of suspensions, the other is the logarithmic derivative method. An extension to multiple relaxations of the logarithmic derivative method is proposed. PMID:27486575

  3. Where the linearized Poisson-Boltzmann cell model fails: Spurious phase separation in charged colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Tamashiro, M. N.; Schiessel, H.

    2003-07-01

    The Poisson-Boltzmann (PB) spherical Wigner-Seitz cell model—introduced to theoretically describe suspensions of spherical charged colloidal particles—is investigated at the nonlinear and linearized levels. The linearization of the mean-field PB functional yields linearized Debye-Hückel-type equations agreeing asymptotically with the nonlinear PB results in the weak-coupling (high-temperature) limit. Both the canonical (fixed number of microions) as well as the semigrand-canonical (in contact with an infinite salt reservoir) cases are considered and discussed in a unified linearized framework. In disagreement with the exact nonlinear PB solution inside a Wigner-Seitz cell, the linearized theory predicts the occurrence of a thermodynamical instability with an associated phase separation of the homogeneous suspension into dilute (gas) and dense (liquid) phases, being thus a spurious result of the linearization. We show that these artifacts, although thermodynamically consistent with quadratic expansions of the nonlinear functional and osmotic pressure, may be traced back to the nonfulfillment of the underlying assumptions of the linearization. This raises questions about the reliability of the prediction of gas/liquid-like phase separation in deionized aqueous suspensions of charged colloids mediated by monovalent counterions obtained by linearized theories.

  4. Stick-slip patterning at low capillary numbers for an evaporating colloidal suspension.

    PubMed

    Bodiguel, Hugues; Doumenc, Frédéric; Guerrier, Béatrice

    2010-07-01

    Pattern formation from a silica colloidal suspension that is evaporating has been studied when a movement is imposed to the contact line. This article focuses on the stick-slip regime observed for very low contact line velocities. A capillary rise experiment has been specially designed for the observation and allows us to measure the pinning force that increases during the pinning of the contact line on the growing deposit. We report systematic measurements of this pinning force and derive scaling laws when the velocity of the contact line, the colloid concentration, and the evaporation rate are varied. Our analysis supports the idea that the pinning of the contact line results from a competition between the geometry of the growing deposit and the force due to gravity. PMID:20429601

  5. Control of particle morphology in the spray drying of colloidal suspensions.

    PubMed

    Lintingre, E; Lequeux, F; Talini, L; Tsapis, N

    2016-09-28

    Powders of nanoparticles are volatile, i.e. easily disperse in air, which makes their handling difficult. Granulation of nanoparticle powders provides a solution to that issue, and it is generally performed by spray drying the nanoparticles that have been suspended in a liquid. Spray drying of a colloidal suspension consists of atomising the suspension into droplets by a fast flowing and hot gas. Once the droplets dried, the resulting dry grains/microparticles can be used in a wide range of applications - food, pharmaceutics, fillers, ceramics, etc. It is well known that the grains resulting from spray-drying may be spherical but may also exhibit other diverse morphologies. Although different influencing parameters have been identified, no clear overview can be found in the literature for the driving mechanisms of grain shaping. In the present work, we review the assumptions made in the literature to explain the different morphologies. We analyse the orders of magnitude of the different effects at stake and show that the grain shape does not result from a hydrodynamic instability but is determined by the drying stage. However, we emphasize that neither the drying time nor the associated Péclet number are critical parameters for the determination of shape morphology. In light of those results, we also review and discuss the single droplet experiments developed to mimic spray drying. Generalising our previous works, we further analyse how the control of morphology can be achieved by tuning the colloidal interactions in the suspension. We detail the model we have developed that relates the colloidal interaction potential to a critical pressure exerted by the solvent as it flows, and we provide a quantitative prediction of the grain shape. Finally, we offer perspectives with regard to spray drying of systems such as molecular solutions, widely performed in e.g. the pharmaceutical industry. PMID:27532509

  6. Kinetics of ergodic-to-nonergodic transitions in charged colloidal suspensions: Aging and gelation

    NASA Astrophysics Data System (ADS)

    Tanaka, Hajime; Jabbari-Farouji, Sara; Meunier, Jacques; Bonn, Daniel

    2005-02-01

    There are two types of isotropic disordered nonergodic states in colloidal suspensions: colloidal glasses and gels. In a recent paper [H. Tanaka, J. Meunier, and D. Bonn, Phys. Rev. E 69, 031404 (2004)], we discussed the static aspect of the differences and the similarities between the two. In this paper, we focus on the dynamic aspect. The kinetics of the liquid-glass transition is called “aging,” while that of the sol-gel transition is called “gelation.” The former is primarily governed by repulsive interactions between particles, while the latter is dominated by attractive interactions. Slowing down of the dynamics during aging reflects the increasing cooperativity required for the escape of a particle from the cage formed by the surrounding particles, while that during gelation reflects the increase in the size of particle clusters towards the percolation transition. Despite these clear differences in the origin of the slowing down of the kinetics between the two, it is not straightforward experimentally to distinguish them in a clear manner. For an understanding of the universal nature of ergodic-to-nonergodic transitions, it is of fundamental importance to elucidate the differences and the similarities in the kinetics between aging and gelation. We consider this problem, taking Laponite suspension as an explicit example. In particular, we focus on the two types of nonergodic states: (i) an attractive gel formed by van der Waals attractions for high ionic strengths and (ii) a repulsive Wigner glass stabilized by long-range Coulomb repulsions for low ionic strengths. We demonstrate that the aging of colloidal Wigner glass crucially differs not only from gelation, but also from the aging of structural and spin glasses. The aging of the colloidal Wigner glass is characterized by the unique cage-forming regime that does not exist in the aging of spin and structural glasses.

  7. Anderson localization of light in a colloidal suspension (TiO2@silica).

    PubMed

    Jimenez-Villar, Ernesto; da Silva, Iran F; Mestre, Valdeci; de Oliveira, Paulo C; Faustino, Wagner M; de Sá, Gilberto F

    2016-06-01

    In recent years, there has been dramatic progress in the photonics field in disordered media, ranging from applications in solar collectors, photocatalyzers, random lasing, and other novel photonic functions, to investigations into fundamental topics, such as light confinement and other phenomena involving photon interactions. This paper reports several pieces of experimental evidence of localization transition in a strongly disordered scattering medium composed of a colloidal suspension of core-shell nanoparticles (TiO2@silica) in ethanol solution. We demonstrate the crossover from a diffusive transport to a localization transition regime as the nanoparticle concentration is increased, and that an enhanced absorption effect arises at localization transition.

  8. Reentrant phase transition in charged colloidal suspensions: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Tata, B. V. R.; Arora, Akhilesh K.; Valsakumar, M. C.

    1993-05-01

    Monte Carlo simulations of aqueous charged colloidal suspensions interacting via an effective pair potential are carried out with a view to elucidate the mechanism of the reentrant phase transition reported in these systems. The computed pair-correlation functions show that a weakly interacting homogeneous suspension phase separates into dense and rare phases and thereafter reenters into a homogeneous state with crystalline or liquidlike order when the concentration of the ionic impurities is decreased. The cluster-size distribution indeed shows the existence of dense-phase droplets for the intermediate range of impurity-ion concentrations where the phase separation occurs. Some of the recent experimental results are discussed in the light of the present simulation results.

  9. Sensing aggregation in highly turbid plasmonic and non-plasmonic colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Ducay, Rey Nann Mark; Philip, Nathan; Boivin, Jordan; Judge, Patrick; Berberich, Jason; Scaffidi, Jonathan; Bali, Lalit; Bali, Samir

    2015-05-01

    We demonstrate a method for sensing the presence of aggregation in highly turbid aqueous suspensions of polystyrene and gold nanospheres. Aggregation is induced either by changing the pH or the ionic strength, by adding small, controlled amounts of an acid or base solution. The particle concentrations used are at least two orders of magnitude higher than previously reported. To the best of our knowledge, this is a first observation of aggregation in highly dense colloidal suspensions without any sample dilution or special sample preparation. We gratefully acknowledge support from the American Chemical Society Petroleum Research Fund and Miami University's Interdisciplinary Roundtable Fund. We also gratefully acknowledge experimental help from the Miami University Instrumentation Laboratory.

  10. Hyperuniform Density Fluctuations and Diverging Dynamic Correlations in Periodically Driven Colloidal Suspensions

    NASA Astrophysics Data System (ADS)

    Tjhung, Elsen; Berthier, Ludovic

    2015-04-01

    The emergence of particle irreversibility in periodically driven colloidal suspensions has been interpreted as resulting either from a nonequilibrium phase transition to an absorbing state or from the chaotic nature of particle trajectories. Using a simple model of a driven suspension, we show that a nonequilibrium phase transition is accompanied by hyperuniform static density fluctuations in the vicinity of the transition, where we also observe strong dynamic heterogeneities reminiscent of dynamics in glassy materials. We find that single particle dynamics becomes intermittent and strongly non-Fickian, and that collective dynamics becomes spatially correlated over diverging length scales. Our results suggest that the two theoretical scenarii can be experimentally discriminated using particle-resolved measurements of standard static and dynamic observables.

  11. Melting and crystallization of colloidal hard-sphere suspensions under shear.

    PubMed

    Wu, Yu Ling; Derks, Didi; van Blaaderen, Alfons; Imhof, Arnout

    2009-06-30

    Shear-induced melting and crystallization were investigated by confocal microscopy in concentrated colloidal suspensions of hard-sphere-like particles. Both silica and polymethylmethacrylate suspensions were sheared with a constant rate in either a countertranslating parallel plate shear cell or a counterrotating cone-plate shear cell. These instruments make it possible to track particles undergoing shear for extended periods of time in a plane of zero velocity. Although on large scales, the flow profile deviated from linearity, the crystal flowed in an aligned sliding layer structure at low shear rates. Higher shear rates caused the crystal to shear melt, but, contrary to expectations, the transition was not sudden. Instead, although the overall order decreased with shear rate, this was due to an increase in the nucleation of localized domains that temporarily lost and regained their ordered structure. Even at shear rates that were considered to have melted the crystal as a whole, ordered regions kept showing up at times, giving rise to very large fluctuations in 2D bond-orientational order parameters. Low shear rates induced initially disordered suspensions to crystallize. This time, the order parameter increased gradually in time without large fluctuations, indicating that shear-induced crystallization of hard spheres does not proceed via a nucleation and growth mechanism. We conclude that the dynamics of melting and crystallization under shear differ dramatically from their counterparts in quiescent suspensions.

  12. Anderson localization of light in a colloidal suspension (TiO2@silica)

    NASA Astrophysics Data System (ADS)

    Jimenez-Villar, Ernesto; da Silva, Iran F.; Mestre, Valdeci; de Oliveira, Paulo C.; Faustino, Wagner M.; de Sá, Gilberto F.

    2016-05-01

    In recent years, there has been dramatic progress in the photonics field in disordered media, ranging from applications in solar collectors, photocatalyzers, random lasing, and other novel photonic functions, to investigations into fundamental topics, such as light confinement and other phenomena involving photon interactions. This paper reports several pieces of experimental evidence of localization transition in a strongly disordered scattering medium composed of a colloidal suspension of core-shell nanoparticles (TiO2@silica) in ethanol solution. We demonstrate the crossover from a diffusive transport to a localization transition regime as the nanoparticle concentration is increased, and that an enhanced absorption effect arises at localization transition.In recent years, there has been dramatic progress in the photonics field in disordered media, ranging from applications in solar collectors, photocatalyzers, random lasing, and other novel photonic functions, to investigations into fundamental topics, such as light confinement and other phenomena involving photon interactions. This paper reports several pieces of experimental evidence of localization transition in a strongly disordered scattering medium composed of a colloidal suspension of core-shell nanoparticles (TiO2@silica) in ethanol solution. We demonstrate the crossover from a diffusive transport to a localization transition regime as the nanoparticle concentration is increased, and that an enhanced absorption effect arises at localization transition. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07540h

  13. Coffee ring effect resulted conductive nanowire patterns by evaporating colloidal suspension droplets without sintering process

    NASA Astrophysics Data System (ADS)

    Wang, Xiaofeng; Seong, Baekhoon; Yudistira, Hadi Teguh; Byun, Doyoung

    2015-11-01

    Drying colloidal suspensions containing non-volatile solute will form a ring like pattern, which is called ``coffee ring effect.'' Here, we present the coffee ring effect with silver nanowires dispersing into DI water, resulting in a highly dense-packed nanowire ring patterns. The effect of nanowire length, concentration, droplet size, and substrate temperature were investigated. With shorter nanowires, a distinct ring could be obtained. Meanwhile, the concentration of the colloidal suspension was found to affect the ring width. The droplet size and nanowire length played a significant role in affecting the occurrence of the coffee ring effect. When smaller droplets (i.e., less than 150 μm) containing long nanowires (~ 20 μm), the coffee ring effect was suppressed. While smaller droplets containing short nanowires (~ 1 μm), the coffee ring effect was not affected. By increasing the temperature of the substrate, multi-ring pattern was formed inside the original ring. The resistivity of the semi-circle of the nanowire ring was measured, and had a minimum value of 1.32 × 10-6 Ωm without any sintering process. These findings could be exploited to basic study of ring stain effect as well as the practical use, such as evaporative lithography and ink-jet printing for conductive film and display. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) (Grant number: 2014-023284).

  14. Interplay between columnar and smectic stability in suspensions of polydisperse colloidal platelets.

    PubMed

    Velasco, Enrique; Martínez-Ratón, Yuri

    2014-01-14

    The phase behavior of a model suspension of colloidal polydisperse platelets is studied using density-functional theory. Platelets are modelled as parallel rectangular prisms of square section l(2) and height h, with length and height distributions given by different polydispersities δ(l) and δ(h). The model is intended to qualitatively represent experimental colloidal platelet suspensions at high densities with a high degree of orientational ordering. We obtain the phase behavior of the model, including nematic, smectic and columnar phases and its dependence on the two polydispersities δ(l) and δ(h). When δ(l) > δ(h) we observe that the smectic phase stabilises first with respect to the columnar. If δ(h) > δ(l) we observe the opposite behavior. Other more complicated cases occur, e.g. the smectic stabilises from the nematic first but then exists a first-order transition to the columnar phase. Our model assumes plate-rod symmetry, but the regions of stability of smectic and columnar phases are non-symmetric in the δ(l) - δ(h) plane due to the different dimensionality of ordering in the two phases. Microsegregation effects, i.e. different spatial distribution for different sizes within the periodic cell, take place in both phases and, in each case, is more apparent in the variable associated with ordering.

  15. Influence of steric interactions on the dielectric and electrokinetic properties in colloidal suspensions.

    PubMed

    López-García, José Juan; Horno, José; Grosse, Constantino

    2015-11-15

    One of the main assumptions of the standard electrokinetic model is that ions behave as point like entities. In this work we remove this assumption and analyze the main consequences of finite ionic size on the dielectric and electrokinetic properties of colloidal suspensions. We represent the steric interactions by means of the Bikerman and the Carnahan-Starling equations and solve numerically the standard linearized electrokinetic equations in the stationary and the frequency domains, for surface charge density and electrolyte solution concentration values typically encountered in colloidal suspensions. In all cases the steric interactions improve upon the predictions of the standard model since the surface potential, the electrophoretic mobility, and the conductivity and permittivity increments increase. However, the corrections introduced by the Bikerman equation are generally small: less than 10% as compared to the standard model. On the contrary, the Carnahan-Starling equation leads to corrections to the surface potential versus surface charge and the electrophoretic mobility values that easily surpass 10% and can attain values as high as 50%. Corrections to the conductivity and permittivity increments are smaller but still non negligible.

  16. Secondary minimum coagulation in charged colloidal suspensions from statistical mechanics methods.

    PubMed

    Cortada, María; Anta, Juan A; Molina-Bolívar, J A

    2007-02-01

    A statistical mechanics approach is applied to predict the critical parameters of coagulation in the secondary minimum for charged colloidal suspensions. This method is based on the solution of the reference hypernetted chain (RHNC) integral equation, and it is intended to estimate only the locus of the critical point instead of the full computation of the "gas-liquid" coexistence. We have used an extrapolation procedure due to the lack of solution of the integral equation in the vicinity of the critical point. Knowing that the osmotic isothermal compressibility of the colloidal system should ideally diverge in the critical point, we work out the critical salt concentration for which the inverse of the compressibility should be zero. This extrapolation procedure is more rapid than that previously proposed by Morales and co-workers [Morales, V.; Anta, J. A.; Lago, S. Langmuir 2003, 19, 475], and it is shown to give equivalent results. We also present experimental results about secondary minimum coagulation for polystyrene latexes and use our method to reproduce the experimental trends. The comparison between theory and experiment is quite good for all colloidal diameters studied.

  17. Preparation of Highly Crystallized Yttrium Oxysulfide Suspension via a Novel Colloidal Processing.

    PubMed

    Wang, Hong; Jiang, Tao; Xing, Ming-Ming; Fu, Yao; Peng, Yong; Luo, Xi-Xian

    2016-04-01

    High-crystallized Y2O2S suspension was synthesized by a novel two-step method of high temperature solid-state reaction and subsequent colloidal processing. The synthesis method proposed in this study retains all advantages of the high temperature solid-state reaction method. The obtained data agrees with that of the PDF card, which indicates the product is pure Y2O2S crystals. The results show that the prepared Y2O2S particles are highly crystallized without any significant defects. The fine smooth particles were almost regular, exhibiting an approximately subspherical shape. Quantitative image analysis of particles suggests a mean particle size of 120±34 nm. That is to say, the yttrium oxysulfide colloid prepared by this method have a very narrow size distribution. The obtained ethanol suspension shows Tyndall effect when irradiated with laser of wavelength 532 nm. In addition, the particles exhibit excellent dispersibility in ethanol solution. This is rarely observed for the covalent compounds, which generally present poor dispersibility in solution. As is known to all, the state of the dispersion depends on the acid leaching process. The acid leaching process facilitates the adsorption of ethanol molecules on the surface of the particles. The electrostatic repulsive force among colloidal particles will improve their rheological properties and dispersibility in solution. In this study, the particles can be dispersed well in ethanol after acid leaching. The method'proposed in this study can be extended for the preparation of mono-dispersed oxysulfide nanophosphors and may provide an efficient way for the preparation of stable covalent compound dispersions. PMID:27451744

  18. Nonlinear oscillatory rheology and structure of wormlike micellar solutions and colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Gurnon, Amanda Kate

    The complex, nonlinear flow behavior of soft materials transcends industrial applications, smart material design and non-equilibrium thermodynamics. A long-standing, fundamental challenge in soft-matter science is establishing a quantitative connection between the deformation field, local microstructure and macroscopic dynamic flow properties i.e., the rheology. Soft materials are widely used in consumer products and industrial processes including energy recovery, surfactants for personal healthcare (e.g. soap and shampoo), coatings, plastics, drug delivery, medical devices and therapeutics. Oftentimes, these materials are processed by, used during, or exposed to non-equilibrium conditions for which the transient response of the complex fluid is critical. As such, designing new dynamic experiments is imperative to testing these materials and further developing micromechanical models to predict their transient response. Two of the most common classes of these soft materials stand as the focus of the present research; they are: solutions of polymer-like micelles (PLM or also known as wormlike micelles, WLM) and concentrated colloidal suspensions. In addition to their varied applications these two different classes of soft materials are also governed by different physics. In contrast, to the shear thinning behavior of the WLMs at high shear rates, the near hard-sphere colloidal suspensions are known to display increases, sometimes quite substantial, in viscosity (known as shear thickening). The stress response of these complex fluids derive from the shear-induced microstructure, thus measurements of the microstructure under flow are critical for understanding the mechanisms underlying the complex, nonlinear rheology of these complex fluids. A popular micromechanical model is reframed from its original derivation for predicting steady shear rheology of polymers and WLMs to be applicable to weakly nonlinear oscillatory shear flow. The validity, utility and limits of

  19. Simulation of the injection of colloidal suspensions for the remediation of contaminated aquifer systems

    NASA Astrophysics Data System (ADS)

    Tosco, Tiziana; Gastone, Francesca; Sethi, Rajandrea

    2014-05-01

    Concentrated suspensions of microscale and nanoscale zerovalent iron particles (MZVI and NZVI) have been studied in recent years for the remediation of contaminated aquifers. The suspensions are injected into the subsurface to generate a reactive zone, and consequently the prediction of the particles distribution during the injection is a key aspect in the design of a field-scale injection. Colloidal dispersions of MZVI and NZVI are not stable in pure water, and shear thinning, environmentally friendly fluids (guar gum and xanthan gum solutions) were found to be effective in improving colloidal stability, thus greatly improving handling and injectability (1 - 3). Shear thinning fluids exhibit high viscosity in static conditions, improving the colloidal stability, and lower viscosity at high flow rates enabling the injection at limited pressures. Shear thinning fluids exhibit high viscosity in static conditions, improving the colloidal stability, and lower viscosity at high flow rates enabling the injection at limited pressures. In this work, co-funded by European Union project AQUAREHAB (FP7 - Grant Agreement Nr. 226565), laboratory and pilot field tests for MZVI injection in saturated porous media are reported. MZVI was dispersed in guar gum solutions, and the transport behaviour under several polymer concentrations and injection rates was assessed in column tests (4). Based on the experimental results, a modelling approach is proposed to simulate the transport in porous media of nanoscale iron slurries, implemented in E-MNM1D (www.polito.it/groundwater/software). Colloid transport mechanisms are controlled by particle-collector and particle-particle interactions, usually modelled by a non equilibrium kinetic model accounting for deposition and release processes. The key aspects included in the E-MNM1D are clogging phenomena (i.e. reduction of porosity and permeability due to particles deposition), and the rheological properties of the carrier fluid (in this

  20. Quantum efficiency of colloidal suspensions containing quantum dot/silica hybrid particles

    NASA Astrophysics Data System (ADS)

    Jeon, Hyungjoon; Yoon, Cheolsang; Lee, Sooho; Lee, Doh C.; Shin, Kyusoon; Lee, Kangtaek

    2016-10-01

    We have investigated the fluorescence properties of colloidal suspensions conntaining quantum dot (QD)/silica hybrid particles. First, we synthesized QD/silica hybrid particles with silica-QD-silica (SQS) core-shell-shell geometry, and monitored the quantum efficiencies of their suspensions at various particle concentrations. We found that the quantum efficiency (QE) of SQS particles in deionized (DI) water was much lower than that of the QDs even at low particle concentration, mainly due to the light scattering of emitted photons at the silica/water interface, followed by reabsorption by QDs. As the concentration of SQS particles was increased, both light scattering and reabsorption by QDs became more important, which further reduced the QE. Refractive index-matched solvent, however, reduced light scattering, yielding greater QE than DI water. Next, we induced aggregation of SQS particles, and found that QE increased as particles aggregated in DI water because of reduced light scattering and reabsorption, whereas it remained almost constant in the refractive index-matched solvent. Finally, we studied aggregation of highly concentrated silica particle suspensions containing a low concentration of SQS particles, and found that QE increased with aggregation because light scattering and reabsorption were reduced.

  1. Non-Newtonian flow effects during spin coating large-area optical coatings with colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Britten, Jerald A.; Thomas, Ian M.

    1992-01-01

    Multilayer sol-gel optical high reflectors with greater than 99% reflection have been prepared on substrates up to 20 cm in diameter by spin coating silica/alumina colloidal suspensions. These coatings are radially nonuniform, owing to the extensive shear-thinning rheology of the high-index alumina suspension. To a large degree the film thickness nonuniformity can be compensated for by the reflection bandwidth. The rheological properties of the alumina suspension under steady shear have been measured. The low-shear reduced viscosity and the shear-thinning time constant are shown to vary exponentially with φ2, where φ is the solids volume fraction. At φ=0.1 the sol has effectively gelled. A model for spincoating with a non-Newtonian fluid has been developed that uses the Carreau rheology model to fit the measured viscometric data. Modeling and experimental results show that as long as these non-Newtonian effects are sufficiently large (as in this case) the radial film uniformity is determined only by these parameters and cannot be significantly influenced by spin rate, initial solids fraction, or any other parameters under the control of the operator. However, most of the film thickness variation occurs in the first 1-2 cm from the substrate center, leaving the remainder almost uniform. Therefore the degree of nonuniformity does not appreciably increase with increasing substrate size.

  2. A scalable parallel Stokesian Dynamics method for the simulation of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Bülow, F.; Hamberger, P.; Nirschl, H.; Dörfler, W.

    2016-07-01

    We have developed a new method for the efficient numerical simulation of colloidal suspensions. This method is designed and especially well-suited for parallel code execution, but it can also be applied to single-core programs. It combines the Stokesian Dynamics method with a variant of the widely used Barnes-Hut algorithm in order to reduce computational costs. This combination and the inherent parallelization of the method make simulations of large numbers of particles within days possible. The level of accuracy can be determined by the user and is limited by the truncation of the used multipole expansion. Compared to the original Stokesian Dynamics method the complexity can be reduced from O(N2) to linear complexity for dilute suspensions of strongly clustered particles, N being the number of particles. In case of non-clustered particles in a dense suspension, the complexity depends on the particle configuration and is between O(N) and O(Pnp,max2) , where P is the number of used processes and np,max = ⌈ N / P ⌉ , respectively.

  3. Quantum efficiency of colloidal suspensions containing quantum dot/silica hybrid particles.

    PubMed

    Jeon, Hyungjoon; Yoon, Cheolsang; Lee, Sooho; Lee, Doh C; Shin, Kyusoon; Lee, Kangtaek

    2016-10-28

    We have investigated the fluorescence properties of colloidal suspensions conntaining quantum dot (QD)/silica hybrid particles. First, we synthesized QD/silica hybrid particles with silica-QD-silica (SQS) core-shell-shell geometry, and monitored the quantum efficiencies of their suspensions at various particle concentrations. We found that the quantum efficiency (QE) of SQS particles in deionized (DI) water was much lower than that of the QDs even at low particle concentration, mainly due to the light scattering of emitted photons at the silica/water interface, followed by reabsorption by QDs. As the concentration of SQS particles was increased, both light scattering and reabsorption by QDs became more important, which further reduced the QE. Refractive index-matched solvent, however, reduced light scattering, yielding greater QE than DI water. Next, we induced aggregation of SQS particles, and found that QE increased as particles aggregated in DI water because of reduced light scattering and reabsorption, whereas it remained almost constant in the refractive index-matched solvent. Finally, we studied aggregation of highly concentrated silica particle suspensions containing a low concentration of SQS particles, and found that QE increased with aggregation because light scattering and reabsorption were reduced. PMID:27658534

  4. Non-Newtonian flow effects during spin coating large-area optical coatings with colloidal suspensions

    SciTech Connect

    Britten, J.A.; Thomas, I.M. )

    1992-01-15

    Multilayer sol-gel optical high reflectors with greater than 99% reflection have been prepared on substrates up to 20 cm in diameter by spin coating silica/alumina colloidal suspensions. These coatings are radially nonuniform, owing to the extensive shear-thinning rheology of the high-index alumina suspension. To a large degree the film thickness nonuniformity can be compensated for by the reflection bandwidth. The rheological properties of the alumina suspension under steady shear have been measured. The low-shear reduced viscosity and the shear-thinning time constant are shown to vary exponentially with {phi}{sup 2}, where {phi} is the solids volume fraction. At {phi}=0.1 the sol has effectively gelled. A model for spincoating with a non-Newtonian fluid has been developed that uses the Carreau rheology model to fit the measured viscometric data. Modeling and experimental results show that as long as these non-Newtonian effects are sufficiently large (as in this case) the radial film uniformity is determined only by these parameters and cannot be significantly influenced by spin rate, initial solids fraction, or any other parameters under the control of the operator. However, most of the film thickness variation occurs in the first 1--2 cm from the substrate center, leaving the remainder almost uniform. Therefore the degree of nonuniformity does not appreciably increase with increasing substrate size.

  5. Quantum efficiency of colloidal suspensions containing quantum dot/silica hybrid particles.

    PubMed

    Jeon, Hyungjoon; Yoon, Cheolsang; Lee, Sooho; Lee, Doh C; Shin, Kyusoon; Lee, Kangtaek

    2016-10-28

    We have investigated the fluorescence properties of colloidal suspensions conntaining quantum dot (QD)/silica hybrid particles. First, we synthesized QD/silica hybrid particles with silica-QD-silica (SQS) core-shell-shell geometry, and monitored the quantum efficiencies of their suspensions at various particle concentrations. We found that the quantum efficiency (QE) of SQS particles in deionized (DI) water was much lower than that of the QDs even at low particle concentration, mainly due to the light scattering of emitted photons at the silica/water interface, followed by reabsorption by QDs. As the concentration of SQS particles was increased, both light scattering and reabsorption by QDs became more important, which further reduced the QE. Refractive index-matched solvent, however, reduced light scattering, yielding greater QE than DI water. Next, we induced aggregation of SQS particles, and found that QE increased as particles aggregated in DI water because of reduced light scattering and reabsorption, whereas it remained almost constant in the refractive index-matched solvent. Finally, we studied aggregation of highly concentrated silica particle suspensions containing a low concentration of SQS particles, and found that QE increased with aggregation because light scattering and reabsorption were reduced.

  6. 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

  7. A Lattice-Boltzmann model for suspensions of self-propelling colloidal particles.

    PubMed

    Ramachandran, S; Sunil Kumar, P B; Pagonabarraga, I

    2006-06-01

    We present a Lattice-Boltzmann method for simulating self-propelling (active) colloidal particles in two dimensions. Active particles with symmetric and asymmetric force distribution on their surface are considered. The velocity field generated by a single active particle, changing its orientation randomly, and the different time scales involved are characterized in detail. The steady-state speed distribution in the fluid, resulting from the activity, is shown to deviate considerably from the equilibrium distribution. PMID:16779527

  8. A Lattice-Boltzmann model for suspensions of self-propelling colloidal particles

    NASA Astrophysics Data System (ADS)

    Ramachandran, S.; Kumar, P. B. Sunil; Pagonabarraga, I.

    2006-06-01

    We present a Lattice-Boltzmann method for simulating self-propelling (active) colloidal particles in two dimensions. Active particles with symmetric and asymmetric force distribution on their surface are considered. The velocity field generated by a single active particle, changing its orientation randomly, and the different time scales involved are characterized in detail. The steady-state speed distribution in the fluid, resulting from the activity, is shown to deviate considerably from the equilibrium distribution.

  9. Rheological signatures of gelation and effect of shear melting on aging colloidal suspension

    SciTech Connect

    Jatav, Shweta; Joshi, Yogesh M

    2014-09-01

    Colloidal suspensions that are out of thermodynamic equilibrium undergo physical aging wherein their structure evolves to lower the free energy. In aqueous suspension of Laponite, physical aging accompanies increases of elastic and viscous moduli as a function of time. In this work, we study temporal evolution of elastic and viscous moduli at different frequencies and observe that freshly prepared aqueous suspension of Laponite demonstrates identical rheological behavior reported for the crosslinking polymeric materials undergoing chemical gelation. Consequently at a certain time, tan δ is observed to be independent of frequency. However, for samples preserved under rest condition for longer duration before applying the shear melting, the liquid to solid transition subsequent to shear melting shows greater deviation from classical gelation. We also obtain continuous relaxation time spectra from the frequency dependence of viscous modulus. We observe that, with an increase in the rest time, continuous relaxation time spectrum shows gradual variation from negative slope, describing dominance of fast relaxation modes to positive slope representing dominance of slow relaxation modes. We propose that the deviation from gelation behavior for the shear melted suspensions originates from inability of shear melting to completely break the percolated structure thereby creating unbroken aggregates. The volume fraction of such unbroken aggregates increases with the rest time. For small rest times presence of fewer number of unbroken aggregates cause deviation from the classical gelation. On the other hand, at high rest times presence of greater fraction of unbroken aggregates subsequent to shear melting demonstrate dynamic arrest leading to inversion of relaxation time spectra.

  10. Cluster formation in binary charge-stabilized colloidal suspensions confined to a two-dimensional plane

    NASA Astrophysics Data System (ADS)

    Kumar, Sanat; Mukherjee, Manjori; Mishra, Pankaj

    2016-09-01

    Hypernetted chain (HNC) integral equation theory has been used to study the structural features of binary charged stabilized colloidal suspensions confined to a two-dimensional plane. The particles interact via purely repulsive Yukawa intermolecular potential, the inverse screening length scaled by the average distance between strongly interacting components of the mixture (dimensionless screening parameter) being 1, 3 and 5. Results of HNC theory for one-component systems are found to be in very good agreement with that of simulation, in the parameter range of our study. Binary Yukawa systems with dimensionless screening parameters 1 and 3 are found to exhibit diffuse clusters of the weakly interacting particles, marked by the emergence of a cluster peak in the corresponding partial structure factor curves. No cluster peak is found in the system with the screening parameter 5. For the entire range of mixture parameters, the strongly interacting particles remain homogeneously distributed.

  11. MHz-ultrasound generation by chirped femtosecond laser pulses from gold nano-colloidal suspensions.

    PubMed

    Masim, Frances Camille P; Hsu, Wei-Hung; Tsai, Chih-Hung; Liu, Hao-Li; Porta, Matteo; Nguyen, Mai Thanh; Yonezawa, Tetsu; Balčytis, Armandas; Wang, Xuewen; Juodkazis, Saulius; Hatanaka, Koji

    2016-07-25

    Strong absorption of femtosecond laser pulses in Au nano-colloidal suspensions was used to generate coherent ultrasound signals at 1-20 MHz frequency range. The most efficient ultrasound generation was observed at negative chirp values and was proportional to the pulse duration. Maximization of a dimensionless factor A ≡ αc0tp defined as the ratio of pulse duration tp and the time required for sound at speed c0 to cross the optical energy deposition length (an inverse of the absorption coefficient α) given by 1/(αc0). Chirp controlled pulse duration allows effective enhancement of ultrasound generation at higher frequencies (shorter wavelengths) and is promising for a high spatial resolution acoustic imaging. PMID:27464156

  12. Preparation of dielectrics HR mirrors from colloidal oxide suspensions containing organic polymer binders

    SciTech Connect

    Thomas, I.M.

    1994-07-19

    Colloidal suspensions of oxides have been used to prepare dielectric HR (high reflective) mirrors, specifically for high power fusion case applications, on substrates up to 38 cm square using a meniscus coater. These coatings consist of porous quarterwave layers of alternating high and low refractive index oxides. Silica was used as the low index oxide and AlOOH, ZrO{sub 2}, or HfO{sub 2} as the high index material. Coatings were weak because of low particle-to-particle adhesion. Use of organic polymer binders in the high index component was found to increase strength, thereby improving the laser damage threshold and also reducing the number of layers required for 99% reflection due to increased refractive index.

  13. Structure and dynamics of concentration fluctuations in a non-equilibrium dense colloidal suspension.

    PubMed

    Giavazzi, Fabio; Savorana, Giovanni; Vailati, Alberto; Cerbino, Roberto

    2016-08-21

    Linearised fluctuating hydrodynamics describes effectively the concentration non-equilibrium fluctuations (NEF) arising during a diffusion process driven by a small concentration gradient. However, fluctuations in the presence of large gradients are not yet fully understood. Here we study the giant concentration NEF arising when a dense aqueous colloidal suspension is allowed to diffuse into an overlying layer of pure water. We use differential dynamic microscopy to determine both the statics and the dynamics of the fluctuations for several values of the wave-vector q. At small q, NEF are quenched by buoyancy, which prevents their full development and sets an upper timescale to their temporal relaxation. At intermediate q, the mean squared amplitude of NEF is characterised by a power law exponent -4, and fluctuations relax diffusively with diffusion coefficient D1. At large q, the amplitude of NEF vanishes and equilibrium concentration fluctuations are recovered, enabling a straightforward determination of the osmotic compressibility of the suspension during diffusion. In this q-range we also find that the relaxation of the fluctuations occurs with a diffusion coefficient D2 significantly different from D1. Both diffusion coefficients exhibit time-dependence with D1 increasing monotonically (by about 15%) and D2 showing the opposite behaviour (about 17% decrease). At equilibrium, the two coefficients coincide as expected. While the decrease of D2 is compatible with a diffusive evolution of the concentration profile, the increase of D1 is still not fully understood and may require considering nonlinearities that are neglected in current theories for highly stressed colloids.

  14. Structure and dynamics of concentration fluctuations in a non-equilibrium dense colloidal suspension.

    PubMed

    Giavazzi, Fabio; Savorana, Giovanni; Vailati, Alberto; Cerbino, Roberto

    2016-08-21

    Linearised fluctuating hydrodynamics describes effectively the concentration non-equilibrium fluctuations (NEF) arising during a diffusion process driven by a small concentration gradient. However, fluctuations in the presence of large gradients are not yet fully understood. Here we study the giant concentration NEF arising when a dense aqueous colloidal suspension is allowed to diffuse into an overlying layer of pure water. We use differential dynamic microscopy to determine both the statics and the dynamics of the fluctuations for several values of the wave-vector q. At small q, NEF are quenched by buoyancy, which prevents their full development and sets an upper timescale to their temporal relaxation. At intermediate q, the mean squared amplitude of NEF is characterised by a power law exponent -4, and fluctuations relax diffusively with diffusion coefficient D1. At large q, the amplitude of NEF vanishes and equilibrium concentration fluctuations are recovered, enabling a straightforward determination of the osmotic compressibility of the suspension during diffusion. In this q-range we also find that the relaxation of the fluctuations occurs with a diffusion coefficient D2 significantly different from D1. Both diffusion coefficients exhibit time-dependence with D1 increasing monotonically (by about 15%) and D2 showing the opposite behaviour (about 17% decrease). At equilibrium, the two coefficients coincide as expected. While the decrease of D2 is compatible with a diffusive evolution of the concentration profile, the increase of D1 is still not fully understood and may require considering nonlinearities that are neglected in current theories for highly stressed colloids. PMID:27425869

  15. Photoreduction of methyl viologen mediated by tris(bipyridyl)ruthenium(II) in inert colloidal suspensions

    SciTech Connect

    Kelly, L.A.; Rodgers, M.A.J. )

    1994-06-23

    The photoreduction of methyl viologen, covalently attached to a tris(bipyridyl)ruthenium(II) chromophore, in suspensions of positively charged alumina-coated colloidal silica particles, via N-phenylglycine electron donor, is reported. In the tris(bipyridyl)ruthenium(II) complexes, the central metal atom is coordinated to two 4,4[prime]-dicarboxy-2,2[prime]-bipyridine ligands and thus carries a net 2-charge at pH 5.0. Coadsorption of the N-phenylglycine and ruthenium chromophore to the colloidal particles results in rapid production of reduced viologen following visible laser flash excitation of the tris(bipyridyl)ruthenium(II) complex. The yield of the radical was dependent upon the concentration of the electron donor added to the system, but its multiphasic decay was independent of both the N-phenylglycine concentration and the initial concentration of viologen radical cation. Furthermore, both the yield and decay kinetics of the viologen radical cation were relatively independent of the number of intervening methylene units between the ruthenium complex and viologen electron acceptor. 18 refs., 5 figs., 2 tabs.

  16. Microstructure, local dynamics, and flow behavior of colloidal suspensions with weak attractive interactions

    NASA Astrophysics Data System (ADS)

    Weis, Clara; Oelschlaeger, Claude; Dijkstra, Dick; Ranft, Meik; Willenbacher, Norbert

    2016-09-01

    We present a comprehensive micro- and macrorheological study of the effect of weak depletion attraction (Ψdep ≈ 1–10 kBT) on dense colloidal suspensions stabilized by short-range repulsive interactions. We used aqueous polymer dispersions as model system and demonstrated the unique capabilities of multiple particle tracking (MPT) to disclose structural changes in such technically important systems exhibiting many characteristic features of hard sphere systems. Below the hard sphere freezing point ϕc, viscosity increases monotonically with increasing Ψdep due to the transition from a fluid to a fluid/crystalline and finally to a gel state. Above ϕc, increasing attraction strength first results in a viscosity reduction corresponding to the formation of large, permeable crystals and then in a viscosity increase when a network of dense, small crystals forms. The fraction of the fluid and crystal phase, particle concentration in each phase as well as the modulus of the micro-crystals are obtained, the latter decreases with Ψdep. Above the colloidal glass transition strong heterogeneities and different local particle mobility in the repulsive and attractive arrested states are found. Particles are trapped in the cage of neighboring particles rather than in an attractive potential well. The intermediate ergodic state exhibits uniform tracer diffusivity.

  17. Particle Deposition in Drying Drops of Colloidal Suspensions Containing Different Surfactants

    NASA Astrophysics Data System (ADS)

    Still, Tim; Yunker, Peter J.; Yodh, A. G.

    2012-02-01

    When a drop of water containing small solid particles dries, most of the solid material is deposited in a ring-shape stain after evaporation (the so-called coffee ring), driven by initial contact line pinning and a subsequent outward-flow. The fluid dynamics and, hence, the deposition mechanism in such suspensions can be dramatically changed when surfactants are introduced into the system. In a colloidal model-system, the ionic sodium dodecyl sulfate (SDS) produces a concentration-driven Marangoni flow counteracting the outward-flow of the coffee ring effect. SDS locally concentrates at the air/water interface next to the contact line, leading to a reduced local surface tension. Thus, a circulating flow (`Marangoni eddy') is introduced that prevents particles from deposition. This flow is visualized by the movements of the dragged particles using video microscopy. Other surfactants can influence this highly non-equilibrium systems in completely other ways. E.g., the non-ionic Polaxamer block-copolymer surfactants lead to a uniform particle deposition, which we explain by hydrophilization of the colloidal particles. Controlling the solid deposition in drying drops is of major importance for many technical applications.

  18. Microstructure, local dynamics, and flow behavior of colloidal suspensions with weak attractive interactions

    PubMed Central

    Weis, Clara; Oelschlaeger, Claude; Dijkstra, Dick; Ranft, Meik; Willenbacher, Norbert

    2016-01-01

    We present a comprehensive micro- and macrorheological study of the effect of weak depletion attraction (Ψdep ≈ 1–10 kBT) on dense colloidal suspensions stabilized by short-range repulsive interactions. We used aqueous polymer dispersions as model system and demonstrated the unique capabilities of multiple particle tracking (MPT) to disclose structural changes in such technically important systems exhibiting many characteristic features of hard sphere systems. Below the hard sphere freezing point ϕc, viscosity increases monotonically with increasing Ψdep due to the transition from a fluid to a fluid/crystalline and finally to a gel state. Above ϕc, increasing attraction strength first results in a viscosity reduction corresponding to the formation of large, permeable crystals and then in a viscosity increase when a network of dense, small crystals forms. The fraction of the fluid and crystal phase, particle concentration in each phase as well as the modulus of the micro-crystals are obtained, the latter decreases with Ψdep. Above the colloidal glass transition strong heterogeneities and different local particle mobility in the repulsive and attractive arrested states are found. Particles are trapped in the cage of neighboring particles rather than in an attractive potential well. The intermediate ergodic state exhibits uniform tracer diffusivity. PMID:27653975

  19. Hydrodynamic interactions and Brownian forces in colloidal suspensions: Coarse-graining over time and length scales

    NASA Astrophysics Data System (ADS)

    Padding, J. T.; Louis, A. A.

    2006-09-01

    We describe in detail how to implement a coarse-grained hybrid molecular dynamics and stochastic rotation dynamics simulation technique that captures the combined effects of Brownian and hydrodynamic forces in colloidal suspensions. The importance of carefully tuning the simulation parameters to correctly resolve the multiple time and length scales of this problem is emphasized. We systematically analyze how our coarse-graining scheme resolves dimensionless hydrodynamic numbers such as the Reynolds number Re, which indicates the importance of inertial effects, the Schmidt number Sc, which indicates whether momentum transport is liquidlike or gaslike, the Mach number, which measures compressibility effects, the Knudsen number, which describes the importance of noncontinuum molecular effects, and the Peclet number, which describes the relative effects of convective and diffusive transport. With these dimensionless numbers in the correct regime the many Brownian and hydrodynamic time scales can be telescoped together to maximize computational efficiency while still correctly resolving the physically relevant processes. We also show how to control a number of numerical artifacts, such as finite-size effects and solvent-induced attractive depletion interactions. When all these considerations are properly taken into account, the measured colloidal velocity autocorrelation functions and related self-diffusion and friction coefficients compare quantitatively with theoretical calculations. By contrast, these calculations demonstrate that, notwithstanding its seductive simplicity, the basic Langevin equation does a remarkably poor job of capturing the decay rate of the velocity autocorrelation function in the colloidal regime, strongly underestimating it at short times and strongly overestimating it at long times. Finally, we discuss in detail how to map the parameters of our method onto physical systems and from this extract more general lessons—keeping in mind that there

  20. Hydrodynamic interactions and Brownian forces in colloidal suspensions: coarse-graining over time and length scales.

    PubMed

    Padding, J T; Louis, A A

    2006-09-01

    We describe in detail how to implement a coarse-grained hybrid molecular dynamics and stochastic rotation dynamics simulation technique that captures the combined effects of Brownian and hydrodynamic forces in colloidal suspensions. The importance of carefully tuning the simulation parameters to correctly resolve the multiple time and length scales of this problem is emphasized. We systematically analyze how our coarse-graining scheme resolves dimensionless hydrodynamic numbers such as the Reynolds number Re, which indicates the importance of inertial effects, the Schmidt number Sc, which indicates whether momentum transport is liquidlike or gaslike, the Mach number, which measures compressibility effects, the Knudsen number, which describes the importance of noncontinuum molecular effects, and the Peclet number, which describes the relative effects of convective and diffusive transport. With these dimensionless numbers in the correct regime the many Brownian and hydrodynamic time scales can be telescoped together to maximize computational efficiency while still correctly resolving the physically relevant processes. We also show how to control a number of numerical artifacts, such as finite-size effects and solvent-induced attractive depletion interactions. When all these considerations are properly taken into account, the measured colloidal velocity autocorrelation functions and related self-diffusion and friction coefficients compare quantitatively with theoretical calculations. By contrast, these calculations demonstrate that, notwithstanding its seductive simplicity, the basic Langevin equation does a remarkably poor job of capturing the decay rate of the velocity autocorrelation function in the colloidal regime, strongly underestimating it at short times and strongly overestimating it at long times. Finally, we discuss in detail how to map the parameters of our method onto physical systems and from this extract more general lessons-keeping in mind that there

  1. Silver clusters onto nanosized colloidal silica as novel surface-enhanced Raman scattering active substrates.

    PubMed

    Muniz-Miranda, Maurizio

    2003-06-01

    A new method is proposed for obtaining surface-enhanced Raman scattering (SERS)-active substrates by photochemical reduction of silver nitrate onto colloidal silica. Transmission electron microscopy (TEM) and UV-visible absorption spectroscopy are employed to investigate the nanoscale structure of the materials. High quality SERS spectra are obtained from different organic ligands to check the efficiency of these substrates. A marked stability of the colloidal suspension is ensured by the scarce tendency of the Ag-doped silica particles to aggregate by either aging or adsorption of ligand.

  2. 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.

  3. Systematic modification of the rheological properties of colloidal suspensions with polyelectrolyte multilayers.

    PubMed

    Hess, Andreas; Pretzl, Melanie; Heymann, Lutz; Fery, Andreas; Aksel, Nuri

    2011-09-01

    Tailoring rheological properties of colloidal suspensions with the adsorption of polyelectrolyte multilayers (PEMs) is based on the idea of controlling macroscopic mechanical properties by modifying the particle surface in a reproducible and well-understood manner. With layer-by-layer self-assembly, monodisperse polystyrene particles are coated with up to ten layers of the oppositely charged strong polyelectrolytes: poly(diallyl dimethyl ammonium chloride) and poly(styrene sulfonate). The conformation of the adsorbed polyelectrolyte is controlled by the ionic strength of the used aqueous polyelectrolyte solution. For 1M NaCl solution, a brushlike adsorption of the polyelectrolyte is expected. The ability of PEMs to serve on a nanoscale level as surface modifiers and influence macroscopic rheological properties like viscoelasticity, yield stress, and shear banding is discussed. The mechanical behavior of these suspensions is qualitatively described by the theory of Derjaguin-Landau-Verwey-Overbeek with short-range repulsion and long-range attraction. A scaling rule is proposed which distinguishes between the precusor and the multilayer regime.

  4. Influence of sedimentation on the threshold for Soret-driven convection in colloidal suspensions.

    PubMed

    Hadji, L; DarAssi, M

    2014-01-01

    The onset of Soret-driven convection in a horizontal layer of a colloidal suspension is investigated by considering a particulate medium model. We consider a dilute suspension of spherical solid particles being subjected to convection in a Rayleigh-Bénard geometry setup. The mathematical model takes into account the effects of thermophoresis, particle sedimentation, and Brownian diffusion. The equations governing the convective motion consist of the momentum equation which includes an extra body force term to account for the thermophoretic force effect, the conservation of particles equation whose mass-flux term couples the Soret and particle diffusion effects and whose advective term includes the sedimentation force, and the heat and mass balance equations. The horizontal boundaries are assumed rigid, perfectly thermally conducting, and impervious to mass flow. Furthermore, the model makes use of the effective viscosity of the suspension whose dependence on the particle concentration is through Einstein's formula. Moreover, we take into account the decrease of both the coefficient of Brownian diffusion and the mixture thermal diffusion with particle concentration due to the particles hindrance effect. The nondimensionalization leads to the emergence of an experimental parameter, β, which depicts the competition between the effects of thermophoresis, sedimentation, and particle diffusion. The parameter β is a function of the particles radius, the shape of which is an inverted parabola having two zeros. A combination of asymptotic and numerical computations is used to determine the threshold for the onset of the mass dominated convection, which corresponds to 0<β≪1. Our findings shed light on the role of particle sedimentation and particle size, as well as the influence of other processing variables on the fluid instability. PMID:24580327

  5. Decisive influence of colloidal suspension conductivity during electrophoretic impregnation of porous anodic film supported on 1050 aluminium substrate.

    PubMed

    Fori, B; Taberna, P L; Arurault, L; Bonino, J P

    2014-01-01

    The present paper studies the influence of suspension conductivity on the electrophoretic deposition (EPD) of nanoparticles inside a porous anodic aluminium oxide film. It is shown that an increase in the suspension's conductivity enhances impregnation of the anodic film by the nanoparticles. Two mechanisms are seen to promote the migration of particles into the pores. Indeed an increase in the suspension conductivity leads on the one hand to a strengthening of the electric field in the anodic film and on the other hand to a thinning of the electric double layer on the pore walls. The results of our study confirm that colloidal suspension conductivity is a key parameter governing the electrophoretic impregnation depth.

  6. Aqueous suspensions of polymer coated magnetite nanoparticles: Colloidal stability, specific absorption rate, and transverse relaxivity

    NASA Astrophysics Data System (ADS)

    Saville, Steven Lee

    The design, functionalization, characterization, and applications of magnetic nanoparticles have garnered significant interest over the past several decades. While this area has garnered increasing attention, several questions remain unanswered about the stability of these systems and it's influence on their biomedical applications. To help answer these questions about the stability of these, a novel tri(nitroDOPA) terminated polymer based ligand has been developed for the stabilization of magnetite nanoparticles. The synthesis involves a process in which ethylene oxide is polymerized using a trivinyl initiator, modified with carboxylic acid using a free radical addition of mercaptoundecanoic acid, and then functionalized with nitroDOPA using N,N-dicyclohexylcarbodiimide (DCC) and N-hydroxysuccinimide (NHS) chemistry. This polymer has displayed robust adhesion even in harsh chemical environments, out performing many polymers used today for the stabilization of magnetite. Along these same lines, the effects of instability of these systems were analyzed in both MRI and magnetic hyperthermia applications. It is widely known that formation of linear aggregates (i.e. chains) occurs in more concentrated ferrofluids systems and that this has an affect on the ferrofluid properties. It has been recently reported that for some suspensions of magnetic nanoparticles the transverse proton relaxation rate, R2, is dependent on the time that the sample is exposed to an applied magnetic field. This time dependence has been linked to the formation of linear aggregates or chains in an applied magnetic field via numerical modeling. In this work the relationships between colloidal stability, the formation of these linear structures, and changes observed in the proton transverse relaxation rate and heating rate in magnetic hyperthermia of aqueous suspensions of magnetic particles are examined. The results indicate that varying the ligand length has a direct effect on the colloidal

  7. Exploration and characterization of new synthesis methods for C60 colloidal suspensions in water

    NASA Astrophysics Data System (ADS)

    Hilburn, Martha E.

