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Sample records for charged colloidal rods

  1. Phase diagrams of charged colloidal rods: Can a uniaxial charge distribution break chiral symmetry?

    PubMed

    Drwenski, Tara; Dussi, Simone; Hermes, Michiel; Dijkstra, Marjolein; van Roij, René

    2016-03-01

    We construct phase diagrams for charged rodlike colloids within the second-virial approximation as a function of rod concentration, salt concentration, and colloidal charge. Besides the expected isotropic-nematic transition, we also find parameter regimes with a coexistence between a nematic and a second, more highly aligned nematic phase including an isotropic-nematic-nematic triple point and a nematic-nematic critical point, which can all be explained in terms of the twisting effect. We compute the Frank elastic constants to see if the twist elastic constant can become negative, which would indicate the possibility of a cholesteric phase spontaneously forming. Although the twisting effect reduces the twist elastic constant, we find that it always remains positive. In addition, we find that for finite aspect-ratio rods the twist elastic constant is also always positive, such that there is no evidence of chiral symmetry breaking due to a uniaxial charge distribution. PMID:26957177

  2. Phase diagrams of charged colloidal rods: Can a uniaxial charge distribution break chiral symmetry?

    NASA Astrophysics Data System (ADS)

    Drwenski, Tara; Dussi, Simone; Hermes, Michiel; Dijkstra, Marjolein; van Roij, René

    2016-03-01

    We construct phase diagrams for charged rodlike colloids within the second-virial approximation as a function of rod concentration, salt concentration, and colloidal charge. Besides the expected isotropic-nematic transition, we also find parameter regimes with a coexistence between a nematic and a second, more highly aligned nematic phase including an isotropic-nematic-nematic triple point and a nematic-nematic critical point, which can all be explained in terms of the twisting effect. We compute the Frank elastic constants to see if the twist elastic constant can become negative, which would indicate the possibility of a cholesteric phase spontaneously forming. Although the twisting effect reduces the twist elastic constant, we find that it always remains positive. In addition, we find that for finite aspect-ratio rods the twist elastic constant is also always positive, such that there is no evidence of chiral symmetry breaking due to a uniaxial charge distribution.

  3. Columnar versus smectic order in systems of charged colloidal rods

    NASA Astrophysics Data System (ADS)

    Wensink, H. H.

    2007-05-01

    We study the stability of inhomogeneous liquid crystalline states in systems of monodisperse, stiff, charged rods. By means of a bifurcation analysis applied to the Onsager free energy for charged rods in strongly nematic states, we investigate nematic-smectic and nematic-columnar instabilities as a function of the Debye screening length κ-1. While the nematic-smectic transition clearly preempts the nematic-columnar one in the regime of strong screening (i.e., small κ-1) a marked stability of hexagonal columnar order is observed at larger screening lengths. The theoretical results are substantiated by Brownian dynamics computer simulation results based on the Yukawa site model. Our connect to experiments on tobacco mosaic virus rods, in particular, but might be relevant for soft rodlike mesogens in strong external directional fields in general.

  4. The effect of charge separation on the phase behavior of dipolar colloidal rods.

    PubMed

    Rutkowski, David M; Velev, Orlin D; Klapp, Sabine H L; Hall, Carol K

    2016-06-14

    Colloids with anisotropic shape and charge distribution can assemble into a variety of structures that could find use as novel materials for optical, photonic, electronic and structural applications. Because experimental characterization of the many possible types of multi-shape and multipolar colloidal particles that could form useful structures is difficult, the search for novel colloidal materials can be enhanced by simulations of colloidal particle assembly. We have simulated a system of dipolar colloidal rods at fixed aspect ratio using discontinuous molecular dynamics (DMD) to investigate how the charge separation of an embedded dipole affects the types of assemblies that occur. Each dipolar rod is modeled as several overlapping spheres fixed in an elongated shape to represent excluded volume and two smaller, embedded spheres to represent the charges that make up the extended dipole. Large charge separations predominately form structures where the rods link head-to-tail while small charge separations predominately form structures where the rods stack side-by-side. Rods with small charge separations tend to form dense aggregates while rods with large charge separations tend to form coarse gel-like structures. Structural phase boundaries between fluid, string-fluid, and "gel" (networked) phases are mapped out and characterized as to whether they have global head-to-tail or global side-by-side order. A structural coarsening transition is observed for particles with large charge separations in which the head-tail networks thicken as temperature is lowered due to an increased tendency to form side-by-side structures. Triangularly connected networks form at small charge separations; these may be useful for encapsulating smaller particles. PMID:27151445

  5. Charge carrier transport in thin films of colloidal CdSe quantum rods

    NASA Astrophysics Data System (ADS)

    Persano, A.; Leo, G.; Manna, L.; Cola, A.

    2008-10-01

    Phototransport properties of organically capped colloidal CdSe quantum rod thin films deposited by spin coating are studied in air at room temperature in planar electrode configuration. Under optical excitation, the observed current-voltage characteristics and current transients are well described by a resonant tunneling model. A significant and irreversible current quenching of the photoresponse occurs with either the aging of the samples or the flowing of the current itself when above few picoamperes. The process, which is still interpreted in the frame of the model, can be attributed to the charge trapping by the defect states at the barrier between rods with a consequent increase in the barrier height.

  6. 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

  7. Electric Field Driven Self-Assembly of Colloidal Rods

    NASA Astrophysics Data System (ADS)

    Juarez, Jaime; Chaudhary, Kundan; Chen, Qian; Granick, Steve; Lewis, Jennifer

    2012-02-01

    The ability to assemble anisotropic colloidal building blocks into ordered configurations is of both scientific and technological importance. We are studying how electric field-induced interactions guide the self-assembly of these blocks into well aligned microstructures. Specifically, we present observations of the assembly of colloidal silica rods (L/D ˜ 4) within planar electrode cells as a function of different electric field parameters. Results from video microscopy and image analysis demonstrate that aligned microstructures form due to the competition between equilibrium interactions of induced dipoles and non-equilibrium processes (i.e., electro-osmosis). Under the appropriate electric field conditions (˜ kHZ AC fields), aligned colloidal rod fluids form over large areas on the electrode surface. The superposition of a DC electric field to this aligned colloidal rod fluid initiates their condensation into a vertically oriented crystalline phase. Ongoing work is now focused on exploring how temporal changes to electric fields influence colloidal rod dynamics and, hence, the assembly kinetics of aligned colloidal monolayers.

  8. Small bright charged colloidal quantum dots.

    PubMed

    Qin, Wei; Liu, Heng; Guyot-Sionnest, Philippe

    2014-01-28

    Using electrochemical charge injection, the fluorescence lifetimes of negatively charged core/shell CdTe/CdSe QDs are measured as a function of core size and shell thickness. It is found that the ensemble negative trion lifetimes reach a maximum (∼4.5 ns) for an intermediate shell thickness. This leads to the smallest particles (∼4.5 nm) with the brightest trion to date. Single dot measurements show that the negative charge suppresses blinking and that the trion can be as bright as the exciton at room temperature. In contrast, the biexciton lifetimes remain short and exhibit only a monotonous increase with shell thickness, showing no correlation with the negative trion decays. The suppression of the Auger process in small negatively charged CdTe/CdSe quantum dots is unprecedented and a significant departure from prior results with ultrathick CdSe/CdS core/shell or dot-in-rod structures. The proposed reason for the optimum shell thickness is that the electron-hole overlap is restricted to the CdTe core while the electron is tuned to have zero kinetic energy in the core for that optimum shell thickness. The different trend of the biexciton lifetime is not explained but tentatively attributed to shorter-lived positive trions at smaller sizes. These results improve our understanding of multiexciton recombination in colloidal quantum dots and may lead to the design of bright charged QDs for more efficient light-emitting devices. PMID:24350673

  9. 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.

  10. Direct determination of absorption anisotropy in colloidal quantum rods

    NASA Astrophysics Data System (ADS)

    Kamal, John Sundar; Gomes, Raquel; Hens, Zeger; Karvar, Masoumeh; Neyts, Kristiaan; Compernolle, Sien; Vanhaecke, Frank

    2012-01-01

    We propose a direct method to determine absorption anisotropy of colloidal quantum rods. In this method, the rods are aligned in solution by using an alternating electric field and we measure simultaneously the resulting average change in absorption. We show that a frequency window for the electric field exists in which the change in absorbance as a function of field strength can be analyzed in terms of the quantum-rod dipole moment and the absorption coefficient for light that is polarized parallel or perpendicular to the long axis of the rod. The approach is verified by measuring the absorbance change of CdSe rods at 400 nm as a function of field strength, where we demonstrate excellent agreement between experiment and theory. This enables us to propose improved values for the CdSe quantum-rod extinction coefficient. Next, we analyze CdSe/CdS dot-in-rods and find that the absorption of the first exciton transition is fully anisotropic, with a vanishing absorption coefficient for light that is polarized perpendicularly to the long axis of the rods.

  11. 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

  12. Fluorescent colloidal silica rods - synthesis and phase behavior

    NASA Astrophysics Data System (ADS)

    Kuijk, A.

    2012-01-01

    Although the experimental study of spherical colloids has been extensive, similar studies on rod-like particles are rare because suitable model systems are scarce. To fulfill this need, we present the synthesis of monodisperse rod-like silica colloids with tunable dimensions. Rods were produced with diameters of 200 nm and larger and lengths up to 10 µm, which resulted in aspect ratios ranging from 1 to 25. The growth mechanism of these rods involves emulsion droplets of water in pentanol, inside which silica condensation takes place. Since the silica nucleus is attached to the water/pentanol interface, the supply of reactants to the nucleus is anisotropic, causing it to grow on one side only, which results in rod formation. The rods were made suitable for quantitative real-space studies by confocal laser scanning microscopy. Several methods of fluorescent labeling are presented that resulted in constant fluorescence levels, gradients from one rod-end to the other, and even patterns of two colors. Single particle imaging was achieved by creating core-shell rods that had a fluorescent core and a non-fluorescent shell. Alternatively, the rods could be dispersed in a solvent with a low dielectric constant to induce micron-sized double layers. To enable quantitative measurements, a tracking algorithm was developed that identifies the rods' positions and orientations. The newly developed model system was used to study the phase behavior of rods. By combining real-space confocal laser scanning microscopy and small angle X-ray scattering methods, a phase diagram depending on concentration and aspect ratio was constructed, which shows good qualitative agreement with simulation results in literature. This phase diagram includes nematic and smectic phases for the higher aspect ratios. Also, the effect of external fields (electric fields, shear and templates) on the phase behavior was studied. In an electric field, rods aligned themselves with the applied field due to an

  13. 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

  14. Do multilayer crystals nucleate in suspensions of colloidal rods?

    PubMed

    Patti, Alessandro; Dijkstra, Marjolein

    2009-03-27

    We study the isotropic-to-crystal transformation in a mixture of colloidal hard rods and nonabsorbing polymer using computer simulations. We determine the height of the nucleation barrier and find that the critical cluster consists of a single crystalline layer growing laterally for all polymer fugacities considered. At lower supersaturation, the free energy of a single hexagonally packed layer increases monotonically with size, while the nucleation barrier of a second crystalline layer is extremely high. Hence, the nucleation of multilayer crystals is never observed. Multilayer crystals form only in the spinodal decomposition regime, either where, in an intermediate stage, single crystalline membranes coalesce into multilayer clusters or where, at higher polymer fugacity, smaller clusters of rods stack on top of each other to form long filaments. Eventually, these transient structures evolve into a thermodynamically stable bulk crystal phase. PMID:19392328

  15. 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

  16. Foam analogy in charged colloidal crystals.

    PubMed

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

    2002-05-01

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

  17. Oppositely charged colloids out of equilibrium

    NASA Astrophysics Data System (ADS)

    Vissers, T.

    2010-11-01

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

  18. Phase behavior of mixtures of colloidal rods and spheres

    NASA Astrophysics Data System (ADS)

    Adams, Marie Elizabeth

    In this thesis we study entropy driven order in mixtures of rods and spheres. Systems of rod-like particles, as pure systems, exhibit rich liquid crystalline phase behavior. We chose to work with aqueous suspensions of either TMV or fd virus particles, both rod-like lyotropic systems. We complicate the phase behavior by adding a second component, colloidal spheres (PEG/PEO, BSA, polystyrene latex, or Dextran). Our first paper explores the phase behavior of TMV mixed with BSA or PEO, mapping out a phase diagram based on optical microscopy observations. We found our qualitative observations of TMV mixtures to be consistent with theoretical models of the depletion force. The second paper extends our study of phase behavior to mixtures of fd virus and polystyrene latex spheres. We qualitatively observe bulk demixing for very small diameter added spheres and for very large diameter added spheres. In addition, we observed microphase separation morphologies, such as lamellar and columnar structures, which formed for fd mixed with polystyrene latex spheres 0.1 microns in diameter. All of these microphase samples were viewed with differential interference microscopy (a few samples were further investigated using electron microscopy). Both our data and theoretical calculations illustrated that 0.1 micron diameter spheres have a stabilizing effect on the smectic phase. Our final work focused on fd virus mixed with Dextran. The purpose of these experiments was to examine the effect of added polymer on the isotropic-cholesteric co-existence region. I-Ch samples were prepared and fd and Dextran concentrations were measured using a spectrophotometer. Several conditions were explored, including two different molecular weights of Dextran and a range of ionic strengths. In agreement with theoretical predictions, the I-Ch coexistence region widens with added Dextran with the polymer preferentially partioned into the isotropic phase.

  19. Electric-field Induced Microdynamics of Charged Rods

    NASA Astrophysics Data System (ADS)

    Kang, Kyongok

    2014-12-01

    Electric-field induced phase/state transitions are observed in AC electric fields with small amplitudes and low frequencies in suspensions of charged fibrous viruses (fd), which are model systems for highly charged rod-like colloids. Texture- and particle-dynamics in these field-induced states, and on crossing transition lines, are explored by image time-correlation and dynamic light scattering, respectively. At relatively low frequencies, starting from a system within the isotropic-nematic coexistence region, a transition from a nematic to a chiral nematic is observed, as well as a dynamical state where nematic domains melt and reform. These transitions are preliminary due to field-induced dissociation/association of condensed ions. At higher frequencies a uniform state is formed that is stabilized by hydrodynamic interactions through field-induced electro-osmotic flow where the rods align along the field direction. There is a point in the field-amplitude versus frequency plane where various transition lines meet. This point can be identified as a “non-equilibrium critical point”, in the sense that a length scale and a time scale diverge on approach of that point. The microscopic dynamics exhibits discontinuities on crossing transition lines that were identified independently by means of image and signal correlation spectroscopy.

  20. Thermoelectricity and thermodiffusion in charged colloids

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  1. 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)

  2. Anomalous columnar order of charged colloidal platelets.

    PubMed

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

    2012-01-21

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

  3. Thermoelectricity and thermodiffusion in charged colloids.

    PubMed

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

    2015-08-01

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

  4. Enhanced color conversion from colloidal CdSe/CdS dot/rods by vertical microcavities

    NASA Astrophysics Data System (ADS)

    Pühringer, H.; Roither, J.; Kovalenko, M. V.; Eibelhuber, M.; Schwarzl, T.; Talapin, D. V.; Heiss, W.

    2010-09-01

    Colloidal CdSe/CdS dot/rods exhibit efficient photoluminescence from the spherical CdSe dots at wavelengths well below the absorption edge of the rod material. This property makes dot/rods advantageous for color conversion applications, especially when they are embedded in optical microcavities to improve light extraction in forward direction. Here, surface emitting half-wavelength microcavities are demonstrated containing films of dot/rods as active material, exhibiting luminescence enhancement factors of up to 21 at the resonator wavelengths, whereas with conventional CdSe/ZnS core-shell nanocrystals only half of this value is obtained.

  5. Interactions and collective behavior of attractive colloidal rods and microspheres grafted with filamentous bacteriophage

    NASA Astrophysics Data System (ADS)

    Huang, Fei

    Interactions and collective behavior are investigated for two systems of attractive colloidal rods and colloidal stars. Attractive colloidal rods are constructed by grafting the temperature-sensitive polymer poly(N-isopropylacrylamide) (PNIPAM) to the surface of the semi-flexible filamentous fd virus. The phase diagram of fd-PNIPAM system becomes independent of ionic strength at high salt concentration and low temperature, i.e., the rods are sterically stabilized by the polymer. However, the network of rods undergoes a sol-gel transition as the temperature is raised. The viscoelastic moduli of fd and fd-PNIPAM suspensions are compared as a function of temperature, and the effect of ionic strength on the gelling behavior of fd-PNIPAM solution is measured. For all fluidlike and solidlike samples, the frequency-dependant linear viscoelastic moduli can be scaled onto universal master curves. Colloidal stars are constructed by grafting to 1 mum polystyrene beads a dense brush of 1 mum long and 10 nm wide semi-flexible filamentous viruses. The pair interaction potentials of colloidal stars are measured using an experimental implementation of umbrella sampling, a technique originally developed in computer simulations in order to probe rare events. The influence of ionic strength and grafting density on the interaction is measured. Good agreements are found between the measured interactions and theoretical predictions based upon the osmotic pressure of counterions.

  6. Synthesis of Cone-Shaped Colloids from Rod-Like Silica Colloids with a Gradient in the Etching Rate.

    PubMed

    Hagemans, Fabian; van der Wee, Ernest B; van Blaaderen, Alfons; Imhof, Arnout

    2016-04-26

    We present the synthesis of monodisperse cone-shaped silica colloids and their fluorescent labeling. Rod-like silica colloids prepared by ammonia-catalyzed hydrolysis and condensation of tetraethyl orthosilicate in water droplets containing polyvinylpyrrolidone cross-linked by citrate ions in pentanol were found to transform into cone-shaped particles upon mild etching by NaOH in water. The diameter and length of the resulting particles were determined by those of the initial rod-like silica colloids. The mechanism responsible for the cone-shape involves silica etching taking place with a varying rate along the length of the particle. Our experiments thus also lead to new insights into the variation of the local particle structure and composition. These are found to vary gradually along the length of the rod, as a result of the way the rod grows out of a water droplet that keeps itself attached to the flat end of the bullet-shaped particles. Subtle differences in composition and structure could also be resolved by high-resolution stimulated emission depletion confocal microscopy on fluorescently labeled particles. The incorporation of a fluorescent dye chemically attached to an amine-based silane coupling agent resulted in a distribution of fluorophores mainly on the outside of the rod-shaped particles. In contrast, incorporation of the silane coupling agent alone resulted in a homogeneous distribution. Additionally, we show that etching rods, where a silane coupling agent alone was incorporated and subsequently coupled to a fluorescent dye, resulted in fluorescent silica cones, the orientation of which can be discerned using super-resolution confocal microscopy. PMID:27046046

  7. Synthesis and Liquid-Crystal Behavior of Bent Colloidal Silica Rods.

    PubMed

    Yang, Yang; Chen, Guangdong; Martinez-Miranda, Luz J; Yu, Hua; Liu, Kun; Nie, Zhihong

    2016-01-13

    The design and assembly of novel colloidal particles are of both academic and technological interest. We developed a wet-chemical route to synthesize monodisperse bent rigid silica rods by controlled perturbation of emulsion-templated growth. The bending angle of the rods can be tuned in a range of 0-50° by varying the strength of perturbation in the reaction temperature or pH in the course of rod growth. The length of each arm of the bent rods can be individually controlled by adjusting the reaction time. For the first time we demonstrated that the bent silica rods resemble banana-shaped liquid-crystal molecules and assemble into ordered structures with a typical smectic B2 phase. The bent silica rods could serve as a visualizable mesoscopic model for exploiting the phase behaviors of bent molecules which represent a typical class of liquid-crystal molecules. PMID:26700616

  8. Thermoreversible Gels Composed of Colloidal Silica Rods with Short-Range Attractions.

    PubMed

    Murphy, Ryan P; Hong, Kunlun; Wagner, Norman J

    2016-08-23

    Dynamic arrest transitions of colloidal suspensions containing nonspherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346-2349) and temperature-dependent attractions were introduced by coating the calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultrasmall angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. The adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions. PMID:27466883

  9. Determination of colloidal particle surface charge from dielectrophoresis

    NASA Astrophysics Data System (ADS)

    Chavez, Marko; Nuansri, Rittirong; Mazza, Jacob; Ou-Yang, H. Daniel

    2015-03-01

    Electrophoresis (EP) is used to determine colloidal particle surface charge. However, when the Debye length is comparable to or larger than the particle size, electrophoresis cannot be reliably used to determine the surface charge due to counter ion retardation flow. Alexander et al. developed a theory relating colloidal osmotic pressure and particle surface charge. We use dielectrophoresis (DEP) to obtain a potential landscape based on the number density distribution of the particles in a non-uniform AC electric field. We determine the osmotic pressure from the DEP force and density profiles using Einstein's osmotic equilibrium equation. Surface charge obtained by DEP (thermodynamics) will be compared to that obtained by EP (electrokinetics).

  10. 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.

  11. Condensation and dissolution of nematic droplets in dispersions of colloidal rods with thermo–sensitive depletants

    PubMed Central

    Modlińska, Anna; Alsayed, Ahmed M.; Gibaud, Thomas

    2015-01-01

    Nematic droplets are droplets composed of elongated molecules that tend to point in the same direction but do not have any positional order. Such droplets are well known to adopt a spindle shape called tactoid. How such droplets condensate or melt and how the orientational symmetry is broken remains however unclear. Here we use a colloidal system composed of filamentous viruses as model rod–like colloids and pnipam microgel particles to induce thermo–sensitive depletion attraction between the rods. Microscopy experiments coupled to particle tracking reveal that the condensation of a nematic droplet is preceded by the formation of a new phase, an isotropic droplet. As the viruses constitute an excellent experimental realization of hard rods, it follows that the phenomenology we describe should be relevant to diverse micro- and nano-sized rods that interact through excluded volume interactions. This transition between isotropic and nematic droplets provides a new and reversible pathway to break the symmetry and order colloidal rods within a droplet with an external stimulus, and could constitute a benchmark experiment for a variety of technologies relying on reconfigurable control of rods. PMID:26656207

  12. Depletion induced isotropic-isotropic phase separation in suspensions of rod-like colloids.

    PubMed

    Jungblut, S; Tuinier, R; Binder, K; Schilling, T

    2007-12-28

    When non-adsorbing polymers are added to an isotropic suspension of rod-like colloids, the colloids effectively attract each other via depletion forces. We performed Monte Carlo simulations to study the phase diagram of such rod-polymer mixture. The colloidal rods were modeled as hard spherocylinders; the polymers were described as spheres of the same diameter as the rods. The polymers may overlap with no energy cost, while the overlap of polymers and rods is forbidden. Large amounts of depletant cause phase separation of the mixture. We estimated the phase boundaries of isotropic-isotropic coexistence both in the bulk and in confinement. To determine the phase boundaries we applied the grand canonical ensemble using successive umbrella sampling [J. Chem. Phys. 120, 10925 (2004)], and we performed a finite size scaling analysis to estimate the location of the critical point. The results are compared with predictions of the free volume theory developed by Lekkerkerker and Stroobants [Nuovo Cimento D 16, 949 (1994)]. We also give estimates for the interfacial tension between the coexisting isotropic phases and analyze its power-law behavior on the approach of the critical point. PMID:18163708

  13. Three-Phase Coexistence in Colloidal Rod-Plate Mixtures.

    PubMed

    Woolston, Phillip; van Duijneveldt, Jeroen S

    2015-09-01

    Aqueous suspensions of clay particles, such as montmorillonite (MMT) platelets and sepiolite (Sep) rods, tend to form gels at concentrations around 1 vol %. For Sep rods, adsorbing sodium polyacrylate to the surface allows for an isotropic-nematic phase separation to be seen instead. Here, MMT is added to such Sep suspensions, resulting in a complex phase behavior. Across a range of clay concentrations, separation into three phases is observed: a lower, nematic phase dominated by Sep rods, a MMT-rich middle layer, which is weakly birefringent and probably a gel, and a dilute top phase. Analysis of phase volumes suggests that the middle layer may contain as much as 6 vol % MMT. PMID:26262770

  14. Thermal Analog of Gimbal Lock in a Colloidal Ferromagnetic Janus Rod

    NASA Astrophysics Data System (ADS)

    Gao, Yongxiang; Balin, Andrew Kaan; Dullens, Roel P. A.; Yeomans, Julia M.; Aarts, Dirk G. A. L.

    2015-12-01

    We report an entropy-driven orientational hopping transition in a magnetically confined colloidal Janus rod. In a magnetic field, the sedimented rod randomly hops between horizontal and vertical states: the latter state comes at a substantial gravitational cost at no reduction of magnetic potential energy. The probability distribution over the angles of the rod shows that the presence of an external magnetic field leads to the emergence of a metastable vertical state separated from the ground state by an effective barrier. This barrier does not come from the potential energy but rather from the vast gain in phase space available to the rod as it approaches the vertical state. The loss of rotational degree of freedom that gives rise to this effect is a statistical mechanical analogue of the phenomenon of gimbal lock from classical mechanics.

  15. Thermal Analog of Gimbal Lock in a Colloidal Ferromagnetic Janus Rod.

    PubMed

    Gao, Yongxiang; Balin, Andrew Kaan; Dullens, Roel P A; Yeomans, Julia M; Aarts, Dirk G A L

    2015-12-11

    We report an entropy-driven orientational hopping transition in a magnetically confined colloidal Janus rod. In a magnetic field, the sedimented rod randomly hops between horizontal and vertical states: the latter state comes at a substantial gravitational cost at no reduction of magnetic potential energy. The probability distribution over the angles of the rod shows that the presence of an external magnetic field leads to the emergence of a metastable vertical state separated from the ground state by an effective barrier. This barrier does not come from the potential energy but rather from the vast gain in phase space available to the rod as it approaches the vertical state. The loss of rotational degree of freedom that gives rise to this effect is a statistical mechanical analogue of the phenomenon of gimbal lock from classical mechanics. PMID:26705660

  16. 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

  17. 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.

  18. Direct numerical simulations of electrophoresis of charged colloids.

    PubMed

    Kim, Kang; Nakayama, Yasuya; Yamamoto, Ryoichi

    2006-05-26

    We propose a numerical method to simulate electrohydrodynamic phenomena in charged colloidal dispersions. This method enables us to compute the time evolutions of colloidal particles, ions, and host fluids simultaneously by solving Newton, advection-diffusion, and Navier-Stokes equations so that the electrohydrodynamic couplings can be fully taken into account. The electrophoretic mobilities of charged spherical particles are calculated in several situations. The comparisons with approximation theories show quantitative agreements for dilute dispersions without any empirical parameters; however, our simulation predicts notable deviations in the case of dense dispersions. PMID:16803214

  19. Solidification of a Charged Colloidal Dispersion Investigated Using Microfluidic Pervaporation.

    PubMed

    Ziane, Nadia; Salmon, Jean-Baptiste

    2015-07-28

    We investigate the dynamics of solidification of a charged colloidal dispersion using an original microfluidic technique referred to as micropervaporation. This technique exploits pervaporation within a microfluidic channel to extract the solvent of a dilute colloidal dispersion. Pervaporation concentrates the colloids in a controlled way up to the tip of the channel until a wet solid made of closely packed colloids grows and invades the microfluidic channel. For the charged dispersion under study, we however evidence a liquid to solid transition (LST) preceding the formation of the solid, owing to the presence of long-range electrostatic interactions. This LST is associated with the nucleation and growth of domains confined in the channel. These domains are then compacted anisotropically up to forming a wet solid of closely packed colloids. This solid then invades the whole channel as in directional drying with a growth rate which depends on the microfluidic geometry. In the final steps of the solidification, we observed the occurrence of cracks and shear bands, the delamination of the wet solid from the channel walls, and its invasion by a receding air front. Interestingly, this air front follows specific patterns within the solid which reveal different microscopic colloidal organizations. PMID:26131999

  20. Active colloids propelled by induced-charge electrophoresis

    NASA Astrophysics Data System (ADS)

    Han, Ming; Luijten, Erik

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

  1. From soft to hard rod behavior in liquid crystalline suspensions of sterically stabilized colloidal filamentous particles.

