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Sample records for adv colloid interface

  1. Interface colloidal robotic manipulator

    DOEpatents

    Aronson, Igor; Snezhko, Oleksiy

    2015-08-04

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

  2. Active colloids at fluid interfaces.

    PubMed

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

    2016-05-01

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

  3. Colloids at NAPL-Interfaces

    NASA Astrophysics Data System (ADS)

    Baumann, Thomas; Metz, Christian

    2014-05-01

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

  4. Gold Nanocups: Colloidal Gold Nanocups with Orientation-Dependent Plasmonic Properties (Adv. Mater. 30/2016).

    PubMed

    Jiang, Ruibin; Qin, Feng; Liu, Yejing; Ling, Xing Yi; Guo, Jun; Tang, Minghua; Cheng, Si; Wang, Jianfang

    2016-08-01

    On page 6322, J. F. Wang and co-workers report a wet-chemistry method for the preparation of colloidal Au nanocups and their plasmonic properties. The Au nanocups are prepared through single-vertex-initiated Au deposition on PbS nano-octahedrons and subsequent selective dissolution of PbS. Owing to the orientation-dependent coupling strengths, the obtained Au nanocups display orientation-dependent plasmonic properties and Raman enhancements when deposited on substrates. PMID:27493069

  5. Liquid-vapor interfaces of patchy colloids.

    PubMed

    Oleksy, A; Teixeira, P I C

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    McGorty, Ryan

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

  7. Liquid-vapor interfaces of patchy colloids

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  8. Polymers at interfaces and in colloidal dispersions.

    PubMed

    Fleer, Gerard J

    2010-09-15

    This review is an extended version of the Overbeek lecture 2009, given at the occasion of the 23rd Conference of ECIS (European Colloid and Interface Society) in Antalya, where I received the fifth Overbeek Gold Medal awarded by ECIS. I first summarize the basics of numerical SF-SCF: the Scheutjens-Fleer version of Self-Consistent-Field theory for inhomogeneous systems, including polymer adsorption and depletion. The conformational statistics are taken from the (non-SCF) DiMarzio-Rubin lattice model for homopolymer adsorption, which enumerates the conformational details exactly by a discrete propagator for the endpoint distribution but does not account for polymer-solvent interaction and for the volume-filling constraint. SF-SCF corrects for this by adjusting the field such that it becomes self-consistent. The model can be generalized to more complex systems: polydispersity, brushes, random and block copolymers, polyelectrolytes, branching, surfactants, micelles, membranes, vesicles, wetting, etc. On a mean-field level the results are exact; the disadvantage is that only numerical data are obtained. Extensions to excluded-volume polymers are in progress. Analytical approximations for simple systems are based upon solving the Edwards diffusion equation. This equation is the continuum variant of the lattice propagator, but ignores the finite segment size (analogous to the Poisson-Boltzmann equation without a Stern layer). By using the discrete propagator for segments next to the surface as the boundary condition in the continuum model, the finite segment size can be introduced into the continuum description, like the ion size in the Stern-Poisson-Boltzmann model. In most cases a ground-state approximation is needed to find analytical solutions. In this way realistic analytical approximations for simple cases can be found, including depletion effects that occur in mixtures of colloids plus non-adsorbing polymers. In the final part of this review I discuss a

  9. Tuning Colloid-Interface Interactions by Salt Partitioning.

    PubMed

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

    2016-08-26

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

  10. Tissue Boundaries: Mimicking Tissue Boundaries by Sharp Multiparameter Matrix Interfaces (Adv. Healthcare Mater. 15/2016).

    PubMed

    Sapudom, Jiranuwat; Rubner, Stefan; Martin, Steve; Pompe, Tilo

    2016-08-01

    Engineering interfaces of extracellular compartments mimicking native tissues is key to study cell behavior in a physiologically relevant context and for a successful translation of these new biomaterials engineering principles in regenerative and therapeutic applications. Tilo Pompe and co-workers demonstrate a strategy to engineer multiparameter matrix interfaces using a sequential reconstitution of two well-defined Collagen I based matrices on page 1861. Such matrix interfaces trigger cell migration directionality normal to the interface plane in dependence on matrix pore size. PMID:27511951

  11. Charged hydrophobic colloids at an oil-aqueous phase interface

    NASA Astrophysics Data System (ADS)

    Kelleher, Colm P.; Wang, Anna; Guerrero-García, Guillermo Iván; Hollingsworth, Andrew D.; Guerra, Rodrigo E.; Krishnatreya, Bhaskar Jyoti; Grier, David G.; Manoharan, Vinothan N.; Chaikin, Paul M.

    2015-12-01

    Hydrophobic poly(methyl methacrylate) (PMMA) colloidal particles, when dispersed in oil with a relatively high dielectric constant, can become highly charged. In the presence of an interface with a conducting aqueous phase, image-charge effects lead to strong binding of colloidal particles to the interface, even though the particles are wetted very little by the aqueous phase. We study both the behavior of individual colloidal particles as they approach the interface and the interactions between particles that are already interfacially bound. We demonstrate that using particles which are minimally wetted by the aqueous phase allows us to isolate and study those interactions which are due solely to charging of the particle surface in oil. Finally, we show that these interactions can be understood by a simple image-charge model in which the particle charge q is the sole fitting parameter.

  12. Pulsed Lasers: Pulsed Lasers Employing Solution-Processed Plasmonic Cu3- x P Colloidal Nanocrystals (Adv. Mater. 18/2016).

    PubMed

    Liu, Zeke; Mu, Haoran; Xiao, Si; Wang, Rongbin; Wang, Zhiteng; Wang, Weiwei; Wang, Yongjie; Zhu, Xiangxiang; Lu, Kunyuan; Zhang, Han; Lee, Shuit-Tong; Bao, Qiaoliang; Ma, Wanli

    2016-05-01

    Q. Bao, W. Ma and co-workers demonstrate the usage of plasmonic Cu3-x P colloidal nanocrystals as a new type of tunable saturable absorber for the generation of high-energy pulses in a fiber laser. As described on page 3535, these low-cost, solution-processed, next-generation nonlinear optical materials can be harnessed for applications in signal processing and optical communication. PMID:27151629

  13. Ultrafast desorption of colloidal particles from fluid interfaces

    PubMed Central

    Poulichet, Vincent; Garbin, Valeria

    2015-01-01

    The self-assembly of solid particles at fluid–fluid interfaces is widely exploited to stabilize emulsions and foams, and in materials synthesis. The self-assembly mechanism is very robust owing to the large capillary energy associated with particle adsorption, of the order of millions of times the thermal energy for micrometer-sized colloids. The microstructure of the interfacial colloid monolayer can also favor stability, for instance in the case of particle-stabilized bubbles, which can be indefinitely stable against dissolution due to jamming of the colloid monolayer. As a result, significant challenges arise when destabilization and particle removal are a requirement. Here we demonstrate ultrafast desorption of colloid monolayers from the interface of particle-stabilized bubbles. We drive the bubbles into periodic compression–expansion using ultrasound waves, causing significant deformation and microstructural changes in the particle monolayer. Using high-speed microscopy we uncover different particle expulsion scenarios depending on the mode of bubble deformation, including highly directional patterns of particle release during shape oscillations. Complete removal of colloid monolayers from bubbles is achieved in under a millisecond. Our method should find a broad range of applications, from nanoparticle recycling in sustainable processes to programmable particle delivery in lab-on-a-chip applications. PMID:25922529

  14. Ultrafast desorption of colloidal particles from fluid interfaces.

    PubMed

    Poulichet, Vincent; Garbin, Valeria

    2015-05-12

    The self-assembly of solid particles at fluid-fluid interfaces is widely exploited to stabilize emulsions and foams, and in materials synthesis. The self-assembly mechanism is very robust owing to the large capillary energy associated with particle adsorption, of the order of millions of times the thermal energy for micrometer-sized colloids. The microstructure of the interfacial colloid monolayer can also favor stability, for instance in the case of particle-stabilized bubbles, which can be indefinitely stable against dissolution due to jamming of the colloid monolayer. As a result, significant challenges arise when destabilization and particle removal are a requirement. Here we demonstrate ultrafast desorption of colloid monolayers from the interface of particle-stabilized bubbles. We drive the bubbles into periodic compression-expansion using ultrasound waves, causing significant deformation and microstructural changes in the particle monolayer. Using high-speed microscopy we uncover different particle expulsion scenarios depending on the mode of bubble deformation, including highly directional patterns of particle release during shape oscillations. Complete removal of colloid monolayers from bubbles is achieved in under a millisecond. Our method should find a broad range of applications, from nanoparticle recycling in sustainable processes to programmable particle delivery in lab-on-a-chip applications. PMID:25922529

  15. Colloidal Particles and Liquid Interfaces: A Spectrum of Interactions

    NASA Astrophysics Data System (ADS)

    Kaz, David Martin

    Young's law predicts that a colloidal sphere in equilibrium with a liquid interface will straddle the two fluids, its height above the interface defined by an equilibrium contact angle. This equilibrium analysis has been used to explain why colloids often bind to liquid interfaces, an effect first observed a century ago by Ramsden and Pickering and later exploited in a wide range of material processes, including emulsification, water purification, mineral recovery, encapsulation, and the making of nanostructured materials. But little is known about the dynamics of binding, or any aspect of the interaction between a particle and an interface outside of equilibrium. This thesis explores the spectrum of particle-interface interactions, from non-binding to non-adsorptive binding and finally adsorptive binding and the relaxation toward equilibrium that ensues. Chapter 2 reviews the importance of interfacial particles in materials science, and serves as a partial motivation for the work presented here. Chapter 3 describes the apparatus and experimental procedures employed in the acquisition of our data, with a short review of experiments that led to the current set. Special attention is paid to the optical apparatus and the custom sample cells we designed. Chapter 4 deals with non-adsorptive interactions between colloidal particles and liquid interfaces. A theoretical discussion founded on (but not wedded to) classical DLVO theory is presented before the results of our experiments are analyzed. It is shown that particle-interface interactions may be purely repulsive or contain an attractive component that results in binding to the interface that is not associated with breach. In chapter 5 the adsorption of polystyrene microspheres to a water-oil interface is shown to be characterized by a sudden breach and an unexpectedly slow relaxation. Particles do not reach equilibrium even after 100 seconds, and the relaxation appears logarithmic in time, suggesting that complete

  16. Ordered and disordered colloidal particle monolayers at liquid crystal interfaces

    NASA Astrophysics Data System (ADS)

    Wei, Wei-Shao; Lohr, Matthew; Gharbi, Mohamed Amine; Stebe, Kathleen; Yodh, A. G.

    2014-03-01

    In this work, we investigate ordered colloidal particle monolayers at the air/liquid-crystal (LC) interface. Specifically, silica microparticles are treated with DMOAP to create homeotropic anchoring of LC mesogens at their surfaces. These particles are then spread on an air-exposed interface of the LC 5CB. Macroscopic ordered patterns of these microparticles form due to long-range interactions between particles that are mediated by elastic deformations of the underlying LC. Different confinement conditions lead to various self-assembled patterns ranging from hexagonal lattices to chain-like dipole formations. Using dark-field video microscopy, we track and analyze the dynamics of the colloidal particles in the hexagonal crystal packing, deriving mean squared displacements, phonon modes and density of states, etc., under several conditions. Further, heating of the nematic LC into its isotropic phase enables us to observe melting dynamics of this unusual quasi-2D crystal. The investigations provide insight into crystalline packings controlled by liquid-crystal mediated colloidal interactions. This work is funded by NSF Grant DMR12-05463, PENN MRSEC Grant DMR11-20901, and NASA Grant NNX08AO0G.

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

    NASA Astrophysics Data System (ADS)

    Nguyen, Duc; Schall, Peter

    2013-03-01

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

  18. Colloidal crystal formation at the "Nafion-water" interface.

    PubMed

    Bunkin, Nikolay F; Gorelik, Vladimir S; Kozlov, Valeriy A; Shkirin, Alexey V; Suyazov, Nikolay V

    2014-03-27

    In our recent work [Bunkin et al. Water 2013, 4, 129-154] it was first obtained that the water layer, having a size of several tens of micrometers and being adjacent to the swollen Nafion interface, is characterized by enhanced optical density; the refractive index of water at the interface is 1.46. Furthermore, the birefringence effect was observed in this layer. To explain these results, it has been hypothesized that because of "disentangling" of charged polymer chains from the Nafion surface toward the bulk of water, a photonic crystal close to the surface is formed [Bunkin et al. Water 2013, 4, 129-154]. In this paper, we describe experiments with laser-stimulated luminescence from dry and swollen Nafion. It was shown in the experiment with dry Nafion that the apparatus function of our experimental setup (Green's function) is well-described by a Gaussian profile. It was obtained that a highly concentrated colloidal suspension of Nafion particles with a steep spatial boundary is formed in the water layer adjacent to the interface. The volume density of the Nafion particles as a function of the distance from the Nafion interface was found. These findings can be considered indirect confirmation of the previously formulated photonic crystal hypothesis [Bunkin et al. Water 2013, 4, 129-154]. PMID:24568638

  19. Interaction of Charged Colloidal Particles at the Air-Water Interface.

    PubMed

    Girotto, Matheus; Dos Santos, Alexandre P; Levin, Yan

    2016-07-01

    We study, using Monte Carlo simulations, the interaction between charged colloidal particles confined to the air-water interface. The dependence of force on ionic strength and counterion valence is explored. For 1:1 electrolyte, we find that the electrostatic interaction at the interface is very close to the one observed in the bulk. On the other hand, for salts with multivalent counterions, an interface produces an enhanced attraction between like charged colloids. Finally, we explore the effect of induced surface charge at the air-water interface on the interaction between colloidal particles. PMID:26551757

  20. Strong collective attraction in colloidal clusters on a liquid-air interface.

    PubMed

    Pergamenshchik, V M

    2009-01-01

    It is shown that in a cluster of many colloids, trapped at a liquid-air interface, the well-known vertical-force-induced pairwise logarithmic attraction changes to a strongly enhanced power-law attraction. In large two-dimensional clusters, the attraction energy scales as the inverse square of the distance between colloids. The enhancement is given by the ratio eta = (square of the capillary length) / (interface surface area per colloid) and can be as large as 10;{5} . This explains why a very small vertical force on colloids, which is too weak to bring two of them together, can stabilize many-body structures on a liquid-air interface. The profile of a cluster is shown to consist of a large slow collective envelope modulated by a fast low-amplitude perturbation due to individual colloids. A closed equation for the slow envelope, which incorporates an arbitrary power-law repulsion between colloids, is derived. For example, this equation is solved for a large circular cluster with the hard-core colloid repulsion. It is suggested that the predicted effect is responsible for mysterious stabilization of colloidal structures observed in experiments on a surface of isotropic liquid and nematic liquid crystal. PMID:19257035

  1. Physical ageing of the contact line on colloidal particles at liquid interfaces

    NASA Astrophysics Data System (ADS)

    Kaz, David M.; McGorty, Ryan; Mani, Madhav; Brenner, Michael P.; Manoharan, Vinothan N.

    2012-02-01

    Young’s law predicts that a colloidal sphere in equilibrium with a liquid interface will straddle the two fluids, its height above the interface defined by an equilibrium contact angle. This has been used to explain why colloids often bind to liquid interfaces, and has been exploited in emulsification, water purification, mineral recovery, encapsulation and the making of nanostructured materials. However, little is known about the dynamics of binding. Here we show that the adsorption of polystyrene microspheres to a water/oil interface is characterized by a sudden breach and an unexpectedly slow relaxation. The relaxation appears logarithmic in time, indicating that complete equilibration may take months. Surprisingly, viscous dissipation appears to play little role. Instead, the observed dynamics, which bear strong resemblance to ageing in glassy systems, agree well with a model describing activated hopping of the contact line over nanoscale surface heterogeneities. These results may provide clues to longstanding questions on colloidal interactions at an interface.

  2. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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.

  4. Effective interaction between a colloid and a soft interface near criticality

    SciTech Connect

    Law, A. D. Harnau, L. Tröndle, M. Dietrich, S.

    2014-10-07

    Within mean-field theory we determine the universal scaling function for the effective force acting on a single colloid located near the interface between two coexisting liquid phases of a binary liquid mixture close to its critical consolute point. This is the first study of critical Casimir forces emerging from the confinement of a fluctuating medium by at least one shape responsive, soft interface, instead of by rigid walls only as studied previously. For this specific system, our semi-analytical calculation illustrates that knowledge of the colloid-induced, deformed shape of the interface allows one to accurately describe the effective interaction potential between the colloid and the interface. Moreover, our analysis demonstrates that the critical Casimir force involving a deformable interface is accurately described by a universal scaling function, the shape of which differs from that one for rigid walls.

  5. 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.

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

    PubMed

    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. PMID:26329221

  7. Probing the PEDOT:PSS/cell interface with conductive colloidal probe AFM-SECM

    NASA Astrophysics Data System (ADS)

    Knittel, P.; Zhang, H.; Kranz, C.; Wallace, G. G.; Higgins, M. J.

    2016-02-01

    Conductive colloidal probe Atomic Force-Scanning Electrochemical Microscopy (AFM-SECM) is a new approach, which employs electrically insulated AFM probes except for a gold-coated colloid located at the end of the cantilever. Hence, force measurements can be performed while biasing the conductive colloid under physiological conditions. Moreover, such colloids can be modified by electrochemical polymerization resulting, e.g. in conductive polymer-coated spheres, which in addition may be loaded with specific dopants. In contrast to other AFM-based single cell force spectroscopy measurements, these probes allow adhesion measurements at the cell-biomaterial interface on multiple cells in a rapid manner while the properties of the polymer can be changed by applying a bias. In addition, spatially resolved electrochemical information e.g., oxygen reduction can be obtained simultaneously. Conductive colloid AFM-SECM probes modified with poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) are used for single cell force measurements in mouse fibroblasts and single cell interactions are investigated as a function of the applied potential.Conductive colloidal probe Atomic Force-Scanning Electrochemical Microscopy (AFM-SECM) is a new approach, which employs electrically insulated AFM probes except for a gold-coated colloid located at the end of the cantilever. Hence, force measurements can be performed while biasing the conductive colloid under physiological conditions. Moreover, such colloids can be modified by electrochemical polymerization resulting, e.g. in conductive polymer-coated spheres, which in addition may be loaded with specific dopants. In contrast to other AFM-based single cell force spectroscopy measurements, these probes allow adhesion measurements at the cell-biomaterial interface on multiple cells in a rapid manner while the properties of the polymer can be changed by applying a bias. In addition, spatially resolved electrochemical

  8. An on-chip micromagnet frictionometer based on magnetically driven colloids for nano-bio interfaces.

    PubMed

    Hu, Xinghao; Goudu, Sandhya Rani; Torati, Sri Ramulu; Lim, Byeonghwa; Kim, Kunwoo; Kim, CheolGi

    2016-09-21

    A novel method based on remotely controlled magnetic forces of bio-functionalized superparamagnetic colloids using micromagnet arrays was devised to measure frictional force at the sub-picoNewton (pN) scale for bio-nano-/micro-electromechanical system (bio-NEMS/MEMS) interfaces in liquid. The circumferential motion of the colloids with phase-locked angles around the periphery of the micromagnets under an in-plane rotating magnetic field was governed by a balance between tangential magnetic force and drag force, which consists of viscous and frictional forces. A model correlating the phase-locked angles of the steady colloid rotation was formulated and validated by measuring the angles under controlled magnetic forces. Hence, the frictional forces on the streptavidin/Teflon interface between the colloids and the micromagnet arrays were obtained using the magnetic forces at the phase-locked angles. The friction coefficient for the streptavidin/Teflon interface was estimated to be approximately 0.036 regardless of both vertical force in the range of a few hundred pN and velocity in the range of a few tenths of μm s(-1). PMID:27456049

  9. Charging and discharging of single colloidal particles at oil/water interfaces

    NASA Astrophysics Data System (ADS)

    Gao, Peng; Xing, Xiaochen; Li, Ye; Ngai, To; Jin, Fan

    2014-05-01

    The physical behavior of solid colloids trapped at a fluid-fluid interface remains in itself an open fundamental issue. Here, we show that the gradients of surface tension can induce particles to jet towards the oil/water interface with velocities as high as ~ 60 mm/s when particle suspensions come in contact with the interface. We hypothesize that rubbing between the particles and oil lead to the spontaneous accumulation of negative charges on the hemisphere of those interfacial particles that contact the oil phase by means of triboelectrification. The charging process is highly dependent on the sliding distances, and gives rise to long-ranged repulsions that protect interfacial particles from coagulating at the interface by the presence of electrolyte. These triboelectric charges, however, are compensated within several hours, which affect the stability of interfacial particles. Importantly, by charging different kinds of colloidal particles using various spreading solvents and dispersion methods, we have demonstrated that charging and discharging of single colloidal particles at oil/water interfaces impacts a broad range of dynamical behavior.

  10. Charging and discharging of single colloidal particles at oil/water interfaces

    PubMed Central

    Gao, Peng; Xing, XiaoChen; Li, Ye; Ngai, To; Jin, Fan

    2014-01-01

    The physical behavior of solid colloids trapped at a fluid-fluid interface remains in itself an open fundamental issue. Here, we show that the gradients of surface tension can induce particles to jet towards the oil/water interface with velocities as high as ≈ 60 mm/s when particle suspensions come in contact with the interface. We hypothesize that rubbing between the particles and oil lead to the spontaneous accumulation of negative charges on the hemisphere of those interfacial particles that contact the oil phase by means of triboelectrification. The charging process is highly dependent on the sliding distances, and gives rise to long-ranged repulsions that protect interfacial particles from coagulating at the interface by the presence of electrolyte. These triboelectric charges, however, are compensated within several hours, which affect the stability of interfacial particles. Importantly, by charging different kinds of colloidal particles using various spreading solvents and dispersion methods, we have demonstrated that charging and discharging of single colloidal particles at oil/water interfaces impacts a broad range of dynamical behavior. PMID:24786477

  11. Squares of spheres: capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature

    NASA Astrophysics Data System (ADS)

    van der Gucht, Jasper; Ershov, Dmitry

    2014-03-01

    Objects floating at a liquid interface, such as breakfast cereals floating in a bowl of milk or bubbles at the surface of a soft drink, clump together in space-saving hexagons to minimize the disruption of the liquid interface. Micrometer-sized colloidal particles embedded in a liquid interface normally do not disrupt the interface, so that such clustering does not occur. Here, we show that this is different when the interface has a curvature that is anisotropic. We find that in this case the condition of constant contact angle along the three-phase contact line can only be satisfied when the interface is deformed. We present experiments and numerical calculations that demonstrate how this leads to quadrupolar capillary interactions between the particles, giving rise to organization into regular square lattices. We demonstrate that the strength of the governing anisotropic interactions can be rescaled with the deviatoric curvature alone, irrespective of the exact shape of the liquid interface. Our results suggest that anisotropic interactions can easily be induced between isotropic colloids through tailoring of the interfacial curvature.

  12. 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.

  13. Cosmology in a petri dish? Simulation of collective of colloids at fluid interfaces

    NASA Astrophysics Data System (ADS)

    Bleibel, J.

    2014-04-01

    Interfacially trapped, micrometer-sized colloidal particles interact via ranged capillary attraction which is analogous to two-dimensional screened Newtonian gravity with the capillary length λ as the tuneable screening length. Using Brownian namics simulations and density functional theory, we study the dynamics of an initially prepared distribution of colloids, either a random homogeneous distribution, or a finitely- sized patch of colloids. Whereas the limit λ → ∞ corresponds to the global collapse self-gravitating fluid, for smaller λ the dynamics crosses over to spinodal decomposition showing a coarsening of regions of enhanced density which emerge from initial fluctuations. For the finite patch of colloids and intermediate λ we predict theoretically and serve in simulations a ringlike density peak at the outer rim of the disclike patch, moving as an inbound shock wave. Experimental realizations of this crossover scenario appear be well possible for colloids trapped at water interfaces and having a radius of around micrometer. Finally, the influence of hydrodynamic interactions on this capillary collapse will be discussed briefly.

  14. Colloidal particles at fluid interfaces: Effective interactions, dynamics and a gravitation-like instability

    NASA Astrophysics Data System (ADS)

    Bleibel, J.; Domínguez, A.; Oettel, M.

    2013-11-01

    Colloidal particles of micrometer size usually become irreversibly trapped at fluid interfaces if they are partially wetted by one phase. This opens the chance to create two-dimensional model systems where the effective interactions between the particles are possibly influenced by the presence of the interface to a great extent. We will review recent developments in the quantitive understanding of these effective interactions with a special emphasis on electrostatics and capillarity. Charged colloids of micrometer size at an interface form effective dipoles whose strength sensitively depends on the double layer structure. We discuss the success of modified Poisson-Boltzmann equations with regard to measured colloidal dipole moments. On the other hand, for somewhat larger particles capillary interactions arise which are long-ranged and analogous to two-dimensional screened Newtonian gravity with the capillary length λ as the screening length. For colloidal diameters of around 10 micrometer, the collective effect of these long-ranged capillary interactions will dominate thermal motion and residual, short-ranged repulsions, and results in an instability towards a collapsed state for a finite patch of particles. Such long-ranged interactions with the associated instability are also of interest in other branches of physics, such as self-gravitating fluids in cosmology, two-dimensional vortex flow in hydrodynamics, and bacterial chemotaxis in biology. Starting from the colloidal case we develop and discuss a dynamical "phase diagram" in the temperature and interaction range variables which appears to be of more general scope and applicable also to other systems.

  15. Correlated Diffusion of Colloidal Particles near a Liquid-Liquid Interface

    PubMed Central

    Zhang, Wei; Chen, Song; Li, Na; Zhang, Jia zheng; Chen, Wei

    2014-01-01

    Optical microscopy and multi-particle tracking are used to investigate the cross-correlated diffusion of quasi two-dimensional colloidal particles near an oil-water interface. The behaviors of the correlated diffusion along longitudinal and transverse direction are asymmetric. It is shown that the characteristic length for longitudinal and transverse correlated diffusion are particle diameter and the distance from particle center to the interface, respectively, for large particle separation . The longitudinal and transverse correlated diffusion coefficient and are independent of the colloidal area fraction when , which indicates that the hydrodynamic interactions(HIs) among the particles are dominated by HIs through the surrounding fluid for small . For high area fraction , the power law exponent for the spatial decay of begins to decrease, which suggests the HIs are more contributed from the 2D particle monolayer self for large . PMID:24465498

  16. The Dynamic Organic/Inorganic Interface of Colloidal PbS Quantum Dots.

    PubMed

    Grisorio, Roberto; Debellis, Doriana; Suranna, Gian Paolo; Gigli, Giuseppe; Giansante, Carlo

    2016-06-01

    Colloidal quantum dots are composed of nanometer-sized crystallites of inorganic semiconductor materials bearing organic molecules at their surface. The organic/inorganic interface markedly affects forms and functions of the quantum dots, therefore its description and control are important for effective application. Herein we demonstrate that archetypal colloidal PbS quantum dots adapt their interface to the surroundings, thus existing in solution phase as equilibrium mixtures with their (metal-)organic ligand and inorganic core components. The interfacial equilibria are dictated by solvent polarity and concentration, show striking size dependence (leading to more stable ligand/core adducts for larger quantum dots), and selectively involve nanocrystal facets. This notion of ligand/core dynamic equilibrium may open novel synthetic paths and refined nanocrystal surface-chemistry strategies. PMID:27038221

  17. Entropic wetting and the free isotropic-nematic interface of hard colloidal platelets.

    PubMed

    Reich, Hendrik; Dijkstra, Marjolein; van Roij, René; Schmidt, Matthias

    2007-07-12

    We study bulk and interfacial properties of a model suspension of hard colloidal platelets with continuous orientations and vanishing thickness using both density functional theory, based on either a second virial approach or fundamental measure theory (FMT), and Monte Carlo (MC) simulations. We calculate the bulk equation of state, bulk isotropic-nematic (IN) coexistence, and properties of the (planar) free IN interface and of adsorption at a planar hard wall, where we find complete wetting of the nematic phase at the isotropic-wall interface upon approaching bulk IN coexistence. We investigate in detail the asymptotic decay of correlations at large distances. In all cases, the results from FMT and MC agree quantitatively. Our findings are of direct relevance to understanding interfacial properties of dispersions of colloidal platelets. PMID:17579390

  18. Stabilization of Pickering emulsions by generating complex colloidal layers at liquid-liquid interfaces.

    PubMed

    Lee, Geun Ju; Son, Han Am; Cho, Jang Woo; Choi, Sang Koo; Kim, Hyun Tae; Kim, Jin Woong

    2014-01-01

    Typical Pickering emulsions accumulate particles to form a robust colloidal layer at an immiscible liquid-liquid interface. However, if the particles are smaller than tens of nanometers, they have a tendency toward coming off from the interface, thereby destabilizing emulsion drops. To solve this problem, a technique that can make the adsorbed nanoparticles stay at the interface should be developed. This study introduces a practical method that allows us to obtain a mechanically stable Pickering emulsions; n-decane was emulsified to form an oil-in-water emulsion of which interface was stabilized with a complex colloidal layer consisting of 12 nm-sized silica nanoparticles, a poly(vinyl alcohol) binder, and an alkyl-chained silane coupling agent. We have found that in the conditions of high salinity, the emulsion drops attract each other and form an emulsion gel phase. However, even in such harsh conditions, the complex silica layer maintains its original structure at the interface, thus stabilizing the emulsion drop against coalescence. PMID:24183436

  19. Colloidal rod-sphere mixtures: fluid-fluid interfaces and the Onsager limit.

    PubMed

    Brader, Joseph M; Esztermann, Ansgar; Schmidt, Matthias

    2002-09-01

    Using a geometry-based density functional theory we investigate the free interface between demixed bulk fluid phases of a colloidal mixture of hard spheres and vanishingly thin needles. Results are presented for the spatial and orientational density distributions of the particles, as well as for the interface tension. Density profiles display oscillations on the sphere-rich side of the interface provided the sphere liquid phase is on the oscillatory side of the Fisher-Widom line in the bulk phase diagram. Needles tend to align parallel (perpendicular) to the interface on the needle-rich (sphere-rich) side displaying biaxial (uniaxial) order. Furthermore, we generalize the theory to the Onsager limit for interacting rods, and give explicit expressions for the functional in simple geometries. PMID:12366111

  20. Concentration-Polarization, Electro-Convection and Colloid Dynamics in Microchannel-Nanochannel Interface Devices

    NASA Astrophysics Data System (ADS)

    Yossifon, Gilad; Leibowitz, Neta; Green, Yoav; Liel, Uri; Schiffbauer, Jarrod; Park, Sinwook

    2014-11-01

    Understanding concentration-polarization (CP) and electroconvection processes along with colloid dynamics in microchannel-nanochannel/membrane interface devices are of particular interest in the field of micro- and nano-fluidics. Our design consists of a nano-slot/permselective membrane bounded by two micro-chambers, wherein we introduce dispersed colloids. Here we report various curios phenomena occurring in these systems. Among them: dielectrophoretic trapping of colloids at the nanoslot entrance in conjunction with the formation of electro-convective instability induced vortices; accumulation of colloids due field-focusing gradient effects within the diffusion layers; depression of the slope in the Warburg branch of the electrochemical impedance spectrum with increasing dc bias voltage as a result of nanochannel net electro-osmotic flow; suppression of the diffusion layer length via AC electrokinetics and its effect on ion transport; anomalous resistance minimum and unique chronopotentiometric signatures due to non-ideal nanochannel permselectivity. All of these stand as examples that highlight the essential differences between fabricated straight nanoslot and permselective membrane systems.

  1. Rapid Facial Fabrication of Silica Colloidal Crystal Film at the Air/Water Interface.

    PubMed

    Wang, Xia; Wang, Yun; Chen, Qiming

    2015-12-01

    A rapid and facial strategy has been developed to self-assemble 2D or 3D silica colloidal crystals at the air/water interface. The surface hydrophilicity of monodisperse silica microspheres were prepared by the Stöber method and modified by physical adsorption of a cationic surfactant (CTAB). The surface-modified silica microspheres were dispersed into an organic solvent and readily self-assemble at the air/water interface to form 2D monolayer film. The surface potential (ζ ) of silica microspheres could be changed with different concentration of CTAB aqueous solution. When the surface potential of silica particles was of -36.67 mV, a 2D monolayer film with close-packed and high-ordered structure could be easily obtained and may further be transferred onto a solid substrate layer by layer to develop a 3D multilayer film. UV-visible spectrophotometer was used to analyze the orderliness of colloidal crystal film, the Bragg diffraction positions and silica diameters were in good agreement with those were theoretically calculated. In addition, Atomic Force microscopy (AFM) was used to observe the arrangement of colloidal crystals. PMID:26682401

  2. Poisson-Boltzmann study of the effective electrostatic interaction between colloids at an electrolyte interface

    NASA Astrophysics Data System (ADS)

    Majee, Arghya; Bier, Markus; Dietrich, S.