    Buckminsterfullerene, C60, has been used in the production of several commercial products from badminton racquets and lubricants for their mechanical properties to cosmetics and even dietary supplements for their "antioxidant" properties. Multi-ton production of C60 began in 2003 encouraging serious consideration of its fate in the environment in the case of an accidental release or improper disposal. Although C60 is practically insoluble in water, it readily forms stable aqueous colloidal suspensions (termed nC60) through solvent exchange methods or long-term vigorous stirring in water. Two new solvent exchange methods for synthesizing nC60 are presented. These methods combine key advantages of multiple existing synthesis methods including high yield, narrow particle size distribution, short synthesis time, and an absence of solvents such as tetrahydrofuran that have historically caused problems in laboratory synthesized aggregates. The resulting samples are attractive candidates for use in controlled environmental impact, biological, and toxicity studies. An improved method for quantifying residual solvents in nC60 samples utilizing solid phase micro extraction gas chromatography mass spectrometry (SPME-GC-MS) is also discussed.

  8. Communication: Dynamical density functional theory for dense suspensions of colloidal hard spheres.

    PubMed

    Stopper, Daniel; Roth, Roland; Hansen-Goos, Hendrik

    2015-11-14

    We study structural relaxation of colloidal hard spheres undergoing Brownian motion using dynamical density functional theory. Contrary to the partial linearization route [D. Stopper et al., Phys. Rev. E 92, 022151 (2015)] which amounts to using different free energy functionals for the self and distinct part of the van Hove function G(r, t), we put forward a unified description employing a single functional for both components. To this end, interactions within the self part are removed via the zero-dimensional limit of the functional with a quenched self component. In addition, we make use of a theoretical result for the long-time mobility in hard-sphere suspensions, which we adapt to the inhomogeneous fluid. Our results for G(r, t) are in excellent agreement with numerical simulations even in the dense liquid phase. In particular, our theory accurately yields the crossover from free diffusion at short times to the slower long-time diffusion in a crowded environment.

  9. Buckling and crumpling of drying droplets of colloid-polymer suspensions.

    PubMed

    Sugiyama, Yoichi; Larsen, Ryan J; Kim, Jin-Woong; Weitz, David A

    2006-07-01

    Spray drying of complex liquids to form solid powders is important in many industrial applications. One of the challenges associated with spray drying is controlling the morphologies of the powders produced; this requires an understanding of how drying mechanics depend on the ingredients and conditions. We demonstrate that the morphology of powders produced by spray drying colloidal polystyrene (PS) suspensions can be significantly altered by changing the molecular weight of dissolved poly(ethylene oxide) (PEO). Samples containing high-molecular-weight PEO produce powders with more crumpled morphologies than those containing low-molecular-weight PEO. Observations of drying droplets suspended by a thin film of vapor suggest that this occurs because the samples with high-molecular-weight PEO buckle earlier in the drying process when the droplets are larger. Earlier buckling times are likely caused by the decreased stability, demonstrated by bulk rheology experiments, of PS particles in the presence of high-molecular-weight PEO at elevated temperatures. We present a consistent picture in which decreased particle stability hastens droplet buckling and leads to more crumpled powder morphologies; this underscores the importance of interparticle forces in determining the buckling of particle-laden droplets.

  10. Analysis of the static magnetic field-dependent optical transmission of Ni nanorod colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Krämer, Florian; Gratz, Micha; Tschöpe, Andreas

    2016-07-01

    The magnetic field-dependent optical transmission of dilute Ni nanorod aqueous suspensions was investigated. A series of four samples of nanorods were synthesized using the AAO template method and processed to stable colloids. The distributions of their length and diameter were characterized by analysis of TEM images and revealed average diameters of ˜25 nm and different lengths in the range of 60 nm-1100 nm. The collinear magnetic and optical anisotropy was studied by static field-dependent transmission measurements of linearly polarized light parallel and perpendicular to the magnetic field direction. The experimental results were modelled assuming the field-dependent orientation distribution function of a superparamagnetic ensemble for the uniaxial ferromagnetic nanorods in liquid dispersion and extinction cross sections for longitudinal and transversal optical polarization derived from different approaches, including the electrostatic approximation and the separation of variables method, both applied to spheroidal particles, as well as finite element method simulations of spheroids and capped cylindrical particles. The extinction cross sections were compared to reveal the differences associated with the approximations of homogeneous polarization and/or particle shape. The consequences of these approximations for the quantitative analysis of magnetic field-dependent optical transmission measurements were investigated and a reliable protocol derived. Furthermore, the changes in optical cross sections induced by electromagnetic interaction between two nanorods in parallel end-to-end and side-by-side configuration as a function of their separation were studied.

  11. Transient Networks and Dense Colloidal Suspensions: From Viscous Flow to Elastic Instabilities

    NASA Astrophysics Data System (ADS)

    Bouchaud, Elisabeth

    2013-03-01

    In order to analyze the mechanical response of viscoelastic materials in highly non-linear regimes, we have designed a new kind of Hele-Shaw cell where both viscous liquids and soft elastic solids can be tested at a controlled loading rate. We first consider model Maxwell liquids - characterized by a single relaxation time - with the project of benchmarking the response of complex, glassy systems. We use several solutions of microemulsions connected by telechelic polymers. We show that these materials undergo instability in a broad range of loading rates. At low rates, this instability is shown to be of the viscous Saffman-Taylor type. At high rates, we observe a purely elastic bulk instability discovered recently in the context of soft elastomers. A microfluidic version of our cell makes it possible to study the response of colloidal suspensions. We use more or less concentrated PNIPA aqueous solutions for which temperature controls the volume fraction. Observations are interpreted in the light of our understanding of their viscoelastic properties. This work was done in collaboration with Maxime Lefranc, Baudouin Saintyves, Olivier Dauchot and Serge Mora. It was funded by ANR, France.

  12. Investigation of the jamming transition using confocal microscopy of dense colloidal suspensions and complex biomaterials

    NASA Astrophysics Data System (ADS)

    Cianci, Gianguido C.

    Jamming is the process by which a liquid stops flowing and assumes some properties commonly associated with solids. Everyday examples include the setting of a bowl of Jell-O(TM) or the vitrification of a molten mixture of silica, lime and soda at the end of a glassblower's blowpipe. In these examples, the system resists flow and can even support some pressure just like a crystalline solid. At the same time its structure is not crystalline and is in fact hardly distinguishable from that of a liquid. Here we focus our attention on two separate but related questions presented by the jamming (or glass) transition. The dynamical properties of a glass (e.g. viscosity) depend on the time elapsed since vitrification. This slow evolution is called aging and is currently poorly understood. For example a static, or structural, measure of the age of a glass has not yet been identified and aging can only be detected by following the system's dynamics. We consider the aging of the microscopic structure in out-of-equilibrium glasses by measuring local tetrahedral geometry in two systems: a monodisperse colloidal suspension observed by confocal microscopy and a binary Lennard-Jones glass simulated by molecular dynamics. While these models differ in some details they are both widely used in the study of glasses. Tetrahedral structure is found to be a poor indicator of age in the experiments though it weakly correlates with the slowing dynamics. In contrast, the structure of the simulated glass shows clear signs of aging. In both cases, tetrahedral structure samples geometry in a non-trivial way. Similarly, a static measure of a liquid's proximity to the glass transition has remained elusive. We present preliminary results from a magnetic tweezers experiment aimed at dynamically exciting a dormant length scale in a binary "supercooled" colloidal liquid. We observe the sample's local response to a point disturbance from a magnetic probe. We find that the disturbance decays

  13. Structure and short-time dynamics in concentrated suspensions of charged colloids.

    PubMed

    Westermeier, Fabian; Fischer, Birgit; Roseker, Wojciech; Grübel, Gerhard; ägele, Gerhard; Heinen, Marco

    2012-09-21

    We report a comprehensive joint experimental-theoretical study of the equilibrium pair-structure and short-time diffusion in aqueous suspensions of highly charged poly-acrylate (PA) spheres in the colloidal fluid phase. Low-polydispersity PA sphere systems with two different hard-core radii, R(0) = 542 and 1117 Å, are explored over a wide range of concentrations and salinities using static and dynamic light scattering (DLS), small angle x-ray scattering, and x-ray photon correlation spectroscopy (XPCS). The measured static and dynamic scattering functions are analyzed using state-of-the-art theoretical methods. For all samples, the measured static structure factor, S(Q), is in good agreement with results by an analytical integral equation method for particles interacting by a repulsive screened Coulomb plus hard-core pair potential. In our DLS and XPCS measurements, we have determined the short-time diffusion function D(Q) = D(0) H(Q)∕S(Q), comprising the free diffusion coefficient D(0) and the hydrodynamic function H(Q). The latter is calculated analytically using a self-part corrected version of the δγ-scheme by Beenakker and Mazur which accounts approximately for many-body hydrodynamic interactions (HIs). Except for low-salinity systems at the highest investigated volume fraction φ ≈ 0.32, the theoretical predictions for H(Q) are in excellent agreement with the experimental data. In particular, the increase in the collective diffusion coefficient D(c) = D(Q → 0), and the decrease of the self-diffusion coefficient, D(s) = D(Q → ∞), with increasing φ is well described. In accord with the theoretical prediction, the peak value, H(Q(m)), of H(Q) relates to the nearest neighbor cage size ∼2π∕Q(m), for which concentration scaling relations are discussed. The peak values H(Q(m)) are globally bound from below by the corresponding neutral hard-spheres peak values, and from above by the limiting peak values for low-salinity charge-stabilized systems

  14. Semi-active suspension for automotive application

    NASA Astrophysics Data System (ADS)

    Venhovens, Paul J. T.; Devlugt, Alex R.

    The theoretical considerations for semi-active damping system evaluation, with respect to semi-active suspension and Kalman filtering, are discussed in terms of the software. Some prototype hardware developments are proposed. A significant improvement in ride comfort performance can be obtained, indicated by root mean square body acceleration values and frequency responses, using a switchable damper system with two settings. Nevertheless the improvement is accompanied by an increase in dynamic tire load variations. The main benefit of semi-active suspensions is the potential of changing the low frequency section of the transfer function. In practice this will support the impression of extra driving stability. It is advisable to apply an adaptive control strategy like the (extended) skyhook version switching more to the 'comfort' setting for straight (and smooth/moderate roughness) road running and switching to 'road holding' for handling maneuvers and possibly rough roads and discrete, severe events like potholes.

  15. Diffusion in active suspension of microswimmers

    NASA Astrophysics Data System (ADS)

    Climent, Eric; Delmotte, Blaise; Plouraboue, Franck; Keaveny, Eric; Martin, Matthieu; Rafai, Salima; Peyla, Philippe; Bertin, Eric; IMFT Team; IC Team; LiPhy Team

    2015-11-01

    The presence of microswimmers in a fluid generates flow agitation due to multi-body hydrodynamic interactions. This agitation of the fluid leads to random trajectories of passive tracers particles and the swimmers themselves, and from a macroscopic point view, it can be interpreted as a diffusive mechanism. By means of experiments (videomicroscopy of suspensions of chlamydomonas reinhardtii)and numerical simulations (Stokesian fluid populated with squirmers), we investigate the evolution of the effective diffusion coefficient when the volumetric concentration of the active suspension varies. By comparing the experimental and numerical results, we quantify the role of active swimming on the measured diffusion and identify the physical mechanisms that lead to diffusion enhancement. Our results aim to provide a better understanding of how swimming organisms affect micron-scale transport in the environment.

  16. Electrostatic correlations in colloidal suspensions: Density profiles and effective charges beyond the Poisson-Boltzmann theory

    NASA Astrophysics Data System (ADS)

    dos Santos, Alexandre P.; Diehl, Alexandre; Levin, Yan

    2009-03-01

    A theory is proposed which allows us to calculate the distribution of the multivalent counterions around a colloidal particle using the cell model. The results are compared with the Monte Carlo simulations and are found to be very accurate in the two asymptotic regimes, close to the colloidal particle and far from it. The theory allows to accurately calculate the osmotic pressure and the effective charge of colloidal particles with multivalent counterions.

  17. Mixing in suspensions of active particles

    NASA Astrophysics Data System (ADS)

    Pushkin, Dmitri O.; Yeomans, Julia M.

    2014-03-01

    Microscopic active particles self-propelling in the surrounding fluid create flows that eventually lead to emergence of non-equilibrium states with long-ranged fluctuations. One of the technologically important consequences of these fluctuations is enhanced mixing of the surrounding fluid. It is also critical for understanding the ecology of a particular type of biological active systems, bacterial suspension, as the enhanced mixing strongly alters the fluxes of nutrients. We consider the theoretical foundations of fluid mixing enhancement in dilute suspensions of active force-free swimmers. We describe the impediments to fluid mixing imposed by the physical nature of fluid flows created by swimmers, and different ways of overcoming them. We show that fluid mixing in 3D suspensions of force-free (dipolar) swimmers is dominated by the effect of curvature of their trajectories, and obtain an exact analytical expression for the corresponding effective diffusion coefficient. Our results highlight limitations of alternative ``effective temperature'' approaches and may serve as a quantitative tool for designing technological applications.

  18. Probing droplets with biological colloidal suspensions on smart surfaces by synchrotron radiation micro- and nano-beams

    NASA Astrophysics Data System (ADS)

    Marinaro, G.; Accardo, A.; Benseny-Cases, N.; Burghammer, M.; Castillo-Michel, H.; Cotte, M.; Dante, S.; De Angelis, F.; Di Cola, E.; Di Fabrizio, E.; Hauser, C.; Riekel, C.

    2016-01-01

    Droplets with colloidal biological suspensions evaporating on substrates with defined wetting properties generate confined environments for initiating aggregation and self-assembly processes. We describe smart micro- and nanostructured surfaces, optimized for probing single droplets and residues by synchrotron radiation micro- and nanobeam diffraction techniques. Applications are presented for Ac-IVD and β-amyloid (1-42) peptides capable of forming cross-β sheet structures. Complementary synchrotron radiation FTIR microspectroscopy addresses secondary structure formation. The high synchrotron radiation source brilliance enables fast raster-scan experiments.

  19. Magneto-induced stress enhancing effect in a colloidal suspension of paramagnetic and superparamagnetic particles dispersed in a ferrofluid medium.

    PubMed

    Liu, Taixiang; Gong, Xinglong; Xu, Yangguang; Xuan, Shouhu

    2014-02-14

    The magneto-induced stress and relative microstructure in a colloidal suspension of paramagnetic and superparamagnetic particles dispersed in a ferrofluid medium is studied using particle-level dynamics simulation. It shows that the stress perpendicular to the direction of an external uniaxial magnetic field can be strongly enhanced by increasing the ratio of paramagnetic particles to approaching that of superparamagnetic particles. The magnetic field-induced net-like or embedded chain-like microstructures formed by paramagnetic and superparamagnetic particles contribute to this stress enhancing effect. PMID:24837318

  20. 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.

  1. Diffusion of passive particles in active suspensions

    NASA Astrophysics Data System (ADS)

    Mussler, Matthias; Rafai, Salima; John, Thomas; Peyla, Philippe; Wagner, Christian

    2013-11-01

    We study how an active suspension consisting of a definite volume fraction of the microswimmer Chlamydomonas Reinhardtii modifies the Brownian movement of small to medium size microspheres. We present measurements and simulations of trajectories of microspheres with a diameter of 20 μm in suspensions of Chlamydomonas Reinhardtii, a so called ``puller,'' and show that the mean squared displacement of such trajectories consist of parabolic and a linear part. The linear part is due to the hydrodynamic noise of the microswimmers while the parabolic part is a consequence of directed motion events that occur randomly, when a microsphere is transported by a microswimmer on a timescale that is in higher order of magnitude than the Brownian like hydrodynamic interaction. In addition, we theoretically describe this effect with a dimensional analysis that takes the force dipole model used to describe ``puller'' like Chlamydomonas Reinhardtii into account.

  2. 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.

  3. Myosin II Activity Softens Cells in Suspension.

    PubMed

    Chan, Chii J; Ekpenyong, Andrew E; Golfier, Stefan; Li, Wenhong; Chalut, Kevin J; Otto, Oliver; Elgeti, Jens; Guck, Jochen; Lautenschläger, Franziska

    2015-04-21

    The cellular cytoskeleton is crucial for many cellular functions such as cell motility and wound healing, as well as other processes that require shape change or force generation. Actin is one cytoskeleton component that regulates cell mechanics. Important properties driving this regulation include the amount of actin, its level of cross-linking, and its coordination with the activity of specific molecular motors like myosin. While studies investigating the contribution of myosin activity to cell mechanics have been performed on cells attached to a substrate, we investigated mechanical properties of cells in suspension. To do this, we used multiple probes for cell mechanics including a microfluidic optical stretcher, a microfluidic microcirculation mimetic, and real-time deformability cytometry. We found that nonadherent blood cells, cells arrested in mitosis, and naturally adherent cells brought into suspension, stiffen and become more solidlike upon myosin inhibition across multiple timescales (milliseconds to minutes). Our results hold across several pharmacological and genetic perturbations targeting myosin. Our findings suggest that myosin II activity contributes to increased whole-cell compliance and fluidity. This finding is contrary to what has been reported for cells attached to a substrate, which stiffen via active myosin driven prestress. Our results establish the importance of myosin II as an active component in modulating suspended cell mechanics, with a functional role distinctly different from that for substrate-adhered cells. PMID:25902426

  4. Myosin II Activity Softens Cells in Suspension

    PubMed Central

    Chan, Chii J.; Ekpenyong, Andrew E.; Golfier, Stefan; Li, Wenhong; Chalut, Kevin J.; Otto, Oliver; Elgeti, Jens; Guck, Jochen; Lautenschläger, Franziska

    2015-01-01

    The cellular cytoskeleton is crucial for many cellular functions such as cell motility and wound healing, as well as other processes that require shape change or force generation. Actin is one cytoskeleton component that regulates cell mechanics. Important properties driving this regulation include the amount of actin, its level of cross-linking, and its coordination with the activity of specific molecular motors like myosin. While studies investigating the contribution of myosin activity to cell mechanics have been performed on cells attached to a substrate, we investigated mechanical properties of cells in suspension. To do this, we used multiple probes for cell mechanics including a microfluidic optical stretcher, a microfluidic microcirculation mimetic, and real-time deformability cytometry. We found that nonadherent blood cells, cells arrested in mitosis, and naturally adherent cells brought into suspension, stiffen and become more solidlike upon myosin inhibition across multiple timescales (milliseconds to minutes). Our results hold across several pharmacological and genetic perturbations targeting myosin. Our findings suggest that myosin II activity contributes to increased whole-cell compliance and fluidity. This finding is contrary to what has been reported for cells attached to a substrate, which stiffen via active myosin driven prestress. Our results establish the importance of myosin II as an active component in modulating suspended cell mechanics, with a functional role distinctly different from that for substrate-adhered cells. PMID:25902426

  5. Myosin II Activity Softens Cells in Suspension.

    PubMed

    Chan, Chii J; Ekpenyong, Andrew E; Golfier, Stefan; Li, Wenhong; Chalut, Kevin J; Otto, Oliver; Elgeti, Jens; Guck, Jochen; Lautenschläger, Franziska

    2015-04-21

    The cellular cytoskeleton is crucial for many cellular functions such as cell motility and wound healing, as well as other processes that require shape change or force generation. Actin is one cytoskeleton component that regulates cell mechanics. Important properties driving this regulation include the amount of actin, its level of cross-linking, and its coordination with the activity of specific molecular motors like myosin. While studies investigating the contribution of myosin activity to cell mechanics have been performed on cells attached to a substrate, we investigated mechanical properties of cells in suspension. To do this, we used multiple probes for cell mechanics including a microfluidic optical stretcher, a microfluidic microcirculation mimetic, and real-time deformability cytometry. We found that nonadherent blood cells, cells arrested in mitosis, and naturally adherent cells brought into suspension, stiffen and become more solidlike upon myosin inhibition across multiple timescales (milliseconds to minutes). Our results hold across several pharmacological and genetic perturbations targeting myosin. Our findings suggest that myosin II activity contributes to increased whole-cell compliance and fluidity. This finding is contrary to what has been reported for cells attached to a substrate, which stiffen via active myosin driven prestress. Our results establish the importance of myosin II as an active component in modulating suspended cell mechanics, with a functional role distinctly different from that for substrate-adhered cells.

  6. The middeck active control experiment: Gravity and suspension effects

    NASA Technical Reports Server (NTRS)

    Crawley, Edward F.; Alexander, H.; Rey, Daniel

    1992-01-01

    Viewgraphs on the Middeck Active Control Experiment (MACE): Gravity and Suspension Effects are presented. Topics covered include: gravity and suspension influences; gravity and suspension effects on structure; gravity effects on sensors and actuators; modeling of gravity and suspension effects on structure; geometric stiffness theory and initial static deformation calculation; modeling gravity's effect on accelerometers and PMA's; application to MACE; MACE EM configuration study; and MACE DM configuration study.

  7. Population-balance description of shear-induced clustering, gelation and suspension viscosity in sheared DLVO colloids.

    PubMed

    Lattuada, Marco; Zaccone, Alessio; Wu, Hua; Morbidelli, Massimo

    2016-06-28

    Application of shear flow to charge-stabilized aqueous colloidal suspensions is ubiquitous in industrial applications and as a means to achieve controlled field-induced assembly of nanoparticles. Yet, applying shear flow to a charge-stabilized colloidal suspension, which is initially monodisperse and in quasi-equilibrium leads to non-trivial clustering phenomena (and sometimes to a gelation transition), dominated by the complex interplay between DLVO interactions and shear flow. The quantitative understanding of these strongly nonequilibrium phenomena is still far from being complete. By taking advantage of a recent shear-induced aggregation rate theory developed in our group, we present here a systematic numerical study, based on the governing master kinetic equation (population-balance) for the shear-induced clustering and breakup of colloids exposed to shear flow. In the presence of sufficiently stable particles, the clustering kinetics is characterized by an initial very slow growth, controlled by repulsion. During this regime, particles are slowly aggregating to form clusters, the reactivity of which increases along with their size growth. When their size reaches a critical threshold, a very rapid, explosive-like growth follows, where shear forces are able to overcome the energy barrier between particles. This stage terminates when a dynamic balance between shear-induced aggregation and cluster breakage is reached. It is also observed that these systems are characterized by a cluster mass distribution that for a long time presents a well-defined bimodality. The model predictions are quantitatively in excellent agreement with available experimental data, showing how the theoretical picture is able to quantitatively account for the underlying nonequilibrum physics. PMID:27222249

  8. Population-balance description of shear-induced clustering, gelation and suspension viscosity in sheared DLVO colloids.

    PubMed

    Lattuada, Marco; Zaccone, Alessio; Wu, Hua; Morbidelli, Massimo

    2016-06-28

    Application of shear flow to charge-stabilized aqueous colloidal suspensions is ubiquitous in industrial applications and as a means to achieve controlled field-induced assembly of nanoparticles. Yet, applying shear flow to a charge-stabilized colloidal suspension, which is initially monodisperse and in quasi-equilibrium leads to non-trivial clustering phenomena (and sometimes to a gelation transition), dominated by the complex interplay between DLVO interactions and shear flow. The quantitative understanding of these strongly nonequilibrium phenomena is still far from being complete. By taking advantage of a recent shear-induced aggregation rate theory developed in our group, we present here a systematic numerical study, based on the governing master kinetic equation (population-balance) for the shear-induced clustering and breakup of colloids exposed to shear flow. In the presence of sufficiently stable particles, the clustering kinetics is characterized by an initial very slow growth, controlled by repulsion. During this regime, particles are slowly aggregating to form clusters, the reactivity of which increases along with their size growth. When their size reaches a critical threshold, a very rapid, explosive-like growth follows, where shear forces are able to overcome the energy barrier between particles. This stage terminates when a dynamic balance between shear-induced aggregation and cluster breakage is reached. It is also observed that these systems are characterized by a cluster mass distribution that for a long time presents a well-defined bimodality. The model predictions are quantitatively in excellent agreement with available experimental data, showing how the theoretical picture is able to quantitatively account for the underlying nonequilibrum physics.

  9. An effective medium approach for the elongational viscosity of non-colloidal and non-Brownian hard-sphere suspensions

    NASA Astrophysics Data System (ADS)

    Housiadas, Kostas D.

    2015-08-01

    An effective-medium fluid mechanics model based on the original idea first presented by Brinkman ["A calculation of the viscous force exerted by a flowing fluid on a dense swarm of particles," Appl. Sci. Res. 1, 27-34 (1949)] for the viscous force exerted by a flowing fluid on a dense swarm of fixed spherical particles is utilized for the prediction of the elongational viscosity of a non-colloidal, non-Brownian hard-sphere suspension in an incompressible Newtonian matrix fluid. The same model was explored by Housiadas and Tanner ["A model for the shear viscosity of non-colloidal suspensions with Newtonian matrix fluids," Rheol. Acta 53, 831-841 (2014)] for the derivation of an analytical formula for the bulk shear viscosity of the suspension as a function of the volume fraction of the solid phase, a formula which is in very good agreement with widely used semi-empirical relationships and available experimental data from the literature. In the present paper, it is assumed that a spherical particle is subject, in an average sense, to a far-field uniform uniaxial elongational flow and a suitable pressure gradient. Under steady, isothermal, creeping conditions, and imposing no-slip and no-penetration conditions at the surface of a particle in a stagnation point of the fluid and the far-field velocity and pressure profiles, the solution of the three-dimensional Brinkman equations is found analytically. The solution shows a faster decay of the velocity disturbances around a reference particle than the single-particle case. A volume average of the total stress tensor gives an analytical formula for the bulk elongational viscosity of the complex system as a function of the particle concentration. A significant increase of the elongation viscosity with increasing the particle concentration is predicted. The increase is larger than the corresponding increase of the shear viscosity, in qualitative accordance with the theoretical formula of Batchelor and Green ["The

  10. Enhanced diffusion self-stimulated by micro-algae in an active, aerotactic bacterial suspension

    NASA Astrophysics Data System (ADS)

    Peaudecerf, François; Goldstein, Raymond E.

    2014-11-01

    Suspensions of swimming bacteria form a new class of active fluids that generate complex phenomena. An ``active bath'' of bacteria for instance produces fluid flows which move passive colloids in a random-like walk, associated with an effective diffusion coefficient higher than for Brownian motion. The value of this enhanced diffusion coefficient depends on the local density of bacteria and their swimming behavior. However, with aerotactic, obligate aerobic bacteria such as B. subtilis, the local oxygen concentration impacts on the distribution of cells and their swimming behavior. We consider the specific case in which non-motile photosynthetic algal cells interacting with a B. subtilis suspension not only play the role of passive colloids, but also produce oxygen under light. We demonstrate that this new kind of active suspension, under heterogeneous illumination, can induce an effective negative phototaxis of the passive algal cells. We explain the origin of this novel phenomenon as the combination of algal oxygen production, diffusion, chemotaxis and motility switching in bacteria resulting in an heterogeneous enhanced diffusion. Finally, we present potential applications for algal cell mixing and sorting, that can inspire new methods for bioengineering. Supported by ERC, Raymond and Beverly Sackler Foundation, and Mines ParisTech.

  11. Shape control and compartmentalization in active colloidal cells

    PubMed Central

    Spellings, Matthew; Engel, Michael; Klotsa, Daphne; Sabrina, Syeda; Drews, Aaron M.; Nguyen, Nguyen H. P.; Bishop, Kyle J. M.; Glotzer, Sharon C.

    2015-01-01

    Small autonomous machines like biological cells or soft robots can convert energy input into control of function and form. It is desired that this behavior emerges spontaneously and can be easily switched over time. For this purpose we introduce an active matter system that is loosely inspired by biology and which we term an active colloidal cell. The active colloidal cell consists of a boundary and a fluid interior, both of which are built from identical rotating spinners whose activity creates convective flows. Similarly to biological cell motility, which is driven by cytoskeletal components spread throughout the entire volume of the cell, active colloidal cells are characterized by highly distributed energy conversion. We demonstrate that we can control the shape of the active colloidal cell and drive compartmentalization by varying the details of the boundary (hard vs. flexible) and the character of the spinners (passive vs. active). We report buckling of the boundary controlled by the pattern of boundary activity, as well as formation of core–shell and inverted Janus phase-separated configurations within the active cell interior. As the cell size is increased, the inverted Janus configuration spontaneously breaks its mirror symmetry. The result is a bubble–crescent configuration, which alternates between two degenerate states over time and exhibits collective migration of the fluid along the boundary. Our results are obtained using microscopic, non–momentum-conserving Langevin dynamics simulations and verified via a phase-field continuum model coupled to a Navier–Stokes equation. PMID:26253763

  12. The "macromolecular tourist": universal temperature dependence of thermal diffusion in aqueous colloidal suspensions.

    PubMed

    Iacopini, S; Rusconi, R; Piazza, R

    2006-01-01

    By performing measurements on a large class of macromolecular and colloidal systems, we show that thermophoresis (particle drift induced by thermal gradients) in aqueous solvents displays a distinctive universal dependence on temperature. For systems of particles interacting via temperature-independent forces, this behavior is strictly related to the solvent thermal expansivity, while an additional, T-independent term is needed to account for the behavior of "thermophilic" (migrating to the warmth) particles. The former relation between thermophoresis and thermal expansion may be exploited to envisage other fruitful studies of colloidal diffusion in inhomogeneous fluids. PMID:16446985

  13. The "macromolecular tourist": universal temperature dependence of thermal diffusion in aqueous colloidal suspensions.

    PubMed

    Iacopini, S; Rusconi, R; Piazza, R

    2006-01-01

    By performing measurements on a large class of macromolecular and colloidal systems, we show that thermophoresis (particle drift induced by thermal gradients) in aqueous solvents displays a distinctive universal dependence on temperature. For systems of particles interacting via temperature-independent forces, this behavior is strictly related to the solvent thermal expansivity, while an additional, T-independent term is needed to account for the behavior of "thermophilic" (migrating to the warmth) particles. The former relation between thermophoresis and thermal expansion may be exploited to envisage other fruitful studies of colloidal diffusion in inhomogeneous fluids.

  14. Microstructure of sheared monosized colloidal suspensions resulting from hydrodynamic and electrostatic interactions

    SciTech Connect

    Xu, Bu; Gilchrist, James F.

    2014-05-28

    Hydrodynamic and near-particle interactions in sheared suspensions are communicated through suspension microstructure to produce a wide variety of rheological behaviors. To characterize this microstructure, the individual positions of monosized silica particles flowing through a microchannel are obtained with near simulation-level detail. The pair distribution functions of the microstructure at moderate to high Péclet number shear rates are very similar to previous numerical studies. Viscometric functions calculated based on the detailed microstructure obtained through this technique show qualitative agreement with computational results. These results elucidate the origins of shear-thickening of suspensions at high shear rates. While efforts are taken to screen electrostatic interactions to study hydrodynamic and Brownian interactions, the role of electrostatic interaction between particles is also investigated by reducing suspension ionic strength. These non-hydrodynamic electrostatic interactions result in a loss of anisotropy that generally agrees with previous findings of “soft” particle systems.

  15. Modeling of water-borne coating: stress relaxation of suspensions of colloids linked by telechelic HEUR polymers

    NASA Astrophysics Data System (ADS)

    Wang, Shihu; Larson, Ronald G.

    In water-borne coatings, the rheology of colloidal suspensions is modified by the presence of rheological modifiers, such as Hydrophobic Ethoxylated Urethane (HEUR) polymers. HEUR is a telechelic polymer with two hydrophobic tails (hydrophobes) and a long hydrophilic interblock consisting of poly(ethylene oxide), and its thickening effect is largely determined by the self-association of hydrophobes as well as their adsorption onto latex particles. Here we describe a model that simulates the complex interactions among latex particles due to the formation of bridges or superbridges via model HEURs. We calculate the stress relaxation of the system and identify different relaxation modes. We explore the relaxation time at different latex volume fractions, HEUR concentrations and energies of association between hydrophobes and latex particles, and discuss its relationship with the bridge or latex cluster formation. These results provide important insights for HEUR adsorption and water-borne coating rheology. We acknowledge the financial support from The Dow Chemical Company.

  16. Femtosecond Laser Pulse Driven Melting in Gold Nanorod Aqueous Colloidal Suspension: Identification of a Transition from Stretched to Exponential Kinetics

    PubMed Central

    Li, Yuelin; Jiang, Zhang; Lin, Xiao-Min; Wen, Haidan; Walko, Donald A.; Deshmukh, Sanket A.; Subbaraman, Ram; Sankaranarayanan, Subramanian K. R. S.; Gray, Stephen K.; Ho, Phay

    2015-01-01

    Many potential industrial, medical, and environmental applications of metal nanorods rely on the physics and resultant kinetics and dynamics of the interaction of these particles with light. We report a surprising kinetics transition in the global melting of femtosecond laser-driven gold nanorod aqueous colloidal suspension. At low laser intensity, the melting exhibits a stretched exponential kinetics, which abruptly transforms into a compressed exponential kinetics when the laser intensity is raised. It is found the relative formation and reduction rate of intermediate shapes play a key role in the transition. Supported by both molecular dynamics simulations and a kinetic model, the behavior is traced back to the persistent heterogeneous nature of the shape dependence of the energy uptake, dissipation and melting of individual nanoparticles. These results could have significant implications for various applications such as water purification and electrolytes for energy storage that involve heat transport between metal nanorod ensembles and surrounding solvents. PMID:25634673

  17. Femtosecond laser pulse driven melting in gold nanorod aqueous colloidal suspension: identification of a transition from stretched to exponential kinetics.

    PubMed

    Li, Yuelin; Jiang, Zhang; Lin, Xiao-Min; Wen, Haidan; Walko, Donald A; Deshmukh, Sanket A; Subbaraman, Ram; Sankaranarayanan, Subramanian K R S; Gray, Stephen K; Ho, Phay

    2015-01-30

    Many potential industrial, medical, and environmental applications of metal nanorods rely on the physics and resultant kinetics and dynamics of the interaction of these particles with light. We report a surprising kinetics transition in the global melting of femtosecond laser-driven gold nanorod aqueous colloidal suspension. At low laser intensity, the melting exhibits a stretched exponential kinetics, which abruptly transforms into a compressed exponential kinetics when the laser intensity is raised. It is found the relative formation and reduction rate of intermediate shapes play a key role in the transition. Supported by both molecular dynamics simulations and a kinetic model, the behavior is traced back to the persistent heterogeneous nature of the shape dependence of the energy uptake, dissipation and melting of individual nanoparticles. These results could have significant implications for various applications such as water purification and electrolytes for energy storage that involve heat transport between metal nanorod ensembles and surrounding solvents.

  18. Femtosecond laser pulse driven melting in gold nanorod aqueous colloidal suspension: Identification of a transition from stretched to exponential kinetics

    DOE PAGES

    Li, Yuelin; Jiang, Zhang; Lin, Xiao -Min; Wen, Haidan; Walko, Donald A.; Deshmukh, Sanket A.; Subbaraman, Ram; Sankaranarayanan, Subramanian K. R. S.; Gray, Stephen K.; Ho, Phay

    2015-01-30

    Many potential industrial, medical, and environmental applications of metal nanorods rely on the physics and resultant kinetics and dynamics of the interaction of these particles with light. We report a surprising kinetics transition in the global melting of femtosecond laser-driven gold nanorod aqueous colloidal suspension. At low laser intensity, the melting exhibits a stretched exponential kinetics, which abruptly transforms into a compressed exponential kinetics when the laser intensity is raised. It is found the relative formation and reduction rate of intermediate shapes play a key role in the transition. Supported by both molecular dynamics simulations and a kinetic model, themore » behavior is traced back to the persistent heterogeneous nature of the shape dependence of the energy uptake, dissipation and melting of individual nanoparticles. These results could have significant implications for various applications such as water purification and electrolytes for energy storage that involve heat transport between metal nanorod ensembles and surrounding solvents.« less

  19. Characterization and Correlation of Particle-Level Interactions to the Macroscopic Rheology of Powders, Granular Slurries, and Colloidal Suspensions

    SciTech Connect

    A.P. Poloski; R.C. Daniel; D.R. Rector; P.R. Bredt; E.C. Buck; Berg, J.C.; Saez, A.E.

    2006-09-29

    This project had two primary objectives. The first was to understand the physical properties and behavior of select Hanford tank sludges under conditions that might exist during retrieval, treatment, packaging, and transportation for disposal at the Waste Isolation Pilot Plant (WIPP). The second objective was to develop a fundamental understanding of these sludge suspensions by correlating the macroscopic properties with particle interactions occurring at the colloidal scale. The specific tank wastes considered herein are contained in thirteen Hanford tanks including three double-shell tanks (DSTs) (AW-103, AW-105, and SY-102) and ten single-shell tanks (SSTs) (B-201 through B-204, T-201 through T-204, T-110, and T-111). At the outset of the project, these tanks were designated as potentially containing transuranic (TRU) process wastes that would be treated and disposed of in a manner different from the majority of the tank wastes.

  20. Femtosecond laser pulse driven melting in gold nanorod aqueous colloidal suspension: Identification of a transition from stretched to exponential kinetics

    SciTech Connect

    Li, Yuelin; Jiang, Zhang; Lin, Xiao -Min; Wen, Haidan; Walko, Donald A.; Deshmukh, Sanket A.; Subbaraman, Ram; Sankaranarayanan, Subramanian K. R. S.; Gray, Stephen K.; Ho, Phay

    2015-01-30

    Many potential industrial, medical, and environmental applications of metal nanorods rely on the physics and resultant kinetics and dynamics of the interaction of these particles with light. We report a surprising kinetics transition in the global melting of femtosecond laser-driven gold nanorod aqueous colloidal suspension. At low laser intensity, the melting exhibits a stretched exponential kinetics, which abruptly transforms into a compressed exponential kinetics when the laser intensity is raised. It is found the relative formation and reduction rate of intermediate shapes play a key role in the transition. Supported by both molecular dynamics simulations and a kinetic model, the behavior is traced back to the persistent heterogeneous nature of the shape dependence of the energy uptake, dissipation and melting of individual nanoparticles. These results could have significant implications for various applications such as water purification and electrolytes for energy storage that involve heat transport between metal nanorod ensembles and surrounding solvents.

  1. Colloidal polyaniline dispersions: antibacterial activity, cytotoxicity and neutrophil oxidative burst.

    PubMed

    Kucekova, Zdenka; Humpolicek, Petr; Kasparkova, Vera; Perecko, Tomas; Lehocký, Marián; Hauerlandová, Iva; Sáha, Petr; Stejskal, Jaroslav

    2014-04-01

    Polyaniline colloids rank among promising application forms of this conducting polymer. Cytotoxicity, antibacterial activity, and neutrophil oxidative burst tests were performed on cells treated with colloidal polyaniline dispersions. The antibacterial effect of colloidal polyaniline against gram-positive and gram-negative bacteria was most pronounced for Bacillus cereus and Escherichia coli, with a minimum inhibitory concentration of 3,500 μg mL(-1). The data recorded on human keratinocyte (HaCaT) and a mouse embryonic fibroblast (NIH/3T3) cell lines using an MTT assay and flow cytometry indicated a concentration-dependent cytotoxicity of colloid, with the absence of cytotoxic effect at around 150 μg mL(-1). The neutrophil oxidative burst test then showed that colloidal polyaniline, in concentrations <150 μg mL(-1), was not able to stimulate the production of reactive oxygen species in neutrophils and whole human blood. However, it worked efficiently as a scavenger of those already formed.

  2. Active microrheology in a colloidal glass

    NASA Astrophysics Data System (ADS)

    Gruber, M.; Abade, G. C.; Puertas, A. M.; Fuchs, M.

    2016-10-01

    We study the dynamics of a probe particle driven by a constant force through a colloidal glass of hard spheres. This nonequilibrium and anisotropic problem is investigated using a new implementation of the mode-coupling approximation with multiple relaxation channels and Langevin dynamics simulations. A force threshold is found, below which the probe remains localized, while above it the probe acquires a finite velocity. We focus on the localized regime, comparing theory and simulations concerning the dynamics in the length scale of the cage and the properties of the transition to the delocalized regime, such as the critical power-law decay of the probe correlation function. Probe van Hove functions predicted by the theory show exponential tails reminiscent of an intermittent dynamics of the probe. This scenario is microscopically supported by simulations.

  3. Pattern matching based active optical sorting of colloids/cells

    NASA Astrophysics Data System (ADS)

    Verma, R. S.; Dasgupta, R.; Ahlawat, S.; Kumar, N.; Uppal, A.; Gupta, P. K.

    2013-08-01

    We report active optical sorting of colloids/cells by employing a cross correlation based pattern matching technique for selection of the desired objects and thereafter sorting using dynamically controllable holographic optical traps. The problem of possible collision between the different sets of objects during sorting was avoided by raising one set of particles to a different plane. We also present the results obtained on using this approach for some representative applications such as sorting of silica particles of two different sizes, of closely packed colloids and of white blood cells and red blood cells from a mixture of the two.

  4. Interactions and Collective Behaviour of Chemotactic Active Colloids

    NASA Astrophysics Data System (ADS)

    Saha, Suropriya; Hablani, Surbhi; Golestanian, Ramin; Ramaswamy, Sriram

    2015-03-01

    Artificial realizations of motility point in the direction of a new paradigm in engineering, through the design of emergent behavior by manipulating properties at the scale of the individual components. Catalytic colloidal swimmers are a particularly promising example of such systems. Here we present a comprehensive theoretical description of gradient-sensing of an individual swimmer, leading controllably to chemotactic or anti-chemotactic behavior. We use it to study the scattering of such a swimmer off a reactant source and construct a framework for studying their two body interactions and finally their collective behavior. We find that both the positional and the orientational degrees of freedom of the active colloids can exhibit condensation, signalling formation of clusters and asters. We present prescriptions for how to tune the surface properties of the colloids during fabrication to achieve each type of behavior. We further study the athermal fluctuations of a pointed tracer particle in a bath of such swimmers.

  5. Stochastic description of the light scattered by a polydisperse colloidal suspension: simulation and experiment.

    PubMed

    Roldán-Vargas, Sándalo; Quesada-Pérez, Manuel; Callejas-Fernández, José

    2009-07-21

    In this work, the stochastic properties of the detected signal in dynamic light scattering experiments are examined in light of Doob's theorem. For Markovian observations of the Brownian particle position, we prove from this theorem that the electric field scattered by a polydisperse suspension can be accounted for by a linear combination of Ornstein-Uhlenbeck processes. A new algorithm for generating the fluctuating field scattered by a polydisperse system is proposed from this alternative formalism. The statistics of our synthetic data is compared satisfactorily with that resulting from the experimental signal scattered by a binary suspension of polystyrene microspheres. PMID:19624211

  6. Stochastic description of the light scattered by a polydisperse colloidal suspension: simulation and experiment.

    PubMed

    Roldán-Vargas, Sándalo; Quesada-Pérez, Manuel; Callejas-Fernández, José

    2009-07-21

    In this work, the stochastic properties of the detected signal in dynamic light scattering experiments are examined in light of Doob's theorem. For Markovian observations of the Brownian particle position, we prove from this theorem that the electric field scattered by a polydisperse suspension can be accounted for by a linear combination of Ornstein-Uhlenbeck processes. A new algorithm for generating the fluctuating field scattered by a polydisperse system is proposed from this alternative formalism. The statistics of our synthetic data is compared satisfactorily with that resulting from the experimental signal scattered by a binary suspension of polystyrene microspheres.

  7. Stable smectic phase in suspensions of polydisperse colloidal platelets with identical thickness

    NASA Astrophysics Data System (ADS)

    Sun, Dazhi; Sue, Hung-Jue; Cheng, Zhengdong; Martínez-Ratón, Yuri; Velasco, Enrique

    2009-10-01

    We report the nematic and smectic ordering in an aqueous suspension of monolayer α -Zirconium phosphate platelets possessing a high polydispersity in diameter but uniform thickness. We observe an isotropic-nematic transition as the platelet volume fraction increases, followed by the formation of a smectic, an elusive phase that has been rarely seen in discotic liquid crystals. The smectic phase is characterized by x-ray diffraction high-resolution transmission electron microscopy, and optical microscopy. The phase equilibria in this highly polydisperse suspension are rationalized in terms of a theoretical approach based on density-functional theory.

  8. Role of particle shape anisotropy on crack formation in drying of colloidal suspension

    NASA Astrophysics Data System (ADS)

    Dugyala, Venkateshwar Rao; Lama, Hisay; Satapathy, Dillip K.; Basavaraj, Madivala G.

    2016-08-01

    Cracks in a colloidal film formed by evaporation induced drying can be controlled by changing drying conditions. We show, for the first time that the crack morphologies in colloidal films are dependent on shape of constituting particles apart from the microstructure and particle assembly. In order to investigate the particle shape effect on crack patterns, monodispered spherical and ellipsoidal particles are used in sessile drop experiments. On observing the dried sessile drop we found cracks along the radial direction for spherical particle dispersions and circular crack patterns for ellipsoidal particle dispersions. The change in crack pattern is a result of self assembly of shape anisotropic particles and their ordering. The ordering of particles dictate the crack direction and the cracks follow the path of least resistance to release the excess stress stored in the particle film. Ellipsoids having different aspect ratio (~3 to 7) are used and circular crack patterns are repeatedly observed in all experiments.

  9. Role of particle shape anisotropy on crack formation in drying of colloidal suspension

    PubMed Central

    Dugyala, Venkateshwar Rao; Lama, Hisay; Satapathy, Dillip K.; Basavaraj, Madivala G.

    2016-01-01

    Cracks in a colloidal film formed by evaporation induced drying can be controlled by changing drying conditions. We show, for the first time that the crack morphologies in colloidal films are dependent on shape of constituting particles apart from the microstructure and particle assembly. In order to investigate the particle shape effect on crack patterns, monodispered spherical and ellipsoidal particles are used in sessile drop experiments. On observing the dried sessile drop we found cracks along the radial direction for spherical particle dispersions and circular crack patterns for ellipsoidal particle dispersions. The change in crack pattern is a result of self assembly of shape anisotropic particles and their ordering. The ordering of particles dictate the crack direction and the cracks follow the path of least resistance to release the excess stress stored in the particle film. Ellipsoids having different aspect ratio (~3 to 7) are used and circular crack patterns are repeatedly observed in all experiments. PMID:27477261

  10. Formation kinetics of particulate films in directional drying of a colloidal suspension.

    PubMed

    Inasawa, S; Oshimi, Y; Kamiya, H

    2016-08-10

    We observed the kinetics of formation of colloidal films through directional drying with a pinned drying interface. The volume fraction of particles accumulated at the pinned drying interface increased in two stages: it rapidly increased in the initial stage of drying and then slowly increased. The final filling factor of the dried films decreased with increasing drying flux. We found a threshold drying flux for the formation of colloidal films below which uneven films are formed at the drying interface. This threshold flux is well explained by the competition between transport of particles by flow and transport by diffusion. We also found a minimum thickness for the formation of a packed layer of particles. The formation kinetics of a packed layer of particles due to drying was discussed. PMID:27471046

  11. Role of particle shape anisotropy on crack formation in drying of colloidal suspension.

    PubMed

    Dugyala, Venkateshwar Rao; Lama, Hisay; Satapathy, Dillip K; Basavaraj, Madivala G

    2016-01-01

    Cracks in a colloidal film formed by evaporation induced drying can be controlled by changing drying conditions. We show, for the first time that the crack morphologies in colloidal films are dependent on shape of constituting particles apart from the microstructure and particle assembly. In order to investigate the particle shape effect on crack patterns, monodispered spherical and ellipsoidal particles are used in sessile drop experiments. On observing the dried sessile drop we found cracks along the radial direction for spherical particle dispersions and circular crack patterns for ellipsoidal particle dispersions. The change in crack pattern is a result of self assembly of shape anisotropic particles and their ordering. The ordering of particles dictate the crack direction and the cracks follow the path of least resistance to release the excess stress stored in the particle film. Ellipsoids having different aspect ratio (~3 to 7) are used and circular crack patterns are repeatedly observed in all experiments.

  12. Colloidal behavior of aqueous montmorillonite suspensions in the presence of non-ionic polymer

    NASA Astrophysics Data System (ADS)

    Gareche, M.; Azri, N.; Allal, A.; Zeraibi, N.

    2015-04-01

    In this paper we characterized at first, the rheological behavior of the bentonite suspensions and the aqueous solutions of polyethylene oxide (PEO), then we were investigated the influence of this polymer in a water-based drilling fluid model (6% of bentonite suspension). The objective is to exhibit how the non ionic polymer with molecular weight 6×103 g/mol. of varying concentration mass (0.7%, 1%, 2% et 3%) significantly alter the rheological properties (yield stress, viscosity, loss and elastic modulus) of the bentonite suspensions. The rheological measurements made in simple shear and in dynamic on the mixture (water-bentonite-PEO), showed rheological properties of bentonite suspensions both in the presence and absence of non-ionic polymer. The PEO presents an affinity for the bentonite particles slowing down their kinetic aggregation. The analysis by X-rays diffraction also allowed understanding the structure of this mixture. It had revealed the intercalation between of the clay platelets on one hand, and the links bridges assured by the chains of polymer between bentonite particles beyond a critical concentration in PEO on the other hand. The Herschel- Bulkley rheological model is used for the correlation of our experimental results.

  13. Active suspension for a two-axle railway vehicle

    NASA Astrophysics Data System (ADS)

    Pacchioni, Alessandro; Goodall, Roger M.; Bruni, Stefano

    2010-12-01

    The aim of this paper is to investigate how the ride quality of a two-axle railway vehicle with single-stage suspension might be improved by the use of active control, compensating for the lack of the double suspension stage, and thereby taking full advantage of vehicle lightweight construction. The basic requirement is to improve the ride quality on random track unevenness while keeping suspension deflection within acceptable levels when the vehicle negotiates deterministic track features such as a gradient. Two active suspension configurations are considered - skyhook damping and linear quadratic Gaussian (LQG) optimal control. Finally, actuator dynamics are included in the analysis, to assess the impact on the overall success of an active suspension implementation. The paper shows that both skyhook and LQG control strategies offer significant improvements in ride quality and also that careful design of the actuators and their force control loops is essential.

  14. Phase behavior of a suspension of colloidal hard rods and nonadsorbing polymer.

    PubMed

    Savenko, S V; Dijkstra, Marjolein

    2006-06-21

    We study the phase behavior of a mixture of colloidal hard rods with a length-to-diameter ratio of L/sigma(c)=5 and nonadsorbing ideal polymer. We map our binary mixture onto an effective one-component system by integrating out the degrees of freedom of the polymer coils. We derive a formal expression for the exact effective Hamiltonian of the colloidal rods, i.e., it includes all effective many-body interactions and it is related to the exact free volume available for the polymer. We determine numerically on a grid the free volume available for the ideal polymer coils "on the fly" for each colloidal rod configuration during our Monte Carlo simulations. This allows us to go beyond first-order perturbation theory, which employs the pure hard-rod system as reference state. We perform free energy calculations for the isotropic, nematic, smectic, and crystal phase using thermodynamic integration and common tangent constructions are used at fixed polymer fugacities to map out the phase diagram. The phase behavior is determined for size ratios q=sigma(p)/sigma(c)=0.15, 0.5, and 1, where sigma(p) is the diameter of the polymer coils. The phase diagrams based on the full effective Hamiltonian are compared with those obtained from first-order perturbation theory, from simulations using the effective pair potential approximation to the effective Hamiltonian, and with those based on an empiric effective depletion potential for the rods. We find that the many-body character of the effective interactions stabilizes the nematic and smectic phases for large q, while the effective pair potential description overestimates the attractive interactions and favors, hence, a broad isotropic-crystal coexistence. PMID:16821948

  15. Correlation between Generated Shear Stress and Generated Permittivity for the Electrorheological Response of Colloidal Silica Suspensions.

    PubMed

    Saimoto; Satoh; Konno

    1999-11-01

    Electrorheological response was experimentally studied by the use of silicone oil suspensions containing submicrometer-sized and supermicrometer-sized silica particles with different amounts of adsorbed water. The simultaneous measurements of dielectric permittivity and shear stress of the suspensions were carried out after the application of alternating current voltage under steady shear in ranges of shear rate (150-1400 s(-1)), electric field strength (0-4 kV/mm), its frequency (30-1000 Hz), and particle volume fraction (0.1-0.3). For the particles with small amounts of adsorbed water, steady shear stress was attained within several minutes after the application of electric field. The steady-state data for both the particles at each electric field strength showed that the shear stress generated by the application of electric field, Deltatau, varied correlatively with the generated permittivity, Deltaepsilon(r) (= epsilon(r) - epsilon(r,oil)), where epsilon(r) and epsilon(r,oil) are the permittivities of the suspension and the silicon oil, respectively. Under a wide variety of experimental conditions, the steady-state data for both the particle sizes could be correlated with a simple relationship, Deltatau ~ (Deltaepsilon(r)E)(2), where E is electric field strength. For the particles with large amounts of adsorbed water, steady state was not attained, and the evolutions of shear stress and permittivity of the suspensions were measured after the application of electric field. Remarkably, the transient values of Deltatau varied with (Deltaepsilon(r)E)(2) and fell along the same correlation line as the steady-state data. Copyright 1999 Academic Press.

