Séminaire Liquides/Mat. molle

Mardi 24 Octobre 2017 à 11h00.

Locally-induced nucleation with thermophoresis in a bulk colloidal gas

''Nucleation of a condensed phase out of a bulk colloidal gas requires a system in supersaturated conditions. This makes experimental observations of nucleation events in the bulk difficult as such metastable samples tend to nucleate undesirably at surfaces and nuclei may form out of the field of view in the sample. We present here a thermophoresis-based method to form nuclei from an undersaturated colloidal bath at well defined positions. In a bath of refractive index- and density-matched PMMA particles, we add titania colloids that can be trapped by optical tweezers. The tweezers heat a titania impurity, which creates a very localized temperature gradient in the fluid, to which the PMMA respond by aggregating towards the heat source. The attraction is strong enough to induce phase transitions and we show that various structures can be obtained, such as amorphous and crystal phases, as well as icosahedral structures.''