Alcohols, chiral smectics

Besides normal alkyl chains, alkenyl chains (-C H2 CH CHCH3) are also important because they exhibit particularly beneficial elastic constants and low rotational viscosities desirable for use in supertwisted nematic (STN) displays. Branched alkyl chains Iowct transition temperatures and increase the viscosity. Thus, chiral liquid crystal compounds, which usually incorporate a branched chain alcohol, e.g., 2-methyl butanol or 2-octanol, are relatively viscous. Compounds with two long alkyl chains favor smectic C phase formation (3, K-S, 48°C S.-S 122°C S -N 128°C N-I 166°C), especially when the core system contains some kind of nonlinear stmcture (such as a lateral substituent and/or este group) which aids the formation of tilted phases. 

---