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