Coagulation behavior of spherical particles embedded in laminar shear flow in presence of DLVO-and non-DLVO forces

Hypothesis: Complex and coupled interaction between coagulation mechanisms results in a nonlinear variation of coagulation rate with shear rate. Calculations: Coagulation behavior of colloidal dispersions is investigated in a laminar shear flow by solving the Fokker-Plank equation for pair probability density function, simultaneously incorporating the effect of (i) Brownian diffusion, (ii) fluid flow, (iii) van der Waals attraction and (iv) double layer repulsion force. Furthermore, analysis foremost studies the effect of non-DLVO solvation force. Findings: Theoretical analysis with experimental validation reveals that, coagulation rate varies nonlinearly with the shear rate in presence of double-layer repulsion force, due to the strong coupling of coagulation mechanisms. This is observed by an occurrence of coagulation minima at intermediate shear rate. Increase in double layer repulsion force either facilitates or hinders the occurrence of redistribution of particles, as observed by early or late fall of coagulation rate. Systems with different ionic strengths show a crossover of coagulation rates, whereas those with different solvation forces do not show similar trend. Analysis also shows that, ad hoc additivity assumption of individual Brownian and shear coagulation rates does not hold in case of laminar shear flow, against to that observed in extensional flow [Melis et al. (AlChE J., 999, 1383)]. (C) 2020 Elsevier Inc. All rights reserved.