77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024;
Salt Lake City, Utah
Session L17: Electrokinetic Transport I
8:00 AM–10:10 AM,
Monday, November 25, 2024
Room: 250 A
Chair: Juan Santiago, Stanford University
Abstract: L17.00008 : Nonlinear electrophoresis of highly charged rigid colloids by incorporating finite ion-size and ion-ion correlation effects
9:31 AM–9:44 AM
Abstract
Presenter:
SUBRATA MAJHI
(Indian Institute of Technology Kharagpur)
Authors:
SUBRATA MAJHI
(Indian Institute of Technology Kharagpur)
Shakyajit Paik
(Indian Institute of Technology Kharagpur)
Somnath Bhattacharyya
(Indian Institute of Technology Kharagpur)
Collaborations:
Shakyajit Paik, Somnath Bhattacharyya, Subrata Majhi
Electrophoresis of colloids at a higher range of the imposed electric field has potential applications in various fields of microfluidics, such as flow separation, mixing, control, and manipulation of suspended particles. Theoretical studies on nonlinear electrophoresis at a strong imposed electric field are all based on the thin electric double layer with low surface conduction in which either the Peclet number (Pe_) is considered to be very small (small ion) or very large. The present study focused on analyzing the electrophoresis of rigid colloids in monovalent or multivalent electrolytes by varying the applied electric field in which Pe_ can vary from low to moderate values. We use the modified Nernst-Planck equation to determine the ionic concentration, where ions are considered to be a finite-sized sphere. The volume exclusion due to the ion steric interactions is modelled by the Boublik–Mansoori–Carnahan–Starling–Leland (BMCSL) equation of state. We have incorporated the ion-ion correlation by modifying the electric potential equation to a biharmonic equation. The modified Navier-Stokes equation describes the motion of ionized fluid, where the viscosity varies with ionic concentration through the Batchelor-Green expression. The numerical solution is obtained by solving the complete set of non-linear coupled partial differential equations along with specified boundary conditions through the finite volume method. We find that the modified model reduced the non-linear electrophoretic velocity contribution as compared to the standard Poisson-Nernst-Planck (PNP) model, although the total mobility of the particle is enhanced. At a higher applied electric field (AEF), the PNP model demonstrates that as AEF increases, the ion cloud transitions from causing a retardation effect to enhancing the overall electrophoretic velocity. However, the transition of the ion cloud always acts as a retardation effect when the modified model is considered. We find that the ion-ion correlations cause the mobility reversal in multivalent electrolytes due to the charge reversal under weak electric fields. However, no such reversal occurs when AEF is higher.