Diffusiophoresis of diffuse porous particles

The present article deals with the diffusiophoresis of diffuse porous particles. The concept of diffuse soft interface is adopted, which describes the continuous distribution of polymer segments and the accompanying volume charge within the porous particle. This approach eliminates the need for boundary conditions on the particle surface because the internal flow variables smoothly transition into the surrounding fluid. In the limiting case of a vanishing decay length, the diffuse model effectively recovers the uniform and step-like monomer distributions. We consider a typical situation when the particle bears a zwitterionic functional group. Three different background electrolyte solutions are chosen for which cations and anions may have similar or dissimilar diffusion rates. The perturbation analysis based on a weak concentration gradient is adopted to linearize the set of governing equations and the resulting equations are solved numerically to analyze the diffusiophoretic motion of the particle. Note that, while the particle is in motion, the diffusiophoretic velocity, net drag force experienced by the particle, and the fluid collection efficiency are the key parameters that are often required to analyze the electrohydrodynamic motion of a particle exposed to a concentration gradient. Such quantities are evaluated without restricting the particle charge and other associated parameters. Additionally, we have established an explicit relation between the net drag force experienced by the particle and fluid collection efficiency while the particle undergoes diffusiophoresis. Furthermore, based on the weak charge and step-like distribution of monomers, we have deduced theoretical results for particle velocity, net drag force, and fluid collection efficiency, and these results are benchmarks that may be used to validate the numerical scheme and other practical uses. The impact of pertinent parameters on the overall diffusiophoretic motion is further illustrated.