Liquid crystal alignment properties of n-alkylsulphonylmethyl-substituted polyoxyethylenes

Abstract

The liquid crystal (LC) alignment properties of LC cells fabricated with films of n-alkylsulphonylmethyl-substituted polyoxyethylenes (#S-PEO, # = 4, 6, 7, 8 and 10), where # is the number of carbon atoms in the n-alkyl side groups having different n-alkyl chain length, were investigated as a function of the rubbing density. The LC cells made from unrubbed #S-PEO (# ≥8) films having more than eight carbon atoms in the n-alkyl side groups showed homeotropic LC alignment. The homeotropic LC alignment behaviour correlated well with the surface energy values of the unrubbed #S-PEO films; homeotropic LC alignment was observed when the surface energy values of the unrubbed #S-PEO films were smaller than about 21.62 mJ m⁻². The LC cells made from rubbed #S-PEO (# ≥7) films having more than seven carbon atoms with a rubbing density of 150 showed homeotropic LC alignment. It was also found that the tilt angle of the LCs on the rubbed #S-PEO films was affected not only by the n-alkyl chain length of the polymers, but also by the rubbing density, regardless of the surface energy value of the #S-PEO film.

Keywords:

• liquid crystal
• alignment
• polyoxyethylene
• rubbing

Acknowledgement

Financial support by the Engineering Research Institute at Seoul National University, Korea Research Foundation through the Basic Research Program (Grant No. KRF-2008-314-D00112), and Soongsil University are gratefully acknowledged.