Electrophoresis of Diffuse Soft Particles

Abstract

A theory is presented for the electrophoresis of diffuse soft particles in a steady dc electric field. The particles investigated consist of an uncharged impenetrable core and a charged diffuse polyelectrolytic shell, which is to some extent permeable to ions and solvent molecules. The diffuse character of the shell is defined by a gradual distribution of the density of polymer segments in the interspatial region separating the core from the bulk electrolyte solution. The hydrodynamic impact of the polymer chains on the electrophoretic motion of the particle is accounted for by a distribution of Stokes resistance centers. The numerical treatment of the electrostatics includes the possibility of partial dissociation of the hydrodynamically immobile ionogenic groups distributed throughout the shell as well as specific interaction between those sites with ions from the background electrolyte other than charge-determining ions. Electrophoretic mobilities are computed on the basis of an original numerical scheme allowing rigorous evaluation of the governing transport and electrostatic equations derived following the strategy reported by Ohshima, albeit within the restricted context of a discontinuous chain distribution. Attention is particularly paid to the influence of the type of distribution adopted on the electrophoretic mobility of the particle as a function of its size, charge, degree of permeability, and solution composition. The results are systematically compared with those obtained with a discontinuous representation of the interface. The theory constitutes a basis for interpreting electrophoretic mobilities of heterogeneous systems such as environmental or biological colloids or swollen/deswollen microgel particles.

Theory of electrostatics and electrokinetics of soft particles

“…Dukhin et al [44] pointed out the importance of the degree of dissociation of charged groups in the polyelectrolyte layer. Duval and Ohshima [45] presented a new electrophoresis model of diffuse soft particles. In that model, a diffuse soft particle consists of an uncharged impenetrable core and a charged diffuse polyelectrolyte layer.…”

“…Successful application of that model has been reported for humic acids [46], bacteria [47] and red blood cells [48]. For numerical calculations of the electrophoretic mobility based on more rigorous theories, the readers are referred to the studies of Hill et al [49][50][51][52] and Lopez-Garcia et al [53][54][55] as well as that of Duval and Ohshima [45].…”

Electrohydrodynamic Properties of Succinoglycan as Probed by Fluorescence Correlation Spectroscopy, Potentiometric Titration and Capillary Electrophoresis

“…The impact of concentration gradients at the molecular interface (heterogeneous soft layer) on the titration data can be taken into account by appropriate choice of a prefactor f(r b) in eq 8. 30 3.3. Modeling the Electrophoretic Mobilities of a Soft Macromolecule.…”

Electric potential profile of a spherical soft particle with a charged core

“…The development for the Ohshima model has been done by taking into account the effect of inhomogeneous charge distribution in the soft layer. In the diffuse soft particle electrokinetic theory (DSPE) given by J. F. Duval [11,12], the gradual decay of the electrodynamic properties of the soft layer inside and outside the particle was considered. The extensions of the DSPE theory to multilayer soft particles have been recently done [13,14].…”