    2016-08-01

    The effective electrostatic interaction between a pair of colloids, both of them located close to each other at an electrolyte interface, is studied by employing the full, nonlinear Poisson-Boltzmann (PB) theory within classical density functional theory. Using a simplified yet appropriate model, all contributions to the effective interaction are obtained exactly, albeit numerically. The comparison between our results and those obtained within linearized PB theory reveals that the latter overestimates these contributions significantly at short inter-particle separations. Whereas the surface contributions to the linear and the nonlinear PB results differ only quantitatively, the line contributions show qualitative differences at short separations. Moreover, a dependence of the line contribution on the solvation properties of the two adjacent fluids is found, which is absent within the linear theory. Our results are expected to enrich the understanding of effective interfacial interactions between colloids.

  3. 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

  4. Isotropic-Nematic Interface and Wetting in Suspensions of Colloidal Platelets

    NASA Astrophysics Data System (ADS)

    van der Beek, D.; Reich, H.; van der Schoot, P.; Dijkstra, M.; Schilling, T.; Vink, R.; Schmidt, M.; van Roij, R.; Lekkerkerker, H.

    2006-08-01

    We study interfacial phenomena in a colloidal dispersion of sterically stabilized gibbsite platelets, exhibiting coexisting isotropic and nematic phases separated by a sharp horizontal interface. The nematic phase wets a vertical glass wall and polarized light micrographs reveal homeotropic surface anchoring both at the free isotropic-nematic interface and at the wall. On the basis of complete wetting of the wall by the nematic phase, as found in our density functional calculations and computer simulations, we analyze the balance between Frank elasticity and surface anchoring near the contact line. Because of weak surface anchoring, the director field in the capillary rise region is uniform. From the measured rise (6μm) of the meniscus at the wall we determine the isotropic-nematic surface tension to be 3nN/m, in quantitative agreement with our theoretical and simulation results.

  5. Dynamics of ordered colloidal particle monolayers at nematic liquid crystal interfaces.

    PubMed

    Wei, Wei-Shao; Gharbi, Mohamed Amine; Lohr, Matthew A; Still, Tim; Gratale, Matthew D; Lubensky, T C; Stebe, Kathleen J; Yodh, A G

    2016-05-25

    We prepare two-dimensional crystalline packings of colloidal particles on surfaces of the nematic liquid crystal (NLC) 5CB, and we investigate the diffusion and vibrational phonon modes of these particles using video microscopy. Short-time particle diffusion at the air-NLC interface is well described by a Stokes-Einstein model with viscosity similar to that of 5CB. Crystal phonon modes, measured by particle displacement covariance techniques, are demonstrated to depend on the elastic constants of 5CB through interparticle forces produced by LC defects that extend from the interface into the underlying bulk material. The displacement correlations permit characterization of transverse and longitudinal sound velocities of the crystal packings, as well as the particle interactions produced by the LC defects. All behaviors are studied in the nematic phase as a function of increasing temperature up to the nematic-isotropic transition. PMID:27109759

  6. Interaction between colloidal particles on an oil-water interface in dilute and dense phases.

    PubMed

    Parolini, Lucia; Law, Adam D; Maestro, Armando; Buzza, D Martin A; Cicuta, Pietro

    2015-05-20

    The interaction between micron-sized charged colloidal particles at polar/non-polar liquid interfaces remains surprisingly poorly understood for a relatively simple physical chemistry system. By measuring the pair correlation function g(r) for different densities of polystyrene particles at the decane-water interface, and using a powerful predictor-corrector inversion scheme, effective pair-interaction potentials can be obtained up to fairly high densities, and these reproduce the experimental g(r) in forward simulations, so are self consistent. While at low densities these potentials agree with published dipole-dipole repulsion, measured by various methods, an apparent density dependence and long range attraction are obtained when the density is higher. This condition is thus explored in an alternative fashion, measuring the local mobility of colloids when confined by their neighbors. This method of extracting interaction potentials gives results that are consistent with dipolar repulsion throughout the concentration range, with the same magnitude as in the dilute limit. We are unable to rule out the density dependence based on the experimental accuracy of our data, but we show that incomplete equilibration of the experimental system, which would be possible despite long waiting times due to the very strong repulsions, is a possible cause of artefacts in the inverted potentials. We conclude that to within the precision of these measurements, the dilute pair potential remains valid at high density in this system. PMID:25924056

  7. Weak electrolyte dependence in the repulsion of colloids at an oil-water interface.

    PubMed

    Wirth, Christopher L; Furst, Eric M; Vermant, Jan

    2014-03-18

    The two-particle interaction between 3.1-μm-diameter polystyrene latex particles at a decane-water interface was measured with time-shared optical tweezers. The water subphase contained either 0.103 mM RbCl or 0.0342 mM MgCl2, which have hydrated cations of different size but identical anions. The choice of both the anion and the concentrations makes a comparison with published data on NaCl possible and also isolates the effect of the nature of the cation on the electrostatic interaction. The measured magnitude of the dipolar force and the relative changes as a function of electrolyte were in quantitative agreement with predictions from a recently published model that uses the Langevin-Poisson-Boltzmann equation including steric effects and the polarization saturation of the medium to predict the dipolar interaction (Frydel, D.; Oettel, M. Phys. Chem. Chem. Phys. 2011, 13, 4109-4118). These results support the hypothesis that a condensed layer of counterions contributes to the electrostatic interaction between colloidal particles at an oil-water interface. Although it has been suggested that the electrostatic interactions between particles at liquid interfaces could serve as a sensitive probe of the structural details of the electric double layer, both the model predictions and experimental measurements showed a maximum change of only ~25% in the magnitude of the interaction with a change in electrolyte under the conditions tested. The ability to resolve this small change was confounded by the heterogeneous nature of the interaction. Thus, despite the apparent importance of the choice of electrolyte, the subtlety of competing effects makes it unlikely that colloidal force measurements could be used to probe the fine structure of the electric double layer. PMID:24598009

  8. Directed Self-assembly of Colloidal Particles on a Blue Phase I Interface

    NASA Astrophysics Data System (ADS)

    Martinez-Gonzalez, Jose; Zhou, Ye; Sadati, Monirosadat; Abbott, Nicholas; de Pablo, Juan

    Blue phases are liquid states of matter with a highly ordered defect structure which confers unique properties among complex fluids. In this work, a free energy model of chiral liquid crystals is used to consider the self-assembly of colloids and nanoparticles on the interface of a Blue Phase I. It is shown that the crystalline defect structure of the blue phase produces intricate, two-dimensional hexagonal and Kagome structures among the nanoparticle arrangements, with lattice parameters that depend on the type of anchoring of the liquid crystal at the particle's surface. These parameters can be tuned via the chirality of the material, thereby offering intriguing possibilities for the creation of hierarchical materials based on the directed assembly of particles in chiral liquid crystals. This work is supported by the Department of Energy, Basic Energy Sciences, Materials Science and Engineering Division, Biomaterials Program, through DE-SC004025.

  9. Photocatalytic electrochemistry at a biological-membrane metal-colloid interface

    NASA Astrophysics Data System (ADS)

    Greenbaum, Elias

    1987-10-01

    A method for electrically contacting the electron-transport chain of photosynthesis is described. Colloidal platinum was prepared and precipitated directly onto photosynthetic thylakoid membranes from aqueous solution, and entrapped on fiberglass filter paper. This composition of matter was capable of sustained simultaneous photoevolution of hydrogen and oxygen when irradiated at any wavelength in the chlorophyll absorption spectrum. Experimental data support the interpretation that part of the platinum metal catalyst is precipitated adjacent to the photosystem-I reduction site of photosynthesis and the electron-transfer occurs across the interface between photosystem I and the catalyst. Photoactivity of the material was dependent on the nature of the ionic species from which the platinum was precipitated. When contacted with metal electrodes, the thylakoid-platinum combination is capable of generating a sustained flow of current through an external load resistor.

  10. Photocatalytic electrochemistry at a biological-membrane metal-colloid interface

    SciTech Connect

    Greenbaum, E.

    1987-10-18

    A method for electrically contacting the electron-transport chain of photosynthesis is described. Colloidal platinum was prepared and precipitated directly onto photosynthetic thylakoid membranes from aqueous solution, and entrapped on fiberglass filter paper. This composition of matter was capable of sustained simultaneous photoevolution of hydrogen and oxygen when irradiated at any wavelength in the chlorophyll absorption spectrum. Experimental data support the interpretation that part of the platinum metal catalyst is precipitated adjacent to the photosystem-I reduction site of photosynthesis and the electron-transfer occurs across the interface between photosystem I and the catalyst. Photoactivity of the material was dependent on the nature of the ionic species from which the platinum was precipitated. When contacted with metal electrodes, the thylakoid-platinum combination is capable of generating a sustained flow of current through an external load resistor. 3 refs.

  11. Generation and stability of bentonite colloids at the bentonite/granite interface of a deep geological radioactive waste repository

    NASA Astrophysics Data System (ADS)

    Missana, Tiziana; Alonso, Úrsula; Turrero, Maria Jesús

    2003-03-01

    The possible mechanisms of colloid generation at the near field/far field interface of a radioactive repository have been investigated by means of novel column experiments simulating the granite/bentonite boundary, both in dynamic and in quasi-static water flow conditions. It has been shown that solid particles and colloids can be detached from the bulk and mobilised by the water flow. The higher the flow rate, the higher the concentration of particles found in the water, according to an erosion process. However, the gel formation and the intrinsic tactoid structure of the clay play an important role in the submicron particle generation even in the compacted clay and in a confined system. In fact, once a bentonite gel is formed, in the regions where the clay is contacted with water, clay colloids can be formed even in quasi-static flow conditions. The potential relevance of these colloids in radionuclide transport has been studied by evaluating their stability in different chemical environments. The coagulation kinetics of natural bentonite colloids was experimentally studied as a function of the ionic strength and pH, by means of time-resolved light scattering techniques. It has been shown that these colloids are very stable in low saline (˜1×10 -3 M) and alkaline (pH≥8) waters.

  12. Generation and stability of bentonite colloids at the bentonite/granite interface of a deep geological radioactive waste repository.

    PubMed

    Missana, Tiziana; Alonso, Ursula; Turrero, Maria Jesús

    2003-03-01

    The possible mechanisms of colloid generation at the near field/far field interface of a radioactive repository have been investigated by means of novel column experiments simulating the granite/bentonite boundary, both in dynamic and in quasi-static water flow conditions. It has been shown that solid particles and colloids can be detached from the bulk and mobilised by the water flow. The higher the flow rate, the higher the concentration of particles found in the water, according to an erosion process. However, the gel formation and the intrinsic tactoid structure of the clay play an important role in the submicron particle generation even in the compacted clay and in a confined system. In fact, once a bentonite gel is formed, in the regions where the clay is contacted with water, clay colloids can be formed even in quasi-static flow conditions. The potential relevance of these colloids in radionuclide transport has been studied by evaluating their stability in different chemical environments. The coagulation kinetics of natural bentonite colloids was experimentally studied as a function of the ionic strength and pH, by means of time-resolved light scattering techniques. It has been shown that these colloids are very stable in low saline (approximately 1 x 10(-3) M) and alkaline (pH > or = 8) waters. PMID:12598091

  13. Colloidal-Particle Monolayers at Liquid Interfaces: Capsules, Membranes and Functional Electronic Junctions

    NASA Astrophysics Data System (ADS)

    Dinsmore, A. D.; McGorty, R.; Edmond, K. V.; Knutson, C. R.; Soyler, S. G.; Marquez, M.

    2004-11-01

    The interface between two liquids, as on the surface of a water droplet in oil, provides a versatile platform for self assembly of functional membranes, capsules, and other devices composed of colloidal particles. Owing to the large liquid interfacial tension, nanometer-to-micron-sized particles in either liquid readily adsorb at the interface, forming a densely packed monolayer. In this way, a shell of cross-linked particles is constructed around water droplets containing nutrients, drugs or, potentially, living cells. The resulting elastic capsules are transferred directly to a continuous aqueous solution, allowing diffusive permeation of macromolecules and small particles while encapsulating the larger objects. Moreover, liquid structures of cylindrical shape are formed by hydrodynamic focusing of a non-Newtonian aqueous solution; these are used as platforms for interfacial assembly. Finally, the assembly of ligand-stabilized nanoparticles on the surfaces of electrically conducting droplets in insulating oil leads to functional electronic devices, including single-electron transistors. We gratefully acknowledge support from Kraft Foods, Inc.

  14. Introducing high-quality planar defects into colloidal crystals via self-assembly at the air/water interface

    NASA Astrophysics Data System (ADS)

    Zhong, Kuo; Demeyer, Pieter-Jan; Zhou, Xingping; Kruglova, Olga; Verellen, Niels; Moshchalkov, Victor V.; Song, Kai; Clays, Koen

    2015-02-01

    We demonstrate a facile method for fabrication of colloidal crystals containing a planar defect by using PS@SiO2 core-shell spheres as building blocks. A monolayer of solid spheres was embedded in core-shell colloidal crystals serving as the defect layer, which formed by means of self-assembly at the air/water interface. Compared with previous methods, this fabrication method results in pronounced passbands in the band gaps of the colloidal photonic crystal. The FWHM of the obtained passband is only ~16nm, which is narrower than the previously reported results. The influence of the defect layer thickness on the optical properties of these sandwiched structures was also investigated. No high-cost processes or specific equipment is needed in our approach. Inverse opals with planar defects can be obtained via calcination of the PS cores, without the need of infiltration. The experimental results are in good agreement with simulations performed using the FDTD method.

  15. Nanoscale Interfaces in Colloidal Quantum Dot Solar Cells: Physical Insights and Materials Engineering Strategies

    NASA Astrophysics Data System (ADS)

    Kemp, Kyle Wayne

    With growing global energy demand there will be an increased need for sources of renewable energy such as solar cells. To make these photovoltaic technologies more competitive with conventional energy sources such as coal and natural gas requires further reduction in manufacturing costs that can be realized by solution processing and roll-to-roll printing. Colloidal quantum dots are a bandgap tunable, solution processible, semiconductor material which may offer a path forward to efficient, inexpensive photovoltaics. Despite impressive progress in performance with these materials, there remain limitations in photocarrier collection that must be overcome. This dissertation focuses on the characterization of charge recombination and transport in colloidal quantum dot photovoltaics, and the application of this knowledge to the development of new and better materials. Core-shell, PbS-CdS, quantum dots were investigated in an attempt to achieve better surface passivation and reduce electronic defects which can limit performance. Optimization of this material led to improved open circuit voltage, exceeding 0.6 V for the first time, and record published performance of 6% efficiency. Using temperature-dependent and transient photovoltage measurements we explored the significance of interface recombination on the operation of these devices. Careful engineering of the electrode using atomic layer deposition of ZnO helped lead to better TiO2 substrate materials and allowed us to realize a nearly two-fold reduction in recombination rate and an enhancement upwards of 50 mV in open circuit voltage. Carrier extraction efficiency was studied in these devices using intensity dependent current-voltage data of an operational solar cell. By developing an analytical model to describe recombination loss within the active layer of the device we were able to accurately determine transport lengths ranging up to 90 nm. Transient absorption and photoconductivity techniques were used to study

  16. Triangular tessellation scheme for the adsorption free energy at the liquid-liquid interface: Towards nonconvex patterned colloids.

    PubMed

    de Graaf, Joost; Dijkstra, Marjolein; van Roij, René

    2009-11-01

    We present a numerical technique, namely, triangular tessellation, to calculate the free energy associated with the adsorption of a colloidal particle at a flat interface. The theory and numerical scheme presented here are sufficiently general to handle nonconvex patchy colloids with arbitrary surface patterns characterized by a wetting angle, e.g., amphiphilicity. We ignore interfacial deformation due to capillary, electrostatic, or gravitational forces, but the method can be extended to take such effects into account. It is verified that the numerical method presented is accurate and sufficiently stable to be applied to more general situations than presented in this paper. The merits of the tessellation method prove to outweigh those of traditionally used semianalytic approaches, especially when it comes to generality and applicability. PMID:20364983

  17. Ligand dissociation mediated charge transfer observed at colloidal W18O49 nanoparticle interfaces.

    PubMed

    Grauer, David C; Alivisatos, A Paul

    2014-03-11

    Understanding charge transfer dynamics through the ligand shell of colloidal nanoparticles has been an important pursuit in solar energy conversion. While charge transport through ligand shells of nanoparticle films has been studied intensely in static dry and electrochemical systems, its influence on charge transfer kinetics in dispersed colloidal systems has received relatively less attention. This work reports the oxidation of amine passivated tungsten oxide nanoparticles by an organically soluble tris-(1,10-phenanthroline) iron(III) derivative. By following the rate of this oxidation optically via the production of the ferroin derivative under various reaction conditions and particle derivatizations, we are able to show that the fluxional ligand shells on dispersed, colloidal nanoparticles provide a separate and more facile pathway for charge transfer, in which the rate-limiting step for charge transfer is the ligand dissociation. Since such ligand shells are frequently required for nanoparticle stability, this observation has significant implications for colloidal nanoparticle photocatalysis. PMID:24564847

  18. 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

    A colloidal suspension is a small constituent of insoluble solid particles suspended in a liquid medium. Control over the wetting, evaporation, and deposition patterns left by colloidal suspensions is valuable in many biological, medical, industrial, and agricultural applications. Understanding the governing principles of wetting and evaporative phenomena of these colloidal suspensions may lead to greater control over resultant deposition patterns. Perhaps the most familiar pattern forms when an initially heterogeneous colloidal suspension leaves a dark ring pattern at the edge of a drop. This pattern is referred to as a coffee-stain and it can be seen from dried droplets of spilled coffee. This coffee-stain effect was first investigated by Deegan et. al. who discovered that these patterns occur when outward radial flows driven by evaporation at the triple contact line dominate over other effects. While the presence of coffee-stain patterns is undesirable in many printing and medical diagnostic processes, it can also be advantageous in the production of low cost transparent conductive films, the deposition of metal vapor, and the manipulation of biological structures. Controlling the interactions between the substrate, liquid, vapor, and particles can lead to control over the size and morphology of evaporative deposition patterns left by aqueous colloidal suspensions. Several methods have been developed to control the evaporation of colloidal suspensions to either suppress or enhance the coffee stain effect. Electrowetting on Dielectric (EWOD) is one promising method that has been used to control colloidal depositions by applying either an AC or DC electric field. EWOD actuation has the potential to dynamically control colloidal deposition left by desiccated droplets to either suppress or enhance the coffee stain effect. It may also allow for independent control of the fluidic interface and deposition of particles via electrowetting and electrokinetic forces

  19. Influence of an Additive-Free Particle Spreading Method on Interactions between Charged Colloidal Particles at an Oil/Water Interface.

    PubMed

    Gao, Peng; Yi, Zonglin; Xing, Xiaochen; Ngai, To; Jin, Fan

    2016-05-17

    The assembly and manipulation of charged colloidal particles at oil/water interfaces represent active areas of fundamental and applied research. Previously, we have shown that colloidal particles can spontaneously generate unstable residual charges at the particle/oil interface when spreading solvent is used to disperse them at an oil/water interface. These residual charges in turn affect the long-ranged electrostatic repulsive forces and packing of particles at the interface. To further uncover the influence arising from the spreading solvents on interfacial particle interactions, in the present study we utilize pure buoyancy to drive the particles onto an oil/water interface and compare the differences between such a spontaneously adsorbed particle monolayer to the spread monolayer based on solvent spreading techniques. Our results show that the solvent-free method could also lead particles to spread well at the interface, but it does not result in violent sliding of particles along the interface. More importantly, this additive-free spreading method can avoid the formation of unstable residual charges at the particle/oil interface. These findings agree well with our previous hypothesis; namely, those unstable residual charges are triboelectric charges that arise from the violently rubbing of particles on oil at the interface. Therefore, if the spreading solvents could be avoided, then we would be able to get rid of the formation of residual charges at interfaces. This finding will provide insight for precisely controlling the interactions among colloidal particles trapped at fluid/fluid interfaces. PMID:27108987

  20. Wall-fluid and liquid-gas interfaces of model colloid-polymer mixtures by simulation and theory.

    PubMed

    Fortini, Andrea; Dijkstra, Marjolein; Schmidt, Matthias; Wessels, Paul P F

    2005-05-01

    We perform a study of the interfacial properties of a model suspension of hard sphere colloids with diameter sigma(c) and nonadsorbing ideal polymer coils with diameter sigma(p) . For the mixture in contact with a planar hard wall, we obtain from simulations the wall-fluid interfacial free energy, gamma(wf) , for size ratios q =sigma(p)/sigma(c) =0.6 and 1, using thermodynamic integration, and study the (excess) adsorption of colloids, Gamma(c) , and of polymers, Gamma(p) , at the hard wall. The interfacial tension of the free liquid-gas interface, gamma(lg) , is obtained following three different routes in simulations: (i) from studying the system size dependence of the interfacial width according to the predictions of capillary wave theory, (ii) from the probability distribution of the colloid density at coexistence in the grand canonical ensemble, and (iii) for state points where the colloidal liquid wets the wall completely, from Young's equation relating gamma(lg) to the difference of wall-liquid and wall-gas interfacial tensions, gamma(wl)-gamma(wg) . In addition, we calculate gamma(wf) ,Gamma(c) , and Gamma(p) using density functional theory and a scaled particle theory based on free volume theory. Good agreement is found between the simulation results and those from density functional theory, while the results from scaled particle theory quantitatively deviate but reproduce some essential features. Simulation results for gamma(lg) obtained from the three different routes are all in good agreement. Density functional theory predicts gamma(lg) with good accuracy for high polymer reservoir packing fractions, but yields deviations from the simulation results close to the critical point. PMID:16089531

  1. Non-equilibrium magnetic colloidal dispersions at liquid-air interfaces: dynamic patterns, magnetic order and self-assembled swimmers.

    SciTech Connect

    Snezhko, A.

    2011-04-20

    Colloidal dispersions of interacting particles subjected to an external periodic forcing often develop nontrivial self-assembled patterns and complex collective behavior. A fundamental issue is how collective ordering in such non-equilibrium systems arises from the dynamics of discrete interacting components. In addition, from a practical viewpoint, by working in regimes far from equilibrium new self-organized structures which are generally not available through equilibrium thermodynamics can be created. In this review spontaneous self-assembly phenomena in magnetic colloidal dispersions suspended at liquid-air interfaces and driven out of equilibrium by an alternating magnetic field are presented. Experiments reveal a new type of nontrivially ordered self-assembled structures emerging in such systems in a certain range of excitation parameters. These dynamic structures emerge as a result of the competition between magnetic and hydrodynamic forces and have complex unconventional magnetic ordering. Nontrivial self-induced hydrodynamic fields accompany each out-of-equilibrium pattern. Spontaneous symmetry breaking of the self-induced surface flows leading to a formation of self-propelled microstructures has been discovered. Some features of the self-localized structures can be understood in the framework of the amplitude equation (Ginzburg-Landau type equation) for parametric waves coupled to the conservation law equation describing the evolution of the magnetic particle density and the Navier-Stokes equation for hydrodynamic flows. To understand the fundamental microscopic mechanisms governing self-assembly processes in magnetic colloidal dispersions at liquid-air interfaces a first-principle model for a non-equilibrium self-assembly is presented. The latter model allows us to capture in detail the entire process of out-of-equilibrium self-assembly in the system and reproduces most of the observed phenomenology.

  2. Sorption of colloids, organics, and metals onto gas-water, interfaces: Transport processes and potential remediation technology. 1997 annual progress report

    SciTech Connect

    Wan, J.

    1997-01-01

    'This research project has two objectives. The first is to improve basic understanding of contaminant interactions with gas-water interfaces, with emphasis on behavior of mixed contaminant systems. The second objective is to develop a sorptive microbubble fractionation remediation technique. Hypotheses supporting these objectives are: (1) contaminants and natural organics can sorb on and alter the interface hydrophobicity of the gas-water interfaces, and therefore influence sorption of colloids, metals, and radionuclides at gas-water interfaces; (2) surfactants can vastly increase sorption of colloids, metals and radionuclides selectively onto gas- water interfaces; (3) a sorptive microbubble fractionation remediation technique can be developed based on understanding of the previously mentioned processes. These hypotheses are being tested through quantification and visualization at both micro- and macro-scales.'

  3. Dynamic Self-Assembly and Self-Propulsion in Nonequilibrium Magnetic Colloidal Ensembles at a Liquid/Liquid Interface

    NASA Astrophysics Data System (ADS)

    Snezhko, Alexey; Aranson, Igor

    2011-03-01

    Ensembles of interacting particles subject to external periodic energy fluxes often develop nontrivial dynamics. Magnetic colloidal particles suspended over an interface of two immiscible liquids and energized by vertical alternating magnetic fields give rise to novel dynamic self-assembled structures (``asters'') which are not accessible at the liquid/air interfaces. Ferromagnetically ordered nickel spherical particles have been used in our experiments. Novel 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 is reported. We show that self-assembled aster structures become distorted in the presence of a small in-plane dc magnetic field and develop self-propulsion. The speed of locomotion can be effectively tuned by the amplitude of the dc field. The research was supported by the U.S. DOE, Office of Basic Energy Sciences, Division of Materials Science and Engineering, under the Contract No. DE AC02-06CH11357.

  4. Particle contact angles at fluid interfaces: pushing the boundary beyond hard uniform spherical colloids

    NASA Astrophysics Data System (ADS)

    Zanini, Michele; Isa, Lucio

    2016-08-01

    Micro and nanoparticles at fluid interfaces have been attracting increasing interest in the last few decades as building blocks for materials, as mechanical and structural probes for complex interfaces and as models for two-dimensional systems. The three-phase contact angle enters practically all aspects of the particle behavior at the interface: its thermodynamics (binding energy to the interface), dynamics (motion and drag at the interface) and interactions with the interface (adsorption and wetting). Moreover, many interactions among particles at the interface also strongly depend on the contact angle. These concepts have been extensively discussed for non-deformable, homogeneous and mostly spherical particles, but recent progress in particle synthesis and fabrication has instead moved in the direction of producing more complex micro and nanoscale objects, which can be responsive, deformable, heterogenous and/or anisotropic in shape, surface chemistry and material properties. These new particles have a much greater potential for applications and new science, and the study of their behavior at interfaces has only very recently started. In this paper, we critically review the current state of the art of the experimental methods available to measure the contact angle of micro and nanoparticles at fluid interfaces, indicating their strengths and limitations. We then comment on new particle systems that are currently attracting increasing interest in relation to their adsorption and assembly at fluid interfaces and discuss if and which ones of the current techniques are suited to investigate their properties at interfaces. Based on this discussion, we will finally try to indicate a direction in which new experimental methods should develop in the future to tackle the new challenges posed by the novel types of particles that more and more often are used at interfaces.

  5. Particle contact angles at fluid interfaces: pushing the boundary beyond hard uniform spherical colloids.

    PubMed

    Zanini, Michele; Isa, Lucio

    2016-08-10

    Micro and nanoparticles at fluid interfaces have been attracting increasing interest in the last few decades as building blocks for materials, as mechanical and structural probes for complex interfaces and as models for two-dimensional systems. The three-phase contact angle enters practically all aspects of the particle behavior at the interface: its thermodynamics (binding energy to the interface), dynamics (motion and drag at the interface) and interactions with the interface (adsorption and wetting). Moreover, many interactions among particles at the interface also strongly depend on the contact angle. These concepts have been extensively discussed for non-deformable, homogeneous and mostly spherical particles, but recent progress in particle synthesis and fabrication has instead moved in the direction of producing more complex micro and nanoscale objects, which can be responsive, deformable, heterogenous and/or anisotropic in shape, surface chemistry and material properties. These new particles have a much greater potential for applications and new science, and the study of their behavior at interfaces has only very recently started. In this paper, we critically review the current state of the art of the experimental methods available to measure the contact angle of micro and nanoparticles at fluid interfaces, indicating their strengths and limitations. We then comment on new particle systems that are currently attracting increasing interest in relation to their adsorption and assembly at fluid interfaces and discuss if and which ones of the current techniques are suited to investigate their properties at interfaces. Based on this discussion, we will finally try to indicate a direction in which new experimental methods should develop in the future to tackle the new challenges posed by the novel types of particles that more and more often are used at interfaces. PMID:27299800

  6. Novel method for Ag colloidal cluster formation by laser ablation at the air-liquid interface

    NASA Astrophysics Data System (ADS)

    Nishi, Teppei; Akimoto, Yusuke; Takahashi, Naoko; Kitazumi, Kosuke; Kajiya, Shuji; Watanabe, Yoshihide

    2015-09-01

    We report a novel method for formation of sub-nanoclusters by laser ablation at the air-liquid interface. The density of plasma induced by laser ablation at the air-liquid interface should be lower than that produced by laser ablation in liquid. In the lower density plasma, the produced clusters rarely grow or aggregate into larger clusters because the collision probability is low, resulting in the formation of small clusters. Ag sub-nanoclusters were observed by electrospray ionization mass spectrometry (ESI-MS) and X-ray photoelectron spectroscopy (XPS). These results show that low-density plasma can be applied to small-cluster formation and that laser ablation at the air-liquid interface produces a good reactive field for the formation of sub-nanoclusters. Our results highlight the importance of low-density plasma induced at the air-liquid interface for sub-nanocluster formation.

  7. A semi-analytical calculation of the electrostatic pair interaction between nonuniformly charged colloidal spheres at an air-water interface

    NASA Astrophysics Data System (ADS)

    Lian, Zengju

    2016-07-01

    We study the electrostatic pair interaction between two nonuniformly like-charged colloidal spheres trapped in an air-water interface. Under the linear Poisson-Boltzmann approximation, a general form of the electrostatic potential for the system is shown in terms of multipole expansions. After combining the translation-rotation transform of the coordinates with the numerical multipoint collection, we give a semi-analytical result of the electrostatic pair interaction between the colloids. The pair interaction changes quantitatively or even qualitatively with different distributions of the surface charges on the particles. Because of the anisotropic distribution of the surface charge and the asymmetric dielectric medium, the dipole moment of the ion cloud associating with the particle orients diagonally to the air-water interface with an angle α. When the angle is large, the colloids interact repulsively, while they attract each other when the angle is small. The attractive colloids may be "Janus-like" charged and be arranged with some specific configurations. Whatever the repulsions or the attractions, they all decay asymptotically ∝1/d3 (d is the center-center distance of the particles) which is consistent with our general acknowledge. The calculation results also provide an insight of the effect of the ion concentration, particle size, and the total charge of the particle on the pair interaction between the particles.

  8. A semi-analytical calculation of the electrostatic pair interaction between nonuniformly charged colloidal spheres at an air-water interface.

    PubMed

    Lian, Zengju

    2016-07-01

    We study the electrostatic pair interaction between two nonuniformly like-charged colloidal spheres trapped in an air-water interface. Under the linear Poisson-Boltzmann approximation, a general form of the electrostatic potential for the system is shown in terms of multipole expansions. After combining the translation-rotation transform of the coordinates with the numerical multipoint collection, we give a semi-analytical result of the electrostatic pair interaction between the colloids. The pair interaction changes quantitatively or even qualitatively with different distributions of the surface charges on the particles. Because of the anisotropic distribution of the surface charge and the asymmetric dielectric medium, the dipole moment of the ion cloud associating with the particle orients diagonally to the air-water interface with an angle α. When the angle is large, the colloids interact repulsively, while they attract each other when the angle is small. The attractive colloids may be "Janus-like" charged and be arranged with some specific configurations. Whatever the repulsions or the attractions, they all decay asymptotically ∝1/d(3) (d is the center-center distance of the particles) which is consistent with our general acknowledge. The calculation results also provide an insight of the effect of the ion concentration, particle size, and the total charge of the particle on the pair interaction between the particles. PMID:27394119

  9. The influence of the membrane-polymer interface on colloidal membrane dynamics and phase behavior

    NASA Astrophysics Data System (ADS)

    Zakhary, Mark J.