    PubMed

    Grelet, Eric; Rana, Richa

    2016-05-18

    The liquid crystalline phase behavior of a colloidal system of sterically stabilized rods is reported. Our colloidal suspensions consist of highly monodisperse, semi-flexible filamentous viruses which have been coated with neutral hydrophilic polymers by irreversibly binding poly(ethylene glycol) (PEG) to the surface of the virus particles. Depending on the size of the grafted polymer, up to three different phase transitions are observed (isotropic-to-chiral nematic, chiral nematic-to-smectic, and smectic-to-columnar). Each phase transition is shown to be independent of ionic strength, confirming the steric stabilization of the viral colloids. A direct, i.e. without any free parameters, comparison with theory and computer simulations of the volume fraction associated with the phase transition can be performed, showing a quantitative agreement with hard rod behavior at a low polymer chain size, and some deviation stemming from soft repulsion by increasing the polymer thickness coating of the rod. Specifically, we demonstrate that the columnar mesophase is not stabilized by electrostatic repulsion, and we discuss the conditions of its existence. PMID:27108523

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

    PubMed

    Savenko, S V; Dijkstra, Marjolein

    2006-06-21

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

  3. Liquid-glass transition in charge-stabilized colloidal dispersions

    NASA Astrophysics Data System (ADS)

    Lai, S. K.; Wang, G. F.; Peng, W. P.

    2000-06-01

    We model the inter-colloidal interactions in a charge-stabilized colloidal dispersion by a hard-core Yukawa potential φ(r)=σ0γ exp(-κr)/r, r>σ0 and apply the rescaled mean spherical approximation to calculate its static structure factor. In conjunction with the idealized mode-coupling theory, we determine the loci of the liquid-glass transition phase boundary for a salt-free suspension of charged colloids evaluated at different counter-ion environment (characterized by the κ) in terms of the macro-ion parameters: volume fraction ɛ, charge Z0 and size σ0. The calculated parametric phase diagrams are quite general since the results, with slight and straightforward modification, can be utilized to study the glass transition in a more realistic colloidal solution such as an aqueous monodisperse suspension of polystyrene charged spheres with an added electrolyte. Confining our discussion, then, to the simplest salt-free colloidal liquids, we extract from our analysis of the calculated liquid-glass transition boundaries some succinct features. Specifically, we show in this work that given a range of interaction Vkgr=κσ0<~3.8, there is a possibility of observing the liquid⇋glass⇋liquid⇋glass(LGLG) re-entrant phenomenon in restrictive regions of the phase diagram ɛ-σ0 or ɛ-Z0 for a monodisperse charge-stabilized solution. However, as the σ0 increases above a critical size, the LGLG re-entrant behavior vanishes. To delve into this re-entrant phenomenon, we compare, for a given Vkgr, the glassy Debye-Waller factor, static structure factor and their spatial counterparts for two cases-nnone for lower-Z0 colloids at a high ɛ and the other for higher-Z0 colloids at a low ɛ. For the former, the glassification is basically driven by the geometric restriction while that, for the latter, it is mainly induced by the Coulomb force. We conclude from this comparison that under the same screening environment both the excluded volume and the electrostatic effects are

  4. Charge renormalization in nominally apolar colloidal dispersions

    NASA Astrophysics Data System (ADS)

    Evans, Daniel J.; Hollingsworth, Andrew D.; Grier, David G.

    2016-04-01

    We present high-resolution measurements of the pair interactions between dielectric spheres dispersed in a fluid medium with a low dielectric constant. Despite the absence of charge control agents or added organic salts, these measurements reveal strong and long-ranged repulsions consistent with substantial charges on the particles whose interactions are screened by trace concentrations of mobile ions in solution. The dependence of the estimated charge on the particles' radii is consistent with charge renormalization theory and, thus, offers insights into the charging mechanism in this interesting class of model systems. The measurement technique, based on optical-tweezer manipulation and artifact-free particle tracking, makes use of optimal statistical methods to reduce measurement errors to the femtonewton frontier while covering an extremely wide range of interaction energies.

  5. Spontaneous formation of stringlike clusters and smectic sheets for colloidal rods confined in thin wedgelike gaps.

    PubMed

    Maeda, Hideatsu; Maeda, Yoshiko

    2013-08-20

    Monodispersed colloidal rods of β-FeOOH with sizes ranging from 270 to 580 nm in length and 50 to 80 nm in width were synthesized. Narrow wedgelike gaps (0 to 700 nm in height) were formed around the inner bottom edge of the suspension glass cells. Optical microscopic observations revealed the formation of stringlike clusters of the rods and smectic sheets (by spontaneous side-by-side clustering of the strings) in the isotropic phase of the rod suspensions confined in narrow gaps; the electrolyte (HCl) concentrations of the suspensions are 5-40 mM, at which inter-rod interactions are attractive. The strings exhibit different colors that were used to investigate the structures of the strings with the help of interference color theory for thin films. The results are as follows. (1) The rods, lying flat on the gap bottom, are connected side-by-side and stacked upward to form stringlike clusters with different thicknesses depending on the gap height. (2) The stacking numbers (N(sr)) of the rods are estimated to be 1-5. With N(sr) increasing from 2 to 5, the volume fractions (ϕ) of the rods in the strings increased typically from 0.25-0.3 to 0.35-0.42 to reach limiting values (close to the ϕ values of the rods in the bulk smectic phase). (3) Unexpected low-ϕ strings are found in regions with an intermediate height in the gaps. These behaviors of ϕ may be caused by thermal fluctuations of the strings. PMID:23876087

  6. Controlling colloid charge in nonpolar liquids with surfactants.

    PubMed

    Smith, Gregory N; Eastoe, Julian

    2013-01-14

    The formation of ions in nonpolar solvents (with relative permittivity ε(r) of approximately 2) is more difficult than in polar liquids; however, these charged species play an important role in many applications, such as electrophoretic displays. The low relative permittivities of these solvents mean that charges have to be separated by large distances to be stable (approximately 28 nm or 40 times that in water). The inverse micelles formed by surfactants in these solvents provide an environment to stabilize ions and charges. Common surfactants used are sodium dioctylsulfosuccinate (Aerosol OT or AOT), polyisobutylene succinimide, sorbitan oleate, and zirconyl 2-ethyl hexanoate. The behavior of charged inverse micelles has been studied on both the bulk and on the microscopic scale and can be used to determine the motion of the micelles, their structure, and the nature of the electrostatic double layer. Colloidal particles are only weakly charged in the absence of surfactant, but in the presence of surfactants, many types, including polymers, metal oxides, carbon blacks, and pigments, have been observed to become positively or negatively charged. Several mechanisms have been proposed as the origin of surface charge, including acid-base reactions between the colloid and the inverse micelle, preferential adsorption of charged inverse micelles, or dissolution of surface species. While most studies vary only the concentration of surfactant, systematic variation of the particle surface chemistry or the surfactant structure have provided insight into the origin of charging in nonpolar liquids. By carefully varying system parameters and working to understand the interactions between surfactants and colloidal surfaces, further advances will be made leading to better understanding of the origin of charge and to the development of more effective surfactants. PMID:23187453

  7. Directing Colloidal Assembly and a Metal-Insulator Transition Using a Quench-Disordered Porous Rod Template

    NASA Astrophysics Data System (ADS)

    Jadrich, Ryan B.; Schweizer, Kenneth S.

    2014-11-01

    Replica and effective-medium theory methods are employed to elucidate how to massively reconfigure a colloidal assembly to achieve globally homogeneous, strongly clustered, and percolated equilibrium states of high electrical conductivity at low physical volume fractions. A key idea is to employ a quench-disordered, large-mesh rigid-rod network as a templating internal field. By exploiting bulk phase separation frustration and the tunable competing processes of colloid adsorption on the low-dimensional network and fluctuation-driven colloid clustering in the pore spaces, two distinct spatial organizations of greatly enhanced particle contacts can be achieved. As a result, a continuous, but very abrupt, transition from an insulating to metallic-like state can be realized via a small change of either the colloid-template or colloid-colloid attraction strength. The approach is generalizable to more complicated template or colloidal architectures.

  8. Alternating strings and clusters in suspensions of charged colloids.

    PubMed

    Everts, J C; van der Linden, M N; van Blaaderen, A; van Roij, R

    2016-08-21

    We report the formation of alternating strings and clusters in a binary suspension of repulsive charged colloids with double layers larger than the particle size. Within a binary cell model we include many-body and charge-regulation effects under the assumption of a constant surface potential, and consider their repercussions on the two-particle interaction potential. We find that the formation of induced dipoles close to a charge-reversed state may explain the formation of these structures. Finally, we will touch upon the formation of dumbbells and small clusters in a one-component system, where the effective electrostatic interaction is always repulsive. PMID:27439990

  9. Numerical study of cluster formation in binary charged colloids

    NASA Astrophysics Data System (ADS)

    Okuzono, Tohru; Odai, Kana; Masuda, Tatsuhiro; Toyotama, Akiko; Yamanaka, Junpei

    2016-07-01

    Cluster formation of oppositely charged colloidal particles is studied numerically. A simple Brownian dynamics method with a screened-Coulomb (Yukawa) potential is employed for numerical simulations. An equilibrium phase which consists of clusters and unassociated particles is obtained. It is shown that the equilibrium association number of clusters and their shapes are determined by charge numbers and charge ratio of the binary particles. The phase diagram of cluster formation for various charge numbers and their ratios is obtained. A simple relation between the association number and the charge ratio is found. It is demonstrated that in the case of high charge ratio the cluster takes a multilayer structure which is highly symmetric. It is also pointed out that the cluster-particle interaction changes dynamically in the cluster formation process, which is involved in the selection of final cluster structure.

  10. Numerical study of cluster formation in binary charged colloids.

    PubMed

    Okuzono, Tohru; Odai, Kana; Masuda, Tatsuhiro; Toyotama, Akiko; Yamanaka, Junpei

    2016-07-01

    Cluster formation of oppositely charged colloidal particles is studied numerically. A simple Brownian dynamics method with a screened-Coulomb (Yukawa) potential is employed for numerical simulations. An equilibrium phase which consists of clusters and unassociated particles is obtained. It is shown that the equilibrium association number of clusters and their shapes are determined by charge numbers and charge ratio of the binary particles. The phase diagram of cluster formation for various charge numbers and their ratios is obtained. A simple relation between the association number and the charge ratio is found. It is demonstrated that in the case of high charge ratio the cluster takes a multilayer structure which is highly symmetric. It is also pointed out that the cluster-particle interaction changes dynamically in the cluster formation process, which is involved in the selection of final cluster structure. PMID:27575181

  11. Polydiacetylenes in solution; charged rods and neutral coils

    NASA Astrophysics Data System (ADS)

    Zacher, Robert A.

    1990-08-01

    We report experimental results on several polydiacetylenes and a polythiophene in solution which demonstrate a change in charge state associated with solvatochromic and thermochromic transitions. The planar conformations are charged and the nonplanar conformations are neutral. When fields of ≊600 V/cm were applied to solutions of polymer in chloroform-hexane mixtures or toluene (i.e., the polymer is in the extended state), the polymers plated out on one electrode. We have measured the current as a function of time associated with the deposition of the polymer to determine the quantity of charge per polymer. The time dependence of the current had two regimes which can be associated with two types of charged material in the solution: the charged polymer, which plates out, and an unidentified charge transfer species which does not plate out. Polydiacetylenes 4BCMU and 3BCMU in solutions of chloroform/hexane became positively charged. Poly-3-hexyl-thiophene also became positively charged. PDA-9PA and PDA-92NA became negatively charged. We found a charge of 3×10-4 e/monomer for 4BCMU, 7×10-3 e/monomer for 3BCMU, and 4×10-2 e/monomer for PDA-9PA. Using this effect, we can demonstrate that both rod and coil segments coexist on the same polymer chain in the intermediate stages of the rod-coil transition. We suggest a mechanism which can qualitatively account for this unusual behavior. We also describe novel experiments in which an electric field was used to drive the polymers across a boundary between two nonmiscible solvents. When the polymer crosses the boundary, it changes color. The possibility of using the plating effect for precise fractionation by electrophoresis is suggested.

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

    NASA Astrophysics Data System (ADS)

    Esztermann, A.; Löwen, H.

    2004-10-01

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

  13. Interaction modes between asymmetrically and oppositely charged rods

    NASA Astrophysics Data System (ADS)

    Antila, Hanne S.; Van Tassel, Paul R.; Sammalkorpi, Maria

    2016-02-01

    The interaction of oppositely and asymmetrically charged rods in salt—a simple model of (bio)macromolecular assembly—is observed via simulation to exhibit two free energy minima, separated by a repulsive barrier. In contrast to similar minima in the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the governing mechanism includes electrostatic attraction at large separation, osmotic repulsion at close range, and depletion attraction near contact. A model accounting for ion condensation and excluded volume is shown to be superior to a mean-field treatment in predicting the effect of charge asymmetry on the free-energy profile.

  14. 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.

  15. Charged micelle depletion attraction and interfacial colloidal phase behavior.

    PubMed

    Iracki, Tara D; Beltran-Villegas, Daniel J; Eichmann, Shannon L; Bevan, Michael A

    2010-12-21

    Ensemble total internal reflection microscopy (TIRM) is used to directly measure the evolution of colloid-surface depletion attraction with increasing sodium dodecyl sulfate (SDS) concentration near the critical micelle concentration (CMC). Measured potentials are well described by a modified Asakura-Oosawa (AO) depletion potential in addition to electrostatic and van der Waals contributions. The modified AO potential includes effects of electrostatic interactions between micelles and surfaces via effective depletant dimensions in an excluded volume term and partitioning in an osmotic pressure term. Directly measured colloid-surface depletion potentials are used in Monte Carlo (MC) simulations to capture video microscopy (VM) measurements of micelle-mediated quasi-two-dimensional phase behavior including fluid, crystal, and gel microstructures. Our findings provide information to develop more rigorous and analytically simple models of depletion attraction in charged micellar systems. PMID:21077612

  16. Novel kinetic trapping in charged colloidal clusters due to self-induced surface charge organization

    PubMed Central

    Klix, Christian L.; Murata, Ken-ichiro; Tanaka, Hajime; Williams, Stephen R.; Malins, Alex; Royall, C. Patrick

    2013-01-01

    Colloidal clusters are an unusual state of matter where tunable interactions enable a sufficient reduction in their degrees of freedom that their energy landscapes can become tractable — they form a playground for statistical mechanics and promise unprecedented control of structure on the submicron lengthscale. We study colloidal clusters in a system where a short-ranged polymer-induced attraction drives clustering, while a weak, long-ranged electrostatic repulsion prevents extensive aggregation. We compare experimental yields of cluster structures with theory which assumes simple addition of competing isotropic interactions between the colloids. Here we show that for clusters of size 4 ≤ m ≤ 7, the yield of minimum energy clusters is much less than expected. We attribute this to an anisotropic self-organized surface charge distribution which leads to unexpected kinetic trapping. We introduce a model for the coupling between counterions and binding sites on the colloid surface with which we interpret our findings. PMID:23797807

  17. 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

  18. Denser fluids of charge-stabilized colloids form denser sediments.

    PubMed

    Nanikashvili, Pilkhaz M; Butenko, Alexander V; Liber, Shir R; Zitoun, David; Sloutskin, Eli

    2014-07-21

    Granular matter, where solid-like elasticity emerges in the absence of crystalline order, has been actively studied over the last few decades, targeting fundamental physical understanding of granular packings and glasses, abundant in everyday life and technology. We employ charge-stabilized sub-micron particles in a solvent, known as colloids, to form granular packings through a well-controlled process, where initially homogeneous and thermodynamically equilibrated colloidal fluids form solid sediments, when subjected to an effective gravity in a centrifuge. We demonstrate that particles' volume fraction φj in these sediments increases linearly with that in the initial fluid φ0, setting an upper limit φRCP≈ 0.64 on both φj and φ0, where φRCP coincides with the well-known, yet highly controversial, 'random close packing' density of spheres, providing new insight into the physics of granular packings. The observed φj(φ0) dependence is similar to the one recently reported for colloidal hard spheres, sterically stabilized by surface-linked polymer combs (S. R. Liber, et al., Proc. Natl. Acad. Sci. U. S. A., 2013, 110, 5769-5773). However, the lower limit on sediment densities drops to φj≈ 0.49 in the present work, suggesting that sedimented charge-stabilized silica are able to overcome mutual electrostatic repulsions, forming gel-like structures stabilized by occasional van der Waals contacts. Finally, by introducing particle size polydispersity, which significantly modifies fluid structure and sedimentation dynamics, we almost completely diminish the φj(φ0) dependence, bringing φj(0) close to its value in frictionless systems. PMID:24870013

  19. Non-additivity of pair interactions in charged colloids

    NASA Astrophysics Data System (ADS)

    Finlayson, Samuel D.; Bartlett, Paul

    2016-07-01

    It is general wisdom that the pair potential of charged colloids in a liquid may be closely approximated by a Yukawa interaction, as predicted by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. We experimentally determine the effective forces in a binary mixture of like-charged particles, of species 1 and 2, with blinking optical tweezers. The measured forces are consistent with a Yukawa pair potential but the (12) cross-interaction is not equal to the geometric mean of the (11) and (22) like-interactions, as expected from DLVO. The deviation is a function of the electrostatic screening length and the size ratio, with the cross-interaction measured being consistently weaker than DLVO predictions. The corresponding non-additivity parameter is negative and grows in magnitude with increased size asymmetry.

  20. One-component plasma of point charges and of charged rods

    SciTech Connect

    Hatlo, Marius M.; Karatrantos, Argyrios; Lue, Leo

    2009-12-15

    An approximate theory is developed to describe the properties of mobile particles with extended charge distributions in the presence of a neutralizing fixed background charge. Long-wavelength fluctuations of the electric potential are handled within a variational perturbation approximation, and the short-wavelength fluctuations are handled within a cumulant (fugacity) expansion. The distinct treatment of these two contributions to the free energy enables the theory to provide quantitative predictions for the properties of these systems from the weak- to the strong-coupling regimes. With this theory, we study three different variations in the classical one-component plasma model: a plasma of point charges, a plasma of particles consisting of 8 linearly bonded point charges (8-mer), and a plasma of line charges. The theory was found to agree well with the available computer simulation data for the electrostatic interaction energy of these systems for all values of the plasma coupling parameter examined (GAMMA=0 to 400). In addition, we find that both the 8-mer rod and the line charge systems form a strongly ordered nematic phase, which is entirely driven by electrostatic interactions. The nematic phase only exists within a finite range of lengths of the charged particles. If the particles are too short or too long, the nematic phase does not appear. Finally, we find that the nematic phase is stable over a broader range of conditions for the line charge system than for the 8-mer rod system; consequently, the phase behavior of the one-component plasma is sensitive to the manner in which the charge is distributed on the particles.

  1. Experimental investigation on the use of highly charged nanoparticles to improve the stability of weakly charged colloidal system.

    PubMed

    Zubir, Mohd Nashrul Mohd; Badarudin, A; Kazi, S N; Misran, Misni; Amiri, Ahmad; Sadri, Rad; Khalid, Solangi

    2015-09-15

    The present work highlighted on the implementation of a unique concept for stabilizing colloids at their incipiently low charge potential. A highly charged nanoparticle was introduced within a coagulated prone colloidal system, serving as stabilizer to resist otherwise rapid flocculation and sedimentation process. A low size asymmetry of nanoparticle/colloid serves as the new topic of investigation in addition to the well-established large size ratio nanoparticle/microparticle study. Highly charged Al2O3 nanoparticles were used within the present research context to stabilize TiO2 and Fe3O4 based colloids via the formation of composite structures. It was believed, based on the experimental evidence, that Al2O3 nanoparticle interact with the weakly charged TiO2 and Fe3O4 colloids within the binary system via absorption and/or haloing modes to increase the overall charge potential of the respective colloids, thus preventing further surface contact via van der Waal's attraction. Series of experimental results strongly suggest the presence of weakly charged colloids in the studied bimodal system where, in the absence of highly charged nanoparticle, experience rapid instability. Absorbance measurement indicated that the colloidal stability drops in accordance to the highly charged nanoparticle sedimentation rate, suggesting the dominant influence of nanoparticles to attain a well-dispersed binary system. Further, it was found that the level of colloidal stability was enhanced with increasing nanoparticle fraction within the mixture. Rheological observation revealed that each hybrid complexes demonstrated behavior reminiscence to water with negligible increase in viscosity which serves as highly favorable condition particularly in thermal transport applications. PMID:26048724

  2. Mobile colloid generation induced by a cementitious plume: mineral surface-charge controls on mobilization.

    PubMed

    Li, Dien; Kaplan, Daniel I; Roberts, Kimberly A; Seaman, John C

    2012-03-01

    Cementitious materials are increasingly used as engineered barriers and waste forms for radiological waste disposal. Yet their potential effect on mobile colloid generation is not well-known, especially as it may influence colloid-facilitated contaminant transport. Whereas previous papers have studied the introduction of cement colloids into sediments, this study examined the influence of cement leachate chemistry on the mobilization of colloids from a subsurface sediment collected from the Savannah River Site, USA. A sharp mobile colloid plume formed with the introduction of a cement leachate simulant. Colloid concentrations decreased to background concentrations even though the aqueous chemical conditions (pH and ionic strength) remained unchanged. Mobile colloids were mainly goethite and to a lesser extent kaolinite. The released colloids had negative surface charges and the mean particle sizes ranged primarily from 200 to 470 nm. Inherent mineralogical electrostatic forces appeared to be the controlling colloid removal mechanism in this system. In the background pH of ~6.0, goethite had a positive surface charge, whereas quartz (the dominant mineral in the immobile sediment) and kaolinite had negative surface charges. Goethite acted as a cementing agent, holding kaolinite and itself onto the quartz surfaces due to the electrostatic attraction. Once the pH of the system was elevated, as in the cementitious high pH plume front, the goethite reversed to a negative charge, along with quartz and kaolinite, then goethite and kaolinite colloids were mobilized and a sharp spike in turbidity was observed. Simulating conditions away from the cementitious source, essentially no colloids were mobilized at 1:1000 dilution of the cement leachate or when the leachate pH was ≤ 8. Extreme alkaline pH environments of cementitious leachate may change mineral surface charges, temporarily promoting the formation of mobile colloids. PMID:22316126

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

    NASA Astrophysics Data System (ADS)

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

    2009-03-01

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

  4. 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

  5. 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

  6. Electrostatic Charging of Insulating Rods and Resulting Particle Transport in the Columbia Non-neutral Torus

    NASA Astrophysics Data System (ADS)

    Senter, Aaron; Rath, Nikolaus; Brenner, Paul; Sarasola, Xabier; Pedersen, Thomas

    2009-11-01

    The Columbia Non-neutral Torus (CNT) is a stellarator created to study non-neutral plasmas confined on magnetic surfaces. To create and diagnose the electron plasma, filaments supported by ceramic rods are inserted into the plasma. These rods charge negatively allowing particles to E xB drift across the confining magnetic surfaces and out of the plasma. A simple model of this process has yielded good qualitative agreement with experimentally observed radial transport[1]. However, when the rod is retracted, it perturbs the plasma more than expected. To better understand the rod perturbations, externally biased conducting rods are now being used. We find the effect of the ceramic rods by measuring the increase in filament emission current with a rod installed. Comparing the radial transport rates of the ceramic and conducting rods, we aim to understand the charge distribution on the former, and to minimize the rod driven transport. Initial experiments show that a uniformly biased rod does not reproduce the transport observed. Experiments using a rod with a varying radial potential profile are being conducted and will be reported on. [1] J.W. Berkery et al., Phys. Plasmas 14, 062503 (2007).

  7. Testing the relevance of effective interaction potentials between highly-charged colloids in suspension

    NASA Astrophysics Data System (ADS)

    Dobnikar, J.; Castañeda-Priego, R.; von Grünberg, H. H.; Trizac, E.

    2006-11-01

    Combining cell and Jellium model mean-field approaches, Monte Carlo together with integral equation techniques, and finally more demanding many-colloid mean-field computations, we investigate the thermodynamic behaviour, pressure and compressibility of highly-charged colloidal dispersions, and at a more microscopic level, the force distribution acting on the colloids. The Kirkwood Buff identity provides a useful probe to challenge the self-consistency of an approximate effective screened Coulomb (Yukawa) potential between colloids. Two effective parameter models are put to the test: cell against renormalized Jellium models.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  9. Spatial inhomogeneities in ionic liquids, charged proteins, and charge stabilized colloids from collective variables theory

    NASA Astrophysics Data System (ADS)

    Patsahan, O.; Ciach, A.

    2012-09-01

    Effects of size and charge asymmetry between oppositely charged ions or particles on spatial inhomogeneities are studied for a large range of charge and size ratios. We perform a stability analysis of the primitive model of ionic systems with respect to periodic ordering using the collective variables-based theory. We extend previous studies [Ciach , Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.75.051505 75, 051505 (2007)] in several ways. First, we employ a nonlocal approximation for the reference hard-sphere fluid which leads to the Percus-Yevick pair direct correlation functions for the uniform case. Second, we use the Weeks-Chandler-Anderson regularization scheme for the Coulomb potential inside the hard core. We determine the relevant order parameter connected with the periodic ordering and analyze the character of the dominant fluctuations along the λ lines. We show that the above-mentioned modifications produce large quantitative and partly qualitative changes in the phase diagrams obtained previously. We discuss possible scenarios of the periodic ordering for the whole range of size and charge ratios of the two ionic species, covering electrolytes, ionic liquids, charged globular proteins or nanoparticles in aqueous solutions, and charge-stabilized colloids.

