Influence of different spacer length and cholesteric monomer percentage on phase behaviors and thermo-optical properties of cyclic siloxane tetramers containing cholesteric and biphenyl groups

In this work, two series of cyclic siloxane tetramers based on polysiloxane, cholesterol derivate monomer, and biphenyl derivate monomer were designed and synthesized to investigate the effect of the length of flexible spacer and cholesteric monomer percentage (X (chol)) on their mesogenic properties. Results revealed that the tetramers exhibited thermotropic liquid crystalline behaviors and their properties were influenced by various factors. With X (chol) increased, abundant mesophases for the tetramers could be observed and their mesogenic temperature ranges were generally widened. Significant effect of the flexible spacer length on the transition temperatures was also found and discussed. Interestingly, blue phases could be easily observed for those tetramers containing more than 50.0 mol% chiral mesogen, and the temperature ranges of blue phase increased with the increasing of X (chol) whereas reduced with the decreasing of length of flexible spacer. Moreover, the thermo-optical properties and helical twisting power of the tetramers were also investigated.