[Phase transitions of surface-stabilized liquid crystal studied by temperature-dependent FTIR spectroscopy]

The FTIR spectra were measured for liquid crystal molecules in CaF2 cell over a temperature range of 40-150 degrees C. The alkyl chain transformed from ordered zigzag-dominated conformation to disordered gaucheness-dominated conformation with increasing temperature. Meanwhile, the degree of freedom of the rotation of the carbonyl group increased, the co-plane interaction between the carbonyl group and the phenyl ring broke, and the conjugation between the C=O bond and the phenyl ring was reduced at the S(CA)* --> S(A) phase transition point, followed by the increase of the plane angle between the two phenyl rings. Due to the surface stability effect of the LC cell, there existed on the cell surface a layer whose structure was independent of the temperature and LC phase. Therefore, the molecules still retained its originally phase property even at temperatures near and above the transition point.