  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. Long-Ranged Oppositely Charged Interactions for Designing New Types of Colloidal Clusters

    NASA Astrophysics Data System (ADS)

    Demirörs, Ahmet Faik; Stiefelhagen, Johan C. P.; Vissers, Teun; Smallenburg, Frank; Dijkstra, Marjolein; Imhof, Arnout; van Blaaderen, Alfons

    2015-04-01

    Getting control over the valency of colloids is not trivial and has been a long-desired goal for the colloidal domain. Typically, tuning the preferred number of neighbors for colloidal particles requires directional bonding, as in the case of patchy particles, which is difficult to realize experimentally. Here, we demonstrate a general method for creating the colloidal analogs of molecules and other new regular colloidal clusters without using patchiness or complex bonding schemes (e.g., DNA coating) by using a combination of long-ranged attractive and repulsive interactions between oppositely charged particles that also enable regular clusters of particles not all in close contact. We show that, due to the interplay between their attractions and repulsions, oppositely charged particles dispersed in an intermediate dielectric constant (4 <ɛ <10 ) provide a viable approach for the formation of binary colloidal clusters. Tuning the size ratio and interactions of the particles enables control of the type and shape of the resulting regular colloidal clusters. Finally, we present an example of clusters made up of negatively charged large and positively charged small satellite particles, for which the electrostatic properties and interactions can be changed with an electric field. It appears that for sufficiently strong fields the satellite particles can move over the surface of the host particles and polarize the clusters. For even stronger fields, the satellite particles can be completely pulled off, reversing the net charge on the cluster. With computer simulations, we investigate how charged particles distribute on an oppositely charged sphere to minimize their energy and compare the results with the solutions to the well-known Thomson problem. We also use the simulations to explore the dependence of such clusters on Debye screening length κ-1 and the ratio of charges on the particles, showing good agreement with experimental observations.

  12. Binary mixtures of rod-like colloids under shear: microscopically-based equilibrium theory and order-parameter dynamics

    NASA Astrophysics Data System (ADS)

    Lugo-Frías, Rodrigo; Klapp, Sabine H. L.

    2016-06-01

    This paper is concerned with the dynamics of a binary mixture of rod-like, repulsive colloidal particles driven out of equilibrium by means of a steady shear flow (Couette geometry). To this end we first derive, starting from a microscopic density functional in Parsons–Lee approximation, a mesoscopic free energy functional whose main variables are the orientational order parameter tensors. Based on this mesoscopic functional we then explore the stability of isotropic and nematic equilibrium phases in terms of composition and rod lengths. Second, by combining the equilibrium theory with the Doi–Hess approach for the order parameter dynamics under shear, we investigate the orientational dynamics of binary mixtures for a range of shear rates and coupling parameters. We find a variety of dynamical states, including synchronized oscillatory states of the two components, but also symmetry breaking behavior where the components display different in-plane oscillatory states.

  13. Binary mixtures of rod-like colloids under shear: microscopically-based equilibrium theory and order-parameter dynamics.

    PubMed

    Lugo-Frías, Rodrigo; Klapp, Sabine H L

    2016-06-22

    This paper is concerned with the dynamics of a binary mixture of rod-like, repulsive colloidal particles driven out of equilibrium by means of a steady shear flow (Couette geometry). To this end we first derive, starting from a microscopic density functional in Parsons-Lee approximation, a mesoscopic free energy functional whose main variables are the orientational order parameter tensors. Based on this mesoscopic functional we then explore the stability of isotropic and nematic equilibrium phases in terms of composition and rod lengths. Second, by combining the equilibrium theory with the Doi-Hess approach for the order parameter dynamics under shear, we investigate the orientational dynamics of binary mixtures for a range of shear rates and coupling parameters. We find a variety of dynamical states, including synchronized oscillatory states of the two components, but also symmetry breaking behavior where the components display different in-plane oscillatory states. PMID:27115342

  14. 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.

  15. The Orbit of Water Droplets Around Charged Rod

    NASA Astrophysics Data System (ADS)

    Ferstl, Andrew; Burns, Andrew

    2013-05-01

    The motion of charges around a centrally charged object is often compared to gravitational orbits (such as satellites around planets). Recently, a video taken by astronaut Don Pettit onboard the International Space Station shows water droplets orbiting a charged knitting needle. Here we attempt to model this motion and estimate the charges on the objects involved in this system.

  16. The Orbit of Water Droplets around Charged Rod

    ERIC Educational Resources Information Center

    Ferstl, Andrew; Burns, Andrew

    2013-01-01

    The motion of charges around a centrally charged object is often compared to gravitational orbits (such as satellites around planets). Recently, a video taken by astronaut Don Pettit onboard the International Space Station shows water droplets orbiting a charged knitting needle. Here we attempt to model this motion and estimate the charges on the…

  17. Phase Behavior of Charged Colloids and the Effect of External Fields

    NASA Astrophysics Data System (ADS)

    Hynninen, A.-P.

    2005-12-01

    Colloids are particles with a size in the nano- to micrometer range that are dispersed in a solvent, and that due to collisions from the solvent molecules, undergo Brownian motion. In most cases, the surface of the colloid acquires a net charge due to dissociation of chemical groups at the surface. In this thesis, we present results of computer simulations on the phase behavior of charged colloidal suspensions using various levels of description: Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, DLVO theory with effective many-body interactions, and the primitive model. We make two attempts to amend the DLVO theory to include many-body interactions: (i) density-dependent truncation and (ii) three-body interactions. In the case of three-body interactions, we find at low salt concentration a very broad coexistence between a fluid and a dense face-centered-cubic (fcc) phase, while at intermediate salt concentration a broad body-centered-cubic (bcc)-fcc coexistence regime appears. However, in our primitive model calculations, we did not find any broad coexistence regions or any other manifestations of three-body interactions. Thus, the effective Hamiltonian of charged colloids seems to be better described by the standard pairwise DLVO potential, than by a Hamiltonian including a density-dependent truncation or three-body interactions. We study the gas-liquid critical point of asymmetric electrolyte mixtures consisting of large multivalent macroions and small monovalent co- and counterions. The system can be seen as a binary mixture of colloids with their counterions and salt at strong electrostatic coupling. We calculate the critical point locus that connects the salt-free state consisting of macroions and counterions with the pure salt state. We calculate the ground-state phase diagram of a mixture of large and small (size ratio 0.31) oppositely charged colloids. The phase diagram displays novel structures, but also colloidal analogs of simple-salt structures and of

  18. Surface treatment of silica nanoparticles for stable and charge-controlled colloidal silica

    PubMed Central

    Kim, Kyoung-Min; Kim, Hye Min; Lee, Won-Jae; Lee, Chang-Woo; Kim, Tae-il; Lee, Jong-Kwon; Jeong, Jayoung; Paek, Seung-Min; Oh, Jae-Min

    2014-01-01

    An attempt was made to control the surface charge of colloidal silica nanoparticles with 20 nm and 100 nm diameters. Untreated silica nanoparticles were determined to be highly negatively charged and have stable hydrodynamic sizes in a wide pH range. To change the surface to a positively charged form, various coating agents, such as amine containing molecules, multivalent metal cation, or amino acids, were used to treat the colloidal silica nanoparticles. Molecules with chelating amine sites were determined to have high affinity with the silica surface to make agglomerations or gel-like networks. Amino acid coatings resulted in relatively stable silica colloids with a modified surface charge. Three amino acid moiety coatings (L-serine, L-histidine, and L-arginine) exhibited surface charge modifying efficacy of L-histidine > L-arginine > L-serine and hydrodynamic size preservation efficacy of L-serine > L-arginine > L-histidine. The time dependent change in L-arginine coated colloidal silica was investigated by measuring the pattern of the backscattered light in a Turbiscan™. The results indicated that both the 20 nm and 100 nm L-arginine coated silica samples were fairly stable in terms of colloidal homogeneity, showing only slight coalescence and sedimentation. PMID:25565824

  19. Electrostatic Deformation of Liquid Surfaces by a Charged Rod and a Van De Graaff Generator

    ERIC Educational Resources Information Center

    Slisko, Josip; García-Molina, Rafael; Abril, Isabel

    2014-01-01

    Authors of physics textbooks frequently use the deflection of a thin, vertically falling water jet by a charged balloon, comb, or rod as a visually appealing and conceptually relevant example of electrostatic attraction. Nevertheless, no attempts are made to explore whether these charged bodies could cause visible deformation of a horizontal water…

  20. Electrostatic Deformation of Liquid Surfaces by a Charged Rod and a Van de Graaff Generator

    NASA Astrophysics Data System (ADS)

    Slisko, Josip; García-Molina, Rafael; Abril, Isabel

    2014-05-01

    Authors of physics textbooks frequently use the deflection of a thin, vertically falling water jet by a charged balloon, comb, or rod as a visually appealing and conceptually relevant example of electrostatic attraction. Nevertheless, no attempts are made to explore whether these charged bodies could cause visible deformation of a horizontal water surface. That being so, we were quite surprised when we discovered that a 19th-century French book10 contained a drawing showing an appreciable deformation of an oil surface caused by a charged rod. When we initially tried to recreate this electrostatics demonstration, we didn't succeed in reproducing the effect with a charged rod. Despite the initial unsuccessful try, we were not discouraged and we modified the demonstration a little bit, finding that it was possible to cause visible deformations of different liquid surfaces by using a Van de Graaff generator, as we will explain later.

  1. Simulation of electric double layers around charged colloids in aqueous solution of variable permittivity.

    PubMed

    Fahrenberger, Florian; Xu, Zhenli; Holm, Christian

    2014-08-14

    The ion distribution around charged colloids in solution has been investigated intensely during the last decade. However, few theoretical approaches have included the influence of variation in the dielectric permittivity within the system, let alone in the surrounding solvent. In this article, we introduce two relatively new methods that can solve the Poisson equation for systems with varying permittivity. The harmonic interpolation method approximately solves the Green's function in terms of a spherical harmonics series, and thus provides analytical ion-ion potentials for the Hamiltonian of charged systems. The Maxwell equations molecular dynamics algorithm features a local approach to electrostatics, allowing for arbitrary local changes of the dielectric constant. We show that the results of both methods are in very good agreement. We also found that the renormalized charge of the colloid, and with it the effective far field interaction, significantly changes if the dielectric properties within the vicinity of the colloid are changed. PMID:25134594

  2. Like-charge interactions between colloidal particles are asymmetric with respect to sign†

    PubMed Central

    Gomez, Esther W.; Clack, Nathan G.; Wu, Hung-Jen; Groves, Jay T.

    2014-01-01

    Two-dimensional dispersions of colloidal particles with a range of surface chemistries and electrostatic potentials are characterized under a series of solution ionic strengths. A combination of optical imaging techniques are employed to monitor both the colloid structure and the electrostatic surface potential of individual particles in situ. We find that like-charge multiparticle interactions can be tuned from exclusively repulsive to long-range attractive by changing the particle surface composition. This behavior is strongly asymmetric with respect to the sign of the surface potential. Collective long-range attractive interactions are only observed among negatively charged particles. PMID:25221611

  3. Spatial configurations of charged rod-like particles in external electric field

    NASA Astrophysics Data System (ADS)

    Lisina, I.; Lisin, E.; Vaulina, O.

    2016-03-01

    Formation of different spatial configurations for system of charged rod-like particles is considered theoretically and numerically, including formation of layered structures in the external electric field. Analytical model for a determination of the angle between the axis of a rod and the symmetry axis of electric trap is presented. New algorithm is proposed here for a dynamical simulation of many interacting non-spherical particles. Conditions for a correct replacement of the interaction between uniformly charged rods by the interaction of "bipoles" (i.e., by two similar point charges) are obtained. Study was performed in a wide range of parameters that are similar to conditions of laboratory experiments in a dusty plasma.

  4. Investigating forces between charged particles in the presence of oppositely charged polyelectrolytes with the multi-particle colloidal probe technique.

    PubMed

    Borkovec, Michal; Szilagyi, Istvan; Popa, Ionel; Finessi, Marco; Sinha, Prashant; Maroni, Plinio; Papastavrou, Georg

    2012-11-01

    Direct force measurements are used to obtain a comprehensive picture of interaction forces acting between charged colloidal particles in the presence of oppositely charged polyelectrolytes. These measurements are achieved by the multi-particle colloidal probe technique based on the atomic force microscope (AFM). This novel extension of the classical colloidal probe technique offers three main advantages. First, the technique works in a colloidal suspension with a huge internal surface area of several square meters, which simplifies the precise dosing of the small amounts of the polyelectrolytes needed and makes this approach less sensitive to impurities. Second, the particles are attached in-situ within the fluid cell, which avoids the formation of nanobubbles on the latex particles used. Third, forces between two similar particles from the same batch are being measured, which allows an unambiguous determination of the surface potential due to the symmetry of the system. Based on such direct force measurements involving positively and negatively charged latex particles and different polyelectrolytes, we find the following forces to be relevant. Repulsive electrostatic double-layer forces and attractive van der Waals forces as described by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) are both important in these systems, whereby the electrostatic forces dominate away from the isoelectric point (IEP), while at this point they vanish. Additional non-DLVO attractive forces are operational, and they have been identified to originate from the electrostatic interactions between the patch-charge heterogeneities of the adsorbed polyelectrolyte films. Highly charged polyelectrolytes induce strong patch-charge attractions, which become especially important at low ionic strengths and high molecular mass. More weakly charged polyelectrolytes seem to form more homogeneous films, whereby patch-charge attractions may become negligible. Individual bridging events

  5. Thermoreversible crystallization of charged colloids due to adsorption/desorption of ionic surfactants.

    PubMed

    Murakado, Ai; Toyotama, Akiko; Yamamoto, Masaaki; Nagano, Ryota; Okuzono, Tohru; Yamanaka, Junpei

    2016-03-01

    We report that charged colloids exhibit thermoreversible crystallization via the adsorption of ionic surfactants onto particle surfaces. Due to the temperature dependence of the adsorption quantity, the colloids crystallized upon cooling and melted upon heating. To clarify the influences of surfactant adsorption on the crystallization, polystyrene (PS) particles dispersed in ethylene glycol (EG)/water mixtures were employed, enabling continuous tuning of the adsorption quantity by changing the EG concentration. The thermoreversible crystallization/melting behavior was found to be mainly attributable to changes in the ionic strength of the medium resulting from variation in the concentration of the non-adsorbed ionic surfactant molecules with temperature. We expect that the present findings will be useful for fine control of colloidal crystallization and the further study of colloidal crystallization in low permittivity media. PMID:26674236

  6. A common neighbor analysis of crystallization kinetics and excess entropy of charged spherical colloids.

    PubMed

    Urrutia Bañuelos, Efraín; Contreras Aburto, Claudio; Maldonado Arce, Amir

    2016-03-01

    The topological analysis tool known as the common neighbor analysis (CNA) is used for the first time in this work to analyze crystallization kinetics and excess entropy of charge-stabilized colloidal suspensions. For this purpose, Brownian dynamics computer simulations are implemented to investigate the crystallization kinetics of homogeneously melted colloidal crystals that are composed of hard-core-screened-Coulomb interacting particles. The results are in agreement with recent static structure factor measurements that could indicate the presence of icosahedral units in the metastable melt, and with the fact that weakly screened charged colloids crystallize into body-centered-cubic (bcc) ordering. A two-step crystallization pathway is found, in which the population of bcc-subunit CNA-pairs satisfactorily obeys a Verhulst model. Moreover, the CNA helped to unveil that the excess entropy obeys a quasi-universal functional form, relating the behavior of colloidal, molecular, and metallic liquid systems. The work contributes to the scientific understanding of the crystallization pathway of charged colloids, and to the development of new ways to assess the degree of crystalline order, starting from the excess entropy. PMID:26957168

  7. A common neighbor analysis of crystallization kinetics and excess entropy of charged spherical colloids

    NASA Astrophysics Data System (ADS)

    Urrutia Bañuelos, Efraín; Contreras Aburto, Claudio; Maldonado Arce, Amir

    2016-03-01

    The topological analysis tool known as the common neighbor analysis (CNA) is used for the first time in this work to analyze crystallization kinetics and excess entropy of charge-stabilized colloidal suspensions. For this purpose, Brownian dynamics computer simulations are implemented to investigate the crystallization kinetics of homogeneously melted colloidal crystals that are composed of hard-core-screened-Coulomb interacting particles. The results are in agreement with recent static structure factor measurements that could indicate the presence of icosahedral units in the metastable melt, and with the fact that weakly screened charged colloids crystallize into body-centered-cubic (bcc) ordering. A two-step crystallization pathway is found, in which the population of bcc-subunit CNA-pairs satisfactorily obeys a Verhulst model. Moreover, the CNA helped to unveil that the excess entropy obeys a quasi-universal functional form, relating the behavior of colloidal, molecular, and metallic liquid systems. The work contributes to the scientific understanding of the crystallization pathway of charged colloids, and to the development of new ways to assess the degree of crystalline order, starting from the excess entropy.

  8. Evaporation of sessile drops containing colloidal rods: coffee-ring and order-disorder transition.

    PubMed

    Dugyala, Venkateshwar Rao; Basavaraj, Madivala G

    2015-03-01

    Liquid drops containing insoluble solutes when dried on solid substrates leave distinct ring-like deposits at the periphery or along the three-phase contact line-a phenomena popularly known as the coffee-ring or the coffee stain effect. The formation of such rings as well as their suppression is shown to have applications in particle separation and disease diagnostics. We present an experimental study of the evaporation of sessile drops containing silica rods to elucidate the structural arrangement of particles in the ring, an effect of the addition of surfactant and salt. To this end, the evaporation of aqueous sessile drops containing model rod-like silica particles of aspect ratio ranging from ∼4 to 15 on a glass slide is studied. We first show that when the conditions such as (1) solvent evaporation, (2) nonzero contact angle, (3) contact line pinning, (4) no surface tension gradient driven flow, and (5) repulsive particle-particle/particle-substrate interactions, that are necessary for the formation of the coffee-ring are met, the suspension drops containing silica rods upon evaporation leave a ring-like deposit. A closer examination of the ring deposits reveals that several layers of silica rods close to the edge of the drop are ordered such that the major axis of the rods are oriented parallel to the contact line. After the first few layers of ordered arrangement of particles, a random arrangement of particles in the drop interior is observed indicating an order-disorder transition in the ring. We monitor the evolution of the ring width and particle velocity during evaporation to elucidate the mechanism of the order-disorder transition. Moreover, when the evaporation rate is lowered, the ordering of silica rods is observed to extend over large areas. We demonstrate that the nature of the deposit can be tuned by the addition of a small quantity of surfactant or salt. PMID:25521279

  9. Phase behaviour of a dispersion of charge-stabilised colloidal spheres with added non-adsorbing interacting polymer chains.

    PubMed

    Gögelein, C; Tuinier, R

    2008-10-01

    We present a theory for the phase behaviour of mixtures of charge-stabilised colloidal spheres plus interacting polymer chains in good and theta -solvents within the framework of free-volume theory. We use simple but accurate combination rules for the depletion thickness around a colloidal particle and for the osmotic pressure up to the semi-dilute concentration regime. Hence, we obtain expressions for the free energy for mixtures of charged colloidal particles and non-adsorbing interacting polymers. From that, we calculate the phase behaviour, and discuss its topology in dependence on the competition between the charge-induced repulsion and the polymer-induced attraction. The homogeneous mixture of colloids and polymers becomes more stabilised against demixing when increasing the electrostatic repulsion. This charge-induced stabilisation is strongest for small polymer-to-colloid size ratios and is more pronounced for charged colloids mixed with polymers in a good solvent than for polymers in a theta -solvent. For the weakly charged regime we find that the phase diagram becomes salt-concentration-independent in the protein limit for charged colloids plus polymers in a theta -solvent. The liquid window, i.e., the concentration regimes where a colloidal liquid exists, is narrowed down upon increasing the charge-induced repulsion. Also this effect is more pronounced when charged colloids are mixed with polymer chains in a good solvent. In summary, we demonstrate that the solvent quality significantly influences the phase behaviour of mixtures of charged colloids plus non-adsorbing polymers if the range of the screened electrostatic repulsion becomes of the order of the range of the depletion-induced attraction. PMID:18791755

  10. Dumping topological charges on neighbors: ice manifolds for colloids and vortices

    NASA Astrophysics Data System (ADS)

    Nisoli, Cristiano

    2014-11-01

    We investigate the recently reported analogies between pinned vortices in nano-structured superconductors or colloids in optical traps, and spin ice materials. It has been found experimentally and numerically that both colloids and vortices exhibit ice or quasi-ice manifolds. However, the frustration of colloids and vortices differs essentially from spin ice at the vertex level. We show that the effective vertex energetics of the colloidal/vortex systems is made identical to that of spin ice materials by the contribution of an emergent field associated to the topological charge of the vertex. The similarity extends to the local low-energy dynamics of the ice manifold, where the effect of geometric hard constraints can be subsumed into the spatial modulation of the emergent field, which mediates an entropic interaction between topological charges. There, as in spin ice materials, genuine ice manifolds enter a Coulomb phase, whereas quasi-ice manifolds posses a well defined screening length, provided by a plasma of embedded topological charges. We also show that such similarities break down in lattices of mixed coordination because of topological charge transfer between sub-latices. This opens interesting perspective for extensions beyond physics, to social and economical networks.

  11. Anion-Dependent Aggregate Formation and Charge Behavior of Colloidal Fullerenes (n-C60)

    EPA Science Inventory

    The fate and transport of colloidal fullerenes (n-C60) in the environment is likely to be guided by electrokinetic and aggregation behavior. In natural water bodies inorganic ions exert significant effects in determining the size and charge of n-C60 nanoparticles. Although the ef...

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

    PubMed

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

    2004-06-01

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

  13. Mixtures of charged colloid and neutral polymer: influence of electrostatic interactions on demixing and interfacial tension.

    PubMed

    Denton, Alan R; Schmidt, Matthias

    2005-06-22

    The equilibrium phase behavior of a binary mixture of charged colloids and neutral, nonadsorbing polymers is studied within free-volume theory. A model mixture of charged hard-sphere macroions and ideal, coarse-grained, effective-sphere polymers is mapped first onto a binary hard-sphere mixture with nonadditive diameters and then onto an effective Asakura-Oosawa model [S. Asakura and F. Oosawa, J. Chem. Phys. 22, 1255 (1954)]. The effective model is defined by a single dimensionless parameter-the ratio of the polymer diameter to the effective colloid diameter. For high salt-to-counterion concentration ratios, a free-volume approximation for the free energy is used to compute the fluid phase diagram, which describes demixing into colloid-rich (liquid) and colloid-poor (vapor) phases. Increasing the range of electrostatic interactions shifts the demixing binodal toward higher polymer concentration, stabilizing the mixture. The enhanced stability is attributed to a weakening of polymer depletion-induced attraction between electrostatically repelling macroions. Comparison with predictions of density-functional theory reveals a corresponding increase in the liquid-vapor interfacial tension. The predicted trends in phase stability are consistent with observed behavior of protein-polysaccharide mixtures in food colloids. PMID:16035820

  14. Surface charges and optical characteristic of colloidal cubic SiC nanocrystals

    PubMed Central

    2011-01-01

    Colloidal cubic silicon carbide (SiC) nanocrystals with an average diameter of 4.4 nm have been fabricated by anisotropic wet chemical etching of microsized cubic SiC powder. Fourier transform infrared spectra show that these cubic SiC nanocrystals contain carboxylic acid, SiH, CH, and CHx groups. UV/Vis absorption and photoluminescence (PL) spectroscopy clearly indicate that water and ethanol colloidal suspensions of the as-fabricated colloidal samples exhibit strong and above band gap blue and blue-green emissions. The cubic SiC nanocrystals show different surface charges in water and ethanol solutions due to the interaction of water molecules with polar Si-terminated surfaces of cubic SiC nanocrystals. The results explain the distinctive optical characteristics of colloidal cubic SiC nanocrystals in water and ethanol, and reveal that quantum confinement and surface charges play a great role in determining the optical characteristics of colloidal cubic SiC nanocrystals. PMID:21762496

  15. Surface charges and optical characteristic of colloidal cubic SiC nanocrystals

    NASA Astrophysics Data System (ADS)

    Li, Yong; Chen, Changxin; Li, Jiang-Tao; Yang, Yun; Lin, Zhi-Ming

    2011-07-01

    Colloidal cubic silicon carbide (SiC) nanocrystals with an average diameter of 4.4 nm have been fabricated by anisotropic wet chemical etching of microsized cubic SiC powder. Fourier transform infrared spectra show that these cubic SiC nanocrystals contain carboxylic acid, SiH, CH, and CHx groups. UV/Vis absorption and photoluminescence (PL) spectroscopy clearly indicate that water and ethanol colloidal suspensions of the as-fabricated colloidal samples exhibit strong and above band gap blue and blue-green emissions. The cubic SiC nanocrystals show different surface charges in water and ethanol solutions due to the interaction of water molecules with polar Si-terminated surfaces of cubic SiC nanocrystals. The results explain the distinctive optical characteristics of colloidal cubic SiC nanocrystals in water and ethanol, and reveal that quantum confinement and surface charges play a great role in determining the optical characteristics of colloidal cubic SiC nanocrystals.

  16. Recrystallization and zone melting of charged colloids by thermally induced crystallization.

    PubMed

    Shinohara, Mariko; Toyotama, Akiko; Suzuki, Misaki; Sugao, Yukihiro; Okuzono, Tohru; Uchida, Fumio; Yamanaka, Junpei

    2013-08-01

    We examined the application of recrystallization and zone-melting crystallization methods, which have been used widely to fabricate large, high-purity crystals of atomic and molecular systems, to charged colloidal crystals. Our samples were aqueous dispersions of colloidal silica (with particle diameters of d = 108 or 121 nm and particle volume fractions of ϕ = 0.035-0.05) containing the weak base pyridine. The samples crystallized upon heating because of increases in the particle charge numbers, and they melted reversibly on cooling. During the recrystallization experiments, the polycrystalline colloids were partially melted in a Peltier cooling device and then were crystallized by stopping the cooling and allowing the system to return to ambient temperature. The zone-melting crystallization was carried out by melting a narrow zone (millimeter-sized in width) of the polycrystalline colloid samples and then moving the sample slowly over a cooling device to recrystallize the molten region. Using both methods, we fabricated a few centimeter-sized crystals, starting from millimeter-sized original polycrystals when the crystallization rates were sufficiently slow (33 μm/s). Furthermore, the optical quality of the colloidal crystals, such as the half-band widths of the diffraction peaks, was significantly improved. These methods were also useful for refining. Small amounts of impurity particles (fluorescent polystyrene particles, d = 333 nm, ϕ = 5 × 10(-5)), added to the colloidal crystals, were excluded from the crystals when the crystallization rates were sufficiently slow (∼0.1 μm/s). We expect that the present findings will be useful for fabricating large, high-purity colloidal crystals. PMID:23841755

  17. Liquid-liquid and liquid-solid phase separation and flocculation for a charged colloidal dispersion.

    PubMed

    Lai, S K; Wu, K L

    2002-10-01

    We model the intercolloidal interaction by a hard-sphere Yukawa repulsion to which is added the long-range van der Waals attraction. In comparison with the Derjaguin-Landau-Verwey-Overbeek repulsion, the Yukawa repulsion explicitly incorporates the spatial correlations between colloids and small ions. As a result, the repulsive part can be expressed analytically and has a coupling strength depending on the colloidal volume fraction. By use of this two-body potential of mean force and in conjunction with a second-order thermodynamic perturbation theory, we construct the colloidal Helmholtz free energy and use it to calculate the thermodynamic quantities, pressure and chemical potential, needed in the determination of the liquid-liquid and liquid-solid phase diagrams. We examine, in an aqueous charged colloidal dispersion, the effects of the Hamaker constant and particle size on the conformation of a stable liquid-liquid phase transition calculated with respect to the liquid-solid coexistence phases. We find that there exists a threshold Hamaker constant or particle size whose value demarcates the stable liquid-liquid coexistence phases from their metastable counterparts. Applying the same technique and using the energetic criterion, we extend our calculations to study the flocculation phenomenon in aqueous charged colloids. Here, we pay due attention to determining the loci of a stability curve stipulated for a given temperature T0, and obtain the parametric phase diagram of the Hamaker constant vs the coupling strength or, at given surface potential, the particle size. By imposing T0 to be the critical temperature T(c), i.e., setting k(B)T0 (=k(B)T(c)) equal to a reasonable potential barrier, we arrive at the stability curve that marks the irreversible/reversible phase transition. The interesting result is that there occurs a minimum size for the colloidal particles below (above) which the colloidal dispersion is driven to an irreversible (reversible) phase

  18. Modified Mason number for charged paramagnetic colloidal suspensions

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  19. Anharmonic and screening corrections to the melting of a two-dimensional charged colloidal crystal

    NASA Technical Reports Server (NTRS)

    Chang, Enson; Hone, Daniel W.

