Electrokinetics of colloidal particles in nonpolar media containing charged inverse micelles (original) (raw)
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Electrophoretic Retardation of Colloidal Particles in Nonpolar Liquids
Physical Review X, 2013
We have measured the electrophoretic mobility of single, optically trapped colloidal particles, while gradually depleting the co-ions and counterions in the liquid around the particle by applying a dc voltage. This is achieved in a nonpolar liquid, where charged reverse micelles act as co-ions and counterions. By increasing the dc voltage, the mobility first increases when the concentrations of co-ions and counterions near the particle start to decrease. At sufficiently high dc voltage (around 2 V), the mobility reaches a saturation value when the co-ions and counterions are fully separated. The increase in mobility is larger when the equilibrium ionic strength is higher. The dependence of the experimental data on the equilibrium ionic strength and on the applied voltage is in good agreement with the standard theory of electrophoretic retardation, assuming that the bare particle charge remains constant. This method is useful for studying the electrophoretic retardation effect and charging mechanisms for nonpolar colloids, and it sheds light on previously unexplained particle acceleration in electronic ink devices.
Fast and precise measurements of particle charge with optical trapping electrophoresis
Complex Light and Optical Forces IV, 2010
We subject micrometer-sized, optically trapped colloidal particles in a non-polar liquid to a sinusoidally varying electric field, and measure their resulting movement. From this movement, we calculate the electrophoretic mobility and charge of the particle in the liquid. The use of high frequencies of the electric field (well above the corner frequency of the optical tweezers) allows us to estimate the electrical charge of colloidal particles with an accuracy of the order of the electron charge in a time interval of only 10 ms. This technique can be used to provide valuable information about the dynamics of the poorly understood processes that lead to the charge on colloidal particles in non-polar liquids.
Electrodiffusiophoresis: Particle motion in electrolytes under direct current
Physics of Fluids, 2010
Colloidal particles in electrolytes move in response to electric fields ͑electrophoresis͒ and salt concentration gradients ͑diffusiophoresis͒, and related flows also occur at fixed surfaces ͑electro-osmosis and diffusio-osmosis, respectively͒. In isolation, these electrokinetic phenomena are well understood, e.g., electrophoresis without far-field concentration gradients and diffusiophoresis without applied electric fields. When the electrolyte passes direct current, however, concentration gradients accompany the bulk electric field ͑concentration polarization͒ and the resulting particle motion, called "electrodiffusiophoresis," involves a nonlinear combination of electrophoresis and diffusiophoresis, depending on ion transference numbers and particle properties. In this work, we analyze the electrodiffusiophoresis of spherical particles in the limit of thin double layers, neglecting surface conduction ͑DuӶ 1͒ and convection ͑PeӶ 1͒, considering both nonpolarizable ͑fixed charge͒ and ideally polarizable ͑induced-charge͒ surfaces. Via asymptotic approximations and numerical solutions, we develop a physical picture to guide potential applications in electrochemical cells, such as analyte focusing, electrophoretic deposition, and microfluidic mixing near membranes or electrodes. By controlling the mean salt concentration, particle size, current, and concentration gradient, significant motion of particles ͑or fluid͒ is possible toward either electrode and toward high or low concentration.
Hydrodynamic interactions in the induced-charge electrophoresis of colloidal rod dispersions
Journal of Fluid Mechanics, 2006
The behaviour of a dispersion of infinitely polarizable slender rods in an electric field is described using theory and numerical simulations. The polarization of the rods results in the formation of dipolar charge clouds around the particle surfaces, which in turn drive nonlinear electrophoretic flows under the action of the applied field. This induced-charge electrophoresis causes no net migration for
arXiv: Soft Condensed Matter, 2019
We considerably extended the accessible range of concentrations for optical investigations of colloidal electro-kinetics using super-heterodyne Doppler velocimetry with multiple scattering correction. We performed measurements of electro-phoretic mobility and DC conductivity of aqueous charged sphere suspensions under realistically salt free conditions covering more than three orders of magnitude in particle number densities, n, and up to transmissions as low as 40%. At low n, the mobility shows an increase with n, then plateaus at intermediate n, and finally decreases at large n. Our study reconciles previous experimental observations made on restricted concentration ranges, and thus demonstrates the existence of a generic density dependence of the electro-phoretic mobility. Comparison to state of the art electro-kinetic theory suggests its relation to a density dependent particle charge.