  16. Many-body microhydrodynamics of colloidal particles with active boundary layers

    NASA Astrophysics Data System (ADS)

    Singh, Rajesh; Ghose, Somdeb; Adhikari, R.

    2015-06-01

    Colloidal particles with active boundary layers—regions surrounding the particles where non-equilibrium processes produce large velocity gradients—are common in many physical, chemical and biological contexts. The velocity or stress at the edge of the boundary layer determines the exterior fluid flow and, hence, the many-body interparticle hydrodynamic interaction. Here, we present a method to compute the many-body hydrodynamic interaction between N spherical active particles induced by their exterior microhydrodynamic flow. First, we use a boundary integral representation of the Stokes equation to eliminate bulk fluid degrees of freedom. Then, we expand the boundary velocities and tractions of the integral representation in an infinite-dimensional basis of tensorial spherical harmonics and, on enforcing boundary conditions in a weak sense on the surface of each particle, obtain a system of linear algebraic equations for the unknown expansion coefficients. The truncation of the infinite series, fixed by the degree of accuracy required, yields a finite linear system that can be solved accurately and efficiently by iterative methods. The solution linearly relates the unknown rigid body motion to the known values of the expansion coefficients, motivating the introduction of propulsion matrices. These matrices completely characterize hydrodynamic interactions in active suspensions just as mobility matrices completely characterize hydrodynamic interactions in passive suspensions. The reduction in the dimensionality of the problem, from a three-dimensional partial differential equation to a two-dimensional integral equation, allows for dynamic simulations of hundreds of thousands of active particles on multi-core computational architectures. In our simulation of 104 active colloidal particle in a harmonic trap, we find that the necessary and sufficient ingredients to obtain steady-state convective currents, the so-called ‘self-assembled pump’, are (a) one

  17. Influence of sodium chloride on the colloidal and rennet coagulation properties of concentrated casein micelle suspensions.

    PubMed

    Zhao, Z; Corredig, M

    2016-08-01

    The research investigated the influence of NaCl on the colloidal and rennet coagulation properties of concentrated milk. Milk was concentrated to 1×, 3×, and 5× using ultrafiltration. Rennet gelation was followed by rheology and diffusing wave spectroscopy. Soluble protein, total and diffusible calcium and phosphate, size, and zeta potential were also measured as a function of concentration history. In the presence of 300mM NaCl, colloidal calcium phosphate solubilized and pH and the negative charge on the surface of casein micelles decreased. Increasing the volume fraction caused the formation of stiffer gels for both samples with or without NaCl. The addition of NaCl caused a significant increase in the bulk viscosity of the milk concentrated 5× and a decrease in turbidity. The concentration had no effect on the gelation time of control samples, nor on the kinetics of caseinomacropeptide release. On the other hand, rennet gelation was retarded by the addition of NaCl, and the gels showed lower elastic moduli compared with those obtained with control milk.

  18. Influence of sodium chloride on the colloidal and rennet coagulation properties of concentrated casein micelle suspensions.

    PubMed

    Zhao, Z; Corredig, M

    2016-08-01

    The research investigated the influence of NaCl on the colloidal and rennet coagulation properties of concentrated milk. Milk was concentrated to 1×, 3×, and 5× using ultrafiltration. Rennet gelation was followed by rheology and diffusing wave spectroscopy. Soluble protein, total and diffusible calcium and phosphate, size, and zeta potential were also measured as a function of concentration history. In the presence of 300mM NaCl, colloidal calcium phosphate solubilized and pH and the negative charge on the surface of casein micelles decreased. Increasing the volume fraction caused the formation of stiffer gels for both samples with or without NaCl. The addition of NaCl caused a significant increase in the bulk viscosity of the milk concentrated 5× and a decrease in turbidity. The concentration had no effect on the gelation time of control samples, nor on the kinetics of caseinomacropeptide release. On the other hand, rennet gelation was retarded by the addition of NaCl, and the gels showed lower elastic moduli compared with those obtained with control milk. PMID:27320668

  19. Colloidal activated carbon for in-situ groundwater remediation--Transport characteristics and adsorption of organic compounds in water-saturated sediment columns.

    PubMed

    Georgi, Anett; Schierz, Ariette; Mackenzie, Katrin; Kopinke, Frank-Dieter

    2015-08-01

    Colloidal activated carbon can be considered as a versatile adsorbent and carrier material for in-situ groundwater remediation. In analogy to other nanoremediation approaches, activated carbon colloids (ACC) can be injected into the subsurface as aqueous suspensions. Deposition of ACC on the sediment creates a sorption barrier against further spreading of hydrophobic pollutants. This study deals with the optimization of ACC and their suspensions with a focus on suspension stability, ACC mobility in saturated porous media and sorption efficiency towards organic contaminants. ACC with an appropriate particle size range (d50=0.8μm) were obtained from a commercial powdered activated carbon product by means of wet-grinding. Among the various methods tested for stabilization of ACC suspensions, addition of humic acid (HA) and carboxymethyl cellulose (CMC) showed the best results. Due to electrosteric stabilization by adsorption of CMC, suspensions remained stable even at high ACC concentrations (11gL(-1)) and conditions typical of very hard water (5mM divalent cations). Furthermore, CMC-stabilized ACC showed high mobility in a water-saturated sandy sediment column (filter coefficient λ=0.2m(-1)). Such mobility is a pre-requisite for in-situ installation of sorption or reaction barriers by simple injection-well or direct-push application of ACC suspensions. Column experiments with organic model compounds proved the efficacy of ACC deposits on sediment for contaminant adsorption and retardation under flow-through conditions. PMID:26070009

  20. Colloidal activated carbon for in-situ groundwater remediation--Transport characteristics and adsorption of organic compounds in water-saturated sediment columns.

    PubMed

    Georgi, Anett; Schierz, Ariette; Mackenzie, Katrin; Kopinke, Frank-Dieter

    2015-08-01

    Colloidal activated carbon can be considered as a versatile adsorbent and carrier material for in-situ groundwater remediation. In analogy to other nanoremediation approaches, activated carbon colloids (ACC) can be injected into the subsurface as aqueous suspensions. Deposition of ACC on the sediment creates a sorption barrier against further spreading of hydrophobic pollutants. This study deals with the optimization of ACC and their suspensions with a focus on suspension stability, ACC mobility in saturated porous media and sorption efficiency towards organic contaminants. ACC with an appropriate particle size range (d50=0.8μm) were obtained from a commercial powdered activated carbon product by means of wet-grinding. Among the various methods tested for stabilization of ACC suspensions, addition of humic acid (HA) and carboxymethyl cellulose (CMC) showed the best results. Due to electrosteric stabilization by adsorption of CMC, suspensions remained stable even at high ACC concentrations (11gL(-1)) and conditions typical of very hard water (5mM divalent cations). Furthermore, CMC-stabilized ACC showed high mobility in a water-saturated sandy sediment column (filter coefficient λ=0.2m(-1)). Such mobility is a pre-requisite for in-situ installation of sorption or reaction barriers by simple injection-well or direct-push application of ACC suspensions. Column experiments with organic model compounds proved the efficacy of ACC deposits on sediment for contaminant adsorption and retardation under flow-through conditions.

  1. Enhancing heat capacity of colloidal suspension using nanoscale encapsulated phase-change materials for heat transfer.

    PubMed

    Hong, Yan; Ding, Shujiang; Wu, Wei; Hu, Jianjun; Voevodin, Andrey A; Gschwender, Lois; Snyder, Ed; Chow, Louis; Su, Ming

    2010-06-01

    This paper describes a new method to enhance the heat-transfer property of a single-phase liquid by adding encapsulated phase-change nanoparticles (nano-PCMs), which absorb thermal energy during solid-liquid phase changes. Silica-encapsulated indium nanoparticles and polymer-encapsulated paraffin (wax) nanoparticles have been made using colloid method, and suspended into poly-alpha-olefin (PAO) and water for potential high- and low-temperature applications, respectively. The shells prevent leakage and agglomeration of molten phase-change materials, and enhance the dielectric properties of indium nanoparticles. The heat-transfer coefficients of PAO containing indium nanoparticles (30% by mass) and water containing paraffin nanoparticles (10% by mass) are 1.6 and 1.75 times higher than those of corresponding single-phase fluids. The structural integrity of encapsulation allows repeated use of such nanoparticles for many cycles in high heat generating devices. PMID:20527779

  2. Correlation between dynamical and structural heterogeneities in colloidal hard-sphere suspensions

    NASA Astrophysics Data System (ADS)

    Golde, Sebastian; Palberg, Thomas; Schöpe, Hans Joachim

    2016-07-01

    Dynamical and structural heterogeneities have long been thought to play a key role in a unified picture of solidification in view of the two competitive processes of crystallization and vitrification. Here, we study these heterogeneities by means of a combination of dynamic and static light-scattering techniques applied to the simplest model system exhibiting crystallization and vitrification: the colloidal hard-sphere system. Our method enables us to quantify and correlate the temporal evolution of the amount of ordered clusters (precursors) and the amount of slow particles. Our analysis shows that their temporal evolutions are closely related and that there is an intimate link between structural and dynamic heterogeneities, crystal nucleation and the non-crystallization transition.

  3. Enhancing heat capacity of colloidal suspension using nanoscale encapsulated phase-change materials for heat transfer.

    PubMed

    Hong, Yan; Ding, Shujiang; Wu, Wei; Hu, Jianjun; Voevodin, Andrey A; Gschwender, Lois; Snyder, Ed; Chow, Louis; Su, Ming

    2010-06-01

    This paper describes a new method to enhance the heat-transfer property of a single-phase liquid by adding encapsulated phase-change nanoparticles (nano-PCMs), which absorb thermal energy during solid-liquid phase changes. Silica-encapsulated indium nanoparticles and polymer-encapsulated paraffin (wax) nanoparticles have been made using colloid method, and suspended into poly-alpha-olefin (PAO) and water for potential high- and low-temperature applications, respectively. The shells prevent leakage and agglomeration of molten phase-change materials, and enhance the dielectric properties of indium nanoparticles. The heat-transfer coefficients of PAO containing indium nanoparticles (30% by mass) and water containing paraffin nanoparticles (10% by mass) are 1.6 and 1.75 times higher than those of corresponding single-phase fluids. The structural integrity of encapsulation allows repeated use of such nanoparticles for many cycles in high heat generating devices.

  4. Dispersion of a passive tracer in the pressure-driven flow of a non-colloidal suspension.

    PubMed

    Nirmal, Ghata M; Ramachandran, Arun

    2016-10-14

    This paper numerically quantifies the dispersion of a solute, and in particular, the Taylor dispersion, in the pressure-driven flow of a non-colloidal suspension at moderately high volume fractions (0.2 to 0.5) through conduits of different cross-sectional shapes. An obvious intuition is that the Taylor dispersivity should increase owing to a decrease in the molecular diffusivity of the solute in the presence of particles impermeable to the solute; however, this is true only at low volume fractions. At higher volume fractions, three other physical effects become important, all of which lead to a reduction in Taylor dispersivity relative to a Newtonian fluid. The first is the blunting of the velocity profile resulting from particle migration into the low shear-stress regions, an effect that has been alluded to in the past by Roht et al. [J. Contam. Hydrol., 2013, 14, 10] and is important only at low Péclet numbers (Pe). At higher Pe, the two stronger effects are shear-induced solute self-diffusion, which arises due to shear-induced particle-particle interactions, and secondary convection, which is observed in non-axisymmetric cross-sections as a result of the second normal stress differences exhibited by concentrated suspensions. For a given volume fraction and cross-sectional geometry, a regime map, developed using a scaling analysis, delineates five regimes of dispersion involving one or a combination of the mass transfer mechanisms mentioned above. Our analysis also suggests that the cross-sectional shape can be exploited to enhance or suppress solute dispersion by modifying the secondary current strength and profile. PMID:27537698

  5. Influence of pH condition on colloidal suspension of exfoliated graphene oxide by electrostatic repulsion

    SciTech Connect

    Meng, Long-Yue; Park, Soo-Jin

    2012-02-15

    A facile chemical process is described to produce graphene oxide utilizing a zwitterions amino acid intermediate from graphite oxide sheets. 11-aminoundecanoic acid molecules were protonated to intercalate molecules into the graphite oxide sheets to achieve ion exchange, and the carboxyl groups were then ionized in a NaOH solution to exfoliate the graphite oxide sheets. In this way, the produced graphene oxide nanosheets were stably dispersed in water. The delaminated graphene nanosheets were confirmed by XRD, AFM, and TEM. XRD patterns indicated the d{sub 002}-spacing of the graphite greatly increased from 0.380 nm and 0.870 nm. AFM and TEM images showed that the ordered graphite crystal structure of graphene nanosheets was effectively exfoliated by this method. The prepared graphene nanosheets films showed 87.1% transmittance and a sheet resistance of 2.1 Multiplication-Sign 10{sup 3} {Omega}/square. - Graphical abstract: A stable graphene oxide suspension could be quickly prepared by exfoliating a graphite oxide suspension by a host-guest electrostatic repulsion in aqueous solution. Highlights: Black-Right-Pointing-Pointer Graphene nanosheets were prepared by a zwitterions amino acid intermediate from graphite oxide. Black-Right-Pointing-Pointer 11-aminoundecanoic acid was protonated to intercalate molecules into the graphene oxide to achieve ion exchange. Black-Right-Pointing-Pointer The d{sub 002}-spacing of the graphite oxide greatly increased from 0.330 nm to 0.415 nm after 11-aminoundecanoic acid treatment.

  6. Facile and highly efficient removal of trace Gd(III) by adsorption of colloidal graphene oxide suspensions sealed in dialysis bag.

    PubMed

    Chen, Weifan; Wang, Linlin; Zhuo, Mingpeng; Liu, Yue; Wang, Yiping; Li, Yongxiu

    2014-08-30

    A facile, highly efficient and second-pollution-free strategy to remove trace Gd(III) from aqueous solutions by adsorption of colloidal graphene oxide (GO) suspensions in dialysis bag has been developed. The effects of pH, ionic strength and temperature on Gd(III) adsorption, and the pH-dependent desorption were investigated. The maximum adsorption capacity of Gd(III)on GO at pH=5.9±0.1 and T=303K was 286.86mgg(-1), higher than any other currently reported. The Gd(III)-saturated GO suspension could resume colloidal state in 0.1M HNO3 with desorption rate of 85.00% in the fifth adsorption-desorption cycle. Gd(III) adsorption rate on GO was dependent more on pH and ionic strength than on temperature. The abundant oxygen-containing functional groups such as carboxyl and hydroxyl played a vital role on adsorption. The thermodynamics and kinetics investigations revealed that the adsorption of Gd(III) on GO was an endothermic, spontaneous and monolayer absorption process, which well fitted the pseudo-second-order model. GO could be a promising adsorbent applied in the enrichment and removal of lanthanides from aqueous solutions. More significantly, the combination of colloidal GO suspension with dialysis membrane facilely solves the re-pollution of the treated solutions due to the great difficulties in separation and recovery of GO.

  7. Facile and highly efficient removal of trace Gd(III) by adsorption of colloidal graphene oxide suspensions sealed in dialysis bag.

    PubMed

    Chen, Weifan; Wang, Linlin; Zhuo, Mingpeng; Liu, Yue; Wang, Yiping; Li, Yongxiu

    2014-08-30

    A facile, highly efficient and second-pollution-free strategy to remove trace Gd(III) from aqueous solutions by adsorption of colloidal graphene oxide (GO) suspensions in dialysis bag has been developed. The effects of pH, ionic strength and temperature on Gd(III) adsorption, and the pH-dependent desorption were investigated. The maximum adsorption capacity of Gd(III)on GO at pH=5.9±0.1 and T=303K was 286.86mgg(-1), higher than any other currently reported. The Gd(III)-saturated GO suspension could resume colloidal state in 0.1M HNO3 with desorption rate of 85.00% in the fifth adsorption-desorption cycle. Gd(III) adsorption rate on GO was dependent more on pH and ionic strength than on temperature. The abundant oxygen-containing functional groups such as carboxyl and hydroxyl played a vital role on adsorption. The thermodynamics and kinetics investigations revealed that the adsorption of Gd(III) on GO was an endothermic, spontaneous and monolayer absorption process, which well fitted the pseudo-second-order model. GO could be a promising adsorbent applied in the enrichment and removal of lanthanides from aqueous solutions. More significantly, the combination of colloidal GO suspension with dialysis membrane facilely solves the re-pollution of the treated solutions due to the great difficulties in separation and recovery of GO. PMID:25108829

  8. Weakly sheared active suspensions: hydrodynamics, stability, and rheology.

    PubMed

    Cui, Zhenlu

    2011-03-01

    We present a kinetic model for flowing active suspensions and analyze the behavior of a suspension subjected to a weak steady shear. Asymptotic solutions are sought in Deborah number expansions. At the leading order, we explore the steady states and perform their stability analysis. We predict the rheology of active systems including an activity thickening or thinning behavior of the apparent viscosity and a negative apparent viscosity depending on the particle type, flow alignment, and the anchoring conditions, which can be tested on bacterial suspensions. We find remarkable dualities that show that flow-aligning rodlike contractile (extensile) particles are dynamically and rheologically equivalent to flow-aligning discoid extensile (contractile) particles for both tangential and homeotropic anchoring conditions. Another key prediction of this work is the role of the concentration of active suspensions in controlling the rheological behavior: the apparent viscosity may decrease with the increase of the concentration. PMID:21517529

  9. Weakly sheared active suspensions: Hydrodynamics, stability, and rheology

    NASA Astrophysics Data System (ADS)

    Cui, Zhenlu

    2011-03-01

    We present a kinetic model for flowing active suspensions and analyze the behavior of a suspension subjected to a weak steady shear. Asymptotic solutions are sought in Deborah number expansions. At the leading order, we explore the steady states and perform their stability analysis. We predict the rheology of active systems including an activity thickening or thinning behavior of the apparent viscosity and a negative apparent viscosity depending on the particle type, flow alignment, and the anchoring conditions, which can be tested on bacterial suspensions. We find remarkable dualities that show that flow-aligning rodlike contractile (extensile) particles are dynamically and rheologically equivalent to flow-aligning discoid extensile (contractile) particles for both tangential and homeotropic anchoring conditions. Another key prediction of this work is the role of the concentration of active suspensions in controlling the rheological behavior: The apparent viscosity may decrease with the increase of the concentration.

  10. Dynamically controlled deposition of colloidal nanoparticle suspension in evaporating drops using laser radiation.

    PubMed

    Ta, V D; Carter, R M; Esenturk, E; Connaughton, C; Wasley, T J; Li, J; Kay, R W; Stringer, J; Smith, P J; Shephard, J D

    2016-05-18

    Dynamic control of the distribution of polystyrene suspended nanoparticles in evaporating droplets is investigated using a 2.9 μm high power laser. Under laser radiation a droplet is locally heated and fluid flows are induced that overcome the capillary flow, and thus a reversal of the coffee-stain effect is observed. Suspension particles are accumulated in a localised area, one order of magnitude smaller than the original droplet size. By scanning the laser beam over the droplet, particles can be deposited in an arbitrary pattern. This finding raises the possibility for direct laser writing of suspended particles through a liquid layer. Furthermore, a highly uniform coating is possible by manipulating the laser beam diameter and exposure time. The effect is expected to be universally applicable to aqueous solutions independent of solutes (either particles or molecules) and deposited substrates.

  11. Dynamically controlled deposition of colloidal nanoparticle suspension in evaporating drops using laser radiation.

    PubMed

    Ta, V D; Carter, R M; Esenturk, E; Connaughton, C; Wasley, T J; Li, J; Kay, R W; Stringer, J; Smith, P J; Shephard, J D

    2016-05-18

    Dynamic control of the distribution of polystyrene suspended nanoparticles in evaporating droplets is investigated using a 2.9 μm high power laser. Under laser radiation a droplet is locally heated and fluid flows are induced that overcome the capillary flow, and thus a reversal of the coffee-stain effect is observed. Suspension particles are accumulated in a localised area, one order of magnitude smaller than the original droplet size. By scanning the laser beam over the droplet, particles can be deposited in an arbitrary pattern. This finding raises the possibility for direct laser writing of suspended particles through a liquid layer. Furthermore, a highly uniform coating is possible by manipulating the laser beam diameter and exposure time. The effect is expected to be universally applicable to aqueous solutions independent of solutes (either particles or molecules) and deposited substrates. PMID:27094902

  12. Structural explanation of the rheology of a colloidal suspension under high dc electric fields

    NASA Astrophysics Data System (ADS)

    Espín, Manuel J.; Delgado, Ángel V.; González-Caballero, Fernando

    2006-04-01

    In this work we describe the electrorheology of suspensions consisting of hematite (α-Fe2O3) particles dispersed in silicone oil in the presence of large dc electric fields. If an electric field pulse is applied to the systems, it is possible to estimate the time that the electrorheological (ER) fluid takes to reach its final microstructure in the presence of the field. Our results indicate that response times of several seconds are typical, and that this time decreases with the field strength. Conventional shear-rate sweeps indicate the existence of a well-defined dynamic yield stress and a shear-thinning behavior. Interestingly, both the yield stress and the shear-thinning slope a [relating the viscosity, η , and the shear rate, γ˙ , as η=aγ˙-b+η(∞) ] show a linear dependence on the field strength, E , in disagreement with the E2 dependence often reported. This deviation is associated with changes in the conductivity of the dispersion medium with the field strength. A simple calculation of the interactions present in our ER fluid demonstrates that the ER behavior is entirely controlled by hydrodynamic (∝γ˙) and electrical forces (∝E) . This is confirmed by the collapse of all experimental results in a single master curve when the relative viscosity is plotted against the ratio γ˙/E . Careful attention has been paid in this work to the microstructure of the suspensions in the presence of both shear and electric fields simultaneously: the particles gather themselves on the walls of the electrorheological measurement cell, forming aggregates with cylindrical symmetry, shaped as rings or lamellas of solids. The electric field induced increase in viscosity is the consequence of the balance between two actions: that of the electric field, tending to keep particles together, and that of the shear field, forcing the flow of the liquid phase in the regions between rings or between rings and walls.

  13. Application of colloidal gas aphron suspensions produced from Sapindus mukorossi for arsenic removal from contaminated soil.

    PubMed

    Mukhopadhyay, Soumyadeep; Mukherjee, Sumona; Hashim, Mohd Ali; Sen Gupta, Bhaskar

    2015-01-01

    Colloidal gas aphron dispersions (CGAs) can be described as a system of microbubbles suspended homogenously in a liquid matrix. This work examines the performance of CGAs in comparison to surfactant solutions for washing low levels of arsenic from an iron rich soil. Sodium Dodecyl Sulfate (SDS) and saponin, a biodegradable surfactant, obtained from Sapindus mukorossi or soapnut fruit were used for generating CGAs and solutions for soil washing. Column washing experiments were performed in down-flow and up flow modes at a soil pH of 5 and 6 using varying concentration of SDS and soapnut solutions as well as CGAs. Soapnut CGAs removed more than 70% arsenic while SDS CGAs removed up to 55% arsenic from the soil columns in the soil pH range of 5-6. CGAs and solutions showed comparable performances in all the cases. CGAs were more economical since it contains 35% of air by volume, thereby requiring less surfactant. Micellar solubilization and low pH of soapnut facilitated arsenic desorption from soil column. FT-IR analysis of effluent suggested that soapnut solution did not interact chemically with arsenic thereby facilitating the recovery of soapnut solution by precipitating the arsenic. Damage to soil was minimal arsenic confirmed by metal dissolution from soil surface and SEM micrograph. PMID:25061940

  14. Antiorthostatic suspension stimulates profiles of macrophage activation in mice

    NASA Technical Reports Server (NTRS)

    Miller, E. S.; Bates, R. A.; Koebel, D. A.; Sonnenfeld, G.

    1999-01-01

    The antiorthostatic suspension model simulates certain physiological effects of spaceflight. We have previously reported BDF1 mice suspended by the tail in the antiorthostatic orientation for 4 days express high levels of resistance to virulent Listeria monocytogenesinfection. In the present study, we examined whether the increased resistance to this organism correlates with profiles of macrophage activation, given the role of the macrophage in killing this pathogen in vivo. We infected BDF1 mice with a lethal dose of virulent L. monocytogenes on day 4 of antiorthostatic suspension and 24 h later constructed profiles of macrophage activation. Viable listeria could not be detected in mice suspended in the antiorthostatic orientation 24 h after infection. Flow cytometric analysis revealed the numbers of granulocytes and mononuclear phagocytes in the spleen of infected mice were not significantly altered as a result of antiorthostatic suspension. Splenocytes from antiorthostatically suspended infected mice produced increased titers of IL-1. Serum levels of neopterin, a nucleotide metabolite secreted by activated macrophages, were enhanced in mice infected during antiorthostatic suspension, but not in antiorthostatically suspended naive mice. Splenic macrophages from mice infected on day 4 of suspension produced enhanced levels of lysozyme. In contrast to the results from antiorthostatically suspended infected mice, macrophages from antiorthostatically suspended uninfected mice did not express enhanced bactericidal activities. The collective results indicate that antiorthostatic suspension can stimulate profiles of macrophage activation which correlate with increased resistance to infection by certain classes of pathogenic bacteria.

  15. Semi-active control of seat suspension with MR damper

    NASA Astrophysics Data System (ADS)

    Yao, H. J.; Fu, J.; Yu, M.; Peng, Y. X.

    2013-02-01

    The vibration control of a seat suspension system with magnetorheological (MR) damper is investigated in this study. Firstly, a dynamical model of the seat suspension system with parameter uncertainties (such as mass, stiffness, damping) and actuator saturation is established. Secondly, based on Lyapunov functional theory and considering constraint conditions for damping force, the semi-active controller is designed, and the controller parameters are derived in terms of linear matrix inequalities (LMIs), which guarantees performance index. Finally, compared control strategy and the passive, skyhook control strategy, the simulation results in time and frequency domains demonstrate the proposed approach can achieve better vertical acceleration attenuation for the seat suspension system and improve ride comfort.

  16. Flow of active suspensions and biased swimming

    NASA Astrophysics Data System (ADS)

    Rafai, Salima; Peyla, Philippe; Garcia, Xabel; Kitenbergs, Guntars; Garcia, Michaël; LIPhy Team

    2012-11-01

    It is a challenge to understand the hydrodynamics associated with individual or collective motion of microswimmers through their fluid-mediated interactions in order for instance to manipulate the cells efficiently for some applications purposes. The motion of these micro-organisms can be often affected by the presence of gradients leading to a biased random walk (chemotaxis in the presence of chemicals, gyrotaxis in a gravity field, phototaxis under light exposure). In this study, we present our experimental results concerning the coupling of a Poiseuille flow with the biased random walk of Chlamydomonas Reinhardtii, a green unicellular micro-alga. This is done by illuminating the microswimmer suspension while flowing in a microchannel device. We show that one can obtain a spontaneous and reversible migration and separation of the microalgae suspension from the rest of the suspending medium under illumination and then dynamically control the concentration of the suspension with light. We present a simple model that accounts for the observed phenomenon. We thank the ANR MOSICOB and MICMACSWIM.

  17. Surface-Enhanced Raman Spectroscopy of Polyelectrolyte-Wrapped Gold Nanoparticles in Colloidal Suspension

    PubMed Central

    Sivapalan, Sean T.; DeVetter, Brent M.; Yang, Timothy K.; Schulmerich, Matthew V.; Bhargava, Rohit; Murphy, Catherine J.

    2013-01-01

    The rapidly expanding field of surface-enhanced Raman spectroscopy (SERS) has helped fuel an intense interest in noble metal nanoparticle synthesis. An in-suspension approach for quantifying SERS enhancement and relating that enhancement to a spontaneous Raman equivalent signal is described. Gold nanoparticles of various shapes were wrapped with polyelectrolyte multilayers that trapped Raman reporter molecules at defined distances from the metal core. Electrospray ionization liquid chromatography mass spectrometry (ESI-LC-MS) on digested samples was employed to measure the average number of bound Raman reporter molecules per gold nanoparticle, and inductively coupled plasma mass spectrometry (ICP-MS) was used to measure the average number of gold atoms per nanoparticle. Using these data, SERS signal intensity was compared to a spontaneous Raman calibration curve to compute a spontaneous Raman equivalent factor. Three different geometries of gold nanoparticles (cubes, spheres, and trisoctahedra) were synthesized to investigate edge and corner effects using these quantitative techniques. Finite element method (FEM) electromagnetic simulations examined the relationship between the different geometries and the observed SERS signal intensities. The experimental observations and theoretical results indicate that cubic gold nanoparticles have the highest effective signal. PMID:24224064

  18. Correlated two-particle diffusion in dense colloidal suspensions at early times: Theory and comparison to experiment.

    PubMed

    Dell, Zachary E; Tsang, Boyce; Jiang, Lingxiang; Granick, Steve; Schweizer, Kenneth S

    2015-11-01

    The spatially resolved diffusive dynamic cross correlations of a pair of colloids in dense quasi-two-dimensional monolayers of identical particles are studied experimentally and theoretically at early times where motion is Fickian. In very dense systems where strong oscillatory equilibrium packing correlations are present, we find an exponential decay of the dynamic cross correlations on small and intermediate length scales. At large separations where structure becomes random, an apparent power law decay with an exponent of approximately -2.2 is observed. For a moderately dense suspension where local structural correlations are essentially absent, this same apparent power law decay is observed over all probed interparticle separations. A microscopic nonhydrodynamic theory is constructed for the dynamic cross correlations which is based on interparticle frictional effects and effective structural forces. Hydrodynamics enters only via setting the very short-time single-particle self-diffusion constant. No-adjustable-parameter quantitative predictions of the theory for the dynamic cross correlations are in good agreement with experiment over all length scales. The origin of the long-range apparent power law is the influence of the constraint of fixed interparticle separation on the amplitude of the mean square force exerted on the two tagged particles by the surrounding fluid. The theory is extended to study high-packing-fraction 3D hard sphere fluids. The same pattern of an oscillatory exponential form of the dynamic cross correlation function is predicted in the structural regime, but the long-range tail decays faster than in monolayers with an exponent of -3.

  19. Out-of-equilibrium processes in suspensions of oppositely charged colloids: liquid-to-crystal nucleation and gel formation

    NASA Astrophysics Data System (ADS)

    Sanz, Eduardo

    2009-03-01

    We study the kinetics of the liquid-to-crystal transformation and of gel formation in colloidal suspensions of oppositely charged particles. We analyse, by means of both computer simulations and experiments, the evolution of a fluid quenched to a state point of the phase diagram where the most stable state is either a homogeneous crystalline solid or a solid phase in contact with a dilute gas. On the one hand, at high temperatures and high packing fractions, close to an ordered-solid/disordered-solid coexistence line, we find that the fluid-to-crystal pathway does not follow the minimum free energy route. On the other hand, a quench to a state point far from the ordered-crystal/disordered-crystal coexistence border is followed by a fluid-to-solid transition through the minimum free energy pathway. At low temperatures and packing fractions we observe that the system undergoes a gas-liquid spinodal decomposition that, at some point, arrests giving rise to a gel-like structure. Both our simulations and experiments suggest that increasing the interaction range favors crystallization over vitrification in gel-like structures. [4pt] In collaboration with Chantal Valeriani, Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands and SUPA, School of Physics, University of Edinburgh, JCMB King's Buildings, Mayfield Road, Edinburgh EH9 3JZ, UK; Teun Vissers, Andrea Fortini, Mirjam E. Leunissen, and Alfons van Blaaderen, Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University; Daan Frenke, FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands and Department of Chemistry, University of Cambridge, Lensfield Road, CB2 1EW, Cambridge, UK; and Marjolein Dijkstra, Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University.

  20. Brownian aggregation rate of colloid particles with several active sites

    SciTech Connect

    Nekrasov, Vyacheslav M.; Yurkin, Maxim A.; Chernyshev, Andrei V.; Polshchitsin, Alexey A.; Yakovleva, Galina E.; Maltsev, Valeri P.

    2014-08-14

    We theoretically analyze the aggregation kinetics of colloid particles with several active sites. Such particles (so-called “patchy particles”) are well known as chemically anisotropic reactants, but the corresponding rate constant of their aggregation has not yet been established in a convenient analytical form. Using kinematic approximation for the diffusion problem, we derived an analytical formula for the diffusion-controlled reaction rate constant between two colloid particles (or clusters) with several small active sites under the following assumptions: the relative translational motion is Brownian diffusion, and the isotropic stochastic reorientation of each particle is Markovian and arbitrarily correlated. This formula was shown to produce accurate results in comparison with more sophisticated approaches. Also, to account for the case of a low number of active sites per particle we used Monte Carlo stochastic algorithm based on Gillespie method. Simulations showed that such discrete model is required when this number is less than 10. Finally, we applied the developed approach to the simulation of immunoagglutination, assuming that the formed clusters have fractal structure.

  1. A hybrid electromagnetic shock absorber for active vehicle suspension systems

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Babak; Bolandhemmat, Hamidreza; Behrad Khamesee, Mir; Golnaraghi, Farid

    2011-02-01

    The use of electromagnetic dampers (ED) in vehicle active suspension systems has drawn considerable attention in the past few years, attributed to the fact that active suspension systems have shown superior performance in improving ride comfort and road handling of terrain vehicles, compared with their passive and semi-active counterparts. Although demonstrating superb performance, active suspensions still have some shortcomings that must be overcome. They have high energy consumption, weight, and cost and are not fail-safe in case of a power breakdown. The novel hybrid ED, which is proposed in this paper, is a potential solution to the above-mentioned drawbacks of conventional active suspension systems. The proposed hybrid ED is designed to inherit the high-performance characteristics of an active ED with the reliability of a passive damper in a single package. The eddy current damping effect is utilised as a source of the passive damping. First, a prototype ED is designed and fabricated. The prototype ED is then utilised to experimentally establish the design requirements for a real-size active ED. This is accomplished by comparing its vibration isolation performance in a 1-DOF quarter-car test rig with that of a same-class semi-active damper. Then, after a real-size active ED is designed, the concept of hybrid damper is introduced to the damper design to address the drawbacks of the active ED. Finally, the finite-element method is used to accurately model and analyse the designed hybrid damper. It is demonstrated that by introducing the eddy current damping effect to the active part, a passive damping of approximately 1570 Ns/m is achieved. This amount of passive damping guarantees that the damper is fail-safe and reduces the power consumption more than 70%, compared with an active ED in an automotive active suspension system.

  2. Anomalous velocity distributions in active Brownian suspensions.

    PubMed

    Fiege, Andrea; Vollmayr-Lee, Benjamin; Zippelius, Annette

    2013-08-01

    Large-scale simulations and analytical theory have been combined to obtain the nonequilibrium velocity distribution, f(v), of randomly accelerated particles in suspension. The simulations are based on an event-driven algorithm, generalized to include friction. They reveal strongly anomalous but largely universal distributions, which are independent of volume fraction and collision processes, which suggests a one-particle model should capture all the essential features. We have formulated this one-particle model and solved it analytically in the limit of strong damping, where we find that f(v) decays as 1/v for multiple decades, eventually crossing over to a Gaussian decay for the largest velocities. Many particle simulations and numerical solution of the one-particle model agree for all values of the damping. PMID:24032806

  3. 31 CFR 903.2 - Suspension of collection activity.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Suspension of collection activity. 903.2 Section 903.2 Money and Finance: Treasury Regulations Relating to Money and Finance (Continued) FEDERAL CLAIMS COLLECTION STANDARDS (DEPARTMENT OF THE TREASURY-DEPARTMENT OF JUSTICE) STANDARDS FOR SUSPENDING OR TERMINATING COLLECTION ACTIVITY...

  4. Active structuring of colloidal armour on liquid drops

    PubMed Central

    Dommersnes, Paul; Rozynek, Zbigniew; Mikkelsen, Alexander; Castberg, Rene; Kjerstad, Knut; Hersvik, Kjetil; Otto Fossum, Jon

    2013-01-01

    Adsorption and assembly of colloidal particles at the surface of liquid droplets are at the base of particle-stabilized emulsions and templating. Here we report that electrohydrodynamic and electro-rheological effects in leaky-dielectric liquid drops can be used to structure and dynamically control colloidal particle assemblies at drop surfaces, including electric-field-assisted convective assembly of jammed colloidal ‘ribbons’, electro-rheological colloidal chains confined to a two-dimensional surface and spinning colloidal domains on that surface. In addition, we demonstrate the size control of ‘pupil’-like openings in colloidal shells. We anticipate that electric field manipulation of colloids in leaky dielectrics can lead to new routes of colloidosome assembly and design for ‘smart armoured’ droplets. PMID:23811716

  5. Active damping control for electrodynamic suspension systems without mechanical transducers

    SciTech Connect

    Brunelli, B.; Casadei, D.; Serra, G.; Tani, A.

    1996-09-01

    In this paper an electrodynamic suspension system for maglev vehicles is analyzed, in which the active damping of the vertical oscillations is obtained without position, velocity and acceleration transducers. The damping effect is accomplished controlling the supply voltage of the damping coil to respond to current changes due to vertical oscillations. The stability of the suspension system is investigated by a linearized analysis of the model equations, emphasizing the influence of the voltage regulator parameters. The performance of the damping system, in terms of step response and ride quality, is also discussed.

  6. 15 CFR 970.2503 - Suspension of exploration activities.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 15 Commerce and Foreign Trade 3 2012-01-01 2012-01-01 false Suspension of exploration activities... Trade (Continued) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR EXPLORATION LICENSES...

  7. 15 CFR 970.2503 - Suspension of exploration activities.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 15 Commerce and Foreign Trade 3 2013-01-01 2013-01-01 false Suspension of exploration activities... Trade (Continued) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR EXPLORATION LICENSES...

  8. 15 CFR 970.2503 - Suspension of exploration activities.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 15 Commerce and Foreign Trade 3 2014-01-01 2014-01-01 false Suspension of exploration activities... Trade (Continued) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR EXPLORATION LICENSES...

  9. 15 CFR 970.2503 - Suspension of exploration activities.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 15 Commerce and Foreign Trade 3 2011-01-01 2011-01-01 false Suspension of exploration activities... Trade (Continued) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR EXPLORATION LICENSES...

  10. 15 CFR 970.2503 - Suspension of exploration activities.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 15 Commerce and Foreign Trade 3 2010-01-01 2010-01-01 false Suspension of exploration activities... Trade (Continued) NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, DEPARTMENT OF COMMERCE GENERAL REGULATIONS OF THE ENVIRONMENTAL DATA SERVICE DEEP SEABED MINING REGULATIONS FOR EXPLORATION LICENSES...

  11. Actively controlled vehicle suspension with energy regeneration capabilities

    NASA Astrophysics Data System (ADS)

    Bar David, Sagiv; Zion Bobrovsky, Ben

    2011-06-01

    The paper presents an innovative dual purpose automotive suspension topology, combining for the first time the active damping qualities with mechanical vibrations power regeneration capabilities. The new configuration consists of a linear generator as an actuator, a power processing stage based on a gyrator operating under sliding mode control and dynamics controllers. The researched design is simple and energetically efficient, enables an accurate force-velocity suspension characteristic control as well as energy regeneration control, with no practical implementation constraints imposed over the theoretical design. Active damping is based on Skyhook suspension control scheme, which enables overcoming the passive damping tradeoff between high- and low-frequency performance, improving both body isolation and the tire's road grip. The system-level design includes configuration of three system operation modes: passive, semi-active or fully active damping, all using the same electro-mechanical infrastructure, and each focusing on different objective: dynamics improvement or power regeneration. Conclusively, the innovative hybrid suspension is theoretically researched, practically designed and analysed, and proven to be feasible as well as profitable in the aspects of power regeneration, vehicle dynamics improvement and human health risks reduction.

  12. 10 CFR 1015.402 - Suspension of collection activity.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 4 2013-01-01 2013-01-01 false Suspension of collection activity. 1015.402 Section 1015.402 Energy DEPARTMENT OF ENERGY (GENERAL PROVISIONS) COLLECTION OF CLAIMS OWED THE UNITED STATES... debt when the debtor's future prospects justify retention of the debt for periodic review...

  13. 10 CFR 1015.402 - Suspension of collection activity.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 4 2014-01-01 2014-01-01 false Suspension of collection activity. 1015.402 Section 1015.402 Energy DEPARTMENT OF ENERGY (GENERAL PROVISIONS) COLLECTION OF CLAIMS OWED THE UNITED STATES... debt when the debtor's future prospects justify retention of the debt for periodic review...

  14. Adsorption, immobilization, and activity of beta-glucosidase on different soil colloids.

    PubMed

    Yan, Jinlong; Pan, Genxing; Li, Lianqing; Quan, Guixiang; Ding, Cheng; Luo, Ailan

    2010-08-15

    For a better understanding of enzyme stabilization and the subsequent catalytic process in a soil environment, the adsorption, immobilization, and activity of beta-glucosidase on various soil colloids from a paddy soil were studied. The calculated parameters maximum adsorption capacity (q(0)) for fine soil colloids ranged from 169.6 to 203.7 microg mg(-1), which was higher than coarse soil colloids in the range of 81.0-94.6 microg mg(-1), but the lower adsorption affinity (K(L)) was found on fine soil colloids. The percentages of beta-glucosidase desorbed from external surfaces of the coarse soil colloids (27.6-28.5%) were higher than those from the fine soil colloids (17.5-20.2%). Beta-glucosidase immobilized on the coarse inorganic and organic soil colloids retained 72.4% and 69.8% of activity, respectively, which indicated the facilitated effect of soil organic matter in the inhibition of enzyme activity. The residual activity for the fine soil clay is 79-81%. After 30 days of storage at 40 degrees C the free beta-glucosidase retained 66.2% of its initial activity, whereas the soil colloidal particle-immobilized enzyme retained 77.1-82.4% of its activity. The half-lives of free beta-glucosidase appeared to be 95.9 and 50.4 days at 25 and 40 degrees C. Immobilization of beta-glucosidase on various soil colloids enhanced the thermal stability at all temperatures, and the thermal stability was greatly affected by the affinity between the beta-glucosidase molecules and the surface of soil colloidal particles. Due to the protective effect of supports, soil colloidal particle-immobilized enzymes were less sensitive to pH and temperature changes than free enzymes. Data obtained in this study are helpful for further research on the enzymatic mechanisms in carbon cycling and soil carbon storage.

  15. [Factors affecting activation and transference of soil colloidal phosphorus and related analysis technologies].

    PubMed

    Zhao, Yue; Liang, Xin-qiang; Fu, Chao-dong; Zhu, Si-rui; Zhang, Yi-xiang; Ji, Yuan-jing

    2015-04-01

    Colloids play a key role in the transference process of phosphorus (P) in soil. Activation and transference of soil colloidal phosphorus have great effect on soil P pool and the surrounding water quality. This paper summarized the current studies on soil colloidal P, discussing the effects of the various factors (e. g., soil physical and chemical properties, fertilization, rainfall and soil amendments) on the transference of soil colloidal P. Some advanced analysis technologies (e.g., flow field-flow fractionation, transmission electron microscope-energy dispersive X-ray spectrometer, X-ray absorption near-edge structure and nuclear magnetic resonance) and methods of reducing soil colloidal P were also involved. This review would provide important information on the mechanism of soil colloidal P transference. PMID:26259473

  16. Microfluidic rheology of active particle suspensions: Kinetic theory.

    PubMed

    Alonso-Matilla, Roberto; Ezhilan, Barath; Saintillan, David

    2016-07-01

    We analyze the effective rheology of a dilute suspension of self-propelled slender particles confined between two infinite parallel plates and subject to a pressure-driven flow. We use a continuum kinetic model to describe the configuration of the particles in the system, in which the disturbance flows induced by the swimmers are taken into account, and use it to calculate estimates of the suspension viscosity for a range of channel widths and flow strengths typical of microfluidic experiments. Our results are in agreement with previous bulk models, and in particular, demonstrate that the effect of activity is strongest at low flow rates, where pushers tend to decrease the suspension viscosity whereas pullers enhance it. In stronger flows, dissipative stresses overcome the effects of activity leading to increased viscosities followed by shear-thinning. The effects of confinement and number density are also analyzed, and our results confirm the apparent transition to superfluidity reported in recent experiments on pusher suspensions at intermediate densities. We also derive an approximate analytical expression for the effective viscosity in the limit of weak flows and wide channels, and demonstrate good agreement between theory and numerical calculations.

  17. Non-equilibrium Stokes-Einstein relation via active microrheology of hydrodynamically interacting suspensions

    NASA Astrophysics Data System (ADS)

    Chu, Henry; Zia, Roseanna

    In our recently developed non-equilibrium Stokes-Einstein relation, we showed that, in the absence of hydrodynamic interactions, the stress in a suspension is given by a balance between fluctuation and dissipation. Here, we generalize our theory for systems of hydrodynamically interacting colloids, via active microrheology, where motion of a Brownian probe through the medium reveals rheological properties. The strength of probe forcing compared to the entropic restoring force defines a Peclet number, Pe. In the absence of hydrodynamics, the first normal stress difference and the osmotic pressure scale as Pe4 and Pe2 respectively when probe forcing is weak, and uniformly as Pe for strong probe forcing. As hydrodynamics become important, interparticle forces give way to lubrication interactions. Hydrodynamic coupling leads to a new low-Pe scaling of the first normal stress difference and the osmotic pressure as Pe2, and high-Pe scaling as Peδ, where 0.799 <= δ <= 1 as hydrodynamics vary from strong to weak. For the entire range of the strength of hydrodynamic interactions and probe forcing, the new phenomenological theory is shown to agree with standard micromechanical definitions of the stress. We further draw a connection between the stress and the energy storage in a suspension, and the entropic nature of such storage is identified.

  18. Study of adsorption process of iron colloid substances on activated carbon by ultrasound

    NASA Astrophysics Data System (ADS)

    Machekhina, K. I.; Shiyan, L. N.; Yurmazova, T. A.; Voyno, D. A.

    2015-04-01

    The paper reports on the adsorption of iron colloid substances on activated carbon (PAC) Norit SA UF with using ultrasound. It is found that time of adsorption is equal to three hours. High-frequency electrical oscillation is 35 kHz. The adsorption capacity of activated carbon was determined and it is equal to about 0.25 mg iron colloid substances /mg PAC. The iron colloid substances size ranging from 30 to 360 nm was determined. The zeta potential of iron colloid substances which consists of iron (III) hydroxide, silicon compounds and natural organic substances is about (-38mV). The process of destruction iron colloid substances occurs with subsequent formation of a precipitate in the form of Fe(OH)3 as a result of the removal of organic substances from the model solution.

  19. Characterizing Fullerene Nanoparticles in Aqueous Suspensions

    EPA Science Inventory

    Studies have indicated that fullerenes can form stable colloidal suspensions in water when introduced to the aqueous phase through solvent exchange, sonication, or extended mixing. The colloidal suspensions created using these techniques have effective aqueous phase concentratio...

  20. Quasi-active suspension design using magnetorheological dampers

    NASA Astrophysics Data System (ADS)

    Potter, Jack N.; Neild, Simon A.; Wagg, David J.

    2011-05-01

    Quasi-active damping is a method of coupled mechanical and control system design using multiple semi-active dampers. By designing the systems such that the desired control force may always be achieved using a combination of the dampers, quasi-active damping seeks to approach levels of vibration isolation achievable through active damping, whilst retaining the desirable attributes of semi-active systems. In this article a design is proposed for a quasi-active, base-isolating suspension system. Control laws are firstly defined in a generalised form, where semi-active dampers are considered as idealised variable viscous dampers. This system is used to demonstrate in detail the principles of quasi-active damping, in particular the necessary interaction between mechanical and control systems. It is shown how such a system can produce a tunable, quasi-active region in the frequency response of very low displacement transmissibility. Quasi-active control laws are then proposed which are specific for use with magnetorheological dampers. These are validated in simulation using a realistic model of the damper dynamics, again producing a quasi-active region in the frequency response. Finally, the robustness of the magnetorheological, quasi-active suspension system is demonstrated.

  1. Multidisciplinary design optimization of mechatronic vehicles with active suspensions

    NASA Astrophysics Data System (ADS)

    He, Yuping; McPhee, John

    2005-05-01

    A multidisciplinary optimization method is applied to the design of mechatronic vehicles with active suspensions. The method is implemented in a GA-A'GEM-MATLAB simulation environment in such a way that the linear mechanical vehicle model is designed in a multibody dynamics software package, i.e. A'GEM, the controllers and estimators are constructed using linear quadratic Gaussian (LQG) method, and Kalman filter algorithm in Matlab, then the combined mechanical and control model is optimized simultaneously using a genetic algorithm (GA). The design variables include passive parameters and control parameters. In the numerical optimizations, both random and deterministic road inputs and both perfect measurement of full state variables and estimated limited state variables are considered. Optimization results show that the active suspension systems based on the multidisciplinary optimization method have better overall performance than those derived using conventional design methods with the LQG algorithm.

  2. Propulsion of Active Colloids by Self-Induced Field Gradients.

    PubMed

    Boymelgreen, Alicia; Yossifon, Gilad; Miloh, Touvia

    2016-09-20

    Previously, metallodielectric Janus particles have been shown to travel with their dielectric hemisphere forward under low frequency applied electric fields as a result of asymmetric induced-charge electroosmotic flow. Here, it is demonstrated that at high frequencies, well beyond the charge relaxation time of the electric double layer induced around the particle, rather than the velocity decaying to zero, the Janus particles reverse direction, traveling with their metallic hemisphere forward. It is proposed that such motion is the result of a surface force, arising from localized nonuniform electric field gradients, induced by the dual symmetry-breaking of an asymmetric particle adjacent to a wall, which act on the induced dipole of the particle to drive net motion even in a uniform AC field. Although the field is external, since the driving gradient is induced on the particle level, it may be considered an active colloid. We have thus termed this propulsion mechanism "self-dielectrophoresis", to distinguish from traditional dielectrophoresis where the driving nonuniform field is externally fixed and the particle direction is restricted. It is demonstrated theoretically and experimentally that the critical frequency at which the particle reverses direction can be characterized by a nondimensional parameter which is a function of electrolyte concentration and particle size.

  3. Propulsion of Active Colloids by Self-Induced Field Gradients.

    PubMed

    Boymelgreen, Alicia; Yossifon, Gilad; Miloh, Touvia

    2016-09-20

    Previously, metallodielectric Janus particles have been shown to travel with their dielectric hemisphere forward under low frequency applied electric fields as a result of asymmetric induced-charge electroosmotic flow. Here, it is demonstrated that at high frequencies, well beyond the charge relaxation time of the electric double layer induced around the particle, rather than the velocity decaying to zero, the Janus particles reverse direction, traveling with their metallic hemisphere forward. It is proposed that such motion is the result of a surface force, arising from localized nonuniform electric field gradients, induced by the dual symmetry-breaking of an asymmetric particle adjacent to a wall, which act on the induced dipole of the particle to drive net motion even in a uniform AC field. Although the field is external, since the driving gradient is induced on the particle level, it may be considered an active colloid. We have thus termed this propulsion mechanism "self-dielectrophoresis", to distinguish from traditional dielectrophoresis where the driving nonuniform field is externally fixed and the particle direction is restricted. It is demonstrated theoretically and experimentally that the critical frequency at which the particle reverses direction can be characterized by a nondimensional parameter which is a function of electrolyte concentration and particle size. PMID:27611819

  4. Shape of dynamical heterogeneities and fractional Stokes-Einstein and Stokes-Einstein-Debye relations in quasi-two-dimensional suspensions of colloidal ellipsoids.

    PubMed

    Mishra, Chandan K; Ganapathy, Rajesh

    2015-05-15

    We examine the influence of the shape of dynamical heterogeneities on the Stokes-Einstein (SE) and Stokes-Einstein-Debye (SED) relations in quasi-two-dimensional suspensions of colloidal ellipsoids. For ellipsoids with repulsive interactions, both SE and SED relations are violated at all area fractions. On approaching the glass transition, however, the extent to which this violation occurs changes beyond a crossover area fraction. Quite remarkably, we find that it is not just the presence of dynamical heterogeneities but their change in the shape from stringlike to compact that coincides with this crossover. On introducing a suitable short-range depletion attraction between the ellipsoids, associated with the lack of morphological evolution of dynamical heterogeneities, the extent to which the SE and SED relations are violated remains unchanged even for deep supercooling.