    1988-01-01

    The Kosterlitz-Thouless-Halperin-Nelson-Young theory of melting is applied to a two-dimensional charged colloidal crystal. The renormalization of elastic constants due to anharmonic and dislocation pair-screening effects is calculated. For colloidal spheres ('polyballs') suspended in a thin film of water confined between two glass plates whose surfaces are highly charged, as in recent experimental configurations, the corrections to the harmonic results simply require an altered effective polyball charge to reproduce virtually the identical melting curve of the harmonic approximation (which agrees well with experiment). The effect on the melting curve of added salt is also calculated; the corresponding experiments have yet to be performed. For a film between uncharged surfaces the anharmonic correction again softens the lattice significantly. Dislocation pair screening causes an additional but minor reduction of the elastic constants. Neither correction eliminates a nonmelting behavior characteristic of the two-dimensional screened Coulomb system in this configuration.

  20. Thermodiffusion in positively charged magnetic colloids: influence of the particle diameter.

    PubMed

    Sehnem, A L; Aquino, R; Campos, A F C; Tourinho, F A; Depeyrot, J; Figueiredo Neto, A M

    2014-03-01

    The Soret coefficient (ST) of positively charged magnetic colloids was measured as a function of the nanoparticles' diameter. The Z-scan technique and the generalization of the thermal lens model proved to be a reliable technique to measure ST. We show that ST is negative and increases with the particle's diameter, being best described by a functional dependence of the type ST∝d0. Potentiometric and conductometric experiments show that the particle's surface charge decreases as the temperature increases, changing the electrostatic interaction between the nanoparticles. The temperature gradient imposed in the ferrofluid by the Gaussian laser beam leads to the formation of the particle's concentration gradient. The origin of this phenomenon is discussed in terms of the decrease of the particle's surface charge in the hottest region of the sample and the thermoelectric field due to the inhomogeneous distribution of hydrogenous ions present in the colloidal suspension. PMID:24730843

  1. Effects of metal oxide nanoparticles on the stability of dispersions of weakly charged colloids.

    PubMed

    Herman, David; Walz, John Y

    2015-05-01

    The stability behavior of dispersions of weakly charged silica colloids was studied in the presence of highly charged metal oxide nanoparticles. Experiments were performed using 5 nm zirconia as well as 10 nm alumina nanoparticles (both positively charged), which were added to 0.1 vol % suspensions of 1.0 μm silica microparticles at the silica IEP. Both types of nanoparticles provided effective stabilization of the silica; i.e., the silica suspensions were stabilized for longer than the observation period (greater than 12 h). Stability was observed at zirconia concentrations as low as 10(-4) vol % and at an alumina concentration of 10(-2) vol %. The nanoparticles adsorbed onto the microparticle surfaces (confirmed via SEM imaging), which increased the zeta-potential of the silica. Force profile measurements performed with colloidal probe atomic force microscopy showed that the adsorption was effectively irreversible. PMID:25860256

  2. 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.

  3. 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

  4. Spontaneous Formation of Eutectic Crystal Structures in Binary and Ternary Charged Colloids due to Depletion Attraction

    PubMed Central

    Toyotama, Akiko; Okuzono, Tohru; Yamanaka, Junpei

    2016-01-01

    Crystallization of colloids has extensively been studied for past few decades as models to study phase transition in general. Recently, complex crystal structures in multi-component colloids, including alloy and eutectic structures, have attracted considerable attention. However, the fabrication of 2D area-filling colloidal eutectics has not been reported till date. Here, we report formation of eutectic structures in binary and ternary aqueous colloids due to depletion attraction. We used charged particles + linear polyelectrolyte systems, in which the interparticle interaction could be represented as a sum of the electrostatic, depletion, and van der Waals forces. The interaction was tunable at a lengthscale accessible to direct observation by optical microscopy. The eutectic structures were formed because of interplay of crystallization of constituent components and accompanying fractionation. An observed binary phase diagram, defined by a mixing ratio and inverse area fraction of the particles, was analogous to that for atomic and molecular eutectic systems. This new method also allows the adjustment of both the number and wavelengths of Bragg diffraction peaks. Furthermore, these eutectic structures could be immobilized in polymer gel to produce self-standing materials. The present findings will be useful in the design of the optical properties of colloidal crystals. PMID:26984298

  5. Spontaneous Formation of Eutectic Crystal Structures in Binary and Ternary Charged Colloids due to Depletion Attraction

    NASA Astrophysics Data System (ADS)

    Toyotama, Akiko; Okuzono, Tohru; Yamanaka, Junpei

    2016-03-01

    Crystallization of colloids has extensively been studied for past few decades as models to study phase transition in general. Recently, complex crystal structures in multi-component colloids, including alloy and eutectic structures, have attracted considerable attention. However, the fabrication of 2D area-filling colloidal eutectics has not been reported till date. Here, we report formation of eutectic structures in binary and ternary aqueous colloids due to depletion attraction. We used charged particles + linear polyelectrolyte systems, in which the interparticle interaction could be represented as a sum of the electrostatic, depletion, and van der Waals forces. The interaction was tunable at a lengthscale accessible to direct observation by optical microscopy. The eutectic structures were formed because of interplay of crystallization of constituent components and accompanying fractionation. An observed binary phase diagram, defined by a mixing ratio and inverse area fraction of the particles, was analogous to that for atomic and molecular eutectic systems. This new method also allows the adjustment of both the number and wavelengths of Bragg diffraction peaks. Furthermore, these eutectic structures could be immobilized in polymer gel to produce self-standing materials. The present findings will be useful in the design of the optical properties of colloidal crystals.

  6. Spontaneous Formation of Eutectic Crystal Structures in Binary and Ternary Charged Colloids due to Depletion Attraction.

    PubMed

    Toyotama, Akiko; Okuzono, Tohru; Yamanaka, Junpei

    2016-01-01

    Crystallization of colloids has extensively been studied for past few decades as models to study phase transition in general. Recently, complex crystal structures in multi-component colloids, including alloy and eutectic structures, have attracted considerable attention. However, the fabrication of 2D area-filling colloidal eutectics has not been reported till date. Here, we report formation of eutectic structures in binary and ternary aqueous colloids due to depletion attraction. We used charged particles + linear polyelectrolyte systems, in which the interparticle interaction could be represented as a sum of the electrostatic, depletion, and van der Waals forces. The interaction was tunable at a lengthscale accessible to direct observation by optical microscopy. The eutectic structures were formed because of interplay of crystallization of constituent components and accompanying fractionation. An observed binary phase diagram, defined by a mixing ratio and inverse area fraction of the particles, was analogous to that for atomic and molecular eutectic systems. This new method also allows the adjustment of both the number and wavelengths of Bragg diffraction peaks. Furthermore, these eutectic structures could be immobilized in polymer gel to produce self-standing materials. The present findings will be useful in the design of the optical properties of colloidal crystals. PMID:26984298

  7. Temporary Charge Carrier Separation Dominates the Photoluminescence Decay Dynamics of Colloidal CdSe Nanoplatelets.

    PubMed

    Rabouw, Freddy T; van der Bok, Johanna C; Spinicelli, Piernicola; Mahler, Benoît; Nasilowski, Michel; Pedetti, Silvia; Dubertret, Benoît; Vanmaekelbergh, Daniël

    2016-03-01

    Luminescent colloidal CdSe nanoplatelets with atomically defined thicknesses have recently been developed, and their potential for various applications has been shown. To understand their special properties, experiments have until now focused on the relatively short time scales of at most a few nanoseconds. Here, we measure the photoluminescence decay dynamics of colloidal nanoplatelets on time scales up to tens of microseconds. The excited state dynamics are found to be dominated by the slow (∼μs) dynamics of temporary exciton storage in a charge-separated state, previously overlooked. We study the processes of charge carrier separation and exciton recovery in pure CdSe nanoplatelets as well as in core-crown and core-shell CdSe/CdS nanoplatelets with high ensemble quantum yields of 50%, and discuss the implications. Our work highlights the importance of reversible charge carrier trapping and experiments over a wide range of time scales for the understanding of colloidal nanoemitters in general and nanoplatelets in particular. PMID:26863992

  8. 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

  9. Asymmetrical phase separation and gelation in binary mixtures of oppositely charged colloids

    NASA Astrophysics Data System (ADS)

    Zong, Yiwu; Yuan, Guangcui; Han, Charles C.

    2016-07-01

    Two types of colloidal particles, which are nearly the same in chemical composition but carry opposite surface charges, are mixed in water. Depending on the relative proportion of the oppositely charged particles, the process of aggregation leads to the formation of discrete clusters of various sizes in dilute dispersions, and to the development of particle gel networks in more concentrated systems. Due to the significant difference in the absolute values of surface charges (negative particle: -48 mV, positive particle: +24 mV), the phase separation and the gelation behaviors are asymmetric with respect to the mixing ratio. Mixtures with excess negative particles are more stable, while mixtures with excess positive particles are easily affected by phase separation. The hetero-aggregation triggered by the addition of microscopically large macro-ions is similar to what is often observed in a mono-component charged colloidal system, i.e., phase separation occurs through addition of small electrolyte ions. Within the concentration region investigated here, it is clear that the gel line is buried inside the phase separation region. Gelation occurs only when the number and size of the clusters are large and big enough to connect up into a space-spanning network. Our results indicate that, in this binary mixture of oppositely charged colloids, although the interaction between unlike species is attractive and that between like species is repulsive, the onset of gelation is in fact governed by the equilibrium phase separation, as in the case of purely attractive systems with short-range isotropic interaction.

  10. Lattice-Boltzmann method for the simulation of transport phenomena in charged colloids.

    PubMed

    Horbach, J; Frenkel, D

    2001-12-01

    We present a simulation scheme based on the lattice-Boltzmann method to simulate the dynamics of charged colloids in an electrolyte. In our model we describe the electrostatics on the level of a Poisson-Boltzmann equation and the hydrodynamics of the fluid by the linearized Navier-Stokes equations. We verify our simulation scheme by means of a Chapman-Enskog expansion. Our method is applied to the calculation of the reduced sedimentation velocity U/U(0) for a cubic array of charged spheres in an electrolyte. We show that we recover the analytical solution first derived by Booth [F. Booth, J. Chem. Phys. 22, 1956 (1954)] for a weakly charged, isolated sphere in an unbounded electrolyte. The present method makes it possible to go beyond the Booth theory, and we discuss the dependence of the sedimentation velocity on the charge of the spheres. Finally we compare our results to experimental data. PMID:11736191

  11. Weakly nonlinear electrophoresis of a highly charged colloidal particle

    NASA Astrophysics Data System (ADS)

    Schnitzer, Ory; Zeyde, Roman; Yavneh, Irad; Yariv, Ehud

    2013-05-01

    At large zeta potentials, surface conduction becomes appreciable in thin-double-layer electrokinetic transport. In the linear weak-field regime, where this effect is quantified by the Dukhin number, it is manifested in non-Smoluchowski electrophoretic mobilities. In this paper we go beyond linear response, employing the recently derived macroscale model of Schnitzer and Yariv ["Macroscale description of electrokinetic flows at large zeta potentials: Nonlinear surface conduction," Phys. Rev. E 86, 021503 (2012), 10.1103/PhysRevE.86.021503] as the infrastructure for a weakly nonlinear analysis of spherical-particle electrophoresis. A straightforward perturbation in the field strength is frustrated by the failure to satisfy the far-field conditions, representing a non-uniformity of the weak-field approximation at large distances away from the particle, where salt advection becomes comparable to diffusion. This is remedied using inner-outer asymptotic expansions in the spirit of Acrivos and Taylor ["Heat and mass transfer from single spheres in Stokes flow," Phys. Fluids 5, 387 (1962), 10.1063/1.1706630], with the inner region representing the particle neighborhood and the outer region corresponding to distances scaling inversely with the field magnitude. This singular scheme furnishes an asymptotic correction to the electrophoretic velocity, proportional to the applied field cubed, which embodies a host of nonlinear mechanisms unfamiliar from linear electrokinetic theories. These include the effect of induced zeta-potential inhomogeneity, animated by concentration polarization, on electro-osmosis and diffuso-osmosis; bulk advection of salt; nonuniform bulk conductivity; Coulomb body forces acting on bulk volumetric charge; and the nonzero electrostatic force exerted upon the otherwise screened particle-layer system. A numerical solution of the macroscale model validates our weakly nonlinear analysis.

  12. Particle Segregation at Contact Lines of Evaporating Colloidal Drops: Influence of the Substrate Wettability and Particle Charge-Mass Ratio.

    PubMed

    Noguera-Marín, Diego; Moraila-Martínez, Carmen L; Cabrerizo-Vílchez, Miguel A; Rodríguez-Valverde, Miguel A

    2015-06-23

    Segregation of particles during capillary/convective self-assembly is interesting for self-stratification in colloidal deposits. In evaporating drops containing colloidal particles, the wettability properties of substrate and the sedimentation of particles can affect their accumulation at contact lines. In this work we studied the size segregation and discrimination of charged particles with different densities. We performed in-plane particle counting at evaporating triple lines by using fluorescence confocal microscopy. We studied separately substrates with very different wettability properties and particles with different charge-mass ratios at low ionic strength. We used binary colloidal suspensions to compare simultaneously the deposition of two different particles. The particle deposition rate strongly depends on the receding contact angle of the substrate. We further observed a singular behavior of charged polystyrene particles in binary mixtures under "salt-free" conditions explained by the "colloidal Brazil nut" effect. PMID:26000909

  13. Charge effects and nanoparticle pattern formation in electrohydrodynamic NanoDrip printing of colloids.

    PubMed

    Richner, Patrizia; Kress, Stephan J P; Norris, David J; Poulikakos, Dimos

    2016-03-21

    Advancing open atmosphere printing technologies to produce features in the nanoscale range has important and broad applications ranging from electronics to photonics, plasmonics and biology. Recently an electrohydrodynamic printing regime has been demonstrated in a rapid dripping mode (termed NanoDrip), where the ejected colloidal droplets from nozzles of diameters of O (1 μm) can controllably reach sizes an order of magnitude smaller than the nozzle and can generate planar and out-of-plane structures of similar sizes. Despite the demonstrated capabilities, our fundamental understanding of important aspects of the physics of NanoDrip printing needs further improvement. Here we address the topics of charge content and transport in NanoDrip printing. We employ quantum dot and gold nanoparticle dispersions in combination with a specially designed, auxiliary, asymmetric electric field, targeting the understanding of charge locality (particles vs. solvent) and particle distribution in the deposits as indicated by the dried nanoparticle patterns (footprints) on the substrate. We show that droplets of alternating charge can be spatially separated when applying an ac field to the nozzle. The nanoparticles within a droplet are distributed asymmetrically under the influence of the auxiliary lateral electric field, indicating that they are the main carriers. We also show that the ligand length of the nanoparticles in the colloid affects their mobility after deposition (in the sessile droplet state). PMID:26928324

  14. Surface vibrational structure of colloidal silica and its direct correlation with surface charge density.

    PubMed

    Lagström, Tove; Gmür, Tobias A; Quaroni, Luca; Goel, Alok; Brown, Matthew A

    2015-03-31

    We show that attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy can be used to determine the surface charge density (SCD) of colloidal silica nanoparticles (NPs) in aqueous solution. We identify the Si-O stretch vibrations of neutral surface bound silanol, ≡Si-OH, and of the deprotonated group, ≡Si-O(-). The position of the Si-(OH) stretch vibration is shown to directly correlate with the NPs SCD as determined by traditional potentiometric titrations, shifting to lower wavenumber (cm(-1)) with increasing density of ≡Si-O(-). The origin of this shift is discussed in terms of inductive effects that reduce the ionic character of the Si-(OH) bond after delocalization of the negative charge left on a terminal ≡Si-O(-) group across the atoms within ∼1 nm of the charged site. Using this new methodology, we quantitatively determine the SCD of 9, 14, and 25 nm diameter colloidal silica in varying concentrations of NaCl electrolyte at different bulk pH. This novel spectroscopic approach to investigate SCDs provides several opportunities for in situ coupling, for example, in microfluidic channels or with liquid microjets, and requires only very little sample—all potential advantages over a traditional potentiometric titration. PMID:25761506

  15. Polymer depletion-driven cluster aggregation and initial phase separation in charged nanosized colloids.

    PubMed

    Gögelein, Christoph; Nägele, Gerhard; Buitenhuis, Johan; Tuinier, Remco; Dhont, Jan K G

    2009-05-28

    We study polymer depletion-driven cluster aggregation and initial phase separation in aqueous dispersions of charge-stabilized silica spheres, where the ionic strength and polymer (dextran) concentration are systematically varied, using dynamic light scattering and visual observation. Without polymers and for increasing salt and colloid content, the dispersions become increasingly unstable against irreversible cluster formation. By adding nonadsorbing polymers, a depletion-driven attraction is induced, which lowers the stabilizing Coulomb barrier and enhances the cluster growth rate. The initial growth rate increases with increasing polymer concentration and decreases with increasing polymer molar mass. These observations can be quantitatively understood by an irreversible dimer formation theory based on the classical Derjaguin, Landau, Verwey, and Overbeek pair potential, with the depletion attraction modeled by the Asakura-Oosawa-Vrij potential. At low colloid concentration, we observe an exponential cluster growth rate for all polymer concentrations considered, indicating a reaction-limited aggregation mechanism. At sufficiently high polymer and colloid concentrations, and lower salt content, a gas-liquidlike demixing is observed initially. Later on, the system separates into a gel and fluidlike phase. The experimental time-dependent state diagram is compared to the theoretical equilibrium phase diagram obtained from a generalized free-volume theory and is discussed in terms of an initial reversible phase separation process in combination with irreversible aggregation at later times. PMID:19485479

  16. Interactions between colloidal particles in the presence of an ultrahighly charged amphiphilic polyelectrolyte.

    PubMed

    Yu, Danfeng; Yang, Hui; Wang, Hui; Cui, Yingxian; Yang, Guang; Zhang, Jian; Wang, Jinben

    2014-12-01

    A novel amphiphilic polyelectrolyte denoted as PAGC8 and a traditional amphiphilic polyelectrolyte denoted as PASC8 were prepared. PAGC8 consisted of gemini-type surfactant segment based on 1,3-bis (N,N-dimethyl-N-octylammonium)-2-propyl acrylate dibromide, while PASC8 incorporated acryloyloxyethyl-N,N-dimethyl-N-dodecylammonium bromide as single chain surfactant units within its repeat unit structure. Turbidity, stability, and zeta potential measurements were performed in the presence of PAGC8 and PASC8, respectively, to evaluate their effectiveness in inducing solid/liquid separations. It was found that the maximum transmittance was observed before the zeta potential values reached the isoelectric point, implying that not only charge neutralization but also charge-patch mechanism contributed to the separation process. Colloid probe atomic force microscopy technique was introduced to directly determine the interactions between surfaces in the presence of ultrahighly charged amphiphilic polyelectrolyte. On the basis of the AFM results, we have successfully interpreted the influence of the charge density of the polyelectrolytes on the phase stability. Electrostatic interaction played the dominant role in the flocculation processes, although both electrostatic interaction and hydrophobic effect provided contributions to the colloidal dispersions. The attractions upon surfaces approach in the case of PAGC8 were significantly larger than that of PASC8 due to the higher charge density. The strong peeling events upon retraction in the presence of PAGC8 implied that the hydrophobic effect was stronger than that of PASC8, which displayed the loose pulling events. A strong attraction was identified at shorter separation distances for both systems. However, these interactions cannot be successfully described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloid stability due to the participation of charge-patch and strong hydrophobic effect. To account for the

  17. Effect of laundry surfactants on surface charge and colloidal stability of silver nanoparticles.

    PubMed

    Skoglund, Sara; Lowe, Troy A; Hedberg, Jonas; Blomberg, Eva; Wallinder, Inger Odnevall; Wold, Susanna; Lundin, Maria

    2013-07-16

    The stability of silver nanoparticles (Ag NPs) potentially released from clothing during a laundry cycle and their interactions with laundry-relevant surfactants [anionic (LAS), cationic (DTAC), and nonionic (Berol)] have been investigated. Surface interactions between Ag NPs and surfactants influence their speciation and stability. In the absence of surfactants as well as in the presence of LAS, the negatively charged Ag NPs were stable in solution for more than 1 day. At low DTAC concentrations (≤1 mM), DTAC-Ag NP interactions resulted in charge neutralization and formation of agglomerates. The surface charge of the particles became positive at higher concentrations due to a bilayer type formation of DTAC that prevents from agglomeration due to repulsive electrostatic forces between the positively charged colloids. The adsorption of Berol was enhanced when above its critical micelle concentration (cmc). This resulted in a surface charge close to zero and subsequent agglomeration. Extended DLVO theory calculations were in compliance with observed findings. The stability of the Ag NPs was shown to depend on the charge and concentration of the adsorbed surfactants. Such knowledge is important as it may influence the subsequent transport of Ag NPs through different chemical transients and thus their potential bioavailability and toxicity. PMID:23758058

  18. Effect of alkyl functionalization on charging of colloidal silica in apolar media.

    PubMed

    Poovarodom, Saran; Poovarodom, Sathin; Berg, John C

    2010-11-15

    The present work examines the effect of alkyl-silane treatment on the charging of colloids in apolar solvent using two otherwise identical 250 nm diameter, spherical silica particles, one with untreated surface and the other treated with hexadecyltrimethoxysilane (C16), dispersed in an apolar isoparaffin solvent (Isopar-L) containing one of three oil-soluble surfactants: Aerosol-OT, OLOA 11,000, and zirconyl 2-ethyl hexanoate. The electrophoretic mobility of each dispersion was determined using phase angle light scattering (PALS). It was found that at sufficiently high surfactant concentration, i.e., where micelles begin to form in the bulk, the particle surfaces could be electrically charged. All three surfactants studied imparted a negative surface charge to the untreated silica particles. In all cases, the C16-treated particles were also found to be negatively charged but had a much higher magnitude of mobility than the untreated silica. Although the increase in magnitude of mobility as a result of the alkyl functionalization was surprising, it could be attributed to the increase in the number of surface hydroxyl groups arising from the hydrolysis of unbound methoxy groups of the silane molecules. The added hydroxyl groups provided additional potential acid-base interaction sites, resulting in higher particle mobility. It was also found that further increases in surfactant concentration lowered the particle mobility, attributed to the increasing concentration of electrically charged micelles, which may partially neutralize the surface charge or compress the electrical double layer. PMID:20728088

  19. Interaction between randomly charged rods and plates: Energy landscapes, stick slip, and recognition at a distance

    NASA Astrophysics Data System (ADS)

    Panyukov, Sergei; Rabin, Yitzhak

    1997-12-01

    We study the interaction between randomly, irreversibly charged objects. We consider arbitrary relative displacements of two parallel rigid rods and of two parallel rigid plates, and calculate the statistical properties of the resulting energy landscape, such as the distribution of the energies of potential minima and maxima, the depth, the radia of curvature, and the width and density of typical energy wells, as functions of the separation between the objects and of the Debye screening length. We show that this complicated energy landscape may lead to stick-slip phenomena during relative displacement of the plates. We study the case of perfectly correlated charge distributions on the two objects, and show that the presence of long range forces may lead to prealignment of the objects, even before contact. The relevance of our results to interacting biological systems and to pattern recognition is discussed.

  20. Drude-type conductivity of charged sphere colloidal crystals: density and temperature dependence.

    PubMed

    Medebach, Martin; Jordán, Raquel Chuliá; Reiber, Holger; Schöpe, Hans-Joachim; Biehl, Ralf; Evers, Martin; Hessinger, Dirk; Olah, Julianna; Palberg, Thomas; Schönberger, Ernest; Wette, Patrick

    2005-09-01

    We report on extensive measurements in the low-frequency limit of the ac conductivity of colloidal fluids and crystals formed from charged colloidal spheres suspended in de-ionized water. Temperature was varied in a range of 5 degrees C < Theta < 35 degrees C and the particle number density n between 0.2 and 25 microm(-3) for the larger, respectively, 2.75 and 210 microm(-3) for the smaller of two investigated species. At fixed Theta the conductivity increased linearly with increasing n without any significant change at the fluid-solid phase boundary. At fixed n it increased with increasing Theta and the increase was more pronounced for larger n. Lacking a rigorous electrohydrodynamic treatment for counterion-dominated systems we describe our data with a simple model relating to Drude's theory of metal conductivity. The key parameter is an effectively transported particle charge or valence Z(*). All temperature dependencies other than that of Z(*) were taken from literature. Within experimental resolution Z(*) was found to be independent of n irrespective of the suspension structure. Interestingly, Z(*) decreases with temperature in near quantitative agreement with numerical calculations. PMID:16178620

  1. Particle size, charge and colloidal stability of humic acids coprecipitated with Ferrihydrite.

    PubMed

    Angelico, Ruggero; Ceglie, Andrea; He, Ji-Zheng; Liu, Yu-Rong; Palumbo, Giuseppe; Colombo, Claudio

    2014-03-01

    Humic acids (HA) have a colloidal character whose size and negative charge are strictly dependent on surface functional groups. They are able to complex large amount of poorly ordered iron (hydr)oxides in soil as a function of pH and other environmental conditions. Accordingly, with the present study we intend to assess the colloidal properties of Fe(II) coprecipitated with humic acids (HA) and their effect on Fe hydroxide crystallinity under abiotic oxidation and order of addition of both Fe(II) and HA. TEM, XRD and DRS experiments showed that Fe-HA consisted of Ferrihydrite with important structural variations. DLS data of Fe-HA at acidic pH showed a bimodal size distribution, while at very low pH a slow aggregation process was observed. Electrophoretic zeta-potential measurements revealed a negative surface charge for Fe-HA macromolecules, providing a strong electrostatic barrier against aggregation. Under alkaline conditions HA chains swelled, which resulted in an enhanced stabilization of the colloid particles. The increasing of zeta potential and size of the Fe-HA macromolecules, reflects a linear dependence of both with pH. The increase in the size and negative charge of the Fe-HA precipitate seems to be more affected by the ionization of the phenolic acid groups, than by the carboxylic acid groups. The main cause of negative charge generation of Fe/HA is due to increased dissociation of phenolic groups in more expanded structure. The increased net negative surface potential induced by coprecipitation with Ferrihydrite and the correspondent changes in configuration of the HA could trigger the inter-particle aggregation with the formation of new negative surface. The Fe-HA coprecipitation can reduce electrosteric repulsive forces, which in turn may inhibit the aggregation process at different pH. Therefore, coprecipitation of Ferrihydrite would be expected to play an important role in the carbon stabilization and persistence not only in organic soils, but

  2. Adsorption and stabilizing effects of highly-charged latex nanoparticles in dispersions of weakly-charged silica colloids.

