Minute viscoelastic observation in isotropic-nematic phase transition of 7CB with a thousandth Kelvin resolution

The temperature dependence of the shear viscosity eta for homeotropically a ligned liquid crystals, 4-n-heptyl-4'-cyanobiphenyl (7CB) at 10 MHz was obs erved in the immediate vicinity of the isotropic-nematic phase transition w ith a thousandth Kelvin resolution by the piezoelectric composite resonator method. The transition process shows a clear hysteresis between heating an d cooling processes. Furthermore, there is an interesting behavior of eta o nly during the cooling process, the value of eta suddenly decreases and the n increases in a very narrow temperature region of 32 mK.