Macromolecules, 1990
The effect of adsorbed polyelectrolytes and uncharged polymers on the 'diffusiophoresis" of charged colloids suspended in electrolyte gradients is investigated theoretically. It is known that the diffusiophoretic velocity of colloidal particles has two components: chemiphoretic and electrophoretic. Semianalytic expressions are derived for two parameters A(c) and A(e), which denote the weighting factors by which each of these velocity components is altered due to polymer adsorption. These factors are shown to depend on four dimensionless parameters: a, 8, B, and ((or Z), where a characterizes the distance to which the segments of the adsorbed polymer extend into the solution (and is the same as the "shielding ratio" defied by Varoqui and Dejardin),' 0 characterizes a dimensionless Debye l_ength, B corresponds to the degree of dissociation of the ionizable groups of the adsorbed polyelectrolyte, and { (or 2) is the zeta potential (or surface charge density) of the particle. The alteration in the particle's velocity due to polymer adsorption is estimated for various values of these dimensionless parameters. It is observed that polyelectrolyte adsorption, in certain situations, could lead to (i) particle migration velocities higher than those possible with 'clean" particles under otherwise identical conditions and (ii) a reversal in the direction of migration. The adsorption of uncharged polymers, on the other hand, leads to a reduction in the particle velocity, if the two parameters { and @-a normalized dimensionless mobility difference of the two ions of the electrolyte-have the same sign. However, when and j3 are of opposite signs, a reversal in the direction of particle migration is possible even with uncharged polymers under some conditions. Finally, an offshoot of the present analysis is the additional result that A(s) also represents the factor by which adsorbed polyelectrolytes/uncharged polymers alter the electrophoretic mobilities of colloidal particles subjected to electrophoresis by an externally applied electric field.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003
Electrokinetic phenomena are considered in a dilute suspension of spherical colloidal particles in a salt-free medium containing counter-ions only. Simple derivation is given for the electrophoretic mobility of the particles. Expressions for the electrical conductivity and the sedimentation potential are also obtained. An Onsager relation is found to hold between electrophoretic mobility and sedimentation potential. It is shown that if the particle charge Q is lower than a certain critical value, then the electrophoretic mobility and the electrical conductivity due to counter-ions increase linearly with increasing Q . If Q is higher than the critical value, then these quantities become constant independent of Q because of counter-ion condensation effects. The sedimentation potential, however, is not subject to the counter-ion condensation effects, since these effects upon the electrical conductivity and the concentration of the counter-ions cancel out with each other. #
Journal of Fluid Mechanics, 1994
The oscillatory motion of an electrically charged non-spherical colloidal particle in an oscillating electric field is investigated. The particle is immersed in an incompressible viscous fluid and assumed to have a thin electric double layer. For moderate-aspect-ration spheroids and cylinders, a simple algebraic expression is derived that accurately describes oscillatory electrophoretic particle motion in terms of the steady Stokes resistance, added mass, and Basset force. The effects of double-layer conduction and displacement currents within dielectric particles are included. The results indicate that electroacoustic measurements may be able to determine the ζ-potential, dielectric constant, surface conductivity (and microstructural information contained therein), size, density, volume fraction, and possibly shape of non-spherical particles in a dilute suspension. A simple formula is obtained for the high-frequency electrical conductivity of a dilute suspension of colloidal sphero...
Hydrodynamic interactions in induced-charge electrophoresis of colloidal rod dispersions
2005
The behavior of a dilute dispersion of ideally polarizable slender rods in an applied electric field is studied theoretically and numerically. The polarization of a rod results in the formation of a dipolar charge cloud around its surface, leading to a non-linear fluid slip, which causes particle alignment and creates a disturbance flow in the surrounding fluid. We derive a