  5. Application of the Z-scan technique to determine the optical Kerr coefficient and two-photon absorption coefficient of magnetite nanoparticles colloidal suspension

    NASA Astrophysics Data System (ADS)

    Vivacqua, Marco; Espinosa, Daniel; Martins Figueiredo Neto, Antônio

    2012-06-01

    We investigate the occurrence of the optical Kerr effect and two-photon absorption when an oil-based magnetic Fe3O4 nanoparticles colloidal suspension is illuminated with high intensity femtosecond laser pulses. The frequency of the pulses is controlled and the Z-scan technique is employed in our measurements of the nonlinear optical Kerr coefficient (n2) and two-photon absorption coefficient (β). From these values it was possible to calculate the real and imaginary parts of the third-order susceptibility. We observed that increasing the pulse frequency, additional physical processes take place, increasing artificially the absolute values of n2 and β. The experimental conditions are discussed to assure the obtention of reliable values of these nonlinear optical parameters, which may be useful in all-optical switching and optical power limiting applications.

  6. Multiplexed model predictive control for active vehicle suspensions

    NASA Astrophysics Data System (ADS)

    Hu, Yinlong; Chen, Michael Z. Q.; Hou, Zhongsheng

    2015-02-01

    Multiplexed model predictive control (MMPC) is a recently proposed efficient model predictive control (MPC) algorithm, which can effectively reduce the computational burden of the online optimisation in MPC implementation by updating the control inputs in an asynchronous manner. This paper investigates the application of MMPC in active vehicle suspension design. An MMPC controller integrated with soft constraints and a Kalman filter is proposed based on a full-car model. Ride comfort, roadholding and suspension deflection are considered in this paper, where ride comfort and roadholding are formulated as a quadratic cost function in terms of sprung mass accelerations and tyre deflections, while suspension deflection performance is formulated as a hard constraint. The saturation of the actuator force is also considered and formulated as a hard constraint as well. Numerical simulation is performed with respect to different choices of weighting factors, vehicle speeds and control horizons. The results show that the overall performance of ride comfort and roadholding can be improved significantly by employing MMPC and the average time taken by MMPC to solve the individual quadratic programming problem is considerably smaller than that of the conventional MPC, which effectively demonstrate the effectiveness of the proposed method.

  7. Colloidal Oatmeal (Avena Sativa) Improves Skin Barrier Through Multi-Therapy Activity.

    PubMed

    Ilnytska, Olha; Kaur, Simarna; Chon, Suhyoun; Reynertson, Kurt A; Nebus, Judith; Garay, Michelle; Mahmood, Khalid; Southall, Michael D

    2016-06-01

    Oats (Avena sativa) are a centuries-old topical treatment for a variety of skin barrier conditions, including dry skin, skin rashes, and eczema; however, few studies have investigated the actual mechanism of action for the skin barrier strengthening activity of colloidal oatmeal. Four extracts of colloidal oatmeal were prepared with various solvents and tested in vitro for skin barrier related gene expression and activity. Extracts of colloidal oatmeal were found to induce the expression of genes related to epidermal differentiation, tight junctions and lipid regulation in skin, and provide pH-buffering capacity. Colloidal oatmeal boosted the expression of multiple target genes related to skin barrier, and resulted in recovery of barrier damage in an in vitro model of atopic dermatitis. In addition, an investigator-blinded study was performed with 50 healthy female subjects who exhibited bilateral moderate to severe dry skin on their lower legs. Subjects were treated with a colloidal oatmeal skin protectant lotion. Clinically, the colloidal oatmeal lotion showed significant clinical improvements in skin dryness, moisturization, and barrier. Taken together, these results demonstrate that colloidal oatmeal can provide clinically effective benefits for dry and compromised skin by strengthening skin barrier.

    J Drugs Dermatol. 2016;15(6):684-690. PMID:27272074

  8. Colloidal Oatmeal (Avena Sativa) Improves Skin Barrier Through Multi-Therapy Activity.

    PubMed

    Ilnytska, Olha; Kaur, Simarna; Chon, Suhyoun; Reynertson, Kurt A; Nebus, Judith; Garay, Michelle; Mahmood, Khalid; Southall, Michael D

    2016-06-01

    Oats (Avena sativa) are a centuries-old topical treatment for a variety of skin barrier conditions, including dry skin, skin rashes, and eczema; however, few studies have investigated the actual mechanism of action for the skin barrier strengthening activity of colloidal oatmeal. Four extracts of colloidal oatmeal were prepared with various solvents and tested in vitro for skin barrier related gene expression and activity. Extracts of colloidal oatmeal were found to induce the expression of genes related to epidermal differentiation, tight junctions and lipid regulation in skin, and provide pH-buffering capacity. Colloidal oatmeal boosted the expression of multiple target genes related to skin barrier, and resulted in recovery of barrier damage in an in vitro model of atopic dermatitis. In addition, an investigator-blinded study was performed with 50 healthy female subjects who exhibited bilateral moderate to severe dry skin on their lower legs. Subjects were treated with a colloidal oatmeal skin protectant lotion. Clinically, the colloidal oatmeal lotion showed significant clinical improvements in skin dryness, moisturization, and barrier. Taken together, these results demonstrate that colloidal oatmeal can provide clinically effective benefits for dry and compromised skin by strengthening skin barrier.

    J Drugs Dermatol. 2016;15(6):684-690.

  9. Experimental investigation on the dissipative and elastic characteristics of a yaw colloidal damper destined to carbody suspension of a bullet train

    NASA Astrophysics Data System (ADS)

    Suciu, B.; Tomioka, T.

    2016-09-01

    Yaw damper represents a major source of excitation for flexural vibration of the railway carbody. In order to reduce transmissibility of such undesired excitation, yaw damper should allow for large force transmission at low working frequencies, but should behave as vibration isolator at high working frequencies. Unfortunately, the yaw oil damper (OD), which is nowadays in service, has poor intrinsic elastic capabilities and provides damping forces varying as a power function versus the piston speed. Since colloidal damper (CD) has intrinsic elastic capabilities and larger damping forces at lower excitation frequencies, it occurs as an attractive alternative solution to traditional yaw dampers. In this work, a yaw CD destined to carbody suspension of a bullet train was designed and manufactured; then, its dynamic characteristics, produced by both the frictional and colloidal effects, were evaluated from the experimental results, obtained during horizontal vibration tests, performed on a ball-screw shaker. Compared to the corresponding classical yaw OD, the trial yaw CD allowed for: weight reduction of 31.6%; large damping force, dissipated energy and spring constant at long piston stroke under low excitation frequency; low damping force, dissipated energy and spring constant at short piston stroke under high excitation frequency. Elastic properties were justified by introducing a model for the spring constant that included the effect of pore size distribution.

  10. Activity-assisted self-assembly of colloidal particles.

    PubMed

    Mallory, S A; Cacciuto, A

    2016-08-01

    We outline a basic strategy of how self-propulsion can be used to improve the yield of a typical colloidal self-assembly process. The success of this approach is predicated on the thoughtful design of the colloidal building block as well as how self-propulsion is endowed to the particle. As long as a set of criteria are satisfied, it is possible to significantly increase the rate of self-assembly, and greatly expand the window in parameter space where self-assembly can occur. In addition, we show that by tuning the relative on-off time of the self-propelling force it is possible to modulate the effective speed of the colloids allowing for further optimization of the self-assembly process.

  11. Activity-assisted self-assembly of colloidal particles

    NASA Astrophysics Data System (ADS)

    Mallory, S. A.; Cacciuto, A.

    2016-08-01

    We outline a basic strategy of how self-propulsion can be used to improve the yield of a typical colloidal self-assembly process. The success of this approach is predicated on the thoughtful design of the colloidal building block as well as how self-propulsion is endowed to the particle. As long as a set of criteria are satisfied, it is possible to significantly increase the rate of self-assembly, and greatly expand the window in parameter space where self-assembly can occur. In addition, we show that by tuning the relative on-off time of the self-propelling force it is possible to modulate the effective speed of the colloids allowing for further optimization of the self-assembly process.

  12. Activity-assisted self-assembly of colloidal particles.

    PubMed

    Mallory, S A; Cacciuto, A

    2016-08-01

    We outline a basic strategy of how self-propulsion can be used to improve the yield of a typical colloidal self-assembly process. The success of this approach is predicated on the thoughtful design of the colloidal building block as well as how self-propulsion is endowed to the particle. As long as a set of criteria are satisfied, it is possible to significantly increase the rate of self-assembly, and greatly expand the window in parameter space where self-assembly can occur. In addition, we show that by tuning the relative on-off time of the self-propelling force it is possible to modulate the effective speed of the colloids allowing for further optimization of the self-assembly process. PMID:27627360

  13. Dual objective active suspension system based on a novel nonlinear disturbance compensator

    NASA Astrophysics Data System (ADS)

    Deshpande, Vaijayanti S.; Shendge, P. D.; Phadke, S. B.

    2016-09-01

    This paper proposes an active suspension system to fulfil the dual objective of improving ride comfort while trying to keep the suspension deflection within the limits of the rattle space. The scheme is based on a novel nonlinear disturbance compensator which employs a nonlinear function of the suspension deflection. The scheme is analysed and validated by simulation and experimentation on a laboratory setup. The performance is compared with a passive suspension system for a variety of road profiles.

  14. Clustering and Pattern Formation in Chemorepulsive Active Colloids

    NASA Astrophysics Data System (ADS)

    Liebchen, Benno; Marenduzzo, Davide; Pagonabarraga, Ignacio; Cates, Michael E.

    2015-12-01

    We demonstrate that migration away from self-produced chemicals (chemorepulsion) generates a generic route to clustering and pattern formation among self-propelled colloids. The clustering instability can be caused either by anisotropic chemical production, or by a delayed orientational response to changes of the chemical environment. In each case, chemorepulsion creates clusters of a self-limiting area which grows linearly with self-propulsion speed. This agrees with recent observations of dynamic clusters in Janus colloids (albeit not yet known to be chemorepulsive). More generally, our results could inform design principles for the self-assembly of chemorepulsive synthetic swimmers and/or bacteria into nonequilibrium patterns.

  15. Clustering and Pattern Formation in Chemorepulsive Active Colloids.

    PubMed

    Liebchen, Benno; Marenduzzo, Davide; Pagonabarraga, Ignacio; Cates, Michael E

    2015-12-18

    We demonstrate that migration away from self-produced chemicals (chemorepulsion) generates a generic route to clustering and pattern formation among self-propelled colloids. The clustering instability can be caused either by anisotropic chemical production, or by a delayed orientational response to changes of the chemical environment. In each case, chemorepulsion creates clusters of a self-limiting area which grows linearly with self-propulsion speed. This agrees with recent observations of dynamic clusters in Janus colloids (albeit not yet known to be chemorepulsive). More generally, our results could inform design principles for the self-assembly of chemorepulsive synthetic swimmers and/or bacteria into nonequilibrium patterns.

  16. Clustering and Pattern Formation in Chemorepulsive Active Colloids.

    PubMed

    Liebchen, Benno; Marenduzzo, Davide; Pagonabarraga, Ignacio; Cates, Michael E

    2015-12-18

    We demonstrate that migration away from self-produced chemicals (chemorepulsion) generates a generic route to clustering and pattern formation among self-propelled colloids. The clustering instability can be caused either by anisotropic chemical production, or by a delayed orientational response to changes of the chemical environment. In each case, chemorepulsion creates clusters of a self-limiting area which grows linearly with self-propulsion speed. This agrees with recent observations of dynamic clusters in Janus colloids (albeit not yet known to be chemorepulsive). More generally, our results could inform design principles for the self-assembly of chemorepulsive synthetic swimmers and/or bacteria into nonequilibrium patterns. PMID:26722949

  17. Gold and silver nanoparticle monomers are non-SERS-active: a negative experimental study with silica-encapsulated Raman-reporter-coated metal colloids.

    PubMed

    Zhang, Yuying; Walkenfort, Bernd; Yoon, Jun Hee; Schlücker, Sebastian; Xie, Wei

    2015-09-01

    Noble metal nanoparticles (NPs) are the most commonly employed plasmonic substrates in surface-enhanced Raman scattering (SERS) experiments. Computer simulations show that monomers of Ag and Au nanocrystals ("spherical" NPs) do not exhibit a notable plasmonic enhancement, i.e., they are essentially non-SERS-active. However, in experiments, SERS enhanced by spherical NP colloids has been frequently reported. This implies that the monomers do not have strong SERS activity, but detectable enhancement should more or less be there. Because of the gap between theory and practice, it is important to demonstrate experimentally how SERS-active the metal colloid actually is and, in case a SERS signal is observed, where it originates from. In particular the aggregation of the colloid, induced by high centrifugal forces in washing steps or due to a harsh ionic environment of the suspension medium, should be controlled since it is the very high SERS activity of NP clusters which dominates the overall SERS signal of the colloid. We report here the experimental evaluation of the SERS activity of 80 nm Au and Ag NP monomers. Instead of showing fancy nanostructures and super SERS enhancement, we present the method on how to obtain negative experimental data. In this approach, no SERS signal was obtained from the colloid with a Raman reporter on the metal surface when the NPs were encapsulated carefully within a thick silica shell. Without silica encapsulation, if a very low centrifugation speed is used for the washing steps, only a negligible SERS signal can be detected even at very high NP concentrations. In contrast, strong SERS signals can be detected when the NPs are suspended in acidic solutions. These results indicate that Au and Ag NP monomers essentially exhibit no SERS activity of practical relevance.

  18. Characterization and Correlation of Particle-Level Interactions to the Macroscopic Rheology of Powders, Granular Slurries, and Colloidal Suspensions

    SciTech Connect

    Poloski, Adam P.; Daniel, Richard C.; Rector, David R.; Bredt, Paul R.; Buck, Edgar C.; Berg, John C.; Saez, Avelino E.

    2006-09-29

    Hanford TRU tank sludges are complex mixtures of undissolved minerals and salt solids in an aqueous phase of high ionic strength. They show complex rheological behavior resulting from interactions at the macroscopic level, such as interparticle friction between grains in the coarse fraction, as well as from interactions at the nano-scale level, such as the agglomeration of colloidal particles. An understanding of how phenomena such as interparticle friction and aggregate stability under shear will allow better control of Hanford TRU tank sludges being processed for disposal. The project described in this report had two objectives. The first was to understand the physical properties and behavior of the Hanford transuranic (TRU) tank sludges under conditions that might exist during retrieval, treatment, packaging, and transportation for disposal at the Waste Isolation Pilot Plant (WIPP). The second objective was to develop a fundamental understanding of sludge physical properties by correlating the macroscopic behavior with interactions occurring at the particle/colloidal scale. These objectives were accomplished by: 1) developing continuum models for coarse granular slurries and 2) studying the behavior of colloidal agglomerates under shear and under irradiation.

  19. Design and analysis of an intelligent controller for active geometry suspension systems

    NASA Astrophysics Data System (ADS)

    Goodarzi, Avesta; Oloomi, Ehsan; Esmailzadeh, Ebrahim

    2011-02-01

    An active geometry suspension (AGS) system is a device to optimise suspension-related factors such as toe angle and roll centre height by controlling vehicle's suspension geometry. The suspension geometry could be changed through control of suspension mounting point's position. In this paper, analysis and control of an AGS system is addressed. First, the effects of suspension geometry change on roll centre height and toe angle are studied. Then, based on an analytical approach, the improvement of the vehicle's stability and handling due to the control of suspension geometry is investigated. In the next section, an eight-degree-of-freedom handling model of a sport utility vehicle equipped with an AGS system is introduced. Finally, a self-tuning proportional-integral controller has been designed, using the fuzzy control theory, to control the actuator that changes the geometry of the suspension system. The simulation results show that an AGS system can improve the handling and stability of the vehicle.

  20. THE INFLUENCE OF OXIDANT TYPE ON THE PROPERTIES OF IRON COLLOIDS AND SUSPENSIONS FORMED FROM FERROUS IRON

    EPA Science Inventory

    "Red water" describes the appearance of drinking water that contains suspended particulate iron although the actual suspension color may be light yellow to brown depending on water chemistry and particle properties. Iron can originate from the source water and from distribution ...

  1. The behavior of active diffusiophoretic suspensions: An accelerated Laplacian dynamics study

    NASA Astrophysics Data System (ADS)

    Yan, Wen; Brady, John F.

    2016-10-01

    Diffusiophoresis is the process by which a colloidal particle moves in response to the concentration gradient of a chemical solute. Chemically active particles generate solute concentration gradients via surface chemical reactions which can result in their own motion — the self-diffusiophoresis of Janus particles — and in the motion of other nearby particles — normal down-gradient diffusiophoresis. The long-range nature of the concentration disturbance created by a reactive particle results in strong interactions among particles and can lead to the formation of clusters and even coexisting dense and dilute regions often seen in active matter systems. In this work, we present a general method to determine the many-particle solute concentration field allowing the dynamic simulation of the motion of thousands of reactive particles. With the simulation method, we first clarify and demonstrate the notion of "chemical screening," whereby the long-ranged interactions become exponentially screened, which is essential for otherwise diffusiophoretic suspensions would be unconditionally unstable. Simulations show that uniformly reactive particles, which do not self-propel, form loosely packed clusters but no coexistence is observed. The simulations also reveal that there is a stability threshold — when the "chemical fuel" concentration is low enough, thermal Brownian motion is able to overcome diffusiophoretic attraction. Janus particles that self-propel show coexistence, but, interestingly, the stability threshold for clustering is not affected by the self-motion.

  2. Optimal design of active and semi-active suspensions including time delays and preview

    NASA Astrophysics Data System (ADS)

    Hac', A.; Youn, I.

    1993-10-01

    Several control laws for active and semi-active suspension based on a linear half car model are derived and investigated. The strategies proposed take full advantage of the fact that the road input to the rear wheels is a delayed version of that to the front wheels, which in turn can be obtained either from the measurements of the front wheels and body motions or by direct preview of road irregularities if preview sensors are available. The suspension systems are optimized with respect to ride comfort, road holding and suspension rattle space as expressed by the mean-square-values of body acceleration (including effects of heave and pitch), tire deflections and front and rear suspension travels. The optimal control laws that minimize the given performance index and include passivity constraints in the semi-active case are derived using calculus of variation. The optimal semi-active suspension becomes piecewise linear, varying between passive and fully active systems and combinations of them. The performances of active and semi-active systems with and without preview were evaluated by numerical simulation in the time and frequency domains. The results show that incorporation of time delay between the front and rear axles in controller design improves the dynamic behavior of the rear axle and control of body pitch motion, while additional preview improves front wheel dynamics and body heave.

  3. Influence of ionic strength and polyelectrolyte concentration on the electrical conductivity of suspensions of soft colloidal polysaccharides.

    PubMed

    Sagou, Jean-Pierre S; Ahualli, Silvia; Thomas, Fabien; Duval, Jérôme

    2015-12-01

    The electrokinetic properties of carboxymethyldextran, a soft and anionic polysaccharide, were analysed in aqueous NaNO3 solutions through measurements of the electrical conductivity of the suspensions. The results, which furnish new experimental support for the structure of soft polysaccharides in electrolyte solution show that the polyion concentration governs the conductance behavior of the suspension as the ionic strength decreases. This is particularly evident for large polymer concentrations, for which electrical double layer overlap is more likely. In contrast, the electrical conductivity of the suspension at high ionic strength reduces to the contribution of the ions in solution, as screening of the polyion charges is more efficient in such conditions. The applicability of Ohshima's general conductivity expression to these electrical conductivity measurements was examined, and a major discrepancy against the theory was observed. The calculated values of the electrical conductivity deduced on the basis of this theory were found to be lower than the experimental ones. Possible reasons for this discrepancy are discussed and a numerical model, based on the use of a cell approach to account for hydrodynamic and electrical interactions between particles, has shown to be a good description of the experimental electrokinetic data.

  4. Non-equilibrium dynamics of an active colloidal ``chucker''

    NASA Astrophysics Data System (ADS)

    Valeriani, C.; Allen, R. J.; Marenduzzo, D.

    2010-05-01

    We report Monte Carlo simulations of the dynamics of a "chucker," a colloidal particle that emits smaller solute particles from its surface, isotropically and at a constant rate kc. We find that the diffusion constant of the chucker increases for small kc, as recently predicted theoretically. At large kc, the chucker diffuses more slowly due to crowding effects. We compare our simulation results to those of a "point particle" Langevin dynamics scheme in which the solute concentration field is calculated analytically, and in which hydrodynamic effects arising from colloid-solvent surface interactions can be accounted for in a coarse-grained way. By simulating the dragging of a chucker, we obtain an estimate of its apparent mobility coefficient which violates the fluctuation-dissipation theorem. We also characterize the probability density profile for a chucker which sediments onto a surface which either repels or absorbs the solute particles, and find that the steady state distributions are very different in the two cases. Our simulations are inspired by the biological example of exopolysaccharide-producing bacteria, as well as by recent experimental, simulation and theoretical work on phoretic colloidal "swimmers."

  5. A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets with high oxidase yield for analytical glucose and choline detections.

    PubMed

    Chen, Hsiao-Chien; Tsai, Rung-Ywan; Chen, Yen-Hsuan; Lee, Ren-Shen; Hua, Mu-Yi

    2013-08-20

    A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets (PBBIns-Gs) was used to modify a gold electrode to form a three-dimensional PBBIns-Gs/Au electrode that was sensitive to hydrogen peroxide (H2O2) in the presence of acetic acid (AcOH). The positively charged nanostructured poly(N-butyl benzimidazole) (PBBIns) separated the graphene sheets (Gs) and kept them suspended in an aqueous solution. Additionally, graphene sheets (Gs) formed "diaphragms" that intercalated Gs, which separated PBBIns to prevent tight packing and enhanced the surface area. The PBBIns-Gs/Au electrode exhibited superior sensitivity toward H2O2 relative to the PBBIns-modified Au (PBBIns/Au) electrode. Furthermore, a high yield of glucose oxidase (GOD) on the PBBIns-Gs of 52.3mg GOD per 1mg PBBIns-Gs was obtained from the electrostatic attraction between the positively charged PBBIns-Gs and negatively charged GOD. The non-destructive immobilization of GOD on the surface of the PBBIns-Gs (GOD-PBBIns-Gs) retained 91.5% and 39.2% of bioactivity, respectively, relative to free GOD for the colloidal suspension of the GOD-PBBIns-Gs and its modified Au (GOD-PBBIns-Gs/Au) electrode. Based on advantages including a negative working potential, high sensitivity toward H2O2, and non-destructive immobilization, the proposed glucose biosensor based on an GOD-PBBIns-Gs/Au electrode exhibited a fast response time (5.6s), broad detection range (10μM to 10mM), high sensitivity (143.5μAmM(-1)cm(-2)) and selectivity, and excellent stability. Finally, a choline biosensor was developed by dipping a PBBIns-Gs/Au electrode into a choline oxidase (ChOx) solution for enzyme loading. The choline biosensor had a linear range of 0.1μM to 0.83mM, sensitivity of 494.9μAmM(-1)cm(-2), and detection limit of 0.02μM. The results of glucose and choline measurement indicate that the PBBIns-Gs/Au electrode provides a useful platform for the development of oxidase-based biosensors. PMID:23910974

  6. Escherichia coli as a model active colloid: A practical introduction.

    PubMed

    Schwarz-Linek, Jana; Arlt, Jochen; Jepson, Alys; Dawson, Angela; Vissers, Teun; Miroli, Dario; Pilizota, Teuta; Martinez, Vincent A; Poon, Wilson C K

    2016-01-01

    The flagellated bacterium Escherichia coli is increasingly used experimentally as a self-propelled swimmer. To obtain meaningful, quantitative results that are comparable between different laboratories, reproducible protocols are needed to control, 'tune' and monitor the swimming behaviour of these motile cells. We critically review the knowledge needed to do so, explain methods for characterising the colloidal and motile properties of E. coli cells, and propose a protocol for keeping them swimming at constant speed at finite bulk concentrations. In the process of establishing this protocol, we use motility as a high-throughput probe of aspects of cellular physiology via the coupling between swimming speed and the proton motive force. PMID:26310235

  7. Escherichia coli as a model active colloid: A practical introduction.

    PubMed

    Schwarz-Linek, Jana; Arlt, Jochen; Jepson, Alys; Dawson, Angela; Vissers, Teun; Miroli, Dario; Pilizota, Teuta; Martinez, Vincent A; Poon, Wilson C K

    2016-01-01

    The flagellated bacterium Escherichia coli is increasingly used experimentally as a self-propelled swimmer. To obtain meaningful, quantitative results that are comparable between different laboratories, reproducible protocols are needed to control, 'tune' and monitor the swimming behaviour of these motile cells. We critically review the knowledge needed to do so, explain methods for characterising the colloidal and motile properties of E. coli cells, and propose a protocol for keeping them swimming at constant speed at finite bulk concentrations. In the process of establishing this protocol, we use motility as a high-throughput probe of aspects of cellular physiology via the coupling between swimming speed and the proton motive force.

  8. Probing effects of polymer adsorption in colloidal particle suspensions by light scattering as relevant for the aquatic environment: An overview.

    PubMed

    Tiraferri, Alberto; Borkovec, Michal

    2015-12-01

    Modification of particle surfaces by adsorption of polymers is a process that governs particle behavior in aqueous environmental systems. The present article briefly reviews the current understanding of the adsorption mechanisms and the properties of the resulting layers, and it discusses two environmentally relevant cases of particle modification by polymers. In particular, the discussion focuses on the usefulness of methods based on light scattering to probe such adsorbed layers together with the resulting properties of the particle suspensions, and it highlights advantages and disadvantages of these techniques. Measurement of the electrophoretic mobility allows to follow the development of the adsorption layer and to characterize the charge of the modified particles. At saturation, the surface charge is governed by the charge of the adsorbed film. Dynamic light scattering provides information on the film thickness and on the behavior of the modified suspensions. The charge and the structure of the adsorbed layer influence the stability of the particles, as well as the applicability of the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). This fundamental knowledge is presented in the light of environmental systems and its significance for applied systems is underlined. In particular, the article discusses two examples of environmental processes involving adsorption of polymers, namely, the modification of particles by natural adsorption of humic substances and the tailoring of surface properties of iron-based particles used to remediate contaminated aquifers.

  9. Active control of an innovative seat suspension system with acceleration measurement based friction estimation

    NASA Astrophysics Data System (ADS)

    Ning, Donghong; Sun, Shuaishuai; Li, Hongyi; Du, Haiping; Li, Weihua

    2016-12-01

    In this paper, an innovative active seat suspension system for vehicles is presented. This seat suspension prototype is built with two low cost actuators each of which has one rotary motor and one gear reducer. A H∞ controller with friction compensation is designed for the seat suspension control system where the friction is estimated and compensated based on the measurement of seat acceleration. This principal aim of this research was to control the low frequency vibration transferred or amplified by the vehicle (chassis) suspension, and to maintain the passivity of the seat suspension at high frequency (isolation vibration) while taking into consideration the trade-off between the active seat suspension cost and its high frequency performance. Sinusoidal excitations of 1-4.5 Hz were applied to test the active seat suspension both when controlled and when uncontrolled and this is compared with a well-tuned passive heavy duty vehicle seat suspension. The results indicate the effectiveness of the proposed control algorithm within the tested frequencies. Further tests were conducted using the excitations generated from a quarter-car model under bump and random road profiles. The bump road tests indicate the controlled active seat suspension has good transient response performance. The Power Spectral Density (PSD) method and ISO 2631-1 standards were applied to analyse the seat suspension's acceleration under random road conditions. Although some low magnitude and high frequency noise will inevitably be introduced by the active system, the weighted-frequency Root Mean Square (RMS) acceleration shows that this may not have a large effect on ride comfort. In fact, the ride comfort is improved from being an 'a little uncomfortable' to a 'not uncomfortable' level when compared with the well-tuned passive seat suspension. This low cost active seat suspension design and the proposed controller with the easily measured feedback signals are very practical for real

  10. Inertia Wheel on Low-Noise Active Magnetic Suspension

    NASA Astrophysics Data System (ADS)

    Carabelli, S.; Genta, G.; Silvagni, M.; Tonoli, A.

    2002-01-01

    Magnetic bearings are particularly suited for space applications for a number of reasons: - they are ideally suited for vacuum applications; - the lack of lubrication and wear enhances the reliability and guaranties a long maintenance-free operation - the low drag torque decreases power consumption and reduces the torque exerted on the stator of the machine. - the possibility of insulating actively the spacecraft from the excitation due to unbalance of the rotating system In the case of reaction wheels, a well designed magnetic suspension allows high speed operation with a very low power consumption and vibration level. Conversely, microgravity (and possibly vacuum) operation is an advantage for magnetic bearings. The absence of static forces allows to operate with low current levels, thus reducing electrical noise and allowing to reach even lower vibration levels than in Earth applications of magnetic bearings. Active magnetic bearings (AMB) allow to adapt the working characteristics of the system to the operating needs: it is possible to use the actuators to lock the system during launch (absence of grabbers) and to stiffen the suspension when the spacecraft is accelerated (impulsive phases), while working in conditions optimised for microgravity when this is needed. Magnetic suspension systems designed for microgravity environment cannot be correctly tested on the ground. Testing in ground conditions results in the need of grossly overdesigning the levitation device; furthermore, in some cases ground testing is completely impossible, if not by introducing devices which compensate for the Earth gravitational field. If the compensation for the gravitational force is supplied by the same actuators used for microgravity operation, the actuators and the power amplifiers must be overdesigned and in some cases the suspension can be altogether impossible. They work in conditions which are much different from nominal ones and, above all, it is impossible to reach the

  11. Colloidal Suspensions of Rodlike Nanocrystals and Magnetic Spheres under an External Magnetic Stimulus: Experiment and Molecular Dynamics Simulation.

    PubMed

    May, Kathrin; Eremin, Alexey; Stannarius, Ralf; Peroukidis, Stavros D; Klapp, Sabine H L; Klein, Susanne

    2016-05-24

    Using experiments and molecular dynamics simulations, we explore magnetic field-induced phase transformations in suspensions of nonmagnetic rodlike and magnetic sphere-shaped particles. We experimentally demonstrate that an external uniform magnetic field causes the formation of small, stable clusters of magnetic particles that, in turn, induce and control the orientational order of the nonmagnetic subphase. Optical birefringence was studied as a function of the magnetic field and the volume fractions of each particle type. Steric transfer of the orientational order was investigated by molecular dynamics (MD) simulations; the results are in qualitative agreement with the experimental observations. By reproducing the general experimental trends, the MD simulation offers a cohesive bottom-up interpretation of the physical behavior of such systems, and it can also be regarded as a guide for further experimental research. PMID:27119202

  12. Active temperature and velocity correlations produced by a swimmer suspension

    NASA Astrophysics Data System (ADS)

    Parra-Rojas, C.; Soto, R.

    2013-05-01

    The agitation produced in a fluid by a suspension of microswimmers in the low Reynolds number limit is studied. In this limit, swimmers are modeled as force dipoles all with equal strength. The agitation is characterized by the active temperature defined, as in kinetic theory, as the mean square velocity, and by the equal-time spatial correlations. Considering the phase in which the swimmers are homogeneously and isotropically distributed in the fluid, it is shown that the active temperature and velocity correlations depend on a single scalar correlation function of the dipole-dipole correlation function. By making a simple medium-range order model, in which the dipole-dipole correlation function is characterized by a single correlation length k0-1 it is possible to make quantitative predictions. It is found that the active temperature depends on the system size, scaling as L4-d at large correlation lengths L≪k0-1, while in the opposite limit it saturates in three dimensions and diverges logarithmically with the system size in two dimensions. In three dimensions the velocity correlations decay as 1/r for small correlation lengths, while at large correlation lengths the transverse correlation function becomes negative at maximum separation r˜L/2, an effect that disappears as the system increases in size.

  13. Reading a suspenseful literary text activates brain areas related to social cognition and predictive inference.

    PubMed

    Lehne, Moritz; Engel, Philipp; Rohrmeier, Martin; Menninghaus, Winfried; Jacobs, Arthur M; Koelsch, Stefan

    2015-01-01

    Stories can elicit powerful emotions. A key emotional response to narrative plots (e.g., novels, movies, etc.) is suspense. Suspense appears to build on basic aspects of human cognition such as processes of expectation, anticipation, and prediction. However, the neural processes underlying emotional experiences of suspense have not been previously investigated. We acquired functional magnetic resonance imaging (fMRI) data while participants read a suspenseful literary text (E.T.A. Hoffmann's "The Sandman") subdivided into short text passages. Individual ratings of experienced suspense obtained after each text passage were found to be related to activation in the medial frontal cortex, bilateral frontal regions (along the inferior frontal sulcus), lateral premotor cortex, as well as posterior temporal and temporo-parietal areas. The results indicate that the emotional experience of suspense depends on brain areas associated with social cognition and predictive inference.

  14. Reading a Suspenseful Literary Text Activates Brain Areas Related to Social Cognition and Predictive Inference

    PubMed Central

    Lehne, Moritz; Engel, Philipp; Rohrmeier, Martin; Menninghaus, Winfried; Jacobs, Arthur M.; Koelsch, Stefan

    2015-01-01

    Stories can elicit powerful emotions. A key emotional response to narrative plots (e.g., novels, movies, etc.) is suspense. Suspense appears to build on basic aspects of human cognition such as processes of expectation, anticipation, and prediction. However, the neural processes underlying emotional experiences of suspense have not been previously investigated. We acquired functional magnetic resonance imaging (fMRI) data while participants read a suspenseful literary text (E.T.A. Hoffmann's “The Sandman”) subdivided into short text passages. Individual ratings of experienced suspense obtained after each text passage were found to be related to activation in the medial frontal cortex, bilateral frontal regions (along the inferior frontal sulcus), lateral premotor cortex, as well as posterior temporal and temporo-parietal areas. The results indicate that the emotional experience of suspense depends on brain areas associated with social cognition and predictive inference. PMID:25946306

  15. Electrochemical analysis in a liposome suspension using lapachol as a hydrophobic electro active species.

    PubMed

    Okumura, Noriko; Wakamatsu, Shiori; Uno, Bunji

    2014-01-01

    This study demonstrated that the electro-chemical analysis of hydrophobic quinones can be performed in liposome suspension systems. We prepared and analyzed liposome suspensions containing lapachol, which is a quinone-based anti-tumor activity compound. In this suspension system, a simple one redox couple of lapachol is observed. These results are quite different from those obtained in organic solvents. In addition, the pH dependence of redox behaviors of lapachol could be observed in multilamellar vesicle (MLV) suspension system. This MLV suspension system method may approximate the electrochemical behavior of hydrophobic compounds in aqueous conditions. A benefit of this liposome suspension system for electrochemical analysis is that it enables to observe water-insoluble compounds without using organic solvents.

  16. Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.

    PubMed

    Tokudome, Yasuaki; Morimoto, Tsuyoshi; Tarutani, Naoki; Vaz, Pedro D; Nunes, Carla D; Prevot, Vanessa; Stenning, Gavin B G; Takahashi, Masahide

    2016-05-24

    Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems. PMID:27124717

  17. Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.

    PubMed

    Tokudome, Yasuaki; Morimoto, Tsuyoshi; Tarutani, Naoki; Vaz, Pedro D; Nunes, Carla D; Prevot, Vanessa; Stenning, Gavin B G; Takahashi, Masahide

    2016-05-24

    Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.

  18. Preparation, characterisation and antibacterial activity of a florfenicol-loaded solid lipid nanoparticle suspension.

    PubMed

    Wang, Ting; Chen, Xiaojin; Lu, Mengmeng; Li, Xihe; Zhou, WenZhong

    2015-12-01

    A florfenicol-loaded solid lipid nanoparticle (FFC-SLN) suspension was prepared by hot homogenisation and ultrasonic technique. The suspension was characterised for its release profile, stability, toxicity, and the physicochemical properties of the nanoparticles. Antibacterial activity of the suspension was evaluated in vitro and in vivo. The results showed that the mean diameter, polydispersity index and zeta potential of the nanoparticles were 253 ± 3 nm, 0.409 ± 0.022 and 47.5 ± 0.21 mV, respectively. In vitro release profile showed the FFC-SLN suspension had sustained release effect. The minimum inhibition concentration values of the FFC-SLN suspension were 6 and 3 µg/mL against Staphylococcus aureus and Escherichia coli respectively, compared with 3.5 and 2 µg/mL of native florfenicol. The suspension was relatively stable at 4°C and less stable at room temperature during 9 months storage. Although the nanoparticle carriers exhibited cytotoxicity in cell cultures, the LD50 of the lyophilised dry power of the suspension was higher than 5 g/kg body weight. Mortality protection against E. coli lethal infection in mice showed that the nanoparticle suspension had much better efficacy (6/10) than native drug (1/10). These results indicate that FFC-SLN suspension could be a promising formulation in veterinary medicine. PMID:26647811

  19. Preparation, characterisation and antibacterial activity of a florfenicol-loaded solid lipid nanoparticle suspension.

    PubMed

    Wang, Ting; Chen, Xiaojin; Lu, Mengmeng; Li, Xihe; Zhou, WenZhong

    2015-12-01

    A florfenicol-loaded solid lipid nanoparticle (FFC-SLN) suspension was prepared by hot homogenisation and ultrasonic technique. The suspension was characterised for its release profile, stability, toxicity, and the physicochemical properties of the nanoparticles. Antibacterial activity of the suspension was evaluated in vitro and in vivo. The results showed that the mean diameter, polydispersity index and zeta potential of the nanoparticles were 253 ± 3 nm, 0.409 ± 0.022 and 47.5 ± 0.21 mV, respectively. In vitro release profile showed the FFC-SLN suspension had sustained release effect. The minimum inhibition concentration values of the FFC-SLN suspension were 6 and 3 µg/mL against Staphylococcus aureus and Escherichia coli respectively, compared with 3.5 and 2 µg/mL of native florfenicol. The suspension was relatively stable at 4°C and less stable at room temperature during 9 months storage. Although the nanoparticle carriers exhibited cytotoxicity in cell cultures, the LD50 of the lyophilised dry power of the suspension was higher than 5 g/kg body weight. Mortality protection against E. coli lethal infection in mice showed that the nanoparticle suspension had much better efficacy (6/10) than native drug (1/10). These results indicate that FFC-SLN suspension could be a promising formulation in veterinary medicine.

  20. On-track tests of active vertical suspension on a passenger train

    NASA Astrophysics Data System (ADS)

    Qazizadeh, Alireza; Persson, Rickard; Stichel, Sebastian

    2015-06-01

    The classic way to design the suspension of a rail vehicle is to use passive elements such as dampers and springs; however, as sensors and actuators are getting more affordable and reliable, their potential benefit in the suspension system is increasingly studied. Active suspension can be used to keep ride comfort at an acceptable level or even improve it, while allowing tougher operation conditions or usage of lighter carbodies. Tougher conditions could be interpreted as higher speed or lower track quality, and lighter carbody means higher level of elastic vibrations. This paper is focused on the implementation and tests of active vertical suspension on the secondary suspension of a high-speed passenger electric multiple unit using hydraulic actuators and the skyhook method as the controller. Results from on-track tests indicate large ride comfort improvements.

  1. Frequency analysis of a semi-active suspension with magneto-rheological dampers

    NASA Astrophysics Data System (ADS)

    Andronic, Florin; Mihai, Ioan; Suciu, Cornel; Beniuga, Marius

    2015-02-01

    Suspension systems for motor vehicles are constantly evolving in order to ensure vehicle stability and traffic safety under all driving conditions. The present work aims to highlight the influence factors in the case of a quarter car model for semi-active suspensions. The functions that must be met by such suspension systems are first presented. Mathematical models for passive systems are first illustrated and then customized for the semi-active case. A simulation diagram was conceived for Matlab Simulink. The obtained simulation results allow conducting a frequency analysis of the passive and semi-active cases of the quarter car model. Various charts for Passive Suspension Transmissibility and for the Effect of Damping on Vertical Acceleration Response were obtained for both passive and semi-active situations. Analysis of obtained results allowed evaluating of the suspension systems behavior and their frequency dependence. Significant differences were found between the behaviors of passive and semi-active suspensions. It was found that semi-active suspensions ensure damping in accordance to the chosen control method, and are much more efficient than passive ones.

  2. Semi-active sliding mode control of vehicle suspension with magneto-rheological damper

    NASA Astrophysics Data System (ADS)

    Zhang, Hailong; Wang, Enrong; Zhang, Ning; Min, Fuhong; Subash, Rakheja; Su, Chunyi

    2015-01-01

    The vehicle semi-active suspension with magneto-rheological damper(MRD) has been a hot topic since this decade, in which the robust control synthesis considering load variation is a challenging task. In this paper, a new semi-active controller based upon the inverse model and sliding mode control (SMC) strategies is proposed for the quarter-vehicle suspension with the magneto-rheological (MR) damper, wherein an ideal skyhook suspension is employed as the control reference model and the vehicle sprung mass is considered as an uncertain parameter. According to the asymptotical stability of SMC, the dynamic errors between the plant and reference systems are used to derive the control damping force acquired by the MR quarter-vehicle suspension system. The proposed modified Bouc-wen hysteretic force-velocity ( F- v) model and its inverse model of MR damper, as well as the proposed continuous modulation (CM) filtering algorithm without phase shift are employed to convert the control damping force into the direct drive current of the MR damper. Moreover, the proposed semi-active sliding mode controller (SSMC)-based MR quarter-vehicle suspension is systematically evaluated through comparing the time and frequency domain responses of the sprung and unsprung mass displacement accelerations, suspension travel and the tire dynamic force with those of the passive quarter-vehicle suspension, under three kinds of varied amplitude harmonic, rounded pulse and real-road measured random excitations. The evaluation results illustrate that the proposed SSMC can greatly suppress the vehicle suspension vibration due to uncertainty of the load, and thus improve the ride comfort and handling safety. The study establishes a solid theoretical foundation as the universal control scheme for the adaptive semi-active control of the MR full-vehicle suspension decoupled into four MR quarter-vehicle sub-suspension systems.

  3. Mycobactericidal activity of selected disinfectants using a quantitative suspension test.

    PubMed

    Griffiths, P A; Babb, J R; Fraise, A P

    1999-02-01

    In this study, a quantitative suspension test carried out under both clean and dirty conditions was used to assess the activity of various instrument and environmental disinfectants against the type strain NCTC 946 and an endoscope washer disinfector isolate of Mycobacterium chelonae, Mycobacterium fortuitum NCTC 10,394, Mycobacterium tuberculosis H37 Rv NCTC 7416 and a clinical isolate of Mycobacterium avium-intracellulare (MAI). The disinfectants tested were; a chlorine releasing agent, sodium dichloroisocyanurate (NaDCC) at 1000 ppm and 10,000 ppm av Cl; chlorine dioxide at 1100 ppm av ClO2 (Tristel, MediChem International Limited); 70% industrial methylated spirits (IMS); 2% alkaline glutaraldehyde (Asep, Galan); 10% succinedialdehyde and formaldehyde mixture (Gigasept, Schulke & Mayr); 0.35% peracetic acid (NuCidex, Johnson & Johnson); and a peroxygen compound at 1% and 3% (Virkon, Antec International). Results showed that the clinical isolate of MAI was much more resistant than M. tuberculosis to all the disinfectants, while the type strains of M. chelonae and M. fortuitum were far more sensitive. The washer disinfector isolate of M. chelonae was extremely resistant to 2% alkaline activated glutaraldehyde and appeared to be slightly more resistant than the type strain to Nu-Cidex, Gigasept, Virkon and the lower concentration of NaDCC. This study has shown peracetic acid (Nu-Cidex), chlorine dioxide (Tristel), alcohol (IMS) and high concentrations of a chlorine releasing agent (NaDCC) are rapidly mycobactericidal. Glutaraldehyde, although effective, is a slow mycobactericide. Gigasept and Virkon are poor mycobactericidal agents and are not therefore recommended for instruments or spillage if mycobacteria are likely to be present. PMID:10063473

  4. Crystallization in a dense suspension of self-propelled particles.

    PubMed

    Bialké, Julian; Speck, Thomas; Löwen, Hartmut

    2012-04-20

    Using Brownian dynamics computer simulations, we show that a two-dimensional suspension of self-propelled ("active") colloidal particles crystallizes at sufficiently high densities. Compared to the equilibrium freezing of passive particles, the freezing density is both significantly shifted and depends on the structural or dynamical criterion employed. In nonequilibrium the transition is accompanied by pronounced structural heterogeneities. This leads to a transition region between liquid and solid in which the suspension is globally ordered but unordered liquidlike "bubbles" still persist.

  5. Impact-activated solidification of cornstarch and water suspensions

    NASA Astrophysics Data System (ADS)

    Waitukaitis, Scott Russell

    Liquids typically offer little resistance to impacting objects . Surprisingly, dense suspensions of liquids mixed with micron-sized particles can provide tremendous impact resistance, even though they appear liquid like when left at rest or perturbed lightly. The most well-known example is a dense mixture of cornstarch and water, which can easily provide enough impact resistance to allow a full-grown person to run across its surface. Previous studies have linked this so-called ``shear thickening'' to experiments carried out under steady state shear and attributed it to hydrodynamic interactions or granular dilation. However, neither of these explanations alone can account for the stress scales required to keep a running person above the free surface. This thesis investigates the mechanism for this impact resistance in dense suspensions. We begin by studying impact directly and watching a rod as it strikes the surface of a dense suspension of cornstarch and water. Using high-speed video and embedded force and acceleration sensing, we show that the rod motion leads to the rapid growth of a solid-like object below the impact site. With X-ray videography to see the dynamics of the suspension interior and laser sheet measurements of the surface profile, we show how this solid drags on the surrounding suspension, creating substantial peripheral flow and leading to the rapid extraction of the impactor's momentum. Suspecting that the solidification below the rod may be related to jamming of the particle sub-phase, we carry out 2D experiments with macroscopic disks to show how uniaxial compression of an initially unjammed system can lead to dynamic jamming fronts. In doing so, we show how these fronts are sensitive to the system's initial packing fraction relative to the point at which it jams and also discover that the widths of these fronts are related to a diverging correlation length. Finally, we take these results back to the suspension, where we perform careful, speed

  6. The liquidlike ordering of lipid A-diphosphate colloidal crystals: The influence of Ca2+, Mg2+, Na+, and K+ on the ordering of colloidal suspensions of lipid A-diphosphate in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Faunce, C. A.; Reichelt, H.; Paradies, H. H.; Quitschau, P.; Zimmermann, K.

    2005-06-01

    M NaCl) or Mg2+ (50μM). By comparing the heights and positions of the structure factor peaks S(Q) for lipid A-diphosphate-Na+ and lipid A-diphosphate-Ca2+, it was concluded that the structure factor does not depend simply on ionic strength but more importantly on the internal structural arrangements of the lipid A-diphosphate assembly in the presence of the bound cations. The liquidlike interactions revealed a considerable degree of ordering in solution accounting for the primary S(Q ) peak and also the secondary minimum at large particle separation. The ordering of lipid A-diphosphate-Ca2+ colloidal crystals in suspension showed six to seven discrete diffraction peaks and revealed a face-centered-cubic (fcc) lattice type (a=56.3nm) at a volume fraction of 3.2×10-4⩽ϕ⩽3.9×10-4. The K+ salt also exhibited a fcc lattice (a=55.92nm) at the same volume fractions, but reveals a different peak intensity distribution, as seen for the lipid A-diphosphate-Ca2+ salt. However, the Mg2+ and the Na+ salts of lipid A-diphosphate showed body-centered-cubic (bcc) lattices with a =45.50nm and a =41.50nm, respectively (3.2×10-4⩽ϕ⩽3.9×10-4), displaying the same intensity distribution with the exception of the (220) diffraction peaks, which differ in intensity for both salts of lipid A-diphosphate.

  7. Vibration control of a nonlinear quarter-car active suspension system by reinforcement learning

    NASA Astrophysics Data System (ADS)

    Bucak, İ. Ö.; Öz, H. R.

    2012-06-01

    This article presents the investigation of performance of a nonlinear quarter-car active suspension system with a stochastic real-valued reinforcement learning control strategy. As an example, a model of a quarter car with a nonlinear suspension spring subjected to excitation from a road profile is considered. The excitation is realised by the roughness of the road. The quarter-car model to be considered here can be approximately described as a nonlinear two degrees of freedom system. The experimental results indicate that the proposed active suspension system suppresses the vibrations greatly. A simulation of a nonlinear quarter-car active suspension system is presented to demonstrate the effectiveness and examine the performance of the learning control algorithm.

  8. Physics of Colloids in Space: Microgravity Experiment Launched, Installed, and Activated on the International Space Station

    NASA Technical Reports Server (NTRS)

    Doherty, Michael P.

    2002-01-01

    The Physics of Colloids in Space (PCS) experiment is a Microgravity Fluids Physics investigation that is presently located in an Expedite the Process of Experiments to Space Station (EXPRESS) Rack on the International Space Station. PCS was launched to the International Space Station on April 19, 2001, activated on May 31, 2001, and will continue to operate about 90 hr per week through May 2002.

  9. Simulation and comparison of quarter-car passive suspension system with Bingham and Bouc-Wen MR semi-active suspension models

    NASA Astrophysics Data System (ADS)

    Perescu, A.; Bereteu, L.

    2013-11-01

    In this paper we want to transposion the suspension system in MATLAB, Simulink®, based on equation of motion. Consider only vertical movement of the car, neglecting roll and pitch. All movements of the car axes are modeled as having equal amplitude. The characteristic equations that describe the behavior of dynamical systems based on FBD (Free Body Diagram) of automotive suspension. It will make two models, one passive and one Bingham semi-active. Their responses will be compared between them, and with another Bouc-Wen semi-active model, more complex. Semi-active suspension systems have received significant attention in recent years because they offer the adaptability of active control devices without requiring large power sources. Given that both passive and semi-active dampers are in mass production will follow the normal parameters and their economic efficiency. These models are used for initial design of suspension system.

  10. Functional Based Adaptive and Fuzzy Sliding Controller for Non-Autonomous Active Suspension System

    NASA Astrophysics Data System (ADS)

    Huang, Shiuh-Jer; Chen, Hung-Yi

    In this paper, an adaptive sliding controller is developed for controlling a vehicle active suspension system. The functional approximation technique is employed to substitute the unknown non-autonomous functions of the suspension system and release the model-based requirement of sliding mode control algorithm. In order to improve the control performance and reduce the implementation problem, a fuzzy strategy with online learning ability is added to compensate the functional approximation error. The update laws of the functional approximation coefficients and the fuzzy tuning parameters are derived from the Lyapunov theorem to guarantee the system stability. The proposed controller is implemented on a quarter-car hydraulic actuating active suspension system test-rig. The experimental results show that the proposed controller suppresses the oscillation amplitude of the suspension system effectively.

  11. Semi-active variable stiffness vibration control of vehicle seat suspension using an MR elastomer isolator

    NASA Astrophysics Data System (ADS)

    Du, Haiping; Li, Weihua; Zhang, Nong

    2011-10-01

    This paper presents a study on continuously variable stiffness control of vehicle seat suspension using a magnetorheological elastomer (MRE) isolator. A concept design for an MRE isolator is proposed in the paper and its behavior is experimentally evaluated. An integrated seat suspension model, which includes a quarter-car suspension and a seat suspension with a driver body model, is used to design a sub-optimal H_{\\infty } controller for an active isolator. The desired control force generated by this active isolator is then emulated by the MRE isolator through its continuously variable stiffness property when the actuating condition is met. The vibration control effect of the MRE isolator is evaluated in terms of driver body acceleration responses under both bump and random road conditions. The results show that the proposed control strategy achieves better vibration reduction performance than conventional on-off control.

  12. Transport of Intrinsic Plutonium Colloids in Saturated Porous Media

    NASA Astrophysics Data System (ADS)

    Zhou, D.; Abdel-Fattah, A.; Boukhalfa, H.; Ware, S. D.; Tarimala, S.; Keller, A. A.