    A primary challenge in the field of self-assembly is to identify simple interactions that produce well-defined, complex, and controllable materials. A large part of this task is to creatively engineer appropriate assembly components with such suitable interactions built-in. Here, we demonstrate that rod-like subunits, experimentally modeled by fd bacteriophage viruses, with simple and predictable hard-core repulsive interactions, exhibit a great wealth of fascinating self-assembly behavior. These rods form two-dimensional liquid crystalline colloidal membranes consisting of monolayers of aligned particles owing purely to entropic considerations. Due to surface tension, rods near the edge of the monolayers twist, resulting in an elastic nematic ring surrounding the fluid-like membrane interior, and it is the rich phenomena rooted in the interplay between the edge and the interior that is the subject of this thesis. The chiral nature of the fd subunits causes a symmetry breaking at the membrane edge, which leads to chiral control of interfacial tension and resultantly a controllable, reversible morphological transition between membranes and one-dimensional twisted ribbons. Using optical microscopic and optical tweezer techniques, we show that a nucleation barrier exists in association with the membrane-ribbon transition, and investigate this barrier using fluctuation analysis as well as highly controlled force-extension experiments. The finite bending rigidity of the membrane edge is studied, and we show that long filamentous polymers spontaneously adhere to the edge, introducing the concept of geometrical edge-active agents. By analyzing the suppressed edge fluctuations of filament-bound membranes, it is found that the edge bending rigidity varies by up to an order of magnitude in a predictable and controllable way. Finally, we study the effect of the monolayer edge on the membrane coalescence, and observe two types of stable liquid crystalline defects that form at

  10. Silicon wafer-contaminant interactions in dilute hydrofluoric acid solutions and related fundamentals in colloid and interface science

    NASA Astrophysics Data System (ADS)

    Chen, Zhan

    With the continuous decrease in device size, it becomes more and more important to have a contamination-free silicon wafer surface. Hydrofluoric acid is inevitably involved in silicon wafer wet cleaning. However, during dilute hydrofluoric acid (DHF) cleaning, particles and noble metals tend to deposit on the silicon wafer surface and the surface roughness could increase. In this study, the mechanisms of particle deposition, noble metal outplating, and the effects of additives were investigated. Particle deposition from DHF solution onto bare silicon surfaces is due to the large van der Waals interaction between silicon and particles. Additives which can increase electrostatic interaction will reduce particle redeposition, and their effectiveness correlates well with the zeta-potential changes on both silicon surface and particles. Direct force measurements between a silicon surface and a silicon nitride surface reveal that additives not only change electrostatic interaction, but change adhesion forces of particles on silicon surfaces also. Nobel metal ions, especially copper ions, tend to deposit on bare silicon surfaces in DHF solution. The nucleation stage of copper deposition is critical and copper preferrentially deposits on surfaces with high defect densities. A novel technique to detect copper outplating in situ was established. Some additives may increase copper deposition due to the formation of copper complex and the subsequent adsorption of the copper complex on silicon surfaces. Some additive reduces copper outplating significantly. Their effects were discussed. Some fundamental aspects of colloid and interface science have been studied as well, including the approximate and numerical solutions of the electric potential distribution near a planar surface in the presence of highly asymmetric electrolytes. More importantly, the surface interaction in a confined/concentrated system was studied and a theory was established. The mysterious long range

  11. 17 CFR 279.8 - Form ADV-E, cover page for certificate of accounting of securities and funds in possession or...

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... certificate of accounting of securities and funds in possession or custody of an investment adviser. 279.8... PRESCRIBED UNDER THE INVESTMENT ADVISERS ACT OF 1940 § 279.8 Form ADV-E, cover page for certificate of... Federal Register citations affecting Form ADV-E, see the List of CFR Sections Affected, which appears...

  12. Colloidal Instability Fosters Agglomeration of Subvisible Particles Created by Rupture of Gels of a Monoclonal Antibody Formed at Silicone Oil-Water Interfaces.

    PubMed

    Mehta, Shyam B; Carpenter, John F; Randolph, Theodore W

    2016-08-01

    In this study, we investigated the effect of ionic strength (1.25-231 mM) on viscoelastic interfacial gels formed by a monoclonal antibody at silicone oil-water interfaces, and the formation of subvisible particles due to rupture of these gels. Rates of gel formation and their elastic moduli did not vary significantly with ionic strength. Likewise, during gel rupture no significant effects of ionic strength were observed on particle formation and aggregation as detected by microflow imaging, resonance mass measurement, and size exclusion chromatography. Subvisible particles formed by mechanical rupturing of the gels agglomerated over time, even during quiescent incubation, due to the colloidal instability of the particles. PMID:27422087

  13. SORPTION OF COLLOIDS, ORGANICS, AND METALS ONTO GAS-WATER INTERFACES: TRANSPORT MECHANISMS AND POTENTIAL REMEDIATION TECHNOLOGY

    EPA Science Inventory

    Although the process of contaminant sorption at mineral surfaces has received much recognition as a major mechanism controlling contaminant behavior in subsurface environments, virtually no attention has been given to the possibility of contaminant sorption at gas-water interface...

  14. 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)

  15. Magnetic cylindrical colloids at liquid interfaces exhibit non-volatile switching of their orientation in an external field.

    PubMed

    Newton, Bethany J; Buzza, D Martin A

    2016-06-28

    We study the orientation of magnetic cylindrical particles adsorbed at a liquid interface in an external field using analytical theory and high resolution finite element simulations. Cylindrical particles are interesting since they possess multiple locally stable orientations at the liquid interface so that the orientational transitions induced by an external field will not disappear when the external field is removed, i.e., the switching effect is non-volatile. We show that, in the absence of an external field, as we reduce the aspect ratio α of the cylinders below a critical value (αc≈ 2) the particles undergo spontaneous symmetry breaking from a stable side-on state to one of two equivalent stable tilted states, similar to the spontaneous magnetisation of a ferromagnet going through the Curie point. By tuning both the aspect ratio and contact angle of the cylinders, we show that it is possible to engineer particles that have one, two, three or four locally stable orientations. We also find that the magnetic responses of cylinders with one or two stable states are similar to that of paramagnets and ferromagnets respectively, while the magnetic response of systems with three or four stable states are even more complex and have no analogs in simple magnetic systems. Magnetic cylinders at liquid interfaces therefore provide a facile method for creating switchable functional monolayers where we can use an external field to induce multiple non-volatile changes in particle orientation and self-assembled structure. PMID:27200513

  16. 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

  17. 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

  18. 17 CFR 275.204-1 - Amendments to Form ADV.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...) When amendment is required. You must amend your Form ADV (17 CFR 279.1): (1) At least annually, within... at http://www.sec.gov/iard. For the annual updating amendment: Summaries of material changes that are... changes, or an annual updating amendment to your brochure, you are not required to file them with...

  19. 17 CFR 275.204-1 - Amendments to Form ADV.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...) When amendment is required. You must amend your Form ADV (17 CFR 279.1): (1) At least annually, within... at http://www.sec.gov/iard. For the annual updating amendment: Summaries of material changes that are... changes, or an annual updating amendment to your brochure, you are not required to file them with...

  20. 17 CFR 275.204-1 - Amendments to Form ADV.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...) When amendment is required. You must amend your Form ADV (17 CFR 279.1): (1) At least annually, within... at http://www.sec.gov/iard. For the annual updating amendment: Summaries of material changes that are... changes, or an annual updating amendment to your brochure, you are not required to file them with...

  1. Using ADV backscatter strength for measuring suspended cohesive sediment concentration

    NASA Astrophysics Data System (ADS)

    Ha, H. K.; Hsu, W.-Y.; Maa, J. P.-Y.; Shao, Y. Y.; Holland, C. W.

    2009-05-01

    Laboratory experiments were conducted at two institutes to reveal the relationship between acoustic backscatter strength and suspended sediment concentration (SSC). In total, three acoustic Doppler velocimeters (ADVs) with different frequencies (5, 10 and 16 MHz) were tested. Two different commercial clays and one natural sediment from Clay Bank site in the York River were checked for acoustic responses. The SSCs of selected sediments were artificially changed between a selected low and a high value in tap or de-ion water. Each ADV showed quite different backscatter responses depending on the sediment type and SSC. Not all devices had a good linear relationship between backscatter strength and SSC. Within a limited range of SSC, however, the backscatter strength can be well correlated with the SSC. Compared with optical backscattering sensor (OBS), the fluctuation of ADV backscatter signals was too noisy to be directly converted to the instantaneous changes of SSC due to high amplification ratio and small sampling volume. For the more accurate signal conversion for finding the fluctuation of SSC, the ensemble average should be applied to increase the signal-to-noise ratio. There are unexpected responses for the averaged backscatter wave strength: (1) high signals from small particles but low signals from large particles; and (2) two linear segments in calibration slope. These phenomena would be most likely caused by the different gain setting built in ADVs. The different acoustic responses to flocculation might also contribute somewhat if flocs are tightly packed. This study suggests that an ADV could be a useful instrument to estimate suspended cohesive sediment concentration and its fluctuation if the above concerns are clarified.

  2. Colloid Mobilization and Transport during Capillary Fringe Fluctuations

    NASA Astrophysics Data System (ADS)

    Aramrak, Surachet; Flury, Markus

    2016-04-01

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

  3. Optimized combination therapies with adefovir dipivoxil (ADV) and lamivudine, telbivudine, or entecavir may be effective for chronic hepatitis B patients with a suboptimal response to ADV monotherapy

    PubMed Central

    Li, Xiangyong; Jie, Yusheng; You, Xu; Shi, Hong; Zhang, Min; Wu, Yuankai; Lin, Guoli; Li, Xinhua; Gao, Zhiliang; Chong, Yutian

    2015-01-01

    Objective: To identify high risk factors in chronic hepatitis B (CHB) patients for suboptimal response to adefovir dipivoxil (ADV) monotherapy, and to assess the efficacy of optimized therapy combining ADV with lamivudine (LAM), telbivudine (LdT), or entecavir (ETV) in patients with a suboptimal response to ADV alone. Methods: Suboptimal response to ADV monotherapy was defined as having a decline in serum hepatitis B virus (HBV) DNA level of more than 1 log compared to baseline, but with viremia still detectable (HBV DNA ≥ 100 IU/mL), after 48 weeks of therapy. All patients who received ADV monotherapy in our clinic were analyzed retrospectively. Both univariate and multivariate logistic regression models were applied for risk factor analysis. Patients who showed suboptimal response completed at least 12 months of optimized combination therapy consisting of ADV plus LAM, ADV plus LdT, ADV plus ETV, or continuous ADV monotherapy. The primary outcome measurement was complete viral suppression, indicated by a reduction of HBV DNA to undetectable levels (CVS, with HBV DNA < 100 IU/mL). Secondary outcome measures were HBeAg seroconversion for HBeAg-positive patients, HBsAg loss, alanine aminotransferase (ALT) normalization and virological breakthrough rates. Results: Of 521 patients who received ADV monotherapy, 170 showed a suboptimal response. These were grouped for continued therapy as follows: 34 in group A (continuous ADV monotherapy), 55 in group B (ADV plus LAM), 38 in group C (ADV plus LdT), and 43 in group D (ADV plus ETV). Using a logistic model, five conditions were identified as high risk factors for suboptimal response: presence of the tyrosine-methionine-aspartate-aspartate (YMDD) HBV DNA polymerase mutation; being HBeAg positive; having a high baseline level of HBV DNA; having a primary virological non-response to ADV; and [initial virological response] to ADV. After 48 weeks of ADV monotherapy, there were no withdrawn patients who had experienced side

  4. 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

  5. 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.

  6. Hexadecapolar colloids

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  7. Hexadecapolar colloids.

    PubMed

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

    2016-01-01

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

  8. Hexadecapolar Colloids

    DOE PAGESBeta

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

    2016-02-11

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

  9. Colloid mobilization and transport during capillary fringe fluctuations.

    PubMed

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

    2014-07-01

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

  10. Topological colloids.

    PubMed

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

    2013-01-10

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

  11. Floc Growth and Changes in ADV Acoustic Backscatter Signal

    NASA Astrophysics Data System (ADS)

    Rouhnia, M.; Keyvani, A.; Strom, K.

    2013-12-01

    A series of experiments were conducted to examine the effect of mud floc growth on the acoustic back-scatter signal recorded by a Nortek Vector acoustic Doppler velocimeter (ADV). Several studies have shown that calibration equations can be developed to link the backscatter strength with average suspended sediment concentration (SSC) when the sediment particle size distribution remains constant. However, when mud is present, the process of flocculation can alter the suspended particle size distribution. Past studies have shown that it is still unclear as to the degree of dependence of the calibration equation on changes in floc size. Part of the ambiguity lies in the fact that flocs can be porous and rather loosely packed and therefore might not scatter to the same extent as a grain of sand. In addition, direct, detailed measurements of floc size have not accompanied experiments examining the dependence of ADV backscatter and suspended sediment concentration. In this research, a set of laboratory experiments is used to test how floc growth affects the backscatter strength. The laboratory data is examined in light of an analytic model that was developed based on scatter theory to account for changes in both SSC and the floc properties of size and density. For the experiments, a turbulent suspension was created in a tank with a rotating paddle. Fixed concentrations of a mixture of kaolinite and montmorillonite were added to the tank in a step-wise manner. For each step, the flocs were allowed to grow to their equilibrium size before breaking the flocs with high turbulent mixing, adding more sediment, and then returning the mixing rate to a range suitable for the re-growth of flocs. During each floc growth phase, data was simultaneously collected at the same elevation in the tank using a floc camera to capture the changes in floc size, a Nortek Vector ADV for the acoustic backscatter, and a Campbell Scientific OBS 3+ for optical backscatter. Physical samples of the

  12. Nucleotide sequence and genomic organization of Aleutian mink disease parvovirus (ADV): sequence comparisons between a nonpathogenic and a pathogenic strain of ADV.

    PubMed Central

    Bloom, M E; Alexandersen, S; Perryman, S; Lechner, D; Wolfinbarger, J B

    1988-01-01

    A DNA sequence of 4,592 nucleotides (nt) was derived for the nonpathogenic ADV-G strain of Aleutian mink disease parvovirus (ADV). The 3'(left) end of the virion strand contained a 117-nt palindrome that could assume a Y-shaped configuration similar to, but less stable than, that of other parvoviruses. The sequence obtained for the 5' end was incomplete and did not contain the 5' (right) hairpin structure but ended just after a 25-nt A + T-rich direct repeat. Features of ADV genomic organization are (i) major left (622 amino acids) and right (702 amino acids) open reading frames (ORFs) in different translational frames of the plus-sense strand, (ii) two short mid-ORFs, (iii) eight potential promoter motifs (TATA boxes), including ones at 3 and 36 map units, and (iv) six potential polyadenylation sites, including three clustered near the termination of the right ORF. Although the overall homology to other parvoviruses is less than 50%, there are short conserved amino acid regions in both major ORFs. However, two regions in the right ORF allegedly conserved among the parvoviruses were not present in ADV. At the DNA level, ADV-G is 97.5% related to the pathogenic ADV-Utah 1. A total of 22 amino acid changes were found in the right ORF; changes were found in both hydrophilic and hydrophobic regions and generally did not affect the theoretical hydropathy. However, there is a short heterogeneous region at 64 to 65 map units in which 8 out of 11 residues have diverged; this hypervariable segment may be analogous to short amino acid regions in other parvoviruses that determine host range and pathogenicity. These findings suggested that this region may harbor some of the determinants responsible for the differences in pathogenicity of ADV-G and ADV-Utah 1. PMID:2839709

  13. 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.

  14. 17 CFR 279.2 - Form ADV-W, notice of withdrawal from registration as investment adviser.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ...: For Federal Register citations affecting Form ADV-W, see the List of CFR Sections Affected, which... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Form ADV-W, notice of... § 279.2 Form ADV-W, notice of withdrawal from registration as investment adviser. This form shall...

  15. 17 CFR 279.2 - Form ADV-W, notice of withdrawal from registration as investment adviser.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...: For Federal Register citations affecting Form ADV-W, see the List of CFR Sections Affected, which... 17 Commodity and Securities Exchanges 3 2012-04-01 2012-04-01 false Form ADV-W, notice of... § 279.2 Form ADV-W, notice of withdrawal from registration as investment adviser. This form shall...

  16. 17 CFR 279.2 - Form ADV-W, notice of withdrawal from registration as investment adviser.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ...: For Federal Register citations affecting Form ADV-W, see the List of CFR Sections Affected, which... 17 Commodity and Securities Exchanges 3 2013-04-01 2013-04-01 false Form ADV-W, notice of... § 279.2 Form ADV-W, notice of withdrawal from registration as investment adviser. This form shall...

  17. 17 CFR 279.2 - Form ADV-W, notice of withdrawal from registration as investment adviser.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ...: For Federal Register citations affecting Form ADV-W, see the List of CFR Sections Affected, which... 17 Commodity and Securities Exchanges 4 2014-04-01 2014-04-01 false Form ADV-W, notice of... § 279.2 Form ADV-W, notice of withdrawal from registration as investment adviser. This form shall...

  18. 17 CFR 279.2 - Form ADV-W, notice of withdrawal from registration as investment adviser.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ...: For Federal Register citations affecting Form ADV-W, see the List of CFR Sections Affected, which... 17 Commodity and Securities Exchanges 3 2011-04-01 2011-04-01 false Form ADV-W, notice of... § 279.2 Form ADV-W, notice of withdrawal from registration as investment adviser. This form shall...

  19. 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,...

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

    SciTech Connect

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

    2012-08-01

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

  1. Research gaps and technology needs in development of PHM for passive AdvSMR components

    NASA Astrophysics Data System (ADS)

    Meyer, Ryan M.; Ramuhalli, Pradeep; Coble, Jamie B.; Hirt, Evelyn H.; Mitchell, Mark R.; Wootan, David W.; Berglin, Eric J.; Bond, Leonard J.; Henagar, Chuck H., Jr.

    2014-02-01

    Advanced small modular reactors (AdvSMRs), which are based on modularization of advanced reactor concepts, may provide a longer-term alternative to traditional light-water reactors and near-term small modular reactors (SMRs), which are based on integral pressurized water reactor (iPWR) concepts. SMRs are challenged economically because of losses in economy of scale; thus, there is increased motivation to reduce the controllable operations and maintenance costs through automation technologies including prognostics health management (PHM) systems. In this regard, PHM systems have the potential to play a vital role in supporting the deployment of AdvSMRs and face several unique challenges with respect to implementation for passive AdvSMR components. This paper presents a summary of a research gaps and technical needs assessment performed for implementation of PHM for passive AdvSMR components.

  2. Research gaps and technology needs in development of PHM for passive AdvSMR components

    SciTech Connect

    Meyer, Ryan M.; Ramuhalli, Pradeep; Hirt, Evelyn H.; Mitchell, Mark R.; Wootan, David W.; Berglin, Eric J.; Henagar, Chuck H. Jr.; Coble, Jamie B.; Bond, Leonard J.

    2014-02-18

    Advanced small modular reactors (AdvSMRs), which are based on modularization of advanced reactor concepts, may provide a longer-term alternative to traditional light-water reactors and near-term small modular reactors (SMRs), which are based on integral pressurized water reactor (iPWR) concepts. SMRs are challenged economically because of losses in economy of scale; thus, there is increased motivation to reduce the controllable operations and maintenance costs through automation technologies including prognostics health management (PHM) systems. In this regard, PHM systems have the potential to play a vital role in supporting the deployment of AdvSMRs and face several unique challenges with respect to implementation for passive AdvSMR components. This paper presents a summary of a research gaps and technical needs assessment performed for implementation of PHM for passive AdvSMR components.

  3. Research Gaps and Technology Needs in Development of PHM for Passive AdvSMR Components

    SciTech Connect

    Meyer, Ryan M.; Ramuhalli, Pradeep; Coble, Jamie B.; Hirt, Evelyn H.; Mitchell, Mark R.; Wootan, David W.; Berglin, Eric J.; Bond, Leonard J.; Henager, Charles H.

    2014-01-01

    Advanced small modular reactors (AdvSMRs), which are based on modularization of advanced reactor concepts, may provide a longer-term alternative to traditional light-water reactors and near term small modular reactors (SMRs), which are based on integral pressurized water reactor (iPWR) concepts. SMRs are challenged economically due to losses in economy of scale, thus, there is increased motivation to reduce the controllable operations and maintenance (O&M) costs through automation technologies including prognostics health management (PHM) systems. In this regard, PHM systems have the potential to play a vital role in supporting the deployment of AdvSMRs and face several unique challenges with respect to implementation for passive AdvSMR components. This paper presents a summary of a research gaps and technical needs assessment performed for implementation of PHM for passive AdvSMR components. state-of-the-art in PHM.

  4. Velocity measurements on highly turbulent free surface flow using ADV

    NASA Astrophysics Data System (ADS)

    Cea, L.; Puertas, J.; Pena, L.

    2007-03-01

    The 3D instantaneous velocity recorded with an acoustic Doppler velocimeter (ADV) in a highly turbulent free surface flow is analysed using several filters in order to eliminate the corrupted data from the sample. The filters used include the minimum/maximum threshold, the acceleration threshold, and the phase-space threshold. Following some ideas of the phase-space filter, a new method based on the 3D velocity cross-correlation is proposed and tested. A way of computing the constants of the acceleration threshold method is proposed, so no parameters need to be fixed by the user, which makes the filtering process simpler, more objective and more efficient. All the samples analysed are highly turbulent. Nevertheless, the turbulence intensity and the air entrainment vary widely in the flow under study, which produces data records of different quality depending on the measurement point. The performance of the filtering methods when applied to samples of different quality, and the effects of the filtering process in the mean velocity, turbulent kinetic energy and frequency spectra are discussed.

  5. 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.

  6. Colloid adhesive parameters for chemical heterogeneous porous media

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  7. Colloidal Silver Products

    MedlinePlus

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

  8. Colloid formation and laser-induced bleaching in fluorite

    SciTech Connect

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

    2004-11-08

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

  9. Electrokinetic properties of polymer colloids

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  10. What Is a Colloid?

    ERIC Educational Resources Information Center

    Lamb, William G.

    1985-01-01

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

  11. Local-Level Prognostics Health Management Systems Framework for Passive AdvSMR Components. Interim Report

    SciTech Connect

    Ramuhalli, Pradeep; Roy, Surajit; Hirt, Evelyn H.; Pardini, Allan F.; Jones, Anthony M.; Deibler, John E.; Pitman, Stan G.; Tucker, Joseph C.; Prowant, Matthew S.; Suter, Jonathan D.

    2014-09-12

    This report describes research results to date in support of the integration and demonstration of diagnostics technologies for prototypical AdvSMR passive components (to establish condition indices for monitoring) with model-based prognostics methods. The focus of the PHM methodology and algorithm development in this study is at the localized scale. Multiple localized measurements of material condition (using advanced nondestructive measurement methods), along with available measurements of the stressor environment, enhance the performance of localized diagnostics and prognostics of passive AdvSMR components and systems.

  12. Two-Step Freezing in Alkane Monolayers on Colloidal Silica Nanoparticles: From a Stretched-Liquid to an Interface-Frozen State.

    PubMed

    Gao, Xia; Huber, Patrick; Su, Yunlan; Zhao, Weiwei; Wang, Dujin

    2016-08-01

    The crystallization behavior of an archetypical soft/hard hybrid nanocomposite, that is, an n-octadecane C18/SiO2-nanoparticle composite, was investigated by a combination of differential scanning calorimetry (DSC) and variable-temperature solid-state (13)C nuclear magnetic resonance (VT solid-state (13)C NMR) as a function of silica nanoparticles loading. Two latent heat peaks prior to bulk freezing, observed for composites with high silica loading, indicate that a sizable fraction of C18 molecules involve two phase transitions unknown from the bulk C18. Combined with the NMR measurements as well as experiments on alkanes and alkanols at planar amorphous silica surfaces reported in the literature, this phase behavior can be attributed to a transition toward a 2D liquid-like monolayer and subsequently a disorder-to-order transition upon cooling. The second transition results in the formation of a interface-frozen monolayer of alkane molecules with their molecular long axis parallel to the nanoparticles' surface normal. Upon heating, the inverse phase sequence was observed, however, with a sizable thermal hysteresis in accord with the characteristics of the first-order phase transition. A thermodynamic model considering a balance of interfacial bonding, chain stretching elasticity, and entropic effects quantitatively accounts for the observed behavior. Complementary synchrotron-based wide-angle X-ray diffraction (WAXD) experiments allow us to document the strong influence of this peculiar interfacial freezing behavior on the surrounding alkane melts and in particular the nucleation of a rotator phase absent in the bulk C18. PMID:27386888

  13. Surface pressure isotherm for a monolayer of charged colloidal particles at a water/nonpolar-fluid interface: experiment and theoretical model.

    PubMed

    Petkov, Plamen V; Danov, Krassimir D; Kralchevsky, Peter A

    2014-03-18

    Monolayers from electrically charged micrometer-sized silica particles, spread on the air/water interface, are investigated. Because of the electrostatic repulsion, the distances between the particles are considerably greater than their diameters, i.e., we are dealing with nondensely packed interfacial layers. The electrostatic repulsion between the particles occurs through the air phase. Surface pressure vs area isotherms were measured by Langmuir trough, and the monolayers' morphology was monitored by microscope. The mean area per particle is determined by Delaunay triangulation and Voronoi diagrams. In terms of mean area, the surface pressure for monolayers from polydisperse and monodisperse particles obeys the same law. The experiments show that Π ∝ L(-3) at large L, where Π is the surface pressure and L is the mean interparticle distance. A theoretical cell model is developed, which predicts not only the aforementioned asymptotic law but also the whole Π(L) dependence. The model presumes a periodic distribution of the surface charge density, which induces a corresponding electric field in the air phase. Then, the Maxwell pressure tensor of the electric field in the air phase is calculated and integrated according to the Bakker's formula to determine the surface pressure. Thus, all collective effects from the electrostatic interparticle interactions are taken into account as well as the effects from the particle finite size. By evaporation of water, the particle monolayers are deposited on a solid substrate placed on the bottom of the trough. The electrostatic interparticle repulsion is strong enough to withstand the attractive lateral capillary immersion forces that are operative during the drying of the monolayer on the substrate. The obtained experimental results and the developed theoretical model can be useful for prediction and control of the properties of nondensely packed interfacial monolayers from charged particles that find applications for

  14. Electrohydrodynamically patterned colloidal crystals

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  15. Hyperbolic interfaces.

    PubMed

    Giomi, Luca

    2012-09-28

    Fluid interfaces, such as soap films, liquid droplets, or lipid membranes, are known to give rise to several special geometries, whose complexity and beauty continue to fascinate us, as observers of the natural world, and challenge us as scientists. Here I show that a special class of surfaces of constant negative Gaussian curvature can be obtained in fluid interfaces equipped with an orientational ordered phase. These arise in various soft and biological materials, such as nematic liquid crystals, cytoskeletal assemblies, or hexatic colloidal suspensions. The purely hyperbolic morphology originates from the competition between surface tension, that reduces the area of the interface at the expense of increasing its Gaussian curvature, and the orientational elasticity of the ordered phase, that in turn suffers for the distortion induced by the underlying curvature. PMID:23030106

  16. Hyperbolic Interfaces

    NASA Astrophysics Data System (ADS)

    Giomi, Luca

    2012-09-01

    Fluid interfaces, such as soap films, liquid droplets, or lipid membranes, are known to give rise to several special geometries, whose complexity and beauty continue to fascinate us, as observers of the natural world, and challenge us as scientists. Here I show that a special class of surfaces of constant negative Gaussian curvature can be obtained in fluid interfaces equipped with an orientational ordered phase. These arise in various soft and biological materials, such as nematic liquid crystals, cytoskeletal assemblies, or hexatic colloidal suspensions. The purely hyperbolic morphology originates from the competition between surface tension, that reduces the area of the interface at the expense of increasing its Gaussian curvature, and the orientational elasticity of the ordered phase, that in turn suffers for the distortion induced by the underlying curvature.

  17. Microfluidic colloid filtration

    PubMed Central

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

    2016-01-01

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

  18. Saturated Zone Colloid Transport

    SciTech Connect

    H. Viswanathan; P. Reimus

    2003-09-05

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

  19. Microfluidic colloid filtration.

    PubMed

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

    2016-01-01

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

  20. Microfluidic colloid filtration

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  1. Autonomous colloidal crystallization in a galvanic microreactor

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  2. 76 FR 255 - Amendments To Form ADV; Extension of Compliance Date

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-04

    ...The Securities and Exchange Commission is extending the compliance date for Part 2B of Form ADV, the brochure supplement, and for certain rule provisions that relate to the delivery of brochure supplements. The Commission is extending the compliance date generally for four months to provide certain investment advisers additional time to design, test and implement systems and controls to......

  3. Saturated Zone Colloid Transport

    SciTech Connect

    H. S. Viswanathan

    2004-10-07

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

  4. Bidisperse colloids: nanoparticles and microemulsions in coexistence.

    PubMed

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

    2010-04-15

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

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

    PubMed

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

    2014-01-01

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

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

    PubMed Central

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

    2014-01-01

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

  7. Ring around the colloid

    NASA Astrophysics Data System (ADS)

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

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

  8. UZ Colloid Transport Model

    SciTech Connect

    M. McGraw

    2000-04-13

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

  9. Analysis of colloid transport

    SciTech Connect

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

    1985-12-31

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

  10. Organized Assemblies of Colloids Formed at the Poles of Micrometer-Sized Droplets of Liquid Crystal

    PubMed Central

    Wang, Xiaoguang; Miller, Daniel S.; de Pablo, Juan J.

    2014-01-01

    We report on the formation of organized assemblies of 1 μm-in-diameter colloids (polystyrene (PS)) at the poles of water-dispersed droplets (diameters 7 - 20 μm) of nematic liquid crystal (LC). For 4-cyano-4′-pentylbiphenyl droplets decorated with two to five PS colloids, we found 32 distinct arrangements of the colloids to form at the boojums of bipolar droplet configurations. Significantly, all but one of these configurations (a ring comprised of five PS colloids) could be mapped onto a local (non-close packed) hexagonal lattice. To provide insight into the origin of the hexagonal lattice, we investigated planar aqueous—LC interfaces, and found that organized assemblies of PS colloids did not form at these interfaces. Experiments involving the addition of salts revealed that a repulsive interaction of electrostatic origin prevented formation of assemblies at planar interfaces, and that regions of high splay near the poles of the LC droplets generated cohesive interactions between colloids that could overcome the repulsion. Support for this interpretation was obtained from a model that included (i) a long-range attraction between adsorbed colloids and the boojum due to the increasing rate of strain (splay) of LC near the boojum (splay attraction), (ii) an attractive inter-colloid interaction that reflects the quadrupolar symmetry of the strain in the LC around the colloids, and (iii) electrostatic repulsion between colloids. The model predicts that electrostatic repulsion between colloids can lead to a ∼1,000 kBT energy barrier at planar interfaces of LC films, and that the repulsive interaction can be overcome by splay attraction of the colloids to the boojums of the LC droplets. Overall, the results reported in this paper advance our understanding of the directed assembly of colloids at interfaces of LC droplets. PMID:25284139

  11. Industrial application of surface and colloid science

    SciTech Connect

    Borgarello, E.

    1995-12-01

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

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

    PubMed

    Dickinson, Eric

    2015-01-01

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

  13. Boundaries Matter for Confined Colloidal Glasses

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  14. Switching light with light - advanced functional colloidal monolayers

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  15. Driving magnetic colloidal polymers

    NASA Astrophysics Data System (ADS)

    Dempster, Joshua; Olvera de La Cruz, Monica

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

  16. Determining concentration and fall velocity of estuarine particle populations using ADV, OBS and LISST

    NASA Astrophysics Data System (ADS)

    Fugate, David C.; Friedrichs, Carl T.

    2002-07-01

    In describing suspended sediment conditions in the lower Chesapeake Bay, VA, USA, this paper reports and develops methods for distinguishing multiple particle populations in the bottom boundary layer of estuaries in general. In addition, a novel application of the acoustic Doppler velocimeter (ADV) is shown to estimate in situ particle fall velocity at a single point without affecting the ambient turbulence. In situ estimates of suspended sediment concentration from ADV, optical backscatter, and laser in situ scattering and transmissometry (LISST) instruments are compared with gravimetrically determined mass concentrations from pumped water samples. In this environment, acoustic backscatter from the ADV proved to be the best estimator of mass concentrations due to its apparent insensitivity to the size or density of muddy aggregates. The concentration estimates and the relative sensitivities of the instruments to particle size and density combined with size distribution information from the LISST reveal the characteristics of multiple particle populations in the bottom boundary layer. Two rapidly settling sediment populations are suggested with similar fall velocities but distinct critical erosion stresses. A slowly settling background population is also identified whose concentration varies over meteorological time scales. Fall velocities are estimated analytically from a balance of settling and diffusive flux gradients using two methods, one employing Reynolds concentration flux, and the other estimating eddy diffusivity using the von-Karman Prandtl equation. Comparison of the local change and advective terms in the solute transport equation to the magnitude of the settling term suggests that a balance between the settling and resuspension term is a good first order approximation at this site, validating the indirect method for estimating settling velocity. Single elevation estimates of fall velocity using the ADV to estimate Reynolds concentration flux produced

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

    PubMed

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

    2005-07-01

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

  18. Switching light with light - advanced functional colloidal monolayers

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  19. Lock and key colloids.

