Colloid Electrophoresis for Strong and Weak Ion Diffusivity

We study the electrophoretic flow of suspensions of charged colloids with a mesoscopic method that allows us to model generic experimental conditions. We show that for highly charged colloids their electrophoretic mobility increases significantly and displays a mobility maximum on increasing the colloidal charge for all salt concentrations. The electrophoretic mobility of highly charged colloids is also enhanced significantly when ion advection is dominant, leading to a strong heterogeneity in the local electrophoretic response especially at low-salt concentration, when ion diffuse layers overlap.

Figure 1

Dimensionless electrophoretic mobility for a spherical colloidal particle, $\tilde{\mu }$, versus the dimensionless $\zeta$ potential $\tilde{\zeta }$. Results from simulations (filled symbols) and OW [12] (empty symbols) for $ka=0.5$ (0.8), triangles down (up).

Figure 2

Dimensionless electrophoretic mobility $\tilde{\mu }$ for a colloidal particle with charge $Z=30$ and radius $a=4.0$ versus colloid volume fraction $\Phi$ (triangle left). No salt is added to the system. Experimental (sphere and square symbols) and simulation results (empty triangles) from Lobaskin et al. [14].

Figure 3

Steady state colloidal velocity $v_l/v_0$ versus Péclet flow number for $\kappa a=0.5,1.0,8.0$. Inset: Dimensionless mobility $\tilde{\mu }$ versus dimensionless $\zeta$ potential $\tilde{\zeta }$, for $\kappa a=0.5$, Pe $\sim {10}^{-3}$ (filled circles), and $\mathrm{Pe}\sim 0.3$ (filled triangles).

Figure 4

Dimensionless mobility $\tilde{\mu }$ versus volume fraction $\Phi$ for a suspension of particles with overlapping EDLs, $\mathrm{Pe}\sim 1,{10}^2$. Inset: Probability distribution of particle velocities $v_l$ when $\Phi =0.32$, $\kappa a=1.0$ (overlapping EDLs).