Liquid crystalline and thermo-optical properties of cyclic siloxane tetramers containing cholestryl-4-allyloxy-benzoate and biphenyl-4-yl 4-allyloxybenzoate

Abstract

A series of cyclic siloxane tetramers covering the whole composition range were synthesised using cyclotetrasiloxane, cholestryl-4-allyloxy-benzoate and biphenyl-4-yl 4-allyloxybenzoate, and the effects of the cholesteryl-based mesogenic units on liquid crystalline and thermo-optical properties were studied. The presence of a cholesteric mesogen was observed to widen the mesogenic temperature range and tended to induce smectic A phases in the tetramers containing a higher mole fraction of cholestryl-4-allyloxy-benzoate (X _chol). The selective reflection of cholesteric tetramers shifted to shorter wavelengths with increasing X _chol and temperature. Blue phases can be easily observed for those tetramers containing more than 50.0 mol% cholesteric mesogen. The shorter pitch sample showed the wider blue phases range. The blue phases range width increased from 2.8°C to 18.5°C as X _chol increased from 0.5 to 1.0.

Keywords:

• cyclic siloxane tetramer
• blue phase
• selective reflection

Acknowledgements

This work was financially supported by Flat-Panel Display Special Project of China 863 Plan (Grant No. 2008AA03A318), Projects of Chinese National Science and Technology Tackling Key Problems (Grant No. 2007BAE31B02), National Science Foundation (Grant No. 50973010) and Fund of Scientific Plan of Beijing City (Grant No. D090803044209001).