    PubMed

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

    2010-03-25

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

  20. Colloidal microcapsules: Surface engineering of nanoparticles for interfacial assembly

    NASA Astrophysics Data System (ADS)

    Patra, Debabrata

    2011-12-01

    Colloidal Microcapsules (MCs), i.e. capsules stabilized by nano-/microparticle shells are highly modular inherently multi-scale constructs with applications in many areas of material and biological sciences e.g. drug delivery, encapsulation and microreactors. These MCs are fabricated by stabilizing emulsions via self-assembly of colloidal micro/nanoparticles at liquid-liquid interface. In these systems, colloidal particles serve as modular building blocks, allowing incorporation of the particle properties into the functional capabilities of the MCs. As an example, nanoparticles (NPs) can serve as appropriate antennae to induce response by external triggers (e.g. magnetic fields or laser) for controlled release of encapsulated materials. Additionally, the dynamic nature of the colloidal assembly at liquid-liquid interfaces result defects free organized nanostructures with unique electronic, magnetic and optical properties which can be tuned by their dimension and cooperative interactions. The physical properties of colloidal microcapsules such as permeability, mechanical strength, and biocompatibility can be precisely controlled through the proper choice of colloids and preparation conditions for their. This thesis illustrates the fabrication of stable and robust MCs through via chemical crosslinking of the surface engineered NPs at oil-water interface. The chemical crosslinking assists NPs to form a stable 2-D network structure at the emulsion interface, imparting robustness to the emulsions. In brief, we developed the strategies for altering the nature of chemical interaction between NPs at the emulsion interface and investigated their role during the self-assembly process. Recently, we have fabricated stable colloidal microcapsule (MCs) using covalent, dative as well as non-covalent interactions and demonstrated their potential applications including encapsulation, size selective release, functional devices and biocatalysts.

  1. Colloidal pen lithography.

    PubMed

    Xue, Mianqi; Cai, Xiaojing; Chen, Ghenfu

    2015-02-01

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

  2. Brownian diffusion of a partially wetted colloid

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  3. Brownian diffusion of a partially wetted colloid.

    PubMed

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

    2015-09-01

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

  4. 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.

  5. 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

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

    PubMed

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

    2014-01-01

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

  7. Centrifugation-assisted Assembly of Colloidal Silica into Crack-Free and Transferrable Films with Tunable Crystalline Structures

    PubMed Central

    Fan, Wen; Chen, Min; Yang, Shu; Wu, Limin

    2015-01-01

    Self-assembly of colloidal particles into colloidal films has many actual and potential applications. While various strategies have been developed to direct the assembly of colloidal particles, fabrication of crack-free and transferrable colloidal film with controllable crystal structures still remains a major challenge. Here we show a centrifugation-assisted assembly of colloidal silica spheres into free-standing colloidal film by using the liquid/liquid interfaces of three immiscible phases. Through independent control of centrifugal force and interparticle electrostatic repulsion, polycrystalline, single-crystalline and quasi-amorphous structures can be readily obtained. More importantly, by dehydration of silica particles during centrifugation, the spontaneous formation of capillary water bridges between particles enables the binding and pre-shrinkage of the assembled array at the fluid interface. Thus the assembled colloidal films are not only crack-free, but also robust and flexible enough to be easily transferred on various planar and curved substrates. PMID:26159121

  8. Centrifugation-assisted Assembly of Colloidal Silica into Crack-Free and Transferrable Films with Tunable Crystalline Structures

    NASA Astrophysics Data System (ADS)

    Fan, Wen; Chen, Min; Yang, Shu; Wu, Limin

    2015-07-01

    Self-assembly of colloidal particles into colloidal films has many actual and potential applications. While various strategies have been developed to direct the assembly of colloidal particles, fabrication of crack-free and transferrable colloidal film with controllable crystal structures still remains a major challenge. Here we show a centrifugation-assisted assembly of colloidal silica spheres into free-standing colloidal film by using the liquid/liquid interfaces of three immiscible phases. Through independent control of centrifugal force and interparticle electrostatic repulsion, polycrystalline, single-crystalline and quasi-amorphous structures can be readily obtained. More importantly, by dehydration of silica particles during centrifugation, the spontaneous formation of capillary water bridges between particles enables the binding and pre-shrinkage of the assembled array at the fluid interface. Thus the assembled colloidal films are not only crack-free, but also robust and flexible enough to be easily transferred on various planar and curved substrates.

  9. Centrifugation-assisted Assembly of Colloidal Silica into Crack-Free and Transferrable Films with Tunable Crystalline Structures.

    PubMed

    Fan, Wen; Chen, Min; Yang, Shu; Wu, Limin

    2015-01-01

    Self-assembly of colloidal particles into colloidal films has many actual and potential applications. While various strategies have been developed to direct the assembly of colloidal particles, fabrication of crack-free and transferrable colloidal film with controllable crystal structures still remains a major challenge. Here we show a centrifugation-assisted assembly of colloidal silica spheres into free-standing colloidal film by using the liquid/liquid interfaces of three immiscible phases. Through independent control of centrifugal force and interparticle electrostatic repulsion, polycrystalline, single-crystalline and quasi-amorphous structures can be readily obtained. More importantly, by dehydration of silica particles during centrifugation, the spontaneous formation of capillary water bridges between particles enables the binding and pre-shrinkage of the assembled array at the fluid interface. Thus the assembled colloidal films are not only crack-free, but also robust and flexible enough to be easily transferred on various planar and curved substrates. PMID:26159121

  10. Spherical colloidal photonic crystals.

    PubMed

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

    2014-12-16

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

  11. DNA hybridization and ligation for directed colloidal assembly

    NASA Astrophysics Data System (ADS)

    Shyr, Margaret

    membrane to achieve well-ordered colloidal crystals. Well-ordered hexagonally close-packed polystyrene colloid monolayers could be assembled by sedimentation, hybridization, and ligation. Layer-by-layer assembly is also possible on the sedimented colloidal crystals. Since the drying and liquid-air interface effects experienced during vertical deposition are not a factor for sedimented colloidal crystals, we attempted to use templated substrates, created by imprint and holographic lithography, to assemble non-FCC colloidal crystals.

  12. Natural Colloid Mobilization in Unsaturated Hanford Coarse Sand Under Transient Flow and Transient Chemical Conditions

    NASA Astrophysics Data System (ADS)

    Cheng, T.; Saiers, J. E.

    2007-12-01

    Colloid-sized clay, carbonate, and metal oxide particles are ubiquitous in the vadose zone and strongly adsorb dissolved contaminants such as metals and radionuclides. Under certain conditions, colloid particles are readily mobilized (released) into pore water and travel in a nearly conservative fashion and thus can facilitate the transport of contaminants. Although much progress has been made toward identifying and modeling colloid mobilization and transport processes in ideal, homogeneous systems, our understanding of the phenomenon in non-ideal, heterogeneous systems is still limited. We investigated natural colloid mobilization and transport in laboratory columns packed with Hanford Coarse Sand, a heterogeneous natural sediment. Our major focus was the role of transient flow and transient chemical conditions on colloid release and transport in unsaturated media. We found that a moving air-water interface had the greatest effects on the mobilization of colloid, and up to ~1000 mg/L of colloid was mobilized during column drainage at an ionic strength of 2 mM. An increase in flow rate or decrease in ionic strength also mobilized colloids. A model that accounts for transient pore water flow, colloid transport, and mass transfer in unsaturated media was developed to describe colloid mobilization in our column experiments. Both our experimental and modeling results showed the important role of moving air-water interfaces, changes in moisture content, and changes in ionic strength in mobilizing natural colloids in heterogeneous natural sediments. This work has contributed to our knowledge of colloid and colloid-associated contaminant mobilization in real vadose-zone environments under transient flow and transient chemical conditions.

  13. Enhanced adhesion of bioinspired nanopatterned elastomers via colloidal surface assembly

    PubMed Central

    Akerboom, Sabine; Appel, Jeroen; Labonte, David; Federle, Walter; Sprakel, Joris; Kamperman, Marleen

    2015-01-01

    We describe a scalable method to fabricate nanopatterned bioinspired dry adhesives using colloidal lithography. Close-packed monolayers of polystyrene particles were formed at the air/water interface, on which polydimethylsiloxane (PDMS) was applied. The order of the colloidal monolayer and the immersion depth of the particles were tuned by altering the pH and ionic strength of the water. Initially, PDMS completely wetted the air/water interface outside the monolayer, thereby compressing the monolayer as in a Langmuir trough; further application of PDMS subsequently covered the colloidal monolayers. PDMS curing and particle extraction resulted in elastomers patterned with nanodimples. Adhesion and friction of these nanopatterned surfaces with varying dimple depth were studied using a spherical probe as a counter-surface. Compared with smooth surfaces, adhesion of nanopatterned surfaces was enhanced, which is attributed to an energy-dissipating mechanism during pull-off. All nanopatterned surfaces showed a significant decrease in friction compared with smooth surfaces. PMID:25392404

  14. Pairwise interactions of colloids in two-dimensional geometric confinement.

    PubMed

    Park, Bum Jun; Lee, Bomsock; Yu, Taekyung

    2014-12-28

    We present the pairwise interaction behaviour of colloids confined to two-dimensional (2D) colloidal cages using optical laser tweezers. A single probe particle inside hexagonal cage particles at a planar oil-water interface is allowed to diffuse freely and the spring constant is extracted from its trajectories. To evaluate the effect of multibody interactions, the pair interactions between the probe particle and each cage particle are directly measured by using optical tweezers. Based on pairwise additivity, Monte Carlo simulations are used to compare the values of the spring constant obtained from experiments and simulations. We find that the multibody interactions negligibly occur and thus the particle interactions confined to such colloidal cages are highly pairwise. This work demonstrates that the use of the pairwise assumption in numerical simulations is rational when interparticle repulsive interactions are sufficiently strong, such as the particle interactions at fluid-fluid interfaces. PMID:25363564

  15. Thermal capillary waves in colloid polymer mixtures in water

    NASA Astrophysics Data System (ADS)

    Jamie, E. A. G.; Davies, G. J.; Howe, M. D.; Dullens, R. P. A.; Aarts, D. G. A. L.

    2008-12-01

    We develop two colloid-polymer mixtures in water and study their phase and interface behaviour by means of confocal scanning laser microscopy. The systems consist either of silica or of poly(methylmethacrylate) particles, fluorescently labelled, with, as the polymer, xanthan. The fluid-fluid phase separation can be clearly followed in time and, depending on the concentrations and system details, we observe coarsening either of a bicontinuous spinodal structure or of a suspension of colloid-rich droplets. After phase separation has completed, we study the thermal capillary waves at the fluid-fluid interface. We construct correlation functions and compare with capillary wave theory. Finally, we demonstrate that these colloid-polymer systems are compatible with microfluidics.

  16. 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.

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

    PubMed

    Manoharan, Vinothan N

    2015-08-28

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

  18. EVALUATION OF RANGE ESTIMATES FOR TOYOTA FCHV-ADV UNDER OPEN ROAD DRIVING CONDITIONS

    SciTech Connect

    Anton, D.; Wipke, K.; Sprik, S.

    2009-07-10

    The objective of this evaluation was to independently and objectively verify driving ranges of >400 miles announced by Toyota for its new advanced Fuel Cell Hybrid Vehicle (FCHV-adv) utilizing 70 MPa compressed hydrogen. To accomplish this, participants from both Savannah River National Laboratory (SRNL) and the National Renewable Energy Laboratory (NREL) witnessed and participated in a 2-vehicle evaluation with Toyota Motor Engineering & Manufacturing North America, Inc. (TEMA) over a typical open road route for over 11 hours in one day with all relevant data recorded. SRNL and TEMA first entered into discussions of verifying the range of the advanced Toyota Fuel Cell Hybrid Vehicle (FCHV-adv) in August 2008 resulting from reported 400+ mile range by Toyota. After extended negotiations, a CRADA agreement, SRNS CRADA No. CR-04-003, was signed on May 6, 2009. Subsequently, on June 30, 2009 SRNL and NREL participated in an all-day evaluation of the FCHV-adv with TEMA to determine the real-world driving range of this vehicle through on-road driving on an extended round-trip drive between Torrance and San Diego, California. SRNL and NREL observed the vehicles being refueled at Toyota's headquarters the day before the evaluation in Torrance, CA on June 29. At 8:00 AM on June 30, the vehicles departed Torrance north toward downtown Los Angeles, then west to the Pacific Coast Highway, and down to San Diego. After lunch the vehicles retraced their route back to Torrance. The traffic encountered was much heavier than anticipated, causing the vehicles to not return to Torrance until 9 PM. Each vehicle was driven by the same Toyota driver all day, with one SRNL/NREL observer in each vehicle the entire route. Data was logged by Toyota and analyzed by NREL. The maximum range of the FCHV-adv vehicles was calculated to be 431 miles under these driving conditions. This distance was calculated from the actual range of 331.5 miles during over 11 hours driving, plus 99.5 miles of

  19. Non-equilibrium phenomena in disordered colloidal solids

    NASA Astrophysics Data System (ADS)

    Yunker, Peter

    Colloidal particles are a convenient tool for studying a variety of non-equilibrium phenomena. I will discuss experiments that investigate the aging and non-equilibrium growth of disordered solids. In the first set of experiments, colloidal glasses are rapidly formed to study aging in jammed packings. A colloidal fluid, composed of micron-sized temperature-sensitive pNIPAM particles, is rapidly quenched into a colloidal glass. After the glass is formed, collective rearrangements occur as the glass ages. Particles that undergo irreversible rearrangements, which break nearest-neighbor pairings and allow the glass to relax, are identified. These irreversible rearrangements are accompanied by large clusters of fast moving particles; the number of particles involved in these clusters increases as the glass ages, leading to the slowing of dynamics that is characteristic of aging. In the second set of experiments, we study the role particle shape, and thus, interparticle interaction, plays in the formation of disordered solids with different structural and mechanical properties. Aqueous suspensions of colloidal particles with different shapes evaporate on glass slides. Convective flows during evaporation carry particles from drop center to drop edge, where they accumulate. The resulting particle deposits grow heterogeneously from the edge on the air-water interface. Three distinct growth processes were discovered in the evaporating colloidal suspensions by tuning particle shape-dependent capillary interactions and thus varying the microscopic rules of deposition. Mechanical testing of these particulate deposits reveals that the deposit bending rigidity increases as particles become more anisotropic in shape.

  20. Effect of fluid-colloid interactions on the mobility of a thermophoretic microswimmer in non-ideal fluids.

    PubMed

    Fedosov, Dmitry A; Sengupta, Ankush; Gompper, Gerhard

    2015-09-01

    Janus colloids propelled by light, e.g., thermophoretic particles, offer promising prospects as artificial microswimmers. However, their swimming behavior and its dependence on fluid properties and fluid-colloid interactions remain poorly understood. Here, we investigate the behavior of a thermophoretic Janus colloid in its own temperature gradient using numerical simulations. The dissipative particle dynamics method with energy conservation is used to investigate the behavior in non-ideal and ideal-gas like fluids for different fluid-colloid interactions, boundary conditions, and temperature-controlling strategies. The fluid-colloid interactions appear to have a strong effect on the colloid behavior, since they directly affect heat exchange between the colloid surface and the fluid. The simulation results show that a reduction of the heat exchange at the fluid-colloid interface leads to an enhancement of colloid's thermophoretic mobility. The colloid behavior is found to be different in non-ideal and ideal fluids, suggesting that fluid compressibility plays a significant role. The flow field around the colloid surface is found to be dominated by a source-dipole, in agreement with the recent theoretical and simulation predictions. Finally, different temperature-control strategies do not appear to have a strong effect on the colloid's swimming velocity. PMID:26223678

  1. Colloidally deposited nanoparticle wires for biophysical detection

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  2. Colloidal Double Quantum Dots

    PubMed Central

    2016-01-01

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

  3. Colloidal Double Quantum Dots.

    PubMed

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

    2016-05-17

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

  4. Colloid-Facilitated Radionuclide Transport at the Potential Yucca Mountain Repository

    NASA Astrophysics Data System (ADS)

    Alcorn, S. R.; Mertz, C. J.

    2001-12-01

    In a geologic repository for nuclear waste, transport of radionuclides on or within colloids may be important for radionuclides of concern that have low solubility and can be entrained in, or sorbed onto, colloidal particles generated within the repository system. It is anticipated that colloids will be formed and mobilized at the potential Yucca Mountain repository as a result of alteration of high-level radioactive waste (HLW) and spent nuclear fuel (SNF) waste forms, as well as corrosion of engineered barrier system (EBS) components. The abundance of colloids leaving a breached waste package and entering the repository drift will depend on the extent of waste form and EBS component alteration and the alteration products formed. Further, colloid abundance and stability will depend on such environmental factors as the ionic strength, pH, cation concentrations, natural colloid content, and organic acid and microbe content of groundwater entering the waste package from the drift. Colloids may flocculate and settle, be chemically retarded, mechanically filtered, or dissolve. In addition, colloids may sorb readily at the interfaces between air and water in rocks and engineered barriers and, depending upon the characteristics and degree of saturation of the porous medium, may be immobilized, retarded, or transported. A methodology for modeling colloid-facilitated radionuclide transport in the potential repository at Yucca Mountain was developed for use in Total System Performance Assessment calculations. The model incorporates several colloid sources and addresses factors affecting colloid stability and concentration as well as distribution and attachment of radionuclides onto colloids. Waste form corrosion tests performed at Argonne National Laboratory (ANL) have focused on determination of colloid composition, stability, concentration, size distribution, and associated radionuclide concentration. Data from these experiments were used as model inputs.

  5. Rapid fabrication of large area binary polystyrene colloidal crystals

    NASA Astrophysics Data System (ADS)

    Luo, Chun-Li; Yang, Rui-Xia; Yan, Wei-Guo; Zhao, Jian; Yang, Guang-Wu; Jia, Guo-Zhi

    2016-07-01

    Binary colloidal crystals (BCCs) possess great potentials in tuning material and optical properties. In this paper, the combination of interface transferred method and spin-coating method is used to fabricate BCCs with different patterns via controlling the size ratio of small (S) to large (L) colloidal spheres and the spin speeds. It is found that BCCs formed LS2, LS4 and LS6 by changing the size ratio. In addition, there are some new and complicated structures, such as LS12, Janus arrays, formed at the low spin speed. This simple assembly method has potential to allow for the creation of optical metmaterials and the plasmonic structures with chiral optical properties.

  6. Development of a model colloidal system for rheology simulation.

    SciTech Connect

    Schunk, Peter Randall; Tallant, David Robert; Piech, Martin; Bell, Nelson Simmons; Frischknecht, Amalie Lucile

    2008-10-01

    The objective of the experimental effort is to provide a model particle system that will enable modeling of the macroscopic rheology from the interfacial and environmental structure of the particles and solvent or melt as functions of applied shear and volume fraction of the solid particles. This chapter describes the choice of the model particle system, methods for synthesis and characterization, and results from characterization of colloidal dispersion, particle film formation, and the shear and oscillatory rheology in the system. Surface characterization of the grafted PDMS interface, dispersion characterization of the colloids, and rheological characterization of the dispersions as a function of volume fraction were conducted.

  7. Colloid migration in fractured media

    SciTech Connect

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

    1989-09-15

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

  8. Magnetofluidic Tweezing of Nonmagnetic Colloids.

    PubMed

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

    2016-05-01

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

  9. 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.

  10. Intermittent filtration of bacteria and colloids in porous media

    NASA Astrophysics Data System (ADS)

    Auset, Maria; Keller, Arturo A.; Brissaud, FrançOis; Lazarova, Valentina

    2005-09-01

    Intermittent filtration through porous media used for water and wastewater treatment can achieve high pathogen and colloid removal efficiencies. To predict the removal of bacteria, the effects of cyclic infiltration and draining events (transient unsaturated flow) were investigated. Using physical micromodels, we visualized the intermittent transport of bacteria and other colloids in unsaturated porous media. Column experiments provided quantitative measurements of the phenomena observed at the pore scale. Tagged Escherichia coli and a conservative tracer (NaI) were introduced in an initial pulse into a 1.5 m sand column. Subsequent hydraulic flushes without tagged bacteria or tracer were repeated every 4 hours for the next 4 days, during which outflow concentrations were monitored. Breakthrough behavior between colloids and dissolved tracer differed significantly, reflecting the differences in transport processes. Advancement of the wetting front remobilized bacteria which were held in thin water films, attached to the air-water interface (AWI), or entrapped in stagnant pore water between gas bubbles. In contrast, the tracer was only remobilized by diffusion from immobile to mobile water. Remobilization led to successive concentration peaks of bacteria and tracer in the effluent but with significant temporal differences. Observations at the pore-scale indicated that the colloids were essentially irreversibly attached to the solid-water interface, which explained to some extent the high removal efficiency of microbes in the porous media. Straining, cluster filtration, cell lysis, protozoa grazing, and bacteriophage parasitism could also contribute to the removal efficiency of bacteria.

  11. Impact of dissolved organic matter on colloid transport in the vadose zone: deterministic approximation of transport deposition coefficients from polymeric coating characteristics.

    PubMed

    Morales, Verónica L; Zhang, Wei; Gao, Bin; Lion, Leonard W; Bisogni, James J; McDonough, Brendan A; Steenhuis, Tammo S

    2011-02-01

    Although numerous studies have been conducted to discern colloid transport and stability processes, the mechanistic understanding of how dissolved organic matter (DOM) affects colloid fate in unsaturated soils (i.e., the vadose zone) remains unclear. This study aims to bridge the gap between the physicochemical responses of colloid complexes and porous media interfaces to solution chemistry, and the effect these changes have on colloid transport and fate. Measurements of adsorbed layer thickness, density, and charge of DOM-colloid complexes and transport experiments with tandem internal process visualization were conducted for key constituents of DOM, humic (HA) and fulvic acids (FA), at acidic, neutral and basic pH and two CaCl(2) concentrations. Polymeric characteristics reveal that, of the two tested DOM constituents, only HA electrosterically stabilizes colloids. This stabilization is highly dependent on solution pH which controls DOM polymer adsorption affinity, and on the presence of Ca(+2) which promotes charge neutralization and inter-particle bridging. Transport experiments indicate that HA improved colloid transport significantly, while FA only marginally affected transport despite having a large effect on particle charge. A transport model with deposition and pore-exclusion parameters fit experimental breakthrough curves well. Trends in deposition coefficients are correlated to the changes in colloid surface potential for bare colloids, but must include adsorbed layer thickness and density for sterically stabilized colloids. Additionally, internal process observations with bright field microscopy reveal that, under optimal conditions for retention, experiments with FA or no DOM promoted colloid retention at solid-water interfaces, while experiments with HA enhanced colloid retention at air-water interfaces, presumably due to partitioning of HA at the air-water interface and/or increased hydrophobic characteristics of HA-colloid complexes. PMID:21193215

  12. Surfactant-induced Marangoni eddies alter the coffee-rings of evaporating colloidal drops.

    PubMed

    Still, Tim; Yunker, Peter J; Yodh, Arjun G

    2012-03-20

    The influence of the small ionic surfactant sodium dodecyl sulfate (SDS) on the evaporation of drying colloidal droplets is quantitatively investigated. The addition of SDS leads to a significantly more uniform deposition of colloidal particles after evaporation (i.e., the so-called "coffee-ring effect" is dramatically altered). We understand this phenomenon in the context of circulating radial Marangoni flows induced by the variation of SDS concentration along the air-water interface. Video microscopy permits the direct visualization of the colloidal particles involved in these flows, revealing a surprisingly stable "Marangoni eddy" that prevents particle deposition at the drop perimeter. PMID:22369657

  13. Experimental study on thermophoresis of colloids in aqueous surfactant solutions.

    PubMed

    Dong, Ruo-Yu; Zhou, Yi; Yang, Chun; Cao, Bing-Yang

    2015-12-16

    Thermophoresis refers to the motion of particles under a temperature gradient and it is one of the particle manipulation techniques. Regarding the thermophoresis of particles in liquid media, however, many open questions still remain, especially the role of the interfacial effect. This work reports on a systematic experimental investigation of surfactant effects, especially the induced interfacial effect, on the thermophoresis of colloids in aqueous solutions via a microfluidic approach. Two kinds of commonly used surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), are selected and the results show that from relatively large concentrations, the two surfactants can greatly enhance the thermophilic mobilities. Specifically, it is found that the colloid-water interfaces modified with more polar end groups can potentially lead to a stronger thermophilic tendency. Due to the complex effects of surfactants, further theoretical model development is needed to quantitatively describe the dependence of thermophoresis on the interface characteristics. PMID:26596230

  14. Experimental study on thermophoresis of colloids in aqueous surfactant solutions

    NASA Astrophysics Data System (ADS)

    Dong, Ruo-Yu; Zhou, Yi; Yang, Chun; Cao, Bing-Yang

    2015-12-01

    Thermophoresis refers to the motion of particles under a temperature gradient and it is one of the particle manipulation techniques. Regarding the thermophoresis of particles in liquid media, however, many open questions still remain, especially the role of the interfacial effect. This work reports on a systematic experimental investigation of surfactant effects, especially the induced interfacial effect, on the thermophoresis of colloids in aqueous solutions via a microfluidic approach. Two kinds of commonly used surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), are selected and the results show that from relatively large concentrations, the two surfactants can greatly enhance the thermophilic mobilities. Specifically, it is found that the colloid-water interfaces modified with more polar end groups can potentially lead to a stronger thermophilic tendency. Due to the complex effects of surfactants, further theoretical model development is needed to quantitatively describe the dependence of thermophoresis on the interface characteristics.

  15. Colloidal aggregation in polymer blends.

    PubMed

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

    2005-06-22

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

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

    NASA Astrophysics Data System (ADS)

    Löwen, Hartmut

    2012-11-01

    tailor a random substrate potential for colloids [20] or to bind colloids optically [21]. External magnetic fields are typically used to create dipolar repulsions of colloids pending at an air-water interface. This provides an avenue to two-dimensional systems, where the freezing transition [22] and various transport phenomena through channels are the focus of recent research [23, 24]. Confinement typically leads to interfaces. The classical problem of the Tolman length for a fluid-fluid interface is reviewed in detail in [25]. In fact, colloid-polymer mixtures constitute ideal model systems for liquid-gas interfaces in various geometries [26] and are also suitable for measuring the Tolman length experimentally. Crystalline phases in confinement [27] and crystal-fluid interfaces [28] are even more complex due to the inhomogeneity of the solid phase. Also in the confined fluid phase, there are still open issues in slit-pore geometry. These include how to scale the interparticle distance [29] and how to measure hydrodynamic interactions between colloidal particles [30]. Other external fields which can be applied to colloids are gravity [31] and temperature [32]. An important field of recently emerging research is active colloidal particles (so-called microswimmers) which possess fascinating nonequilibrium properties; for recent reviews see [33-35]. Two examples are also included in this issue: an active deformable particle [36] moving in gravity and the collective turbulent swarming behaviour of dense self-propelled colloidal rod suspensions [37]. References [1]Löwen H 2001 J. Phys. Condens. Matter 13 R415 [2]Löwen H and Likos C N (ed) 2004 J. Phys. Condens. Matter 16 (special issue) [3]Löwen H 1976 J. Phys. Condens. Matter 20 404201 [4]Guu D, Dhont J K G, Vliegenthart G A and Lettinga M P 2012 J. Phys. Condens. Matter 24 464101 [5]Gupta S, Kundu S, Stellbrink J, Willner L, Allgaier J and Richter D 2012 J. Phys. Condens. Matter 24 464102 [6]Singh S P, Fedosov D A

  17. Colloids in Acute Burn Resuscitation.

    PubMed

    Cartotto, Robert; Greenhalgh, David

    2016-10-01

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

  18. Two-dimensional dipolar nematic colloidal crystals.

    PubMed

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

    2007-11-01

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

  19. Colloid labelled with radionuclide and method

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1990-01-01

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

  20. Method of making colloid labeled with radionuclide

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1991-01-01

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

  1. Colloid labelled with radionuclide and method

    DOEpatents

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

    1990-11-13

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

  2. Adhesion of colloidal particles on modified electrodes.

    PubMed

    Kuznetsov, Volodymyr; Papastavrou, Georg

    2012-12-01

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

  3. Emergent behavior in active colloids

    NASA Astrophysics Data System (ADS)

    Zöttl, Andreas; Stark, Holger

    2016-06-01

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

  4. Colloidal Suspended Iron in Rivers

    NASA Astrophysics Data System (ADS)

    Shiller, A. M.

    2009-12-01

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

  5. Re-shaping colloidal clusters

    NASA Astrophysics Data System (ADS)

    Kraft, Daniela

    2015-03-01

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

  6. Mechanical Failure in Colloidal Gels

    NASA Astrophysics Data System (ADS)

    Kodger, Thomas Edward

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

  7. Aggregation of Heterogeneously Charged Colloids.

    PubMed

    Dempster, Joshua M; Olvera de la Cruz, Monica

    2016-06-28

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

  8. MOLECULAR DESIGN OF COLLOIDS IN SUPERCRITICAL FLUIDS

    SciTech Connect

    Keith P. Johnston

    2009-04-06

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

  9. Imbibition kinetics of spherical colloidal aggregates.

    PubMed

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

    2014-07-11

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

  10. Building devices from colloidal quantum dots.

    PubMed

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

    2016-08-26

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

  11. A coupled field study of subsurface fracture flow and colloid transport

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Tang, Xiang-Yu; Weisbrod, Noam; Zhao, Pei; Reid, Brian J.

    2015-05-01

    Field studies of subsurface transport of colloids, which may act as carriers of contaminants, are still rare. This is particularly true for heterogeneous and fractured matrices. To address this knowledge gap, a 30-m long monitoring trench was constructed at the lower end of sloping farmland in central Sichuan, southwest China. During the summer of 2013, high resolution dynamic and temporal fracture flow discharging from the interface between fractured mudrock and impermeable sandstone was obtained at intervals of 5 min (for fast rising stages), 30-60 min (for slow falling stages) or 15 min (at all other times). This discharge was analyzed to elucidate fracture flow and colloid transport in response to rainfall events. Colloid concentrations were observed to increase quickly once rainfall started (∼15-90 min) and reached peak values of up to 188 mg/L. Interestingly, maximum colloid concentration occurred prior to the arrival of flow discharge peak (i.e. maximum colloid concentration was observed before saturation of the soil layer). Rainfall intensity (rather than its duration) was noted to be the main factor controlling colloid response and transport. Dissolved organic carbon concentration and δ18O dynamics in combination with soil water potential were used to apportion water sources of fracture flow at different stages. These approaches suggested the main source of the colloids discharged to be associated with the flushing of colloids from the soil mesopores and macropores. Beyond the scientific interest of colloid mobilization and transport at the field scale, these results have important implications for a region of about 160,000 km2 in southwest China that featured similar hydrogeologic settings as the experimental site. In this agriculture-dominated area, application of pesticides and fertilizers to farmland is prevalent. These results highlight the need to avoid such applications immediately before rainfall events in order to reduce rapid migration to

  12. Do changes in the size of mud flocs affect the acoustic backscatter values recorded by a Vector ADV?

    NASA Astrophysics Data System (ADS)

    Rouhnia, Mohamad; Keyvani, Ali; Strom, Kyle

    2014-08-01

    A series of experiments were conducted to examine the effect of mud floc growth on the acoustic back-scatter signal recorded by a Nortek Vector acoustic Doppler velocimeter (ADV). Several studies have shown that calibration equations can be developed to link the backscatter strength with average suspended sediment concentration (SSC) when the sediment particle size distribution remains constant. However, when mud is present, the process of flocculation can alter the suspended particle size distribution. Past studies have shown that it is still unclear as to the degree of dependence of the calibration equation on changes in floc size. Part of the ambiguity lies in the fact that flocs can be porous and rather loosely packed and therefore will not scatter sound waves as a solid particle would. In addition, direct, detailed measurements of floc size have not accompanied experiments examining the dependence of ADV backscatter and suspended sediment concentration. In this set of experiments, direct measurement of the floc size distribution is made with time in a mixing chamber using a floc camera system. A Vector ADV and an OBS are also placed within the tank to measure acoustic backscatter and SSC as the flocs change size with time; concentration in the experiments ranges from 15 to 90 mg/l. Results showed that the growth of mud flocs did influence the SNR recorded by the Vector ADV, and that the sensitivity of the SNR signal to changes in floc size was higher for flocs with diameters less than ≈80 μm (it kr=1 at a diameter of 80 μm). The response of SNR to changes in floc size and SSC was modeled with a modified sonar equation. If properly calibrated, the model was able to capture the functional behavior of SNR with changes in floc size and concentration. Values of the calibration coefficients showed that while changes in floc diameter up to about 80 μm did alter the SNR, the change was less than what would be expected from a similar change in the size of solid

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

    NASA Astrophysics Data System (ADS)

    Derks, D.