    2011-12-01

    Actinide contaminants were introduced to the subsurface environment as a result of nuclear weapons development and testing, as well as for nuclear power generation and related research activities for defense and civilian applications. Even though most actinide species were believed to be fairly immobile once in the subsurface, recent studies have shown the transport of actinides kilometers away from their disposal sites. For example, the treated liquid wastes released into Mortandad Canyon at the Los Alamos National Laboratory were predicted to travel less than a few meters; however, plutonium and americium have been detected 3.4 km away from the waste outfall. A colloid-facilitated mechanism has been suggested to account for this unexpected transport of these radioactive wastes. Clays, oxides, organic matters, and actinide hydroxides have all been proposed as the possible mobile phase. Pu ions associated with natural colloids are often referred to as pseudo-Pu colloids, in contrast with the intrinsic Pu colloids that consist of Pu oxides. Significant efforts have been made to investigate the role of pseudo-Pu colloids, while few studies have evaluated the environmental behavior of the intrinsic Pu colloids. Given the fact that Pu (IV) has extremely low solubility product constant, it can be inferred that the transport of Pu in the intrinsic form is highly likely at suitable environmental conditions. This study investigates the transport of intrinsic Pu colloids in a saturated alluvium material packed in a cylindrical column (2.5-cm Dia. x 30-cm high) and compares the results to previous data on the transport of pseudo Pu colloids in the same material. A procedure to prepare a stable intrinsic Pu colloid suspension that produced consistent and reproducible electrokinetic and stability data was developed. Electrokinetic properties and aggregation stability were characterized. The Pu colloids, together with trillium as a conservative tracer, were injected into the

  13. Modeling of Semi-Active Vehicle Suspension with Magnetorhological Damper

    NASA Astrophysics Data System (ADS)

    Hasa, Richard; Danko, Ján; Milesich, Tomáš; Magdolen, Ľuboš

    2014-12-01

    Modeling of suspension is a current topic. Vehicle users require both greater driving comfort and safety. There is a space to invent new technologies like magnetorheological dampers and their control systems to increase these conflicting requirements. Magnetorheological dampers are reliably mathematically described by parametric and nonparametric models. Therefore they are able to reliably simulate the driving mode of the vehicle. These simulations are important for automotive engineers to increase vehicle safety and passenger comfort.

  14. Active colloids at liquid-liquid interfaces: dynamic self-assembly and functionality

    NASA Astrophysics Data System (ADS)

    Snezhko, Alexey; Aranson, Igor

    2012-02-01

    Self-assembled materials must actively consume energy and remain out of equilibrium in order to support structural complexity and functional diversity. Colloids of interacting particles suspended at liquid-liquid interfaces and maintained out of equilibrium by external alternating electromagnetic fields develop nontrivial collective dynamics and self-assembly. We use ferromagnetic colloidal micro-particles (so the magnetic moment is fixed in each particle and interactions between colloids is highly anisotropic and directional) suspended over an interface of two immiscible liquids and energized by vertical alternating magnetic fields to demonstrate novel dynamic and active self-assembled structures (``asters'') which are not accessible through thermodynamic assembly. Structures are attributed to the interplay between surface waves, generated at the liquid/liquid interface by the collective response of magnetic microparticles to the alternating magnetic field, and hydrodynamic fields induced in the boundary layers of both liquids forming the interface. Two types of magnetic order are reported. We demonstrate that asters develop self-propulsion in the presence of a small in-plane dc magnetic field. We show that asters can capture, transport, and position target microparticles.

  15. Assessment of antimicrobial activity of nanosized Ag doped TiO(2) colloids.

    PubMed

    Yaşa, Ihsan; Lkhagvajav, Natsag; Koizhaiganova, Meruyert; Celik, Erdal; Sarı, Ozcan

    2012-07-01

    In the present research, the antimicrobial effects of nanosized silver (Ag) doped TiO(2) colloidal solutions prepared using a sol-gel technique were investigated. In order to determine the solution characteristics, the turbidity, viscosity and pH of the colloidal solutions were measured. Differential thermal analysis-thermogravimetry equipment was used to determine the chemical structures and reaction types of the films formed from these solutions. The morphology of Ag doped TiO(2) nanoparticles was evaluated by atomic force microscopy. The disc diffusion method was employed to explore antimicrobial activity, and the Broth Microdilution method was used to obtain MIC values of nanosized Ag doped TiO(2) colloidal solutions against the test microorganisms Escherichia coli, Staphylococcus aureus, Candida albicans, Bacillus subtilis, and Salmonella typhimurium. It was found that the silver doped TiO(2) nanoparticles inhibited the growth and multiplication of the test microorganisms, including the fungus C. albicans. Antimicrobial activity was observed against all tested microorganisms at a very low concentration of 1.125-2.81 μg/ml of nano silver in 1-25 % Ag-TiO(2) solutions.

  16. Phase separation of biphasic mixture of active Janus colloids

    NASA Astrophysics Data System (ADS)

    Yan, Jing; Han, Ming; Luijten, Erik; Granick, Steve

    2014-03-01

    Recently there is a surge of interest in the phase behavior of active matter in which building blocks display self-propelling motion. Although much has been known from theory and simulation, experimental examples are very rare. Specifically, the epitomic problem of a binary mixture of active matter defies any experiment or theory so far. Here we present an experimental realization of binary mixture of particles, which only acquires activity when they collisionally interact with the opposite kind. We used a system in which the only difference in the two particles is the phase in their cyclic motion, precluding any artifact due to difference in interparticle potential. We observe phenomena strikingly similar to spinodal decomposition of molecular system, in addition to new features due to the nonequilibrium nature of the system. We derived a general, effective Flory-Huggins theory for spinodal decomposition of bicomponent active system, and rationalized the 1/3 power law growth of the domain size in regions where thermodynamic analogy is valid. The system also presents a plethora of nonequilibrium phenomena such as critical fluctuation, lane formation, and dynamic absorbing state in different parameter space.

  17. Robust H∞ control of active vehicle suspension under non-stationary running

    NASA Astrophysics Data System (ADS)

    Guo, Li-Xin; Zhang, Li-Ping

    2012-12-01

    Due to complexity of the controlled objects, the selection of control strategies and algorithms in vehicle control system designs is an important task. Moreover, the control problem of automobile active suspensions has been become one of the important relevant investigations due to the constrained peculiarity and parameter uncertainty of mathematical models. In this study, after establishing the non-stationary road surface excitation model, a study on the active suspension control for non-stationary running condition was conducted using robust H∞ control and linear matrix inequality optimization. The dynamic equation of a two-degree-of-freedom quarter car model with parameter uncertainty was derived. The H∞ state feedback control strategy with time-domain hard constraints was proposed, and then was used to design the active suspension control system of the quarter car model. Time-domain analysis and parameter robustness analysis were carried out to evaluate the proposed controller stability. Simulation results show that the proposed control strategy has high systemic stability on the condition of non-stationary running and parameter uncertainty (including suspension mass, suspension stiffness and tire stiffness). The proposed control strategy can achieve a promising improvement on ride comfort and satisfy the requirements of dynamic suspension deflection, dynamic tire loads and required control forces within given constraints, as well as non-stationary running condition.

  18. Tuning the morphology, stability and photocatalytic activity of TiO{sub 2} nanocrystal colloids by tungsten doping

    SciTech Connect

    Xu, Haiping; Liao, Jianhua; Yuan, Shuai; Zhao, Yin; Zhang, Meihong; Wang, Zhuyi; Shi, Liyi

    2014-03-01

    Graphical abstract: - Highlights: • W{sup 6+}-doped TiO{sub 2} nanocrystal colloids were prepared by hydrothermal methods. • The properties of TiO{sub 2} nanocrystal colloids can be tuned by tungsten doping. • W{sup 6+}-doped TiO{sub 2} nanocrystal colloids show higher stability and dispersity. • W{sup 6+}-doped TiO{sub 2} nanocrystal colloids show higher photocatalytic activity. - Abstract: The effects of tungsten doping on the morphology, stability and photocatalytic activity of TiO{sub 2} nanocrystal colloids were investigated. The nanostructure, chemical state of Ti, W, O, and the properties of tungsten doped TiO{sub 2} samples were investigated carefully by TEM, XRD, XPS, UV–vis, PL and photocatalytic degradation experiments. And the structure–activity relationship was discussed according to the analysis and measurement results. The analysis results reveal that the morphology, zeta potential and photocatalytic activity of TiO{sub 2} nanocrystals can be easily tuned by changing the tungsten doping concentration. The tungsten doped TiO{sub 2} colloid combines the characters of high dispersity and high photocatalytic activity.

  19. Antibacterial activity of cerium colloids against opportunistic microorganisms in vitro.

    PubMed

    Babenko, L P; Zholobak, N M; Shcherbakov, A B; Voychuk, S I; Lazarenko, L M; Spivak, M Ya

    2012-01-01

    The CeO2 sol with the size of nanoparticles 2-4 nm has been synthesized. It has been determined that the synthesized nanocrystalline cerium has antibacterial activity in vitro against different groups of opportunistic microorganisms: clinical strains of Escherichia coli, Staphylococcus aureus and Candida albicans. The rate of viability depression of test-cultures depends on the concentration of cerium dioxide nanoparticles and time of incubation. It is shown that the sol interacts with the bacterial cell surface. It is suggested that the observed differences of antibacterial action of nanocrystalline cerium dioxide can be related to the structural characteristics of the cell surface.

  20. Classical Nucleation Theory Description of Active Colloid Assembly

    NASA Astrophysics Data System (ADS)

    Redner, Gabriel S.; Wagner, Caleb G.; Baskaran, Aparna; Hagan, Michael F.

    2016-09-01

    Nonaligning self-propelled particles with purely repulsive excluded volume interactions undergo athermal motility-induced phase separation into a dilute gas and a dense cluster phase. Here, we use enhanced sampling computational methods and analytic theory to examine the kinetics of formation of the dense phase. Despite the intrinsically nonequilibrium nature of the phase transition, we show that the kinetics can be described using an approach analogous to equilibrium classical nucleation theory, governed by an effective free energy of cluster formation with identifiable bulk and surface terms. The theory captures the location of the binodal, nucleation rates as a function of supersaturation, and the cluster size distributions below the binodal, while discrepancies in the metastable region reveal additional physics about the early stages of active crystal formation. The success of the theory shows that a framework similar to equilibrium thermodynamics can be obtained directly from the microdynamics of an active system, and can be used to describe the kinetics of evolution toward nonequilibrium steady states.

  1. Active dynamics of colloidal particles in time-varying laser speckle patterns.

    PubMed

    Bianchi, Silvio; Pruner, Riccardo; Vizsnyiczai, Gaszton; Maggi, Claudio; Di Leonardo, Roberto

    2016-01-01

    Colloidal particles immersed in a dynamic speckle pattern experience an optical force that fluctuates both in space and time. The resulting dynamics presents many interesting analogies with a broad class of non-equilibrium systems like: active colloids, self propelled microorganisms, transport in dynamical intracellular environments. Here we show that the use of a spatial light modulator allows to generate light fields that fluctuate with controllable space and time correlations and a prescribed average intensity profile. In particular we generate ring-shaped random patterns that can confine a colloidal particle over a quasi one-dimensional random energy landscape. We find a mean square displacement that is diffusive at both short and long times, while a superdiffusive or subdiffusive behavior is observed at intermediate times depending on the value of the speckles correlation time. We propose two alternative models for the mean square displacement in the two limiting cases of a short or long speckles correlation time. A simple interpolation formula is shown to account for the full phenomenology observed in the mean square displacement across the entire range from fast to slow fluctuating speckles. PMID:27279540

  2. Active dynamics of colloidal particles in time-varying laser speckle patterns

    PubMed Central

    Bianchi, Silvio; Pruner, Riccardo; Vizsnyiczai, Gaszton; Maggi, Claudio; Di Leonardo, Roberto

    2016-01-01

    Colloidal particles immersed in a dynamic speckle pattern experience an optical force that fluctuates both in space and time. The resulting dynamics presents many interesting analogies with a broad class of non-equilibrium systems like: active colloids, self propelled microorganisms, transport in dynamical intracellular environments. Here we show that the use of a spatial light modulator allows to generate light fields that fluctuate with controllable space and time correlations and a prescribed average intensity profile. In particular we generate ring-shaped random patterns that can confine a colloidal particle over a quasi one-dimensional random energy landscape. We find a mean square displacement that is diffusive at both short and long times, while a superdiffusive or subdiffusive behavior is observed at intermediate times depending on the value of the speckles correlation time. We propose two alternative models for the mean square displacement in the two limiting cases of a short or long speckles correlation time. A simple interpolation formula is shown to account for the full phenomenology observed in the mean square displacement across the entire range from fast to slow fluctuating speckles. PMID:27279540

  3. Active dynamics of colloidal particles in time-varying laser speckle patterns

    NASA Astrophysics Data System (ADS)

    Bianchi, Silvio; Pruner, Riccardo; Vizsnyiczai, Gaszton; Maggi, Claudio; di Leonardo, Roberto

    2016-06-01

    Colloidal particles immersed in a dynamic speckle pattern experience an optical force that fluctuates both in space and time. The resulting dynamics presents many interesting analogies with a broad class of non-equilibrium systems like: active colloids, self propelled microorganisms, transport in dynamical intracellular environments. Here we show that the use of a spatial light modulator allows to generate light fields that fluctuate with controllable space and time correlations and a prescribed average intensity profile. In particular we generate ring-shaped random patterns that can confine a colloidal particle over a quasi one-dimensional random energy landscape. We find a mean square displacement that is diffusive at both short and long times, while a superdiffusive or subdiffusive behavior is observed at intermediate times depending on the value of the speckles correlation time. We propose two alternative models for the mean square displacement in the two limiting cases of a short or long speckles correlation time. A simple interpolation formula is shown to account for the full phenomenology observed in the mean square displacement across the entire range from fast to slow fluctuating speckles.

  4. Influence of iron solubility and charged surface-active compounds on lipid oxidation in fatty acid ethyl esters containing association colloids.

    PubMed

    Homma, Rika; Johnson, David R; McClements, D Julian; Decker, Eric A

    2016-05-15

    The impact of iron compounds with different solubilities on lipid oxidation was studied in the presence and absence of association colloids. Iron (III) sulfate only accelerated lipid oxidation in the presence of association colloids while iron (III) oleate accelerated oxidation in the presence and absence of association colloids. Further, iron (III) oxide retarded lipid oxidation both with and without association colloids. The impact of charged association colloids on lipid oxidation in ethyl oleate was also investigated. Association colloids consisting of the anionic surface-active compound dodecyl sulphosuccinate sodium salt (AOT), cationic surface-active compound hexadecyltrimethylammonium bromide (CTAB), and nonionic surface-active compound 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100) retarded, promoted, and had no effect on lipid oxidation rates, respectively. These results indicate that the polarity of metal compounds and the charge of association colloids play a big role in lipid oxidation.

  5. Influence of iron solubility and charged surface-active compounds on lipid oxidation in fatty acid ethyl esters containing association colloids.

    PubMed

    Homma, Rika; Johnson, David R; McClements, D Julian; Decker, Eric A

    2016-05-15

    The impact of iron compounds with different solubilities on lipid oxidation was studied in the presence and absence of association colloids. Iron (III) sulfate only accelerated lipid oxidation in the presence of association colloids while iron (III) oleate accelerated oxidation in the presence and absence of association colloids. Further, iron (III) oxide retarded lipid oxidation both with and without association colloids. The impact of charged association colloids on lipid oxidation in ethyl oleate was also investigated. Association colloids consisting of the anionic surface-active compound dodecyl sulphosuccinate sodium salt (AOT), cationic surface-active compound hexadecyltrimethylammonium bromide (CTAB), and nonionic surface-active compound 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100) retarded, promoted, and had no effect on lipid oxidation rates, respectively. These results indicate that the polarity of metal compounds and the charge of association colloids play a big role in lipid oxidation. PMID:26776045

  6. Influence of tire damping on mixed H2/H∞ synthesis of half-car active suspensions

    NASA Astrophysics Data System (ADS)

    Akçay, Hüseyin; Türkay, Semiha

    2009-04-01

    In this paper, multi-objective control of a half-car suspension system using linear matrix inequalities is studied. It is observed that when tire damping is precisely known, road-holding quality of the suspension system can be improved to some extent by the design procedure while ride comfort and compactness of suspension rattling space are only slightly affected as tire damping coefficients are increased. In the absence of tire damping information, a robust controller is designed for a suspension system with polytopic tire damping uncertainties. In contrast to multi-objective control of quarter-car models with polytopic tire damping uncertainties, this robust design does not offer any advantage over an active suspension system designed by neglecting tire damping. The results, based on the assumption that the front and the rear road velocity inputs are uncorrelated white-noise processes, demonstrate that the body pitch significantly impacts the closed-loop performance of the active suspension system. This implies that decomposition of a half-car model into two independent quarter-car models by a linear transformation is not realistic for a study of the performance limitations and the trade-offs.

  7. Wall-induced self-diffusiophoresis of active isotropic colloids

    NASA Astrophysics Data System (ADS)

    Yariv, Ehud

    2016-07-01

    While chemically active homogeneous spherical particles do not undergo self-diffusiophoresis in free solution, they may do so when suspended in the vicinity of a solid boundary. We explore this possibility using a first-order kinetic model of solute absorption, where the relative magnitude of reaction to diffusion is characterized by the Damköhler number Da . When the particle is remote from the wall, it is repelled from it with a velocity that scales inversely with the square of distance. The opposite extreme, when the ratio δ of separation distance to particle size is small, results in the anomalous scaling δ√{1/+2 Da }-1 2 of the solute concentration in the narrow gap separating the particle and wall. This irrational power may only be obtained by asymptotic matching with solute transport outside the gap. For Da <4 the self-propulsion speed possesses the same scaling, being set by the large pressures forming in the gap through a lubrication-type mechanism. For Da >4 the particle velocity is O (δ ) , set by the flow in the region outside the gap. Solute advection is subdominant to diffusion in both the remote and near-contact limits and accordingly affects neither the above scaling nor the resulting approximations.

  8. Validating the colloid model to optimise the design and operation of both moving-bed biofilm reactor and integrated fixed-film activated sludge systems.

    PubMed

    Albizuri, J; Grau, P; Christensson, M; Larrea, L

    2014-01-01

    The paper presents a systematic study of simulations, using a previously calibrated Colloid model, from which it was found that: (i) for pure moving-bed biofilm reactor (MBBR) processes with tertiary nitrification conditions (no influent chemical oxygen demand (COD)), dissolved oxygen = 5 mg/L and residual NH4-N > 4 mgN/L, a nitrification rate of 1.2 gN/(m(2)d) was obtained at 10 °C. This rate decreases sharply when residual NH4-N is lower than 2 mgN/L, (ii) for MBBR systems with predenitrification-nitrification zones and COD in the influent (soluble and particulate), the nitrification rate (0.6 gN/(m(2)d)) is half of that in tertiary nitrification due to the effect of influent colloidal XS (particulate slowly biodegradable COD) and (iii) for integrated fixed-film activated sludge (IFAS) processes the nitrification rate in the biofilm (0.72 gN/(m(2)d)) is 20% higher than for the pure MBBR due to the lower effect of influent XS since it is adsorbed onto flocs. However, it is still 40% lower than the tertiary nitrification rate. In the IFAS, the fraction of the nitrification rate in suspension ranges from 10 to 70% when the aerobic solids retention time varies from 1.4 to 6 days.

  9. Validating the colloid model to optimise the design and operation of both moving-bed biofilm reactor and integrated fixed-film activated sludge systems.

    PubMed

    Albizuri, J; Grau, P; Christensson, M; Larrea, L

    2014-01-01

    The paper presents a systematic study of simulations, using a previously calibrated Colloid model, from which it was found that: (i) for pure moving-bed biofilm reactor (MBBR) processes with tertiary nitrification conditions (no influent chemical oxygen demand (COD)), dissolved oxygen = 5 mg/L and residual NH4-N > 4 mgN/L, a nitrification rate of 1.2 gN/(m(2)d) was obtained at 10 °C. This rate decreases sharply when residual NH4-N is lower than 2 mgN/L, (ii) for MBBR systems with predenitrification-nitrification zones and COD in the influent (soluble and particulate), the nitrification rate (0.6 gN/(m(2)d)) is half of that in tertiary nitrification due to the effect of influent colloidal XS (particulate slowly biodegradable COD) and (iii) for integrated fixed-film activated sludge (IFAS) processes the nitrification rate in the biofilm (0.72 gN/(m(2)d)) is 20% higher than for the pure MBBR due to the lower effect of influent XS since it is adsorbed onto flocs. However, it is still 40% lower than the tertiary nitrification rate. In the IFAS, the fraction of the nitrification rate in suspension ranges from 10 to 70% when the aerobic solids retention time varies from 1.4 to 6 days. PMID:24718350

  10. Extraction and Analysis of C60, C70 and PCBM in Aqueous Suspensions

    EPA Science Inventory

    The goal of this work is to develop sampling and analytical methodologies for extracting and quantifying fullerenes in aqueous colloidal suspensions. Sampling and analysis of colloidal suspensions pose some unique challenges not encountered when working with true solutions. For...

  11. Vehicle active suspension system using skyhook adaptive neuro active force control

    NASA Astrophysics Data System (ADS)

    Priyandoko, G.; Mailah, M.; Jamaluddin, H.

    2009-04-01

    This paper aims to highlight the practical viability of a new and novel hybrid control technique applied to a vehicle active suspension system of a quarter car model using skyhook and adaptive neuro active force control (SANAFC). The overall control system essentially comprises four feedback control loops, namely the innermost proportional-integral (PI) control loop for the force tracking of the pneumatic actuator, the intermediate skyhook and active force control (AFC) control loops for the compensation of the disturbances and the outermost proportional-integral-derivative (PID) control loop for the computation of the optimum target/commanded force. A neural network (NN) with a modified adaptive Levenberg-Marquardt learning algorithm was used to approximate the estimated mass and inverse dynamics of the pneumatic actuator in the AFC loop. A number of experiments were carried out on a physical test rig using a hardware-in-the-loop configuration that fully incorporates the theoretical elements. The performance of the proposed control method was evaluated and compared to examine the effectiveness of the system in suppressing the vibration effect on the suspension system. It was found that the simulation and experimental results were in good agreement, particularly for the sprung mass displacement and acceleration behaviours in which the proposed SANAFC scheme is found to outperform the PID and passive counterparts.

  12. A new active variable stiffness suspension system using a nonlinear energy sink-based controller

    NASA Astrophysics Data System (ADS)

    Anubi, Olugbenga Moses; Crane, Carl D.

    2013-10-01

    This paper presents the active case of a variable stiffness suspension system. The central concept is based on a recently designed variable stiffness mechanism which consists of a horizontal control strut and a vertical strut. The horizontal strut is used to vary the load transfer ratio by actively controlling the location of the point of attachment of the vertical strut to the car body. The control algorithm, effected by a hydraulic actuator, uses the concept of nonlinear energy sink (NES) to effectively transfer the vibrational energy in the sprung mass to a control mass, thereby reducing the transfer of energy from road disturbance to the car body at a relatively lower cost compared to the traditional active suspension using the skyhook concept. The analyses and simulation results show that a better performance can be achieved by subjecting the point of attachment of a suspension system, to the chassis, to the influence of a horizontal NES system.

  13. Hydraulic actuation technology for full- and semi-active railway suspensions

    NASA Astrophysics Data System (ADS)

    Goodall, Roger; Freudenthaler, Gerhard; Dixon, Roger

    2014-12-01

    The paper describes a simulation study that provides a comprehensive comparison between full-active and semi-active suspensions for improving the vertical ride quality of railway vehicles. It includes an assessment of the ride quality benefits that can theoretically be achieved with idealised devices, and also examines the impact of real devices based upon hydraulic actuation technology.

  14. A semi-active control suspension system for railway vehicles with magnetorheological fluid dampers

    NASA Astrophysics Data System (ADS)

    Wei, Xiukun; Zhu, Ming; Jia, Limin

    2016-07-01

    The high-speed train has achieved great progress in the last decades. It is one of the most important modes of transportation between cities. With the rapid development of the high-speed train, its safety issue is paid much more attention than ever before. To improve the stability of the vehicle with high speed, extra dampers (i.e. anti-hunting damper) are used in the traditional bogies with passive suspension system. However, the curving performance of the vehicle is undermined due to the extra lateral force generated by the dampers. The active suspension systems proposed in the last decades attempt to solve the vehicle steering issue. However, the active suspension systems need extra actuators driven by electrical power or hydraulic power. There are some implementation and even safety issues which are not easy to be overcome. In this paper, an innovative semi-active controlled lateral suspension system for railway vehicles is proposed. Four magnetorheological fluid dampers are fixed to the primary suspension system of each bogie. They are controlled by online controllers for enhancing the running stability on the straight track line on the one hand and further improving the curving performance by controlling the damper force on the other hand. Two control strategies are proposed in the light of the pure rolling concept. The effectiveness of the proposed strategies is demonstrated by SIMPACK and Matlab co-simulation for a full railway vehicle with two conventional bogies.

  15. Out-of-Equilibrium effects in suspensions of light-activated artificial microwimmers

    NASA Astrophysics Data System (ADS)

    Palacci, Jeremie; Sacanna, Stefano; Pine, David; Chaikin, Paul; CSMR, NYU Team

    2011-11-01

    We present a new type of colloidal artificial swimmers propelled by the decomposition of hydrogen peroxide and activated by light. The effect is reversible and allows external control of the swimming/non swimming behavior of the particles. Moreover the bulk synthesis makes possible the study of very concentrated assemblies of monodisperse and identical microswimmers. These active agents are used to explore fancy effects of out-of-equilibrium systems, e.g. clustering, ``tugboat'' effect.

  16. Lipid colloidal carriers for improvement of anticancer activity of orally delivered quercetin: formulation, characterization and establishing in vitro-in vivo advantage.

    PubMed

    Jain, Ankitkumar S; Shah, Sanket M; Nagarsenker, Mangal S; Nikam, Yuvraj; Gude, Rajiv P; Steiniger, Frank; Thamm, Jana; Fahr, Alfred

    2013-07-01

    Novel lipid nanocarriers, GeluPearl (GP) comprising of Precirol ATO 5 lipid nanoparticles with (GPNLC) or without oil (GPSLN), loaded with Quercetin (QR), were successfully fabricated to improve therapeutic efficacy. QR loaded GP nanoparticles were optimized to yield adequate colloidal stability, mean particle size in range of 350-380 nm and entrapment efficiency of more than 90%. GPSLN and GPNLC were characterized for morphological evaluation by virtue of cryo-TEM, surface charge, protection offered to QR against alkali mediated degradation and fluorescence studies to evaluate QR-lipid interaction. DSC analysis was performed to get insight into physical state of QR loaded in nanosystems. The in vitro release studies demonstrated sustained drug release potential of QR loaded GP. In vitro lipolysis studies confirmed that lipidic nanocarriers can improve QR solubilization. QR loaded GP nanosystems significantly (P < 0.05) reduced flank tumor volumes in C57BL/6 mice over a 22 day study period compared to QR suspension. GPSLN significantly reduced lung colonization and enhanced antimetastatic activity (P < 0.05) of drug against B16F10 melanoma cells in C57BL/6 mice as compared to QR suspension. QR loaded GPSLN and GPNLC could be effectively lyophilized without much change in particle size and drug content using 15% w/v mannitol as cryoprotectant.

  17. Fuzzy and Internal Model Control of an Active Suspension System for a 2-DOF Vehicle Model

    NASA Astrophysics Data System (ADS)

    Demir, Özgür; Karakurt, Derya; Alarçin, Fuat

    2007-09-01

    In this study, Fuzzy-Logic-Based (FL) controller and Internal Model Control (IMC) scheme are designed for active suspension system. An aim of active suspension systems for a vehicle model is to provide good road handling and high passenger comfort by shaping the output function. The simulated system was considered to be a two-degree-of-freedom (2-DOF) model. The effectiveness of this Fuzzy Control is verified by comparison with Internal Model Control simulation results. Simulation results show that the effectiveness of the fuzzy controller is better than Internal Model Control under the same conditions.

  18. Rapid electrostatics-assisted layer-by-layer assembly of near-infrared-active colloidal photonic crystals.

    PubMed

    Askar, Khalid; Leo, Sin-Yen; Xu, Can; Liu, Danielle; Jiang, Peng

    2016-11-15

    Here we report a rapid and scalable bottom-up technique for layer-by-layer (LBL) assembling near-infrared-active colloidal photonic crystals consisting of large (⩾1μm) silica microspheres. By combining a new electrostatics-assisted colloidal transferring approach with spontaneous colloidal crystallization at an air/water interface, we have demonstrated that the crystal transfer speed of traditional Langmuir-Blodgett-based colloidal assembly technologies can be enhanced by nearly 2 orders of magnitude. Importantly, the crystalline quality of the resultant photonic crystals is not compromised by this rapid colloidal assembly approach. They exhibit thickness-dependent near-infrared stop bands and well-defined Fabry-Perot fringes in the specular transmission and reflection spectra, which match well with the theoretical calculations using a scalar-wave approximation model and Fabry-Perot analysis. This simple yet scalable bottom-up technology can significantly improve the throughput in assembling large-area, multilayer colloidal crystals, which are of great technological importance in a variety of optical and non-optical applications ranging from all-optical integrated circuits to tissue engineering. PMID:27494632

  19. Influence of naturally occurring dissolved organic matter, colloids, and cations on nanofiltration of pharmaceutically active and endocrine disrupting compounds.

    PubMed

    Sadmani, A H M Anwar; Andrews, Robert C; Bagley, David M

    2014-12-01

    This study examined the rejection of selected pharmaceutically active (PhAC) and endocrine disrupting compounds (EDCs) when using nanofiltration as a function of naturally occurring dissolved organic matter (DOM), colloidal particles, cations and their interactions. Lake Ontario water served as a source of natural DOM and colloidal particles. PhAC/EDC rejection experiments were conducted using raw Lake Ontario water and Lake Ontario water that was pre-treated with either ultrafiltration to remove colloidal particles, or fluidized ion exchange resins to remove DOM. Additionally, the concentration of cations (Ca(2+), Mg(2+), and Na(+)) in the raw and pre-treated water matrices was varied. While ionic PhACs and EDCs exhibited high rejections from all the water matrices examined, neutral compounds were most effectively rejected in water containing DOM and no colloids, and least effectively rejected from colloid-containing water with increased cations but no DOM. The presence of DOM significantly improved compound rejection and the increase in cation concentration significantly decreased rejection. The presence of colloids had comparatively little effect except to mitigate the impact of increased cation concentration, apparently providing some cation-buffering capacity. The sequence in which constituents are removed from waters during treatment may significantly impact PhAC and EDC removal, especially of neutral compounds.

  20. Rapid electrostatics-assisted layer-by-layer assembly of near-infrared-active colloidal photonic crystals.

    PubMed

    Askar, Khalid; Leo, Sin-Yen; Xu, Can; Liu, Danielle; Jiang, Peng

    2016-11-15

    Here we report a rapid and scalable bottom-up technique for layer-by-layer (LBL) assembling near-infrared-active colloidal photonic crystals consisting of large (⩾1μm) silica microspheres. By combining a new electrostatics-assisted colloidal transferring approach with spontaneous colloidal crystallization at an air/water interface, we have demonstrated that the crystal transfer speed of traditional Langmuir-Blodgett-based colloidal assembly technologies can be enhanced by nearly 2 orders of magnitude. Importantly, the crystalline quality of the resultant photonic crystals is not compromised by this rapid colloidal assembly approach. They exhibit thickness-dependent near-infrared stop bands and well-defined Fabry-Perot fringes in the specular transmission and reflection spectra, which match well with the theoretical calculations using a scalar-wave approximation model and Fabry-Perot analysis. This simple yet scalable bottom-up technology can significantly improve the throughput in assembling large-area, multilayer colloidal crystals, which are of great technological importance in a variety of optical and non-optical applications ranging from all-optical integrated circuits to tissue engineering.

  1. Multi-objective control for active vehicle suspension with wheelbase preview

    NASA Astrophysics Data System (ADS)

    Li, Panshuo; Lam, James; Cheung, Kie Chung

    2014-10-01

    This paper presents a multi-objective control method with wheelbase preview for active vehicle suspension. A four-degree-of-freedom half-car model with active suspension is considered in this study. H∞ norm and generalized H2 norm are used to improve ride quality and ensure that hard constraints are satisfied. Disturbances at the front wheel are obtained as preview information for the rear wheel. Static output-feedback is utilized in designing controllers, the solution is derived by iterative linear matrix inequality (ILMI) and cone complementarity linearization (CCL) algorithms. Simulation results confirm that multi-objective control with wheelbase preview achieves a significant improvement of ride quality (a maximum 27 percent and 60 percent improvement on vertical and angular acceleration, respectively) comparing with that of control without preview, while suspension deflections, tyre deflections and actuator forces remaining within given bounds. The extent of the improvement on the ride quality for different amount of preview information used is also illustrated.

  2. Magnetic manipulation of self-assembled colloidal asters

    NASA Astrophysics Data System (ADS)

    Snezhko, Alexey; Aranson, Igor S.

    2011-09-01

    Self-assembled materials must actively consume energy and remain out of equilibrium to support structural complexity and functional diversity. Here we show that a magnetic colloidal suspension 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, which exhibit locomotion and shape change. By controlling a small external magnetic field applied parallel to the interface, we show that asters can capture, transport, and position target microparticles. The ability to manipulate colloidal structures is crucial for the further development of self-assembled microrobots.

  3. Magnetic manipulation of self-assembled colloidal asters.

    SciTech Connect

    Snezhko, A.; Aranson, I. S.

    2011-09-01

    Self-assembled materials must actively consume energy and remain out of equilibrium to support structural complexity and functional diversity. Here we show that a magnetic colloidal suspension 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, which exhibit locomotion and shape change. By controlling a small external magnetic field applied parallel to the interface, we show that asters can capture, transport, and position target microparticles. The ability to manipulate colloidal structures is crucial for the further development of self-assembled microrobots

  4. Pro-active optimal control for semi-active vehicle suspension based on sensitivity updates

    NASA Astrophysics Data System (ADS)

    Michael, Johannes; Gerdts, Matthias

    2015-12-01

    This article suggests a strategy to control semi-active suspensions of vehicles in a pro-active way to adapt to future road profiles. The control strategy aims to maximise comfort while maintaining good handling properties. It employs suitably defined optimal control problems in combination with a parametric sensitivity analysis. The optimal control techniques are used to optimise the time-dependent damper coefficients in an electro-rheological damper for given nominal road profiles. The parametric sensitivity analysis is used to adapt the computed nominal optimal controls to perturbed road profiles in real time. The method is particularly useful for events with a low excitation frequency such as ramps, bumps, or potholes. For high-frequency excitations standard controllers are preferable; so we propose a switched open-closed-loop controller design. Various examples demonstrate the performance of the approach.

  5. Colloidal particle adsorption at liquid interfaces: capillary driven dynamics and thermally activated kinetics.

    PubMed

    Rahmani, Amir M; Wang, Anna; Manoharan, Vinothan N; Colosqui, Carlos E

    2016-08-14

    The adsorption of single colloidal microparticles (0.5-1 μm radius) at a water-oil interface has been recently studied experimentally using digital holographic microscopy [Kaz et al., Nat. Mater., 2012, 11, 138-142]. An initially fast adsorption dynamics driven by capillary forces is followed by an unexpectedly slow relaxation to equilibrium that is logarithmic in time and can span hours or days. The slow relaxation kinetics has been attributed to the presence of surface "defects" with nanoscale dimensions (1-5 nm) that induce multiple metastable configurations of the contact line perimeter. A kinetic model considering thermally activated transitions between such metastable configurations has been proposed [Colosqui et al., Phys. Rev. Lett., 2013, 111, 028302] to predict both the relaxation rate and the crossover point to the slow logarithmic regime. However, the adsorption dynamics observed experimentally before the crossover point has remained unstudied. In this work, we propose a Langevin model that is able to describe the entire adsorption process of single colloidal particles by considering metastable states produced by surface defects and thermal motion of the particle and liquid interface. Invoking the fluctuation dissipation theorem, we introduce a drag term that considers significant dissipative forces induced by thermal fluctuations of the liquid interface. Langevin dynamics simulations based on the proposed adsorption model yield close agreement with experimental observations for different microparticles, capturing the crossover from (fast) capillary driven dynamics to (slow) thermally activated kinetics. PMID:27373956

  6. Colloidal Confinement of Polyphosphate on Gold Nanoparticles Robustly Activates the Contact Pathway of Blood Coagulation.

    PubMed

    Szymusiak, Magdalena; Donovan, Alexander J; Smith, Stephanie A; Ransom, Ross; Shen, Hao; Kalkowski, Joseph; Morrissey, James H; Liu, Ying

    2016-01-20

    Platelet-sized polyphosphate (polyP) was functionalized on the surface of gold nanoparticles (GNPs) via a facile conjugation scheme entailing EDAC (N-(3-(dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride)-catalyzed phosphoramidation of the terminal phosphate of polyP to cystamine. Subsequent reduction of the disulfide moiety allowed for anchoring to the colloidal surface. The ability of the synthesized polyP-GNPs to initiate the contact pathway of clotting in human pooled normal plasma (PNP) was then assayed by quantifying changes in viscous, mechanical, and optical properties upon coagulation. It is revealed that the polyP-GNPs are markedly superior contact activators compared to molecularly dissolved, platelet-sized polyP (of equivalent polymer chain length). Moreover, the particles' capacity to mobilize Factor XII (FXII) and its coactivating proteins appear to be identical to very-long-chain polyP typically found in bacteria. These data imply that nanolocalization of anionic procoagulants on colloidal surfaces, achieved through covalent anchoring, may yield a robust contact surface with the ability to sufficiently cluster active clotting factors together above their threshold concentrations to cease bleeding. The polyP-GNPs therefore serve as a promising foundation in the development of a nanoparticle hemostat to treat a range of hemorrhagic scenarios. PMID:26624923

  7. Design and experiment study of a semi-active energy-regenerative suspension system

    NASA Astrophysics Data System (ADS)

    Shi, Dehua; Chen, Long; Wang, Ruochen; Jiang, Haobin; Shen, Yujie

    2015-01-01

    A new kind of semi-active energy-regenerative suspension system is proposed to recover suspension vibration energy, as well as to reduce the suspension cost and demands for the motor-rated capacity. The system consists of an energy-regenerative damper and a DC-DC converter-based energy-regenerative circuit. The energy-regenerative damper is composed of an electromagnetic linear motor and an adjustable shock absorber with three regulating levels. The linear motor just works as the generator to harvest the suspension vibration energy. The circuit can be used to improve the system’s energy-regenerative performance and to continuously regulate the motor’s electromagnetic damping force. Therefore, although the motor works as a generator and damps the isolation without an external power source, the motor damping force is controllable. The damping characteristics of the system are studied based on a two degrees of freedom vehicle vibration model. By further analyzing the circuit operation characteristics under different working modes, the double-loop controller is designed to track the desired damping force. The external-loop is a fuzzy controller that offers the desired equivalent damping. The inner-loop controller, on one hand, is used to generate the pulse number and the frequency to control the angle and the rotational speed of the step motor; on the other hand, the inner-loop is used to offer the duty cycle of the energy-regenerative circuit. Simulations and experiments are conducted to validate such a new suspension system. The results show that the semi-active energy-regenerative suspension can improve vehicle ride comfort with the controllable damping characteristics of the linear motor. Meanwhile, it also ensures energy regeneration.

  8. Fe-Impregnated Mineral Colloids for Peroxide Activation: Effects of Mineral Substrate and Fe Precursor.

    PubMed

    Li, Yue; Machala, Libor; Yan, Weile

    2016-02-01

    Heterogeneous iron species at the mineral/water interface are important catalysts for the generation of reactive oxygen species at circumneutral pH. One significant pathway leading to the formation of such species arises from deposition of dissolved iron onto mineral colloids due to changes in redox conditions. This study investigates the catalytic properties of Fe impregnated on silica, alumina, and titania nanoparticles (as prototypical mineral colloids). Fe impregnation was carried out by immersing the mineral nanoparticles in dilute Fe(II) or Fe(III) solutions at pH 6 and 3, respectively, in an aerobic environment. The uptake of iron per unit surface area follows the order of nTiO2 > nAl2O3 > nSiO2 for both types of Fe precursors. Impregnation of mineral particles in Fe(II) solutions results in predominantly Fe(III) species due to efficient surface-mediated oxidation. The catalytic activity of the impregnated solids to produce hydroxyl radical (·OH) from H2O2 decomposition was evaluated using benzoic acid as a probe compound under dark conditions. Invariably, the rates of benzoic acid oxidation with different Fe-laden particles increase with the surface density of Fe until a critical density above which the catalytic activity approaches a plateau, suggesting active Fe species are formed predominantly at low surface loadings. The critical surface density of Fe varies with the mineral substrate as well as the aqueous Fe precursor. Fe impregnated on TiO2 exhibits markedly higher activity than its Al2O3 and SiO2 counterparts. The speciation of interfacial Fe is analyzed with diffuse reflectance UV-vis analysis and interpretation of the data in the context of benzoic oxidation rates suggests that the surface activity of the solids for ·OH generation correlates strongly with the isolated (i.e., mononuclear) Fe species. Therefore, iron dispersed on mineral colloids is a significant form of reactive iron surfaces in the aquatic environment.

  9. Fe-Impregnated Mineral Colloids for Peroxide Activation: Effects of Mineral Substrate and Fe Precursor.

    PubMed

    Li, Yue; Machala, Libor; Yan, Weile

    2016-02-01

    Heterogeneous iron species at the mineral/water interface are important catalysts for the generation of reactive oxygen species at circumneutral pH. One significant pathway leading to the formation of such species arises from deposition of dissolved iron onto mineral colloids due to changes in redox conditions. This study investigates the catalytic properties of Fe impregnated on silica, alumina, and titania nanoparticles (as prototypical mineral colloids). Fe impregnation was carried out by immersing the mineral nanoparticles in dilute Fe(II) or Fe(III) solutions at pH 6 and 3, respectively, in an aerobic environment. The uptake of iron per unit surface area follows the order of nTiO2 > nAl2O3 > nSiO2 for both types of Fe precursors. Impregnation of mineral particles in Fe(II) solutions results in predominantly Fe(III) species due to efficient surface-mediated oxidation. The catalytic activity of the impregnated solids to produce hydroxyl radical (·OH) from H2O2 decomposition was evaluated using benzoic acid as a probe compound under dark conditions. Invariably, the rates of benzoic acid oxidation with different Fe-laden particles increase with the surface density of Fe until a critical density above which the catalytic activity approaches a plateau, suggesting active Fe species are formed predominantly at low surface loadings. The critical surface density of Fe varies with the mineral substrate as well as the aqueous Fe precursor. Fe impregnated on TiO2 exhibits markedly higher activity than its Al2O3 and SiO2 counterparts. The speciation of interfacial Fe is analyzed with diffuse reflectance UV-vis analysis and interpretation of the data in the context of benzoic oxidation rates suggests that the surface activity of the solids for ·OH generation correlates strongly with the isolated (i.e., mononuclear) Fe species. Therefore, iron dispersed on mineral colloids is a significant form of reactive iron surfaces in the aquatic environment. PMID:26713453

  10. Active photonic devices based on colloidal semiconductor nanocrystals and organometallic halide perovskites

    NASA Astrophysics Data System (ADS)

    Suárez Alvarez, Isaac

    2016-10-01

    Semiconductor nanocrystals have arisen as outstanding materials to develop a new generation of optoelectronic devices. Their fabrication under simple and low cost colloidal chemistry methods results in cheap nanostructures able to provide a wide range of optical functionalities. Their attractive optical properties include a high absorption cross section below the band gap, a high quantum yield emission at room temperature, or the capability of tuning the band-gap with the size or the base material. In addition, their solution process nature enables an easy integration on several substrates and photonic structures. As a consequence, these nanoparticles have been extensively proposed to develop several photonic applications, such as detection of light, optical gain, generation of light or sensing. This manuscript reviews the great effort undertaken by the scientific community to construct active photonic devices based on these nanoparticles. The conditions to demonstrate stimulated emission are carefully studied by comparing the dependence of the optical properties of the nanocrystals with their size, shape and composition. In addition, this paper describes the design of different photonic architectures (waveguides and cavities) to enhance the generation of photoluminescence, and hence to reduce the threshold of optical gain. Finally, semiconductor nanocrystals are compared to organometallic halide perovskites, as this novel material has emerged as an alternative to colloidal nanoparticles.

  11. On the achievable performance using variable geometry active secondary suspension systems in commercial vehicles

    NASA Astrophysics Data System (ADS)

    Evers, Willem-Jan; Besselink, Igo; Teerhuis, Arjan; Nijmeijer, Henk

    2011-10-01

    There is a need to further improve driver comfort in commercial vehicles. The variable geometry active suspension offers an interesting option to achieve this in an energy efficient way. However, the optimal control strategy and the overal performance potential remains unclear. The aim of this paper is to quantify the level of performance improvement that can theoretically be obtained by replacing a conventional air sprung cabin suspension design with a variable geometry active suspension. Furthermore, the difference between the use of a linear quadratic (LQ) optimal controller and a classic skyhook controller is investigated. Hereto, an elementary variable geometry actuator model and experimentally validated four degrees of freedom quarter truck model are adopted. The results show that the classic skyhook controller gives a relatively poor performance while a comfort increase of 17-28% can be obtained with the LQ optimal controller, depending on the chosen energy weighting. Furthermore, an additional 75% comfort increase and 77% energy cost reduction can be obtained, with respect to the fixed gain energy optimal controller, using condition-dependent control gains. So, it is concluded that the performance potential using condition-dependent controllers is huge, and that the use of the classic skyhook control strategy should, in general, be avoided when designing active secondary suspensions for commercial vehicles.

  12. Active Shape-Morphing Elastomeric Colloids in Short-Pitch Cholesteric Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Evans, Julian S.; Sun, Yaoran; Senyuk, Bohdan; Keller, Patrick; Pergamenshchik, Victor M.; Lee, Taewoo; Smalyukh, Ivan I.

    2013-05-01

    Active elastomeric liquid crystal particles with initial cylindrical shapes are obtained by means of soft lithography and polymerization in a strong magnetic field. Gold nanocrystals infiltrated into these particles mediate energy transfer from laser light to heat, so that the inherent coupling between the temperature-dependent order and shape allows for dynamic morphing of these particles and well-controlled stable shapes. Continuous changes of particle shapes are followed by their spontaneous realignment and transformations of director structures in the surrounding cholesteric host, as well as locomotion in the case of a nonreciprocal shape morphing. These findings bridge the fields of liquid crystal solids and active colloids, may enable shape-controlled self-assembly of adaptive composites and light-driven micromachines, and can be understood by employing simple symmetry considerations along with electrostatic analogies.

  13. Hyperuniformity in periodically sheared dilute suspensions

    NASA Astrophysics Data System (ADS)

    Wilken, Sam; Guerra, Rodrigo; Pine, David J.; Chaikin, Paul M.

    Periodically sheared dilute, non-Brownian suspensions explore new configurations through collisions in an otherwise reversible flow. Below a critical strain, the particles remain active until they find a configuration with no collisions and reach an absorbing state. Recent simulations by Hexner and Levine have shown that the configuration of particles in the critically absorbing state is hyperuniform. The particle number fluctuations of hyperuniform systems decrease with counting box size more rapidly than random systems (like the same suspension that is not in a critically absorbing state). We built a compact, lightweight uni-axial shear cell where particle coordinates can be measured while shearing with a confocal microscope. We have identified hyperuniform structures with density fluctuation measurements in colloidal suspensions of up to 40% volume fraction in the critically absorbing state with a strain ramp down protocol and find hyperuniform scaling of the density fluctuations.

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

    NASA Astrophysics Data System (ADS)

    Löwen, Hartmut

    2012-11-01

    third conference in a series that began in 2004 [2] and was continued in 2008 [3]. The CODEF meeting series is held in conjunction with the German Dutch Transregional Collaborative Research Centre SFB TR6 with the title Physics of Colloidal Dispersions in External Fields. Papers from scientists working within this network as well as those from further invited contributors are summarized in this issue. They are organized according to the type of field applied, namely: shear flow electric field laser-optical and magnetic field confinement other fields and active particles To summarize the highlights of this special issue as regards shear fields, the response of depletion-induced colloidal clusters to shear is explored in [4]. Soft particles deform under shear and their structural and dynamical behaviour is studied both by experiment [5] and theory [6]. Transient dynamics after switching on shear is described by a joint venture of theory, simulation and experiment in [7]. Colloids provide the fascinating possibility to drag single particles through the suspension, which gives access to microrheology (as opposed to macrorheology, where macroscopic boundaries are moved). Several theoretical aspects of microrheology are discussed in this issue [8-10]. Moreover, a microscopic theory for shear viscosity is presented [11]. Various aspects of colloids in electric fields are also included in this issue. Electrokinetic phenomena for charged suspensions couple flow and electric phenomena in an intricate way and are intensely discussed both by experiment and simulation in contributions [12-14]. Dielectric phenomena are also influenced by electric fields [15]. Electric fields can induce effective dipolar forces between colloids leading to string formation [16]. Finally, binary mixtures in an electric driving field exhibit laning [17]. Simulation [18] and theoretical [19] studies of this nonequilibrium phenomenon are also discussed in this issue. Laser-optical fields can be used to

  15. State observer-based sliding mode control for semi-active hydro-pneumatic suspension

    NASA Astrophysics Data System (ADS)

    Ren, Hongbin; Chen, Sizhong; Zhao, Yuzhuang; Liu, Gang; Yang, Lin

    2016-02-01

    This paper proposes an improved virtual reference model for semi-active suspension to coordinate the vehicle ride comfort and handling stability. The reference model combines the virtues of sky-hook with ground-hook control logic, and the hybrid coefficient is tuned according to the longitudinal and lateral acceleration so as to improve the vehicle stability especially in high-speed condition. Suspension state observer based on unscented Kalman filter is designed. A sliding mode controller (SMC) is developed to track the states of the reference model. The stability of the SMC strategy is proven by means of Lyapunov function taking into account the nonlinear damper characteristics and sprung mass variation of the vehicle. Finally, the performance of the controller is demonstrated under three typical working conditions: the random road excitation, speed bump road and sharp acceleration and braking. The simulation results indicated that, compared with the traditional passive suspension, the proposed control algorithm can offer a better coordination between vehicle ride comfort and handling stability. This approach provides a viable alternative to costlier active suspension control systems for commercial vehicles.

  16. Controlling Defects and Flow in Active Nematic Suspensions

    NASA Astrophysics Data System (ADS)

    Shankar, Suraj; Guillamat Bassedas, Pau; Ignés-Mullol, Jordi; Sagués, Francesc; Marchetti, M. Cristina

    Experiments on active nematics composed of cytoskeletal biopolymers activated by molecular motors have shown that in these systems topological defects drive self-sustained flows and the transition to spatio-temporal chaos. In active nematics, defects become dynamical entities and behave like self-propelled particles. In a freely suspended nematic layer the defect speed is controlled by the activity and the viscosity of the active fluid that is so far unknown. Experiments, however, are carried out on very thin nematic layers at an oil-water interface. Our collaborators in Barcelona have shown that increasing the viscosity of the oil can substantially slow down the defects and increase their number. Considering a model of an active nematic at an oil-water interface, we have calculated the defect speed as a function of oil viscosity and find that theory and experiments agree well when the oil viscosity is changed over four orders of magnitude. Importantly, by combining theory and experiments these results provide a parameter-free estimate for the interfacial viscosity of the active nematic layer, which has never been measured before. This research was supported by the Grants NSF-DMR-1305184 and MINECO FIS 2013-41144P.

  17. Theory of activated-rate processes under shear with application to shear-induced aggregation of colloids.

    PubMed

    Zaccone, Alessio; Wu, Hua; Gentili, Daniele; Morbidelli, Massimo

    2009-11-01

    Using an approximation scheme within the convective diffusion (two-body Smoluchowski) equation framework, we unveil the shear-driven aggregation mechanism at the origin of structure formation in sheared colloidal systems. The theory, verified against numerics and experiments, explains the induction time followed by explosive (irreversible) rise of viscosity observed in charge-stabilized colloidal and protein systems under steady shear. The Arrhenius-type equation with shear derived here, extending Kramers' theory in the presence of shear, clearly demonstrates the important role of shear drive in activated-rate processes as they are encountered in soft condensed matter.

  18. 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.

