Marangoni flow across different phases in cyanobiphenyl liquid crystals under temperature gradient

Marangoni flows driven by temperature gradient in two-phase coexisting states are investigated in this study, using several liquid crystals of the cyanobiphenyl (CB) series. The flow field is measured using the fluorescence photo-bleaching method in sandwich cells, and the characteristic flow is observed near the air interface in all samples. The flow direction is from the isotropic phase to the nematic phase in 5CB and 6CB and from the nematic to the smectic phase in 8CB, which is the case for the three different coating materials of the cell substrates. However, the flow direction observed in 7CB and 8CB changes depending on the coating material in the coexisting state of the nematic and isotropic phases. These results can be explained by the temperature dependence of surface tension γ and the air-interface shape ls near phase-transition temperatures.