    2006-09-01

    decomposition pattern is observed. As the structure coarsens, the domains become highly stretched along the flow direction, and the domain width along the vorticity axis reaches a stationary size, corresponding to a steady state. In the final stage of phase separation the denser colloidal liquid phase settles on the bottom of the cell, while the gas phase floats on top. The interface between these phases is the topic of Chapter 5. We investigate the thermal fluctuations of the colloidal gas-liquid interface subjected to a shear flow parallel to the interface. Strikingly, we find that the shear strongly suppresses capillary waves, making the interface smoother. Finally, we consider the demixing process in systems of attractive rods (Chapter 6). A mixture of rod-like viruses (fd) and polymer (dextran) is quenched from a flow-induced fully nematic state into the region where the nematic and the isotropic phase coexist (at zero shear). Dependent on the concentration of rods we observe either demixing by nucleation-and-growth (high concentration) or spinodal decomposition (low concentration). At intermediate concentrations we see the transition between both types of demixing processes, where we locate the spinodal point.

  14. Preliminary 3-D site-scale studies of radioactive colloid transortin the unsaturated zone at Yucca Mountain, Nevada

    SciTech Connect

    Moridis, G.J.; Hu, Q.; Wu, Y.-S.; Bodvarsson, G.S.

    2001-09-01

    The U.S: Department of Energy is actively investigating the technical feasibility of permanent disposal of high-level nuclear waste in a repository to be situated in the unsaturated zone at Yucca Mountain, Nevada. In this study we investigate, by means of numerical simulation, the transport of radioactive colloids under ambient conditions from the potential repository horizon to the water table. The site hydrology and the effects of the spatial distribution of hydraulic and transport properties in the Yucca Mountain subsurface are considered. The study of migration and retardation of colloids accounts for the complex processes in the unsaturated zone of Yucca Mountain, and includes advection, diffusion, hydrodynamic dispersion, kinetic colloid filtration, colloid straining, and radioactive decay. The results of the study indicate that the most important factors affecting colloid transport are the subsurface geology and site hydrology, i.e., the presence of faults (they dominate and control transport), fractures (the main migration pathways), and the relative distribution of zeolitic and vitric tuffs. The transport of colloids is strongly influenced by their size (as it affects diffusion into the matrix, straining at hydrogeologic unit interfaces, and transport velocity) and by the parameters of the kinetic-filtration model used for the simulations. Arrival times at the water table decrease with an increasing colloid size because of smaller diffusion, increased straining, and higher transport velocities. The importance of diffusion as a retardation mechanism increases with a decreasing colloid size, but appears to be minimal in large colloids.

  15. Preliminary 3-D site-scale studies of radioactive colloid transport in the unsaturated zone at Yucca Mountain, Nevada.

    PubMed

    Moridis, G J; Hu, Q; Wu, Y-S; Bodvarsson, G S

    2003-02-01

    The U.S. Department of Energy (DOE) is actively investigating the technical feasibility of permanent disposal of high-level nuclear waste in a repository to be situated in the unsaturated zone (UZ) at Yucca Mountain (YM), Nevada. In this study we investigate, by means of numerical simulation, the transport of radioactive colloids under ambient conditions from the potential repository horizon to the water table. The site hydrology and the effects of the spatial distribution of hydraulic and transport properties in the Yucca Mountain subsurface are considered. The study of migration and retardation of colloids accounts for the complex processes in the unsaturated zone of Yucca Mountain, and includes advection, diffusion, hydrodynamic dispersion, kinetic colloid filtration, colloid straining, and radioactive decay. The results of the study indicate that the most important factors affecting colloid transport are the subsurface geology and site hydrology, i.e., the presence of faults (they dominate and control transport), fractures (the main migration pathways), and the relative distribution of zeolitic and vitric tuffs. The transport of colloids is strongly influenced by their size (as it affects diffusion into the matrix, straining at hydrogeologic unit interfaces, and transport velocity) and by the parameters of the kinetic-filtration model used for the simulations. Arrival times at the water table decrease with an increasing colloid size because of smaller diffusion, increased straining, and higher transport velocities. The importance of diffusion as a retardation mechanism increases with a decreasing colloid size, but appears to be minimal in large colloids. PMID:12504362

  16. Edge pinning and transformation of defect lines induced by faceted colloidal rings in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Senyuk, Bohdan; Liu, Qingkun; Yuan, Ye; Smalyukh, Ivan I.

    2016-06-01

    Nematic colloids exhibit a large diversity of topological defects and structures induced by colloidal particles in the orientationally ordered liquid crystal host fluids. These defects and field configurations define elastic interactions and medium-mediated self-assembly, as well as serve as model systems in exploiting the richness of interactions between topologies and geometries of colloidal surfaces, nematic fields, and topological singularities induced by particles in the nematic bulk and at nematic-colloidal interfaces. Here we demonstrate formation of quarter-strength surface-pinned disclinations, as well as a large variety of director field configurations with splitting and reconnections of singular defect lines, prompted by colloidal particles with sharp edges and size large enough to define strong boundary conditions. Using examples of faceted ring-shaped particles of genus g =1 , we explore transformation of defect lines as they migrate between locations in the bulk of the nematic host to edge-pinned locations at the surfaces of particles and vice versa, showing that this behavior is compliant with topological constraints defined by mathematical theorems. We discuss how transformation of bulk and surface defect lines induced by faceted colloids can enrich the diversity of elasticity-mediated colloidal interactions and how these findings may impinge on prospects of their controlled reconfigurable self-assembly in nematic hosts.

  17. Edge pinning and transformation of defect lines induced by faceted colloidal rings in nematic liquid crystals.

    PubMed

    Senyuk, Bohdan; Liu, Qingkun; Yuan, Ye; Smalyukh, Ivan I

    2016-06-01

    Nematic colloids exhibit a large diversity of topological defects and structures induced by colloidal particles in the orientationally ordered liquid crystal host fluids. These defects and field configurations define elastic interactions and medium-mediated self-assembly, as well as serve as model systems in exploiting the richness of interactions between topologies and geometries of colloidal surfaces, nematic fields, and topological singularities induced by particles in the nematic bulk and at nematic-colloidal interfaces. Here we demonstrate formation of quarter-strength surface-pinned disclinations, as well as a large variety of director field configurations with splitting and reconnections of singular defect lines, prompted by colloidal particles with sharp edges and size large enough to define strong boundary conditions. Using examples of faceted ring-shaped particles of genus g=1, we explore transformation of defect lines as they migrate between locations in the bulk of the nematic host to edge-pinned locations at the surfaces of particles and vice versa, showing that this behavior is compliant with topological constraints defined by mathematical theorems. We discuss how transformation of bulk and surface defect lines induced by faceted colloids can enrich the diversity of elasticity-mediated colloidal interactions and how these findings may impinge on prospects of their controlled reconfigurable self-assembly in nematic hosts. PMID:27415331

  18. Dielectrophoresis force of colloidal nanoparticles

    NASA Astrophysics Data System (ADS)

    Huang, Hao; Ou-Yang, Daniel

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

  19. Self-assembly of skyrmion-dressed chiral nematic colloids with tangential anchoring.

    PubMed

    Pandey, M B; Porenta, T; Brewer, J; Burkart, A; Copar, S; Zumer, S; Smalyukh, Ivan I

    2014-06-01

    We describe dipolar nematic colloids comprising mutually bound solid microspheres, three-dimensional skyrmions, and point defects in a molecular alignment field of chiral nematic liquid crystals. Nonlinear optical imaging and numerical modeling based on minimization of Landau-de Gennes free energy reveal that the particle-induced skyrmions resemble torons and hopfions, while matching surface boundary conditions at the interfaces of liquid crystal and colloidal spheres. Laser tweezers and videomicroscopy reveal that the skyrmion-colloidal hybrids exhibit purely repulsive elastic pair interactions in the case of parallel dipoles and an unexpected reversal of interaction forces from repulsive to attractive as the center-to-center distance decreases for antiparallel dipoles. The ensuing elastic self-assembly gives rise to colloidal chains of antiparallel dipoles with particles entangled by skyrmions. PMID:25019708

  20. A test of the ADV-based Reynolds flux method for in situ estimation of sediment settling velocity in a muddy estuary

    NASA Astrophysics Data System (ADS)

    Cartwright, Grace M.; Friedrichs, Carl T.; Smith, S. Jarrell

    2013-12-01

    Under conditions common in muddy coastal and estuarine environments, acoustic Doppler velocimeters (ADVs) can serve to estimate sediment settling velocity ( w s) by assuming a balance between upward turbulent Reynolds flux and downward gravitational settling. Advantages of this method include simple instrument deployment, lack of flow disturbance, and relative insensitivity to biofouling and water column stratification. Although this method is being used with increasing frequency in coastal and estuarine environments, to date it has received little direct ground truthing. This study compared in situ estimates of w s inferred by a 5-MHz ADV to independent in situ observations from a high-definition video settling column over the course of a flood tide in the bottom boundary layer of the York River estuary, Virginia, USA. The ADV-based measurements were found to agree with those of the settling column when the current speed at about 40 cm above the bed was greater than about 20 cm/s. This corresponded to periods when the estimated magnitude of the settling term in the suspended sediment continuity equation was four or more times larger than the time rate of change of concentration. For ADV observations restricted to these conditions, ADV-based estimates of w s (mean 0.48±0.04 mm/s) were highly consistent with those observed by the settling column (mean 0.45±0.02 mm/s). However, the ADV-based method for estimating w s was sensitive to the prescribed concentration of the non-settling washload, C wash. In an objective operational definition, C wash can be set equal to the lowest suspended solids concentration observed around slack water.

  1. Capillary Force on a Micrometric Sphere Trapped at a Fluid Interface Exhibiting Arbitrary Curvature Gradients

    NASA Astrophysics Data System (ADS)

    Blanc, Christophe; Fedorenko, Denys; Gross, Michel; In, Martin; Abkarian, Manouk; Gharbi, Mohamed Amine; Fournier, Jean-Baptiste; Galatola, Paolo; Nobili, Maurizio

    2013-08-01

    We report theoretical predictions and measurements of the capillary force acting on a spherical colloid smaller than the capillary length that is placed on a curved fluid interface of arbitrary shape. By coupling direct imaging and interferometry, we are able to measure the in situ colloid contact angle and to correlate its position with respect to the interface curvature. Extremely tiny capillary forces down to femtonewtons can be measured with this method. Measurements agree well with a theory relating the capillary force to the gradient of Gaussian curvature and to the mean curvature of the interface prior to colloidal deposition. Numerical calculations corroborate these results.

  2. Crack formation and prevention in colloidal drops.

    PubMed

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

    2015-01-01

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

  3. 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.

  4. 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

  5. Acoustic Stimulation of Colloid Behavior at the Pore and Core Scales

    NASA Astrophysics Data System (ADS)

    Roberts, P. M.

    2006-12-01

    Acoustic waves can influence the attachment and/or detachment of colloids at solid/liquid interfaces. They can also induce colloid-colloid interactions leading to colloid trapping or clustering. Subsequent accumulation or release of colloids in a porous medium can alter its permeability. This can cause either good or bad effects on porous fluid-flow behavior in the Earth and geomaterials. Prior experiments using a microscopic, video image- processing system focused on a glass flow-visualization cell indicated that 0.5 to 5 MHz acoustic energy can induce attachment and detachment of sub-micron-size polystyrene microspheres at solid/liquid interfaces. New experiments were performed to investigate the effect of particle size, concentration (volume fraction), ionic strength, and acoustic energy on the deposition and removal kinetics of colloidal particles onto different solid surfaces. Additional experiments demonstrated that acoustically excited particles can attract other particles and cause them to orbit each other in directions that depend on the acoustic frequency. Other prior experiments on centimeter-size sandstone cores showed that 50 Hz mechanical stress oscillations can mobilize trapped in-situ colloids as well as injected 300-nm polystyrene microspheres. A unique core-holder apparatus that mechanically strains 2.54-cm-diameter porous rock samples during constant-rate fluid flow was used for those experiments. To investigate the effect of particle size on trapping and acoustic release of colloids, new experiments were performed by injecting 1-micron microspheres suspended in deionized water and 0.1M NaCl solution. The larger size microspheres were trapped at both high and low ionic strengths, unlike the smaller 300-nm microspheres which were only trapped at high ionic strength. Stress stimulation at less than 100 Hz caused enhanced release of the trapped microspheres at a rate much higher than the average background production rate during water flow alone

  6. Entropy favours open colloidal lattices

    NASA Astrophysics Data System (ADS)

    Mao, Xiaoming; Chen, Qian; Granick, Steve

    2013-03-01

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

  7. Doped colloidal artificial spin ice

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  8. Polymeric stabilization of colloidal asphaltenes

    NASA Astrophysics Data System (ADS)

    Hashmi, Sara; Firoozabadi, Abbas

    2010-03-01

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

  9. Gel transitions in colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Bergenholtz, J.; Fuchs, M.

    1999-12-01

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

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

    PubMed

    Kwon, Younghwan

    2014-10-01

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

  11. Bicompartmental phase transfer vehicles based on colloidal dimers.

    PubMed

    Wang, Sijia; Wu, Ning

    2014-11-26

    Colloidal particles have been used extensively for stabilizing oil-water interfaces in petroleum, food, and cosmetics industries. They have also demonstrated promising potential in the encapsulation and delivery of drugs. Our work is motivated by challenging applications that require protecting and transporting active agents across the water-oil interfaces, such as delivering catalysts to underground oil phase through water flooding for in situ cracking of crude oil. In this Research Article, we successfully design, synthesize, and test a unique type of bicompartmental targeting vehicle that encapsulates catalytic molecules, finds and accumulates at oil-water interface, releases the catalysts toward the oil phase, and performs hydrogenation reaction of unsaturated oil. This vehicle is based on colloidal dimers that possess structural anisotropy between two compartments. We encapsulate active species, such as fluorescent dye and catalytic molecules in one lobe which consists of un-cross-linked polymers, while the other polymeric lobe is highly cross-linked. Although dimers are dispersible in water initially, the un-cross-linked lobe swells significantly upon contact with a trace amount of oil in aqueous phase. The dimers then become amphiphilic, migrate toward, and accumulate at the oil-water interface. As the un-cross-linked lobe swells and eventually dissolves in oil, the encapsulated catalysts are fully released. We also show that hydrogenation of unsaturated oil can be performed subsequently with high conversion efficiency. By further creating the interfacial anisotropy on the dimers, we can reduce the catalyst release time from hundred hours to 30 min. Our work demonstrates a new concept in making colloidal emulsifiers and phase-transfer vehicles that are important for encapsulation and sequential release of small molecules across two different phases. PMID:25322697

  12. Exploiting the colloidal nanocrystal library to construct electronic devices

    NASA Astrophysics Data System (ADS)

    Choi, Ji-Hyuk; Wang, Han; Oh, Soong Ju; Paik, Taejong; Sung, Pil; Sung, Jinwoo; Ye, Xingchen; Zhao, Tianshuo; Diroll, Benjamin T.; Murray, Christopher B.; Kagan, Cherie R.

    2016-04-01

    Synthetic methods produce libraries of colloidal nanocrystals with tunable physical properties by tailoring the nanocrystal size, shape, and composition. Here, we exploit colloidal nanocrystal diversity and design the materials, interfaces, and processes to construct all-nanocrystal electronic devices using solution-based processes. Metallic silver and semiconducting cadmium selenide nanocrystals are deposited to form high-conductivity and high-mobility thin-film electrodes and channel layers of field-effect transistors. Insulating aluminum oxide nanocrystals are assembled layer by layer with polyelectrolytes to form high–dielectric constant gate insulator layers for low-voltage device operation. Metallic indium nanocrystals are codispersed with silver nanocrystals to integrate an indium supply in the deposited electrodes that serves to passivate and dope the cadmium selenide nanocrystal channel layer. We fabricate all-nanocrystal field-effect transistors on flexible plastics with electron mobilities of 21.7 square centimeters per volt-second.

  13. Amphiphilic colloidal surfactants based on electrohydrodynamic co-jetting.

    PubMed

    Yoon, Jaewon; Kota, Arun; Bhaskar, Srijanani; Tuteja, Anish; Lahann, Joerg

    2013-11-13

    A novel synthetic route for the preparation of amphiphilic Janus particles based on electrohydrodynamic cojetting has been developed. In this approach, selective encapsulation of hydrophobic fluorodecyl-polyhedral oligomeric silsesquioxane (F-POSS) in one compartment and a poly(vinyl alcohol) in the second compartment results in colloidal particles with surfactant-like properties including the self-organization at oil-water and air-water interfaces. Successful localization of the respective polymers in different compartments of the same particle is confirmed by a combination of fluorescence microscopy, vibrational spectroscopy, and ζ-potential measurements. We believe that this straightforward synthetic approach may lead to a diverse class of surface-active colloids that will have significant relevance ranging from basic scientific studies to immediate applications in areas, such as pharmaceutical sciences or cosmetics. PMID:24111894

  14. Exploiting the colloidal nanocrystal library to construct electronic devices.

    PubMed

    Choi, Ji-Hyuk; Wang, Han; Oh, Soong Ju; Paik, Taejong; Sung, Pil; Sung, Jinwoo; Ye, Xingchen; Zhao, Tianshuo; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

    2016-04-01

    Synthetic methods produce libraries of colloidal nanocrystals with tunable physical properties by tailoring the nanocrystal size, shape, and composition. Here, we exploit colloidal nanocrystal diversity and design the materials, interfaces, and processes to construct all-nanocrystal electronic devices using solution-based processes. Metallic silver and semiconducting cadmium selenide nanocrystals are deposited to form high-conductivity and high-mobility thin-film electrodes and channel layers of field-effect transistors. Insulating aluminum oxide nanocrystals are assembled layer by layer with polyelectrolytes to form high-dielectric constant gate insulator layers for low-voltage device operation. Metallic indium nanocrystals are codispersed with silver nanocrystals to integrate an indium supply in the deposited electrodes that serves to passivate and dope the cadmium selenide nanocrystal channel layer. We fabricate all-nanocrystal field-effect transistors on flexible plastics with electron mobilities of 21.7 square centimeters per volt-second. PMID:27124455

  15. Colloid cyst: a case report.

    PubMed

    Grasu, Beatrice L; Alberico, Anthony M

    2011-01-01

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

  16. When Colloidal Particles Become Polymer Coils.

    PubMed

    Mourran, Ahmed; Wu, Yaodong; Gumerov, Rustam A; Rudov, Andrey A; Potemkin, Igor I; Pich, Andrij; Möller, Martin

    2016-01-26

    This work concerns interfacial adsorption and attachment of swollen microgel with low- to medium-level cross-linking density. Compared to colloids that form a second, dispersed phase, the suspended swollen microgel particles are ultrahigh molecular weight molecules, which are dissolved like a linear polymer, so that solvent and solute constitute only one phase. In contrast to recent literature in which microgels are treated as particles with a distinct surface, we consider solvent-solute interaction as well as interfacial adsorption based on the chain segments that can form trains of adsorbed segments and loops protruding from the surface into the solvent. We point out experimental results that support this discrimination between particles and microgels. The time needed for swollen microgels to adsorb at the air/water interface can be 3 orders of magnitude shorter than that for dispersed particles and decreases with decreasing cross-linking density. Detailed analysis of the microgels deformation, in the dry state, at a solid surface enabled discrimination particle like microgel in which case spreading was controlled predominantly by the elasticity and molecule like adsorption characterized by a significant overstreching, ultimately leading to chain scission of microgel strands. Dissipative particle dynamics simulations confirms the experimental findings on the interfacial activity and spreading of microgel at liquid/air interface. PMID:26717422

  17. 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

  18. Colloids and Nucleation

    NASA Technical Reports Server (NTRS)

    Ackerson, Bruce

    1997-01-01

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

  19. Colloid Transport in Unsaturated Porous Media: 3D Visualization Using Synchrotron X-Ray Microtomography

    NASA Astrophysics Data System (ADS)

    Brueck, C. L.; Meisenheimer, D.; Wildenschild, D.

    2015-12-01

    Understanding the mechanisms controlling colloid transport and deposition in the vadose zone is an important step in protecting our water resources. Not only may these particles themselves be undesirable contaminants, but they can also aid in the transport of smaller, molecular-scale contaminants by chemical attachment. In this research, we examined the influence that air-water interfaces (AWI) and air-water-solid contact lines (AWS) have on colloid deposition and mobilization in three-dimensional systems. We used x-ray microtomography to visualize the transport of hydrophobic colloids as they move through a partially saturated glass bead pack. Drainage and imbibition experiments were conducted using syringe pumps to control the flow of a colloid suspension through the porous media at 0.6 mL/hr. The high ionic strength fluid was adjusted to a pH of 9.5 and a concentration of 1.0 mol/L KI. During the drainage and imbibition, the flow was periodically halted and allowed to equilibrate before collecting the microtomography scans. Dopants were used to enhance the contrast between the four phases (water, air, beads, and colloids), including potassium iodide dissolved in the fluid, and an outer layer of silver coating the colloids. We hypothesized that AWIs and AWSs will scour and mobilize a significant percentage of colloids, and therefore reduce the concentration of colloids along the vertical profile of the column. The concentration of potassium iodide, and thus the ionic strength, necessary for adequate image segmentation was also explored in separate experiments so that the influence of ionic strength on colloid deposition and mobilization can be studied.

  20. Evaluation of Colloid Retention Site Dominance in Variably Saturated Porous Media: An All Pores Pore-Scale Analysis

    NASA Astrophysics Data System (ADS)

    Morales, Veronica; Perez-Reche, Francisco; Holzner, Markus; Kinzelbach, Wolfgang

    2016-04-01

    It is well accepted that colloid and nanoparticle transport processes in porous media differ substantially between water saturated and unsaturated conditions. Differences are frequently ascribed to particle immobilization by association with interfaces with the gas, as well as to restrictions of the liquid medium through which colloids are transported. Yet, the current understanding of the importance of particle retention at gas interfaces is based on observations of single pores or two-dimensional pore network representations, leaving open the question of their statistical significance when all pores in the medium are considered. In order to address this question, column experiments were performed using a model porous medium of glass beads through which Silver particles were transported for conditions of varying water content and water chemistry. X-ray microtomography was subsequently employed as a non-destructive imaging technique to obtain pore-scale information of the entire column regarding: i) the presence and distribution of the main locations where colloids can become retained (interfaces with the water-solid, air-water, air-solid, and air-water-solid, grain-grain contacts, and the bulk liquid), ii) deposition profiles of colloids along the column classified by the available retention location, and iii) channel widths of 3-dimensional pore-water network representations. The results presented provide a direct statistical evaluation on the significance of colloid retention by attachment to interfaces or by strainig at contact points where multiple interfaces meet.

  1. Electrohydrodynamic simulation of an electrospray in a colloid thruster

    NASA Astrophysics Data System (ADS)

    Jugroot, Manish; Forget, Martin; Malardier-Jugroot, Cecile

    2012-02-01

    A precise understanding of electrosprays is highly interesting as the complexity of micro-technology (such as nano-material processing, spacecraft propulsion and mass-spectrometers) systems increases. A multi-component CFD-based model coupling fluid dynamics, charged species dynamics and electric field is developed. The simulations describe the charged fluid interface with emphasis on the Taylor cone formation and cone-jet transition under the effect of a electric field. The goal is to recapture this transition from a rounded liquid interface into a Taylor cone from an initial uniform distribution, without making assumptions on the behaviour, geometry or charge distribution of the system. The time evolution of the interface highlights the close interaction among space charge, coulombic forces and the surface tension, which appear as governing and competing processes in the transition. The results from the coupled formalism provide valuable insights on the physical phenomena and will be applied to a colloid thruster for small spacecrafts.

  2. Sensitivity analyses of a colloid-facilitated contaminant transport model for unsaturated heterogeneous soil conditions.

    NASA Astrophysics Data System (ADS)

    Périard, Yann; José Gumiere, Silvio; Rousseau, Alain N.; Caron, Jean

    2013-04-01

    Certain contaminants may travel faster through soils when they are sorbed to subsurface colloidal particles. Indeed, subsurface colloids may act as carriers of some contaminants accelerating their translocation through the soil into the water table. This phenomenon is known as colloid-facilitated contaminant transport. It plays a significant role in contaminant transport in soils and has been recognized as a source of groundwater contamination. From a mechanistic point of view, the attachment/detachment of the colloidal particles from the soil matrix or from the air-water interface and the straining process may modify the hydraulic properties of the porous media. Šimůnek et al. (2006) developed a model that can simulate the colloid-facilitated contaminant transport in variably saturated porous media. The model is based on the solution of a modified advection-dispersion equation that accounts for several processes, namely: straining, exclusion and attachement/detachement kinetics of colloids through the soil matrix. The solutions of these governing, partial differential equations are obtained using a standard Galerkin-type, linear finite element scheme, implemented in the HYDRUS-2D/3D software (Šimůnek et al., 2012). Modeling colloid transport through the soil and the interaction of colloids with the soil matrix and other contaminants is complex and requires the characterization of many model parameters. In practice, it is very difficult to assess actual transport parameter values, so they are often calibrated. However, before calibration, one needs to know which parameters have the greatest impact on output variables. This kind of information can be obtained through a sensitivity analysis of the model. The main objective of this work is to perform local and global sensitivity analyses of the colloid-facilitated contaminant transport module of HYDRUS. Sensitivity analysis was performed in two steps: (i) we applied a screening method based on Morris' elementary

  3. Modification of hybrid active bilayer for enhanced efficiency and stability in planar heterojunction colloidal quantum dot photovoltaics

    PubMed Central

    2013-01-01

    Solution-processed planar heterojunction colloidal quantum dot photovoltaics with a hybrid active bilayer is demonstrated. A power conversion efficiency of 1.24% under simulated air mass 1.5 illumination conditions is reported. This was achieved through solid-state treatment with cetyltrimethylammonium bromide of PbS colloidal quantum dot solid films. That treatment was used to passivate Br atomic ligands as well as to engineer the interface within the hybrid active bilayer. PMID:24252664

  4. Colloid characterization and quantification in groundwater samples

    SciTech Connect

    K. Stephen Kung

    2000-06-01

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

  5. Microbial effects on colloidal agglomeration

    SciTech Connect

    Hersman, L.

    1995-11-01

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

  6. 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.

  7. Sonochemical synthesis of iron colloids

    SciTech Connect

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

    1996-11-27

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

  8. Physics of Colloids in Space

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  9. 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.

  10. Towards Structural Complexity with Colloids

    NASA Astrophysics Data System (ADS)

    Engel, Michael

    2012-02-01

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

  11. 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

  12. Quantification of Capillary Force Acting on Colloids in a Three-phase Model System of Partially Saturated Porous Media

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Morales, V. L.; Gao, B.; Geohring, L. D.; Parlange, J.; Hay, A. G.; Steenhuis, T. S.

    2008-12-01

    Colloid transport in the vadose zone has gained increasing importance due to groundwater contamination of colloidal-size pathogens and colloid-facilitated transport of contaminants. Although colloid transport in saturated system is well understood, the presence of air phase in partially saturated zone poses an additional challenge for elucidating the mechanisms of the colloid transport. Capillary forces that occur when a colloid protrudes through water film around the grain or near air-water meniscus-solid interface has been identified as the major mechanism for colloid retention. Capillary force could be several orders of magnitude greater than the electrostatic DLVO force. Our current study investigates the effect of colloid surface properties, fluid chemistry, and film thickness on capillary force and associated meniscus configuration in a three-phase model system consisting of a particle protruding out of a spread film. Particles ranging from 100 to 600 micrometer are used as surrogates for colloids since the menisci of colloids cannot be visualized using currently available microscopic resolution. In our experimental setup, menisci configuration of soda-lime glass beads and polystyrene beads are visualized with high resolution Hirox digital bright field microscope in dionized water and solutions of 1:1 electrolyte (NaCl), 1:2 electrolyte (CaCl2), natural organic matters, and anionic, cationic or nonionic surfactants. The hydrophilic glass beads can be made hydrophobic by treating with octadecyltrichlorosilane, while the hydrophobic polystyrene can be made hydrophilic by carboxylation. The film thickness is also varied by allowing for evaporation. Contact angle, radius of three-phase contact line, and other relevant parameters for calculation of capillary force are measured. The changes of surface properties, fluid chemistry, and film thickness are expected to result in the observable changes of capillary force and associated meniscus configuration. This

  13. 17 CFR 279.4 - Form ADV-NR, appointment of agent for service of process by non-resident general partner and non...

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... Form ADV-NR, see the List of CFR Sections Affected, which appears in the Finding Aids section of the... agent for service of process by non-resident general partner and non-resident managing agent of an... agent for service of process by non-resident general partner and non-resident managing agent of...

  14. 17 CFR 279.4 - Form ADV-NR, appointment of agent for service of process by non-resident general partner and non...

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... Form ADV-NR, see the List of CFR Sections Affected, which appears in the Finding Aids section of the... agent for service of process by non-resident general partner and non-resident managing agent of an... agent for service of process by non-resident general partner and non-resident managing agent of...

  15. 17 CFR 279.4 - Form ADV-NR, appointment of agent for service of process by non-resident general partner and non...

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... Form ADV-NR, see the List of CFR Sections Affected, which appears in the Finding Aids section of the... agent for service of process by non-resident general partner and non-resident managing agent of an... agent for service of process by non-resident general partner and non-resident managing agent of...

  16. Distorted colloidal arrays as designed template

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  17. Glass/Jamming Transition in Colloidal Aggregation

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  18. Colloid particle size-dependent dispersivity

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  19. ADV-based estimates of sediment settling velocity on the shelf of the Yellow and East China seas: evidence of marked seasonal and intra-tidal variations

    NASA Astrophysics Data System (ADS)

    Bian, Changwei; Mao, Xinyan; Jiang, Wensheng; Gu, Yanzhen

    2015-02-01

    Sediment settling velocity ( w s) patterns are well established at the Huanghe and Changjiang river mouths, but no w s results have been reported for the Yellow Sea and the East China Sea (YSECS) shelves due to the labor-intensive and time-consuming aspect of traditional w s measurement approaches (e.g., settling column method). This disadvantage can be overcome by the acoustic Doppler velocimeter (ADV). In this study, ten ADV-based field campaigns were conducted over various seasons of the years 2011 and 2013 at six YSECS sites, five on the East China Sea shelf (28 to 87 m depth) and one on the Yellow Sea shelf (74 m depth). The results demonstrate that ADV backscatter was a reliable proxy of suspended sediment concentration over a measurement range of 1 to 1,000 mg/L. The ADV-estimated w s was highest (1.43-1.88 mm/s) in summer in the southern East China Sea, and lowest (0.07 mm/s) in spring in the northern Yellow Sea. This can plausibly be explained by the hydrodynamic environment and bottom sediment type at the campaign sites. More importantly, the data reveal evidence of marked seasonal variations of w s in the middle sector of the East China Sea, as well as intra-tidal variations at all campaign sites. However, these variations of w s are not directly regulated by current velocity or suspended sediment concentration. This aspect represents a major challenge in future research in this shelf region and, for that matter, in similar settings worldwide. Evidently, expanding on the well-resolved continuous time series provided by the ADV approach is a key step in this direction.

