Marangoni convection driven by temperature gradient in cyanobiphenyl liquid crystals

Drastic changes in surface tension σ near phase transition temperatures have been reported in cyanobiphenyl liquid crystals (CBLC) [1,2]. According to the reports, however, σ largely depended on the measurements, and hence the precise value of σ in such systems might not be determined. In this study, the Marangoni convection driven by surface tension gradient was paid attention to. The strong flow is expected to be induced in CBLC systems owing to the drastic change in σ near phase transition temperatures. CBLCs from 5 to 8CB were prepared with fluorescence dyes dispersed. Under temperature gradient, the flow field in these LCs was measured by fluorescence photo-bleaching method [3]. On the basis of our measurements, we have successfully observed the strong flow induced in the coexistence state between the nematic (N) and isotropic (I) phases. Furthermore, near air interface, the flow from I- to N- phase was observed in 5CB, while the opposite flow direction was observed in 7CB. These flows are considered to be driven by the surface tension difference between the N and I phases in each sample. [1] M. Tintal, et al, Liq. Cryst., 28, 793, 2001. [2] L. S. Gomes and N. R. Demarquette, Mol. Cryst. Liq. Cryst., 437, 181, 2005. [3] J. Yoshioka, et al, Phys. Rev. E, 105, L012701, 2022.