  19. 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

  20. Integrating an electrically active colloidal quantum dot photodiode with a graphene phototransistor

    PubMed Central

    Nikitskiy, Ivan; Goossens, Stijn; Kufer, Dominik; Lasanta, Tania; Navickaite, Gabriele; Koppens, Frank H. L.; Konstantatos, Gerasimos

    2016-01-01

    The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. Two classes of photodetectors that have been developed are photodiodes and phototransistors, each of them with specific drawbacks. Here we merge both types into a hybrid photodetector device by integrating a colloidal quantum dot photodiode atop a graphene phototransistor. Our hybrid detector overcomes the limitations of a phototransistor in terms of speed, quantum efficiency and linear dynamic range. We report quantum efficiencies in excess of 70%, gain of 105 and linear dynamic range of 110 dB and 3 dB bandwidth of 1.5 kHz. This constitutes a demonstration of an optoelectronically active device integrated directly atop graphene and paves the way towards a generation of flexible highly performing hybrid two-dimensional (2D)/0D optoelectronics. PMID:27311710

  1. Direct visualization of free-volume-triggered activation of β relaxation in colloidal glass

    NASA Astrophysics Data System (ADS)

    Lu, Yunzhuo; Lu, Xing; Qin, Zuoxiang; Shen, Jun

    2016-07-01

    β relaxation, which is predicted by mode coupling theory and involves the localized motions of particles, initiates in a supercooled liquid and continues into glassy state. It correlates essentially with many fundamental properties of amorphous materials. Despite its importance, the underlying mechanisms leading to the β relaxation have remained elusive. As natural heterogeneity, the original distributed free volume has been supposed to be associated with the activation of β relaxation in amorphous solids. However, there has been no direct experimental proof for this hypothesis. Here we used a colloidal glass to directly observe the β relaxation and free-volume distribution. We found a spatial correlation between the β relaxation and free volume. The large free volume regions were observed to possess a low-energy cost of relaxation-induced strain, indicating that the large free volume region presenting a low-energy barrier for structural relaxation benefits the β relaxation.

  2. Direct visualization of free-volume-triggered activation of β relaxation in colloidal glass.

    PubMed

    Lu, Yunzhuo; Lu, Xing; Qin, Zuoxiang; Shen, Jun

    2016-07-01

    β relaxation, which is predicted by mode coupling theory and involves the localized motions of particles, initiates in a supercooled liquid and continues into glassy state. It correlates essentially with many fundamental properties of amorphous materials. Despite its importance, the underlying mechanisms leading to the β relaxation have remained elusive. As natural heterogeneity, the original distributed free volume has been supposed to be associated with the activation of β relaxation in amorphous solids. However, there has been no direct experimental proof for this hypothesis. Here we used a colloidal glass to directly observe the β relaxation and free-volume distribution. We found a spatial correlation between the β relaxation and free volume. The large free volume regions were observed to possess a low-energy cost of relaxation-induced strain, indicating that the large free volume region presenting a low-energy barrier for structural relaxation benefits the β relaxation. PMID:27575178

  3. Integrating an electrically active colloidal quantum dot photodiode with a graphene phototransistor

    NASA Astrophysics Data System (ADS)

    Nikitskiy, Ivan; Goossens, Stijn; Kufer, Dominik; Lasanta, Tania; Navickaite, Gabriele; Koppens, Frank H. L.; Konstantatos, Gerasimos

    2016-06-01

    The realization of low-cost photodetectors with high sensitivity, high quantum efficiency, high gain and fast photoresponse in the visible and short-wave infrared remains one of the challenges in optoelectronics. Two classes of photodetectors that have been developed are photodiodes and phototransistors, each of them with specific drawbacks. Here we merge both types into a hybrid photodetector device by integrating a colloidal quantum dot photodiode atop a graphene phototransistor. Our hybrid detector overcomes the limitations of a phototransistor in terms of speed, quantum efficiency and linear dynamic range. We report quantum efficiencies in excess of 70%, gain of 105 and linear dynamic range of 110 dB and 3 dB bandwidth of 1.5 kHz. This constitutes a demonstration of an optoelectronically active device integrated directly atop graphene and paves the way towards a generation of flexible highly performing hybrid two-dimensional (2D)/0D optoelectronics.

  4. Development and optimization of the activated charcoal suspension composition based on a mixture design approach.

    PubMed

    Ronowicz, Joanna; Kupcewicz, Bogumiła; Pałkowski, Łukasz; Krysiński, Jerzy

    2015-03-01

    In this study, a new drug product containing activated charcoal was designed and developed. The excipient levels in the pharmaceutical formulation were optimized using a mixture design approach. The adsorption power of the activated charcoal suspension was selected as the critical quality attribute influencing the efficacy of medical treatment. Significant prognostic models (p<0.05) were obtained to describe in detail the interrelations between excipient levels and the adsorption power of the formulation. Liquid flavour had a critical impact on the adsorption power of the suspension. Formulations containing the largest amount of liquid flavour showed the lowest adsorption power. Sorbitol was not adsorbed onto activated charcoal so strongly as liquid flavour. A slight increase in the content of carboxymethylcellulose sodium led to a marked decrease in adsorption power. The obtained mathematical models and response surface allowed selection of the optimal composition of excipients in a final drug product.

  5. 41 CFR 105-55.027 - Suspension of collection activity.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... debtor agrees to pay interest on the amount of the debt on which collection will be suspended, and such... interest at a later date. (c)(1) GSA will suspend collection activity during the time required for... waiver or review is frivolous or was made primarily to delay collection. (d) When GSA learns a...

  6. 45 CFR 30.29 - Suspension of collection activity.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... debtor agrees to pay interest on the amount of the debt on which collection will be suspended, and such... interest at a later date. (c) Waiver or review. (1) The Secretary shall suspend collection activity during... frivolous or was made primarily to delay collection. (d) Bankruptcy. Upon learning that a...

  7. Superdiffusion in dispersions of active colloids driven by an external field and their sedimentation equilibrium

    NASA Astrophysics Data System (ADS)

    Chen, Yen-Fu; Wei, Hsien-Hung; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2016-04-01

    The diffusive behaviors of active colloids with run-and-tumble movement are explored by dissipative particle dynamics simulations for self-propelled particles (force dipole) and external field-driven particles (point force). The self-diffusion of tracers (solvent) is investigated as well. The influences of the active force, run time, and concentration associated with active particles are studied. For the system of self-propelled particles, the normal diffusion is observed for both active particles and tracers. The diffusivity of the former is significantly greater than that of the latter. For the system of field-driven particles, the superdiffusion is seen for both active particles and tracers. In contrast, it is found that the anomalous diffusion exponent of the former is slightly less than that of the latter. The anomalous diffusion is caused by the many-body, long-range hydrodynamic interactions. In spite of the superdiffusion, the sedimentation equilibrium of field-driven particles can be acquired and the density profile is still exponentially decayed. The sedimentation length of field-driven particles is always greater than that of self-propelled particles.

  8. Superdiffusion in dispersions of active colloids driven by an external field and their sedimentation equilibrium.

    PubMed

    Chen, Yen-Fu; Wei, Hsien-Hung; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2016-04-01

    The diffusive behaviors of active colloids with run-and-tumble movement are explored by dissipative particle dynamics simulations for self-propelled particles (force dipole) and external field-driven particles (point force). The self-diffusion of tracers (solvent) is investigated as well. The influences of the active force, run time, and concentration associated with active particles are studied. For the system of self-propelled particles, the normal diffusion is observed for both active particles and tracers. The diffusivity of the former is significantly greater than that of the latter. For the system of field-driven particles, the superdiffusion is seen for both active particles and tracers. In contrast, it is found that the anomalous diffusion exponent of the former is slightly less than that of the latter. The anomalous diffusion is caused by the many-body, long-range hydrodynamic interactions. In spite of the superdiffusion, the sedimentation equilibrium of field-driven particles can be acquired and the density profile is still exponentially decayed. The sedimentation length of field-driven particles is always greater than that of self-propelled particles. PMID:27176356

  9. Semi-active H∞ control of high-speed railway vehicle suspension with magnetorheological dampers

    NASA Astrophysics Data System (ADS)

    Zong, Lu-Hang; Gong, Xing-Long; Xuan, Shou-Hu; Guo, Chao-Yang

    2013-05-01

    In this paper, semi-active H∞ control with magnetorheological (MR) dampers for railway vehicle suspension systems to improve the lateral ride quality is investigated. The proposed semi-active controller is composed of a H∞ controller as the system controller and an adaptive neuro-fuzzy inference system (ANFIS) inverse MR damper model as the damper controller. First, a 17-degree-of-freedom model for a full-scale railway vehicle is developed and the random track irregularities are modelled. Then a modified Bouc-Wen model is built to characterise the forward dynamic characteristics of the MR damper and an inverse MR damper model is built with the ANFIS technique. Furthermore, a H∞ controller composed of a yaw motion controller and a rolling pendulum motion (lateral motion+roll motion) controller is established. By integrating the H∞ controller with the ANFIS inverse model, a semi-active H∞ controller for the railway vehicle is finally proposed. Simulation results indicate that the proposed semi-active suspension system possesses better attenuation ability for the vibrations of the car body than the passive suspension system.

  10. Active vibration attenuating seat suspension for an armored helicopter crew seat

    NASA Astrophysics Data System (ADS)

    Sztein, Pablo Javier

    An Active Vibration Attenuating Seat Suspension (AVASS) for an MH-60S helicopter crew seat is designed to protect the occupants from harmful whole-body vibration (WBV). Magnetorheological (MR) suspension units are designed, fabricated and installed in a helicopter crew seat. These MR isolators are built to work in series with existing Variable Load Energy Absorbers (VLEAs), have minimal increase in weight, and maintain crashworthiness for the seat system. Refinements are discussed, based on testing, to minimize friction observed in the system. These refinements include the addition of roller bearings to replace friction bearings in the existing seat. Additionally, semi-active control of the MR dampers is achieved using special purpose built custom electronics integrated into the seat system. Experimental testing shows that an MH-60S retrofitted with AVASS provides up to 70.65% more vibration attenuation than the existing seat configuration as well as up to 81.1% reduction in vibration from the floor.

  11. Semi-active magnetorheological seat suspensions for enhanced crashworthiness and vibration isolation of rotorcraft seats

    NASA Astrophysics Data System (ADS)

    Hiemenz, Gregory J.

    current state-of-the-art rotorcraft seat suspensions which can provide no better than 20% risk of occupant injury. Finally, an MR-based seat suspension designed solely for the purposes of vibration isolation was designed, analyzed, and experimentally demonstrated. MR dampers were integrated into the current crashworthy SH-60 crew seat with minimal weight impact such that the original crashworthy capabilities were maintained. Then, utilizing semi-active control, experimental vibration testing demonstrated that the system reduced vertical cockpit vibrations transmitted to the occupant by 76%. This is a significant advance over current state-of-the-art rotorcraft seats which provide no attenuation of cockpit vibrations.

  12. Non-dimensionalised closed-form parametric analysis of semi-active vehicle suspensions using a quarter-car model

    NASA Astrophysics Data System (ADS)

    Ahmadian, Mehdi; Blanchard, Emmanuel

    2011-02-01

    This article provides a non-dimensionalised closed-form analysis of semi-active vehicle suspensions, using a quarter-car model. The derivation of the closed-form solutions for three indices that can be used for ride comfort, vehicle handling, and stability are presented based on non-dimensionalised suspension parameters. The behaviour of semi-active vehicle suspensions is evaluated using skyhook, groundhook, and hybrid control policies, and compared with passive suspensions. The relationship between vibration isolation, suspension deflection, and road holding is studied, using three performance indices based on the mean square of the sprung mass acceleration, rattle space, and tyre deflection, respectively. The results of the study indicate that the hybrid control policy yields significantly better comfort than a passive suspension, without reducing the road-holding quality or increasing the suspension displacement for typical passenger cars. The results also indicate that for typical passenger cars, the hybrid control policy results in a better compromise between comfort, road holding and suspension travel requirements than both the skyhook and groundhook control methods.

  13. Electrocatalytically Active Nickel-Based Electrode Coatings Formed by Atmospheric and Suspension Plasma Spraying

    NASA Astrophysics Data System (ADS)

    Aghasibeig, M.; Mousavi, M.; Ben Ettouill, F.; Moreau, C.; Wuthrich, R.; Dolatabadi, A.

    2014-01-01

    Ni-based electrode coatings with enhanced surface areas, for hydrogen production, were developed using atmospheric plasma spray (APS) and suspension plasma spray (SPS) processes. The results revealed a larger electrochemical active surface area for the coatings produced by SPS compared to those produced by APS process. SEM micrographs showed that the surface microstructure of the sample with the largest surface area was composed of a large number of small cauliflower-like aggregates with an average diameter of 10 μm.

  14. Using the lead vehicle as preview sensor in convoy vehicle active suspension control

    NASA Astrophysics Data System (ADS)

    Rahman, Mustafizur; Rideout, Geoff

    2012-12-01

    Both ride quality and roadholding of actively suspended vehicles can be improved by sensing the road ahead of the vehicle and using this information in a preview controller. Previous applications have used look-ahead sensors mounted on the front bumper to measure terrain beneath. Such sensors are vulnerable, potentially confused by water, snow, or other soft obstacles and offer a fixed preview time. For convoy vehicle applications, this paper proposes using the overall response of the preceding vehicle(s) to generate preview controller information for follower vehicles. A robust observer is used to estimate the states of a quarter-car vehicle model, from which road profile is estimated and passed on to the follower vehicle(s) to generate a preview function. The preview-active suspension, implemented in discrete time using a shift register approach to improve simulation time, reduces sprung mass acceleration and dynamic tyre deflection peaks by more than 50% and 40%, respectively. Terrain can change from one vehicle to the next if a loose obstacle is dislodged, or if the vehicle paths are sufficiently different so that one vehicle misses a discrete road event. The resulting spurious preview information can give suspension performance worse than that of a passive or conventional active system. In this paper, each vehicle can effectively estimate the road profile based on its own state trajectory. By comparing its own road estimate with the preview information, preview errors can be detected and suspension control quickly switched from preview to conventional active control to preserve performance improvements compared to passive suspensions.

  15. 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)

  16. Active seat suspension for a small vehicle: considerations for control system including observer

    NASA Astrophysics Data System (ADS)

    Katsumata, Hiroyuki; Shiino, Hiroshi; Oshinoya, Yasuo; Ishibashi, Kazuhisa; Ozaki, Koichi; Ogino, Hirohiko

    2007-12-01

    We have examined the improvement of ride quality and the reduction of riding fatigue brought about by the active control of the seat suspension of small vehicles such as one-seater electric automobiles. A small active seat suspension, which is easy to install, was designed and manufactured for one-seater electric automobiles. For the actuator, a maintenance-free voice coil motor used as a direct drive was adopted. For fundamental considerations, we designed a one-degree-of-freedom model for the active seat suspension system. Then, we designed a disturbance cancellation control system that includes the observer for a two-degree-of-freedom model. In an actual driving test, a test road, in which the concavity and convexity of an actual road surface were simulated using hard rubber, was prepared and the control performance of vertical vibrations of the seat surface during driving was examined. As a result, in comparison with the one-degree-of-freedom control system, it was confirmed that the control performance was improved by the two-degree-of-freedom control system that includes the observer.

  17. Tunable long range forces mediated by self-propelled colloidal hard spheres

    NASA Astrophysics Data System (ADS)

    Ni, Ran; Cohen Stuart, Martien; Bolhuis, Peter

    2015-03-01

    Most colloidal interactions can be tuned by changing properties of the medium. Here we show that activating colloidal particles with random self-propulsion can induce giant effective interactions between large objects immersed in such a suspension. Using Brownian dynamics simulations we find that the effective force between two hard walls in a 2D suspension of self-propelled (active) colloidal hard spheres can be tuned from a long range repulsion into a long range attraction by changing the active particle density. At relatively high densities, the active hard spheres can form a dynamic crystalline bridge, which induces a strong oscillating long range dynamic wetting repulsion between the walls. With decreasing density, the dynamic bridge gradually breaks, and an intriguing long range dynamic depletion attraction arises. A similar effect occurs in a quasi-2D suspension of self-propelled colloidal hard spheres by changing the height of the confinement. Our results open up new possibilities to manipulate the motion and assembly of microscopic objects by using active matter.

  18. Off-road motorbike performance analysis using a rear semi-active suspension

    NASA Astrophysics Data System (ADS)

    Lozoya-Santos, Jorge de J.; Cervantes-Muñoz, Damián.; Ramírez Mendoza, Ricardo

    2015-04-01

    The topic of this paper is the analysis of a control system for a semi active rear suspension in an off-road 2-wheel vehicle. Several control methods are studied, as well as the recently proposed Frequency Estimation Based (FEB) algorithm. The test motorcycle dynamics, as well as the passive, semi active, and the algorithm controlled shock absorber models are loaded into BikeSim, a professional two-wheeled vehicle simulation software, and tested in several road conditions. The results show a detailed comparison of the theoretical performance of the different control approaches in a novel environment for semi active dampers.

  19. Muscle Activation during Push-Ups with Different Suspension Training Systems

    PubMed Central

    Calatayud, Joaquin; Borreani, Sebastien; Colado, Juan C.; Martín, Fernando F; Rogers, Michael E.; Behm, David G.; Andersen, Lars L.

    2014-01-01

    The purpose of this study was to analyze upper extremity and core muscle activation when performing push-ups with different suspension devices. Young fit male university students (n = 29) performed 3 push-ups each with 4 different suspension systems. Push-up speed was controlled using a metronome and testing order was randomized. Average amplitude of the electromyographic root mean square of Triceps Brachii, Upper Trapezius, Anterior Deltoid, Clavicular Pectoralis, Rectus Abdominis, Rectus Femoris, and Lumbar Erector Spinae was recorded. Electromyographic signals were normalized to the maximum voluntary isometric contraction (MVIC). Electromyographic data were analyzed with repeated-measures analysis of variance with a Bonferroni post hoc. Based upon global arithmetic mean of all muscles analyzed, the suspended push-up with a pulley system provided the greatest activity (37.76% of MVIC; p < 0.001). Individually, the suspended push-up with a pulley system also provided the greatest triceps brachii, upper trapezius, rectus femoris and erector lumbar spinae muscle activation. In contrast, more stable conditions seem more appropriate for pectoralis major and anterior deltoid muscles. Independent of the type of design, all suspension systems were especially effective training tools for reaching high levels of rectus abdominis activation. Key Points Compared with standard push-ups on the floor, suspended push-ups increase core muscle activation. A one-anchor system with a pulley is the best option to increase TRICEP, TRAPS, LUMB and FEM muscle activity. More stable conditions such as the standard push-up or a parallel band system provide greater increases in DELT and PEC muscle activation. A suspended push-up is an effective method to achieve high muscle activity levels in the ABS. PMID:25177174

  20. Phase separation and rotor self-assembly in active particle suspensions

    PubMed Central

    Schwarz-Linek, J.; Valeriani, C.; Cacciuto, A.; Cates, M. E.; Marenduzzo, D.; Morozov, A. N.; Poon, W. C. K.

    2012-01-01

    Adding a nonadsorbing polymer to passive colloids induces an attraction between the particles via the “depletion” mechanism. High enough polymer concentrations lead to phase separation. We combine experiments, theory, and simulations to demonstrate that using active colloids (such as motile bacteria) dramatically changes the physics of such mixtures. First, significantly stronger interparticle attraction is needed to cause phase separation. Secondly, the finite size aggregates formed at lower interparticle attraction show unidirectional rotation. These micro-rotors demonstrate the self-assembly of functional structures using active particles. The angular speed of the rotating clusters scales approximately as the inverse of their size, which may be understood theoretically by assuming that the torques exerted by the outermost bacteria in a cluster add up randomly. Our simulations suggest that both the suppression of phase separation and the self-assembly of rotors are generic features of aggregating swimmers and should therefore occur in a variety of biological and synthetic active particle systems. PMID:22392986

  1. Performance analysis of a semi-active railway vehicle suspension featuring MR dampers

    NASA Astrophysics Data System (ADS)

    Kim, Hwan-Choong; Choi, Seung-Bok; Lee, Gyu-Seop; An, Chae-Hun; You, Won-Hee

    2014-03-01

    This paper presents performance analysis of semi-active railway vehicle suspension system using MR damper. In order to achieve this goal, a mathematical dynamic model of railway vehicle is derived by integrating car body, bogie frame and wheel-set which can be able to represent lateral, yaw and roll motion. Based on this model, the dynamic range of MR damper at the railway secondary suspension system and design parameters of MR damper are calculated. Subsequently, control performances of railway vehicle including car body lateral motion and acceleration of MR damper are evaluated through computer simulations. Then, the MR damper is manufactured to be retrofitted with the real railway vehicle and its characteristics are experimentally measured. Experimental performance of MR damper is assessed using test rig which is composed of a car body and two bogies.

  2. Active vibration control for nonlinear vehicle suspension with actuator delay via I/O feedback linearization

    NASA Astrophysics Data System (ADS)

    Lei, Jing; Jiang, Zuo; Li, Ya-Li; Li, Wu-Xin

    2014-10-01

    The problem of nonlinear vibration control for active vehicle suspension systems with actuator delay is considered. Through feedback linearization, the open-loop nonlinearity is eliminated by the feedback nonlinear term. Based on the finite spectrum assignment, the quarter-car suspension system with actuator delay is converted into an equivalent delay-free one. The nonlinear control includes a linear feedback term, a feedforward compensator, and a control memory term, which can be derived from a Riccati equation and a Sylvester equation, so that the effects produced by the road disturbances and the actuator delay are compensated, respectively. A predictor is designed to implement the predictive state in the designed control. Moreover, a reduced-order observer is constructed to solve its physical unrealisability problem. The stability proofs for the zero dynamics and the closed-loop system are provided. Numerical simulations illustrate the effectiveness and the simplicity of the designed control.

  3. Robust fault-tolerant H∞ control of active suspension systems with finite-frequency constraint

    NASA Astrophysics Data System (ADS)

    Wang, Rongrong; Jing, Hui; Karimi, Hamid Reza; Chen, Nan

    2015-10-01

    In this paper, the robust fault-tolerant (FT) H∞ control problem of active suspension systems with finite-frequency constraint is investigated. A full-car model is employed in the controller design such that the heave, pitch and roll motions can be simultaneously controlled. Both the actuator faults and external disturbances are considered in the controller synthesis. As the human body is more sensitive to the vertical vibration in 4-8 Hz, robust H∞ control with this finite-frequency constraint is designed. Other performances such as suspension deflection and actuator saturation are also considered. As some of the states such as the sprung mass pitch and roll angles are hard to measure, a robust H∞ dynamic output-feedback controller with fault tolerant ability is proposed. Simulation results show the performance of the proposed controller.

  4. Skyhook-based semi-active control of full-vehicle suspension with magneto-rheological dampers

    NASA Astrophysics Data System (ADS)

    Zhang, Hailong; Wang, Enrong; Min, Fuhong; Subash, Rakheja; Su, Chunyi

    2013-05-01

    The control study of vehicle semi-active suspension with magneto-rheological (MR) dampers has been attracted much attention internationally. However, a simple, real time and easy implementing semi-active controller has not been proposed for the MR full-vehicle suspension system, and a systematic analysis method has not been established for evaluating the multi-objective suspension performances of MR full-vehicle vertical, pitch and roll motions. For this purpose, according to the 7-degree of freedom (DOF) full-vehicle dynamic system, a generalized 7-DOF MR and passive full-vehicle dynamic model is set up by employing the modified Bouc-wen hysteretic force-velocity ( F-v) model of the MR damper. A semi-active controller is synthesized to realize independent control of the four MR quarter-vehicle sub-suspension systems in the full-vehicle, which is on the basis of the proposed modified skyhook damping scheme of MR quarter-vehicle sub-suspension system. The proposed controller can greatly simplify the controller design complexity of MR full-vehicle suspension and has merits of easy implementation in real application, wherein only absolute velocities of sprung and unsprung masses with reference to the road surface are required to measure in real time when the vehicle is moving. Furthermore, a systematic analysis method is established for evaluating the vertical, pitch and roll motion properties of both MR and passive full-vehicle suspensions in a more realistic road excitation manner, in which the harmonic, rounded pulse and real road measured random signals with delay time are employed as different road excitations inserted on the front and rear two wheels, by considering the distance between front and rear wheels in full-vehicle. The above excitations with different amplitudes are further employed as the road excitations inserted on left and right two wheels for evaluating the roll motion property. The multi-objective suspension performances of ride comfort and

  5. 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.

  6. Synthesis, characterization and antibacterial activity of colloidal NiO nanoparticles.

    PubMed

    Khashan, Khawlah Salah; Sulaiman, Ghassan Mohammad; Abdul Ameer, Farah Abdul Kareem; Napolitano, Giuliana

    2016-03-01

    The Colloidal solutions of nickel oxide (NiO) nanoparticles synthesized via Nd-Yag pulse ablation of nickel immersed in H2O were studied. The created nanoparticles were characterized by UV-VIS absorption, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). FTIR characterization confirms the formation of nickel oxide nanoparticles. The optical band gap values, determined by UV-VIS absorption measurements, are found to be (4.5 ev). TEM shows that nanoparticles size ranged from 2-21 nm. The antimicrobial activity was carried out against pseudomonas aurogenisa, Escherichia coli (gram negative bacteria), Staphylococcus aureus and Streptococcus pneumonia (gram positive bacteria). The NiO nanoparticles showed inhibitory activity in both strains of bacteria with best selectivity against gram-positive bacteria. The findings of present study indicate that NiO nanoparticles could potentiate the permeability of bacterial cell wall, and remarkably increase the accumulation of amoxicillin in bacteria, suggesting that NiO nanoparticles together with amoxicillin would facilitate the synergistic impact on growth inhibition of bacterial strains. PMID:27087098

  7. Synthesis, characterization and antibacterial activity of colloidal NiO nanoparticles.

    PubMed

    Khashan, Khawlah Salah; Sulaiman, Ghassan Mohammad; Abdul Ameer, Farah Abdul Kareem; Napolitano, Giuliana

    2016-03-01

    The Colloidal solutions of nickel oxide (NiO) nanoparticles synthesized via Nd-Yag pulse ablation of nickel immersed in H2O were studied. The created nanoparticles were characterized by UV-VIS absorption, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). FTIR characterization confirms the formation of nickel oxide nanoparticles. The optical band gap values, determined by UV-VIS absorption measurements, are found to be (4.5 ev). TEM shows that nanoparticles size ranged from 2-21 nm. The antimicrobial activity was carried out against pseudomonas aurogenisa, Escherichia coli (gram negative bacteria), Staphylococcus aureus and Streptococcus pneumonia (gram positive bacteria). The NiO nanoparticles showed inhibitory activity in both strains of bacteria with best selectivity against gram-positive bacteria. The findings of present study indicate that NiO nanoparticles could potentiate the permeability of bacterial cell wall, and remarkably increase the accumulation of amoxicillin in bacteria, suggesting that NiO nanoparticles together with amoxicillin would facilitate the synergistic impact on growth inhibition of bacterial strains.

  8. Engineering of Novel Biocolloid Suspensions

    NASA Technical Reports Server (NTRS)

    Hammer, D. A.; Rodges, S.; Hiddessen, A.; Weitz, D. A.

    1999-01-01

    Colloidal suspensions are materials with a variety of uses from cleaners and lubricants to food, cosmetics, and coatings. In addition, they can be used as a tool for testing the fundamental tenets of statistical physics. Colloidal suspensions can be synthesized from a wide variety of materials, and in the form of monodisperse particles, which can self-assemble into highly ordered colloidal crystal structures. As such they can also be used as templates for the construction of highly ordered materials. Materials design of colloids has, to date, relied on entropic self-assembly, where crystals form as result of lower free energy due to a transition to order. Here, our goal is to develop a completely new method for materials fabrication using colloidal precursors, in which the self-assembly of the ordered colloidal structures is driven by a highly controllable, attractive interaction. This will greatly increase the range of potential structures that can be fabricated with colloidal particles. In this work, we demonstrate that colloidal suspensions can be crosslinked through highly specific biological crosslinking reactions. In particular, the molecules we use are protein-carbohydrate interactions derived from the immune system. This different driving force for self-assembly will yield different and novel suspensions structures. Because the biological interactions are heterotypic (A binding to B), this chemical system can be used to make binary alloys in which the two colloid subpopulations vary in some property - size, density, volume fraction, magnetic susceptibility, etc. An additional feature of these molecules which is unique - even within the realm of biological recognition - is that the molecules bind reversibly on reasonable time-scales, which will enable the suspension to sample different configurations, and allow us to manipulate and measure the size of the suspension dynamically. Because of the wide variety of structures that can be made from these novel

  9. Chain Dynamics in Magnetorheological Suspensions

    NASA Technical Reports Server (NTRS)

    Gast, A. P.; Furst, E. M.

    1999-01-01

    Magnetorheological (MR) suspensions are composed of colloidal particles which acquire dipole moments when subjected to an external magnetic field. At sufficient field strengths and concentrations, the dipolar particles rapidly aggregate to form long chains. Subsequent lateral cross-linking of the dipolar chains is responsible for a rapid liquid-to-solid-like rheological transition. The unique, magnetically-activated rheological properties of MR suspensions make them ideal for interfacing mechanical systems to electronic controls. Additionally, the ability to experimentally probe colloidal suspensions interacting through tunable anisotropic potentials is of fundamental interest. Our current experimental work has focused on understanding the fluctuations of dipolar chains. It has been proposed by Halsey and Toor (HT) that the strong Landau-Peierls thermal fluctuations of dipolar chains could be responsible for long-range attractions between chains. Such interactions will govern the long-time relaxation of MR suspensions. We have synthesized monodisperse neutrally buoyant MR suspensions by density matching stabilized ferrofluid emulsion droplets with D2O. This allows us to probe the dynamics of the dipolar chains using light scattering without gravitational, interfacial, and polydispersity effects to resolve the short-wavelength dynamics of the dipolar chains. We used diffusing wave spectroscopy to measure these dynamics. The particle displacements at short times that show an independence to the field strength, but at long times exhibit a constrained, sub-diffusive motion that slows as the dipole strength is increased. The experiments are in good qualitative agreement with Brownian dynamics simulations of dipolar chains. Although there have been several important and detailed studies of the structure and interactions in MR suspensions, there has not been conclusive evidence that supports or contradicts the HT model prediction that long-range interactions exist between

  10. Optimization and static output-feedback control for half-car active suspensions with constrained information

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Chen, Changzheng; Yu, Shenbo

    2016-09-01

    In this paper, the static output-feedback control problem of active suspension systems with information structure constraints is investigated. In order to simultaneously improve the ride comfort and stability, a half car model is used. Other constraints such as suspension deflection, actuator saturation, and controller constrained information are also considered. A novel static output-feedback design method based on the variable substitution is employed in the controller design. A single-step linear matrix inequality (LMI) optimization problem is solved to derive the initial feasible solution with a sparsity constraint. The initial infeasibility issue of the static output-feedback is resolved by using state-feedback information. Specifically, an optimization algorithm is proposed to search for less conservative results based on the feasible controller gain matrix. Finally, the validity of the designed controller for different road profiles is illustrated through numerical examples. The simulation results indicate that the optimized static output-feedback controller can achieve better suspension performances when compared with the feasible static output-feedback controller.

  11. Multi-objective H ∞ control for vehicle active suspension systems with random actuator delay

    NASA Astrophysics Data System (ADS)

    Li, Hongyi; Liu, Honghai; Hand, Steve; Hilton, Chris

    2012-12-01

    This article is concerned with the problem of multi-objective H ∞ control for vehicle active suspension systems with random actuator delay, which can be represented by signal probability distribution. First, the dynamical equations of a quarter-car suspension model are established for the control design purpose. Secondly, when taking into account vehicle performance requirements, namely, ride comfort, suspension deflection and the probability distributed actuator delay, we present the corresponding dynamic system, which will be transformed to the stochastic system for the problem of multi-objective H ∞ controller design. Third, based on the stochastic stability theory, the state feedback controller is proposed to render that the closed-loop system is exponentially stable in mean-square while simultaneously satisfying H ∞ performance and the output constraint requirement. The presented condition is expressed in the form of convex optimisation problems so that it can be efficiently solved via standard numerical software. Finally, a practical design example is given to demonstrate the effectiveness of the proposed method.

  12. 234U /238U and 230Th /234U activity ratios in the colloidal phases of aquifers in lateritic weathered zones

    NASA Astrophysics Data System (ADS)

    Short, Stephen A.; Lowson, Richard T.; Ellis, John

    1988-11-01

    A procedure was developed for comparing solute and colloid phases of groundwaters in contact with uranium ore bodies at Nabarlek and Koongarra in the Alligator Rivers region, Northern Territory, Australia. Single-pass ultrafiltration of large volumes with cut-offs of 18 nm and 1 μm was used. Colloids were composed of Fe and Si species with sorbed U and U daughters. Uranium isotopes were mostly present as soluble species. Thorium was significantly associated with the colloids. The 234U /238U activity ratios (ARs) were similar in solute and colloid phases close to the ore bodies but further down-gradient colloids were generally more depleted of 234U than the solute. The 230Th /234U ARs rose from very low values for both solute and colloid phases close to the ore bodies through several orders of magnitude to much higher values further down-gradient. Colloid 230Th /234U ARs were always significantly greater than solute ARs. Results were consistent with a systematic leaching of U from colloids going down-gradient and very little mobilization of ore-body 230Th relative to U. Ubiquitous complexed 232Th appeared to suppress the solubility of 230Th.

  13. Synthesis, photocatalytic activity, and photogenerated hydroxyl radicals of monodisperse colloidal ZnO nanospheres

    NASA Astrophysics Data System (ADS)

    Yang, Chong; Li, Qingsong; Tang, Limei; Xin, Kun; Bai, Ailing; Yu, Yingmin

    2015-12-01

    In the present study, monodisperse colloidal zinc oxide (ZnO) nanospheres were successfully synthesized via a newly developed two-stage solution method followed by facile calcination at various temperatures. The effects of calcination temperature on the structure, morphology, and optical properties as well as the photocatalytic activity of the as-made ZnO samples were investigated systematically by Fourier transform infrared spectrometry, X-ray diffraction, field emission scanning electron microscopy, nitrogen adsorption/desorption isotherms, diffuse reflectance UV-visible spectroscopy (DRS), photoluminescence, and related photocatalytic activity tests. The thermal decomposition was analyzed by thermogravimetric analysis. The crystallinity was found to gradually increase with increasing calcination temperature, whereas the decrease in the Brunauer-Emmett-Teller specific surface area of the samples with calcination may be ascribed to the increased particle size. The DRS results provided clear evidence for the decrease in band gap energy of ZnO samples with an increase in calcination temperature. The photoluminescence spectra demonstrated the calcination-dependent emission features, especially the UV emission intensity. In particular, the ZnO product calcined at 400 °C exhibited the highest photocatalytic activity, degrading methylene blue by almost 99.1% in 70 min, which is ascribed to the large specific surface area and pore volume, high electron-hole pair separation efficient, and great redox potential of the obtained ZnO nanoparticles. In addition, the production of photogenerated hydroxyl radicals (•OH) was consistent with the methylene blue degradation efficiency over the as-made ZnO nanoparticles. Using isopropanol as a hydroxyl radical scavenger, •OH was determined to be the main active oxygen species in the photocatalytic process. A possible mechanism of photodegradation under UV light irradiation also is proposed.

  14. Plasmon-mediated large enhancement of magneto-optical activity in colloidal magnetic metals

    NASA Astrophysics Data System (ADS)

    Herranz, Gervasi; Vlasin, Ondrej; Pascu, Oana; Roig, Anna

    2014-03-01

    Magnetic properties may undergo dramatic changes at the nanoscale that, eventually, can be exploited as a basis for enhanced functionality. This is the case that we present here, in which we analyzed the rotation and ellipticity that magnetic nanoparticles exerted on the polarization of light. More specifically, we observed an outstanding increase of the magneto-optical activity at the frequencies of the plasmon resonances of the metallic magnetic nanoparticles, yielding a dramatic increase of the Verdet constant. Furthermore, we have established an innovative theoretical framework in excellent quantitative agreement with the experimental data, endowing our model with a powerful predictive character for the interaction of polarized light with magnetic nanoclusters embedded in dielectric hosts. The relevance of our results goes well beyond the particular case of colloidal metals, as other systems such as metal inclusions in polymers or glasses containing small magnetic clusters can be as well considered. In addition, the observed large Verdet constants allow envisioning the exploitation of light polarization, instead as the commonly used reflectance, as a probe for plasmon-sensing devices. Our results provide new routes for plasmon-based biological and chemical detection.

  15. Optimisation of active suspension control inputs for improved vehicle handling performance

    NASA Astrophysics Data System (ADS)

    Čorić, Mirko; Deur, Joško; Kasać, Josip; Tseng, H. Eric; Hrovat, Davor

    2016-11-01

    Active suspension is commonly considered under the framework of vertical vehicle dynamics control aimed at improvements in ride comfort. This paper uses a collocation-type control variable optimisation tool to investigate to which extent the fully active suspension (FAS) application can be broaden to the task of vehicle handling/cornering control. The optimisation approach is firstly applied to solely FAS actuator configurations and three types of double lane-change manoeuvres. The obtained optimisation results are used to gain insights into different control mechanisms that are used by FAS to improve the handling performance in terms of path following error reduction. For the same manoeuvres the FAS performance is compared with the performance of different active steering and active differential actuators. The optimisation study is finally extended to combined FAS and active front- and/or rear-steering configurations to investigate if they can use their complementary control authorities (over the vertical and lateral vehicle dynamics, respectively) to further improve the handling performance.

  16. Antimicrobial activity of copper surfaces against suspensions of Salmonella enterica and Campylobacter jejuni

    PubMed Central

    Faúndez, Gustavo; Troncoso, Miriam; Navarrete, Paola; Figueroa, Guillermo

    2004-01-01

    Background Salmonella enterica and Campylobacter jejuni are amongst the more prevalent bacterial pathogens that cause foodborne diseases. These microorganisms are common contaminants of poultry and poultry products. This study was aimed to evaluate the antibacterial activity of metallic copper surfaces on these important enteropathogens, and to determine the potential acquisition of copper by food exposed to this metal. Results The antibacterial activity of copper surfaces was evaluated overlying them with suspensions of 106 CFU/ml of S. enterica and C. jejuni. Bacterial counts obtained after 0, 2, 4 and 8 hours at 10°C and 25°C were compared with those obtained in stainless steel and a synthetic polymer as control surfaces. The results showed that when these enteropathogens were kept in contact with copper a significant antibacterial activity was noted, on the contrary when the same load of pathogen suspensions were tested over the control surfaces it was found that the bacterial counts remained unchanged or even increased with time. The potential acquisition of copper by food exposed to this surface was also evaluated. Meat exposed for one hour to a copper surface adsorbed residual copper in a time dependant manner. Conclusions These results shows that metallic copper surfaces have an antibacterial activity against S. enterica and C. jejuni and suggest its potential application as an inhibitory agent in the various stages of the food processing operations. PMID:15119960

  17. Tunable long range forces mediated by self-propelled colloidal hard spheres.

    PubMed

    Ni, Ran; Cohen Stuart, Martien A; Bolhuis, Peter G

    2015-01-01

    Using Brownian dynamics simulations, we systematically study the effective interaction between two parallel hard walls in a 2D suspension of self-propelled (active) colloidal hard spheres, and we find that the effective force between two hard walls can be tuned from a long range repulsion into a long range attraction by changing the density of active particles. At relatively high densities, the active hard spheres can form a dynamic crystalline bridge, which induces a strong oscillating long range dynamic wetting repulsion between the walls. With decreasing density, the dynamic bridge gradually breaks, and an intriguing long range dynamic depletion attraction arises. A similar effect occurs in a quasi-2D suspension of self-propelled colloidal hard spheres by changing the height of the confinement. Our results open up new possibilities to manipulate the motion and assembly of microscopic objects by using active matter. PMID:25615510

  18. Tunable Long Range Forces Mediated by Self-Propelled Colloidal Hard Spheres

    NASA Astrophysics Data System (ADS)

    Ni, Ran; Cohen Stuart, Martien A.; Bolhuis, Peter G.

    2015-01-01

    Using Brownian dynamics simulations, we systematically study the effective interaction between two parallel hard walls in a 2D suspension of self-propelled (active) colloidal hard spheres, and we find that the effective force between two hard walls can be tuned from a long range repulsion into a long range attraction by changing the density of active particles. At relatively high densities, the active hard spheres can form a dynamic crystalline bridge, which induces a strong oscillating long range dynamic wetting repulsion between the walls. With decreasing density, the dynamic bridge gradually breaks, and an intriguing long range dynamic depletion attraction arises. A similar effect occurs in a quasi-2D suspension of self-propelled colloidal hard spheres by changing the height of the confinement. Our results open up new possibilities to manipulate the motion and assembly of microscopic objects by using active matter.

  19. Formation of Aqueous Suspensions of Fullerenes

    EPA Science Inventory

    Colloidal suspensions of C60, C70 and a derivative of C60, PCBM ([6,6]-Phenyl C61-butyric acid methyl ester) were produced by extended mixing in water. We examined the contribution of background solution chemistry (pH, ionic strength) on the formation kinetics of colloidal suspe...

  20. Active suspension design for a Large Space Structure ground test facility

    NASA Technical Reports Server (NTRS)

    Lange, Thomas J. H.; Schlegel, Clemens

    1993-01-01

    The expected future high performance requirements for Large Space Structures (LSS) enforce technology innovations such as active vibration damping techniques e.g., by means of structure sensors and actuators. The implementation of new technologies like that requires an interactive and integrated structural and control design with an increased effort in hardware validation by ground testing. During the technology development phase generic system tests will be most important covering verification and validation aspects up to the preparation and definition of relevant space experiments. For many applications using advanced designs it is deemed necessary to improve existing testing technology by further reducing disturbances and gravity coupling effects while maintaining high performance reliability. A key issue in this context is the improvement of suspension techniques. The ideal ground test facility satisfying these requirements completely will never be found. The highest degree of reliability will always be obtained by passive suspension methods taking into account severe performance limitations such as non-zero rigid body modes, restriction of degrees of freedom of motion and frequency response limitations. Passive compensation mechanisms, e.g., zero-spring-rate mechanisms, either require large moving masses or they are limited with respect to low-frequency performance by friction, stiction or other non-linear effects. With active suspensions these limitations can be removed to a large extent thereby increasing the range of applications. Despite an additional complexity which is associated with a potential risk in reliability their development is considered promising due to the amazing improvement of real-time control technology which is still continuing.

  1. Direct activation of gelatinase B (MMP-9) by hay dust suspension and different components of organic dust.

    PubMed

    Simonen-Jokinen, Terhi; Maisi, Päivi; Tervahartiala, Taina; McGorum, Bruce; Pirie, Scott; Sorsa, Timo

    2006-02-15

    Matrix metalloproteinases (MMPs) are involved in tissue destruction in allergic airway diseases. We studied the ability of various allergenic substances to directly activate recombinant 92kDa proMMP-9. The substances included hay dust suspension (HDS) and its components (supernatant, particulate matter and wash fluid of particulate matter), storage mite extract and two Aspergillus fumigatus extracts. The allergen suspensions were incubated in vitro with proMMP-9. After incubation the conversion of proMMP-9 to 10kDa lower active forms were studied using gelatin zymography and Western immunoblot quantified by computerized densitometry. All studied allergens except HDS significantly and efficiently activated proMMP-9 as compared to a negative control. At the concentrations employed, the most potent activators were A. fumigatus extracts and mite suspension. The greater potency of mite and fungi as proMMP-9 activators suggests that these allergens may be more damaging to airways even at low concentrations. PMID:16181685

  2. Hydrodynamic length-scale selection in microswimmer suspensions

    NASA Astrophysics Data System (ADS)

    Heidenreich, Sebastian; Dunkel, Jörn; Klapp, Sabine H. L.; Bär, Markus

    2016-08-01

    A universal characteristic of mesoscale turbulence in active suspensions is the emergence of a typical vortex length scale, distinctly different from the scale invariance of turbulent high-Reynolds number flows. Collective length-scale selection has been observed in bacterial fluids, endothelial tissue, and active colloids, yet the physical origins of this phenomenon remain elusive. Here, we systematically derive an effective fourth-order field theory from a generic microscopic model that allows us to predict the typical vortex size in microswimmer suspensions. Building on a self-consistent closure condition, the derivation shows that the vortex length scale is determined by the competition between local alignment forces, rotational diffusion, and intermediate-range hydrodynamic interactions. Vortex structures found in simulations of the theory agree with recent measurements in Bacillus subtilis suspensions. Moreover, our approach yields an effective viscosity enhancement (reduction), as reported experimentally for puller (pusher) microorganisms.

  3. Hydrodynamic length-scale selection in microswimmer suspensions.

    PubMed

    Heidenreich, Sebastian; Dunkel, Jörn; Klapp, Sabine H L; Bär, Markus

    2016-08-01

    A universal characteristic of mesoscale turbulence in active suspensions is the emergence of a typical vortex length scale, distinctly different from the scale invariance of turbulent high-Reynolds number flows. Collective length-scale selection has been observed in bacterial fluids, endothelial tissue, and active colloids, yet the physical origins of this phenomenon remain elusive. Here, we systematically derive an effective fourth-order field theory from a generic microscopic model that allows us to predict the typical vortex size in microswimmer suspensions. Building on a self-consistent closure condition, the derivation shows that the vortex length scale is determined by the competition between local alignment forces, rotational diffusion, and intermediate-range hydrodynamic interactions. Vortex structures found in simulations of the theory agree with recent measurements in Bacillus subtilis suspensions. Moreover, our approach yields an effective viscosity enhancement (reduction), as reported experimentally for puller (pusher) microorganisms. PMID:27627229

  4. Optimization of LiFePO4 Nanoparticle Suspensions with Polyethyleneimine for Aqueous Processing

    SciTech Connect

    Li, Jianlin; Armstrong, Beth L; Kiggans, Jim; Daniel, Claus; Wood III, David L

    2012-01-01

    Addition of dispersants to aqueous based lithium-ion battery electrode formulations containing LiFePO{sub 4} is critical to obtaining a stable suspension. The resulting colloidal suspensions enable dramatically improved coating deposition when processing electrodes. This research examines the colloidal chemistry modifications based on polyethyleneimine (PEI) addition and dispersion characterization required to produce high quality electrode formulations and coatings for LiFePO{sub 4} active cathode material. The isoelectric point, a key parameter in characterizing colloidal dispersion stability, of LiFePO{sub 4} and super P C45 were determined to be pH = 4.3 and 3.4, respectively. PEI, a cationic surfactant, was found to be an effective dispersant. It is demonstrated that 1.0 wt % and 0.5 wt % PEI were required to stabilize the LiFePO{sub 4} and super P C45 suspension, respectively. LiFePO{sub 4} cathode suspensions with 1.5 wt % PEI demonstrated the best dispersibility of all components, as evidenced by viscosity and agglomerate size of the suspensions and elemental distribution within dry cathodes. The addition of PEI significantly improved the LiFePO{sub 4} performance.

  5. Transport phenomena and dynamics of externally and self-propelled colloids in confined geometry

    NASA Astrophysics Data System (ADS)

    Kreuter, C.; Siems, U.; Nielaba, P.; Leiderer, P.; Erbe, A.

    2013-11-01

    Over the last decades, colloidal suspensions have been proven as powerful model systems to reveal fundamental questions in soft matter or general physics. In this work, we will focus on the influence of interaction and confinement to the mobility of colloidal particles as well as to the transport behavior of particles over obstacles placed in a micro-channel. Both experiments are supported with Brownian dynamics simulations to complete the experimental work. The paper concludes with the investigation of the behavior of single active swimmers close to a wall.

  6. Fuzzy chaos control for vehicle lateral dynamics based on active suspension system

    NASA Astrophysics Data System (ADS)

    Huang, Chen; Chen, Long; Jiang, Haobin; Yuan, Chaochun; Xia, Tian

    2014-07-01

    The existing research of the active suspension system (ASS) mainly focuses on the different evaluation indexes and control strategies. Among the different components, the nonlinear characteristics of practical systems and control are usually not considered for vehicle lateral dynamics. But the vehicle model has some shortages on tyre model with side-slip angle, road adhesion coefficient, vertical load and velocity. In this paper, the nonlinear dynamic model of lateral system is considered and also the adaptive neural network of tire is introduced. By nonlinear analysis methods, such as the bifurcation diagram and Lyapunov exponent, it has shown that the lateral dynamics exhibits complicated motions with the forward speed. Then, a fuzzy control method is applied to the lateral system aiming to convert chaos into periodic motion using the linear-state feedback of an available lateral force with changing tire load. Finally, the rapid control prototyping is built to conduct the real vehicle test. By comparison of time response diagram, phase portraits and Lyapunov exponents at different work conditions, the results on step input and S-shaped road indicate that the slip angle and yaw velocity of lateral dynamics enter into stable domain and the results of test are consistent to the simulation and verified the correctness of simulation. And the Lyapunov exponents of the closed-loop system are becoming from positive to negative. This research proposes a fuzzy control method which has sufficient suppress chaotic motions as an effective active suspension system.

  7. Multiphysics modelling of multibody systems: application to car semi-active suspensions

    NASA Astrophysics Data System (ADS)

    Docquier, N.; Poncelet, A.; Delannoy, M.; Fisette, P.

    2010-12-01

    The goal of the present article is to analyse the performances of a modern vehicle equipped with a novel suspension system linking front, rear, right and left cylinders via a semi-active hydraulic circuit, developed by the Tenneco Automotive company. In addition to improving the vehicle's vertical performances (in terms of comfort), both the stiff roll motion of the carbody and the soft wrap motion of the rear/front wheel-axle units can be obtained and tuned via eight electrovalves. The proposed system avoids the use of classical anti-roll bars, which would be incompatible with the wrap performance. A major problem of the project is to produce a realistic and efficient 3D multibody dynamic model of an Audi A6 coupled, at the equational level, with an hydraulic model of the suspension including cylinders, accumulators, valve characteristics, oil compressibility and pipe dynamics. As regards the hydraulic submodel, a particular attention is paid to assemble resistive components properly without resorting to the use of artificial volumes, as proposed by some software dealing with the dynamics of hydraulic systems. According to Tenneco Automotive requirements, this model must be produced in a Matlab/Simulink form, in particular for control purposes. Thanks to the symbolic approach underlying our multibody program; a unified hybrid model can be obtained as a unique plant dynamic block to be real-time integrated in the Simulink environment on a standard computer. Simulation results highlight the advantages of this new suspension system, in particular regarding the behaviour of the car which can remain stiff in roll for curve negotiation, while maintaining a soft wrap behaviour on uneven surfaces.

  8. Nanostructured colloidal crystals from forced hydrolysis methods.

    PubMed

    Otal, Eugenio H; Granada, Mara; Troiani, Horacio E; Cánepa, Horacio; Walsöe de Reca, Noemí E

    2009-08-18

    In this work, an original route for ZnO nanostructured spherical colloids and their assembly into colloidal crystals are presented. The temporal evolution of crystal size and shape was followed by X-ray diffraction and the colloids size distribution by scanning electron microscopy. These spherical colloids showed a change in their size dispersion with aging time. Early stage suspensions, with a narrow size distribution, were settled to the bottom and dried with a slow evaporation rate to obtain colloidal crystals. This original route provides a new material for future applications in opalline photonic crystals, with a dielectric constant higher than that of classical materials (silica and latex). Moreover, this route means an improvement of previously reported data from the literature since it involves a one-pot strategy and room-temperature colloid assembly.

  9. Dynamic DNA Interactions with Functionalized Colloids

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; Zhu, Yingxi Elaine

    2009-03-01

    Many biomedical processes, such as protein adsorption, DNA hybridization and enzyme reactivity, are intimately related to their interactions with surfaces and complex ionic environments, yet the details of biomacromolecular interaction remain insufficiently understood. In this work, we use confocal laser scanning microscopy to examine the interaction between DNA molecules and functionalized colloidal particles in aqueous suspension. We observe an intriguing attractive interaction between DNAs and carboxyl-functionalized silica particles of varied sizes from 50 nm to 3 um, resulting in complex DNA-colloid aggregation with a strong dependence on DNA/colloid size ration and ionic strength. As colloidal size becomes larger than DNA dimensions, colloidal doublets and triplets with adsorbed DNAs are observed at high DNA concentration and ionic strength. The intriguing DNA-colloid complex structures are further confirmed by SEM and appear stable for at least 2 weeks.

  10. Pneumatic active suspension system for a one-wheel car model using fuzzy reasoning and a disturbance observer.

    PubMed

    Yoshimura, Toshio; Takagi, Atsushi

    2004-09-01

    This paper presents the construction of a pneumatic active suspension system for a one-wheel car model using fuzzy reasoning and a disturbance observer. The one-wheel car model can be approximately described as a nonlinear two degrees of freedom system subject to excitation from a road profile. The active control is composed of fuzzy and disturbance controls, and functions by actuating a pneumatic actuator. A phase lead-lag compensator is inserted to counter the performance degradation due to the delay of the pneumatic actuator. The experimental result indicates that the proposed active suspension improves much the vibration suppression of the car model.