  20. Micro- and Nanotechnologies for Optical Neural Interfaces

    PubMed Central

    Pisanello, Ferruccio; Sileo, Leonardo; De Vittorio, Massimo

    2016-01-01

    In last decade, the possibility to optically interface with the mammalian brain in vivo has allowed unprecedented investigation of functional connectivity of neural circuitry. Together with new genetic and molecular techniques to optically trigger and monitor neural activity, a new generation of optical neural interfaces is being developed, mainly thanks to the exploitation of both bottom-up and top-down nanofabrication approaches. This review highlights the role of nanotechnologies for optical neural interfaces, with particular emphasis on new devices and methodologies for optogenetic control of neural activity and unconventional methods for detection and triggering of action potentials using optically-active colloidal nanoparticles. PMID:27013939

  1. Contact line of adsorbed colloid-polymer droplets in theory and experiment.

    PubMed

    Koning, Jesper; Hennequin, Yves; Bonn, Daniel; Indekeu, Joseph O

    2016-05-01

    The contact line between the colloid-rich bulk liquid and an adsorbed thin film in colloid-polymer mixtures (CPM) is studied by means of an interface displacement model. The interface displacement profiles are compared to laser scanning confocal microscopy (LSCM) images. The mixtures consist of poly(methylmetacrylate) (PMMA) colloids and polystyrene (PS) polymers with polymer-to-colloid size ratio q = 1.18. Based on the experimental parameters, the theoretical model predicts a contact angle for colloid-rich liquid droplets adsorbed on glass of θ∞ = 59°, assuming a contact line with infinite radius, R = ∞. When a contact-line curvature correction and a correction for the protein-limit character of the CPM are taken into account, a modest shift is obtained. The refined theory predicts θ≈ 56°. The contact angle determined visually from the LSCM images is θ≈ 30°. The model predicts a three-phase contact-line tension of τ = -1.2 × 10(-12) N (uncorrected) and τ = -2.3 × 10(-13) N (with protein-limit correction), which is physically sound both in sign and magnitude. The line tension influences the contact angle to a small extent due to the contact line curvature. The predicted width of the transition zone between the thin film and the droplet is about 2 μm. The effect of gravity is noticeable as a deformation near the middle of the droplet. PMID:27029605

  2. Emulsification of partially miscible liquids using colloidal particles: nonspherical and extended domain structures.

    PubMed

    Clegg, Paul S; Herzig, Eva M; Schofield, Andrew B; Egelhaaf, Stefan U; Horozov, Tommy S; Binks, Bernard P; Cates, Michael E; Poon, Wilson C K

    2007-05-22

    We present microscopy studies of particle-stabilized emulsions with unconventional morphologies. The emulsions comprise pairs of partially miscible fluids and are stabilized by colloids. Alcohol-oil mixtures are employed; silica colloids are chemically modified so that they have partial wettability. We create our morphologies by two distinct routes: starting with a conventional colloid-stabilized emulsion or starting in the single-fluid phase with the colloids dispersed. In the first case temperature cycling leads to the creation of extended fluid domains built around some of the initial fluid droplets. In the second case quenching into the demixed region leads to the formation of domains which reflect the demixing kinetics. The structures are stable due to a jammed, semisolid, multilayer of colloids on the liquid-liquid interface. The differing morphologies reflect the roles in formation of the arrested state of heterogeneous and homogeneous nucleation and spinodal decomposition. The latter results in metastable, bicontinuous emulsions with frozen interfaces, at least for the thin-slab samples, investigated here. PMID:17439257

  3. Shells on lattice-mismatched colloidal spheres, cubes, and peanuts

    NASA Astrophysics Data System (ADS)

    Sindoro, Melinda; Granick, Steve

    2015-03-01

    Cavities form spontaneously due to geometrical frustration when crystalline shells is gradually grown on non-linear surfaces. This we conclude experimentally from growing lattice mismatched shells on colloidal spheres, cubes, and peanuts, all of them providing different local curvature. According to the core shape, the underlying interfacial curvature promotes different cavity formation which we can follow over time. The resulting spatio-temporal heterogeneity adds up to a propagation of an increasingly strong mechanical stress at the core-shell interface, inducing core-shells transformation to yolk-shells.

  4. Optically induced melting of colloidal crystals and their recrystallization.

    PubMed

    Harada, Masashi; Ishii, Masahiko; Nakamura, Hiroshi

    2007-04-15

    Colloidal crystals melt by applying focused light of optical tweezers and recrystallize after removing it. The disturbed zone by the light grows radially from the focus point and the ordering starts from the interface with the crystal. Although the larger disturbed zone is observed for the higher power optical tweezers, a master curve is extracted by normalization of the disturbed zone. The temporal changes of the normalized disturbed zone are well described with exponential functions, indicating that the melting and recrystallization process is governed by a simple relaxation mechanism. PMID:17049820

  5. Colloidal aspects of texture perception.

    PubMed

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

    2009-08-30

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

  6. Statistical Physics of Colloidal Dispersions.

    NASA Astrophysics Data System (ADS)

    Canessa, E.

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

  7. 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

  8. Preparatiion of metal colloids in inverse micelles

    SciTech Connect

    Wilcoxon, J.P.

    1990-11-23

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

  9. 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

  10. Mesoscale models of dispersions stabilized by surfactants and colloids.

    PubMed

    van der Sman, R G M; Meinders, M B J

    2014-09-01

    In this paper we discuss and give an outlook on numerical models describing dispersions, stabilized by surfactants and colloidal particles. Examples of these dispersions are foams and emulsions. In particular, we focus on the potential of the diffuse interface models based on a free energy approach, which describe dispersions with the surface-active agent soluble in one of the bulk phases. The free energy approach renders thermodynamic consistent models with realistic sorption isotherms and adsorption kinetics. The free energy approach is attractive because of its ability to describe highly complex dispersions, such as emulsions stabilized by ionic surfactants, or surfactant mixtures and dispersions with surfactant micelles. We have classified existing numerical methods into classes, using either a Eulerian or a Lagrangian representation for fluid and for the surfactant/colloid. A Eulerian representation gives a more coarse-grained, mean field description of the surface-active agent, while a Lagrangian representation can deal with steric effects and larger complexity concerning geometry and (amphiphilic) wetting properties of colloids and surfactants. However, the similarity between the description of wetting properties of both Eulerian and Lagrangian models allows for the development of hybrid Eulerian/Lagrangian models having advantages of both representations. PMID:24980050

  11. Predicting crystals of Janus colloids.

    PubMed

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

    2013-04-28

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

  12. Magnetic Assisted Colloidal Pattern Formation

    NASA Astrophysics Data System (ADS)

    Yang, Ye

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

  13. Superconductivity in colloidal lead nanocrystals

    NASA Astrophysics Data System (ADS)

    Zolotavin, Pavlo

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

  14. Linear viscoelasticity of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Cichocki, B.; Felderhof, B. U.

    1992-12-01

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

  15. Solid colloidal optical wavelength filter

    NASA Astrophysics Data System (ADS)

    Alvarez, J. L.

    1990-05-01

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

  16. 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.

  17. Colloidal assembly by ice templating.

    PubMed

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

    2016-04-12

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

  18. Colloidal thermoresponsive gel forming hybrids.

    PubMed

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

    2010-09-15

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

  19. 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

  20. Crystallization of DNA-coated colloids

    PubMed Central

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

    2015-01-01

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

  1. Crystallization of DNA-coated colloids.

    PubMed

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

    2015-01-01

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

  2. Binodal Colloidal Aggregation Test - 4: Polydispersion

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.

    2008-01-01

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

  3. Binary Colloidal Alloy Test Conducted on Mir

    NASA Technical Reports Server (NTRS)

    Hoffmann, Monica I.; Ansari, Rafat R.

    1999-01-01

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

  4. Microspheres: Microfluidic Generation of Monodisperse and Photoreconfigurable Microspheres for Floral Iridescence-Inspired Structural Colorization (Adv. Mater. 26/2016).

    PubMed

    Yeo, Seon Ju; Park, Kyung Jin; Guo, Kai; Yoo, Pil J; Lee, Seungwoo

    2016-07-01

    Flowering plants have advanced their colorization strategies to divide incoming white light into spatially sequenced vivid colors, especially by using 2D grating diffractive motifs. On page 5268, P. J. Yoo, S. Lee, and co-workers conceive a new idea for a microfluidic approach to mimic this wonderful biological strategy and its practical application to the color encoding of colloidal particles. PMID:27383025

  5. Relationship between the Averaged Deposition Rate Coefficients for Colloids in a Single Pore and Various Pore-scale Parameters

    NASA Astrophysics Data System (ADS)

    Narayanan, S.; Mohan Kumar, M.; Hassanizadeh, S. M.; Raoof, A.

    2014-12-01

    The colloid deposition behavior observed at the Darcy scale represents an average of the processes occurring at the pore scale. Hence, a better understanding of the processes occurring at the Darcy scale can be obtained by studying colloid transport at the pore-scale and then upscaling the results. In this study, we have developed a mathematical model to simulate the transport of colloids in a cylindrical pore by considering various processes such as advection, diffusion, colloid-soil surface interactions and hydrodynamic wall effects. The pore space is divided into three different regions, namely, the bulk, diffusion and potential regions, based on the dominant processes acting in each of these regions. In the bulk region, colloid transport is governed by advection and diffusion; whereas in the diffusion region, colloid mobility due to diffusion is retarded by hydrodynamic wall effects. Colloid-solid interaction forces dominate the transport in the potential region where colloid deposition occurs and are calculated using DLVO theory. The expressions for mass transfer rate coefficients between the diffusion and potential regions have been derived for different DLVO energy profiles. These are incorporated in the pore-scale equations in the form of a boundary condition at the diffusion-potential region interface. The model results are used to obtain the colloid breakthrough curve at the end of a long pore, and then it is fitted with 1D advection-dispersion-adsorption model so as to determine the averaged attachment and detachment rate coefficients at the scale of a single pore. A sensitivity analysis of the model to six pore-scale parameters (colloid and wall surface potentials, solution ionic strength, average pore-water velocity, colloid radius, and pore radius) is carried out so as to find the relation between the averaged deposition rate coefficients at pore scale vs the pore-scale parameters. We found an hyper exponential relation between the colloid attachment

  6. 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.

  7. Colloid Coalescence with Focused X Rays

    SciTech Connect

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

    2011-07-01

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

  8. Conductivity maximum in a charged colloidal suspension

    SciTech Connect

    Bastea, S

    2009-01-27

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

  9. 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.

  10. Nonequilibrium forces between dragged ultrasoft colloids.

    PubMed

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

    2011-10-01

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

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

    ERIC Educational Resources Information Center

    Ueno, Keihei; Kina, Ken'yu

    1985-01-01

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

  12. The role of ionic strength and grain size on the transport of colloids in unsaturated sand columns

    NASA Astrophysics Data System (ADS)

    Mitropoulou, Polyxeni N.; Syngouna, Vasiliki I.; Chrysikopoulos, Constantinos V.

    2013-04-01

    The main objective of this study was to better understand the combined effects of ionic strength, and sand grain size on colloid fate and transport in unsaturated porous media. Spherical fluorescent polymer microspheres with three different sizes (0.075, 0.30 and 2.1 μm), and laboratory columns packed with two size fractions of clean quartz sand (0.513 and 0.181 mm) were used. The saturation level of the packed columns was set to 83-95% with solutions having a wide range of ionic strength (0.1-1000 mM). The electrophoretic mobility of colloids and sand grains were evaluated for all the experimental conditions employed. The various experimental collision efficiencies were quantified using the classical colloid filtration theory. The theoretical collision efficiencies were estimated with appropriate DLVO energies using a Maxwell model. The experimental results suggested that the retention of the bigger colloids (2.1 μm) was slightly higher compared to the conservative tracer and smaller colloids (0.3 and 0.075 μm) in deionized-distilled-water, indicating sorption at air-water interfaces or straining. Moreover, relatively smaller attachment was observed onto fine than medium quartz sand. The mass recovery of the 0.3 μm microspheres in NaCl solution was shown to significantly decrease with increasing ionic strength. Both the experimental and theoretical collision efficiencies based on colloid interactions with solid-water interfaces, were increased with increasing ionic strength.

  13. Work Domain Analysis of a Predecessor Sodium-cooled Reactor as Baseline for AdvSMR Operational Concepts

    SciTech Connect

    Ronald Farris; David Gertman; Jacques Hugo

    2014-03-01

    This report presents the results of the Work Domain Analysis for the Experimental Breeder Reactor (EBR-II). This is part of the phase of the research designed to incorporate Cognitive Work Analysis in the development of a framework for the formalization of an Operational Concept (OpsCon) for Advanced Small Modular Reactors (AdvSMRs). For a new AdvSMR design, information obtained through Cognitive Work Analysis, combined with human performance criteria, can and should be used in during the operational phase of a plant to assess the crew performance aspects associated with identified AdvSMR operational concepts. The main objective of this phase was to develop an analytical and descriptive framework that will help systems and human factors engineers to understand the design and operational requirements of the emerging generation of small, advanced, multi-modular reactors. Using EBR-II as a predecessor to emerging sodium-cooled reactor designs required the application of a method suitable to the structured and systematic analysis of the plant to assist in identifying key features of the work associated with it and to clarify the operational and other constraints. The analysis included the identification and description of operating scenarios that were considered characteristic of this type of nuclear power plant. This is an invaluable aspect of Operational Concept development since it typically reveals aspects of future plant configurations that will have an impact on operations. These include, for example, the effect of core design, different coolants, reactor-to-power conversion unit ratios, modular plant layout, modular versus central control rooms, plant siting, and many more. Multi-modular plants in particular are expected to have a significant impact on overall OpsCon in general, and human performance in particular. To support unconventional modes of operation, the modern control room of a multi-module plant would typically require advanced HSIs that would

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  15. Transient colloidal stability controls the particle formation of SBA-15.

    PubMed

    Ruan, Juanfang; Kjellman, Tomas; Sakamoto, Yasuhiro; Alfredsson, Viveka

    2012-08-01

    A hypothesis about (transient) colloidal stability as a controlling mechanism for particle formation in SBA-15 is presented. The hypothesis is based on results from both in situ and ex situ investigations, including cryogenic transmission electron microscopy (cryo-TEM), UV-vis spectroscopy, and dynamic light scattering (DLS). Cryo-TEM images show that particles grow via the formation of silica-Pluronic-water "flocs", which coalesce in a seemingly arbitrary manner. Despite this, the final material consists of well-defined particles with a small size distribution. We argue that the interface between the flocs and surrounding media is covered by Pluronic molecules, which provide steric stabilization. As the flocs grow, the coverage of polymers at the interface is increased until a stable size is reached, and that regulates the particle size. By targeting the characteristics of the Pluronic molecules, during the on-going synthesis, the hypothesis is tested. The results are consistent with the concept of (transient) colloidal stability. PMID:22758927

  16. Transient Colloidal Stability Controls the Particle Formation of SBA-15

    PubMed Central

    2012-01-01

    A hypothesis about (transient) colloidal stability as a controlling mechanism for particle formation in SBA-15 is presented. The hypothesis is based on results from both in situ and ex situ investigations, including cryogenic transmission electron microscopy (cryo-TEM), UV–vis spectroscopy, and dynamic light scattering (DLS). Cryo-TEM images show that particles grow via the formation of silica–Pluronic–water “flocs”, which coalesce in a seemingly arbitrary manner. Despite this, the final material consists of well-defined particles with a small size distribution. We argue that the interface between the flocs and surrounding media is covered by Pluronic molecules, which provide steric stabilization. As the flocs grow, the coverage of polymers at the interface is increased until a stable size is reached, and that regulates the particle size. By targeting the characteristics of the Pluronic molecules, during the on-going synthesis, the hypothesis is tested. The results are consistent with the concept of (transient) colloidal stability. PMID:22758927

  17. Convection associated with exclusion zone formation in colloidal suspensions.

    PubMed

    Musa, Sami; Florea, Daniel; Wyss, Hans M; Huyghe, Jacques M

    2016-01-28

    The long-range repulsion of colloids from various interfaces has been observed in a wide range of studies from different research disciplines. This so-called exclusion zone (EZ) formation occurs near surfaces such as hydrogels, polymers, or biological tissues. It was recently shown that the underlying physical mechanism leading to this long-range repulsion is a combination of ion-exchange at the interface, diffusion of ions, and diffusiophoresis of colloids in the resulting ion concentration gradients. In this paper, we show that the same ion concentration gradients that lead to exclusion zone formation also imply that diffusioosmosis near the walls of the sample cell must occur. This should lead to convective flow patterns that are directly associated with exclusion zone formation. We use multi-particle tracking to study the dynamics of particles during exclusion zone formation in detail, confirming that indeed two pronounced vortex-like convection rolls occur near the cell walls. These dramatic flow patterns persist for more than 4 hours, with the typical velocity decreasing as a function of time. We find that the flow velocity depends strongly on the surface properties of the sample cell walls, consistent with diffusioosmosis being the main physical mechanism that governs these convective flows. PMID:26616213

  18. Influences of Flow Transients and Porous Medium Heterogeneity on Colloid-Associated Contaminants Transport in the Vadose Zone

    SciTech Connect

    Saiers, James E.; Ryan, Joseph

    2003-06-15

    During the past year (June 2003 to June 2004), work at Yale has centered on investigating the influences of porewater pH, flow transients, and the presence of natural organic matter (NOM) on the deposition and mobilization of clay colloids (kaolinite and illite) within columns packed with unsaturated porous media. The experiments on pH and flow-transient effects were described in our First-Term Progress Report (which covered the initial 18 months of the study) and will not be repeated here. More recent experiments on the role of NOM in colloid transport proved equally as interesting. Even at porewater concentrations as low as 0.2 mg/L, soil-humic acid substantially lowered clay-colloid deposition rates compared to the case in which soil-humic acid was absent from the porewater. We attribute this to adsorption of the humic acid to the positively charged edge sites of the clay colloids, which effectively reduced the colloid affinity for negatively charged air- and solid-water interfaces. Comparison of the results of the column experiments to calculations of a new mathematical model has sharpened our inferences regarding mechanisms that govern the rate-limited deposition and mobilization of colloids. We are testing these inferences by carrying out flow-and-transport visualization experiments. We have constructed a semi-transparent representation of a porous medium, consisting of a rectangular parallel-plate chamber that encloses 3-5 layers of uniformly sized sand grains. Ceramic plates fused to the ends of the chamber maintain the capillary tension and syringe pumps (located at the inlet and outlet ends) regulate the flow of water and colloids through the partially saturated sand. By placing the chamber beneath a microscope, we can examine the distribution of colloids between air-water and solid-water interfaces, directly measure the kinetics of deposition onto these interfaces, and observe the mechanisms that contribute to the release of immobile colloids. To date

  19. Analysis on laser plasma emission for characterization of colloids by video-based computer program

    NASA Astrophysics Data System (ADS)

    Putri, Kirana Yuniati; Lumbantoruan, Hendra Damos; Isnaeni

    2016-02-01

    Laser-induced breakdown detection (LIBD) is a sensitive technique for characterization of colloids with small size and low concentration. There are two types of detection, optical and acoustic. Optical LIBD employs CCD camera to capture the plasma emission and uses the information to quantify the colloids. This technique requires sophisticated technology which is often pricey. In order to build a simple, home-made LIBD system, a dedicated computer program based on MATLAB™ for analyzing laser plasma emission was developed. The analysis was conducted by counting the number of plasma emissions (breakdowns) during a certain period of time. Breakdown probability provided information on colloid size and concentration. Validation experiment showed that the computer program performed well on analyzing the plasma emissions. Optical LIBD has A graphical user interface (GUI) was also developed to make the program more user-friendly.

  20. Analysis of colloid and tracer breakthrough curves

    NASA Astrophysics Data System (ADS)

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

    1996-02-01

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

  1. Structural color from colloidal glasses

    NASA Astrophysics Data System (ADS)

    Magkiriadou, Sofia

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

  2. Highly uniform polyhedral colloids formed by colloidal crystal templating

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    PubMed

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

    2011-09-01

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

  4. Theoretical study of line and boundary tension in adsorbed colloid-polymer mixtures.

    PubMed

    Koning, Jesper; Vandecan, Yves; Indekeu, Joseph

    2014-07-28

    An extended theoretical study of interface potentials in adsorbed colloid-polymer mixtures is performed. To describe the colloid-polymer mixture near a hard wall, a simple Cahn-Nakanishi-Fisher free-energy functional is used. The bulk phase behaviour and the substrate-adsorbate interaction are modelled by the free-volume theory for ideal polymers with polymer-to-colloid size ratios q = 0.6 and q = 1. The interface potentials are constructed with help from a Fisher-Jin crossing constraint. By manipulating the crossing density, a complete interface potential can be obtained from natural, single-crossing, profiles. The line tension in the partial wetting regime and the boundary tension along prewetting are computed from the interface potentials. The line tensions are of either sign, and descending with increasing contact angle. The line tension takes a positive value of 10(-14)-10(-12) N near a first-order wetting transition, passes through zero and decreases to minus 10(-14)-10(-12) N away from the first-order transition. The calculations of the boundary tension along prewetting yield values increasing from zero at the prewetting critical point up to the value of the line tension at first-order wetting. PMID:25084953

  5. Theoretical study of line and boundary tension in adsorbed colloid-polymer mixtures

    NASA Astrophysics Data System (ADS)

    Koning, Jesper; Vandecan, Yves; Indekeu, Joseph

    2014-07-01

    An extended theoretical study of interface potentials in adsorbed colloid-polymer mixtures is performed. To describe the colloid-polymer mixture near a hard wall, a simple Cahn-Nakanishi-Fisher free-energy functional is used. The bulk phase behaviour and the substrate-adsorbate interaction are modelled by the free-volume theory for ideal polymers with polymer-to-colloid size ratios q = 0.6 and q = 1. The interface potentials are constructed with help from a Fisher-Jin crossing constraint. By manipulating the crossing density, a complete interface potential can be obtained from natural, single-crossing, profiles. The line tension in the partial wetting regime and the boundary tension along prewetting are computed from the interface potentials. The line tensions are of either sign, and descending with increasing contact angle. The line tension takes a positive value of 10-14-10-12 N near a first-order wetting transition, passes through zero and decreases to minus 10-14-10-12 N away from the first-order transition. The calculations of the boundary tension along prewetting yield values increasing from zero at the prewetting critical point up to the value of the line tension at first-order wetting.

  6. Colloid transport in dual-permeability media

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  7. Colloidal Electrolytes and the Critical Micelle Concentration

    ERIC Educational Resources Information Center

    Knowlton, L. G.

    1970-01-01

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

  8. Binary Colloidal Alloy Test-5: Aspheres

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.; Hollingsworth, Andrew D.

    2008-01-01

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

  9. Density-functional study of interfacial properties of colloid-polymer mixtures.

    PubMed

    Moncho-Jordá, A; Dzubiella, J; Hansen, J P; Louis, A A

    2005-04-14

    Interfacial properties of colloid-polymer mixtures are examined within an effective one-component representation, where the polymer degrees of freedom are traced out, leaving a fluid of colloidal particles interacting via polymer-induced depletion forces. Restriction is made to zero-, one-, and two-body effective potentials, and a free energy functional is used that treats colloid excluded volume correlations within Rosenfeld's fundamental measure theory, and depletion-induced attraction within first-order perturbation theory. This functional allows a consistent treatment of both ideal and interacting polymers. The theory is applied to surface properties near a hard wall, to the depletion interaction between two walls, and to the fluid-fluid interface of demixed colloid-polymer mixtures. The results of the present theory compare well with predictions of a fully two-component representation of mixtures of colloids and ideal polymers (the Asakura-Oosawa model) and allow a systematic investigation of the effects of polymer-polymer interactions on interfacial properties. In particular, the wall surface tension is found to be significantly larger for interacting than for ideal polymers, whereas the opposite trend is predicted for the fluid-fluid interfacial tension. PMID:16851746

  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. Stability of Ionic Colloidal Crystals (ICCs)

    NASA Astrophysics Data System (ADS)

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

    2003-03-01

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

  13. Shaping Colloids for Self-Assembly

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  14. Shaping colloids for self-assembly

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  15. Characterization of Colloidal Nanoparticles Released from Hg-bearing Mine Wastes

    NASA Astrophysics Data System (ADS)

    Shaw, S.; Lowery, G. V.; Kim, C.; Rytuba, J. J.; Brown, G. E.

    2001-12-01

    The release of mercury from mine waste tailings at historic mining sites in the California coastal ranges is a significant pollution threat to local water sources and fish populations. The transport of mercury associated with nanometer-scale (¯50-400 nm) colloidal particles is one of the major pathways for mercury release from these mine sites. This study has used laboratory column ex-periments to generate colloids from calcines and unprocessed waste rock from the New Idria (NI) and Sulphur Bank (SB) mines. Colloid generation was initiated by flowing two solutions of vary-ing ionic strength through the columns in the presence of malonic acid. The colloidal material generated was characterized by ATEM, Extend X-ray absorption fine structure (EXAFS) analysis, and chemical sequential extraction techniques. ATEM analysis indicates that the colloids generated from the NI calcines consist of crystalline alunite-jarosite and hematite, a poorly ordered Si-Al gel and HgS. This mixture is very similar to that present in the bulk calcine material and suggests that these colloids are formed by detach-ment/breakup of the bulk material. Hg-LIII-EXAFS and sequential extractions indicate that 90% of the mercury present in these colloids is in the HgS form. The column experiments on the SB calcines produced only a small amount of colloidal material when the first few pore volumes of solution were flowed through. These consist of quartz, poorly ordered Si-Al-Fe gel and HgS. Hg-LIII-EXAFS spectra confirms that HgS is the dominant mercury species in these colloids. Raising the pH of the colloid-free column effluent from the SB calcines experiment results in the precipita-tion of a poorly ordered Si-Al-Fe rich gel, which is similar to that observed at the waste pile/lake interface next to the SB mine (Clear lake, CA). EXAFS and ATEM results indicate that mercury can be associated with this precipitated colloidal material. Colloids generated using unprocessed waste rock from the SB

  16. Kinetically guided colloidal structure formation

    PubMed Central

    Hecht, Fabian M.; Bausch, Andreas R.

    2016-01-01

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

  17. Synthesis of substantially monodispersed colloids

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  18. Nonlinear rheology of colloidal dispersions.

    PubMed

    Brader, J M

    2010-09-15

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

  19. Cocklebur-shaped colloidal dispersions.

    PubMed

    Lestage, David J; Urban, Marek W

    2005-11-01

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

  20. Colloid-Associated Radionuclide Concentration Limits: ANL

    SciTech Connect

    C. Mertz

    2000-12-21

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

  1. Pickering emulsions stabilized by oppositely charged colloids: Stability and pattern formation

    NASA Astrophysics Data System (ADS)

    Christdoss Pushpam, Sam David; Basavaraj, Madivala G.; Mani, Ethayaraja

    2015-11-01

    A binary mixture of oppositely charged colloids can be used to stabilize water-in-oil or oil-in-water emulsions. A Monte Carlo simulation study to address the effect of charge ratio of colloids on the stability of Pickering emulsions is presented. The colloidal particles at the interface are modeled as aligned dipolar hard spheres, with attractive interaction between unlike-charged and repulsive interaction between like-charged particles. The optimum composition (fraction of positively charged particles) required for the stabilization corresponds to a minimum in the interaction energy per particle. In addition, for each charge ratio, there is a range of compositions where emulsions can be stabilized. The structural arrangement of particles or the pattern formation at the emulsion interface is strongly influenced by the charge ratio. We find well-mixed isotropic, square, and hexagonal arrangements of particles on the emulsion surface for different compositions at a given charge ratio. The distribution of coordination numbers is calculated to characterize structural features. The simulation study is useful for the rational design of Pickering emulsifications wherein oppositely charged colloids are used, and for the control of pattern formation that can be useful for the synthesis of colloidosomes and porous shells derived thereof.

  2. Exploiting imperfections in the bulk to direct assembly of surface colloids

    PubMed Central

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

    2013-01-01

    We exploit the long-ranged elastic fields inherent to confined nematic liquid crystals (LCs) to assemble colloidal particles trapped at the LC interface into reconfigurable structures with complex symmetries and packings. Spherical colloids with homeotropic anchoring trapped at the interface between air and the nematic LC 4-cyano-4′-pentylbiphenyl create quadrupolar distortions in the director field causing particles to repel and consequently form close-packed assemblies with a triangular habit. Here, we report on complex open structures organized via interactions with defects in the bulk. Specifically, by confining the nematic LC in an array of microposts with homeotropic anchoring conditions, we cause defect rings to form at well-defined locations in the bulk of the sample. These defects source elastic deformations that direct the assembly of the interfacially trapped colloids into ring-like assemblies, which recapitulate the defect geometry even when the microposts are completely immersed in the nematic. When the surface density of the colloids is high, they form a ring near the defect and a hexagonal lattice far from it. Because topographically complex substrates are easily fabricated and LC defects are readily reconfigured, this work lays the foundation for a versatile, robust mechanism to direct assembly dynamically over large areas by controlling surface anchoring and associated bulk defect structure. PMID:24191037

  3. Recent Advances in Colloidal and Interfacial Phenomena Involving Liquid Crystals

    PubMed Central

    Bai, Yiqun; Abbott, Nicholas L.

    2011-01-01

    This article describes recent advances in several areas of research involving the interfacial ordering of liquid crystals (LCs). The first advance revolves around the ordering of LCs at bio/chemically functionalized surfaces. Whereas the majority of past studies of surface-induced ordering of LCs have involved surfaces of solids that present a limited diversity of chemical functional groups (surfaces at which van der Waals forces dominate surface-induced ordering), recent studies have moved to investigate the ordering of LCs on chemically complex surfaces. For example, surfaces decorated with biomolecules (e.g. oligopeptides and proteins) and transition metal ions have been investigated, leading to an understanding of the roles that metal-ligand coordination interactions, electrical double-layers, acid-base interactions, and hydrogen bonding can have on the interfacial ordering of LCs. The opportunity to create chemically-responsive LCs capable of undergoing ordering transitions in the presence of targeted molecular events (e.g., ligand exchange around a metal center) has emerged from these fundamental studies. A second advance has focused on investigations of the ordering of LCs at interfaces with immiscible isotropic fluids, particularly water. In contrast to prior studies of surface-induced ordering of LCs on solid surfaces, LC- aqueous interfaces are deformable and molecules at these interfaces exhibit high levels of mobility and thus can reorganize in response to changes in interfacial environment. A range of fundamental investigations involving these LC-aqueous interfaces have revealed that (i) the spatial and temporal characteristics of assemblies formed from biomolecular interactions can be reported by surface-driven ordering transitions in the LCs, (ii) the interfacial phase behaviour of molecules and colloids can be coupled to (and manipulated via) the ordering (and nematic elasticity) of LCs, and (iii) confinement of LCs leads to unanticipated size

  4. Plutonium and Cesium Colloid Mediated Transport

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    SciTech Connect

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

    2013-05-11

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

  6. MODFLOW-2000 : the U.S. Geological Survey modular ground-water model--documentation of the Advective-Transport Observation (ADV2) Package

    USGS Publications Warehouse

    Anderman, Evan R.; Hill, Mary Catherine

    2001-01-01

    Observations of the advective component of contaminant transport in steady-state flow fields can provide important information for the calibration of ground-water flow models. This report documents the Advective-Transport Observation (ADV2) Package, version 2, which allows advective-transport observations to be used in the three-dimensional ground-water flow parameter-estimation model MODFLOW-2000. The ADV2 Package is compatible with some of the features in the Layer-Property Flow and Hydrogeologic-Unit Flow Packages, but is not compatible with the Block-Centered Flow or Generalized Finite-Difference Packages. The particle-tracking routine used in the ADV2 Package duplicates the semi-analytical method of MODPATH, as shown in a sample problem. Particles can be tracked in a forward or backward direction, and effects such as retardation can be simulated through manipulation of the effective-porosity value used to calculate velocity. Particles can be discharged at cells that are considered to be weak sinks, in which the sink applied does not capture all the water flowing into the cell, using one of two criteria: (1) if there is any outflow to a boundary condition such as a well or surface-water feature, or (2) if the outflow exceeds a user specified fraction of the cell budget. Although effective porosity could be included as a parameter in the regression, this capability is not included in this package. The weighted sum-of-squares objective function, which is minimized in the Parameter-Estimation Process, was augmented to include the square of the weighted x-, y-, and z-components of the differences between the simulated and observed advective-front locations at defined times, thereby including the direction of travel as well as the overall travel distance in the calibration process. The sensitivities of the particle movement to the parameters needed to minimize the objective function are calculated for any particle location using the exact sensitivity

  7. Colloidal membranes: The rich confluence of geometry and liquid crystals

    NASA Astrophysics Data System (ADS)

    Kaplan, Cihan Nadir

    A simple and experimentally realizable model system of chiral symmetry breaking is liquid-crystalline monolayers of aligned, identical hard rods. In these materials, tuning the chirality at the molecular level affects the geometry at systems level, thereby inducing a myriad of morphological transitions. This thesis presents theoretical studies motivated by the rich phenomenology of these colloidal monolayers. High molecular chirality leads to assemblages of rods exhibiting macroscopic handedness. In the first part we consider one such geometry, twisted ribbons, which are minimal surfaces to a double helix. By employing a theoretical approach that combines liquid-crystalline order with the preferred shape, we focus on the phase transition from simple flat monolayers to these twisted structures. In these monolayers, regions of broken chiral symmetry nucleate at the interfaces, as in a chiral smectic A sample. The second part particularly focuses on the detailed structure and thermodynamic stability of two types of observed interfaces, the monolayer edge and domain walls in simple flat monolayers. Both the edge and "twist-walls" are quasi-one-dimensional bands of molecular twist deformations dictated by local chiral interactions and surface energy considerations. We develop a unified theory of these interfaces by utilizing the de Gennes framework accompanied by appropriate surface energy terms. The last part turns to colloidal "cookies", which form in mixtures of rods with opposite handedness. These elegant structures are essentially flat monolayers surrounded by an array of local, three dimensional cusp defects. We reveal the thermodynamic and structural characteristics of cookies. Furthermore, cookies provide us with a simple relation to determine the intrinsic curvature modulus of our model system, an important constant associated with topological properties of membranes. Our results may have impacts on a broader class of soft thin films.

