Thermodynamic implication of the dependence of mesomorphic transition entropy on chain-length

Meaning of the alkyl chain-length dependence of transition entropy in liquid crystal is discussed and clarified in a long-chain region. A method to deduce contributions of the alkyl chain and the molecular core is proposed. Application of the method suggests that, in most smectic A (SmA) - nematic (N) phase transitions, not only a molecular core (modeled by a hard-rod) but also a (terminal) alkyl chain is disordered upon the SmA→N transition.