Electric-field-induced polarization of the layer of condensed ions on cylindrical colloids

Abstract

In concentrated suspensions of charged colloids, interactions between colloids can be induced by an external electric field through the polarization of charge distributions (within the diffusive double layer and the layer of condensed ions) and/or electro-osmotic flow. In case of rod-like colloids, these field-induced inter-colloidal interactions have recently been shown to lead to anomalous orientation perpendicular to the external field, and to phase/state transitions and dynamical states, depending on the field amplitude and frequency of the external field. As a first step towards a (semi-) quantitative understanding of these phenomena we present a linear-response analysis of the frequency dependent polarization of the layer of condensed ions on a single, long and thin cylindrical colloid. The in-phase and out-phase response functions for the charge distribution and the electric potential are calculated for arbitrary orientation of the cylindrical colloid. The frequency dependent degree of alignment, which is proportional to the electric-field induced birefringence, is calculated as well, and compared to experiments on dilute fd-virus suspensions.

Influence of charge density and calcium salt on stiffness of polysaccharides multilayer film

“…It should be mentioned that "anomalous" (perpendicular) alignment of anisometric particles has already been observed by diverse optical techniques like electrical birefringence, light scattering or dichroism, in micellar and polyelectrolyte solutions, solutions of clays, viruses and fibers [36][37][38]. The electro-optical signal was found to change its sign as a function of the concentration of the particles, the electric field strength or the frequency when the measurement is carried out with ac-fields.…”

Electric birefringence anomaly of solutions of ionically charged anisometric particles

“…The perpendicular or parallel orientation depends strongly on the ratio of the diffuse to the condensed counter-ions [49].…”

An electric-field induced dynamical state in dispersions of highly charged colloidal rods: comparison of experiment and theory

“…The contribution Δ p o l is the contribution due to interactions from polarization charges, while Δ t o r q u e accounts for single-particle torques with which the external field acts on polarization charges, where is the dimensionless external field strength (with β =1/ k B T , and E 0 the external field strength), and is an abbreviation for, with is the unit vector in the direction of the external field. The frequency-dependent functions appearing in the above equations are, where [ 31 ], is a dimensionless frequency, with ω the frequency of the external field, and with D e f f the effective translational diffusion coefficient of the condensed ions, which is equal to, where D is the free translational diffusion coefficient of condensed ions. The second term within the square brackets accounts for the repulsive interactions between the condensed ions, with, the inverse “condensate length.” The frequency-dependent functions h (Ω) and I (Ω) are essentially zero for Ω>3, for which the polarization of the layer of condensed ions ceases to occur.…”