  8. 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.

  9. The immobilization of hepatocytes on 24 nm-sized gold colloid for enhanced hepatocytes proliferation.

    PubMed

    Gu, Hai-Ying; Chen, Zhong; Sa, Rong-Xiao; Yuan, Su-Su; Chen, Hong-Yuan; Ding, Yi-Tao; Yu, Ai-Min

    2004-08-01

    Bioartificial liver and hepatocyte transplantation is anticipated to supply a temporary metabolic support for candidates of liver transplantation or for patients with fulminant liver failure. An essential restriction of this form is the inability to acquire an enough amount of hepatocytes. Enhancement of the proliferation and differentiated function of hepatocytes is becoming a pursued target. Here, porcine hepatocytes were successfully immobilized on nano-sized gold colloid particles to construct a "hepatocyte/gold colloid" interface at which hepatocytes can be quickly proliferated. The properties of this resulting interface were characterized and confirmed by scanning electron microscopy and atomic force microscopy. The proliferative mechanism of hepatocytes was also discussed. The proliferated hepatocytes could be applied to the clinic based on their excellent functions for the synthesis of protein, glucose and urea as well as lower lactate dehydrogenase release. PMID:15020118

  10. 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.

  11. Quantification of hydrophobic interaction affinity of colloids

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1997-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  14. Transport of colloidal silica in unsaturated sand: Effect of charging properties of sand and silica particles.

    PubMed

    Fujita, Yosuke; Kobayashi, Motoyoshi

    2016-07-01

    We have studied the transport of colloidal silica in various degrees of a water-saturated Toyoura sand column, because silica particles are widely used as catalyst carriers and abrasive agents, and their toxicity is reported recently. Since water-silica, water-sand, and air-water interfaces have pH-dependent negative charges, the magnitude of surface charge was controlled by changing the solution pH. The results show that, at high pH conditions (pH 7.4), the deposition of colloidal silica to the sand surface is interrupted and the silica concentration at the column outlet immediately reaches the input concentration in saturated conditions. In addition, the relative concentration of silica at the column outlet only slightly decreases to 0.9 with decreasing degrees of water saturation to 38%, because silica particles are trapped in straining regions in the soil pore and air-water interface. On the other hand, at pH 5 conditions (low pH), where sand and colloid have less charge, reduced repulsive forces result in colloidal silica attaching onto the sand in saturated conditions. The deposition amount of silica particles remarkably increases with decreasing degrees of water saturation to 37%, which is explained by more particles being retained in the sand column associated with the air-water interface. In conclusion, at higher pH, the mobility of silica particles is high, and the air-water interface is inactive for the deposition of silica. On the other hand, at low pH, the deposition amount increases with decreasing water saturation, and the particle transport is inhibited. PMID:27045635

  15. Colloidal Synthesis of Gold Semishells

    PubMed Central

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

    2012-01-01

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

  16. Colloidal QDs-polymer nanocomposites

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  17. Three-dimensional ultrasonic colloidal crystals

    NASA Astrophysics Data System (ADS)

    Caleap, Mihai; Drinkwater, Bruce W.

    2016-05-01

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

  18. 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

  19. A colloidal quantum dot spectrometer

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

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

  20. Straining soft colloids in aqueous nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Mushenheim, Peter C.; Pendery, Joel S.; Weibel, Douglas B.; Spagnolie, Saverio E.; Abbott, Nicholas L.

    2016-05-01

    Liquid crystals (LCs), because of their long-range molecular ordering, are anisotropic, elastic fluids. Herein, we report that elastic stresses imparted by nematic LCs can dynamically shape soft colloids and tune their physical properties. Specifically, we use giant unilamellar vesicles (GUVs) as soft colloids and explore the interplay of mechanical strain when the GUVs are confined within aqueous chromonic LC phases. Accompanying thermal quenching from isotropic to LC phases, we observe the elasticity of the LC phases to transform initially spherical GUVs (diameters of 2–50 µm) into two distinct populations of GUVs with spindle-like shapes and aspect ratios as large as 10. Large GUVs are strained to a small extent (R/r < 1.54, where R and r are the major and minor radii, respectively), consistent with an LC elasticity-induced expansion of lipid membrane surface area of up to 3% and conservation of the internal GUV volume. Small GUVs, in contrast, form highly elongated spindles (1.54 < R/r < 10) that arise from an efflux of LCs from the GUVs during the shape transformation, consistent with LC-induced straining of the membrane leading to transient membrane pore formation. A thermodynamic analysis of both populations of GUVs reveals that the final shapes adopted by these soft colloids are dominated by a competition between the LC elasticity and an energy (˜0.01 mN/m) associated with the GUV–LC interface. Overall, these results provide insight into the coupling of strain in soft materials and suggest previously unidentified designs of LC-based responsive and reconfigurable materials.

  1. Straining soft colloids in aqueous nematic liquid crystals.

    PubMed

    Mushenheim, Peter C; Pendery, Joel S; Weibel, Douglas B; Spagnolie, Saverio E; Abbott, Nicholas L

    2016-05-17

    Liquid crystals (LCs), because of their long-range molecular ordering, are anisotropic, elastic fluids. Herein, we report that elastic stresses imparted by nematic LCs can dynamically shape soft colloids and tune their physical properties. Specifically, we use giant unilamellar vesicles (GUVs) as soft colloids and explore the interplay of mechanical strain when the GUVs are confined within aqueous chromonic LC phases. Accompanying thermal quenching from isotropic to LC phases, we observe the elasticity of the LC phases to transform initially spherical GUVs (diameters of 2-50 µm) into two distinct populations of GUVs with spindle-like shapes and aspect ratios as large as 10. Large GUVs are strained to a small extent (R/r < 1.54, where R and r are the major and minor radii, respectively), consistent with an LC elasticity-induced expansion of lipid membrane surface area of up to 3% and conservation of the internal GUV volume. Small GUVs, in contrast, form highly elongated spindles (1.54 < R/r < 10) that arise from an efflux of LCs from the GUVs during the shape transformation, consistent with LC-induced straining of the membrane leading to transient membrane pore formation. A thermodynamic analysis of both populations of GUVs reveals that the final shapes adopted by these soft colloids are dominated by a competition between the LC elasticity and an energy (∼0.01 mN/m) associated with the GUV-LC interface. Overall, these results provide insight into the coupling of strain in soft materials and suggest previously unidentified designs of LC-based responsive and reconfigurable materials. PMID:27140607

  2. Stability and interactions of nanocolloids at fluid interfaces: effects of capillary waves and line tensions

    NASA Astrophysics Data System (ADS)

    Lehle, H.; Oettel, M.

    2008-10-01

    We analyze the effective potential for nanoparticles trapped at a fluid interface within a simple model which incorporates surface and line tensions as well as a thermal average over interface fluctuations (capillary waves). For a single colloid, a reduced steepness of the potential well hindering movements out of the interface plane compared to rigid interface models is observed, and an instability of the capillary wave partition sum in the case of negative line tensions is pointed out. For two colloids, averaging over the capillary waves leads to an effective Casimir-type interaction which is long ranged, power-like in the inverse distance, but whose power sensitively depends on possible restrictions of the colloid degrees of freedom. A nonzero line tension leads to changes in the magnitude but not in the functional form of the effective potential asymptotics.

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

    SciTech Connect

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

    2006-05-31

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

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

    PubMed

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

    2011-10-27

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

  5. Theoretical study of the three-phase contact line and its tension in adsorbed colloid-polymer mixtures.

    PubMed

    Vandecan, Yves; Indekeu, Joseph O

    2008-03-14

    We perform a theoretical study of the three-phase contact line and the line tension in an adsorbed colloid-polymer mixture near a first-order wetting transition, employing an interface displacement model. We use a simple free-energy functional to describe a colloid-polymer mixture near a hard wall. The bulk phase behavior and the substrate-adsorbate interaction are modeled by the free-volume theory for ideal polymers. The large size of the colloidal particles and the suppression of the van der Waals interaction by optical matching of colloid and solvent justify the planar hard wall model for the substrate. Following the Fisher-Jin scheme, we derive from the free-energy functional an interface potential V(l) for these mixtures. For a particle diameter of 10-100 nm, the calculations indicate a line tension tau approximately 10(-12)-10(-13) N at room temperature. In view of the ultralow interfacial tension in colloid-polymer mixtures, gamma approximately 10(-7) Nm, this leads to a rather large characteristic length scale taugamma in the micrometer range for the three-phase contact zone width. In contrast with molecular fluids, this zone could be studied directly with optical techniques such as confocal scanning laser microscopy. PMID:18345923

  6. 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

  7. Universal Scaling of Correlated Diffusion in Colloidal Monolayers

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Li, Na; Bohinc, Klemen; Tong, Penger; Chen, Wei

    2013-10-01

    Using the techniques of optical microscopy and particle tracking, we measure the correlated diffusion in a monolayer of uniform silica spheres dispersed at a water-air interface. It is found that the correlated motion of the interfacial particles can be well described by two universal response functions, the normalized longitudinal and transverse diffusion coefficients D˜∥(r/r0) and D˜⊥(r/r0), where r is the interparticle distance and r0=a(λS/a)3/2 is a new scaling length, which depends on both the Saffman length λS and particle radius a. The obtained response functions characterize the crossover behavior of the colloidal monolayers from the subphase-dominated three-dimensional hydrodynamics at low surface coverage to the monolayer-dominated 2D hydrodynamics at high concentrations. The surface viscosity ηs(2) of the colloidal monolayer obtained by two-particle rheology compares well with the one-particle measurements.

  8. Charged colloids and polyelectrolytes: from statics to electrokinetics

    NASA Astrophysics Data System (ADS)

    Löwen, H.; Esztermann, A.; Wysocki, A.; Allahyarov, E.; Messina, R.; Jusufi, A.; Hoffmann, N.; Gottwald, D.; Kahl, G.; Konieczny, M.; Likos, C. N.

    2005-01-01

    A review is given on recent studies of charged colloidal suspensions and polyelectrolytes both in static and non-equilibrium situations. As far as static equilibrium situations are concerned, we discuss three different problems: 1) Sedimentation density profiles in charged suspensions are shown to exhibit a stretched non-bariometric wing at large heights and binary suspensions under gravity can exhibit an analog of the brazil-nut effect known from granular matter, i.e. the heavier particles settle on top of the lighter ones. 2) Soft polyelectrolyte systems like polyelectrolyte stars and microgels show an ultra-soft effective interaction and this results into an unusual equilibrium phase diagram including reentrant melting transitions and stable open crystalline lattices. 3) The freezing transition in bilayers of confined charged suspensions is discussed and a reentrant behaviour is obtained. As far as nonequilibrium problems are concerned, we discuss an interface instability in oppositely driven colloidal mixtures and discuss possible approaches to simulate electrokinetic effects in charged suspensions.

  9. Long range transport of colloids in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Florea, Daniel; Musa, Sami; Huyghe, Jacques M. R. J.; Wyss, Hans M.

    2013-03-01

    Colloids in aqueous suspensions can experience strong, extremely long range repulsive forces near interfaces such as biological tissues, gels, ion exchange resins or metals. As a result exclusion zones extending over several millimeters can be formed. While this phenomenon has been previously described, a physical understanding of this process is still lacking. This exclusion zone formation is puzzling because the typical forces acting on colloidal particles are limited to much shorter distances and external fields that could drive the particles are absent. Here we study the exclusion zone formation in detail by following the time and distance-dependent forces acting on the particles. We present a simple model that accounts for our experimental data and directly links the exclusion zone formation to an already known physical transport phenomenon. We show that the effect can be tuned by changing the zeta potential of the particles or by varying the species present in the aqueous solution. We thus provide a direct physical explanation for the intriguing exclusion zone formation and we illustrate how this effect can be exploited in a range of industrial applications.

  10. Colloidal suspension simulates linear dynamic pressure profile

    NASA Technical Reports Server (NTRS)

    Mc Cann, R. J.

    1966-01-01

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

  11. Mesoscopic modelling of colloids in chiral nematics.

    PubMed

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

    2010-01-01

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

  12. Polydispersity effects in colloid-polymer mixtures.

    PubMed

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

    2011-05-18

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

  13. Ultrasonically assisted deposition of colloidal crystals

    SciTech Connect

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

    2014-07-21

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

  14. A Course in Colloid and Surface Science.

    ERIC Educational Resources Information Center

    Scamehorn, John F.

    1984-01-01

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

  15. Dynamical Threshold of Diluteness of Soft Colloids

    SciTech Connect

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

    2014-01-01

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

  16. Colloidal gold: a pluripotent receptor probe.

    PubMed

    Handley, D A; Chien, S

    1983-10-01

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

  17. Self-similarity in active colloid motion

    NASA Astrophysics Data System (ADS)

    Constant, Colin; Sukhov, Sergey; Dogariu, Aristide

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

  18. Sulfonated nanoporous colloidal films and membranes

    NASA Astrophysics Data System (ADS)

    Smith, Joanna Jane

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

  19. Colloids generation from metallic uranium fuel

    SciTech Connect

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

    2000-07-20

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

  20. Sterically stabilized colloids with tunable repulsions.

    PubMed

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

    2013-09-10

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

  1. Self-replication with magnetic dipolar colloids

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  2. Self-replication with magnetic dipolar colloids.

    PubMed

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

    2015-10-01

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

  3. Linked topological colloids in a nematic host.

    PubMed

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

    2015-04-14

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

  4. Colloidal diffusion over a periodic energy landscape

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  5. 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.

  6. Linked topological colloids in a nematic host

    PubMed Central

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

    2015-01-01

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

  7. Tunable Time-Dependent Colloidal Interactions

    NASA Astrophysics Data System (ADS)

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

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

  8. Compact Video Microscope Imaging System Implemented in Colloid Studies

    NASA Technical Reports Server (NTRS)

    McDowell, Mark

    2002-01-01

    Long description Photographs showing fiber-optic light source, microscope and charge-coupled discharge (CCD) camera head connected to camera body, CCD camera body feeding data to image acquisition board in PC, and Cartesian robot controlled via PC board. The Compact Microscope Imaging System (CMIS) is a diagnostic tool with intelligent controls for use in space, industrial, medical, and security applications. CMIS can be used in situ with a minimum amount of user intervention. This system can scan, find areas of interest in, focus on, and acquire images automatically. Many multiple-cell experiments require microscopy for in situ observations; this is feasible only with compact microscope systems. CMIS is a miniature machine vision system that combines intelligent image processing with remote control. The software also has a user-friendly interface, which can be used independently of the hardware for further post-experiment analysis. CMIS has been successfully developed in the SML Laboratory at the NASA Glenn Research Center and adapted for use for colloid studies and is available for telescience experiments. The main innovations this year are an improved interface, optimized algorithms, and the ability to control conventional full-sized microscopes in addition to compact microscopes. The CMIS software-hardware interface is being integrated into our SML Analysis package, which will be a robust general-purpose image-processing package that can handle over 100 space and industrial applications.

  9. Floating nematic phase in colloidal platelet-sphere mixtures.

    PubMed

    de las Heras, Daniel; Doshi, Nisha; Cosgrove, Terence; Phipps, Jonathan; Gittins, David I; van Duijneveldt, Jeroen S; Schmidt, Matthias

    2012-01-01

    The phase behaviour of colloidal dispersions is interesting for fundamental reasons and for technological applications such as photonic crystals and electronic paper. Sedimentation, which in everyday life is relevant from blood analysis to the shelf life of paint, is a means to determine phase boundaries by observing distinct layers in samples that are in sedimentation-diffusion equilibrium. However, disentangling the effects due to interparticle interactions, which generate the bulk phase diagram, from those due to gravity is a complex task. Here we show that a line in the space of chemical potentials µ(i), where i labels the species, represents a sedimented sample and that each crossing of this sedimentation path with a binodal generates an interface under gravity. Complex phase stacks can result, such as the sandwich of a floating nematic layer between top and bottom isotropic phases that we observed in a mixture of silica spheres and gibbsite platelets. PMID:23145313

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

    SciTech Connect

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

    1997-07-01

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

  11. Colloidal-sized metal-organic frameworks: synthesis and applications.

    PubMed

    Sindoro, Melinda; Yanai, Nobuhiro; Jee, Ah-Young; Granick, Steve

    2014-02-18

    Colloidal metal-organic frameworks (CMOFs), nanoporous colloidal-sized crystals that are uniform in both size and polyhedral shape, are crystals composed of metal ions and organic bridging ligands, which can be used as building blocks for self-assembly in organic and aqueous liquids. They stand in contrast to conventional metal-organic frameworks (MOFs), which scientists normally study in the form of bulk crystalline powders. However, powder MOFs generally have random crystal size and shape and therefore do not possess either a definite mutual arrangement with adjacent particles or uniformity. CMOFs do have this quality, which can be important in vital uptake and release kinetics. In this Account, we present the diverse methods of synthesis, pore chemistry control, surface modification, and assembly techniques of CMOFs. In addition, we survey recent achievements and future applications in this emerging field. There is potential for a paradigm shift, away from using just bulk crystalline powders, towards using particles whose size and shape are regulated. The concept of colloidal MOFs takes into account that nanoporous MOFs, conventionally prepared in the form of bulk crystalline powders with random crystal size, shape, and orientation, may also form colloidal-sized objects with uniform size and morphology. Furthermore, the traditional MOF functions that depend on porosity present additional control over those MOF functions that depend on pore interactions. They also can enable controlled spatial arrangements between neighboring particles. To begin, we discuss progress regarding synthesis of MOF nano- and microcrystals whose crystal size and shape are well regulated. Next, we review the methods to modify the surfaces with dye molecules and polymers. Dyes are useful when seeking to observe nonluminescent CMOFs in situ by optical microscopy, while polymers are useful to tune their interparticle interactions. Third, we discuss criteria to assess the stability of CMOFs

  12. Magnetic nanostructures by colloidal lithography

    NASA Astrophysics Data System (ADS)

    Zhu, Frank Qing

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

  13. Dipolar capillary interactions between tilted ellipsoidal particles adsorbed at fluid-fluid interfaces.

    PubMed

    Davies, Gary B; Botto, Lorenzo

    2015-10-28

    Capillary interactions have emerged as a tool for the directed assembly of particles adsorbed at fluid-fluid interfaces, and play a role in controlling the mechanical properties of emulsions and foams. In this paper, following Davies et al. [Adv. Mater., 2014, 26, 6715] investigation into the assembly of ellipsoidal particles at interfaces interacting via dipolar capillary interactions, we numerically investigate the interaction between tilted ellipsoidal particles adsorbed at a fluid-fluid interface as their aspect ratio, tilt angle, bond angle, and separation vary. High-resolution Surface Evolver simulations of ellipsoidal particle pairs in contact reveal an energy barrier between a metastable tip-tip configuration and a stable side-side configuration. The side-side configuration is the global energy minimum for all parameters we investigated. Lattice Boltzmann simulations of clusters of up to 12 ellipsoidal particles show novel highly symmetric flower-like and ring-like arrangements. PMID:26323324

  14. Statistical thermodynamics of charge-stabilized colloids

    NASA Astrophysics Data System (ADS)

    Torres Valderrama, A.

    2008-06-01

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

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

    NASA Technical Reports Server (NTRS)

    Hoffmann, Monica T.

    2000-01-01

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

  16. Colloids in the River Inn

    NASA Astrophysics Data System (ADS)

    Ueckert, Martina; Baumann, Thomas

    2014-05-01

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

  17. Colloidal Bandpass and Bandgap Filters

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  18. Direct numerical simulations of agglomeration of circular colloidal particles in two-dimensional shear flow

    NASA Astrophysics Data System (ADS)

    Choi, Young Joon; Djilali, Ned

    2016-01-01

    Colloidal agglomeration of nanoparticles in shear flow is investigated by solving the fluid-particle and particle-particle interactions in a 2D system. We use an extended finite element method in which the dynamics of the particles is solved in a fully coupled manner with the flow, allowing an accurate description of the fluid-particle interfaces without the need of boundary-fitted meshes or of empirical correlations to account for the hydrodynamic interactions between the particles. Adaptive local mesh refinement using a grid deformation method is incorporated with the fluid-structure interaction algorithm, and the particle-particle interaction at the microscopic level is modeled using the Lennard-Jones potential. Motivated by the process used in fabricating fuel cell catalysts from a colloidal ink, the model is applied to investigate agglomeration of colloidal particles under external shear flow in a sliding bi-periodic Lees-Edwards frame with varying shear rates and particle fraction ratios. Both external shear and particle fraction are found to have a crucial impact on the structure formation of colloidal particles in a suspension. Segregation intensity and graph theory are used to analyze the underlying agglomeration patterns and structures, and three agglomeration regimes are identified.

  19. Assembling nanoparticle coatings to improve the drug delivery performance of lipid based colloids

    NASA Astrophysics Data System (ADS)

    Simovic, Spomenka; Barnes, Timothy J.; Tan, Angel; Prestidge, Clive A.

    2012-02-01

    Lipid based colloids (e.g. emulsions and liposomes) are widely used as drug delivery systems, but often suffer from physical instabilities and non-ideal drug encapsulation and delivery performance. We review the application of engineered nanoparticle layers at the interface of lipid colloids to improve their performance as drug delivery systems. In addition we focus on the creation of novel hybrid nanomaterials from nanoparticle-lipid colloid assemblies and their drug delivery applications. Specifically, nanoparticle layers can be engineered to enhance the physical stability of submicron lipid emulsions and liposomes, satbilise encapsulated active ingredients against chemical degradation, control molecular transport and improve the dermal and oral delivery characteristics, i.e. increase absorption, bioavailability and facilitate targeted delivery. It is feasible that hybrid nanomaterials composed of nanoparticles and colloidal lipids are effective encapsulation and delivery systems for both poorly soluble drugs and biological drugs and may form the basis for the next generation of medicines. Additional pre-clinical research including specific animal model studies are required to advance the peptide/protein delivery systems, whereas the silica lipid hybrid systems have now entered human clinical trials for poorly soluble drugs.

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

    SciTech Connect

    Roberts, Peter M; Abdel-fattah, Amr I

    2008-01-01

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

  1. Modeling colloid transport for performance assessment.

    PubMed

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

    2001-02-01

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

  2. Ceramic Interfaces

    SciTech Connect

    Yet-Ming Chiang

    2004-10-28

    During the period of this grant, we significantly advanced the understanding of stable surface amorphous films (SAFs), the existence of which was first postulated and then demonstrated under this program. SAFs are nanometer-thick amorphous films which are characterized by a self-selecting thickness, and a composition and structure distinct from the bulk phases with which they coexist. Importantly, they are present as an equilibrium, disordered phase below bulk solidus temperatures where all other phases in the system are crystalline. They are true surface phases which coexist in thermodynamic equilibrium with the bulk phases. We have shown that SAFs form in a number of binary oxide systems, and that they play an important role in the processing of materials (e.g., solid-state activated sintering in ZnO-Bi2O3) and in forming surface-active layers in supported catalyst systems. These experimental results as well as a theoretical model for the stability of SAFs have now been published. We believe that SAFs can be controlled and manipulated in a wide range of systems, with potential applications in nanotechnology, MEMS, microelectronics, adhesion, and colloidal crystals.

  3. Liquid crystals and their interactions with colloidal particles and phospholipid membranes: Molecular simulation studies

    NASA Astrophysics Data System (ADS)

    Kim, Evelina B.

    Experimentally, liquid crystals (LC) can be used as the basis for optical biomolecular sensors that rely on LC ordering. Recently, the use of LC as a reporting medium has been extended to investigations of molecular scale processes at lipid laden aqueous-LC interfaces and at biological cell membranes. In this thesis, we present two related studies where liquid crystals are modelled at different length scales. We examine (a) the behavior of nanoscopic colloidal particles in LC systems, using Monte Carlo (MC) molecular simulations and a mesoscopic dynamic field theory (DyFT); and (b) specific interactions of two types of mesogens with a model phospholipid bilayer, using atomistic molecular dynamics (MD) at the A-nm scale. In (a), we consider colloidal particles suspended in a LC, confined between two walls. We calculate the colloid-substrate and colloid-colloid potentials of mean force (PMF). For the MC simulations, we developed a new technique (ExEDOS or Expanded Ensemble Density Of States) that ensures good sampling of phase space without prior knowledge of the energy landscape of the system. Both results, simulation and DyFT, indicate a repulsive force acting between a colloid and a wall. In contrast, both techniques indicate an overall colloid-colloid attraction and predict a new topology of the disclination lines that arises when the particles approach each other. In (b), we find that mesogens (pentylcyanobiphenyl [5CB] or difluorophenyl-pentylbicyclohexyl [5CF]) preferentially partition from the aqueous phase into a dipalmitoylphosphatidylcholine (DPPC) bilayer. We find highly favorable free energy differences for partitioning (-18kBT for 5CB, -26k BT for 5CF). We also simulated fully hydrated bilayers with embedded 5CB or 5CF at concentrations used in recent experiments (6 mol% and 20 mol%). The presence of mesogens in the bilayer enhances the order of lipid acyl tails and changes the spatial and orientational arrangement of lipid headgroup atoms. A stronger

  4. Capillary migration of microdisks on curved interfaces.

    PubMed

    Yao, Lu; Sharifi-Mood, Nima; Liu, Iris B; Stebe, Kathleen J

    2015-07-01

    The capillary energy landscape for particles on curved fluid interfaces is strongly influenced by the particle wetting conditions. Contact line pinning has now been widely reported for colloidal particles, but its implications in capillary interactions have not been addressed. Here, we present experiment and analysis for disks with pinned contact lines on curved fluid interfaces. In experiment, we study microdisk migration on a host interface with zero mean curvature; the microdisks have contact lines pinned at their sharp edges and are sufficiently small that gravitational effects are negligible. The disks migrate away from planar regions toward regions of steep curvature with capillary energies inferred from the dissipation along particle trajectories which are linear in the deviatoric curvature. We derive the curvature capillary energy for an interface with arbitrary curvature, and discuss each contribution to the expression. By adsorbing to a curved interface, a particle eliminates a patch of fluid interface and perturbs the surrounding interface shape. Analysis predicts that perfectly smooth, circular disks do not migrate, and that nanometric deviations from a planar circular, contact line, like those around a weakly roughened planar disk, will drive migration with linear dependence on deviatoric curvature, in agreement with experiment. PMID:25618486

  5. Interparticle interactions and polarization effects in colloids

    SciTech Connect

    Hayter, J.B.

    1987-01-01

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

  6. Diffusing colloidal probes of cell surfaces.

    PubMed

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

    2016-05-25

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

  7. Method for electrohydrodynamically assembling patterned colloidal structures

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

  8. Apparatus for electrohydrodynamically assembling patterned colloidal structures

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  9. Colloidal spirals in nematic liquid crystals.

    PubMed

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

    2015-12-01

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

  10. Colloids with continuously tunable surface charge.

    PubMed

    van Ravensteijn, Bas G P; Kegel, Willem K

    2014-09-01

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

  11. Soft Interfaces

    NASA Astrophysics Data System (ADS)

    Gilles de Gennes, Pierre; Edwards, Introduction By Sam

    1997-04-01

    Paul Adrien Maurice Dirac, one of the greatest physicists of the twentieth century, died in 1984. Dirac's college, St. John's of Cambridge, generously endowed annual lectures to be held at Cambridge University in his memory. This volume contains a much expanded version of the 1994 Dirac Lecture by Nobel Laureate Pierre Gilles de Gennes. The book presents an impressionistic tour of the physics of soft interfaces. Full of insight and interesting asides, it not only provides an accessible introduction to this topic, but also lays down many markers and signposts that will be of interest to researchers in physics or chemistry. Features discussions of wetting and dewetting, the dynamics of different types of interface and adhesion and polymer/polymer welding.

  12. Stimuli-responsive surface localized ionic cluster (SLICs) formation from nonspherical colloidal particles.

    PubMed

    Lestage, David J; Urban, Marek W

    2005-07-19

    Structural features of phospholipids provide a unique opportunity for utilizing these amphiphilic species to stabilize the synthesis of colloidal dispersion particles by controlling concentration levels relative to dispersion synthesis components. 1,2-Bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DCPC) phospholipid was utilized as cosurfactant in the synthesis of sodium dioctyl sulfosuccinate (SDOSS) stabilized methyl methacrylate/n-butyl acrylate (MMA/nBA) colloidal dispersions. Aqueous dispersions containing various concentration levels of DCPC result in the formation of cocklebur particle morphologies, and when prepared in the presence of Ca2+ and annealed at various temperatures, stimuli-responsive behaviors of coalesced films were elucidated. The formation of surface localized ionic clusters (SLICs) at the film-air (F-A) and film-substrate (F-S) interfaces is shown to be responsive to concentration levels of DCPC, Ca2+/DCPC ratios, and temperature. These studies show that it is possible to control stratification and mobility to the F-A and F-S interfaces during and after coalescence. Using attenuated total reflectance Fourier transform infrared (ATR-FTIR) and internal reflection infrared imaging (IRIRI) spectroscopies, molecular entities responsible for SLIC formation were determined. These studies also show that stimuli-responsive behaviors during film formation can be controlled by colloidal solution morphologies and synergistic interactions of individual components. PMID:16008384

  13. Stimuli-responsive surfactant/phospholipid stabilized colloidal dispersions and their film formation.

    PubMed

    Lestage, David J; Yu, Min; Urban, Marek W

    2005-01-01

    Methyl methacrylate (MMA) and n-butyl acrylate (nBA) were copolymerized into stable colloidal particles in the presence of micelle forming sodium dioctyl sulfosuccinate (SDOSS) and liposome forming 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) in aqueous media that serve as thermodynamically stable loci for lipophilic monomers and nanostructured templates. These studies show for the first time that hollow colloidal particles may coalesce to form polymeric films and the combination of SDOSS and DLPC dispersing agents provides a stimuli-responsive environment during film formation through which individual surface stabilizing components can be driven to the film-air (F-A) or film-substrate (F-S) interface. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) of p-MMA/nBA colloidal dispersions revealed preferential and enhanced mobility of SDOSS and DLPC lipid rafts to the F-A and F-S interfaces in response to thermal, ionic, and enzymatic stimuli. PMID:15877379

  14. Design, synthesis, and film formation of stimuli-responsive colloidal dispersions containing phospholipids

    NASA Astrophysics Data System (ADS)

    Lestage, David Jackson

    These studies were undertaken to further understand the design of colloidal dispersions containing bio-active phospholipids (PL) as stabilizing agents and their stimuli-responsive behaviors during film formation. Methyl methacrylate (MMA) and n-butyl acrylate (nBA) dispersions were synthesized using anionic surfactants and PL, and the surface-responsiveness of coalesced films was monitored at the film-air (F-A) and film-substrate (F-S) interfaces after exposure to temperature, UV, pH, ionic strength, and enzymatic stimuli. Using spectroscopic molecular-level probes such as attenuated total reflectance (ATR) and internal reflection IR imaging (IRIRI), these studies show that structural features of PL and surfactants significantly affect stimuli-responsiveness of polymeric films. MMA/nBA homopolymer, blend, copolymer, and core-shell particle coalescence studies indicated that controlled permeability is influenced by particle composition and sodium dioctyl sulfosuccinate (SDOSS) mobility to the F-A interface is enhanced in response to temperature. Utilization of hydrogenated soybean phosphocholine (HSPC) as a co-surfactant with SDOSS resulted in bimodal p-MMA/nBA colloidal particles, and experiments showed that ionic interactions with HSPC inhibit SDOSS mobility. However, the controlled release of individual species is detected in the presence of Ca2+ ionic strength stimuli. Utilizing 1,2-bis(10,12-tricosadiynoyl)- sn-glycero-3-phosphocholine (DCPC), cocklebur-shape particle morphologies were obtained and using transmission electron microscopy (TEM), self-assembled tubules were detected at particle interfaces, but not in the presence of Ca 2+. At altered concentration levels of DCPC, surface localized ionic clusters (SLICs) composed of SDOSS and DCPC form at the F-A and F-S interfaces in response to temperature and ionic strength stimuli. Micelle formation of 1-myristoyl-2-hydroxy-sn-glycero-phosphocholine (MHPC) stabilizes unimodal p-MMA/nBA colloidal particles

  15. Particles at fluid-fluid interfaces: A new Navier-Stokes-Cahn-Hilliard surface- phase-field-crystal model.

    PubMed

    Aland, Sebastian; Lowengrub, John; Voigt, Axel

    2012-10-01

    Colloid particles that are partially wetted by two immiscible fluids can become confined to fluid-fluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids form an emulsion with interesting material properties and offer an important route to new soft materials. A promising approach to simulate these emulsions was presented in Aland et al. [Phys. Fluids 23, 062103 (2011)], where a Navier-Stokes-Cahn-Hilliard model for the macroscopic two-phase fluid system was combined with a surface phase-field-crystal model for the microscopic colloidal particles along the interface. Unfortunately this model leads to spurious velocities which require very fine spatial and temporal resolutions to accurately and stably simulate. In this paper we develop an improved Navier-Stokes-Cahn-Hilliard-surface phase-field-crystal model based on the principles of mass conservation and thermodynamic consistency. To validate our approach, we derive a sharp interface model and show agreement with the improved diffuse interface model. Using simple flow configurations, we show that the new model has much better properties and does not lead to spurious velocities. Finally, we demonstrate the solid-like behavior of the crystallized interface by simulating the fall of a solid ball through a colloid-laden multiphase fluid. PMID:23214691

  16. Particles at fluid-fluid interfaces: A new Navier-Stokes-Cahn-Hilliard surface- phase-field-crystal model

    NASA Astrophysics Data System (ADS)

    Aland, Sebastian; Lowengrub, John; Voigt, Axel

    2012-10-01

    Colloid particles that are partially wetted by two immiscible fluids can become confined to fluid-fluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids form an emulsion with interesting material properties and offer an important route to new soft materials. A promising approach to simulate these emulsions was presented in Aland [Phys. FluidsPHFLE61070-663110.1063/1.3584815 23, 062103 (2011)], where a Navier-Stokes-Cahn-Hilliard model for the macroscopic two-phase fluid system was combined with a surface phase-field-crystal model for the microscopic colloidal particles along the interface. Unfortunately this model leads to spurious velocities which require very fine spatial and temporal resolutions to accurately and stably simulate. In this paper we develop an improved Navier-Stokes-Cahn-Hilliard-surface phase-field-crystal model based on the principles of mass conservation and thermodynamic consistency. To validate our approach, we derive a sharp interface model and show agreement with the improved diffuse interface model. Using simple flow configurations, we show that the new model has much better properties and does not lead to spurious velocities. Finally, we demonstrate the solid-like behavior of the crystallized interface by simulating the fall of a solid ball through a colloid-laden multiphase fluid.