    PubMed

    Herman, David; Walz, John Y

    2015-07-01

    An experimental study was undertaken to determine the effectiveness of using highly-charged nanoparticles as stabilizers for colloidal dispersions. The specific systems used here involved cationic (amidine) and anionic (sulfate) polystyrene latex nanoparticles with an approximate diameter of 20 nm and silica microparticles of diameter 1.0 μm, and experiments were conducted at the isoelectric point of the silica. It was found that while both types of nanoparticles adsorbed to the silica microparticles and increased the zeta potential to values where stability was expected, long term stability was not achieved, even at bulk nanoparticle concentrations as high as 0.5 vol.%. It is theorized that the incomplete coverage of the microparticles by the nanoparticles (i.e., surface coverage never exceeded 50%) allowed either direct contact between bare patches of the underlying microparticles or, alternatively, for nanoparticles adsorbed on one microparticle to bridge to bare spots on a neighboring microparticle. PMID:25498877

  3. Coupled effect of pH and porous media type on transport and deposition of variably-charged soil colloids in saturated sands

    NASA Astrophysics Data System (ADS)

    Sharma, A.; Kawamoto, K.; Moldrup, P.; de Jonge, L. W.; Komatsu, T.

    2011-12-01

    Understanding colloid transport and deposition in subsurface is essential for predicting colloid-associated contaminant transport and developing effective remedial strategies. Compared to numerous studies using model colloids and model porous media, limited studies have been conducted with natural soil-colloids and porous media. This study investigated transport and deposition of suspended soil-colloids with diameter less than 1 μm extracted from a volcanic ash-soil (VAS colloids) from Nishi-Tokyo, Japan and a red-yellow soil (RYS colloids) from Okinawa, Japan. The extracted soil colloids were applied to 10-cm long saturated sand columns repacked with either Narita sand (mean diameter = 0.64 mm) or Toyoura sand (mean diameter = 0.21 mm) at different flow rates, input concentrations and pH conditions. The pH was adjusted using 0.1 M HCl and 0.01 M NaBr was used as a conservative tracer. Colloid transport and deposition were studied by analyzing colloid effluent concentration breakthrough curves, corresponding deposition profiles and particle size distributions. Based on zeta potential measurements, VAS colloids and Toyoura sand were characterized as pH-dependent surface charge dominant whereas, RYS colloids and Narita sand were categorized as less pH-dependent surface charge dominant colloids and porous media. The results of column studies indicated that decreasing pH decreased the colloid breakthrough curves and increased the deposition of colloids through both porous media. The effect of pH was more significant for VAS colloids than for RYS colloids and for Toyoura sand than for Narita sand, mainly attributed to the pH-dependent surface charge characteristics of VAS colloids and Toyoura sand. The results also demonstrated that if either a colloid or a porous medium is pH-dependent, a significant decrease in breakthrough curves is accompanied by depth-dependent deposition profiles. This study indicated that surface charge properties of colloids coupled with

  4. Competing nucleation pathways in a mixture of oppositely charged colloids: Out-of-equilibrium nucleation revisited

    NASA Astrophysics Data System (ADS)

    Peters, Baron

    2009-12-01

    Recent simulations of crystal nucleation from a compressed liquid of oppositely charged colloids show that the natural Brownian dynamics results in nuclei of a charge-disordered FCC (DFCC) solid whereas artificially accelerated dynamics with charge swap moves result in charge-ordered nuclei of a CsCl phase. These results were interpreted as a breakdown of the quasiequilibrium assumption for precritical nuclei. We use structure-specific nucleus size coordinates for the CsCl and DFCC structures and equilibrium based sampling methods to understand the dynamical effects on structure selectivity in this system. Nonequilibrium effects observed in previous simulations emerge from a diffusion tensor that dramatically changes when charge swap moves are used. Without the charge swap moves diffusion is strongly anisotropic with very slow motion along the charge-ordered CsCl axis and faster motion along the DFCC axis. Kramers-Langer-Berezhkovskii-Szabo theory predicts that under the realistic dynamics, the diffusion anisotropy shifts the current toward the DFCC axis. The diffusion tensor also varies with location on the free energy landscape. A numerical calculation of the current field with a diffusion tensor that depends on the location in the free energy landscape exacerbates the extent to which the current is skewed toward DFCC structures. Our analysis confirms that quasiequilibrium theories based on equilibrium properties can explain the nonequilibrium behavior of this system. Our analysis also shows that using a structure-specific nucleus size coordinate for each possible nucleation product can provide mechanistic insight on selectivity and competition between nucleation pathways.

  5. Charge effects and nanoparticle pattern formation in electrohydrodynamic NanoDrip printing of colloids

    NASA Astrophysics Data System (ADS)

    Richner, Patrizia; Kress, Stephan J. P.; Norris, David J.; Poulikakos, Dimos

    2016-03-01

    Advancing open atmosphere printing technologies to produce features in the nanoscale range has important and broad applications ranging from electronics to photonics, plasmonics and biology. Recently an electrohydrodynamic printing regime has been demonstrated in a rapid dripping mode (termed NanoDrip), where the ejected colloidal droplets from nozzles of diameters of O (1 μm) can controllably reach sizes an order of magnitude smaller than the nozzle and can generate planar and out-of-plane structures of similar sizes. Despite the demonstrated capabilities, our fundamental understanding of important aspects of the physics of NanoDrip printing needs further improvement. Here we address the topics of charge content and transport in NanoDrip printing. We employ quantum dot and gold nanoparticle dispersions in combination with a specially designed, auxiliary, asymmetric electric field, targeting the understanding of charge locality (particles vs. solvent) and particle distribution in the deposits as indicated by the dried nanoparticle patterns (footprints) on the substrate. We show that droplets of alternating charge can be spatially separated when applying an ac field to the nozzle. The nanoparticles within a droplet are distributed asymmetrically under the influence of the auxiliary lateral electric field, indicating that they are the main carriers. We also show that the ligand length of the nanoparticles in the colloid affects their mobility after deposition (in the sessile droplet state).Advancing open atmosphere printing technologies to produce features in the nanoscale range has important and broad applications ranging from electronics to photonics, plasmonics and biology. Recently an electrohydrodynamic printing regime has been demonstrated in a rapid dripping mode (termed NanoDrip), where the ejected colloidal droplets from nozzles of diameters of O (1 μm) can controllably reach sizes an order of magnitude smaller than the nozzle and can generate planar and

  6. 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,...

  7. Phase Behavior of 2D Charged Hydrophobic Colloids in Flat and Curved Space

    NASA Astrophysics Data System (ADS)

    Kelleher, Colm; Guerra, Rodrigo; Chaikin, Paul

    Charged hydrophobic colloids, 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, particles bind strongly to the interface via image-charge attraction. At sufficiently high density, these charged interfacial particles self-organize into a 2D repulsive (Wigner) crystalline solid phase, while at lower densities, the particles form a 2D fluid. By observing samples prepared at different densities, we can probe various points in the phase diagram of this soft 2D material, and compare our results with applicable theory and simulations. In this talk, we present two sets of experiments we have performed on this system: first, we show how we can use gravity as an external force to create a controlled density gradient, and thereby directly measure the equation of state and other quantities of interest. Second, we discuss how, by observing particles which are bound to the surface of spherical droplets, we can explore how the presence of finite background curvature affects the phase behavior of the system.

  8. Correlated adsorption of polyelectrolytes in the "charge inversion" of colloidal particles

    NASA Astrophysics Data System (ADS)

    Sennato, S.; Bordi, F.; Cametti, C.

    2004-10-01

    In this letter, we study the complexation of spherical colloidal particles induced by oppositely charged polyelectrolytes by means of dynamic light scattering technique. We employed cationic liposomes, 100 nm in diameter, and compared their aggregation behavior in the presence of differently organized counterions, i.e. simple uni-valent ions, deriving from the dissociation of NaCl salt, and multi-ions bounded to a polymer chain (large-valence polyions deriving from the ionization of two polyelectrolyte chains, polyacrylate and DNA). We show that the system behaves differently and, in the presence of oppositely charged polyions, undergoes a well-defined re-entrant condensation, following a charge inversion effect, as a function of the counterion concentration in the aqueous phase. Our results present a clear evidence of the role played by the lateral correlation of polyion chains onto the charged-particle surface, in terms of a simple Wigner crystal theory, according to the idea developed by Nguyen et al. (Rev. Mod. Phys. 74 (2002) 329).

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

    PubMed

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

    2016-05-15

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

  10. Elastic properties of static charge-stabilized colloidal crystal with two-dimensional hexagonal lattice

    NASA Astrophysics Data System (ADS)

    Alexandrov, Y. V.; Batanova, A. A.; Gladkova, E. V.; Dyshlovenko, P. E.; Nagatkin, A. N.; Nizametdinov, A. F.

    2016-02-01

    Two-dimensional charge-stabilized colloidal crystal with a hexagonal crystal lattice and constant electric potential on the particles is studied numerically. The properties of the crystal are described by the theory based on the Poisson-Boltzmann non-linear differential equation. The force constants and the equilibrium pressure in the crystals are calculated for a broad range of the lattice parameters. The numerical procedures of the force constant and pressure determination is briefly described. Elastic constants of the first and second order are also calculated on the base of the force constants to obtain information about the many-body effective interactions in the system. It was shown that the Cauchy relation between the elastic constants breaks down in the whole range of the lattice parameter especially at higher densities. This can be interpreted as an effect of the many-body effective interaction between the particles in the crystal.

  11. Wrinkled-graphene wrapped silicon nanoparticles synthesized through charged colloidal assembly for enhanced battery performance

    NASA Astrophysics Data System (ADS)

    Li, Hai; Lu, Chunxiang; Ma, Canliang; Zhang, Baoping

    2014-10-01

    Elastic composite of wrinkled graphene sheets and Si nanoparticles has been prepared through engineering charged Si nanoparticles capping with 3-aminopropyl triethoxysilane and graphene oxide in colloidal state. In the composite, the Si nanoparticles are uniformly wrapped by the graphene sheets. When used as an anode for lithium-ion batteries, the as-obtained material exhibits high Coulombic efficiency, good cycling stability of 1044 mAh g-1 at a current density of 200 mA g-1 after 100 cycles, and superior rate capability. Such excellent electrochemical performance should be attributed to the wrinkled graphene sheets, which not only buffer volume expansion of Si nanoparticles during the cycling but also act as electrical conducting pathway.

  12. Long-range repulsive charged colloids in and out of equilibrium

    NASA Astrophysics Data System (ADS)

    van der Linden, M. N.

    2013-04-01

    The research described in this thesis focusses on the behaviour of charged colloidal particles with long-range repulsive interactions. The experimental model system we used consisted of sterically stabilised charged poly(methyl methacrylate) (PMMA) colloids suspended in cyclohexyl bromide (CHB). In this low-polar solvent very low ionic concentrations can be achieved, resulting in a large Debye screening length (on the order of the particle diameter), i.e. long-range interactions. The pair interaction in these systems is often modelled by the hard-core repulsive Yukawa (or screened Coulomb) potential, which we used for our computer simulations. In Monte Carlo simulations we investigated the effect of size polydispersity on the crystal-fluid transition. We observed a shift to higher volume fraction of the crystal-fluid transition upon increasing the polydispersity. At high polydispersities parts of the higher charged systems that were initially crystalline became amorphous. The amorphous parts had a higher polydispersity than the crystalline parts, indicating the presence of a terminal polydispersity beyond which the homogeneous crystal phase was no longer stable. We investigated the slow dynamics close to the glass transition as a function of the range of the potential, also in simulations. We determined the long-time structural relaxation time and long-time self-diffusion coefficient, which could be well fitted by a power law predicted by mode-coupling theory (MCT) and by the Vogel-Fulcher-Tammann (VFT) equation. In experiments we used confocal microscopy to study the system quantitatively in 3D on a single-particle level. We performed micro-electrophoresis measurements to determine the surface potential and charge of the PMMA particles at a volume fraction around 0.02. The surface potential was roughly independent of the diameter of the particle and was found to be lower for unlocked particles (steric stabiliser adsorbed to surface) than for locked particles

  13. Effect of many-body interactions on the solid-liquid phase behavior of charge-stabilized colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Dobnikar, J.; Rzehak, R.; von Grünberg, H. H.

    2003-03-01

    The solid-liquid phase diagram of charge-stabilized colloidal suspensions has been calculated using a technique that combines a continuous Poisson-Boltzmann description for the microscopic electrolyte ions with a molecular-dynamics simulation for the macroionic colloidal spheres. While correlations between the microions are neglected in this approach, many-body interactions between the colloids, mediated by the screening ionic fluid between them, are fully included. The Lindemann criterion has been used to determine the solid-to-liquid transition temperature in a colloidal system at a relatively high colloid volume fraction where many-body interactions are expected to be strong. With a view to the Derjaguin-Landau-Verwey-Overbeek theory predicting that colloids interact via Yukawa pair potentials, we compare our results with the phase diagram of a simple Yukawa liquid. We find an agreement under high-salt conditions, but considerable differences at low ionic strength. Using effective force calculations and data from molecular-dynamics simulations with simple model potentials, we further demonstrate that these differences are due to many-body interactions.

  14. One-step solvothermal synthesis of highly water-soluble, negatively charged superparamagnetic Fe3O4 colloidal nanocrystal clusters

    NASA Astrophysics Data System (ADS)

    Gao, Jining; Ran, Xinze; Shi, Chunmeng; Cheng, Humin; Cheng, Tianmin; Su, Yongping

    2013-07-01

    Highly charged hydrophilic superparamagnetic Fe3O4 colloidal nanocrystal clusters with an average diameter of 195 nm have been successfully synthesized using a modified one-step solvothermal method. Anionic polyelectrolyte poly(4-styrenesulfonic acid-co-maleic acid) sodium salt containing both sulfonate and carboxylate groups was used as the stabilizer. The clusters synthesized under different experimental conditions were characterized with transmission electron microscopy and dynamic light scattering; it was found that the size distribution and water dispersity were significantly affected by the concentration of the polyelectrolyte stabilizer and iron sources in the reaction mixtures. A possible mechanism involving novel gel-like large molecular networks that confined the nucleation and aggregation process was proposed and discussed. The colloidal nanocrystal clusters remained negatively charged in the experimental pH ranges from 2 to 11, and also showed high colloidal stability in phosphate buffered saline (PBS) and ethanol. These highly colloidal stable superparamagnetic Fe3O4 clusters could find potential applications in bioseparation, targeted drug delivery, and photonics.Highly charged hydrophilic superparamagnetic Fe3O4 colloidal nanocrystal clusters with an average diameter of 195 nm have been successfully synthesized using a modified one-step solvothermal method. Anionic polyelectrolyte poly(4-styrenesulfonic acid-co-maleic acid) sodium salt containing both sulfonate and carboxylate groups was used as the stabilizer. The clusters synthesized under different experimental conditions were characterized with transmission electron microscopy and dynamic light scattering; it was found that the size distribution and water dispersity were significantly affected by the concentration of the polyelectrolyte stabilizer and iron sources in the reaction mixtures. A possible mechanism involving novel gel-like large molecular networks that confined the nucleation and

  15. Propagation and Separation of Charged Colloids by Cylindrical Passivated Gel Electrophoresis.

    PubMed

    Bikos, Dimitri; Mason, Thomas G

    2016-07-01

    We explore the electrophoretic propagation of charged colloidal objects, monodisperse anionically stabilized polystyrene spheres, in large-pore agarose gels that have been passivated using polyethylene glycol (PEG) when a radial electric field is applied in a cylindrical geometry. By contrast to standard Cartesian gel-electrophoresis geometries, in a cylindrical geometry, charged particles that start at a ring well near the central axis propagate outward more rapidly initially and then slow down as they move further away from the axis. By building a full-ring cylindrical gel electrophoresis chamber and taking movies of scattered light from propagating nanospheres undergoing electrophoresis, we experimentally demonstrate that the ring-like front of monodisperse nanospheres propagates stably in PEG-passivated agarose gels and that the measured ring radius as a function of time agrees with a simple model that incorporates the electric field of a cylindrical geometry. Moreover, we show that this cylindrical geometry offers a potential advantage when performing electrophoretic separations of objects that have widely different sizes: smaller objects can still be retained in a cylindrical gel that has a limited size over long electrophoretic run times required for separating larger objects. PMID:27109865

  16. Single-mode lasing from colloidal water-soluble CdSe/CdS quantum dot-in-rods.

    PubMed

    Di Stasio, Francesco; Grim, Joel Q; Lesnyak, Vladimir; Rastogi, Prachi; Manna, Liberato; Moreels, Iwan; Krahne, Roman

    2015-03-18

    Core-shell CdSe/CdS nanocrystals are a very promising material for light emitting applications. Their solution-phase synthesis is based on surface-stabilizing ligands that make them soluble in organic solvents, like toluene or chloroform. However, solubility of these materials in water provides many advantages, such as additional process routes and easier handling. So far, solubilization of CdSe/CdS nanocrystals in water that avoids detrimental effects on the luminescent properties poses a major challenge. This work demonstrates how core-shell CdSe/CdS quantum dot-in-rods can be transferred into water using a ligand exchange method employing mercaptopropionic acid (MPA). Key to maintaining the light-emitting properties is an enlarged CdS rod diameter, which prevents potential surface defects formed during the ligand exchange from affecting the photophysics of the dot-in-rods. Films made from water-soluble dot-in-rods show amplified spontaneous emission (ASE) with a similar threshold (130 μJ/cm(2)) as the pristine material (115 μJ/cm(2)). To demonstrate feasibility for lasing applications, self-assembled microlasers are fabricated via the "coffee-ring effect" that display single-mode operation and a very low threshold of ∼10 μJ/cm(2). The performance of these microlasers is enhanced by the small size of MPA ligands, enabling a high packing density of the dot-in-rods. PMID:25335769

  17. Effect of charging on CdSe/CdS dot-in-rods single-photon emission

    NASA Astrophysics Data System (ADS)

    Manceau, M.; Vezzoli, S.; Glorieux, Q.; Pisanello, F.; Giacobino, E.; Carbone, L.; De Vittorio, M.; Bramati, A.

    2014-07-01

    The photon statistics of CdSe/CdS dot-in-rods nanocrystals is studied with a method involving postselection of the photon detection events based on the photoluminescence count rate. We show that flickering between two states needs to be taken into account to interpret the single-photon emission properties. With postselection we are able to identify two emitting states: the exciton and the charged exciton (trion), characterized by different lifetimes and different second-order correlation functions. Measurements of the second-order autocorrelation function at zero delay with postselection shows a degradation of the single-photon emission for CdSe/CdS dot-in-rods in a charged state that we explain by deriving the neutral and charged biexciton quantum yields.

  18. Polarimetry-based analysis of dipolar transitions of single colloidal CdSe/CdS dot-in-rods

    NASA Astrophysics Data System (ADS)

    Lethiec, C.; Pisanello, F.; Carbone, L.; Bramati, A.; Coolen, L.; Maître, A.

    2014-09-01

    We use polarization resolved micro-photoluminescence to analyze the dipolar nature of single core/shell cadmium selenide/cadmium sulfide (CdSe/CdS) dot-in-rods. Polarization analysis, anisotropy measurements on more than 400 nanoparticles, and defocused imaging suggest that these nanoparticles behave as linear dipoles. The same methods were also used to determine the three-dimensional orientation of the emission dipole, which proved to be consistent with the hypothesis of a linear dipole tilted with respect to the rod axis. Moreover, we observe that for high-energy pumping, the excitation transition of the dot-in-rod cannot be approximated by a single linear dipole, contrary to the emission transition.

  19. Surface charge of polymer coated SPIONs influences the serum protein adsorption, colloidal stability and subsequent cell interaction in vitro

    NASA Astrophysics Data System (ADS)

    Hirsch, Vera; Kinnear, Calum; Moniatte, Marc; Rothen-Rutishauser, Barbara; Clift, Martin J. D.; Fink, Alke

    2013-04-01

    It is known that the nanoparticle-cell interaction strongly depends on the physicochemical properties of the investigated particles. In addition, medium density and viscosity influence the colloidal behaviour of nanoparticles. Here, we show how nanoparticle-protein interactions are related to the particular physicochemical characteristics of the particles, such as their colloidal stability, and how this significantly influences the subsequent nanoparticle-cell interaction in vitro. Therefore, different surface charged superparamagnetic iron oxide nanoparticles were synthesized and characterized. Similar adsorbed protein profiles were identified following incubation in supplemented cell culture media, although cellular uptake varied significantly between the different particles. However, positively charged nanoparticles displayed a significantly lower colloidal stability than neutral and negatively charged particles while showing higher non-sedimentation driven cell-internalization in vitro without any significant cytotoxic effects. The results of this study strongly indicate therefore that an understanding of the aggregation state of NPs in biological fluids is crucial in regards to their biological interaction(s).It is known that the nanoparticle-cell interaction strongly depends on the physicochemical properties of the investigated particles. In addition, medium density and viscosity influence the colloidal behaviour of nanoparticles. Here, we show how nanoparticle-protein interactions are related to the particular physicochemical characteristics of the particles, such as their colloidal stability, and how this significantly influences the subsequent nanoparticle-cell interaction in vitro. Therefore, different surface charged superparamagnetic iron oxide nanoparticles were synthesized and characterized. Similar adsorbed protein profiles were identified following incubation in supplemented cell culture media, although cellular uptake varied significantly between

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

    We report a comprehensive joint experimental-theoretical study of the equilibrium pair-structure and short-time diffusion in aqueous suspensions of highly charged poly-acrylate (PA) spheres in the colloidal fluid phase. Low-polydispersity PA sphere systems with two different hard-core radii, R0 = 542 and 1117 Å, are explored over a wide range of concentrations and salinities using static and dynamic light scattering (DLS), small angle x-ray scattering, and x-ray photon correlation spectroscopy (XPCS). The measured static and dynamic scattering functions are analyzed using state-of-the-art theoretical methods. For all samples, the measured static structure factor, S(Q), is in good agreement with results by an analytical integral equation method for particles interacting by a repulsive screened Coulomb plus hard-core pair potential. In our DLS and XPCS measurements, we have determined the short-time diffusion function D(Q) = D0 H(Q)/S(Q), comprising the free diffusion coefficient D0 and the hydrodynamic function H(Q). The latter is calculated analytically using a self-part corrected version of the δγ-scheme by Beenakker and Mazur which accounts approximately for many-body hydrodynamic interactions (HIs). Except for low-salinity systems at the highest investigated volume fraction ϕ ≈ 0.32, the theoretical predictions for H(Q) are in excellent agreement with the experimental data. In particular, the increase in the collective diffusion coefficient Dc = D(Q → 0), and the decrease of the self-diffusion coefficient, Ds = D(Q → ∞), with increasing ϕ is well described. In accord with the theoretical prediction, the peak value, H(Qm), of H(Q) relates to the nearest neighbor cage size ˜2π/Qm, for which concentration scaling relations are discussed. The peak values H(Qm) are globally bound from below by the corresponding neutral hard-spheres peak values, and from above by the limiting peak values for low-salinity charge-stabilized systems. HIs usually slow short

  1. Effect of the polydispersion in the crystallization and micro-structure of the high charged colloids

    NASA Astrophysics Data System (ADS)

    Urrutia-Bañuelos, Efraín; Aranda-Espinosa, Helim; Chasvez-Paez, Martin

    2008-03-01

    In this work we investigate the effect of the polydipersion in the crystallization and micro-structure of the high charged colloids particles with tow and three different types and different concentrations of that types. This results were obtained by computer simulation, the particles interaction was modeled by a screened Coulomb potential. We used 4000 particles in our simulation cell to let them evolution from an initial random configuration, periodic boundary conditions was imposed to simulate the bulk. The temporal evolutions of the configuration show long-ranged self-ordering and a crystalline transition, the crystalline nucleation depend of the concentrations of different kinds as well as of types of particle. The common neighbor analysis (CNA) exhibit the competition of two micro-structures, icosahedral and bcc, in the equilibrium bcc crystalline order is dominant with relative abundance over the other micro-structures. 1.- U. Gasser, Eric R. Weeks et al, Science, 292 (258), 2001. 2.- Stefan Auer, Daan Frenkel, Letter of Nature, 409 (1020), 2001. 3.- J.P. Hoogenboom, et al , Phys. Rev. Leeters, 89 (256104), 2002. 4.- M. Ch'avez-P'aez, E. Urrutia-Bañuelos and M. Medina --Noyola, Phys. Rev. E, 58 (681),1998 5.- Andrew S. Clarke and Hannes J'onsson, Phys. Rev. E, 47 (3975), 1993.

  2. Thermal activation of non-radiative Auger recombination in charged colloidal nanocrystals.

    PubMed

    Javaux, C; Mahler, B; Dubertret, B; Shabaev, A; Rodina, A V; Efros, Al L; Yakovlev, D R; Liu, F; Bayer, M; Camps, G; Biadala, L; Buil, S; Quelin, X; Hermier, J-P

    2013-03-01

    Applications of semiconductor nanocrystals such as biomarkers and light-emitting optoelectronic devices require that their fluorescence quantum yield be close to 100%. However, such quantum yields have not been obtained yet, in part, because non-radiative Auger recombination in charged nanocrystals could not be suppressed completely. Here, we synthesize colloidal core/thick-shell CdSe/CdS nanocrystals with 100% quantum yield and completely quenched Auger processes at low temperatures, although the nanocrystals are negatively photocharged. Single particle and ensemble spectroscopy in the temperature range 30-300 K shows that the non-radiative Auger recombination is thermally activated around 200 K. Experimental results are well described by a model suggesting a temperature-dependent delocalization of one of the trion electrons from the CdSe core and enhanced Auger recombination at the abrupt CdS outer surface. These results point to a route for the design of core/shell structures with 100% quantum yield at room temperature. PMID:23396313

  3. Anion-Dependent Aggregate Formation and Charge Behavior of Colloidal Fullerenes (n-C60)

    NASA Astrophysics Data System (ADS)

    Mukherjee, B.; Weaver, J. W.

