Comparative study of liquid-crystalline ordering in a monomer, linear polymer, and graft copolymer by the photon transmission technique

Abstract

The photon transmission technique was used to study the phase transitions of a liquid crystalline acrylate monomer, 6-(4-cyanobiphenyl-4′oxy)hexyl acrylate (LC6), its homopolymer (PLC6) and its graft copolymer (GLC6) with polytetrahydrofuran grafts. The phase transitions were also confirmed by DSC and polarizing microscopy. We observed the phase transition sequence isotropic–nematic–smectic A–smectic C in the LC6 monomer. In PLC6 and GLC6 polymers, the nematic and smectic A phases appear dominant. The apparent nematic–smectic A transition is of first order in PLC6 and of second order in GLC6, with the transition temperature remaining the same. The effects of quenched random constraints introduced in GLC6 are consistent with the theory of quenched random interactions. The critical exponents were also evaluated.

Keywords:

• Photon transmission technique
• Liquid crystal homopolymer
• Graft copolymer
• Nematic order
• Quenched random constraints
• Critical exponent

Acknowledgements

This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) under Grant No: TBAG-1951 (100T074), and the Research Fund of stanbul Technical University, Grant No. 1426 and 1538. This work was performed with partial financial support from the Turkish TÜBITAK and the Italian CNR.