  11. Combined control effects of brake and active suspension control on the global safety of a full-car nonlinear model

    NASA Astrophysics Data System (ADS)

    Tchamna, Rodrigue; Youn, Edward; Youn, Iljoong

    2014-05-01

    This paper focuses on the active safety of a full-vehicle nonlinear model during cornering. At first, a previously developed electronic stability controller (ESC) based on vehicle simplified model is applied to the full-car nonlinear model in order to control the vehicle yaw rate and side-slip angle. The ESC system was shown beneficial not only in tracking the vehicle path as close as possible, but it also helped in reducing the vehicle roll angle and influences ride comfort and road-holding capability; to tackle that issue and also to have better attitude motion, making use of optimal control theory the active suspension control gain is developed from a vehicle linear model and used to compute the active suspension control force of the vehicle nonlinear model. The active suspension control algorithm used in this paper includes the integral action of the suspension deflection in order to make zero the suspension deflection steady state and keep the vehicle chassis flat. Keeping the chassis flat reduces the vehicle load transfer and that is helpful for road holding and yaw rate tracking. The effects of the two controllers when they work together are analysed using various computer simulations with different steering wheel manoeuvres.

  12. Non-linear dynamic modeling of an automobile hydraulic active suspension system

    NASA Astrophysics Data System (ADS)

    Mrad, R. Ben; Levitt, J. A.; Fassois, S. D.

    1994-09-01

    Motived by the strong need for realistically describing the dynamical behaviour of automotive systems through adequate mathematical models, a computer-stimulation-suitable non-linear quarter-car model of a hydraulic active suspension system is developed. Unlike previously available linear models characterised by idealised actuator and component behaviour, the developed model accounts for the dynamics of the main system components, including the suspension bushing, pump, accumulator, power and bypass valves, and hydraulic actuator, while also incorporating preliminary versions of the system controllers. Significant system characteristics, such as non-linear pressure-flow relationships, fluid compressibility, pump and valve non-linearities, leakages, as well as Coulomb friction, are also explicitly accounted for, and the underpinning assumptions are discussed. Simulation results obtained by exercising the model provide insight into the system behavior, illustrate the importance of the actuator/component dynamics and their associated non-linearities and reveal the inadequacy of the idealised linear models in capturing the system behaviour, demonstrate specific effects of valve leakage and fluid bulk modulus, are in qualitative agreement with experimental measurements, and stress the need for proper control law design and tuning. The developed model is particularly suitable for analysis, design, control law optimisation, and diagnostic strategies development.

  13. Anisotropic Model Colloids

    NASA Astrophysics Data System (ADS)

    van Kats, C. M.

    2008-10-01

    The driving forces for fundamental research in colloid science are the ability to manage the material properties of colloids and to unravel the forces that play a role between colloids to be able to control and understand the processes where colloids play an important role. Therefore we are searching for colloidal materials with specific physical properties to better understand our surrounding world.Until recently research in colloid science was mainly focused on spherical (isotropic) particles. Monodisperse spherical colloids serve as a model system as they exhibit similar phase behaviour as molecular and atomic systems. Nevertheless, in many cases the spherical shape is not sufficient to reach the desired research goals. Recently the more complex synthesis methods of anisotropic model colloids has strongly developed. This thesis should be regarded as a contribution to this research area. Anisotropic colloids can be used as a building block for complex structures and are expected not only to lead to the construction of full photonic band gap materials. They will also serve as new, more realistic, models systems for their molecular analogues. Therefore the term ‘molecular colloids” is sometimes used to qualify these anisotropic colloidal particles. In the introduction of this thesis, we give an overview of the main synthesis techniques for anisotropic colloids. Chapter 2 describes the method of etching silicon wafers to construct monodisperse silicon rods. They subsequently were oxidized and labeled (coated) with a fluorescent silica layer. The first explorative phase behaviour of these silica rods was studied. The particles showed a nematic ordering in charge stabilized suspensions. Chapter 3 describes the synthesis of colloidal gold rods and the (mesoporous) silica coating of gold rods. Chapter 4 describes the physical and optical properties of these particles when thermal energy is added. This is compared to the case where the particles are irradiated with

  14. Lipoxygenase activity and sanguinarine production in cell suspension cultures of California poppy (Eschscholtzia californica CHAM.).

    PubMed

    Kollárová, R; Oblozinský, M; Kováciková, V; Holková, I; Balazová, A; Pekárová, M; Hoffman, P; Bezáková, L

    2014-08-01

    In this study we investigated the influence of biotic elicitor (phytopathogenic fungus Botrytis cinerea) and abiotic elicitors (methyljasmonate [MJ] and salicylic acid [SA]) on lipoxygenase (LOX) activity and sanguinarine production in cell suspension cultures of California poppy (Eschscholtzia californica CHAM.). We have observed different time effects of elicitors (10, 24, 48 and 72 h) on LOX activity and production of sanguinarine in in vitro cultures. All elicitors used in the experiments evidently increased the LOX activity and sanguinarine production in contrast to control samples. The highest LOX activities were determined in samples elicitated by MJ after 48 h and 72 h and the lowest LOX activities (in contrast to control samples) were detected after biotic elicitation by Botrytis cinerea. These activities showed about 50% lower level against the activities after MJ elicitation. The maximal amount of sanguinarine was observed after 48 h in MJ treated cultures (429.91 mg/g DCW) in comparision with control samples. Although all elicitors affect the sanguinarine production, effect of SA and biotic elicitor on sanguinarine accumulation in in vitrocultures was not so significant than after MJ elicitation.

  15. Colloid update.

    PubMed

    Argalious, Maged Y

    2012-01-01

    This update aims to provide an evidence based review of natural and synthetic colloids with a special emphasis on the various generations of the synthetic colloid hydroxyethyl starch. The effect of 1(st), 2(nd) and 3(rd) generation hetastarches on bleeding, coagulopathy, acute kidney injury and mortality will be discussed. The results of randomised controlled trials addressing morbidity and mortality outcomes of colloid versus crystalloid resuscitation in critically ill patients will be described. In addition, the rationale and evidence behind early goal directed fluid therapy (EGDFT) including a practical approach to assessment of dynamic measures of fluid responsiveness will be presented.

  16. 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.

  17. Hexadecapolar Colloids

    DOE PAGES

    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

  18. 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

  19. VFC - Variational Feedback Controller and its application to semi-active suspensions

    NASA Astrophysics Data System (ADS)

    Pepe, G.; Carcaterra, A.

    2016-08-01

    Active and semi-active control of oscillating devices and structures is a challenging field and this paper proposes an original investigation based on variational controls that can be successfully applied to mechanical systems. The method produces a general class of new controllers, named VFC - Variational Feedback Controllers, that is the main theoretical contribution of the paper. The value of the theory relies on using a reformulation of the Variational Optimal Control Theory, that has in general the limit of producing control program strategies and not directly feedback control methods. The difficulties are in fact related to the intrinsic nature of the variational optimal control, that must solve initial and final boundary conditions. A special definition of the class of the considered objective functions, permits to skip this difficulty, producing a pure feedback control. The presented theory goes beyond with respect to the most acknowledged LQR variational-based techniques, in that VFC can be applied to more general nonlinear dynamical systems, even with finite time horizon. To test the effectiveness of the novel approach in real engineering problems, a deep investigation on nonlinear suspension systems treated by VFC is proposed in this paper. To this aim, VFC is systematically compared with the most recent methods available in this field and suitable to deal with nonlinear system control of car suspensions. In particular, the comparative analysis is made in terms of both comfort and handling key performance indexes, that permits to easily and significantly compare different control logics, such as the Sky-hook and Ground-hook control families, the Acceleration and Power Driven Dampers. The results of this comparison are collected in a performance plane, having comfort and handling indexes as coordinate axes, showing that VFC controllers completely cover the regions reached by the other mentioned control logics in this plane, but reveal to have access to

  20. Colloid-based multiplexed method for screening plant biomass-degrading glycoside hydrolase activities in microbial communities

    SciTech Connect

    Reindl, W.; Deng, K.; Gladden, J.M.; Cheng, G.; Wong, A.; Singer, S.W.; Singh, S.; Lee, J.-C.; Yao, J.-S.; Hazen, T.C.; Singh, A.K; Simmons, B.A.; Adams, P.D.; Northen, T.R.

    2011-05-01

    The enzymatic hydrolysis of long-chain polysaccharides is a crucial step in the conversion of biomass to lignocellulosic biofuels. The identification and characterization of optimal glycoside hydrolases is dependent on enzyme activity assays, however existing methods are limited in terms of compatibility with a broad range of reaction conditions, sample complexity, and especially multiplexity. The method we present is a multiplexed approach based on Nanostructure-Initiator Mass Spectrometry (NIMS) that allowed studying several glycolytic activities in parallel under diverse assay conditions. Although the substrate analogs carried a highly hydrophobic perfluorinated tag, assays could be performed in aqueous solutions due colloid formation of the substrate molecules. We first validated our method by analyzing known {beta}-glucosidase and {beta}-xylosidase activities in single and parallel assay setups, followed by the identification and characterization of yet unknown glycoside hydrolase activities in microbial communities.

  1. Photophysics of carbon-60 colloids

    NASA Astrophysics Data System (ADS)

    Clements, Andrew F.

    The goal of this dissertation is to study the photophysics of suspensions of colloidal C60 particles to determine if their nonlinear optical (NLO) response is superior in any way to benchmark NLO materials such as molecular solutions of C60 and carbon black suspensions (CBS). C60 in molecular form is known to exhibit strong reverse saturable absorption (RSA) and it is posited that colloidal particles composed of many C60 molecules would maintain some degree of RSA behavior upon association, although some quenching is to be expected. CBS is known to have an NLO response that is dominated by nonlinear scattering resulting from a phase change due to heating of the carbon black particles by absorbed energy. Colloidal C 60 particles that are many nanometers in diameter are similar to CBS, so it is posited that they would also have a nonlinear scattering mechanism contributing to their NLO response. Three samples of C60 colloids are characterized by several techniques, along with two carbon black suspensions and one molecular solution of C60. Transmission electron microscopy is used to determine morphology. Femtosecond pump-probe spectroscopy is used to determine the absorption spectrum and the relaxation kinetics of the first excited singlet state. Nanosecond laser flash photolysis is used to determine the absorption spectrum and the relaxation kinetics of the first excited triplet state. Z-scan is used to determine triplet-triplet absorption cross-sections. An experiment is performed to determine the percentage of the input energy that is transmitted, scattered, or absorbed by each sample. Computer modeling is performed to compare the experimental results to theory. Results show that all materials that exhibit nonlinear scattering have a constant extinction coefficient in the nonlinear regime, implying a characteristic size for the scattering centers that is independent of input energy. Quenching processes in C60 colloids are found to be morphology dependent, with more

  2. 76 FR 22423 - Agency Information Collection Activities; Submission for OMB Review; Comment Request; Suspension...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-04-21

    ... Federal Register on November 10, 2010 (75 FR 69130). Interested parties are encouraged to send comments to...; Suspension of Pension Benefits ACTION: Notice. SUMMARY: The Department of Labor (DOL) is submitting the..., ``Suspension of Pension Benefits,'' to the Office of Management and Budget (OMB) for review and approval...

  3. 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.

  4. Investigation of influence of NaOH and NaCl activating solutions on bentonite stabilization in suspension fertilizers

    NASA Astrophysics Data System (ADS)

    Hoffmann, Krystyna; Hoffmann, Józef; Mikła, Daniel; Huculak-Mä Czka, Marta; Skut, Jakub

    2010-05-01

    1. INTRODUCTION Regular plants growth and their metabolic activity are determined by the macro- (C, H, O, N, P, S, K, Ca, Mg) and micronutrients (Fe, Mn, Zn, Cu, B, Mo, Cl, Ni). The role of these elements is very important, the excess as well as the deficiency have the negative influence on their development [1]. In order to increase yields and quality of crops a mineral, organic and mineral-organic fertilizers are applied. In the last years suspension fertilizers have been of great significance, taking the agricultural benefits into consideration. Suspension fertilizers are products of a new generation on account of higher nutrients concentrations than in the majority of other fertilizers, what makes them more efficient. Suspension fertilizers differ from solid fertilizers in more regular distribution on field. Nutrients are more concentrated what is economically relevant on account of the facilitated transportation. Examinations indicated, that nutrients from suspension fertilizers are more available than from solid fertilizers. The high concentration of nutrients in fertilizer is obtained by introducing a substance which holds them regularly in the suspension. Bentonites are the substances used for stabilization of suspension fertilizers most often [2,3]. Bentonites belong to ore of clay minerals, primarily made from minerals of smectite group, montmorillonite especially [4]. Bentonite loams were formulated as a result of Aluminium Silicate-bearing Rocks weathering and subsequent sedimentation in the aqueous environment. Characteristic features of rocks of the smectite group are their ability to absorb water (swelling), to form thixotrophic suspensions which aren't undergoing sedimentation process for a long time; as well as susceptibility to absorb cations and organic substances [4,5]. Therefore investigations have been carried out in order to evaluate the possibility of application of diverse loamy raw materials as suspension stabilizers for fertilizer

  5. 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

  6. Study of the surface-enhanced Raman spectroscopy of residual impurities in hydroxylamine-reduced silver colloid and the effects of anions on the colloid activity.

    PubMed

    Dong, Xiao; Gu, Huaimin; Liu, Fangfang

    2012-03-01

    The paper investigated the residual ions in hydroxylamine-reduced silver colloid (HRSC) and the relationship between the condition of HRSC and the enhanced mechanisms of this colloid. We also detected the SERS of MB and studied the effects of anions on the Raman signal. In the case of HRSC, the bands of residual ions diminish while the bands of Ag-anions increase gradually with increasing the concentrations of Cl(-) and NO(3)(-). It means the affinity of residual ions on the silver surface is weaker than that of Cl(-) and NO(3)(-) and the residual ions are replaced gradually by the added Cl(-) or NO(3)(-). The Raman signal of residual ions can be detected by treatment with anions that do not bind strongly to the silver surface, such as SO(4)(2-). The most intense band of Ag-anions bonds can be also observed when adding weakly binding anions to the colloid. However, the anions which make up the Ag-anions bonds are residual Cl(-) and the effect of weakly binding anions is only to aggregate the silver particles. Residual Cl(-) can be replaced by I(-) which has the highest affinity. From the detection of methylene blue (MB), the effects of anions on the enhancement of Raman signal are discussed in detail, and these findings could make the conditions suitable for detecting analytes in high efficiency. This study will have a profound implication to SERS users about their interpretation of SERS spectra when obtaining these anomalous bands.

  7. Antiulcer activity of Amlapitta Mishran suspension in rats: A pilot study

    PubMed Central

    Vemula, Sampath K.; Chawada, Mukesh B.; Thakur, Kapil S.; Vahalia, Mahesh K.

    2012-01-01

    Context: Amlapitta Mishran suspension is a poly herbal ayurvedic formulation, which has been traditionally used for acidity and gastric ulcers. Aim: The aim of this study is to evaluate the antiulcer activity of Amlapitta Mishran on non-steroidal anti-inflammatory drugs (NSAID's) -induced ulcers in the rat model. Subjects and Methods: The antiulcer activity of Amlapitta Mishran was investigated on indomethacin (100 mg/kg) NSAID's induced ulcers in rats. Effect of two different doses of Amlapitta Mishran was studied by calculating the total number of ulcers, ulcer index and percentage inhibition. Statistical Analysis Used: Data was analyzed by the Student's t-test (P < 0.05). Results: Amlapitta Mishran treated rats have shown significant (P < 0.0001) decrease in the total number of ulcers and ulcer index and significant increase in % inhibition of ulcers as compared with positive control group. Conclusion: The results indicate that Amlapitta Mishran has showed a dose dependent antiulcer activity in experimental animals and confirms ayurvedic use of Amlapitta Mishran in gastric ulcers. PMID:24167338

  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. 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.

  10. The effects of perioperatively administered crystalloids and colloids on concentrations of molecular markers of activated coagulation and fibrinolysis.

    PubMed

    Fries, Dietmar; Streif, Werner; Margreiter, Josef; Klingler, Anton; Kühbacher, Gabriele; Schobersberger, Wolfgang; Wirleitner, Barbara; Innerhofer, Petra

    2004-04-01

    To explore whether intravenous administration of routinely used crystalloid or colloid solutions differently affects the coagulation system, we investigated orthopaedic patients. Since crystalloid solutions might cause hypercoagulability, we here present our results on molecular markers of coagulation and fibrinolysis. Patients undergoing knee replacement surgery randomly received isovolemic amounts of lactated Ringer's solution, 6% hydroxyethyl starch 200/0.5 or 4% modified gelatine. Arterial blood samples for determination of specific molecular markers of activated coagulation (thrombin/antithrombin complex, D-dimer, prothrombin fragment F1 + 2), fibrinolysis (plasmin/alpha 2-antiplasmin complex, tissue plasminogen activator, plasminogen activator inhibitor-1), and concentrations of coagulation factor XIII were obtained at baseline, before tourniquet release, at the end of surgery and 2 h after operation. During the observation period, thrombin/antithrombin complex increased from 4.8 to 54.7 microg/l, D-dimer increased from 0.3 to 6.0 mg/ml, prothrombin fragment F1 + 2 increased from 1.7 to 5.9 nmol/l, tissue plasminogen activator decreased from 7.3 to 6.7 ng/ml, plasminogen activator inhibitor-1 increased from 68.4 to 71.0 ng/ml, plasmin/alpha 2-antiplasmin complex increased from 281.5 to 884 microg/l and factor XIII decreased from 89.0 to 58.5%. All parameters changed significantly but without any detectable difference in the response profile between the groups receiving different intravenous fluids. During knee replacement surgery a pronounced activation of the coagulation/fibrinolytic system was observed, regardless of whether patients received crystalloid or colloid fluids. Thus, these results cannot confirm the hypothesis that crystalloid fluids per se cause hypercoagulability in vivo.

  11. Effects of woohwangcheongsimwon suspension on the pharmacokinetics of bupropion and its active metabolite, 4-hydroxybupropion, in healthy subjects

    PubMed Central

    Kim, Hyunmi; Bae, Soo Kyung; Park, Soo-Jin; Shim, Eon-Jeong; Kim, Ho-Sook; Shon, Ji-Hong; Liu, Kwang-Hyeon; Shin, Jae-Gook

    2010-01-01

    AIMS To examine the effects of woohwangcheongsimwon suspension on the pharmacokinetics of bupropion and its active metabolite, 4-hydroxybupropion, formed via CYP2B6 in vivo. METHODS A two-way crossover clinical trial with a 2 week washout period was conducted in 14 healthy volunteers. In phases I and II, subjects received 150 mg bupropion with or without woohwangcheongsimwon suspension four times (at −0.17, 3.5, 23.5 and 47.5 h, with the time of bupropion administration taken as 0 h) in a randomized balanced crossover order. Bupropion and 4-hydroxybupropion plasma concentrations were measured for up to 72 h by LC-MS/MS. Urine was collected up to 24 h to calculate the renal clearance. In addition, the CYP2B6*6 genotype was also analyzed. RESULTS The geometric mean ratios and 90% confidence interval of bupropion with woohwangcheongsimwon suspension relative to bupropion alone were 0.976 (0.917, 1.04) for AUC(0,∞) and 0.948 (0.830,1.08) for Cmax, respectively. The corresponding values for 4-hydroxybupropion were 0.856 (0.802, 0.912) and 0.845 (0.782, 0.914), respectively. The tmax values of bupropion and 4-hydroxybupropion were not significantly different between the two groups (P > 0.05). The pharmacokinetic parameters of bupropion and 4-hydroxybupropion were unaffected by woohwangcheongsimwon suspension. CONCLUSIONS These results indicate that woohwangcheongsimwon suspension has a negligible effect on the disposition of a single dose of bupropion in vivo. As a result, temporary co-administration with woohwangcheongsimwon suspension does not seem to require a dosage adjustment of bupropion. PMID:20642555

  12. Sorption and toxicity reduction of pharmaceutically active compounds and endocrine disrupting chemicals in the presence of colloidal humic acid.

    PubMed

    Kim, Injeong; Kim, Hyo-Dong; Jeong, Tae-Yong; Kim, Sang Don

    2016-01-01

    This study investigated the toxicity changes and sorption of pharmaceuticals and endocrine disrupters in the presence of humic acid (HA). For the sorption experiment, a dead end filtration (DEF) system was used to separate bound and free-form target compounds. An algae growth inhibition test and E-screen assay were conducted to estimate the toxic effect of pharmaceutically active compounds (PhACs) and endocrine disrupting chemicals (EDCs), respectively. The permeate concentration was confirmed using liquid chromatography-mass spectrometry. In the sorption test, we observed significant sorption of PhACs and EDCs on colloidal HA, except for sulfamethoxazole (SMX). The values of log KCOC derived from DEF determinations ranged from 4.40 to 5.03. The removal efficiency varied with the HA concentration and the target chemical properties. Tetracycline and 4-octylphenol showed the highest sorption or removal efficiency (≈50%), even at 5 mg C/L HA. The algal growth inhibition of PhACs and the estrogenic effects of EDCs were significantly decreased in proportion to HA concentrations, except for SMX. In addition, the chemical analysis results showed a positive relationship with the bioassay results. Consequently, the sorption of PhACs and EDCs onto colloidal HA should be emphasized in natural environments because it significantly reduces bioavailable concentrations and toxicity to aquatic organisms. PMID:27533865

  13. Programmed cell death activated by Rose Bengal in Arabidopsis thaliana cell suspension cultures requires functional chloroplasts

    PubMed Central

    Gutiérrez, Jorge; González-Pérez, Sergio; García-García, Francisco; Daly, Cara T.; Lorenzo, Óscar; Revuelta, José L.; McCabe, Paul F.; Arellano, Juan B.

    2014-01-01

    Light-grown Arabidopsis thaliana cell suspension culture (ACSC) were subjected to mild photooxidative damage with Rose Bengal (RB) with the aim of gaining a better understanding of singlet oxygen-mediated defence responses in plants. Additionally, ACSC were treated with H2O2 at concentrations that induced comparable levels of protein oxidation damage. Under low to medium light conditions, both RB and H2O2 treatments activated transcriptional defence responses and inhibited photosynthetic activity, but they differed in that programmed cell death (PCD) was only observed in cells treated with RB. When dark-grown ACSC were subjected to RB in the light, PCD was suppressed, indicating that the singlet oxygen-mediated signalling pathway in ACSC requires functional chloroplasts. Analysis of up-regulated transcripts in light-grown ACSC, treated with RB in the light, showed that both singlet oxygen-responsive transcripts and transcripts with a key role in hormone-activated PCD (i.e. ethylene and jasmonic acid) were present. A co-regulation analysis proved that ACSC treated with RB exhibited higher correlation with the conditional fluorescence (flu) mutant than with other singlet oxygen-producing mutants or wild-type plants subjected to high light. However, there was no evidence for the up-regulation of EDS1, suggesting that activation of PCD was not associated with the EXECUTER- and EDS1-dependent signalling pathway described in the flu mutant. Indigo Carmine and Methylene Violet, two photosensitizers unable to enter chloroplasts, did not activate transcriptional defence responses in ACSC; however, whether this was due to their location or to their inherently low singlet oxygen quantum efficiencies was not determined. PMID:24723397

  14. Programmed cell death activated by Rose Bengal in Arabidopsis thaliana cell suspension cultures requires functional chloroplasts.

    PubMed

    Gutiérrez, Jorge; González-Pérez, Sergio; García-García, Francisco; Daly, Cara T; Lorenzo, Oscar; Revuelta, José L; McCabe, Paul F; Arellano, Juan B

    2014-07-01

    Light-grown Arabidopsis thaliana cell suspension culture (ACSC) were subjected to mild photooxidative damage with Rose Bengal (RB) with the aim of gaining a better understanding of singlet oxygen-mediated defence responses in plants. Additionally, ACSC were treated with H2O2 at concentrations that induced comparable levels of protein oxidation damage. Under low to medium light conditions, both RB and H2O2 treatments activated transcriptional defence responses and inhibited photosynthetic activity, but they differed in that programmed cell death (PCD) was only observed in cells treated with RB. When dark-grown ACSC were subjected to RB in the light, PCD was suppressed, indicating that the singlet oxygen-mediated signalling pathway in ACSC requires functional chloroplasts. Analysis of up-regulated transcripts in light-grown ACSC, treated with RB in the light, showed that both singlet oxygen-responsive transcripts and transcripts with a key role in hormone-activated PCD (i.e. ethylene and jasmonic acid) were present. A co-regulation analysis proved that ACSC treated with RB exhibited higher correlation with the conditional fluorescence (flu) mutant than with other singlet oxygen-producing mutants or wild-type plants subjected to high light. However, there was no evidence for the up-regulation of EDS1, suggesting that activation of PCD was not associated with the EXECUTER- and EDS1-dependent signalling pathway described in the flu mutant. Indigo Carmine and Methylene Violet, two photosensitizers unable to enter chloroplasts, did not activate transcriptional defence responses in ACSC; however, whether this was due to their location or to their inherently low singlet oxygen quantum efficiencies was not determined.

  15. 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

  16. 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

  17. Smectic filaments in colloidal suspensions of rods.

    PubMed

    Frenkel, Daan; Schilling, Tanja

    2002-10-01

    In supersaturated isotropic mixtures of hard rods, smectic filaments have recently been observed. We propose a model for formation and growth of these filaments similar to the Hoffman-Lauritzen model for polymer crystallization. Filament thickness is determined by a compromise between maximizing the amount of smectic phase formed and minimizing the nucleation barrier for adding new segments to the growing filament. We compare our analytical results to kinetic Monte Carlo simulations.

  18. Nanodiamond in Colloidal Suspension: Electrophoresis; Other Observations

    NASA Technical Reports Server (NTRS)

    Meshik, A. P.; Pravdivtseva, O. V.; Hohenberg, C. M.

    2002-01-01

    Selective laser extraction has demonstrated that meteoritic diamonds may consist of subpopulations with different optical absorption properties, but it is not clear what makes them optically different. More work is needed to understand the mechanism for selective laser extraction. Additional information is contained in the original extended abstract.

  19. 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.

  20. SERS active colloidal nanoparticles for the detection of small blood biomarkers using aptamers

    NASA Astrophysics Data System (ADS)

    Marks, Haley; Mabbott, Samuel; Jackson, George W.; Graham, Duncan; Cote, Gerard L.

    2015-03-01

    Functionalized colloidal nanoparticles for SERS serve as a promising multifunctional assay component for blood biomarker detection. Proper design of these nanoprobes through conjugation to spectral tags, protective polymers, and sensing ligands can provide experimental control over the sensitivity, range, reproducibility, particle stability, and integration with biorecognition assays. Additionally, the optical properties and degree of electromagnetic SERS signal enhancement can be altered and monitored through tuning the nanoparticle shape, size, material and the colloid's local surface plasmon resonance (LSPR). Aptamers, synthetic affinity ligands derived from nucleic acids, provide a number of advantages for biorecognition of small molecules and toxins with low immunogenicity. DNA aptamers are simpler and more economical to produce at large scale, are capable of greater specificity and affinity than antibodies, are easily tailored to specific functional groups, can be used to tune inter-particle distance and shift the LSPR, and their intrinsic negative charge can be utilized for additional particle stability.1,2 Herein, a "turn-off" competitive binding assay platform involving two different plasmonic nanoparticles for the detection of the toxin bisphenol A (BPA) using SERS is presented. A derivative of the toxin is immobilized onto a silver coated magnetic nanoparticle (Ag@MNP), and a second solid silver nanoparticle (AgNP) is functionalized with the BPA aptamer and a Raman reporter molecule (RRM). The capture (Ag@MNP) and probe (AgNP) particles are mixed and the aptamer binding interaction draws the nanoparticles closer together, forming an assembly that results in an increased SERS signal intensity. This aptamer mediated assembly of the two nanoparticles results in a 100x enhancement of the SERS signal intensity from the RRM. These pre-bound aptamer/nanoparticle conjugates were then exposed to BPA in free solution and the competitive binding event was monitored

  1. 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

  2. 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

  3. Optimisation of active suspension control inputs for improved vehicle ride performance

    NASA Astrophysics Data System (ADS)

    Čorić, Mirko; Deur, Joško; Xu, Li; Tseng, H. Eric; Hrovat, Davor

    2016-07-01

    A collocation-type control variable optimisation method is used in the paper to analyse to which extent the fully active suspension (FAS) can improve the vehicle ride comfort while preserving the wheel holding ability. The method is first applied for a cosine-shaped bump road disturbance of different heights, and for both quarter-car and full 10 degree-of-freedom vehicle models. A nonlinear anti-wheel hop constraint is considered, and the influence of bump preview time period is analysed. The analysis is then extended to the case of square- or cosine-shaped pothole with different lengths, and the quarter-car model. In this case, the cost function is extended with FAS energy consumption and wheel damage resilience costs. The FAS action is found to be such to provide a wheel hop over the pothole, in order to avoid or minimise the damage at the pothole trailing edge. In the case of long pothole, when the FAS cannot provide the wheel hop, the wheel is travelling over the pothole bottom and then hops over the pothole trailing edge. The numerical optimisation results are accompanied by a simplified algebraic analysis.

  4. Secretion of active recombinant phytase from soybean cell-suspension cultures.

    PubMed Central

    Li, J; Hegeman, C E; Hanlon, R W; Lacy, G H; Denbow, M D; Grabau, E A

    1997-01-01

    Phytase, an enzyme that degrades the phosphorus storage compound phytate, has the potential to enhance phosphorus availability in animal diets when engineered into soybean (Glycine max) seeds. The phytase gene from Aspergillus niger was inserted into soybean transformation plasmids under control of constitutive and seed-specific promoters, with and without a plant signal sequence. Suspension cultures were used to confirm phytase expression in soybean cells. Phytase mRNA was observed in cultures containing constitutively expressed constructs. Phytase activity was detected in the culture medium from transformants that received constructs containing the plant signal sequence, confirming expectations that the protein would follow the default secretory pathway. Secretion also facilitated characterization of the biochemical properties of recombinant phytase. Soybean-synthesized phytase had a lower molecular mass than did the fungal enzyme. However, deglycosylation of the recombinant and fungal phytase yielded polypeptides of identical molecular mass (49 kD). Temperature and pH optima of the recombinant phytase were indistinguishable from the commercially available fungal phytase. Thermal inactivation studies of the recombinant phytase suggested that the additional protein stability would be required to withstand the elevated temperatures involved in soybean processing. PMID:9232886

  5. Non-linear modelling and control of semi-active suspensions with variable damping

    NASA Astrophysics Data System (ADS)

    Chen, Huang; Long, Chen; Yuan, Chao-Chun; Jiang, Hao-Bin

    2013-10-01

    Electro-hydraulic dampers can provide variable damping force that is modulated by varying the command current; furthermore, they offer advantages such as lower power, rapid response, lower cost, and simple hardware. However, accurate characterisation of non-linear f-v properties in pre-yield and force saturation in post-yield is still required. Meanwhile, traditional linear or quarter vehicle models contain various non-linearities. The development of a multi-body dynamics model is very complex, and therefore, SIMPACK was used with suitable improvements for model development and numerical simulations. A semi-active suspension was built based on a belief-desire-intention (BDI)-agent model framework. Vehicle handling dynamics were analysed, and a co-simulation analysis was conducted in SIMPACK and MATLAB to evaluate the BDI-agent controller. The design effectively improved ride comfort, handling stability, and driving safety. A rapid control prototype was built based on dSPACE to conduct a real vehicle test. The test and simulation results were consistent, which verified the simulation.

  6. 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.

  7. Modelling a Suspension Bridge.

    ERIC Educational Resources Information Center

    Rawlins, Phil

    1991-01-01

    The quadratic function can be modeled in real life by a suspension bridge that supports a uniform weight. This activity uses concrete models and computer generated graphs to discover the mathematical model of the shape of the main cable of a suspension bridge. (MDH)

  8. Proteome-Based Analysis of Colloidal Instability Enables the Detection of Haze-Active Proteins in Beer.

    PubMed

    Schulte, Fabian; Flaschel, Erwin; Niehaus, Karsten

    2016-09-01

    Colloidal haze is a serious quality defect of bright beers that considerably reduces their shelf life and is thought to be triggered by hordeins, a class of proline-rich barley proteins. In this work, the proteomes of fresh and old beers were investigated in bottled pilsners and compared to the protein inventory of haze to identify specific haze-active proteins. Haze isolates dissolved in rehydration buffer contained high concentrations of proteins and sugars but provided protein gels with weak spot signals. Consequently, a treatment for the chemical deglycation with trifluoromethanesulfonic acid was applied, which resulted in the identification of protein Z4, LTP1, CMb, CMe, pUP13, 3a, and Bwiph as constituents of the haze proteome. Because only one hordein was detectable and the proline content in haze hydrolysates was lower than those of barley prolamins, our results suggest that this class of proteins is of minor importance for haze development.

  9. Proteome-Based Analysis of Colloidal Instability Enables the Detection of Haze-Active Proteins in Beer.

    PubMed

    Schulte, Fabian; Flaschel, Erwin; Niehaus, Karsten

    2016-09-01

    Colloidal haze is a serious quality defect of bright beers that considerably reduces their shelf life and is thought to be triggered by hordeins, a class of proline-rich barley proteins. In this work, the proteomes of fresh and old beers were investigated in bottled pilsners and compared to the protein inventory of haze to identify specific haze-active proteins. Haze isolates dissolved in rehydration buffer contained high concentrations of proteins and sugars but provided protein gels with weak spot signals. Consequently, a treatment for the chemical deglycation with trifluoromethanesulfonic acid was applied, which resulted in the identification of protein Z4, LTP1, CMb, CMe, pUP13, 3a, and Bwiph as constituents of the haze proteome. Because only one hordein was detectable and the proline content in haze hydrolysates was lower than those of barley prolamins, our results suggest that this class of proteins is of minor importance for haze development. PMID:27515584

  10. Development of a systematic and practical methodology for the design of vehicles semi-active suspension control system

    NASA Astrophysics Data System (ADS)

    Bolandhemmat, Hamidreza; Clark, Christopher M.; Golnaraghi, Farid

    2010-05-01

    In this paper, a novel systematic and practical methodology is presented for design of vehicle semi-active suspension systems. Typically, the semi-active control strategies developed to improve vehicle ride comfort and stability have a switching nature. This makes the design of the controlled suspension systems difficult and highly dependent on an extensive trial-and-error process. The proposed methodology maps the discontinuous control system model to a continuous linear region, where all the time and frequency design techniques, established in the conventional control system theory, can be applied. If the semi-active control system is designed to satisfy some ride and stability requirements, an inverse mapping offers the ultimate control law. At the end, the entire design procedure is summarised in six steps. The effectiveness of the proposed methodology in the design of a semi-active suspension system for a Cadillac SRX 2005 is demonstrated with road tests results. Real-time experiments confirm that the use of the newly developed systematic design method reduces the required time and effort in real industrial problems.

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

    NASA Astrophysics Data System (ADS)

    Löwen, Hartmut

    2012-11-01

    third conference in a series that began in 2004 [2] and was continued in 2008 [3]. The CODEF meeting series is held in conjunction with the German Dutch Transregional Collaborative Research Centre SFB TR6 with the title Physics of Colloidal Dispersions in External Fields. Papers from scientists working within this network as well as those from further invited contributors are summarized in this issue. They are organized according to the type of field applied, namely: shear flow electric field laser-optical and magnetic field confinement other fields and active particles To summarize the highlights of this special issue as regards shear fields, the response of depletion-induced colloidal clusters to shear is explored in [4]. Soft particles deform under shear and their structural and dynamical behaviour is studied both by experiment [5] and theory [6]. Transient dynamics after switching on shear is described by a joint venture of theory, simulation and experiment in [7]. Colloids provide the fascinating possibility to drag single particles through the suspension, which gives access to microrheology (as opposed to macrorheology, where macroscopic boundaries are moved). Several theoretical aspects of microrheology are discussed in this issue [8-10]. Moreover, a microscopic theory for shear viscosity is presented [11]. Various aspects of colloids in electric fields are also included in this issue. Electrokinetic phenomena for charged suspensions couple flow and electric phenomena in an intricate way and are intensely discussed both by experiment and simulation in contributions [12-14]. Dielectric phenomena are also influenced by electric fields [15]. Electric fields can induce effective dipolar forces between colloids leading to string formation [16]. Finally, binary mixtures in an electric driving field exhibit laning [17]. Simulation [18] and theoretical [19] studies of this nonequilibrium phenomenon are also discussed in this issue. Laser-optical fields can be used to

  12. Colloid-polymer mixtures in solution with refractive index matched acrylate colloids.

    PubMed

    Kramer, Thomas; Scholz, Stephanie; Maskos, Michael; Huber, Klaus

    2004-11-15

    Colloid-polymer (CP) mixtures extend between two limiting cases, the colloid limit with the polymer coil size small compared to the colloid radius Rcol and the protein limit with the colloidal particles much smaller in size than the radius of gyration of the polymer chains Rg. In the present work, model systems are developed for the protein limit. The colloid-solvent pairs are optimized in terms of their isorefractivity in order to facilitate the characterization of large polystyrene chains in suspensions of small colloids. The degree of isorefractivity of colloidal particles was successfully evaluated in terms of a reduced scattering intensity. Two polystyrene samples with radii of gyration of Rg = 96 nm and Rg = 78 nm, respectively, are used. The radii of the colloidal particles are close to Rcol = 12 nm, leading to size ratios of Rg/Rcol = 8 and Rg/Rcol = 6.5. Four colloid solvent systems were found to be suitable for polymer characterization by light scattering, one based on silica particles and three systems with acrylate particles. The present investigation is focused on the three acrylate systems: poly(methyl methacrylate) in ethyl benzoate (ETB) at 7 degrees C, poly(ethyl methacrylate) in toluene at 7 degrees C and poly(ethyl methacrylate) in ETB at 40 degrees C. Characterization of PS chains is for the first time performed in colloid concentrations up to 2.5% by weight. In all cases, the size and shape of the polymer chains remain unchanged. A slight mismatch of the colloid scattering or a limited colloid solubility prevented investigation of PS chains at higher colloid concentration.

  13. 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.

  14. Combining support vector machines with linear quadratic regulator adaptation for the online design of an automotive active suspension system

    NASA Astrophysics Data System (ADS)

    Chiou, J.-S.; Liu, M.-T.

    2008-02-01

    As a powerful machine-learning approach to pattern recognition problems, the support vector machine (SVM) is known to easily allow generalization. More importantly, it works very well in a high-dimensional feature space. This paper presents a nonlinear active suspension controller which achieves a high level performance by compensating for actuator dynamics. We use a linear quadratic regulator (LQR) to ensure optimal control of nonlinear systems. An LQR is used to solve the problem of state feedback and an SVM is used to address the question of the estimation and examination of the state. These two are then combined and designed in a way that outputs feedback control. The real-time simulation demonstrates that an active suspension using the combined SVM-LQR controller provides passengers with a much more comfortable ride and better road handling.

  15. Formation Kinetics of Aqueous Suspensions of Fullerenes:Meeting in New Orleans.

    EPA Science Inventory

    Stable colloidal suspension of C60 is commonly achieved through various solvent exchange techniques. Nevertheless, the additives such as tetrahydrofuran may be retained in the C60 aggregates, which may influence the surface properties of the suspension. In this study, colloidal...

  16. Influence of the active mass particle suspension in electrolyte upon corrosion of negative electrode of a lead-acid battery

    NASA Astrophysics Data System (ADS)

    Kamenev, Yu.; Shtompel, G.; Ostapenko, E.; Leonov, V.

    2014-07-01

    The influence of the suspension of positive active mass particles in the electrolyte on the performance of the negative electrode in a lead-acid battery is studied. A significant increase in the rate of corrosion of the lead electrode is shown when slime particles get in contact with its surface, which may result in the rise of macro-defects on the lugs of the negative electrodes.

  17. Non-fragile multi-objective static output feedback control of vehicle active suspension with time-delay

    NASA Astrophysics Data System (ADS)

    Kong, Yongsu; Zhao, Dingxuan; Yang, Bin; Han, Chenghao; Han, Kyongwon

    2014-07-01

    This paper presents an approach to design a delay-dependent non-fragile H∞/L2-L∞ static output feedback (SOF) controller for active suspension with input time-delay. The control problem of quarter-car active suspension with actuator time-delay is formulated to a H∞/L2-L∞ control problem. By employing a delay-dependent Lyapunov function, new existence conditions of delay-dependent non-fragile SOF H∞ controller and L2-L∞ controller are derived, respectively, in terms of the feasibility of bilinear matrix inequalities (BMIs). Then, a procedure based on linear matrix inequality optimisation and a hybrid algorithm of the particle swarm optimisation and differential evolution is used to solve an optimisation problem with BMI constraints. Design and simulation results of non-fragile H∞/L2-L∞ controller for active suspension show that the designed controller not only can achieve the optimal performance and stability of the closed-loop system in spite of the existence of the actuator time-delay, but also has significantly improved the non-fragility characteristics over controller perturbations.

  18. 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.

  19. Axial dispersion of Brownian colloids in microfluidic channels

    NASA Astrophysics Data System (ADS)

    Howard, Michael P.; Gautam, Aishwarya; Panagiotopoulos, Athanassios Z.; Nikoubashman, Arash

    2016-08-01

    We present a complete theoretical framework for the axial dispersion of a Brownian colloidal suspension confined in a parallel plate channel, extending the Taylor-Aris treatment to particles with diameters comparable to the channel width. The theoretical model incorporates the effects of confinement on the colloid distribution, corrections to the velocity profile due to the effects of colloid concentration on the suspension viscosity, and position-dependent diffusivities. We test the theoretical model using explicit-solvent molecular dynamics simulations that fully incorporate hydrodynamic correlations and thermal fluctuations and obtain good quantitative agreement between theory and simulations. We find that the nonuniform colloid distributions that arise in confinement due to excluded volume between the colloids and channel walls significantly impact the axial dispersion.

  20. [Poly (allylamine)-stabilized colloidal copper nanoparticles: synthesis and their SERS activities].

    PubMed

    Wang, Yan-Fei; Xiao, Zhan-Min; Zhang, Chun-Guang

    2012-06-01

    Poly(allylamine)-stabilized spherical and rod-shaped copper nanoparticles were synthesized by a simple chemical reaction. The synthesis was performed by the reduction of copper (II) salt with hydrazine in aqueous solution under atmospheric air in the presence of poly(allylamine) (PAAm) capping agent. Besides providing long-term stability to the nanoparticles by preventing particle agglomeration, polymer capping agents such as PAAm make the particles dispersible in aqueous solution. Noteworthy advantages of the synthetic method include its production of water dispersible nanoparticles at room temperature without inert atmosphere, making the synthesis more environmentally friendly. The resulting copper nanoparticles were investigated by UV-Vis spectroscopy and transmission electron microscopy. The authors found that several factors, including the amount of NaOH solution, concentration of PAAm, and reaction time, affect the composition, size, morphology, and degree of agglomeration of the resulting copper nanoparticles. The amount of NaOH in the reaction is crucial for the synthesis to result in either pure copper or copper oxide-containing copper nanoparticles as well as to produce the highest possible yield of copper nanoparticles. In addition, the reaction time and concentration of PAAm play key roles in controlling the size and shape of the nanoparticles, respectively. The resulting colloidal copper nanoparticles exhibit large surface-enhanced Raman spectroscopy (SERS) signals. PMID:22870639

  1. Stability of nystatin in mouthrinses; effect of pH temperature, concentration and colloidal silver addition, studied using an in vitro antifungal activity.

    PubMed

    Vermerie, N; Malbrunot, C; Azar, M; Arnaud, P

    1997-08-01

    Alkaline low concentration nystatin mouthrinses extemporanely prepared can be used to treat oropharyngeal candidiasis in immunodeficient patients. However, their expiration dates are not distinctly determined. The stability of nystatin, added (as Mycostatine) at a concentration of 14,400 U/ml in 10-4N hydrochloric acid, purified water and 1.4% injectable sodium hydrogen carbonate with or without 0.002% colloidal silver (an antiseptic agent added because of its known antifungal potency) was studied after storage in tinted glass bottles at 5 degrees C and 22 degrees C over 11 days, and compared with reconstituted 100,000 U/ml aqueous Mycostatine oral suspension. At 2, 4, 7, 9, and 11 days after preparation. Samples were tested for pH, microbial contamination, and assayed by an in vitro microbiological test. Neither significant variation of pH nor microbial contamination were in evidence. Nystatin 14400 U/ml maintained at least 90% of its initial concentration for 4 days in acid at both temperatures, for 7 days (5 degrees C) and 4 days (22 degrees C) in aqueous and alkaline environments, for 9 days (5 degrees C) and 7 days (22 degrees C) in 1.4% injectable sodium hydrogen carbonate containing colloidal silver which showed an antifungal potency. The 100,000 U/ml aqueous Mycostatine oral suspension was stable for 9 days and 4 days at 5 degrees C and 22 degrees C respectively. An ambulant patient can keep a low concentration alkaline antifungal mouthrinse at home for a week at 5 degrees C.

  2. Micro-mechanics of electrostatically stabilized suspensions of cellulose nanofibrils under steady state shear flow.

    PubMed

    Martoïa, F; Dumont, P J J; Orgéas, L; Belgacem, M N; Putaux, J-L

    2016-02-14

    In this study, we characterized and modeled the rheology of TEMPO-oxidized cellulose nanofibril (NFC) aqueous suspensions with electrostatically stabilized and unflocculated nanofibrous structures. These colloidal suspensions of slender and wavy nanofibers exhibited a yield stress and a shear thinning behavior at low and high shear rates, respectively. Both the shear yield stress and the consistency of these suspensions were power-law functions of the NFC volume fraction. We developed an original multiscale model for the prediction of the rheology of these suspensions. At the nanoscale, the suspensions were described as concentrated systems where NFCs interacted with the Newtonian suspending fluid through Brownian motion and long range fluid-NFC hydrodynamic interactions, as well as with each other through short range hydrodynamic and repulsive colloidal interaction forces. These forces were estimated using both the experimental results and 3D networks of NFCs that were numerically generated to mimic the nanostructures of NFC suspensions under shear flow. They were in good agreement with theoretical and measured forces for model colloidal systems. The model showed the primary role played by short range hydrodynamic and colloidal interactions on the rheology of NFC suspensions. At low shear rates, the origin of the yield stress of NFC suspensions was attributed to the combined contribution of repulsive colloidal interactions and the topology of the entangled NFC networks in the suspensions. At high shear rates, both concurrent colloidal and short (in some cases long) range hydrodynamic interactions could be at the origin of the shear thinning behavior of NFC suspensions.

  3. Carbon starvation increases endoglycosidase activities and production of "unconjugated N-glycans" in Silene alba cell-suspension cultures.

    PubMed Central

    Lhernould, S; Karamanos, Y; Priem, B; Morvan, H

    1994-01-01

    We previously reported the occurrence of oligomannosides and xylomannosides corresponding to unconjugated N-glycans (UNGs) in the medium of a white campion (Silene alba) cell suspension. Attention has been focused on these oligosaccharides since it was shown that they confer biological activities in plants. In an attempt to elucidate the origin of these oligosaccharides, we studied two endoglycosidase activities, putative enzymes involved in their formation. The previously described peptide-N4-(N-acetyl-glucosaminyl) asparagine amidase activity and the endo-N-acetyl-beta-D-glucosaminidase activity described in this paper were both quantified in white campion cells during the culture cycle with variable initial concentrations of sucrose. The lower the sucrose supply, the higher the two activities. Furthermore, endoglycosidase activities were greatly enhanced after the disappearance of sugar from the medium. The production of UNGs in the culture medium rose correlatively. These data strongly suggest that the production of UNGs in our white campion cell-suspension system is due to the increase of these endoglycosidase activities, which reach their highest levels of activity during conditions of carbon starvation. PMID:7991689

  4. Influence of rare earth elements on metabolism and related enzyme activity and isozyme expression in Tetrastigma hemsleyanum cell suspension cultures.

    PubMed

    Xin, Peng; Shuang-Lin, Zhou; Jun-Yao, He; Li, Ding

    2013-04-01

    The effects of rare earth elements (REEs) not only on cell growth and flavonoid accumulation of Tetrastigma hemsleyanum suspension cells but also on the isoenzyme patterns and activities of related enzymes were studied in this paper. There were no significant differences in enhancement of flavonoid accumulation in T. hemsleyanum suspension cells among La(3+), Ce(3+), and Nd(3+). Whereas their inductive effects on cell proliferation varied greatly. The most significant effects were achieved with 100 μM Ce(3+)and Nd(3+). Under treatment over a 25-day culture period, the maximal biomass levels reached 1.92- and 1.74-fold and the total flavonoid contents are 1.45- and 1.49-fold, than that of control, respectively. Catalase, phenylalanine ammonia-lyase (PAL), and peroxidase (POD) activity was activated significantly when the REE concentration range from 0 to 300 μM, whereas no significant changes were found in superoxide dismutase activity. Differences of esterase isozymes under REE treatment only laid in expression level, and there were no specific bands. The expression level of some POD isozymes strengthened with increasing concentration of REEs within the range of 50-200 μM. When REE concentration was higher than 300 μM, the expression of some POD isozymes was inhibited; meanwhile, some other new POD isozymes were induced. Our results also showed REEs did not directly influence PAL activity. So, we speculated that 50-200 μM REEs could activate some of antioxidant enzymes, adjust some isozymes expression, trigger the defense responses of T. hemsleyanum suspension cells, and stimulate flavonoid accumulation by inducing PAL activity.

  5. Total-hip arthroplasty: Periprosthetic indium-111-labeled leukocyte activity and complementary technetium-99m-sulfur colloid imaging in suspected infection

    SciTech Connect

    Palestro, C.J.; Kim, C.K.; Swyer, A.J.; Capozzi, J.D.; Solomon, R.W.; Goldsmith, S.J. )

    1990-12-01

    Indium-111-labeled leukocyte images of 92 cemented total-hip arthroplasties were correlated with final diagnoses. Prostheses were divided into four zones: head (including acetabulum), trochanter, shaft, and tip. The presence (or absence) and intensity of activity in each zone was noted, and compared to the corresponding contralateral zone. Though present in all 23 infected arthroplasties, periprosthetic activity was also present in 77% of uninfected arthroplasties, and was greater than the contralateral zone 51% of the time. When analyzed by zone, head zone activity was the best criterion for infection (87% sensitivity, 94% specificity, 92% accuracy). Fifty of the arthroplasties were studied with combined labeled leukocyte/sulfur colloid imaging. Using incongruence of images as the criterion for infection, the sensitivity, specificity, and accuracy of the study were 100%, 97%, and 98%, respectively. While variable periprosthetic activity makes labeled leukocyte imaging alone unreliable for diagnosing hip arthroplasty infection, the addition of sulfur colloid imaging results in a highly accurate diagnostic procedure.

  6. 77 FR 43606 - Agency Information Collection Activities: Application for Suspension of Deportation or Special...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-25

    ... FR 23271, allowing for a 60-day public comment period. USCIS did not receive comments in response to... for Suspension of Deportation or Special Rule Cancellation of Removal (Pursuant to Section 203 of... Deportation or Special Rule Cancellation of Removal (Pursuant to Section 203 of Public Law 105-100,...

  7. A Photosynthesis Lab. Response of Algal Suspensions to a Gradient of Photosynthetically Active Radiation (PAR).

    ERIC Educational Resources Information Center

    Zee, Delmar Vander

    1995-01-01

    This photosynthesis exercise is intended for introductory college biology or botany courses. It is based on the principle that a closed suspension of algal cells may be expected to produce more dissolved oxygen with a greater photon fluence rate, but within limits of the photosynthetic capacity of the system. Describes materials and methods. (LZ)

  8. Semi-active control of automotive suspension systems with magnetorheological dampers

    NASA Astrophysics Data System (ADS)

    Lam, Hiu Fung; Liao, Wei-Hsin

    2001-08-01

    Vibration in today's increasingly high-speed vehicles including automobiles severely affects their ride comfort and safety. The objective of this paper is to develop and study automotive suspension systems with magneto-rheological (MR) fluid dampers for vibration control in order to improve the passenger's comfort and safety. A two degree-of-freedom quarter car model is considered. A mathematical model of MR fluid damper is adopted. In this study, a sliding mode controller is developed by considering loading uncertainty to result in a robust control system. Two kinds of excitations are inputted in order to investigate the performance of the suspension system. The vibration responses are evaluated in both time and frequency domains. Compared to the passive system, the acceleration of the sprung mass is significantly reduced for the system with a controlled MR damper. Under random excitation, the ability of the MR fluid damper to reduce both peak response and root-mean-square response is also shown. The effectiveness of the MR suspension system is also demonstrated via hardware-in-the-loop simulation. The results of this study can be used to develop guidelines to effectively integrate automotive suspensions with MR dampers.