    2009-12-01

    The fate and transport of colloidal fullerenes (n-C60) in the environment are likely to be guided by their electrokinetic and aggregation behavior. In natural water bodies inorganic ions exert significant effects in determining the size and charge of dispersed n-C60. Although the effects of cations on the behavior of n-C60 have been studied extensively; studies on the effect of anions are relatively few and thus were the focus of our investigation. The effects of anions (e.g., Cl- , SO42-) on average aggregate size (DH) and zeta potential (ZP) of n-C60 were found to be absent in presence of monovalent cations (e.g., Na+) over the tested range of pH (3-to-12) and ionic strength (0-to-20 mM). Similar observations were noted in the presence of multivalent cations (e.g., Mg2+) near acidic and neutral pH conditions. However, under alkaline conditions (pH~10) a strong anion-dependent reversal of surface charge was noted. The ZP of n-C60 changed from -65 mV, when dispersed in DI water, to +4 mV and +40 mV in the presence of SO42- and Cl-, respectively in a 10mM salt concentration (i.e., MgCl2 and MgSO4). The corresponding DH of the dispersed n-C60 changed simultaneously from 115 nm, in DI water, to 1450 nm and 225 nm for the MgSO4 and MgCl2 electrolytes. These findings provide a better understanding of interfacial interaction characteristics of n-C60 NPs, and may lead to remediation strategies for n-C60 NPs in the environment.

  4. Determination of the positions and orientations of concentrated rod-like colloids from 3D microscopy data.

    PubMed

    Besseling, T H; Hermes, M; Kuijk, A; de Nijs, B; Deng, T-S; Dijkstra, M; Imhof, A; van Blaaderen, A

    2015-05-20

    Confocal microscopy in combination with real-space particle tracking has proven to be a powerful tool in scientific fields such as soft matter physics, materials science and cell biology. However, 3D tracking of anisotropic particles in concentrated phases remains not as optimized compared to algorithms for spherical particles. To address this problem, we developed a new particle-fitting algorithm that can extract the positions and orientations of fluorescent rod-like particles from three dimensional confocal microscopy data stacks. The algorithm is tailored to work even when the fluorescent signals of the particles overlap considerably and a threshold method and subsequent clusters analysis alone do not suffice. We demonstrate that our algorithm correctly identifies all five coordinates of uniaxial particles in both a concentrated disordered phase and a liquid-crystalline smectic-B phase. Apart from confocal microscopy images, we also demonstrate that the algorithm can be used to identify nanorods in 3D electron tomography reconstructions. Lastly, we determined the accuracy of the algorithm using both simulated and experimental confocal microscopy data-stacks of diffusing silica rods in a dilute suspension. This novel particle-fitting algorithm allows for the study of structure and dynamics in both dilute and dense liquid-crystalline phases (such as nematic, smectic and crystalline phases) as well as the study of the glass transition of rod-like particles in three dimensions on the single particle level. PMID:25922931

  5. Determination of the positions and orientations of concentrated rod-like colloids from 3D microscopy data

    NASA Astrophysics Data System (ADS)

    Besseling, T. H.; Hermes, M.; Kuijk, A.; de Nijs, B.; Deng, T.-S.; Dijkstra, M.; Imhof, A.; van Blaaderen, A.

    2015-05-01

    Confocal microscopy in combination with real-space particle tracking has proven to be a powerful tool in scientific fields such as soft matter physics, materials science and cell biology. However, 3D tracking of anisotropic particles in concentrated phases remains not as optimized compared to algorithms for spherical particles. To address this problem, we developed a new particle-fitting algorithm that can extract the positions and orientations of fluorescent rod-like particles from three dimensional confocal microscopy data stacks. The algorithm is tailored to work even when the fluorescent signals of the particles overlap considerably and a threshold method and subsequent clusters analysis alone do not suffice. We demonstrate that our algorithm correctly identifies all five coordinates of uniaxial particles in both a concentrated disordered phase and a liquid-crystalline smectic-B phase. Apart from confocal microscopy images, we also demonstrate that the algorithm can be used to identify nanorods in 3D electron tomography reconstructions. Lastly, we determined the accuracy of the algorithm using both simulated and experimental confocal microscopy data-stacks of diffusing silica rods in a dilute suspension. This novel particle-fitting algorithm allows for the study of structure and dynamics in both dilute and dense liquid-crystalline phases (such as nematic, smectic and crystalline phases) as well as the study of the glass transition of rod-like particles in three dimensions on the single particle level.

  6. Hexadecapolar Colloids

    DOE PAGESBeta

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

    2016-02-11

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

  7. 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.

  8. 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

  9. 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

  10. Quantitative analysis of PEG-functionalized colloidal gold nanoparticles using charged aerosol detection.

    PubMed

    Smith, Mackensie C; Crist, Rachael M; Clogston, Jeffrey D; McNeil, Scott E

    2015-05-01

    Surface characteristics of a nanoparticle, such as functionalization with polyethylene glycol (PEG), are critical to understand and achieve optimal biocompatibility. Routine physicochemical characterization such as UV-vis spectroscopy (for gold nanoparticles), dynamic light scattering, and zeta potential are commonly used to assess the presence of PEG. However, these techniques are merely qualitative and are not sensitive enough to distinguish differences in PEG quantity, density, or presentation. As an alternative, two methods are described here which allow for quantitative measurement of PEG on PEGylated gold nanoparticles. The first, a displacement method, utilizes dithiothreitol to displace PEG from the gold surface. The dithiothreitol-coated gold nanoparticles are separated from the mixture via centrifugation, and the excess dithiothreitol and dissociated PEG are separated through reversed-phase high-performance liquid chromatography (RP-HPLC). The second, a dissolution method, utilizes potassium cyanide to dissolve the gold nanoparticles and liberate PEG. Excess CN(-), Au(CN)2 (-), and free PEG are separated using RP-HPLC. In both techniques, the free PEG can be quantified against a standard curve using charged aerosol detection. The displacement and dissolution methods are validated here using 2-, 5-, 10-, and 20-kDa PEGylated 30-nm colloidal gold nanoparticles. Further value in these techniques is demonstrated not only by quantitating the total PEG fraction but also by being able to be adapted to quantitate the free unbound PEG and the bound PEG fractions. This is an important distinction, as differences in the bound and unbound PEG fractions can affect biocompatibility, which would not be detected in techniques that only quantitate the total PEG fraction. PMID:25749798

  11. Charge Stabilized Crystalline Colloidal Arrays As Templates For Fabrication of Non-Close-Packed Inverted Photonic Crystals

    PubMed Central

    Bohn, Justin J.; Ben-Moshe, Matti; Tikhonov, Alexander; Qu, Dan; Lamont, Daniel N.

    2010-01-01

    We developed a straightforward method to form non close-packed highly ordered fcc direct and inverse opal silica photonic crystals. We utilize an electrostatically self assembled crystalline colloidal array (CCA) template formed by monodisperse, highly charged polystyrene particles. We then polymerize a hydrogel around the CCA (PCCA) and condense the silica to form a highly ordered silica impregnated (siPCCA) photonic crystal. Heating at 450 °C removes the organic polymer leaving a silica inverse opal structure. By altering the colloidal particle concentration we independently control the particle spacing and the wall thickness of the inverse opal photonic crystals. This allows us to control the optical dielectric constant modulation in order to optimize the diffraction; the dielectric constant modulation is controlled independently of the photonic crystal periodicity. These fcc photonic crystals are better ordered than typical close-packed photonic crystals because their self assembly utilizes soft electrostatic repulsive potentials. We show that colloidal particle size and charge polydispersity has modest impact on ordering, in contrast to that for close-packed crystals. PMID:20163800

  12. Efficient Light-driven Long Distance Charge Separation and H2 Generation in Semiconductor Quantum Rods and Nanoplatelets

    NASA Astrophysics Data System (ADS)

    Lian, Tianquan

    Quantum confined semiconductor nanocrystals (0D quantum dots, 1D quantum rods and 2D quantum platlets) have been intensively investigated as light harvesting and charge separation materials for photovoltaic and photocatalytic applications. The efficiency of these semiconductor nanocrystal-based devices depends on many fundamental processes, including light harvesting, carrier relaxation, exciton localization and transport, charge separation and charge recombination. The competition between these processes determines the overall solar energy conversion (solar to electricity or fuel) efficiency. Semiconductor nano-heterostructures, combining two or more material components, offer unique opportunities to control their charge separation properties by tailoring their compositions, dimensions and spatial arrangement. Further integration of catalysts (heterogeneous or homogeneous) to these materials form multifunctional nano-heterostructures. Using 0D, 1D and 2D CdSe/CdS/Pt heterostructures as model systems, we directly probe the above-mentioned fundamental exciton and carrier processes by transient absorption and time-resolved fluorescence spectroscopy. We are examining how to control these fundamental processes through the design of heterostructures to achieve long-lived charge separation and efficient H2 generation. In this talk, we will discuss a new model for exciton dissociation by charge transfer in quantum dots (i.e. Auger assisted electron transfer), mechanism of 1D and 2D exciton transport and dissociation in nanorods, and key factors limiting H2 generation efficiency in CdSe/CdS/Pt nanorod heterostructures.

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

    NASA Astrophysics Data System (ADS)

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

    2005-02-01

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

  14. Electric response of a magnetic colloid to periodic external excitation for different nanoparticles concentrations: Determination of the particles' effective charge

    NASA Astrophysics Data System (ADS)

    Batalioto, F.; Barbero, G.; Sehnem, A. L.; Figueiredo Neto, A. M.

    2016-08-01

    The effective electric charge of a nanoparticle in an ionic magnetic colloidal system (an ionic ferrofluid) is determined by using the impedance spectroscopy technique. The electric response of the samples to a harmonic external electric field excitation is described by means of the Poisson-Nernst-Planck model. The model proposed for the theoretical interpretation of the impedance spectroscopy data considers that the magnetic particles are electrically charged with H+ and have in their vicinity Cl- counterions, resulting in an effective charge Qeff. In the presence of an harmonic, in time, external field (frequency bigger than 10 4 Hz ) particles are assumed to be at rest, due to inertial reason. In this framework, the response of the cell is due to the H+ and Cl- present in the solution. From the spectra of the real and imaginary components of the electric impedance of the cell, by means of a best fit procedure to our model, we derive the effective electric charge of the magnetic particles and the bulk density of ions. From an independent measurement of the ζ-potential of the suspension, it is possible to calculate the hydrodynamic radius of the particle, in good agreement with that independently measured.

  15. 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.

  16. 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

  17. Aspect-ratio-dependent phase transitions and concentration fluctuations in aqueous colloidal dispersions of charged platelike particles

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Daisuke; Miyamoto, Nobuyoshi; Fujita, Takako; Nakato, Teruyuki; Koizumi, Satoshi; Ohta, Noboru; Yagi, Naoto; Hashimoto, Takeji

    2012-01-01

    Phase transitions of aqueous colloidal dispersions of charged platelike particles of niobate nanosheets were investigated as a function of the aspect ratio (rasp) and particle volume concentration (φp) by means of small-angle neutron scattering and small-angle x-ray scattering. The results elucidated the following three pieces of evidence: (1) the macroscopic phase separation of the dispersions into an isotropic phase and a liquid crystalline (LC) phase under the conditions of (a) varying rasp (1.3×10-4 ≤ rasp ≤ 2.5×10-3) at a constant φp = 0.01 and (b) varying φp (0.01 ≤ φp ≤ 0.025) at a constant rasp = 2.5×10-3, a mechanism of which is proposed in the text, where rasp ≡ d/L¯, with d and L¯ being thickness and the average lateral size of the plates, respectively; (2) the rasp-induced phase transition of the LC phase from a nematic phase to a highly periodic layered phase, the line shapes of the scattering peaks of which were examined by Caillé's analysis, upon increasing rasp under the condition (a); (3) the LC phase having remarkable concentration fluctuations of the particles which are totally unexpected for the conventional lyotropic molecular LC but which are anticipated to be general for the platelike colloidal particles.

  18. 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

  19. Block Liposomes: Vesicles of Charged Lipids with Distinctly Shaped Nanoscale Sphere-, Pear-, Tube-, or Rod-Segments

    PubMed Central

    Zidovska, Alexandra; Ewert, Kai K.; Quispe, Joel; Carragher, Bridget; Potter, Clinton S.; Safinya, Cyrus R.

    2016-01-01

    We describe the preparation and characterization of block liposomes, a new class of liquid vesicles, from mixtures of the highly charged (+16 e) multivalent cationic lipid MVLBG2 and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). Block liposomes (BLs) consist of distinct spherical, tubular, and micellar liposomes which remain connected, forming a single liposome. This is in contrast to typical vesicle systems, where distinctly shaped liposomes are macroscopically separated. In a narrow composition range (8-10 mol % MVLBG2), an abundance of micrometer-scale BLs (typically sphere-tube-sphere triblocks) was observed. Cryo-TEM revealed that BLs are also present at the nanometer scale, where the blocks consist of distinctly shaped nanoscale spheres, pears, tubes, or rods. Pear-tube diblock and pear-tube-pear triblock liposomes contain nanotubes with inner lumen diameter 10-50 nm. In addition, sphere-rod diblock liposomes are present, containing rigid micellar nanorods ≈4 nm in diameter and several μm in length. Block liposomes may find a range of applications in chemical and nucleic acid delivery and as building blocks in the design of templates for hierarchical structures. PMID:19913164

  20. High reduction of interfacial charge recombination in colloidal quantum dot solar cells by metal oxide surface passivation

    NASA Astrophysics Data System (ADS)

    Chang, Jin; Kuga, Yuki; Mora-Seró, Iván; Toyoda, Taro; Ogomi, Yuhei; Hayase, Shuzi; Bisquert, Juan; Shen, Qing

    2015-03-01

    Bulk heterojunction (BHJ) solar cells based on colloidal QDs and metal oxide nanowires (NWs) possess unique and outstanding advantages in enhancing light harvesting and charge collection in comparison to planar architectures. However, the high surface area of the NW structure often brings about a large amount of recombination (especially interfacial recombination) and limits the open-circuit voltage in BHJ solar cells. This problem is solved here by passivating the surface of the metal oxide component in PbS colloidal quantum dot solar cells (CQDSCs). By coating thin TiO2 layers onto ZnO-NW surfaces, the open-circuit voltage and power conversion efficiency have been improved by over 40% in PbS CQDSCs. Characterization by transient photovoltage decay and impedance spectroscopy indicated that the interfacial recombination was significantly reduced by the surface passivation strategy. An efficiency as high as 6.13% was achieved through the passivation approach and optimization for the length of the ZnO-NW arrays (device active area: 16 mm2). All solar cells were tested in air, and exhibited excellent air storage stability (without any performance decline over more than 130 days). This work highlights the significance of metal oxide passivation in achieving high performance BHJ solar cells. The charge recombination mechanism uncovered in this work could shed light on the further improvement of PbS CQDSCs and/or other types of solar cells.Bulk heterojunction (BHJ) solar cells based on colloidal QDs and metal oxide nanowires (NWs) possess unique and outstanding advantages in enhancing light harvesting and charge collection in comparison to planar architectures. However, the high surface area of the NW structure often brings about a large amount of recombination (especially interfacial recombination) and limits the open-circuit voltage in BHJ solar cells. This problem is solved here by passivating the surface of the metal oxide component in PbS colloidal quantum dot solar

  1. A differential dielectric spectroscopy setup to measure the electric dipole moment and net charge of colloidal quantum dots

    SciTech Connect

    Kortschot, R. J.; Bakelaar, I. A.; Erné, B. H.; Kuipers, B. W. M.

    2014-03-15

    A sensitive dielectric spectroscopy setup is built to measure the response of nanoparticles dispersed in a liquid to an alternating electric field over a frequency range from 10{sup −2} to 10{sup 7} Hz. The measured complex permittivity spectrum records both the rotational dynamics due to a permanent electric dipole moment and the translational dynamics due to net charges. The setup consists of a half-transparent capacitor connected in a bridge circuit, which is balanced on pure solvent only, using a software-controlled compensating voltage. In this way, the measured signal is dominated by the contributions of the nanoparticles rather than by the solvent. We demonstrate the performance of the setup with measurements on a dispersion of colloidal CdSe quantum dots in the apolar liquid decalin.

  2. Approximate Analytic Expression for the Electrophoretic Mobility of Moderately Charged Cylindrical Colloidal Particles.

    PubMed

    Ohshima, Hiroyuki

    2015-12-29

    An approximate analytic expression for the electrophoretic mobility of an infinitely long cylindrical colloidal particle in a symmetrical electrolyte solution in a transverse electric field is obtained. This mobility expression, which is correct to the order of the third power of the zeta potential ζ of the particle, considerably improves Henry's mobility formula correct to the order of the first power of ζ (Proc. R. Soc. London, Ser. A 1931, 133, 106). Comparison with the numerical calculations by Stigter (J. Phys. Chem. 1978, 82, 1417) shows that the obtained mobility formula is an excellent approximation for low-to-moderate zeta potential values at all values of κa (κ = Debye-Hückel parameter and a = cylinder radius). PMID:26639309

  3. Hydrodynamic interactions in metal rod-like particle suspensions due to induced charge electroosmosis

    SciTech Connect

    Rose, K A; Hoffman, B; Saintillan, D; Shaqfeh, E G; Santiago, J G

    2008-05-05

    We present a theoretical and experimental study of the role of hydrodynamic interactions on the motion and dispersion of metal rod-like particles in the presence of an externally applied electric field. In these systems, the electric field polarizes the particles and induces an electroosmosis flow relative to the surface of each particle. The simulations include the effect of the gravitational body force, buoyancy, far-field hydrodynamic interactions, near-field lubrication forces, and electric field interactions. The particles in the simulations and experiments were observed to experience repeated pairing interactions in which they come together axially with their ends approaching each other, slide past one another until their centers approach, and then push apart. These interactions were confirmed in measurements of particle orientations and velocities, pair distribution functions, and net dispersion of the suspension. For large electric fields, the pair distribution functions show accumulation and depletion regions consistent with many pairing events. For particle concentrations of 1e8 particles/mL and higher, dispersion within the suspension dramatically increases with increased field strength.

  4. Finite compressibility in shaped charge jet and long rod penetration—the effect of shocks

    NASA Astrophysics Data System (ADS)

    Haugstad, B. S.; Dullum, O. S.

    1981-08-01

    The classical theory of high speed jet and long rod penetration assumes incompressibility of both projectile and target. We extend here previous analyses of the implications of finite compressibility by including the effect of stationary shocks. For uniform projectile velocities V≲6×103 ms-1, depending on the type of target material, the total effect of compressibility is in the order of 10% or less, and is well approximated by the volume compressison work considered in the previous analyses [A. Coombs, private communication, Royal Air Force Research and Development Establishment, 1978; B. S. Haugstad, J. Appl. Phys. 52, 1243 (1981)]. At higher velocities shocks play an increasingly dominant role, contributing at least equally to the total compressibility effect at V≲104 ms-1. At these velocities there is a reduction in penetration depth of 10-20% in targets of aluminium or lead, while for plexiglass a full 35% reduction is predicted. Targets of lead or plexiglass experience local melting or even sublimation during penetration. In targets of aluminium, steel, platinum, and probably also in most other metallic targets, melting or sublimation first occurs well above typical projectile velocities.

  5. Charging behavior of the gibbsite basal (001) surface in NaCl solution investigated by AFM colloidal probe technique.

    PubMed

    Gan, Yang; Franks, George V

    2006-07-01

    The charging behavior of the gibbsite gamma-Al(OH)3 basal (001) surface in aqueous solution is important for correctly modeling the overall charging properties of gibbsite particles which controls surface phenomena such as adsorption and crystal growth. However, the question of whether the hydroxyl groups on the basal plane are proton active has been raised recently both from experimental and theoretical points of view. Using gibbsite crystals prepared from industrial Bayer process, the surface potentials of cleaved (001) surfaces were calculated from forces measured by the colloidal probe technique in 1 mM NaCl solution with differing pH. It was surprisingly found that the basal plane is proton active in pH less than 7 and protonation seems to level off at about pH 5. The potential-pH data was accurately fitted with a single pKa surface protonation model with pK(a) = 5.9 +/- 0.2. PMID:16800663

  6. Interaction between like-charged polyelectrolyte-colloid complexes in electrolyte solutions: A Monte Carlo simulation study in the Debye-Hückel approximation

    NASA Astrophysics Data System (ADS)

    Truzzolillo, D.; Bordi, F.; Sciortino, F.; Sennato, S.

    2010-07-01

    We study the effective interaction between differently charged polyelectrolyte-colloid complexes in electrolyte solutions via Monte Carlo simulations. These complexes are formed when short and flexible polyelectrolyte chains adsorb onto oppositely charged colloidal spheres, dispersed in an electrolyte solution. In our simulations the bending energy between adjacent monomers is small compared to the electrostatic energy, and the chains, once adsorbed, do not exchange with the solution, although they rearrange on the particles surface to accommodate further adsorbing chains or due to the electrostatic interaction with neighbor complexes. Rather unexpectedly, when two interacting particles approach each other, the rearrangement of the surface charge distribution invariably produces antiparallel dipolar doublets that invert their orientation at the isoelectric point. These findings clearly rule out a contribution of dipole-dipole interactions to the observed attractive interaction between the complexes, pointing out that such suspensions cannot be considered dipolar fluids. On varying the ionic strength of the electrolyte, we find that a screening length κ-1, short compared with the size of the colloidal particles, is required in order to observe the attraction between like-charged complexes due to the nonuniform distribution of the electric charge on their surface ("patch attraction"). On the other hand, by changing the polyelectrolyte/particle charge ratio ξs, the interaction between like-charged polyelectrolyte-decorated particles, at short separations, evolves from purely repulsive to strongly attractive. Hence, the effective interaction between the complexes is characterized by a potential barrier, whose height depends on the net charge and on the nonuniformity of their surface charge distribution.

  7. Aggregation and stability of anisotropic charged clay colloids in aqueous medium in the presence of salt.

    PubMed

    Ali, Samim; Bandyopadhyay, Ranjini

    2016-01-01

    Na-montmorillonite nanoclay is a colloid of layered mineral silicate. When dispersed in water, this mineral swells on absorption of water and exfoliates into platelets with electric double layers on their surfaces. Even at low particle concentration, the aqueous dispersion can exhibit a spontaneous ergodicity breaking phase transition from a free flowing liquid to nonequilibrium, kinetically arrested and disordered states such as gels and glasses. In an earlier publication [Applied Clay Science, 2015, 114, 8592], we showed that the stability of clay gels can be enhanced by adding a salt later to the clay dispersion prepared in deionized water, rather than by adding the clay mineral to a previously mixed salt solution. Here, we directly track the collapsing interface of sedimenting clay gels using an optical method and show that adding salt after dispersing the clay mineral does indeed result in more stable gels even in very dilute dispersions. These weak gels are seen to exhibit a transient collapse after a finite delay time, a phenomenon observed previously in depletion gels. The velocity of the collapse oscillates with the age of the sample. However, the average velocity of collapse increases with sample age up to a peak value before decreasing at higher ages. With increasing salt concentration, the delay time for transient collapse decreases, while the peak value of the collapsing velocity increases. Using ultrasound attenuation spectroscopy, rheometry and cryogenic scanning electron microscopy, we confirm that morphological changes of the gel network assembly, facilitated by thermal fluctuations, lead to the observed collapse phenomenon. Since clay minerals are used extensively in polymer nanocomposites, as rheological modifiers, stabilizers and gas absorbents, we believe that the results reported in this work are extremely useful for several practical applications and also for understanding geophysical phenomena such as the formation and stability of quicksand

  8. Dictyostelium Myosin Bipolar Thick Filament Formation: Importance of Charge and Specific Domains of the Myosin Rod

    PubMed Central

    2004-01-01

    Myosin-II thick filament formation in Dictyostelium is an excellent system for investigating the phenomenon of self-assembly, as the myosin molecule itself contains all the information required to form a structure of defined size. Phosphorylation of only three threonine residues can dramatically change the assembly state of myosin-II. We show here that the C-terminal 68 kDa of the myosin-II tail (termed AD-Cterm) assembles in a regulated manner similar to full-length myosin-II and forms bipolar thick filament (BTF) structures when a green fluorescent protein (GFP) “head” is added to the N terminus. The localization of this GFP-AD-Cterm to the cleavage furrow of dividing Dictyostelium cells depends on assembly state, similar to full-length myosin-II. This tail fragment therefore represents a good model system for the regulated formation and localization of BTFs. By reducing regulated BTF assembly to a more manageable model system, we were able to explore determinants of myosin-II self-assembly. Our data support a model in which a globular head limits the size of a BTF, and the large-scale charge character of the AD-Cterm region is important for BTF formation. Truncation analysis of AD-Cterm tail fragments shows that assembly is delicately balanced, resulting in assembled myosin-II molecules that are poised to disassemble due to the phosphorylation of only three threonines. PMID:15492777

  9. Dictyostelium myosin bipolar thick filament formation: importance of charge and specific domains of the myosin rod.

    PubMed

    Hostetter, Daniel; Rice, Sarah; Dean, Sara; Altman, David; McMahon, Peggy M; Sutton, Shirley; Tripathy, Ashutosh; Spudich, James A

    2004-11-01

    Myosin-II thick filament formation in Dictyostelium is an excellent system for investigating the phenomenon of self-assembly, as the myosin molecule itself contains all the information required to form a structure of defined size. Phosphorylation of only three threonine residues can dramatically change the assembly state of myosin-II. We show here that the C-terminal 68 kDa of the myosin-II tail (termed AD-Cterm) assembles in a regulated manner similar to full-length myosin-II and forms bipolar thick filament (BTF) structures when a green fluorescent protein (GFP) "head" is added to the N terminus. The localization of this GFP-AD-Cterm to the cleavage furrow of dividing Dictyostelium cells depends on assembly state, similar to full-length myosin-II. This tail fragment therefore represents a good model system for the regulated formation and localization of BTFs. By reducing regulated BTF assembly to a more manageable model system, we were able to explore determinants of myosin-II self-assembly. Our data support a model in which a globular head limits the size of a BTF, and the large-scale charge character of the AD-Cterm region is important for BTF formation. Truncation analysis of AD-Cterm tail fragments shows that assembly is delicately balanced, resulting in assembled myosin-II molecules that are poised to disassemble due to the phosphorylation of only three threonines. PMID:15492777

  10. Dynamic Arrest in Charged Colloidal Systems Exhibiting Large-Scale Structural Heterogeneities

    SciTech Connect

    Haro-Perez, C.; Callejas-Fernandez, J.; Hidalgo-Alvarez, R.; Rojas-Ochoa, L. F.; Castaneda-Priego, R.; Quesada-Perez, M.; Trappe, V.

    2009-01-09

    Suspensions of charged liposomes are found to exhibit typical features of strongly repulsive fluid systems at short length scales, while exhibiting structural heterogeneities at larger length scales that are characteristic of attractive systems. We model the static structure factor of these systems using effective pair interaction potentials composed of a long-range attraction and a shorter range repulsion. Our modeling of the static structure yields conditions for dynamically arrested states at larger volume fractions, which we find to agree with the experimentally observed dynamics.

