Electrophoresis of a spherical particle normal to an air–water interface

Abstract

Electrophoresis of a spherical particle normal to an air-water interface is considered theoretically in this study. The presence of the air-water interface is found to reduce the particle mobility in general, especially when the double layer is very thick. This boundary effect diminishes as the double layer gets very thin. The higher the surface potential, the more significant the reduction of mobility due to the polarization effect from the double layer deformation when the particle is in motion. Local extrema are observed in the mobility profiles with varying double layer thickness as a result. Comparison with a solid planar boundary is made. It is found that the particle mobility near an air-water interface is smaller than that near a solid one when the double layer is thick, and vice versa when the double layer is thin, with a critical threshold value of double layer thickness corresponding roughly to the touch of the interface. The reason behind it is clearly explained as the buildup of electric potential at the air-water interface, which reduces the driving force as a result.

Gel electrophoresis in suspensions of charged spherical particles

“…An induced electric field opposite to the applied field is generated as a result, which slows down particle motion in general, and is referred to the polarization effect here. 23,30,34 When the double layer gets thinner even further, the driving force becomes dominant and the mobility increases eventually. The above observations of ka and f r effects are consistent with the corresponding case of single sphere in an electrolyte solution.…”

“…5 for their disturbed state during electrophoresis at ka ¼ 1 where the double layer polarization is found to be significant in general. 23,34,35 As upward electric field is applied to the system, the positive ions cluster near the front end (north pore) of the particle motion, while the negative ions cluster near the rear end (south pore), as shown clearly in the plots of dr * . This polarization of ion distribution generates an induced downward electric field (denoted as E p in Fig.…”

“…The method is very powerful in solving the general electrokinetic systems of interest. 17,23 It has several desirable properties, such as a fast rate of convergence and the convergent properties are independent of the associated boundary conditions. Key factors are examined for their effects on the electrophoretic mobility, such as the double layer thickness, the z potential of the particles, the friction coefficient of the porous gels, the suspension concentration, and so on.…”

Electrophoresis of a charged porous sphere normal to an air–water interface

“…(v) The air-water interface remains planar when the particle approaches it. 3,9,21 (vi) There is no intrinsic charge at the air-water interface. 10 (vii) The system is at the quasi-steady state when the particle is in motion.…”

“…Lee and his coworkers 9,10 investigated theoretically the electrophoretic motion of a charged entity toward an air-water interface in response to an applied electric field. The charge entity can be a rigid solid sphere with constant surface potential 9 or a chargeregulated particle. 10 The charge-regulated surface considered by them is the generalization of conventional constant surface potential and constant surface charge density situations and models well for some biocolloids or particles coated with an infinitely thin film of polyelectrolytes.…”