The phase transition behaviour and electro-rheological effect of liquid crystalline siloxane dimers

Abstract

Symmetrical liquid crystalline dimers have been synthesised, composed of rod-like mesogenic units with polar groups and a siloxane core of varying length in the central region. All the dimers containing siloxane units have been shown to exhibit a smectic A phase, confirmed by polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Rheological properties under an applied electric field were investigated by rotational rheometer. The influence of the siloxane core length on rheological properties has been investigated, and in addition the behaviour of the liquid crystalline dimers in the smectic A phase under an applied electric field has been observed by POM.

Keywords:

• dimer
• siloxane
• electro-rheological effect
• smectic

Acknowledgements

The authors are indebted to Professor N. Nakamura of Ritsumeikan University for his helpful discussions and advice. A High-Tech Research Center Project for Private Universities, matching the subsidy from Ministry of Education, Culture, Sport, Science and Technology, is gratefully acknowledged for partial support of this study during the year 2010.