  11. ELECTRON MICROSCOPE ANALYSIS OF YOUNG AND OLD RED BLOOD CELLS STAINED WITH COLLOIDAL IRON FOR SURFACE CHARGE EVALUATION

    PubMed Central

    Marikovsky, Y.; Danon, D.

    1969-01-01

    Human and rabbit red blood cells, separated into "young" and "old" age groups by differential flotation on phthalate esters, were fixed with glutaraldehyde and labeled with colloidal ferric oxide. Electron micrographs of thin sections of young cells showed a uniform and dense depostion of positive iron particles. Old cells showed particles deposited irregularly, leaving unlabeled gaps on the membrane surface. Red cells incubated with 10 units/ml receptor-destroying enzyme (RDE) demonstrate a reduced labeling, similar to that of old cells. After neuraminic acid had been removed from red cells by 20 units/ml RDE, no iron particles were found on membrane surfaces. The different labeling of young, old, and RDE-treated human and rabbit red cells was correlated with their electric mobility and agglutinability by poly-L-lysine. The contradiction between the apparent similarity in charge density of human and rabbit red cells as estimated by density of iron particles and the markedly lower electric mobility of rabbit red cells is discussed. PMID:4186411

  12. Electron microscope analysis of young and old red blood cells stained with colloidal iron for surface charge evaluation.

    PubMed

    Marikovsky, Y; Danon, D

    1969-10-01

    Human and rabbit red blood cells, separated into "young" and "old" age groups by differential flotation on phthalate esters, were fixed with glutaraldehyde and labeled with colloidal ferric oxide. Electron micrographs of thin sections of young cells showed a uniform and dense depostion of positive iron particles. Old cells showed particles deposited irregularly, leaving unlabeled gaps on the membrane surface. Red cells incubated with 10 units/ml receptor-destroying enzyme (RDE) demonstrate a reduced labeling, similar to that of old cells. After neuraminic acid had been removed from red cells by 20 units/ml RDE, no iron particles were found on membrane surfaces. The different labeling of young, old, and RDE-treated human and rabbit red cells was correlated with their electric mobility and agglutinability by poly-L-lysine. The contradiction between the apparent similarity in charge density of human and rabbit red cells as estimated by density of iron particles and the markedly lower electric mobility of rabbit red cells is discussed. PMID:4186411

  13. Investigation of the nonlinear effects during the sedimentation process of a charged colloidal particle by direct numerical simulation.

    PubMed

    Keller, Florian; Feist, Markus; Nirschl, Hermann; Dörfler, Willy

    2010-04-01

    In this article we study the settling process of a colloidal particle under the influence of a gravitational or centrifugal field in an unbounded electrolyte solution. Since particles in aqueous solutions normally carry a non-zero surface charge, a microscopic electric field develops which alters the sedimentation process compared to an uncharged particle. This process can be mathematically modelled via the Stokes-Poisson-Nernst-Planck system, a system of coupled partial differential equations that have to be solved in an exterior domain. After a dimensional analysis we investigate the influence of the various characteristic dimensionless numbers on the sedimentation velocity. Thereby the linear-response (weak-field) approximation that underpins almost all existing theoretical work on classical electrokinetic phenomena is relaxed, such that no additional assumption on the thickness of the double layer as well as on its displacement is needed. We show that there exists a strong influence of the fluid Reynolds number and the ionic strength on the sedimentation velocity. Further we have developed an asymptotic expansion to describe the limit of small values of the surface potential of a single particle. This expansion incorporates all nonlinear effects and extends the well-known results of Booth (1954) [1] and Ohshima et al. (1984) [2] to higher fluid Reynolds numbers. PMID:20097350

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

    NASA Astrophysics Data System (ADS)

    Sanz, Eduardo; Valeriani, Chantal; Vissers, Teun; Fortini, Andrea; Leunissen, Mirjam E.; van Blaaderen, Alfons; Frenkel, Daan; Dijkstra, Marjolein

    2008-12-01

    We study the kinetics of the liquid-to-crystal transformation and of gel formation in colloidal suspensions of oppositely charged particles. We analyse, by means of both computer simulations and experiments, the evolution of a fluid quenched to a state point of the phase diagram where the most stable state is either a homogeneous crystalline solid or a solid phase in contact with a dilute gas. On the one hand, at high temperatures and high packing fractions, close to a substitutionally-ordered/substitutionally-disordered solid-solid coexistence line, we find that the fluid-to-crystal pathway does not follow the minimum free energy route. On the other hand, a quench to a state point far from the substitutionally-ordered/substitutionally-disordered crystal coexistence border is followed by a fluid-to-solid transition through the minimum free energy pathway. At low temperatures and packing fractions we observe that the system undergoes a gas-liquid spinodal decomposition that, at some point, stops, giving rise to a gel-like structure. Both our simulations and experiments suggest that increasing the interaction range favours crystallization over vitrification in gel-like structures.

  15. Delocalized and localized charged excitons in single CdSe/CdS dot-in-rods revealed by polarized photoluminescence blinking

    NASA Astrophysics Data System (ADS)

    Ihara, Toshiyuki; Sato, Ryota; Teranishi, Toshiharu; Kanemitsu, Yoshihiko

    2014-07-01

    CdSe/CdS heterostructured nanocrystals with quasi-type-II band alignments provide an interesting platform for studying the photoluminescence (PL) blinking associated with their unique morphologies. By using simultaneous measurements of the PL intensity, lifetime, and polarization anisotropy, we reveal the role of the electron delocalization during the blinking of single CdSe/CdS dot-in-rods. We found that a significant change in the PL polarization anisotropy distinguishes between two kinds of charged excitons with different electron delocalizations. We report our observation of unique polarized PL blinking governed by the band alignments and the Coulomb interactions between the charges inside and outside the dot-in-rod.

  16. Rodding Surgery

    MedlinePlus

    ... Rods can be made of stainless steel or titanium. Regular rods do not expand. They have many ... v regular), the rod materials (stainless steel v titanium) and the age for a first rodding surgery. ...

  17. Electrophoresis of a charged colloidal particle in porous media: boundary effect of a solid plane.

    PubMed

    Tsai, Peter; Huang, Cheng-Hsuan; Lee, Eric

    2011-11-15

    Electrokinetic treatments such as the electrophoretic technique have been applied successfully to various soil remediation and contaminant removal situations. To understand further the fundamental features involved, the electrophoretic motion of a charged particle in porous media is investigated theoretically in this study, focusing on the boundary effect of a nearby solid plane toward which the particle moves perpendicularly. The porous medium is modeled as a Brinkman fluid with a characteristic screening length (λ(-1)) that can be obtained directly from the experimental data. General electrokinetic equations are used to describe the system and are solved with a pseudospectral method based on Chebyshev polynomials. We found that the particle motion is deterred by the boundary effect in general. The closer the particle is to the boundary, the more severe this effect is. Up to a 90% reduction in particle mobility is observed in some situations. This indicates that a drastic overestimation (10-fold!) of the overall transport rate of particles may occur for large-scale in situ operations in porous media, such as soil remediation utilizing large planar electrodes, should a portable analytical formula valid for bulk systems only be used. Correction factors for various situations in porous media are presented as convenient charts with which to aid engineers and researchers in the field of environmental engineering, for instance, as a realistic estimation of the actual transport rate obtainable. In addition, the results of present study can be applied to biomedical engineering and drug delivery as well because polymer gels and skin barriers both have a porous essence. PMID:21967511

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

    NASA Astrophysics Data System (ADS)

    Sanz, Eduardo

    2009-03-01

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

  19. Plasmon-induced charge separation at two-dimensional gold semishell arrays on SiO{sub 2}@TiO{sub 2} colloidal crystals

    SciTech Connect

    Wu, Ling; Nishi, Hiroyasu; Tatsuma, Tetsu

    2015-10-01

    Photoelectrodes based on plasmonic Au semishell (or halfshell) arrays are developed. A colloidal crystal consisting of SiO{sub 2}@TiO{sub 2} core-shell particles is prepared on a TiO{sub 2}-coated transparent electrode. A Au semishell (or halfshell) array is deposited by sputtering or evaporation on the colloidal crystal. An electrode with the semishell (or halfshell) array exhibits negative photopotential shifts and anodic photocurrents under visible light at 500-800 nm wavelengths in an aqueous electrolyte containing an electron donor. In particular, hydroquinone and ethanol are good electron donors. The photocurrents can be explained in terms of plasmon-induced charge separation at the Au-TiO{sub 2} interface.

  20. Plasmon-induced charge separation at two-dimensional gold semishell arrays on SiO2@TiO2 colloidal crystals

    NASA Astrophysics Data System (ADS)

    Wu, Ling; Nishi, Hiroyasu; Tatsuma, Tetsu

    2015-10-01

    Photoelectrodes based on plasmonic Au semishell (or halfshell) arrays are developed. A colloidal crystal consisting of SiO2@TiO2 core-shell particles is prepared on a TiO2-coated transparent electrode. A Au semishell (or halfshell) array is deposited by sputtering or evaporation on the colloidal crystal. An electrode with the semishell (or halfshell) array exhibits negative photopotential shifts and anodic photocurrents under visible light at 500-800 nm wavelengths in an aqueous electrolyte containing an electron donor. In particular, hydroquinone and ethanol are good electron donors. The photocurrents can be explained in terms of plasmon-induced charge separation at the Au-TiO2 interface.

  1. Trap-Assisted Transport and Non-Uniform Charge Distribution in Sulfur-Rich PbS Colloidal Quantum Dot-based Solar Cells with Selective Contacts.

    PubMed

    Malgras, Victor; Zhang, Guanran; Nattestad, Andrew; Clarke, Tracey M; Mozer, Attila J; Yamauchi, Yusuke; Kim, Jung Ho

    2015-12-01

    This study reports evidence of dispersive transport in planar PbS colloidal quantum dot heterojunction-based devices as well as the effect of incorporating a MoO3 hole selective layer on the charge extraction behavior. Steady state and transient characterization techniques are employed to determine the complex recombination processes involved in such devices. The addition of a selective contact drastically improves the device efficiency up to 3.15% (especially due to increased photocurrent and decreased series resistance) and extends the overall charge lifetime by suppressing the main first-order recombination pathway observed in device without MoO3. The lifetime and mobility calculated for our sulfur-rich PbS-based devices are similar to previously reported values in lead-rich quantum dots-based solar cells. Nevertheless, strong Shockley-Read-Hall mechanisms appear to keep restricting charge transport, as the equilibrium voltage takes more than 1 ms to be established. PMID:26541422

  2. Directed self-assembly of colloidal model systems on charge-selective surfaces in external electric fields: theory and numerical analysis.

    PubMed

    Falk, Guido

    2013-02-14

    Membrane electrophoretic deposition has a long-established reputation in delivering high quality nanoparticle compact and coating solutions in the field of high performance nanoparticle architectures made from aqueous nanoparticle suspensions. Although for a long time, it has been common practice in nanoparticle science and particle-based nanotechnology to use membrane electrophoretic shaping of nanoparticles, little is known about long-range electrohydrodynamic manipulation of the engineered assembly of colloidal particles at the nanoscale. Here, we analyze the interfacial field-induced flow of a strong electrolyte and its implications for the directed self-assembly of colloidal nanoparticles on nonuniform charge-selective ion-exchange membrane surfaces as well as on conducting microelectrodes imposed to electrophoretic deposition boundary conditions. Numerical calculations of the vortex streamlines are derived for the case of extreme diffusion limitation, concentration polarization near the limiting current, and induced electric forces acting upon the residual space charge. The system is modeled by coupled mass balances, Ohmic law, Navier-Stokes, and Nernst-Planck equations. Particularly, numerical calculations under bulk electroconvection conditions show that the latter provides an efficient intrinsic interfacial mechanism capable of accounting for the experimentally observed local electrophoretic deposition behavior of nanoparticles at ideal permselective membranes with nonplanar periodic charge discontinuity and metal microelectrodes. PMID:22913482

  3. Enhanced emission of charged-exciton polaritons from colloidal quantum dots on a SiN/SiO2 slab waveguide

    PubMed Central

    Xu, Xingsheng; Li, Xingyun

    2015-01-01

    We investigate the photoluminescence (PL) spectra and the time-resolved PL decay process from colloidal quantum dots on SiN/SiO2 wet etched via BOE (HF:NH4F:H2O). The spectrum displays multi-peak shapes that vary with irradiation time. The evolution of the spectral peaks with irradiation time and collection angle demonstrates that the strong coupling of the charged-exciton emission to the leaky modes of the SiN/SiO2 slab waveguide predominantly produces short-wavelength spectral peaks, resulting in multi-peak spectra. We conclude that BOE etching enhances the charged-exciton emission efficiency and its contribution to the total emission compared with the unetched case. BOE etching smoothes the electron confinement potential, thus decreasing the Auger recombination rate. Therefore, the charged-exciton emission efficiency is high, and the charged-exciton-polariton emission can be further enhanced through strong coupling to the leaky mode of the slab waveguide. PMID:25988709

  4. EDITORIAL: Colloidal suspensions Colloidal suspensions

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

    fluid-fluid interface [2]. Together with Remco Tuinier, Henk has recently completed a book in this area which is to appear later this year. A major theme in Henk's research is that of phase transitions in lyotropic liquid crystals. Henk, together with Daan Frenkel and Alain Stroobants, realized in the 1980s that a smectic phase in dispersions of rod-like particles can be stable without the presence of attractive interactions, similar to nematic ordering as predicted earlier by Onsager [3]. Together with Gert-Jan Vroege he wrote a seminal review in this area [4]. Henk once said that 'one can only truly develop one colloidal model system in one's career' and in his case this must be that of gibbsite platelets. Initially Henk's group pursued another polymorph of aluminium hydroxide, boehmite, which forms rod-like particles [5], which already displayed nematic liquid crystal phases. The real breakthrough came when the same precursors treated the produced gibbsite platelets slightly differently. These reliably form a discotic nematic phase [6] and, despite the polydispersity in their diameter, a columnar phase [7]. A theme encompassing a wide range of soft matter systems is that of colloidal dynamics and phase transition kinetics. Many colloidal systems have a tendency to get stuck in metastable states, such as gels or glasses. This is a nuisance if one wishes to study phase transitions, but it is of great practical significance. Such issues feature in many of Henk's publications, and with Valerie Anderson he wrote a highly cited review in this area [8]. Henk Lekkerkerker has also invested significant effort into the promotion of synchrotron radiation studies of colloidal suspensions. He was one of the great supporters of the Dutch-Belgian beamline 'DUBBLE' project at the ESRF [9]. He attended one of the very first experiments in Grenoble in 1999, which led to a Nature publication [7]. He was strongly involved in many other experiments which followed and also has been a

  5. EDITORIAL: Colloidal suspensions Colloidal suspensions

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

    fluid-fluid interface [2]. Together with Remco Tuinier, Henk has recently completed a book in this area which is to appear later this year. A major theme in Henk's research is that of phase transitions in lyotropic liquid crystals. Henk, together with Daan Frenkel and Alain Stroobants, realized in the 1980s that a smectic phase in dispersions of rod-like particles can be stable without the presence of attractive interactions, similar to nematic ordering as predicted earlier by Onsager [3]. Together with Gert-Jan Vroege he wrote a seminal review in this area [4]. Henk once said that 'one can only truly develop one colloidal model system in one's career' and in his case this must be that of gibbsite platelets. Initially Henk's group pursued another polymorph of aluminium hydroxide, boehmite, which forms rod-like particles [5], which already displayed nematic liquid crystal phases. The real breakthrough came when the same precursors treated the produced gibbsite platelets slightly differently. These reliably form a discotic nematic phase [6] and, despite the polydispersity in their diameter, a columnar phase [7]. A theme encompassing a wide range of soft matter systems is that of colloidal dynamics and phase transition kinetics. Many colloidal systems have a tendency to get stuck in metastable states, such as gels or glasses. This is a nuisance if one wishes to study phase transitions, but it is of great practical significance. Such issues feature in many of Henk's publications, and with Valerie Anderson he wrote a highly cited review in this area [8]. Henk Lekkerkerker has also invested significant effort into the promotion of synchrotron radiation studies of colloidal suspensions. He was one of the great supporters of the Dutch-Belgian beamline 'DUBBLE' project at the ESRF [9]. He attended one of the very first experiments in Grenoble in 1999, which led to a Nature publication [7]. He was strongly involved in many other experiments which followed and also has been a

  6. 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)

  7. The role of charged particles in the positive corona-generated photon count in a rod to plane air gap

    SciTech Connect

    Bian, X. M.; Wang, Y. J.; MacAlpine, J. M. K.; Chen, L.; Wang, L. M.; Guan, Z. C.; Wan, S. W.; Liu, L.

    2013-08-26

    The relationship between the calculated charged-particle densities in positive corona, the rate of streamer production, and the photon count from the corona were investigated and found to be closely related. Both the densities of electrons and positive ions peaked at 11.8 kV, near the corona inception voltage; they then fell rapidly before slowly rising again. This behavior was exactly matched by the measured photon count. The calculation of the charged-particle density in a positive corona was achieved by means of a fluid model.

  8. Effect of surface charge on the colloidal stability and in vitro uptake of carboxymethyl dextran-coated iron oxide nanoparticles

    PubMed Central

    Ayala, Vanessa; Herrera, Adriana P.; Latorre-Esteves, Magda; Torres-Lugo, Madeline

    2013-01-01

    Nanoparticle physicochemical properties such as surface charge are considered to play an important role in cellular uptake and particle–cell interactions. In order to systematically evaluate the role of surface charge on the uptake of iron oxide nanoparticles, we prepared carboxymethyl-substituted dextrans with different degrees of substitution, ranging from 38 to 5 groups per chain, and reacted them using carbodiimide chemistry with amine–silane-coated iron oxide nanoparticles with narrow size distributions in the range of 33–45 nm. Surface charge of carboxymethyl-substituted dextran-coated nano-particles ranged from −50 to 5 mV as determined by zeta potential measurements, and was dependent on the number of carboxymethyl groups incorporated in the dextran chains. Nanoparticles were incubated with CaCo-2 human colon cancer cells. Nanoparticle–cell interactions were observed by confocal laser scanning microscopy and uptake was quantified by elemental analysis using inductively coupled plasma mass spectroscopy. Mechanisms of internalization were inferred using pharmacological inhibitors for fluid-phase, clathrin-mediated, and caveola-mediated endocytosis. Results showed increased uptake for nanoparticles with greater negative charge. Internalization patterns suggest that uptake of the most negatively charged particles occurs via non-specific interactions. PMID:24470787

  9. Charge transfer between a CdSe/CdS quantum rod and an attached ferrocene molecule: a first principle study

    NASA Astrophysics Data System (ADS)

    Tarafder, Kartick; Wang, Lin-Wang

    2013-03-01

    Semiconductor quantum dot (QD) shows interesting opto-electrical properties, very different from bulk semiconductors. However, one major challenge for opto-electrical application is to get the charge carrier out of the QD. One approach is to use an attached molecule to extract the photon generated carrier from the QD. Ferrocene has a potential to change its electron transition level either by adjusting the Ferrocene and Ferrocene + ratio in a solvent, or by adding other functional groups. However, proper understanding of the interactions between QD and molecule is limited, which is extremely useful for further design of such system. One of the main difficult is that there are thousands of atoms contained in the system, a first principle study of which is beyond the limit of existing computational power using direct density functional theory method. In this work we used a novel technique called charge-patching method, and combined that with Marcus model to study the electron and hole transfer between ferrocene and CdS/CdSe core-shell quantum dot. This study allows us to gain insights into the molecule dot interactions and underlying photoluminescence quenching process.

  10. An insight into the mechanism of charge-transfer of hybrid polymer:ternary/quaternary chalcopyrite colloidal nanocrystals

    PubMed Central

    Chawla, Parul; Singh, Son

    2014-01-01

    Summary In this work, we have demonstrated the structural and optoelectronic properties of the surface of ternary/quaternary (CISe/CIGSe/CZTSe) chalcopyrite nanocrystallites passivated by tri-n-octylphosphine-oxide (TOPO) and tri-n-octylphosphine (TOP) and compared their charge transfer characteristics in the respective polymer: chalcopyrite nanocomposites by dispersing them in poly(3-hexylthiophene) polymer. It has been found that CZTSe nanocrystallites due to their high crystallinity and well-ordered 3-dimensional network in its pristine form exhibit a higher steric- and photo-stability, resistance against coagulation and homogeneity compared to the CISe and CIGSe counterparts. Moreover, CZTSe nanocrystallites display efficient photoluminescence quenching as evident from the high value of the Stern–Volmer quenching constant (K SV) and eventually higher charge transfer efficiency in their respective polymer P3HT:CZTSe composites. We modelled the dependency of the charge transfer from the donor and the charge separation mechanism across the donor–acceptor interface from the extent of crystallinity of the chalcopyrite semiconductors (CISe/CIGSe/CZTSe). Quaternary CZTSe chalcopyrites with their high crystallinity and controlled morphology in conjunction with regioregular P3HT polymer is an attractive candidate for hybrid solar cells applications. PMID:25161859

  11. An insight into the mechanism of charge-transfer of hybrid polymer:ternary/quaternary chalcopyrite colloidal nanocrystals.

    PubMed

    Chawla, Parul; Singh, Son; Sharma, Shailesh Narain

    2014-01-01

    In this work, we have demonstrated the structural and optoelectronic properties of the surface of ternary/quaternary (CISe/CIGSe/CZTSe) chalcopyrite nanocrystallites passivated by tri-n-octylphosphine-oxide (TOPO) and tri-n-octylphosphine (TOP) and compared their charge transfer characteristics in the respective polymer: chalcopyrite nanocomposites by dispersing them in poly(3-hexylthiophene) polymer. It has been found that CZTSe nanocrystallites due to their high crystallinity and well-ordered 3-dimensional network in its pristine form exhibit a higher steric- and photo-stability, resistance against coagulation and homogeneity compared to the CISe and CIGSe counterparts. Moreover, CZTSe nanocrystallites display efficient photoluminescence quenching as evident from the high value of the Stern-Volmer quenching constant (K SV) and eventually higher charge transfer efficiency in their respective polymer P3HT:CZTSe composites. We modelled the dependency of the charge transfer from the donor and the charge separation mechanism across the donor-acceptor interface from the extent of crystallinity of the chalcopyrite semiconductors (CISe/CIGSe/CZTSe). Quaternary CZTSe chalcopyrites with their high crystallinity and controlled morphology in conjunction with regioregular P3HT polymer is an attractive candidate for hybrid solar cells applications. PMID:25161859

  12. Hopf solitons and elastic rods

    SciTech Connect

    Harland, Derek; Sutcliffe, Paul; Speight, Martin

    2011-03-15

    Hopf solitons in the Skyrme-Faddeev model are stringlike topological solitons classified by the integer-valued Hopf charge. In this paper we introduce an approximate description of Hopf solitons in terms of elastic rods. The general form of the elastic rod energy is derived from the field theory energy and is found to be an extension of the classical Kirchhoff rod energy. Using a minimal extension of the Kirchhoff energy, it is shown that a simple elastic rod model can reproduce many of the qualitative features of Hopf solitons in the Skyrme-Faddeev model. Features that are captured by the model include the buckling of the charge three solution, the formation of links at charges five and six, and the minimal energy trefoil knot at charge seven.

  13. Trapping and chaining self-assembly of colloidal polystyrene particles over a floating electrode by using combined induced-charge electroosmosis and attractive dipole-dipole interactions.

    PubMed

    Liu, Weiyu; Shao, Jinyou; Jia, Yankai; Tao, Ye; Ding, Yucheng; Jiang, Hongyuan; Ren, Yukun

    2015-11-01

    We propose a novel low-frequency strategy to trap 10 μm colloidal polystyrene (PS) particles of small buoyancy velocity on the surface of a floating electrode, on the basis of combined induced-charge electroosmotic (ICEO) flow and dipole-dipole chaining phenomenon. For field frequencies of 5-50 Hz, much lower than the reciprocal RC time scale, double-layer polarization makes electric field lines pass around the 'insulating' surface of the ideally polarizable floating electrode. Once the long-range ICEO convective micro-vortexes transport particles quickly from the bulk fluid to the electrode surface, neighbouring particles aligned along the local horizontal electric field attract one another by attractive dipolar interactions, and form arrays of particle chains that are almost parallel with the applied electric field. Most importantly, this low-frequency trapping method takes advantage of the dielectrophoretic (DEP) particle-particle interaction to enhance the downward buoyancy force of this dipolar chaining assembly structure, in order to overcome the upward ICEO fluidic drag and realize stable particle trapping around the flow stagnation region. For the sake of comparison, the field frequency is further raised far above the DC limit. At the intermediate frequencies of 200 Hz-2 kHz, this trapping method fails to work, since the normal electric field component emanates from the conducting electrode surface. Besides, at high field frequencies (>3 kHz), particles can be once again effectively trapped at the electrode center, though with a compact (3 kHz) or disordered (10 kHz) 2D packing state on the electrode surface and mainly governed by the short-range negative DEP force field, resulting in requiring a much longer trapping time. To gain a better interpretation of the various particle behaviours observed in experiments, we develop a theoretical framework that takes into account both Maxwell-Wagner interfacial charge relaxation at the particle

  14. Many facets of the polyelectrolyte and oppositely charged colloidal particle complexation: counterion release and electrical conductivity behavior.

    PubMed

    Cametti, C; Truzzolillo, D

    2011-06-01

    The lateral correlated adsorption of polyions onto oppositely charged vesicles, leading to the formation of stable equilibrium clusters of mesoscopic size, is associated to the release of a fraction of counterions, initially condensed on the polyion chains. This ulterior release of counterions provokes an increase of the number of free ions, besides the ones due to the partial ionization of both charged particles and polyions, that can be appropriately monitored by means of electrical conductivity measurements of the whole system. We have investigated this behavior in a suspension of cationic vesicles made up by dioleoyl trimethyl ammonium propane (DOTAP) liposomial vesicles interacting with an anionic polyelectrolyte composed by polyacrylate sodium salt. This system has been in the past extensively studied by us by means of different experimental techniques, and its behavior has been sufficiently characterized, as far as hydrodynamic and electrical properties are concerned. In this note, we report on the dc electrical conductivity behavior during the whole aggregation process, from the single polyion-coated liposomal particles, to polyion-induced liposome clusters, to finally polyion-fully covered liposomes, in polyion excess conditions. We have evaluated the excess of released counterions on the basis of the standard theory of the electrical properties of aqueous charged solutions and compared this quantity with the one predicted by the lateral correlation adsorption model. The agreement is quite good, offering strong experimental evidence of the role played by the release of counterions in the aggregation process. Finally, we have considered a similar liposomial system, where the lateral correlation adsorption was inhibited by structural reasons, having replaced the polyion by a simple electrolyte, whose dissociated ions will adsorb randomly at the particle surface, rather than in a correlated manner. In this case, no counterion release upon complexation occurs

  15. Role of detergents in driving complex structural arrangements in colloidal suspensions of Photosystem I (PS I) via charge stabilization and neutralization

    NASA Astrophysics Data System (ADS)

    Niroomand, Hanieh; Mukherjee, Dibyendu; Khomami, Bamin

    2012-02-01

    Specific concentrations of detergents such as DM (n-Dodecyl-β-D-Maltoside) and Triton X-100 (TX-100) used for Photosystem I (PS I) stabilization in buffer solutions play significant roles in controlling the solution-phase protein-protein interactions. Such control on PS I-PS I interactions facilitates uniform monolayer deposition of PS I on self-assembled monolayer (SAM)/Au substrates, a critical step for their future incorporation into bio-hybrid photovoltaic devices. Moreover, electric-field assisted assembly from PS I solutions with TX-100 as the detergent facilitates the formation of uniform PS I monolayer. But, the same phenomenon is not observed for PS I suspensions with DM as the detergent. To explain the underlying colloidal physics of these systems, in-situ dynamic light scattering experiments under various incubation times and applied voltages reveal the role of DM in charge neutralization and in turn, significant reduction of the PS I dipole moment in solution. Furthermore, small angle X-ray scattering measurements provide the much-needed structural information for a detailed understanding of the protein-detergent complexation process. These detailed investigations point towards the use of random sequential adsorption techniques in creating systematic dense monolayers of PS I.

