Thermal convection in a thermosensitive colloidal suspension

Thermal convection is investigated experimentally in a microgel suspension that consists of core-shell colloids, which change their size with temperature. The swelling and shrinking of the particles strongly modify their volume fraction in the carrier fluid and therefore the viscosity of the suspension. In this experiment, thermal convection in a Hele-Shaw-like apparatus is monitored using the shadowgraph technique. When compared to a normal fluid, the threshold temperature difference is reduced dramatically, which is interpreted as a manifestation of the Soret effect, i.e. the temperature gradient applied to the suspension induces an unstable gradient of the colloid concentration. The wavelength in the nonlinear regime is very different from the one observed in water. Furthermore, transient oscillations of the patterns are detected in the nonlinear regime and are investigated as a function of the applied temperature difference.