Despite its potential relevance in biomedical and biochemical fields, the study of diffusiophoresis in viscoplastic fluids remains scarce in the literature due to the challenges created by finite yield stress and nonlinear shear-dependent viscosity. This study investigate the diffusiophoresis of a uniformly charged rigid colloid in non-Newtonian viscoplastic fluids where rheological models are considered as Casson, Herschel-Bulkley, and Bingham fluids. We solve the governing nonlinear equations in their full form by adopting a pressure-correction-based finite-volume approach. We also derive a semianalytical expression for particle mobility in the thin electric double layer regime under the zero-yield-stress limit, and establishes a good agreement with the exact numerical solution. The shear-thinning effect amplifies the magnitude of the diffusiophoretic velocity, whereas, the yield stress imposes a stalling effect on the diffusiophoresis. In a shear-thinning fluid, a reversal in diffusiophoresis is found for a lower flow consistency index, which is suppressed when the diffusion dominated process amplifies in a multivalent electrolyte, higher yield stress as well as in a shear-thickening fluid. Our results reveal a monotonic declination of the magnitude of the diffusiophoretic velocity with increasing flow behavior index.

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• Electrokinetic flows
• Microfluidics
• Nanofluidics
• Complex fluids
• Non-Newtonian fluids