The Primary Electroviscous Effect: Thin Double Layers (aκ⪢1) and a Stern Layer

Abstract

The primary electroviscous effect due to the charge clouds surrounding spherical charged particles suspended in an electrolyte was studied by Hinch and Sherwood (J. Fluid Mech.132, 337 (1983)) in the limit of double layers thin compared to the particle radius a. Here we introduce the effect of a dynamic Stern layer into that analysis, in order to explain the numerical results of Rubio-Hernández et al. (J. Colloid Interface Sci.206, 334 (1998)) in terms of the ratio of the tangential ionic fluxes within the charge cloud to those within the Stern layer. The predictions of the asymptotic analysis are compared with those of numerical computations. The thickness of the charge cloud is characterized by the Debye length κ−1. If aκ>10 the predictions of the asymptotic analysis exhibit the same qualitative behavior as the numerical results, but aκ>1000 is required to achieve quantitative agreement to within 2.5%.