  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. Design of robust-stable and quadratic finite-horizon optimal controllers with low trajectory sensitivity for uncertain active suspension systems

    NASA Astrophysics Data System (ADS)

    Chen, Shinn-Horng; Chou, Jyh-Horng; Zheng, Liang-An; Lin, Sheng-Kai

    2010-08-01

    This paper presents a design method for designing the robust-stable and quadratic-finite-horizon-optimal controllers of uncertain active suspension systems. The method integrates a robust stabilisability condition, the orthogonal functions approach (OFA) and the hybrid Taguchi-genetic algorithm (HTGA). Using the integrative computational method, a robust-stable and quadratic-finite-horizon-optimal controller with low-trajectory sensitivity can be obtained such that (i) the active suspension system with elemental parametric uncertainties is stabilised and (ii) a quadratic-finite-horizon-integral performance index including a quadratic trajectory sensitivity term for the nominal active suspension system is minimised. The robust stabilisability condition is proposed in terms of linear matrix inequalities (LMIs). Based on the OFA, an algebraic algorithm only involving the algebraic computation is derived for solving the nominal active suspension feedback dynamic equations. By using the OFA and the LMI-based robust stabilisability condition, the dynamic optimisation problem for the robust-stable and quadratic-finite-horizon-optimal controller design of the linear uncertain active suspension system is transformed into a static-constrained-optimisation problem represented by the algebraic equations with constraint of LMI-based robust stabilisability condition; thus greatly simplifies the design problem. Then, for the static-constrained-optimisation problem, the HTGA is employed to find the robust-stable and quadratic-finite-horizon-optimal controllers of the linear uncertain active suspension systems. A design example is given to demonstrate the applicability of the proposed integrative computational approach.

  11. Ionic colloidal crystals of oppositely charged particles.

    PubMed

    Leunissen, Mirjam E; Christova, Christina G; Hynninen, Antti-Pekka; Royall, C Patrick; Campbell, Andrew I; Imhof, Arnout; Dijkstra, Marjolein; van Roij, René; van Blaaderen, Alfons

    2005-09-01

    Colloidal suspensions are widely used to study processes such as melting, freezing and glass transitions. This is because they display the same phase behaviour as atoms or molecules, with the nano- to micrometre size of the colloidal particles making it possible to observe them directly in real space. Another attractive feature is that different types of colloidal interactions, such as long-range repulsive, short-range attractive, hard-sphere-like and dipolar, can be realized and give rise to equilibrium phases. However, spherically symmetric, long-range attractions (that is, ionic interactions) have so far always resulted in irreversible colloidal aggregation. Here we show that the electrostatic interaction between oppositely charged particles can be tuned such that large ionic colloidal crystals form readily, with our theory and simulations confirming the stability of these structures. We find that in contrast to atomic systems, the stoichiometry of our colloidal crystals is not dictated by charge neutrality; this allows us to obtain a remarkable diversity of new binary structures. An external electric field melts the crystals, confirming that the constituent particles are indeed oppositely charged. Colloidal model systems can thus be used to study the phase behaviour of ionic species. We also expect that our approach to controlling opposite-charge interactions will facilitate the production of binary crystals of micrometre-sized particles, which could find use as advanced materials for photonic applications.

  12. 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.

  13. Neural network compensation of semi-active control for magneto-rheological suspension with time delay uncertainty

    NASA Astrophysics Data System (ADS)

    Dong, Xiao Min; Yu, Miao; Li, Zushu; Liao, Changrong; Chen, Weimin

    2009-01-01

    This study presents a new intelligent control method, human-simulated intelligent control (HSIC) based on the sensory motor intelligent schema (SMIS), for a magneto-rheological (MR) suspension system considering the time delay uncertainty of MR dampers. After formulating the full car dynamic model featuring four MR dampers, the HSIC based on eight SMIS is derived. A neural network model is proposed to compensate for the uncertain time delay of the MR dampers. The HSIC based on SMIS is then experimentally realized for the manufactured full vehicle MR suspension system on the basis of the dSPACE platform. Its performance is evaluated and compared under various road conditions and presented in both time and frequency domains. The results show that significant gains are made in the improvement of vehicle performance. Results include a reduction of over 35% in the acceleration peak-to-peak value of a sprung mass over a bumpy road and a reduction of over 24% in the root-mean-square (RMS) sprung mass acceleration over a random road as compared to passive suspension with typical original equipment (OE) shock absorbers. In addition, the semi-active full vehicle system via HSIC based on SMIS provides better isolation than that via the original HSIC, which can avoid the effect of the time delay uncertainty of the MR dampers.

  14. Design of robust H ∞ controller for a half-vehicle active suspension system with input delay

    NASA Astrophysics Data System (ADS)

    Li, Hongyi; Liu, Honghai; Hand, Steve; Hilton, Chris

    2013-04-01

    This article is concerned with the problem of robust H ∞ control for a half-vehicle active suspension system with input delay. The delay is assumed to be interval time-varying delay with unknown derivative. The vehicle front sprung mass and the rear unsprung mass are assumed to be varying due to vehicle load variation and may result in parameter uncertainties being modelled by polytopic uncertainty. First of all, regarding the heave and pitch accelerations as the optimisation objectives, and suspension deflection and relative tire load constraints as the output constraints, we build the corresponding suspension systems. Then, by constructing a novel Lyapunov functional involved with the lower and upper bounds of the delay, sufficient condition for the existence of robust H ∞ controller is given to ensure robust asymptotical stability of the closed-loop system and also guarantee the constrained performance. The condition can be converted into convex optimisation problem and verified easily by means of standard software. Finally, a design example is exploited to demonstrate the effectiveness of the proposed design method.

  15. Analysis and testing of an integrated semi-active seat suspension for both longitudinal and vertical vibration control

    NASA Astrophysics Data System (ADS)

    Bai, Xian-Xu; Jiang, Peng; Pan, Hui; Qian, Li-Jun

    2016-04-01

    An integrated semi-active seat suspension for both longitudinal and vertical vibration control is analyzed and tested in this paper. The seat suspension consists of a switching mechanism transforming both longitudinal and vertical motions into a rotary motion and a real-time damping-controllable system-a rotary magnetorheological (MR) damper working in pure shear mode and its corresponding control system. The switching mechanism employs the parallelogram frames as a motion guide which keeps the seat moving longitudinally and vertically. At the same time, both longitudinal and vertical motions are transformed into a reciprocating rotary motion that is transmitted to the rotary MR damper after an amplification by a gear mechanism. Both the longitudinal and vertical vibrations can be attenuated in real time through controlling the damping force (or torque) of the rotary MR damper. The mathematical model of the seat suspension system is established, simulated, and analyzed. The experimental test based on the test rig in Hefei University of Technology is implemented, and the results of simulation and experimental test are compared and analyzed.

  16. Influence of pH on colloidal properties and surface activity of polyglycerol fatty acid ester vesicles.

    PubMed

    Duerr-Auster, N; Eisele, T; Wepf, R; Gunde, R; Windhab, E J

    2008-11-15

    Certain polyglycerol esters of fatty acids (PGE) form dispersions of uni- or multilamellar vesicles in dilute aqueous solution. These self-assembled aggregates reduce the surface-activity of PGE monomers such that interfacial films may take several hours to form. This is undesirable for processes, which rely on rapid surfactant adsorption, for example foaming. In the present work, we study the effect of pH on the colloidal (size distribution, morphology, surface charge) and interfacial (adsorption kinetics) properties of a commercial, non-purified PGE. Using dynamic light scattering, zeta-potential measurements and cryo-SEM, we show that changing the pH of the dispersion media can cause agglomeration and eventually osmotic rupture of PGE vesicles. The change in dispersion state also impacts the adsorption behavior at the water surface. Direct evidence that destabilized vesicle dispersion are more surface-active is provided by comparing the dynamic surface tension of solutions of different pH. The faster adsorption kinetics at low pH correlate with a remarkably increased foaming power. We suggest that an osmotic shock induced by changes in pH causes vesicles to deform and partially open, so that their hydrocarbon core is exposed to the dispersion media. This energetically unfavorable condition promotes the hydrophobically driven adsorption of surfactant monomers at surfaces and hence stimulates the foaming ability.

  17. Effective SERS-active substrates composed of hierarchical micro/nanostructured arrays based on reactive ion etching and colloidal masks.

    PubMed

    Zhang, Honghua; Liu, Dilong; Hang, Lifeng; Li, Xinyang; Liu, Guangqiang; Cai, Weiping; Li, Yue

    2016-09-30

    A facile route has been proposed for the fabrication of morphology-controlled periodic SiO2 hierarchical micro/nanostructured arrays by reactive ion etching (RIE) using monolayer colloidal crystals as masks. By effectively controlling the experimental conditions of RIE, the morphology of a periodic SiO2 hierarchical micro/nanostructured array could be tuned from a dome-shaped one to a circular truncated cone, and finally to a circular cone. After coating a silver thin layer, these periodic micro/nanostructured arrays were used as surface-enhanced Raman scattering (SERS)-active substrates and demonstrated obvious SERS signals of 4-Aminothiophenol (4-ATP). In addition, the circular cone arrays displayed better SERS enhancement than those of the dome-shaped and circular truncated cone arrays due to the rougher surface caused by physical bombardment. After optimization of the circular cone arrays with different periodicities, an array with the periodicity of 350 nm exhibits much stronger SERS enhancement and possesses a low detection limit of 10(-10) M 4-ATP. This offers a practical platform to conveniently prepare SERS-active substrates.

  18. Effective SERS-active substrates composed of hierarchical micro/nanostructured arrays based on reactive ion etching and colloidal masks

    NASA Astrophysics Data System (ADS)

    Zhang, Honghua; Liu, Dilong; Hang, Lifeng; Li, Xinyang; Liu, Guangqiang; Cai, Weiping; Li, Yue

    2016-09-01

    A facile route has been proposed for the fabrication of morphology-controlled periodic SiO2 hierarchical micro/nanostructured arrays by reactive ion etching (RIE) using monolayer colloidal crystals as masks. By effectively controlling the experimental conditions of RIE, the morphology of a periodic SiO2 hierarchical micro/nanostructured array could be tuned from a dome-shaped one to a circular truncated cone, and finally to a circular cone. After coating a silver thin layer, these periodic micro/nanostructured arrays were used as surface-enhanced Raman scattering (SERS)-active substrates and demonstrated obvious SERS signals of 4-Aminothiophenol (4-ATP). In addition, the circular cone arrays displayed better SERS enhancement than those of the dome-shaped and circular truncated cone arrays due to the rougher surface caused by physical bombardment. After optimization of the circular cone arrays with different periodicities, an array with the periodicity of 350 nm exhibits much stronger SERS enhancement and possesses a low detection limit of 10‑10 M 4-ATP. This offers a practical platform to conveniently prepare SERS-active substrates.

  19. Effective SERS-active substrates composed of hierarchical micro/nanostructured arrays based on reactive ion etching and colloidal masks.

    PubMed

    Zhang, Honghua; Liu, Dilong; Hang, Lifeng; Li, Xinyang; Liu, Guangqiang; Cai, Weiping; Li, Yue

    2016-09-30

    A facile route has been proposed for the fabrication of morphology-controlled periodic SiO2 hierarchical micro/nanostructured arrays by reactive ion etching (RIE) using monolayer colloidal crystals as masks. By effectively controlling the experimental conditions of RIE, the morphology of a periodic SiO2 hierarchical micro/nanostructured array could be tuned from a dome-shaped one to a circular truncated cone, and finally to a circular cone. After coating a silver thin layer, these periodic micro/nanostructured arrays were used as surface-enhanced Raman scattering (SERS)-active substrates and demonstrated obvious SERS signals of 4-Aminothiophenol (4-ATP). In addition, the circular cone arrays displayed better SERS enhancement than those of the dome-shaped and circular truncated cone arrays due to the rougher surface caused by physical bombardment. After optimization of the circular cone arrays with different periodicities, an array with the periodicity of 350 nm exhibits much stronger SERS enhancement and possesses a low detection limit of 10(-10) M 4-ATP. This offers a practical platform to conveniently prepare SERS-active substrates. PMID:27573436

  20. Effective SERS-active substrates composed of hierarchical micro/nanostructured arrays based on reactive ion etching and colloidal masks

    NASA Astrophysics Data System (ADS)

    Zhang, Honghua; Liu, Dilong; Hang, Lifeng; Li, Xinyang; Liu, Guangqiang; Cai, Weiping; Li, Yue

    2016-09-01

    A facile route has been proposed for the fabrication of morphology-controlled periodic SiO2 hierarchical micro/nanostructured arrays by reactive ion etching (RIE) using monolayer colloidal crystals as masks. By effectively controlling the experimental conditions of RIE, the morphology of a periodic SiO2 hierarchical micro/nanostructured array could be tuned from a dome-shaped one to a circular truncated cone, and finally to a circular cone. After coating a silver thin layer, these periodic micro/nanostructured arrays were used as surface-enhanced Raman scattering (SERS)-active substrates and demonstrated obvious SERS signals of 4-Aminothiophenol (4-ATP). In addition, the circular cone arrays displayed better SERS enhancement than those of the dome-shaped and circular truncated cone arrays due to the rougher surface caused by physical bombardment. After optimization of the circular cone arrays with different periodicities, an array with the periodicity of 350 nm exhibits much stronger SERS enhancement and possesses a low detection limit of 10-10 M 4-ATP. This offers a practical platform to conveniently prepare SERS-active substrates.

  1. Production of Bacillus subtilis-fermented red alga Porphyra dentata suspension with fibrinolytic and immune-enhancing activities.

    PubMed

    Lin, Hong-Ting Victor; Hwang, Pai-An; Lin, Tzu-Chun; Tsai, Guo-Jane

    2014-01-01

    The fermented marine alga Porphyra dentata suspension was tested for its fibrinolytic and immune-enhancing activities. An isolated Bacillus subtilis N2 strain was selected for its fibrinolytic activity on fibrin plates. After investigating the effects of biomass amounts of P. dentata powder in water, various additives including sugars, nitrogen-containing substances, lipids and minerals, and cultural conditions of temperature and agitation in flask, the highest fibrinolytic activity in the cultural filtrate was obtained by cultivating N2 strain in 3% (w/v) P. dentata powder suspension containing 1% peanut oil at 37 °C, 150 rpm for 48 h. A fermentor system was further established using the same medium with controlled pH value of 7.0 at 37 °C, 150 rpm, 2.0 vvm for 48 h for the best fibrinolytic activity. The fermented product also showed its immune-enhancing activity by increasing cell proliferation and stimulating the secretion of IL-1β, IL-6, and TNF-α in J774.1 cells.

  2. Automated video-microscopic imaging and data acquisition system for colloid deposition measurements

    DOEpatents

    Abdel-Fattah, Amr I.; Reimus, Paul W.

    2004-12-28

    A video microscopic visualization system and image processing and data extraction and processing method for in situ detailed quantification of the deposition of sub-micrometer particles onto an arbitrary surface and determination of their concentration across the bulk suspension. The extracted data includes (a) surface concentration and flux of deposited, attached and detached colloids, (b) surface concentration and flux of arriving and departing colloids, (c) distribution of colloids in the bulk suspension in the direction perpendicular to the deposition surface, and (d) spatial and temporal distributions of deposited colloids.

  3. Differences in the Activities of Eight Enzymes from Ten Soil Fungi and Their Possible Influences on the Surface Structure, Functional Groups, and Element Composition of Soil Colloids

    PubMed Central

    Wang, Wenjie; Li, Yanhong; Wang, Huimei; Zu, Yuangang

    2014-01-01

    How soil fungi function in soil carbon and nutrient cycling is not well understood by using fungal enzymatic differences and their interactions with soil colloids. Eight extracellular enzymes, EEAs (chitinase, carboxymethyl cellulase, β-glucosidase, protease, acid phosphatase, polyphenol oxidase, laccase, and guaiacol oxidase) secreted by ten fungi were compared, and then the fungi that showed low and high enzymatic activity were co-cultured with soil colloids for the purpose of finding fungi-soil interactions. Some fungi (Gomphidius rutilus, Russula integra, Pholiota adiposa, and Geastrum mammosum) secreted 3–4 enzymes with weak activities, while others (Cyathus striatus, Suillus granulate, Phallus impudicus, Collybia dryophila, Agaricus sylvicola, and Lactarius deliciosus) could secret over 5 enzymes with high activities. The differences in these fungi contributed to the alterations of functional groups (stretching bands of O-H, N-H, C-H, C = O, COO- decreased by 11–60%, while P = O, C-O stretching, O-H bending and Si-O-Si stretching increased 9–22%), surface appearance (disappearance of adhesive organic materials), and elemental compositions (11–49% decreases in C1s) in soil colloids. Moreover, more evident changes were generally in high enzymatic fungi (C. striatus) compared with low enzymatic fungi (G. rutilus). Our findings indicate that inter-fungi differences in EEA types and activities might be responsible for physical and chemical changes in soil colloids (the most active component of soil matrix), highlighting the important roles of soil fungi in soil nutrient cycling and functional maintenance. PMID:25398013

  4. Differences in the activities of eight enzymes from ten soil fungi and their possible influences on the surface structure, functional groups, and element composition of soil colloids.

    PubMed

    Wang, Wenjie; Li, Yanhong; Wang, Huimei; Zu, Yuangang

    2014-01-01

    How soil fungi function in soil carbon and nutrient cycling is not well understood by using fungal enzymatic differences and their interactions with soil colloids. Eight extracellular enzymes, EEAs (chitinase, carboxymethyl cellulase, β-glucosidase, protease, acid phosphatase, polyphenol oxidase, laccase, and guaiacol oxidase) secreted by ten fungi were compared, and then the fungi that showed low and high enzymatic activity were co-cultured with soil colloids for the purpose of finding fungi-soil interactions. Some fungi (Gomphidius rutilus, Russula integra, Pholiota adiposa, and Geastrum mammosum) secreted 3-4 enzymes with weak activities, while others (Cyathus striatus, Suillus granulate, Phallus impudicus, Collybia dryophila, Agaricus sylvicola, and Lactarius deliciosus) could secret over 5 enzymes with high activities. The differences in these fungi contributed to the alterations of functional groups (stretching bands of O-H, N-H, C-H, C = O, COO- decreased by 11-60%, while P = O, C-O stretching, O-H bending and Si-O-Si stretching increased 9-22%), surface appearance (disappearance of adhesive organic materials), and elemental compositions (11-49% decreases in C1s) in soil colloids. Moreover, more evident changes were generally in high enzymatic fungi (C. striatus) compared with low enzymatic fungi (G. rutilus). Our findings indicate that inter-fungi differences in EEA types and activities might be responsible for physical and chemical changes in soil colloids (the most active component of soil matrix), highlighting the important roles of soil fungi in soil nutrient cycling and functional maintenance.

  5. Differences in the activities of eight enzymes from ten soil fungi and their possible influences on the surface structure, functional groups, and element composition of soil colloids.

    PubMed

    Wang, Wenjie; Li, Yanhong; Wang, Huimei; Zu, Yuangang

    2014-01-01

    How soil fungi function in soil carbon and nutrient cycling is not well understood by using fungal enzymatic differences and their interactions with soil colloids. Eight extracellular enzymes, EEAs (chitinase, carboxymethyl cellulase, β-glucosidase, protease, acid phosphatase, polyphenol oxidase, laccase, and guaiacol oxidase) secreted by ten fungi were compared, and then the fungi that showed low and high enzymatic activity were co-cultured with soil colloids for the purpose of finding fungi-soil interactions. Some fungi (Gomphidius rutilus, Russula integra, Pholiota adiposa, and Geastrum mammosum) secreted 3-4 enzymes with weak activities, while others (Cyathus striatus, Suillus granulate, Phallus impudicus, Collybia dryophila, Agaricus sylvicola, and Lactarius deliciosus) could secret over 5 enzymes with high activities. The differences in these fungi contributed to the alterations of functional groups (stretching bands of O-H, N-H, C-H, C = O, COO- decreased by 11-60%, while P = O, C-O stretching, O-H bending and Si-O-Si stretching increased 9-22%), surface appearance (disappearance of adhesive organic materials), and elemental compositions (11-49% decreases in C1s) in soil colloids. Moreover, more evident changes were generally in high enzymatic fungi (C. striatus) compared with low enzymatic fungi (G. rutilus). Our findings indicate that inter-fungi differences in EEA types and activities might be responsible for physical and chemical changes in soil colloids (the most active component of soil matrix), highlighting the important roles of soil fungi in soil nutrient cycling and functional maintenance. PMID:25398013

  6. Regulation of Glutamate Dehydrogenase Activity in Relation to Carbon Limitation and Protein Catabolism in Carrot Cell Suspension Cultures 1

    PubMed Central

    Robinson, Sharon A.; Stewart, George R.; Phillips, Richard

    1992-01-01

    Glutamate dehydrogenase (GDH) specific activity and function have been studied in cell suspension cultures of carrot (Daucus carota L. cv Chantenay) in response to carbon and nitrogen supply in the culture medium. The specific activity of GDH was derepressed in sucrose-starved cells concomitant with protein catabolism, ammonium excretion, and the accumulation of metabolically active amino acids. The addition of sucrose led to a rapid decrease in GDH specific activity, an uptake of ammonium from the medium, and a decrease in amino acid levels. The extent of GDH derepression was correlated positively with cellular glutamate concentration. These findings strengthen the view that the function of GDH is the catabolism of glutamate, which under conditions of carbon stress provides carbon skeletons for tricarboxylic acid cycle activity. PMID:16668745

  7. Colloidal caterpillars for cargo transportation.

    PubMed

    Sasaki, Yuji; Takikawa, Yoshinori; Jampani, V S R; Hoshikawa, Hikaru; Seto, Takafumi; Bahr, Christian; Herminghaus, Stephan; Hidaka, Yoshiki; Orihara, Hiroshi

    2014-11-28

    Tunable transport of tiny objects in fluid systems is demanding in diverse fields of science such as drug delivery, active matter far from equilibrium, and lab-on-a-chip applications. Here, we report the directed motion of colloidal particles and self-assembled colloidal chains in a nematic liquid crystal matrix using electrohydrodynamic convection (EHC) rolls. The asymmetric distortion of the molecular orientation around the particles results - for single particles - in a hopping motion from one EHC roll to the next and - for colloidal chains - in a caterpillar-like motion in the direction perpendicular to the roll axes. We demonstrate the use of colloidal chains as microtraction engines for the transport of various types of microcargo.

  8. Hemolytic activity of a bacterial trehalose lipid biosurfactant produced by Rhodococcus sp.: evidence for a colloid-osmotic mechanism.

    PubMed

    Zaragoza, Ana; Aranda, Francisco J; Espuny, María J; Teruel, José A; Marqués, Ana; Manresa, Angeles; Ortiz, Antonio

    2010-06-01

    A succinoyl trehalose lipid produced by Rhodococcus sp. behaves as a biological surfactant and also displays various interesting biological activities. Trehalose lipid has been shown to have a great tendency to partition into phospholipid membranes; therefore, the characterization of its interaction with biological membranes is of central importance. In this work, human red blood cells have been used as an experimental model. Trehalose lipid causes the swelling of human erythrocytes followed by hemolysis at concentrations well below its critical micellar concentration. Kinetic measurements show that, upon addition of trehalose lipid, K(+) release precedes that of hemoglobin. Osmotic protectants of the appropriate size added to the external medium make it possible to avoid hemolysis. The results indicate that trehalose lipid causes the hemolysis of human erythrocytes by a colloid-osmotic mechanism, most likely by formation of enhanced permeability domains, or "pores" enriched in the biosurfactant, within the erythrocyte membrane. Scanning electron microscopy shows trehalose lipid-induced spherocytosis and echinocytosis of red blood cells, which fits well within the framework of the bilayer-couple hypothesis. The presented results contribute to establishing a molecular basis for the biological properties of this trehalose lipid biosurfactant. PMID:20146489

  9. Lectin-induced increase in microvascular permeability to colloidal carbon in vitro may involve protein kinase C activation.

    PubMed

    Northover, A M; Northover, B J

    1994-05-01

    Two plant lectins, wheat germ agglutinin (WGA) and concanavalin A (Con A), which are known to bind to endothelial cells (ECs), were found to increase the leakage of colloidal carbon (CC) into the walls of microvessels in the villi of rat small intestine, when added to a gelatin-containing perfusate (GPSS) at a concentration of 10 micrograms/ml. Pretreatment of the microvessels with the protein kinase C (PKC) inhibitor Ro 31-8220 (1 x 10(-6) M) significantly reduced this effect. In contrast, the leakage of CC in response to A23187 (1 x 10(-4) M) was not affected by Ro 31-8220. Peanut agglutinin (PNA) and succinyl concanavalin A (SuccCon A), which do not bind to ECs, had no effect at a concentration of 10 micrograms/ml. A lower concentration of WGA (1 microgram/ml) had no significant effect of its own, but significantly reduced the leakage of CC in response to both platelet-activating factor (PAF, 5 x 10(-6) M) and 5-hydroxytryptamine (5-HT, 1 x 10(-4) M), but not to beta-phorbol 12,13-dibutyrate (PDB, 1 x 10(-6) M). These results suggest that all these effects of WGA and Con A involve cell surface receptors, albeit in a non-specific way. A possible mode of action is discussed.

  10. Controls of maglev suspension systems

    SciTech Connect

    Cai, Y.; Zhu, S.; Chen, S.S.; Rote, D.M.

    1993-06-01

    This study investigates alternative control designs of maglev vehicle suspension systems. Active and semi-active control law designs are introduced into primary and secondary suspensions of maglev vehicles. A one-dimensional vehicle with two degrees of freedom, to simulate the German Transrapid Maglev System, is used for suspension control designs. The transient and frequency responses of suspension systems and PSDs of vehicle accelerations are calculated to evaluate different control designs. The results show that active and semi-active control designs indeed improve the response of vehicle and provide an acceptable ride comfort for maglev systems.

  11. 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.

  12. Melting in temperature sensitive suspensions

    NASA Astrophysics Data System (ADS)

    Alsayed, Ahmed M.

    We describe two experimental studies about melting in colloidal systems. In particular we studied melting of 1-dimensional lamellar phases and 3-dimensional colloidal crystals. In the first set of experiments we prepared suspensions composed of rodlike fd virus and the thermosensitive polymer, poly(N-isopropylacrylamide). The phase diagram of this systems is temperature and concentration dependent. Using video microscopy, we directly observed melting of lamellar phases and single lamellae into nematic phase. We found that lamellar phases swell with increasing temperature before melting into the nematic phase. The highly swollen lamellae can be superheated as a result of topological nucleation barriers that slow the formation of the nematic phase. In another set of experiments we prepared colloidal crystals from thermally responsive microgel spheres. The crystals are equilibrium close-packed three-dimensional structures. Upon increasing the temperature slightly above room temperature, particle volume fraction decreased from 0.74 to less than 0.5. Using video microscopy, we observed premelting at grain boundaries and dislocations within bulk colloidal crystals. Premelting is the localized loss of crystalline order at surfaces and defects at sample volume fractions above the bulk melting transition. Particle tracking revealed 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. In total these observations suggest that interfacial free energy is the crucial parameter for premelting in colloidal and in atomic scale crystals.

  13. 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

  14. Rethinking Suspensions

    ERIC Educational Resources Information Center

    Stetson, Frank H.; Collins, Betty J.

    2010-01-01

    The overrepresentation of the Black and Hispanic subgroups in suspension data is a national problem and a troubling issue for schools and school systems across the United States. In Maryland, an analysis of student suspensions by school districts for the 2006-2007 school year revealed disproportionality issues. In 23 of the 24 jurisdictions,…

  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. 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).

  17. Quantifying colloid retention in partially saturated porous media

    NASA Astrophysics Data System (ADS)

    Zevi, Yuniati; Dathe, Annette; Gao, Bin; Richards, Brian K.; Steenhuis, Tammo S.

    2006-12-01

    The transport of colloid-contaminant complexes and colloid-sized pathogens through soil to groundwater is of concern. Visualization and quantification of pore-scale colloid behavior will enable better description and simulation of retention mechanisms at individual surfaces, in contrast to breakthrough curves which only provide an integrated signal. We tested two procedures for quantifying colloid movement and retention as observed in pore-scale image sequences. After initial testing with static images, three series of images of synthetic microbead suspensions passing through unsaturated sand were examined. The region procedure (implemented in ImageJ) and the Boolean procedure (implemented in KS400) yielded nearly identical results for initial test images and for total colloid-covered areas in three image series. Because of electronic noise resulting in pixel-level brightness fluctuations the Boolean procedure tended to underestimate attached colloid counts and conversely overestimate mobile colloid counts. The region procedure had a smaller overestimation error of attached colloids. Reliable quantification of colloid retention at pore scale can be used to improve current understanding on the transport mechanisms of colloids in unsaturated porous media. For example, attachment counts at individual air/water meniscus/solid interface were well described by Langmuir isotherms.

  18. 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.

  19. Viscosity of Sheared Helical filament Suspensions

    NASA Astrophysics Data System (ADS)

    Sartucci, Matthew; Urbach, Jeff; Blair, Dan; Schwenger, Walter

    The viscosity of suspensions can be dramatically affected by high aspect ratio particles. Understanding these systems provides insight into key biological functions and can be manipulated for many technological applications. In this talk, the viscosity as a function of shear rate of suspensions of helical filaments is compared to that of suspensions of straight rod-like filaments. Our goal is to determine the impact of filament geometry on low volume fraction colloidal suspensions in order to identify strategies for altering viscosity with minimal volume fraction. In this research, the detached flagella of the bacteria Salmonella Typhimurium are used as a model system of helical filaments and compared to mutated straight flagella of the Salmonella. We compare rheological measurements of the suspension viscosity in response to shear flow and use a combination of the rheology and fluorescence microscopy to identify the microstructural changes responsible for the observed rheological response.

  20. 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.

  1. Dynamics of colloids in confined geometries.

    PubMed

    Almenar, L; Rauscher, M

    2011-05-11

    We discuss the Brownian dynamics of colloids in confinement with special emphasis on the influence of the solvent dynamics. We review the derivation of a dynamic density functional theory (DDFT) including some aspects of hydrodynamic interactions and its application to the micro-rheology of suspensions. In particular we discuss the failure of Stokes' law in suspensions and non-equilibrium solvent structure mediated interactions. With regard to hydrodynamic chromatography we also discuss the stationary transport of particles in narrow channels, and the reasons for the failure of DDFT in this situation.

  2. On-Board Prediction of Power Consumption in Automobile Active Suspension SYSTEMS—II: Validation and Performance Evaluation

    NASA Astrophysics Data System (ADS)

    Ben Mrad, R.; Fassois, S. D.; Levitt, J. A.; Bachrach, B. I.

    1996-03-01

    The focus of this part of the paper is on validation and performance evaluation. The indirect (standard) and novel direct predictors or part I, which use time-recursive realisations and no leading indicators, are critically compared by using the non-linear active suspension system model. The results, constituting the first known comparison between indirect and direct schemes, show similar performance with a slight superiority of the former. Experimental validation is based on an especially developed active suspension vehicle. The power consumption non-stationarity is, in this case, shown to be of the homogeneous type, and completely "masking" the signal's second-order characteristics, which revealed only after the non-stationarity's effective removal. The analysis leads to two distinct types of indirect predictors: An explicit type, based on non-stationary integrated autoregressive moving average models, and an implicit type, based on stationary autoregressive moving average model. The explicit predictor is shown to be uniformly better than the implicit, although the difference is small for short prediction horizons. The experimental results indicate that accurate power consumption prediction is possible, with errors ranging from 2.22% for a prediction horizon of 0.156 s, to still less than 10% for horizons that are up to 0.470 s long, and about 25% for 1.563 s long horizons.

  3. On-Board Prediction of Power Consumption in Automobile Active Suspension SYSTEMS—I: Predictor Design Issues

    NASA Astrophysics Data System (ADS)

    Ben Mrad, R.; Fassois, S. D.; Levitt, J. A.; Bachrach, B. I.

    1996-03-01

    On-board prediction of automobile active suspension power consumption is considered important in securing fast engine response and avoiding potential vehicle hesitation or surge. In this study the problem is considered within the context of a broad-bandwidth hydraulic active suspension design, with the following main objectives: (a) power consumption prediction feasibility assessment, (b) examination of predictor design options, and (c) achievable prediction accuracy assessment. In this part I the first two objectives are pursued based on a detailed, non-linear, mathematical system model. The power consumption signal is found to be non-stationary, but stationarily is shown to be possible to impose through a moving-average transformation. Predictor design options are then considered: first, the wheel vertical acceleration is shown to be ineffective as a prediction leading indicator; second, the relative merits of time/step-recursive and time-recursive predictor realizations are examined, and the latter are shown to be presently preferable from the point of view of computational complexity, error propagation, and predictor stability; third, indirect (standard) vs. direct predictor types are considered, and a direct predictor is developed based on a novel estimator characterised by features important for on-board implementation.

  4. Effect of soil sorption and aquatic natural organic matter on the antibacterial activity of a fullerene water suspension.

    PubMed

    Li, Dong; Lyon, Delina Y; Li, Qilin; Alvarez, Pedro J J

    2008-09-01

    The present study investigated the association of a C60 water suspension (nC6) with natural organic matter, present as a soil constituent or dissolved in the water column, and its effect on the antibacterial activity of nC60. Sorption of nC60 to soil reduced its bioavailability and antibacterial activity, and the sorption capacity strongly depended on the organic content of the soil. Adsorption of aquatic dissolved humic substances onto nC60 and possible subsequent reactions also were found to eliminate nC60 toxicity at humic acid concentrations as low as 0.05 mg/L. These findings indicate that natural organic matter in the environment can mitigate significantly the potential impacts of nC60 on microbial activities that are important to ecosystem health.

  5. Effect of hydrogen peroxide on contractility and citrate synthase activity of the rabbit urinary bladder in the presence and absence of resveratrol and a whole-grape suspension.

    PubMed

    Francis, Johdi-Ann; Leggett, Robert E; Schuler, Catherine; Levin, Robert M

    2014-06-01

    One etiology related directly to obstructive urinary bladder dysfunction is ischemia/reperfusion resulting in significant oxidative stress to the bladder. Grapes, a natural source of antioxidants, have been proven effective in preventing obstructive and ischemic bladder dysfunction. Many investigators believe that resveratrol is the primary active antioxidant ingredient in grapes. We compared the ability of a whole-grape suspension with pure resveratrol in their ability to protect the bladder from in vitro oxidative stress mediated by hydrogen peroxide (H2O2). Four male rabbit bladders were used. Two strips from each bladder were incubated in the presence of 1 mg/mL grape suspension for 30 min, another two strips were incubated in the presence of 1 mg/mL resveratrol solution, and the last two strips were incubated in the presence of 1 mg/mL sucrose/and fructose as controls. The rest of the bladder was separated into muscle and mucosa, frozen and stored for biochemical evaluation. (1) Chemically, resveratrol has about 20 times the antioxidant capacity of the grape suspension. (2) The grape suspension had significant protective effects when the rate of tension was quantitated at all concentrations of H2O2, while the resveratrol had no effect. (3) Citrate synthase activities of the muscle and mucosa were significantly protected by the grape suspension but not by resveratrol. These data demonstrate that the grape suspension protects the mitochondria to a significantly greater degree than resveratrol, which suggests that the antioxidant activities are due to the combination of active components found in the grape suspension and not just resveratrol.

  6. Manipulation of long-term dynamics in a colloidal active matter system using speckle light fields

    NASA Astrophysics Data System (ADS)

    Pince, Ercag; Velu, Sabareesh K. P.; Callegari, Agnese; Elahi, Parviz; Gigan, Sylvain; Volpe, Giovanni; Volpe, Giorgio

    Particles undergoing a stochastic motion within a disordered medium is a ubiquitous physical and biological phenomena. Examples can be given from organelles performing tasks in the cytoplasm to large animals moving in patchy environment. Here, we use speckle light fields to study the anomalous diffusion in an active matter system consisting of micron-sized silica particles(diameter 5 μm) and motile bacterial cells (E. coli). The speckle light fields are generated by mode mixing inside a multimode optical fiber where a small amount of incident laser power is needed to obtain an effective disordered optical landscape for the purpose of optical manipulation. We experimentally show how complex potentials contribute to the long-term dynamics of the active matter system and observed an enhanced diffusion of particles interacting with the active bacterial bath in the speckle light fields. We showed that this effect can be tuned and controlled by varying the intensity and the statistical properties of the speckle pattern. Potentially, these results could be of interest for many technological applications, such as the manipulation of microparticles inside optically disordered media of biological interest.

  7. Controlling the Transient Interface Shape and Deposition Profile Left by Desiccation of Colloidal Droplets on Multiple Polymer Surfaces

    NASA Astrophysics Data System (ADS)

    Dunning, Peter David

    . Implementation of this technique requires that the colloidal droplet be separated from the active electrode by a dielectric layer to prevent electrolysis. A variety of polymer layers have been used in EWOD devices for a variety of applications. In applications that involve desiccation of colloidal suspensions, the material for this layer should be chosen carefully as it can play an important role in the resulting deposition pattern. An experimental method to monitor the transient evolution of the shape of an evaporating colloidal droplet and optically quantify the resultant deposition pattern is presented. Unactuated colloidal suspensions will be desiccated on a variety of substrates commonly used in EWOD applications. Transient image profiles and particle deposition patterns are examined for droplets containing fluorescent micro-particles. Qualitative and quantitative comparisons of these results will be used to compare multiple different cases in an effort to provide insight into the effects of polymer selection on the drying dynamics and resultant deposition patterns of desiccated colloidal materials. It was found that the equilibrium and receding contact angles between the surface and the droplet play a key role in the evaporation dynamics and the resulting deposition patterns left by a desiccated colloidal suspension. The equilibrium contact angle controls the initial contact diameter for a droplet of a given volume. As a droplet on a surface evaporates, the evolution of the interface shape and the contact diameter can generally be described by three different regimes. The Constant Contact Radius (CCR) regime occurs when the contact line is pinned while the contact angle decreases. The Constant Contact Angle (CCA) regime occurs when the contact line recedes while the contact angle remains constant. The Mixed regime occurs when the contact radius and angle both reduce over time. The presence of the CCA regime allows the contact line to recede creating a more uniform

  8. Differentiation of colloidal and dissolved silica: Analytical separation using spectrophotometry and inductively coupled plasma atomic emission spectrometry

    USGS Publications Warehouse

    Lewis-Russ, A.; Ranville, J.; Kashuba, A.T.

    1991-01-01

    A method is described that differentiates between solutions containing silica-dominated colloids and solutions that are essentially free of colloids. Suspensions of tuff particles were treated to remove colloids by centrifugation, filtration or both. Agreement of silica concentrations determined by inductively coupled plasma atomic emission spectrometry and by a spectrophotometric method was taken as an indication of colloid-free solutions. For two tuffs, centrifugation was effective for removing colloids. For the third, highly altered tuff, filtration was more effective for removing colloids.

  9. Experimental evidence of colloids and nanoparticles presence from 25 waste leachates

    SciTech Connect

    Hennebert, Pierre; Avellan, Astrid; Yan, Junfang; Aguerre-Chariol, Olivier

    2013-09-15

    Highlights: • This work is the first assessment of colloids in waste leachates. • Analytical methods are proposed and discussed. • All the waste have at least one element in colloidal form, and some elements are always colloidal. • Man-made nanoparticles are observed. • It can change the interpretation of leachate elemental concentration. - Abstract: The potential colloids release from a large panel of 25 solid industrial and municipal waste leachates, contaminated soil, contaminated sediments and landfill leachates was studied. Standardized leaching, cascade filtrations and measurement of element concentrations in the microfiltrate (MF) and ultrafiltrate (UF) fraction were used to easily detect colloids potentially released by waste. Precautions against CO{sub 2} capture by alkaline leachates, or bacterial re-growth in leachates from wastes containing organic matter should be taken. Most of the colloidal particles were visible by transmission electron microscopy with energy dispersion spectrometry (TEM–EDS) if their elemental MF concentration is greater than 200 μg l{sup −1}. If the samples are dried during the preparation for microscopy, neoformation of particles can occur from the soluble part of the element. Size distribution analysis measured by photon correlation spectroscopy (PCS) were frequently unvalid, particularly due to polydispersity and/or too low concentrations in the leachates. A low sensitivity device is required, and further improvement is desirable in that field. For some waste leachates, particles had a zeta potential strong enough to remain in suspension. Mn, As, Co, Pb, Sn, Zn had always a colloidal form (MF concentration/UF concentration > 1.5) and total organic carbon (TOC), Fe, P, Ba, Cr, Cu, Ni are partly colloidal for more than half of the samples). Nearly all the micro-pollutants (As, Ba, Co, Cr, Cu, Mo, Ni, Pb, Sb, Sn, V and Zn) were found at least once in colloidal form greater than 100 μg l{sup −1}. In particular

  10. Colloidally stable surface-modified iron oxide nanoparticles: Preparation, characterization and anti-tumor activity

    NASA Astrophysics Data System (ADS)

    Macková, Hana; Horák, Daniel; Donchenko, Georgiy Viktorovich; Andriyaka, Vadim Ivanovich; Palyvoda, Olga Mikhailovna; Chernishov, Vladimir Ivanovich; Chekhun, Vasyl Fedorovich; Todor, Igor Nikolaevich; Kuzmenko, Oleksandr Ivanovich

    2015-04-01

    Maghemite (γ-Fe2O3) nanoparticles were obtained by co-precipitation of Fe(II) and Fe(III) chlorides and subsequent oxidation with sodium hypochlorite and coated with poly(N,N-dimethylacrylamide-co-acrylic acid) [P(DMAAm-AA)]. They were characterized by a range of methods including transmission electron microscopy (TEM), elemental analysis, dynamic light scattering (DLS) and zeta potential measurements. The effect of superparamagnetic P(DMAAm-AA)-γ-Fe2O3 nanoparticles on oxidation of blood lipids, glutathione and proteins in blood serum was detected using 2-thiobarbituric acid and the ThioGlo fluorophore. Finally, mice received magnetic nanoparticles administered per os and the antitumor activity of the particles was tested on Lewis lung carcinoma (LLC) in male mice line C57BL/6 as an experimental in vivo metastatic tumor model; the tumor size was measured and the number of metastases in lungs was determined. Surface-modified γ-Fe2O3 nanoparticles showed higher antitumor and antimetastatic activities than commercial CuFe2O4 particles and the conventional antitumor agent cisplatin.

  11. Stabilization of Colloidal Silica Using Small Polyols

    SciTech Connect

    GULLEY, GERALD L.; MARTIN, JAMES E.

    1999-09-07

    We have discovered that small polyols are reasonably effective at stabilizing colloidal silica against aggregation, even under the conditions of high pH and salt concentration. Both quasielastic and elastic light scattering were used to show that these polyols dramatically decrease the aggregation rate of the suspension, changing the growth kinetics from diffusion-limited cluster-cluster aggregation to reaction-limited cluster-cluster aggregation. These polyols maybe useful in the treatment of tank wastes at the Hanford site.

  12. Physics in ordered and disordered colloidal matter composed of poly(N-isopropylacrylamide) microgel particles.

    PubMed

    Yunker, Peter J; Chen, Ke; Gratale, Matthew D; Lohr, Matthew A; Still, Tim; Yodh, A G

    2014-05-01

    This review collects and describes experiments that employ colloidal suspensions to probe physics in ordered and disordered solids and related complex fluids. The unifying feature of this body of work is its clever usage of poly(N-isopropylacrylamide) (PNIPAM) microgel particles. These temperature-sensitive colloidal particles provide experimenters with a 'knob' for in situ control of particle size, particle interaction and particle packing fraction that, in turn, influence the structural and dynamical behavior of the complex fluids and solids. A brief summary of PNIPAM particle synthesis and properties is given, followed by a synopsis of current activity in the field. The latter discussion describes a variety of soft matter investigations including those that explore formation and melting of crystals and clusters, and those that probe structure, rearrangement and rheology of disordered (jammed/glassy) and partially ordered matter. The review, therefore, provides a snapshot of a broad range of physics phenomenology which benefits from the unique properties of responsive microgel particles.

  13. Manipulating semiconductor colloidal stability through doping.

    PubMed

    Fleharty, Mark E; van Swol, Frank; Petsev, Dimiter N

    2014-10-10

    The interface between a doped semiconductor material and electrolyte solution is of considerable fundamental interest, and is relevant to systems of practical importance. Both adjacent domains contain mobile charges, which respond to potential variations. This is exploited to design electronic and optoelectronic sensors, and other enabling semiconductor colloidal materials. We show that the charge mobility in both phases leads to a new type of interaction between semiconductor colloids suspended in aqueous electrolyte solutions. This interaction is due to the electrostatic response of the semiconductor interior to disturbances in the external field upon the approach of two particles. The electrostatic repulsion between two charged colloids is reduced from the one governed by the charged groups present at the particles surfaces. This type of interaction is unique to semiconductor particles and may have a substantial effect on the suspension dynamics and stability.

  14. Effect of phenylalanine on Taxol production and antioxidant activity of extracts of suspension-cultured hazel (Corylus avellana L.) cells.

    PubMed

    Bemani, Ebrahim; Ghanati, Faezeh; Rezaei, Ayatollah; Jamshidi, Mitra

    2013-07-01

    Taxol is produced by a few microorganisms and plants such as yew (Taxus sp.). Recent researches have shown that hazel (Corylus avellana L.) is also able to produce Taxol. In the present study, effects of different concentrations of phenylalanine (Phe) on the production of Taxol, antioxidant activity, and cytotoxic effects of extracts of suspension-cultured hazel cells were investigated. The cells were treated with different concentrations of Phe on day 7 of subculture and were harvested on day 14. The results showed that the amounts of Taxol and antioxidant activity were increased by increasing the phenylalanine supply. Interestingly, the cytotoxic effects of hazel cell extract were even stronger than that of pure Taxol (standard), suggesting hazel cell extract as a novel and suitable probe for treating human cancer. Application of phenylalanine to hazel cells exaggerates their effects.

  15. Effect of Solar Particle Event Radiation and Hindlimb Suspension on Gastrointestinal Tract Bacterial Translocation and Immune Activation

    PubMed Central

    Zhou, Yu; Ni, Houping; Li, Minghong; Sanzari, Jenine K.; Diffenderfer, Eric S.; Lin, Liyong; Kennedy, Ann R.; Weissman, Drew

    2012-01-01

    The environmental conditions that could lead to an increased risk for the development of an infection during prolonged space flight include: microgravity, stress, radiation, disturbance of circadian rhythms, and altered nutritional intake. A large body of literature exists on the impairment of the immune system by space flight. With the advent of missions outside the Earth's magnetic field, the increased risk of adverse effects due to exposure to radiation from a solar particle event (SPE) needs to be considered. Using models of reduced gravity and SPE radiation, we identify that either 2 Gy of radiation or hindlimb suspension alone leads to activation of the innate immune system and the two together are synergistic. The mechanism for the transient systemic immune activation is a reduced ability of the GI tract to contain bacterial products. The identification of mechanisms responsible for immune dysfunction during extended space missions will allow the development of specific countermeasures. PMID:23028522

  16. Antidepressant-like activity of liposomal formulation containing nimodipine treatment in the tail suspension test, forced swim test and MAOB activity in mice.

    PubMed

    Moreno, Lina Clara Gayoso E Almendra Ibiapina; Rolim, Hercília Maria Lins; Freitas, Rivelilson Mendes; Santos-Magalhães, Nereide Stela

    2016-09-01

    Previous studies have shown that intracellular calcium ion dysfunction may be an etiological factor in affective illness. Nimodipine (NMD) is a Ca(2+) channel blocker that has been extensively investigated for therapy of central nervous system (CNS) disorders. In this work, we have evaluated the antidepressant-like activity of nimodipine encapsulated into liposomes (NMD-Lipo) in mice through tail suspension and forced swim assays, as well as MAOB activity. During the tail suspension test, the administration of NMD-Lipo at 0.1, 1 and 10mg/kg was able to promote a reduction in the immobility time of animals greater than the positive control (imipramine). In the forced swim test, the immobility time of mice treated with NMD-Lipo was reduced. This reduction was significantly greater than that found in the animals treated with imipramine and paroxetine. This may suggest that NMD-Lipo provides more antidepressant-like activity than in positive controls. The groups that received a combination of liposomal NMD and antidepressant drugs showed lower immobility time than the groups, which were treated only with imipramine or paroxetine. The mice treated with the combination of NMD-Lipo and reserpine presented an increase in the time of immobility compared with animals treated only with NMD-Lipo. There was a significant decrease in MAOB activity in animals treated with NMD-Lipo compared with untreated animals. The results of the tail suspension test, forced swim test and MAOB activity suggested that the antidepressant activity of NMD-Lipo may be related to an increase in the cerebral monoamine concentrations.

  17. 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.

  18. Surface speciation of myo-inositol hexakisphosphate adsorbed on TiO2 nanoparticles and its impact on their colloidal stability in aqueous suspension: A comparative study with orthophosphate.

    PubMed

    Wan, Biao; Yan, Yupeng; Liu, Fan; Tan, Wenfeng; He, Jiajie; Feng, Xionghan

    2016-02-15

    Despite extensive research demonstrating the influence of organic matter and inorganic phosphate on the stability of TiO2 nanoparticles (NPs), far less research has assessed the impact of myo-inositol hexakisphosphate (IHP), a common organic phosphate widely present in the environment. In this study, the adsorption of IHP on TiO2 NPs and its impact on their colloidal stability were investigated using batch experiments, dynamic light scattering (DLS) techniques, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) and solid-state (31)P nuclear magnetic resonance (NMR) spectroscopy. Inorganic orthophosphate (Pi) adsorption was run for comparison. The ratio of the Pi/IHP adsorption density (1.528: 0.453) at pH5.0 suggested that IHP may complex on the TiO2 surface through three of its six phosphate groups. Zeta potential measurements, ATR-FTIR and NMR spectra indicated that IHP/Pi adsorbed onto TiO2 NPs by forming inner-sphere complexes and modified the surface charge of these NPs, which exerted a great impact on their colloidal stability. Interactions between NPs measured by sedimentation and aggregation size highly depended on the pH, surface phosphorus coverage, and surface phosphorus species. The impact of IHP on the aggregation and dispersion of TiO2 NPs was significantly larger than that of Pi, in agreement with the calculation from the DLVO theory. This study highlighted the impact of IHP relative to Pi on the colloidal stability of TiO2 NPs in phosphorus-enriched environments. PMID:26657256

  19. A randomized controlled clinical study to evaluate the effectiveness of an active moisturizing lotion with colloidal oatmeal skin protectant versus its vehicle for the relief of xerosis.

    PubMed

    Kalaaji, Amer N; Wallo, Warren

    2014-10-01

    Xerosis is a common skin condition, occurring most often in the winter and in low relative humidity, which results in loss of moisture, cracking, and desquamation. Many emollient creams and lotions are available for use as preventive moisturizers. However, few controlled experiments have been published comparing the efficacy of active moisturizing products versus the vehicle used to deliver the products to the skin. Therefore, we conducted this randomized, double-blind, controlled clinical study to objectively compare a commercially available moisturizing product against its own vehicle. The active colloidal oatmeal moisturizer used in this study showed significant benefits versus its vehicle control in several dermatological parameters used to measure skin dryness. PMID:25607563

  20. A randomized controlled clinical study to evaluate the effectiveness of an active moisturizing lotion with colloidal oatmeal skin protectant versus its vehicle for the relief of xerosis.

    PubMed

    Kalaaji, Amer N; Wallo, Warren

    2014-10-01

    Xerosis is a common skin condition, occurring most often in the winter and in low relative humidity, which results in loss of moisture, cracking, and desquamation. Many emollient creams and lotions are available for use as preventive moisturizers. However, few controlled experiments have been published comparing the efficacy of active moisturizing products versus the vehicle used to deliver the products to the skin. Therefore, we conducted this randomized, double-blind, controlled clinical study to objectively compare a commercially available moisturizing product against its own vehicle. The active colloidal oatmeal moisturizer used in this study showed significant benefits versus its vehicle control in several dermatological parameters used to measure skin dryness.