Tracer colloids close to an isotropic–nematic domain interface with phase transition-induced solute transport

In mixtures of nematogens with isotropic solutes, the equilibrium solute concentration in the nematic phase of the medium is usually lower than in the isotropic phase. Under constant cooling this results in continuous solute transport across the domain interface during phase transformation, leading to a non-homogeneous solute concentration around the drop. In this case, the interaction of colloids with an approaching isotropic–nematic interface is influenced by the interaction with the transferred solute. In 4-pentyl-4-cyanobiphenyl (5CB) mixtures containing small amounts of octane or tetrachloroethylene, we visualized an attractive interaction between tracer colloids and nematic droplets within a range of several micrometers from the droplet surface. This attraction depends on the interaction of the colloid surface with the solute and requires droplet growth, i.e., a non-homogeneous solute concentration around the droplet. The colloid interaction with this concentration gradient is consistent with prediction from diffusiophoretic models.