Degree of disorder in cubic mesophases in thermotropics: thermodynamic study of a liquid crystal showing two cubic mesophases.
Heat capacity of a thermotropic mesogen ANBC(22) (4(')-alkoxy-3(')-nitrobiphenyl-4-carboxylic acid with 22 carbon atoms in alkyl chain) showing two cubic mesophases was measured by adiabatic calorimetry between 13 and 480 K. Excess enthalpies and entropies due to phase transitions were determined. A small thermal anomaly due to the cubic Im3m-->cubic Ia3d phase transition was successfully detected. Through an analysis of chain-length dependence of the entropy of transition, the sequence of two cubic mesophases (with space groups Ia3d and Im3m) is deduced for thermotropic mesogens ANBC(n). It is shown that the disorder of the core arrangement decreases in the order of Sm-C-->cubic (Im3m)-->cubic (Ia3d) while that of the chain in the reverse order cubic (Ia3d)-->cubic (Im3m)-->Sm C.
Saito
Kazuya
K
Research Center for Molecular Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
Shinhara
Takashi
T
Nakamoto
Tadahiro
T
Kutsumizu
Shoichi
S
Yano
S
S
Sorai
Michio
M