Numerical Analysis of Thermophoresis of a Charged Spheroidal Colloid in Aqueous Media

Abstract

Thermophoresis of charged colloids in aqueous media has wide applications in biology. Most existing studies of thermophoresis focused on spherical particles, but biological compounds are usually non-spherical. The present paper reports a numerical analysis of the thermophoresis of a charged spheroidal colloid in aqueous media. The model accounts for the strongly coupled temperature field, the flow field, the electric potential field, and the ion concentration field. Numerical simulations revealed that prolate spheroids move faster than spherical particles, and oblate spheroids move slower than spherical particles. For the arbitrary electric double layer (EDL) thickness, the thermodiffusion coefficient of prolate (oblate) spheroids increases (decreases) with the increasing particle’s dimension ratio between the major and minor semiaxes. For the extremely thin EDL case, the hydrodynamic effect is significant, and the thermodiffusion coefficient for prolate (oblate) spheroids converges to a fixed value with the increasing particle’s dimension ratio. For the extremely thick EDL case, the particle curvature’s effect also becomes important, and the increasing (decreasing) rate of thermodiffusion coefficient for prolate (oblate) spheroids is reduced slightly.

Analytical analysis of anisotropic thermophoresis of a charged spheroidal colloid in aqueous media for extremely thin EDL cases

“…Eq. () is the same with the predictions of Fayolle [43] and Rasulis [39] for spherical particles. Comparing Eq.…”

“…It was found that the intensity and the direction of the thermophoretic force for rod-like colloids depended on the aspect ratio, surface geometry, and colloid-fluid interaction. Nevertheless, Tan's analysis neglected the EDL effect, which induces the dominating forces governing the thermophoresis of charged particles in electrolyte solutions [39].…”

Thermal conductivity effect on thermophoresis of charged spheroidal colloids in aqueous media

“…Equation (25) represents that the thermal conductivity effect on the thermophoresis of rodlike colloids is negligible, and Equation ( 26) represents the disklike colloids is static. Equations (23)(24)(25) are proportional to the square of zeta potential 𝜁 2 .…”

Numerical analysis of thermophoresis of charged colloidal particles in non‐Newtonian concentrated electrolyte solutions

“…and the Cauchy momentum equation [36] subjected to an electric body force and a dielectrophoretic body force [16,37]:…”

“…As the viscosity of non‐Newtonian fluids is no longer a constant, the flow field is governed by the following continuity equation: $$\begin{equation}\nabla \cdot {\bf{u}} = 0\end{equation}$$and the Cauchy momentum equation [36] subjected to an electric body force and a dielectrophoretic body force [16, 37]: $$\begin{equation}\rho {\bf{u}} \cdot \nabla {\bf{u}} = - \nabla p + \nabla \cdot \left( {\mu \nabla {\bf{u}}} \right) - {\rho _e}\nabla \phi - \frac{1}{2}{\left( {\nabla \phi } \right)^2}\nabla \varepsilon \end{equation}$$where u is the fluid velocity vector, ρ and ε are the fluid density and the temperature‐dependent electric permittivity, respectively, p is the fluid pressure, $${\rho _e}$$ is the electric free charge density, and $$ - \nabla \phi $$ is the electric field. For incompressible fluid, the fluid density ρ is a constant.…”