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| Hauptseite > Publikationsdatenbank > Single-Particle Thermophoresis and Electric-Field Induced Phases/States |
| Hauptseite > Publikationsdatenbank > Single-Particle Thermophoresis and Electric-Field Induced Phases/States |
| Conference Presentation (Invited) | FZJ-2023-02217 |
2023
Abstract: In the first part of this presentation, I will discuss colloidal mass transport induced by temperature gradients (commonly referred to as thermophoresis) resulting from the electric double layer of charged spherical colloids. There are three contributions to the thermophoresis of charged colloids. The temperature dependence of the internal energy of the electric double layer leads to migration from high to low temperatures. The temperature-gradient induced asymmetry of the double layer gives rise to an electrostatic force onto the surface charges of the colloid. Finally, the asymmetry of the double layer leads to an electro osmotic flow, that acts with a friction force onto the core of the colloid. All three contributions will be discussed, and the theoretical results will be compared to experiments. In the second part, the phases and dynamical states that are induced by external electric fields in a system of very long and thin and highly charged rod-like colloids will be discussed. The experimental phase/state diagram, for a concentration within the two-phase isotropic-nematic coexistence region, will be presented. Depending on the electric field strength and the frequency, several phase/state-transitions are induced: a transition from nematic to chiral nematic, from a nematic to a homeotropic state, and a transition to a dynamical state where nematic domains persistently melt and reform. An explanation of these phenomena is presented, both on an intuitive level and based on the Smoluchowski equation, which is an equation of motion for the probability density function for the positions and orientations of the rods.
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