Transport in polymer-gel composites: Response to a bulk concentration gradient

摘要

This paper examines the response of electrolyte-saturated polymer gels,embedded with charged spherical inclusions, to a weak gradient of electrolyteconcentration. These composites present a model system to study microscaleelectrokinetic transport processes, and a rigorous theoretical prediction ofthe bulk properties will benefit novel diagnostic applications. Anelectrokinetic model was presented in an earlier publication, and the responseof homogeneous composites to a weak electric field was calculated. In thiswork, the influence of the inclusions on bulk ion fluxes and the strength of anelectric field (or membrane diffusion potential) induced by the bulkelectrolyte concentration gradient are computed. Effective ion diffusioncoefficients are significantly altered by the inclusions, so--depending on theinclusion surface charge or $\zeta$-potential--asymmetric electrolytes canbehave as symmetrical electrolytes, and vice versa. The theory also quantifiesthe strength of flow driven by concentration-gradient-induced perturbations tothe equilibrium diffuse double layers. Similarly to diffusiophoresis, the flowmay be either up or down the applied concentration gradient.