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

    PubMed

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

    2016-09-01

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

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

    SciTech Connect

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

    1980-11-01

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

  19. COLLOIDAL CONSIDERATIONS IN GROUNDWATER SAMPLING AND CONTAMINANT TRANSPORT PREDICTIONS

    EPA Science Inventory

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

  20. Nematic colloidal tilings as photonic materials

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  1. Shape-shifting colloids via stimulated dewetting

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  2. Dynamic Assembly of Magnetic Colloidal Vortices.

    PubMed

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

    2016-05-24

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

  3. Collective behavior of thermally active colloids.

    PubMed

    Golestanian, Ramin

    2012-01-20

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

  4. Collective Behavior of Thermally Active Colloids

    NASA Astrophysics Data System (ADS)

    Golestanian, Ramin

    2012-01-01

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

  5. Shape-shifting colloids via stimulated dewetting.

    PubMed

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

    2016-01-01

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

  6. 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)

  7. Premelting at Defects Within Bulk Colloidal Crystals

    NASA Astrophysics Data System (ADS)

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

    2005-08-01

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

  8. Targeted delivery of colloids by swimming bacteria

    PubMed Central

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

    2013-01-01

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

  9. Shape-shifting colloids via stimulated dewetting

    PubMed Central

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

    2016-01-01

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

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

    NASA Technical Reports Server (NTRS)

    2004-01-01

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

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

    PubMed

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

    2016-07-01

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

  12. Two-dimensional colloidal alloys.

    PubMed

    Law, Adam D; Buzza, D Martin A; Horozov, Tommy S

    2011-03-25

    We study the structure of mixed monolayers of large (3 μm diameter) and small (1 μm diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ξ. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations. PMID:21517357

  13. Two-Dimensional Colloidal Alloys

    NASA Astrophysics Data System (ADS)

    Law, Adam D.; Buzza, D. Martin A.; Horozov, Tommy S.

    2011-03-01

    We study the structure of mixed monolayers of large (3μm diameter) and small (1μm diameter) very hydrophobic silica particles at an octane-water interface as a function of the number fraction of small particles ξ. We find that a rich variety of two-dimensional hexagonal super-lattices of large (A) and small (B) particles can be obtained in this system due to strong and long-range electrostatic repulsions through the nonpolar octane phase. The structures obtained for the different compositions are in good agreement with zero temperature calculations and finite temperature computer simulations.

  14. Colloid and materials science for the conservation of cultural heritage: cleaning, consolidation, and deacidification.

    PubMed

    Baglioni, Piero; Chelazzi, David; Giorgi, Rodorico; Poggi, Giovanna

    2013-04-30

    Serendipity and experiment have been a frequent approach for the development of materials and methodologies used for a long time for either cleaning or consolidation of works of art. Recently, new perspectives have been opened by the application of materials science, colloid science, and interface science frameworks to conservation, generating a breakthrough in the development of innovative tools for the conservation and preservation of cultural heritage. This Article is an overview of the most recent contributions of colloid and materials science to the art conservation field, mainly focusing on the use of amphiphile-based fluids, gels, and alkaline earth metal hydroxide nanoparticles dispersions for the cleaning of pictorial surfaces, the consolidation of artistic substrates, and the deacidification of paper, canvas, and wood. Future possible directions for solving several conservation issues that still need to be faced are also highlighted. PMID:23432390

  15. Colloidal-gold electrosensor measuring device

    DOEpatents

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

    1995-01-01

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

  16. Dynamic Light Scattering From Colloidal Gels

    NASA Technical Reports Server (NTRS)

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

    1996-01-01

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

  17. Wetting reversal in colloid-polymer systems.

    PubMed

    Blokhuis, Edgar M; Kuipers, Joris

    2010-05-01

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

  18. Fabrication of anisotropic multifunctional colloidal carriers

    NASA Astrophysics Data System (ADS)

    Jerri, Huda A.

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

  19. Synthesis of Ionic Colloidal Crystals (ICCs)

    NASA Astrophysics Data System (ADS)

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

    2003-03-01

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

  20. Colloidal-gold electrosensor measuring device

    DOEpatents

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

    1995-11-21

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

  1. Controlling colloidal interaction through asymetric functionalization

    NASA Astrophysics Data System (ADS)

    Snyder, Charles E.

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

  2. Dynamics of Colloidal Disorder-Order Transition

    NASA Technical Reports Server (NTRS)

    2001-01-01

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

  3. Partial rejuvenation of a colloidal glass.

    PubMed

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

    2003-09-01

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

  4. Binary Colloidal Alloy Test-5: Compete

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

  5. Self-assembly of colloidal surfactants

    NASA Astrophysics Data System (ADS)

    Kegel, Willem

    2012-02-01

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

  6. Collective sliding states for colloidal molecular crystals

    SciTech Connect

    Reichhardt, Charles; Reichhardt, Cynthia

    2008-01-01

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

  7. Binary Colloidal Alloy Test-5: Phase Separation

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

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

  8. The role of colloidal plasmonic nanostructures in organic solar cells.

    PubMed

    Singh, C R; Honold, T; Gujar, T P; Retsch, M; Fery, A; Karg, M; Thelakkat, M

    2016-08-17

    Plasmonic particles can contribute via multiple processes to the light absorption process in solar cells. These particles are commonly introduced into organic solar cells via deposition techniques such as spin-coating or dip-coating. However, such techniques are inherently challenging to achieve homogenous surface coatings as they lack control of inter-particle spacing and particle density on larger areas. Here we introduce interface assisted colloidal self-assembly as a concept for the fabrication of well-defined macroscopic 2-dimensional monolayers of hydrogel encapsulated plasmonic gold nanoparticles. The monolayers showed a pronounced extinction in the visible wavelength range due to localized surface plasmon resonance with excellent optical homogeneity. Moreover this strategy allowed for the investigation of the potential of plasmonic monolayers at different interfaces of P3HT:PCBM based inverted organic solar cells. In general, for monolayers located anywhere underneath the active layer, the solar cell performance decreased due to parasitic absorption. However with thick active layers, where low hole mobility limited the charge transport to the top electrode, the plasmonic monolayer near that electrode spatially redistributed the light and charge generation close to the electrode led to an improved performance. This work systematically highlights the trade-offs that need to be critically considered for designing an efficient plasmonically enhanced organic solar cell. PMID:27494082

  9. Hydrogel-colloid interfacial interactions: a study of tailored adhesion using optical tweezers.

    PubMed

    Sheikhi, Amir; Hill, Reghan J

    2016-08-21

    Dynamics of colloidal particles adhering to soft, deformable substrates, such as tissues, biofilms, and hydrogels play a key role in many biological and biomimetic processes. These processes, including, but not limited to colloid-based delivery, stitching, and sorting, involve microspheres exploring the vicinity of soft, sticky materials in which the colloidal dynamics are affected by the fluid environment (e.g., viscous coupling), inter-molecular interactions between the colloids and substrates (e.g., Derjaguin-Landau-Verwey-Overbeek (DLVO) theory), and the viscoelastic properties of contact region. To better understand colloidal dynamics at soft interfaces, an optical tweezers back-focal-plane interferometry apparatus was developed to register the transverse Brownian motion of a silica microsphere in the vicinity of polyacrylamide (PA) hydrogel films. The time-dependent mean-squared displacements are well described by a single exponential relaxation, furnishing measures of the transverse interfacial diffusion coefficient and binding stiffness. Substrates with different elasticities were prepared by changing the PA crosslinking density, and the inter-molecular interactions were adjusted by coating the microspheres with fluid membranes. Stiffer PA hydrogels (with bulk Young's moduli ≈1-10 kPa) immobilize the microspheres more firmly (lower diffusion coefficient and position variance), and coating the particles with zwitterionic lipid bilayers (DOPC) completely eliminates adhesion, possibly by repulsive dispersion forces. Remarkably, embedding polyethylene glycol-grafted lipid bilayers (DSPE-PEG2k-Amine) in the zwitterionic fluid membranes produces stronger adhesion, possibly because of polymer-hydrogel attraction and entanglement. This study provides new insights to guide the design of nanoparticles and substrates with tunable adhesion, leading to smarter delivery, sorting, and screening of micro- and nano-systems. PMID:27425660

  10. Fabrication of High Sensitive Immunochromato Kit Using Au Colloid

    NASA Astrophysics Data System (ADS)

    Okamoto, Koji

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

  11. Ultrasound Propagation in Colloidal Dispersions.

    NASA Astrophysics Data System (ADS)

    Sherman, Nigel E.

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

  12. Colloids in the River Inn

    NASA Astrophysics Data System (ADS)

    Ueckert, Martina; Niessner, Reinhard; Baumann, Thomas

    2015-04-01

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

  13. Imaging in-plane and normal stresses near an interface crack using traction force microscopy

    PubMed Central

    Xu, Ye; Engl, Wilfried C.; Jerison, Elizabeth R.; Wallenstein, Kevin J.; Hyland, Callen; Wilen, Larry A.; Dufresne, Eric R.

    2010-01-01

    Colloidal coatings, such as paint, are all around us. However, we know little about the mechanics of the film-forming process because the composition and properties of drying coatings vary dramatically in space and time. To surmount this challenge, we extend traction force microscopy to quantify the spatial distribution of all three components of the stress at the interface of two materials. We apply this approach to image stress near the tip of a propagating interface crack in a drying colloidal coating and extract the stress intensity factor. PMID:20696929

  14. 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

  15. Modelling self-assembling of colloid particles in multilayered structures

    NASA Astrophysics Data System (ADS)

    Adamczyk, Zbigniew; Weroński, Paweł; Barbasz, Jakub; Kolasińska, Marta

    2007-04-01

    Simulations of particle multilayer build-up in the layer by layer (LbL) self-assembling processes have been performed according to the generalized random sequential adsorption (RSA) scheme. The first (precursor) layer having an arbitrary coverage of adsorption centers was generated using the standard RSA scheme pertinent to homogeneous surface. Formation of the consecutive layers (up to 20) was simulated by assuming short-range interaction potentials for two kinds of particles of equal size. Interaction of two particles of different kind resulted in irreversible and localized adsorption upon their contact, whereas particles of the same kind were assumed to interact via the hard potential (no adsorption possible). Using this algorithm theoretical simulations were performed aimed at determining the particle volume fraction as a function of the distance from the interface, as well as the multilayer film roughness and thickness as a function of the number of layers. The simulations revealed that particle concentration distribution in the film was more uniform for low precursor layer density than for higher density, where well-defined layers of closely packed particles appeared. On the other hand, the roughness of the film was the lowest at the highest precursor layer density. It was also predicted theoretically that for low precursor layer density the film thickness increased with the number of layers in a non-linear way. However, for high precursor layer density, the film thickness increased linearly with the number of layers and the average layer thickness was equal to 1.58 of the particle radius, which is close to the closely packed hexagonal layer thickness equal to 1.73. It was concluded by analysing the existing data for colloid particles and polyelectrolytes that the theoretical results can be effectively exploited for interpretation of the LbL processes involving colloid particles and molecular species like polymers or proteins.

  16. Prospects of Colloidal Copper Chalcogenide Nanocrystals.

    PubMed

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

    2016-03-01

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

  17. Advanced Colloids Experiment (ACE-T1)

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

  18. Colloid Formation at Waste Plume Fronts

    SciTech Connect

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

    2004-05-22

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

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

    NASA Technical Reports Server (NTRS)

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

    2015-01-01

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

  20. Colloidal crystal grain boundary formation and motion

    PubMed Central

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

    2014-01-01

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

  1. Self assembly of anisotropic colloidal particles

    NASA Astrophysics Data System (ADS)

    Florea, Daniel; Wyss, Hans

    2012-02-01

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

  2. Practical colloidal processing of multication ceramics

    SciTech Connect

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

    2015-09-07

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

  3. Practical colloidal processing of multication ceramics

    DOE PAGESBeta

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

    2015-09-07

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

  4. Photoelectrochromism in Tungsten Trioxide Colloidal Solutions

    ERIC Educational Resources Information Center

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

    2004-01-01

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

  5. Cobalt-doped cadmium selenide colloidal nanowires.

    PubMed

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

    2011-11-21

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

  6. Solid colloids with surface-mobile linkers.

    PubMed

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

    2015-06-17

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

  7. Motile Fluids: Granular, Colloidal and Living

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Sriram

    2014-03-01

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

  8. Collective dynamics of rotating colloidal particles

    NASA Astrophysics Data System (ADS)

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

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

  9. Grafting of oligosaccharides onto synthetic polymer colloids.

    PubMed

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

    2007-06-01

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

  10. The colloidal chemistry of ceramic clays

    NASA Technical Reports Server (NTRS)

    Phelps, G. W.

    1984-01-01

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

  11. Colloidal nickel boride catalyst for hydrogenation of olefins

    SciTech Connect

    Nakao, Y.; Fujishige, S.

    1981-04-01

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

  12. Bonded boojum-colloids in nematic liquid crystals.

    PubMed

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

    2013-08-20

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

  13. Assembly of Colloidal Materials Using Bioadhesive Interactions

    NASA Astrophysics Data System (ADS)

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

    2002-11-01

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

  14. Assembly of Colloidal Materials Using Bioadhesive Interactions

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

  15. Films of bacteria at interfaces: three stages of behaviour.

    PubMed

    Vaccari, Liana; Allan, Daniel B; Sharifi-Mood, Nima; Singh, Aayush R; Leheny, Robert L; Stebe, Kathleen J

    2015-08-14

    We report an investigation of the formation of films by bacteria at an oil-water interface using a combination of particle tracking and pendant drop elastometry. The films display a remarkably varied series of dynamical and mechanical properties as they evolve over the course of minutes to hours following the creation of an initially pristine interface. At the earliest stage of formation, which we interrogate using dispersions of colloidal probes, the interface is populated with motile bacteria. Interactions with the bacteria dominate the colloidal motion, and the interface displays canonical features of active matter in a quasi-two-dimensional context. This active stage gives way to a viscoelastic transition, presumably driven by the accumulation at the interface of polysaccharides and surfactants produced by the bacteria, which instill the interface with the hallmarks of soft glassy rheology that we characterize with microrheology. Eventually, the viscoelastic film becomes fully elastic with the capability to support wrinkling upon compression, and we investigate this final stage with the pendant drop measurements. We characterize quantitatively the dynamic and mechanical properties of the films during each of these three stages - active, viscoelastic, and elastic - and comment on their possible significance for the interfacial bacterial colony. This work also brings to the forefront the important role that interfacial mechanics may play in bacterial suspensions with free surfaces. PMID:26135879

  16. 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.

  17. Analysis of colloids released from bentonite and crushed rock

    NASA Astrophysics Data System (ADS)

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

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

  18. Colloid Bound Transport of Contaminats In The Unsaturated Zone

    NASA Astrophysics Data System (ADS)

    Hofmann, T.; Christ, A.

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

  19. Scattering from correlations in colloidal systems

    SciTech Connect

    Hayter, J.B.

    1984-01-01

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

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

    PubMed

    Wang, D; Xiang, L; Luo, J

    1996-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    SciTech Connect

    Li Shihhai; Jen, C.-P

    2001-02-15

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

  3. Gallium Adhesion: Phase Change of Gallium Enables Highly Reversible and Switchable Adhesion (Adv. Mater. 25/2016).

    PubMed

    Ye, Zhou; Lum, Guo Zhan; Song, Sukho; Rich, Steven; Sitti, Metin

    2016-07-01

    M. Sitti and co-workers find that gallium exhibits highly reversible and switchable adhesive characteristics during the liquid-solid phase change. As described on page 5088, this reversible adhesive allows miniature capsule-like robots, which are able to easily pick-and-place objects with irregular geometries and rough surfaces, and thus assemble such objects into a complex structure. The contact interface between gallium and the rough object is illustrated in the magnified image. PMID:27372722

  4. Quantitative uptake of colloidal particles by cell cultures.

    PubMed

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

    2016-10-15

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

  5. Stimuli-responsive surface crystallization of phospholipids from bimodal colloidal particles.

    PubMed

    Lestage, David J; Schleis, Daniel J; Urban, Marek W

    2004-08-17

    These studies focus on the effect of phospholipids in the presence of ionic surfactants on the behavior of poly(methylmethactrylate/n-butyl acrylate) (p-MMA/nBA) colloidal particles during film formation. With the presence of two surfactants, it is possible to obtain particles that exhibit two distinct particle sizes. The presence of hydrogenated soybean phosphatidylcholine (HSPC) and sodium dioctyl sulfosuccinate (SDOSS), which stabilize these bimodal colloidal dispersions, has a significant effect on the mobility of individual components during coalescence. Specifically, the presence of HSPC inhibits migration of SDOSS to the film-air (F-A) interface. Furthermore, the presence of electrolyte species such as aqueous CaCl2 has a very pronounced effect on film formation. When the Ca2+/HSPC ratio is 0.1/1.0, SDOSS is released to the F-A interface during coalescence. At 2.0/1.0 Ca2+/HSPC, HSPC diffuses to the F-A interface and crystalline domains consisting of HSPC are formed. This stimuli-responsive behavior is confirmed using IRIR imaging that ultimately exhibits different surface morphologies. These studies illustrate for the first time that it is possible to control the release of two different surface-active species during coalescence that form crystalline domains. PMID:15301484

  6. Amphiphilic crescent-moon-shaped microparticles formed by selective adsorption of colloids.

    PubMed

    Kim, Shin-Hyun; Abbaspourrad, Alireza; Weitz, David A

    2011-04-13

    We use a microfluidic device to prepare monodisperse amphiphilic particles in the shape of a crescent-moon and use these particles to stabilize oil droplets in water. The microfluidic device is comprised of a tapered capillary in a theta (θ) shape that injects two oil phases into water in a single receiving capillary. One oil is a fluorocarbon, while the second is a photocurable monomer, which partially wets the first oil drop; silica colloids in the monomer migrate and adsorb to the interface with water but do not protrude into the oil interface. Upon UV-induced polymerization, solid particles with the shape of a crescent moon are formed; removal of fluorocarbon oil yields amphiphilic particles due to the selective adsorption of silica colloids. The resultant amphiphilic microparticles can be used to stabilize oil drops in a mixture of water and ethanol; if they are packed to sufficient surface density on the interface of the oil drop, they become immobilized, preventing direct contact between neighboring drops, thereby providing the stability. PMID:21417254

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

    NASA Astrophysics Data System (ADS)

    Löwen, Hartmut

    2012-11-01

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

  8. 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

  9. Synthesis and characterization of FE colloid catalysts in inverse micelle solutions

    SciTech Connect

    Martino, A.; Sault, A.G.; Kawola, J.S.; Stoker, M.; Hicks, M.; Bartholomew, C.H.

    1995-02-01

    Formation of Fe clusters in inverse micelles was studied. Iron salts are solubilized within the polar interior of inverse micelles, and addition of LiBH{sub 4} initiates reduction to produce monodisperse, nanometer-sized Fe based particles. The reaction sequence is sustained by material exchange between inverse micelles. Surfactant interface provides a spatial constraint on reaction volume, and reactions carried out in these micro-heterogeneous solutions produce colloidal sized particles (10--100 {Angstrom}) stabilized in solution against flocculation by surfactant. In this paper, the clusters were characterized using TEM, Moessbauer spectroscopy, electron diffraction, and x-ray photoelectron spectroscopy.

  10. A Landau-de Gennes theory for hard colloidal rods: Defects and tactoids.

    PubMed

    Everts, J C; Punter, M T J J M; Samin, S; van der Schoot, P; van Roij, R

    2016-05-21

    We construct a phenomenological Landau-de Gennes theory for hard colloidal rods by performing an order parameter expansion of the chemical-potential dependent grand potential. By fitting the coefficients to known results of Onsager theory, we are not only able to describe the isotropic-nematic phase transition as function of density, including the well-known density jump, but also the isotropic-nematic planar interface. The resulting theory is applied in calculations of the isotropic core size in a radial hedgehog defect, the density dependence of linear defects of hard rods in square confinement, and the formation of a nematic droplet in an isotropic background. PMID:27208968

  11. A Landau-de Gennes theory for hard colloidal rods: Defects and tactoids

    NASA Astrophysics Data System (ADS)

    Everts, J. C.; Punter, M. T. J. J. M.; Samin, S.; van der Schoot, P.; van Roij, R.

    2016-05-01

    We construct a phenomenological Landau-de Gennes theory for hard colloidal rods by performing an order parameter expansion of the chemical-potential dependent grand potential. By fitting the coefficients to known results of Onsager theory, we are not only able to describe the isotropic-nematic phase transition as function of density, including the well-known density jump, but also the isotropic-nematic planar interface. The resulting theory is applied in calculations of the isotropic core size in a radial hedgehog defect, the density dependence of linear defects of hard rods in square confinement, and the formation of a nematic droplet in an isotropic background.

  12. Interfacial structuring in a phase-separating mixed biopolymer solution containing colloidal particles.

    PubMed

    Firoozmand, Hassan; Murray, Brent S; Dickinson, Eric

    2009-02-01

    We report confocal microscopy observations of the spatial distribution of monodisperse charge-stabilized colloidal particles (amphoteric polystyrene latex) incorporated within a spinodal-type phase-separating system of mixed biopolymers (gelatin + oxidized starch). Images from samples aged at 40 degrees C demonstrate a strong tendency for the added particles to accumulate at the liquid-liquid interface and to influence the rate of coarsening of the complex bicontinuous microstructure. Large variations in the local curvature of particle-rich interfacial regions are suggestive of a liquid-liquid boundary that is substantially viscoelastic. PMID:19138064

  13. Approaches to separations using silica colloidal membranes

    NASA Astrophysics Data System (ADS)

    Ignacio-de Leon, Patricia Anne Argana

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

  14. Advanced Colloids Experiment (ACE) Science Overview

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  15. 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.

  16. Colloidal mode of transport in the Potomac River watershed

    SciTech Connect

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

    1995-12-31

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

  17. Methods for colloid transport visualization in pore networks

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

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

    SciTech Connect

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

    1993-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  20. Shape recognition of microbial cells by colloidal cell imprints

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  1. And yet it moves - propulsion of colloidal clusters under reciprocal actuation

    NASA Astrophysics Data System (ADS)

    Steinbach, Gabi; Gemming, Sibylle; Erbe, Artur

    In the regime of low Reynolds numbers, the challenge of torque-based magnetic actuation lies in the conversion of torque into an effective force via symmetry breaking without inertial effects. Most reported systems rely on the hydrodynamic coupling between rotation and translation by an asymmetry in the environment (surfaces/interfaces) or the object shape. There, net translation can be realized only under non-reciprocal actuation given by precessing and rotating fields. In contrast, under oscillating fields, which are easier to realize, hydrodynamic coupling intrinsically leads to cyclic, reciprocal translation (Scallop theorem) unless the object has a certain flexible shape such as a flagellum. We present an alternative approach where symmetry breaking can be realized by magnetically interacting colloids which have been effectively modeled by spheres with shifted dipoles. If such colloids self-assemble, they form rigid clusters. We show how the collective, non-equilibrium dynamics of the colloids under oscillating fields propel the cluster. Depending on the configuration of the cluster it can rotate, translate and perform screw-like motion. Grants funding by DFG: FOR 1713 GE 1202/9-1 and ER 341/9-1.

  2. Low Reynolds Number Interactions between Colloidal Particles near the Entrance to a Cylindrical Pore.

    PubMed

    Ramachandran; Venkatesan; Tryggvason; Scott Fogler H

    2000-09-15

    The interaction between stable colloidal particles arriving at a pore entrance was studied using a numerical method for the case where the particle size is smaller than but of the same order as the pore size. The numerical method was adapted from a front-tracking technique developed for studying incompressible, multifluid flow by S. O. Unverdi and G. Tryggvason (J. Comp. Phys. 100, 25, 1992). The method is based on the finite difference solution of Navier-Stokes equation on a stationary, structured, Cartesian grid and the explicit representation of the particle-liquid interface using an unstructured grid that moves through the stationary grid. The simulations are in two dimensions, considering both deformable and nondeformable particles, and include interparticle colloidal interactions. The interparticle and particle-pore hydrodynamic interactions, which are very difficult to determine using existing analytical and semi-numerical, semi-analytical techniques in microhydrodynamics, are naturally accounted for in our numerical method and need not be explicity determined. Two- and three-particle motion toward a pore has been considered in our simulations. The simulations demonstrate how the competition between hydrodynamic forces and colloidal forces acting on particles dictate their flow behavior near the pore entrance. The predicted dependence of the particle flow behavior on the flow velocity and the ratio of pore size to particle size are qualitatively consistent with the experimental observations of V. Ramachandran and H. S. Fogler (J. Fluid Mech. 385, 129, 1999). Copyright 2000 Academic Press. PMID:10985810

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

    NASA Astrophysics Data System (ADS)

    Chen, Kunfeng; Xue, Dongfeng; Komarneni, Sridhar

    2015-04-01

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

  4. Slab photonic crystals with dimer colloid bases

    SciTech Connect

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

    2014-06-14

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

  5. Microscopic dynamics of synchronization in driven colloids

    PubMed Central

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

    2015-01-01

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

  6. Glassy Spin Dynamics in Buckled Colloidal Crystal

    NASA Astrophysics Data System (ADS)

    Zhou, Di; Wang, Feng; Han, Yilong

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

  7. Structure and hydrodynamics of colloidal systems

    NASA Astrophysics Data System (ADS)

    Hayter, John B.

    1986-02-01

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

  8. Structure and hydrodynamics of colloidal systems

    NASA Astrophysics Data System (ADS)

    Hayter, J. B.

    1985-07-01

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

  9. Functionalized patchy particles using colloidal lenses

    NASA Astrophysics Data System (ADS)

    Middleton, Christine

    2014-03-01

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

  10. Collective motion in populations of colloidal robots

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  11. Knot theory realizations in nematic colloids.

    PubMed

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

    2015-02-10

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

  12. Colloidal cholesteric liquid crystal in spherical confinement.

    PubMed

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

    2016-01-01

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

  13. The NASA GSFC MEMS Colloidal Thruster

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  14. Colloidal cholesteric liquid crystal in spherical confinement

    PubMed Central

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

    2016-01-01

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

  15. Particles with changeable topology in nematic colloids.

    PubMed

    Ravnik, Miha; Čopar, Simon; Žumer, Slobodan

    2015-09-01

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

  16. Particles with changeable topology in nematic colloids

    NASA Astrophysics Data System (ADS)

    Ravnik, Miha; Čopar, Simon; Žumer, Slobodan

    2015-09-01

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

  17. Knot theory realizations in nematic colloids

    PubMed Central

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

    2015-01-01

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

  18. Magnetic Colloids By Pulsed Laser Ablation

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

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

  19. Structure and hydrodynamics of colloidal systems

    SciTech Connect

    Hayter, J.B.

    1985-07-01

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

  20. Microscopic dynamics of synchronization in driven colloids.

    PubMed

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

    2015-01-01

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

  1. Nanoparticle engineering of colloidal suspension behavior

    NASA Astrophysics Data System (ADS)

    Chan, Angel Thanda

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

  2. Colloidal Nanocrystals Fluoresced by Surface Coordination Complexes

    PubMed Central

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

    2014-01-01

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

  3. Structure and dynamics of biphasic colloidal mixtures.

    PubMed

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

    2008-06-01

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

  4. Effective refractive index of face-centered-cubic and hexagonal close-packed 250 nm-SiO2 based colloidal crystals

    NASA Astrophysics Data System (ADS)

    Salcedo-Reyes, Juan Carlos

    2012-01-01

    A quantitative kinematic analysis, of the refraction properties of face-centered-cubic and hexagonal close-packed 250 nm-SiO2-based colloidal crystals, was performed using the plane wave expansion method. The angle-dependent effective refractive index, for different frequencies, was calculated taking into account the continuity of the tangential component of the wave vector across the interface and the energy conservation principle as well. The results demonstrate that the unusual optical properties, of the close packed SiO2-based colloidal crystals, depend strongly on the sphere-packing symmetry rather than from the material itself.

  5. Dynamics of Polymers in Colloidal Flows

    NASA Astrophysics Data System (ADS)

    Chen, Hsieh; Alexander-Katz, Alfredo

    2011-03-01

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

  6. Microfluidic Rheology of Soft Colloidal Suspensions

    NASA Astrophysics Data System (ADS)

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

    2008-11-01

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

  7. Synthesis of metal colloids in inverse microemulsions

    NASA Astrophysics Data System (ADS)

    Barnickel, P.; Wokaun, A.

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

  8. Colloidal particle deposition in turbulent flow

    SciTech Connect

    Morton, D.S.

    1994-05-01

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

  9. Dense colloidal fluids form denser amorphous sediments

    PubMed Central

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

    2013-01-01

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

  10. An evaporation model of colloidal suspension droplets

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

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

  11. Composition of estuarine colloidal material: organic components

    USGS Publications Warehouse

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

    1982-01-01

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

  12. Equilibrium crystal phases of triblock Janus colloids.

    PubMed

    Reinhart, Wesley F; Panagiotopoulos, Athanassios Z

    2016-09-01

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

  13. Nanosized gismondine grown in colloidal precursor solutions.

    PubMed

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

    2004-06-22

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

  14. Theory of dynamic arrest in colloidal mixtures

    NASA Astrophysics Data System (ADS)

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

    2008-05-01

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

  15. 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

  16. Colloidal particle deposition in turbulent flow

    NASA Astrophysics Data System (ADS)

    Morton, D. S.

    1994-05-01

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

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

    NASA Technical Reports Server (NTRS)

    Kurk, Michael A. (Andy)

    2015-01-01

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

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

    PubMed

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

    2011-02-01

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

  19. Spatially and temporally reconfigurable assembly of colloidal crystals

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  20. A molecular view of latex-water interfaces

    NASA Astrophysics Data System (ADS)

    Li, Zifeng; Fichthorn, Kristen; Milner, Scott; Yuan, Fang; Larson, Ronald

    2013-03-01

    Latex paints and coatings are colloidal suspensions, in which amorphous polymer particles are dispersed in an aqueous phase. The polymer-water interface plays a key role in the stability and rheology of the suspension. To obtain a molecular level view of this interface, atomistic simulations were performed for a slab of poly(methyl methacrylate)-poly(butyl acrylate) random copolymer in water, focusing on polymer and water density profiles, the hydrogen bonding of water with polymer carbonyl groups, and surface tension. The carbonyl groups at the interface were found to orient significantly towards water. We also calculated the temperature dependence of the surface tension between the polymer/water and polymer/ vacuum interfaces, including tail corrections for cut-off dispersion interactions, and we predict the contact angle of a water droplet at room temperature. Dow Chemical Corporate