  16. Self-Assembly of Charged Amphiphilic Diblock Copolymers with Insoluble Blocks of Decreasing Hydrophobicity: From Kinetically Frozen Colloids to Macrosurfactants

    SciTech Connect

    M Jacquin; P Muller; H Cottet; O Theodoly

    2011-12-31

    We have investigated the self-assembly properties in aqueous solution of amphiphilic diblock copolymers with insoluble blocks of different hydrophobicity and demonstrated that the condition to obtain dynamic micelles is to design samples with insoluble blocks of low enough hydrophobicity. We focus here on results with new water-soluble amphiphilic diblock copolymers poly(diethyleneglycol ethylether acrylate)-b-poly(acrylic acid), or PDEGA-b-PAA. The physical characteristics of PDEGA-b-PAA micelles at high ionization have been determined by small angle neutron scattering (SANS). We show that PDEGA-b-PAA samples form micelles at thermodynamic equilibrium. The critical micelle concentrations (CMCs) decrease strongly with ionic strength and temperature due to a solvent quality decrease for, respectively, the corona and the core. This behavior of reversible aggregation is remarkable as compared to the behavior of kinetically frozen aggregation that has been widely observed with samples of similar architecture and different hydrophobic blocks, for example, poly(styrene)-b-poly(acrylic acid), PS-b-PAA, and poly(butyl acrylate)-b-poly(acrylic acid), PBA-b-PAA. We have measured the interfacial tension between water and the homopolymers PDEGA and PBA at, respectively, 3 and 20 mN/m at room temperature, which permits one to estimate the energy cost to extract a unimer from a micelle. The results are consistent with a micelle association that is fast for PDEGA-b-PAA and kinetically frozen PBA-b-PAA. Hence, PDEGA-b-PAA samples form a new system of synthetic charged macrosurfactant with unique properties of fast dynamic association, tunable charge, and water solubility even at temperatures and NaCl concentrations as high as 65 C and 1 M.

  17. 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

  18. Nucleation and crystal growth in a suspension of charged colloidal silica spheres with bi-modal size distribution studied by time-resolved ultra-small-angle X-ray scattering.

    PubMed

    Hornfeck, Wolfgang; Menke, Dirk; Forthaus, Martin; Subatzus, Sebastian; Franke, Markus; Schöpe, Hans-Joachim; Palberg, Thomas; Perlich, Jan; Herlach, Dieter

    2014-12-01

    A suspension of charged colloidal silica spheres exhibiting a bi-modal size distribution of particles, thereby mimicking a binary mixture, was studied using time-resolved ultra-small-angle synchrotron X-ray scattering (USAXS). The sample, consisting of particles of diameters d(A) = (104.7 ± 9.0) nm and d(B) = (88.1 ± 7.8) nm (d(A)/d(B) ≈ 1.2), and with an estimated composition A(0.6(1))B(0.4(1)), was studied with respect to its phase behaviour in dependance of particle number density and interaction, of which the latter was modulated by varying amounts of added base (NaOH). Moreover, its short-range order in the fluid state and its eventual solidification into a long-range ordered colloidal crystal were observed in situ, allowing the measurement of the associated kinetics of nucleation and crystal growth. Key parameters of the nucleation kinetics such as crystallinity, crystallite number density, and nucleation rate density were extracted from the time-resolved scattering curves. By this means an estimate on the interfacial energy for the interface between the icosahedral short-range ordered fluid and a body-centered cubic colloidal crystal was obtained, comparable to previously determined values for single-component colloidal systems. PMID:25481168

  19. Quantum confined colloidal nanorod heterostructures for solar-to-fuel conversion.

    PubMed

    Wu, Kaifeng; Lian, Tianquan

    2016-07-11

    Solar energy conversion, particularly solar-driven chemical fuel formation, has been intensely studied in the past decades as a potential approach for renewable energy generation. Efficient solar-to-fuel conversion requires artificial photosynthetic systems with strong light absorption, long-lived charge separation and efficient catalysis. Colloidal quantum confined nanoheterostructures have emerged as promising materials for this application because of the ability to tailor their properties through size, shape and composition. In particular, colloidal one-dimensional (1D) semiconductor nanorods (NRs) offer the opportunity to simultaneously maintain quantum confinement in radial dimensions for tunable light absorptions and bulk like carrier transport in the axial direction for long-distance charge separations. In addition, the versatile chemistry of colloidal NRs enables the formation of semiconductor heterojunctions (such as CdSe/CdS dot-in-rod NRs) to separate photogenerated electron-hole pairs and deposition of metallic domains to accept charges and catalyze redox reactions. In this review, we summarize research progress on colloidal NR heterostructures and their applications for solar energy conversion, emphasizing mechanistic insights into the working principle of these systems gained from spectroscopic studies. Following a brief overview of synthesis of various NRs and heterostructures, we introduce their electronic structures and dynamics of exciton and carrier transport and interfacial transfer. We discuss how these exciton and carrier dynamics are controlled by their structures and provide key mechanistic understanding on their photocatalytic performance, including the photo-reduction of a redox mediator (methyl viologen) and light driven H2 generation. We discuss the solar-driven H2 generation mechanism, key efficiency limiting steps, and potential approaches for rational improvement in semiconductor NR/metal heterostructures (such as Pt tipped Cd

  20. 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).

  1. 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.

  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. 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

  4. 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.

  5. CONTROL ROD

    DOEpatents

    Zinn, W.H.; Ross, H.V.

    1958-11-18

    A control rod is described for a nuclear reactor. In certaln reactor designs it becomes desirable to use a control rod having great width but relatively llttle thickness. This patent is addressed to such a need. The neutron absorbing material is inserted in a triangular tube, leaving volds between the circular insert and the corners of the triangular tube. The material is positioned within the tube by the use of dummy spacers to achleve the desired absorption pattern, then the ends of the tubes are sealed with suitable plugs. The tubes may be welded or soldered together to form two flat surfaces of any desired width, and covered with sheetmetal to protect the tubes from damage. This design provides a control member that will not distort under the action of outside forces or be ruptured by gases generated within the jacketed control member.

  6. Semiconductor Quantum Rods as Single Molecule FluorescentBiological Labels

    SciTech Connect

    Fu, Aihua; Gu, Weiwei; Boussert, Benjamine; Koski, Kristie; Gerion, Daniele; Manna, Liberato; Le Gros, Mark; Larabell, Carolyn; Alivisatos, A. Paul

    2006-05-29

    In recent years, semiconductor quantum dots have beenapplied with great advantage in a wide range of biological imagingapplications. The continuing developments in the synthesis of nanoscalematerials and specifically in the area of colloidal semiconductornanocrystals have created an opportunity to generate a next generation ofbiological labels with complementary or in some cases enhanced propertiescompared to colloidal quantum dots. In this paper, we report thedevelopment of rod shaped semiconductor nanocrystals (quantum rods) asnew fluorescent biological labels. We have engineered biocompatiblequantum rods by surface silanization and have applied them fornon-specific cell tracking as well as specific cellular targeting. Theproperties of quantum rods as demonstrated here are enhanced sensitivityand greater resistance for degradation as compared to quantum dots.Quantum rods have many potential applications as biological labels insituations where their properties offer advantages over quantumdots.

  7. 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

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

    SciTech Connect

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

    1993-10-01

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

  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. 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

  11. 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

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

    NASA Astrophysics Data System (ADS)

    Löwen, Hartmut

    2012-11-01

    Messina and H Löwen Mode expansion for the density profiles of crystal-fluid interfaces: hard spheres as a test caseM Oettel Scaling of layer spacing of charged particles under slit-pore confinement: an effect of concentration or of effective particle diameter?Yan Zeng and Regine von Klitzing Hydrodynamic interactions between colloidal particles in a planar poreB Bonilla-Capilla, A Ramírez-Saito, M A Ojeda-López and J L Arauz-Lara Ageing in a system of polydisperse goethite boardlike particles showing rich phase behaviourA B G M Leferink op Reinink, E van den Pol, D V Byelov, A V Petukhov and G J Vroege Temperature as an external field for colloid-polymer mixtures: 'quenching' by heating and 'melting' by coolingShelley L Taylor, Robert Evans and C Patrick Royall Spinning motion of a deformable self-propelled particle in two dimensionsMitsusuke Tarama and Takao Ohta Emergent states in dense systems of active rods: from swarming to turbulenceH H Wensink and H Löwen

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. Close packing of rods on spherical surfaces

    NASA Astrophysics Data System (ADS)

    Smallenburg, Frank; Löwen, Hartmut

    2016-04-01

    We study the optimal packing of short, hard spherocylinders confined to lie tangential to a spherical surface, using simulated annealing and molecular dynamics simulations. For clusters of up to twelve particles, we map out the changes in the geometry of the closest-packed configuration as a function of the aspect ratio L/D, where L is the cylinder length and D the diameter of the rods. We find a rich variety of cluster structures. For larger clusters, we find that the best-packed configurations up to around 100 particles are highly dependent on the exact number of particles and aspect ratio. For even larger clusters, we find largely disordered clusters for very short rods (L/D = 0.25), while slightly longer rods (L/D = 0.5 or 1) prefer a global baseball-like geometry of smectic-like domains, similar to the behavior of large-scale nematic shells. Intriguingly, we observe that when compared to their optimal flat-plane packing, short rods adapt to the spherical geometry more efficiently than both spheres and longer rods. Our results provide predictions for experimentally realizable systems of colloidal rods trapped at the interface of emulsion droplets.

  18. Close packing of rods on spherical surfaces.

    PubMed

    Smallenburg, Frank; Löwen, Hartmut

    2016-04-28

    We study the optimal packing of short, hard spherocylinders confined to lie tangential to a spherical surface, using simulated annealing and molecular dynamics simulations. For clusters of up to twelve particles, we map out the changes in the geometry of the closest-packed configuration as a function of the aspect ratio L/D, where L is the cylinder length and D the diameter of the rods. We find a rich variety of cluster structures. For larger clusters, we find that the best-packed configurations up to around 100 particles are highly dependent on the exact number of particles and aspect ratio. For even larger clusters, we find largely disordered clusters for very short rods (L/D = 0.25), while slightly longer rods (L/D = 0.5 or 1) prefer a global baseball-like geometry of smectic-like domains, similar to the behavior of large-scale nematic shells. Intriguingly, we observe that when compared to their optimal flat-plane packing, short rods adapt to the spherical geometry more efficiently than both spheres and longer rods. Our results provide predictions for experimentally realizable systems of colloidal rods trapped at the interface of emulsion droplets. PMID:27131565

  19. Rod examination gauge

    SciTech Connect

    Bacvinskas, W.S.; Bayer, J.E.; Davis, W.W.; Fodor, G.; Kikta, T.J.; Matchett, R.L.; Nilsen, R.J.; Wilczynski, R.

    1991-12-31

    The present invention is directed to a semi-automatic rod examination gauge for performing a large number of exacting measurements on radioactive fuel rods. The rod examination gauge performs various measurements underwater with remote controlled machinery of high reliability. The rod examination gauge includes instruments and a closed circuit television camera for measuring fuel rod length, free hanging bow measurement, diameter measurement, oxide thickness measurement, cladding defect examination, rod ovality measurement, wear mark depth and volume measurement, as well as visual examination. A control system is provided including a programmable logic controller and a computer for providing a programmed sequence of operations for the rod examination and collection of data.

  20. FUEL ROD ASSEMBLY

    DOEpatents

    Hutter, E.

    1959-09-01

    A cluster of nuclear fuel rods aod a tubular casing through which a coolant flows in heat-change contact with the ruel rods are described. The casting is of trefoil section and carries the fuel rods, each of which has two fin engaging the serrated fins of the other two fuel rods, whereby the fuel rods are held in the casing and are interlocked against relative longitudinal movement.

  1. 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

  2. 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.

  3. Electric field in the vicinity of long thin conducting rods

    NASA Astrophysics Data System (ADS)

    Rezinkina, M. M.; Rezinkin, O. L.; Svetlichnaya, E. E.

    2015-09-01

    We report on the results of numerical and analytical calculations of distributions of potentials and electric fields in the vicinity of thin conducting rods that model the leader channel of lightning and lightning rods. We consider rods represented in the form of a uniformly charged filament, a conducting ellipsoid with a free charge on its surface, as well an ellipsoid or a cylinder in a uniform external electric field. The effect of parameters of conducting rods modeling the leader channel of lightning and lightning rods, as well as the region containing a space charge around the tip of the leader channel, on the distribution of potentials and field strengths are analyzed. The conditions for the propagation of the counter leader from the lightning rod are specified.

  4. Control rod drive hydraulic system

    DOEpatents

    Ose, Richard A.

    1992-01-01

    A hydraulic system for a control rod drive (CRD) includes a variable output-pressure CR pump operable in a charging mode for providing pressurized fluid at a charging pressure, and in a normal mode for providing the pressurized fluid at a purge pressure, less than the charging pressure. Charging and purge lines are disposed in parallel flow between the CRD pump and the CRD. A hydraulic control unit is disposed in flow communication in the charging line and includes a scram accumulator. An isolation valve is provided in the charging line between the CRD pump and the scram accumulator. A controller is operatively connected to the CRD pump and the isolation valve and is effective for opening the isolation valve and operating the CRD pump in a charging mode for charging the scram accumulator, and closing the isolation valve and operating the CRD pump in a normal mode for providing to the CRD through the purge line the pressurized fluid at a purge pressure lower than the charging pressure.

  5. 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.

  6. 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 ...

  7. Colloid Bound Transport of Contaminats In The Unsaturated Zone

    NASA Astrophysics Data System (ADS)

    Hofmann, T.; Christ, A.

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

  8. Control rod drive

    SciTech Connect

    Hawke, Basil C.

    1986-01-01

    A control rod drive uses gravitational forces to insert one or more control rods upwardly into a reactor core from beneath the reactor core under emergency conditions. The preferred control rod drive includes a vertically movable weight and a mechanism operatively associating the weight with the control rod so that downward movement of the weight is translated into upward movement of the control rod. The preferred control rod drive further includes an electric motor for driving the control rods under normal conditions, an electrically actuated clutch which automatically disengages the motor during a power failure and a decelerator for bringing the control rod to a controlled stop when it is inserted under emergency conditions into a reactor core.

  9. 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)

  10. Optimal Navigation of Self-Propelled Colloids in Microstructured Mazes

    NASA Astrophysics Data System (ADS)

    Yang, Yuguang; Bevan, Michael

    Controlling navigation of self-propelled microscopic `robots' subject to random Brownian motion in complex microstructured environments (e.g., porous media, tumor vasculature) is important to many emerging applications (e.g., enhanced oil recovery, drug delivery). In this work, we design an optimal feedback policy to navigate an active self-propelled colloidal rod in complex mazes with various obstacle types. Actuation of the rods is modelled based on a light-controlled osmotic flow mechanism, which produces different propulsion velocities along the rod's long axis. Actuator-parameterized Langevin equations, with soft rod-obstacle repulsive interactions, are developed to describe the system dynamics. A Markov decision process (MDP) framework is used for optimal policy calculations with design goals of colloidal rods reaching target end points in minimum time. Simulations show that optimal MDP-based policies are able to control rod trajectories to reach target regions order-of-magnitudes faster than uncontrolled rods, which diverges as maze complexity increases. An efficient multi-graph based implementation for MDP is also presented, which scales linearly with the maze dimension.

  11. Using Microfluidics to Measure the Equation of State for a 2D Colloidal Membrane

    NASA Astrophysics Data System (ADS)

    Balchunas, Andrew; Cabanas, Rafael; Fraden, Seth; Dogic, Zvonimir

    2015-03-01

    In the presence of non-adsorbing polymer, monodisperse filamentous viruses assembles into colloidal membranes which are 2D liquid-like one-rod-length-thick monolayers of aligned rods. Colloidal membranes are of particular interest because their properties are accounted for by the same theoretical models that are used to describe biophysics of conventional lipid bilayers. However, bulk membrane formation only occurs over a very limited range of depletant concentrations and ionic strengths. In order to explore the properties of the colloidal membranes under a much wider range of molecular parameters, we have develop a microfluidics technique that allows for in-site exchange of the enveloping polymer suspension thus allowing us to access the region of phase space where membranes are metastable. Using our technique we determine how the colloidal membrane area depends on applied osmotic pressure allowing us to determine its equation of state. We also characterize the dynamics of the constituent rods by using single molecules tracking techniques.

  12. Non-blinking single-photon generation with anisotropic colloidal nanocrystals: towards room-temperature, efficient, colloidal quantum sources.

    PubMed

    Pisanello, Ferruccio; Leménager, Godefroy; Martiradonna, Luigi; Carbone, Luigi; Vezzoli, Stefano; Desfonds, Pascal; Cozzoli, Pantaleo Davide; Hermier, Jean-Pierre; Giacobino, Elisabeth; Cingolani, Roberto; De Vittorio, Massimo; Bramati, Alberto

    2013-04-11

    Blinking and single-photon emission can be tailored in CdSe/CdS core/shell colloidal dot-in-rods. By increasing the shell thickness it is possible to obtain almost non-blinking nanocrystals, while the shell length can be used to control single-photon emission probability. PMID:23334905

  13. Piston rod seal

    DOEpatents

    Lindskoug, Stefan

    1984-01-01

    In a piston rod seal of the type comprising a gland through which the piston rod is passed the piston is provided with a sleeve surrounding the piston rod and extending axially so as to axially partly overlap the gland when the piston is in its bottom dead center position.

  14. Directed Self-Assembly of Colloidal Janus Matchsticks

    NASA Astrophysics Data System (ADS)

    Chaudhary, Kundan; Chen, Qian; Juarez, Jaime; Granick, Steve; Lewis, Jennifer

    2013-03-01

    The ability to assemble anisotropic colloidal building blocks into ordered configurations is scientifically and technologically important for developing new classes of soft materials. We are studying the fabrication and electric field driven assembly of end- and side-coated Janus rods. Specifically, we fabricate silica rods (L/D = 2-4) functionalized with hydrophobic gold (Au) patches using a multistep process involving electric field alignment and crystallization, microcontact printing, and selective metallization. In the absence of an applied electric filed, the Janus matchsticks (end-coated rods) self-assemble into multi pods (e.g., bi-, tri- and tetrapods) of varying coordination number and patch angle in aqueous solution. By contrast, both Janus matchsticks and side-coated Janus rods form complex chains in applied AC electric fields of varying magnitude and frequency, whose configurations vary significantly from those formed by pure silica rods.

  15. 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.

  16. 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

  17. Photoinduced ultrafast charge separation in colloidal 2-dimensional CdSe/CdS-Au hybrid nanoplatelets and corresponding application in photocatalysis.

    PubMed

    Chauhan, Himani; Kumar, Yogesh; Dana, Jayanta; Satpati, Biswarup; Ghosh, Hirendra N; Deka, Sasanka

    2016-08-25

    Multicomponent hybrid nanocrystals (HNC) consisting of a semiconductor and metallic domains are an important class of nanostructured materials demonstrating useful applications and interesting basic knowledge. In this scenario, Au nanoparticle (NP) islands of ∼2 nm have been grown on unique two dimensional (2D) CdSe/CdS core@shell hexagonal nanoheteroplatelets of 20 nm diameter to form unprecedented 2D CdSe/CdS-Au HNCs and detailed optical characterization has been carried out to determine the dimensionality based electron transfer dynamics on the ultrafast scale. Steady state optical absorption studies show that upon growing Au NPs onto the 2D nanoplates, a new band appears in the red region of the spectra (500-800 nm), which suggests a strong interaction between the exciton of the core-shell and the plasmon of the metal NPs. Fluorescence studies showed the quenching of emission of the semiconductor domains upon the growth of the metallic domains. Detailed optical and TRPL studies suggested efficient charge transfer from the 2D CdSe/CdS to the Au domains, irrespective of excitation wavelength. Femtosecond transient absorption studies suggest that the electron transfer from the 2D hybrid nanocrystals to the metal domain is on an ultrafast time scale (∼800 fs). No evidence is observed for charge transfer from the 2 nm Au domains to the semiconductor seeds. The broad absorption in the visible region of the hybrid nanocrystals and the ultrafast charge transfer facilitates very efficient photo-catalytic reactions under direct sun light, as a case study. PMID:27533050

  18. 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.

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

    PubMed

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

    2015-04-01

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

  20. Singlet-Triplet Splittings in the Luminescent Excited States of Colloidal Cu(+):CdSe, Cu(+):InP, and CuInS2 Nanocrystals: Charge-Transfer Configurations and Self-Trapped Excitons.

    PubMed

    Knowles, Kathryn E; Nelson, Heidi D; Kilburn, Troy B; Gamelin, Daniel R

    2015-10-14

    The electronic and magnetic properties of the luminescent excited states of colloidal Cu(+):CdSe, Cu(+):InP, and CuInS2 nanocrystals were investigated using variable-temperature photoluminescence (PL) and magnetic circularly polarized luminescence (MCPL) spectroscopies. The nanocrystal electronic structures were also investigated by absorption and magnetic circular dichroism (MCD) spectroscopies. By every spectroscopic measure, the luminescent excited states of all three materials are essentially indistinguishable. All three materials show very similar broad PL line widths and large Stokes shifts. All three materials also show similar temperature dependence of their PL lifetimes and MCPL polarization ratios. Analysis shows that this temperature dependence reflects Boltzmann population distributions between luminescent singlet and triplet excited states with average singlet-triplet splittings of ∼1 meV in each material. These similarities lead to the conclusion that the PL mechanism in CuInS2 NCs is fundamentally different from that of bulk CuInS2 and instead is the same as that in Cu(+)-doped NCs, which are known to luminesce via charge-transfer recombination of conduction-band electrons with copper-localized holes. The luminescence of CuInS2 nanocrystals is explained well by invoking exciton self-trapping, in which delocalized photogenerated holes contract in response to strong vibronic coupling at lattice copper sites to form a luminescent excited state that is essentially identical to that of the Cu(+)-doped semiconductor nanocrystals. PMID:26389577

  1. 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

  2. CONTROL ROD DRIVE

    DOEpatents

    Chapellier, R.A.; Rogers, I.

    1961-06-27

    Accurate and controlled drive for the control rod is from an electric motor. A hydraulic arrangement is provided to balance a piston against which a control rod is urged by the application of fluid pressure. The electric motor drive of the control rod for normal operation is made through the aforementioned piston. In the event scramming is required, the fluid pressure urging the control rod against the piston is relieved and an opposite fluid pressure is applied. The lack of mechanical connection between the electric motor and control rod facilitates the scramming operation.

  3. Charge dynamics at heterojunctions for PbS/ZnO colloidal quantum dot solar cells probed with time-resolved surface photovoltage spectroscopy

    NASA Astrophysics Data System (ADS)

    Spencer, B. F.; Leontiadou, M. A.; Clark, P. C. J.; Williamson, A. I.; Silly, M. G.; Sirotti, F.; Fairclough, S. M.; Tsang, S. C. E.; Neo, D. C. J.; Assender, H. E.; Watt, A. A. R.; Flavell, W. R.

    2016-02-01

    Time-resolved laser-pump X-ray-photoemission-probe spectroscopy of a ZnO ( 10 1 ¯ 0 ) substrate with and without PbS quantum dots (QDs) chemically linked to the surface is performed, using laser photon energies resonant with and below the band gap energy of the substrate (λ = 372 and 640 nm, hν = 3.33 and 1.94 eV). Charge injection from the photoexcited QDs to ZnO is demonstrated through the change in the surface photovoltage of the ZnO substrate observed when the heterojunction is illuminated with 1.94 eV radiation. The measured carrier dynamics are limited by the persistent photoconductivity of ZnO, giving dark carrier lifetimes of the order of 200 μs in a depletion layer at the interface. The chemical specificity of soft X-rays is used to separately measure the charge dynamics in the quantum dots and the substrate, yielding evidence that the depletion region at the interface extends into the PbS QD layer.

  4. 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.

  5. 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

  6. 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.

  7. 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

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

    SciTech Connect

    zzuoping@lbl.gov

    2004-04-10

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

  9. CRUCIFORM CONTROL ROD JOINT

    DOEpatents

    Thorp, A.G. II

    1962-08-01

    An invention is described which relates to nuclear reactor control rod components and more particularly to a joint between cruciform control rod members and cruciform control rod follower members. In one embodiment this invention provides interfitting crossed arms at adjacent ends of a control rod and its follower in abutting relation. This holds the members against relative opposite longitudinal movement while a compression member keys the arms against relative opposite rotation around a common axis. Means are also provided for centering the control rod and its follower on a common axis and for selectively releasing the control rod from its follower for the insertion of a replacement of the control rod and reuse of the follower. (AEC)

  10. Synchronized oscillations of dimers in biphasic charged fd-virus suspensions

    NASA Astrophysics Data System (ADS)

    Kang, K.; Piao, S. H.; Choi, H. J.

    2016-08-01

    Micron-sized colloidal spheres that are dispersed in an isotropic-nematic biphasic host suspension of charged rods (fd-virus particles) are shown to spontaneously form dimers, which exhibit a synchronized oscillatory motion. Dimer formation is not observed in the monophase of isotropic and nematic suspensions. The synchronized oscillations of dimers are connected to the inhomogeneous state of the host suspension of charged rods (fd viruses) where nematic domains are in coexistence with isotropic regions. The synchronization of oscillations occurs in bulk states, in the absence of an external field. With a low field strength of an applied electric field, the synchronization is rather reduced, but it recovers again when the field is turned off. In this Rapid Communication, we report this observation as an example of the strange attractor, occurring in the mixture of PS (polystyrene) dimers in an isotropic-nematic coexistence biphasic fd-virus network. Furthermore, we highlight that the synchronization of PS-dimer oscillations is the result of a global bifurcation diagram, driven by a delicate balance between the short-attractive "twisted" interaction of PS dimers and long-ranged electrostatic repulsive interactions of charged fd rods. The interest is then in the local enhancement of "twist-nematic" elasticity in reorientation of the dimer oscillations. An analysis of image-time correlations is provided with the data movies and Fourier transforms of averaged orientations for the synchronized oscillations of dimers in the biphasic I -N coexistence concentration of charged fd-virus suspensions.