Dipolophoresis in concentrated suspensions of ideally polarizable spheres

Abstract

The dynamics of ideally polarizable spherical particles in concentrated suspensions under the effects of nonlinear electrokinetic phenomena is analysed using large-scale numerical simulations. Particles are assumed to carry no net charge and considered to undergo the combination of dielectrophoresis and induced-charge electrophoresis termed dipolophoresis. Chaotic motion and resulting hydrodynamic diffusion are known to be driven by the induced-charge electrophoresis, which dominates the dielectrophoresis. Up to a volume fraction φ ≈ 35%, the particle dynamics seems to be hindered by the increase in the magnitude of excluded volume interactions with concentration. However, a non-trivial suspension behaviour is observed in concentrated regimes, where the hydrodynamic diffusivity starts to increase with a volume fraction at φ ≈ 35% before reaching a local maximum and then drastically decreases as approaching random close packing. Similar non-trivial behaviours are observed in the particle velocity and number-density fluctuations around volume fractions that the non-trivial behaviour of the hydrodynamic diffusion is observed. We explain these non-trivial behaviours as a consequence of particle contacts, which are related to the dominant mechanism of particle pairings. The particle contacts are classified into attractive and repulsive classes by the nature of contacts, and in particular, the strong repulsive contact becomes predominant at φ > 20%. Moreover, this transition is visible in the pair distribution functions, which also reveal the change in the suspension microstructure in concentrated regimes. It appears that strong and massive repulsive contacts along the direction perpendicular to an electric field promote the non-trivial suspension behaviours observed in concentrated regimes. †

On the Electro-Active Control of Nanocellulose-Based Functional Biolubricants

“…As Park and Saintillan and Mirfendereski and Park have pointed out that the distance between polarized nanoparticles in a given volume of the continuous medium decreases with the weight fraction. Then, repulsive contacts with nearby particles are likely to occur . Under such a scenario, the nanocellulose particle motion was restrained owing to strong steric hindrance that caused the particles to be pushed to contact nearby particles and pack in a random configuration.…”

“…From 0.25 wt %, enough chain bridges spanning two electrodes were formed, which promoted continuity, and the leak current intensity increased until reaching the maximum values reported at 1 wt % . In contrast, higher weight fractions than 2 wt % involved a random close packing, as a consequence of the massive repulsive contact and stearic interactions among polarized nanoparticles that caused the particles to be pushed to contact nearby particles in the transverse electric field direction . This phenomenon compromised the optimal formation of the chain-like structures, and the leak current intensity decreased.…”

“…This apparent yielding behavior tended to disappear at nanocellulose weight fractions equal to or higher than 2 wt % (Figure 5). As Park and Saintillan 48 and Mirfendereski and Park 49 have pointed out that the distance between polarized nanoparticles in a given volume of the continuous medium decreases with the weight fraction. Then, repulsive contacts with nearby particles are likely to occur.…”

“…Then, repulsive contacts with nearby particles are likely to occur. 49 Under such a scenario, the nanocellulose particle motion was restrained owing to strong steric hindrance that caused the particles to be pushed to contact nearby particles and pack in a random configuration. Thus, for CNF-or CNC-based dispersions at concentrations of 2 wt % and higher, the described structure better supports the shear stresses resulted from the flow process and hampers the particle orientation provoked by the hydrodynamic forces, even at moderate electric field strengths.…”

“…31 In contrast, higher weight fractions than 2 wt % involved a random close packing, as a consequence of the massive repulsive contact and stearic interactions among polarized nanoparticles that caused the particles to be pushed to contact nearby particles in the transverse electric field direction. 49 This phenomenon compromised the optimal formation of the chain-like structures, and the leak current intensity decreased. Moreover, the highest weight fractions might have promoted nanoparticle pooling.…”