STUDIES ON THE NEMATIC-ISOTROPIC PHASE-TRANSITION OF 4-METHOXYBENZYLIDENE 4-N-BUTYLANILINE (MBBA)

The isothermao compressibilities (K//T) and the thermal expansion coefficients ( alpha //p) of 4-methoxybenzylidene 4-n-butylaniline (MBBA) were measured in the temperature range of 307. 15-323. 15 K up to 140 bar. The isothermal compressibility and the thermal expansion coefficient were fitted to the equations of the form as K//T equals K//T degree plus W vertical T minus T//c* vertical ** minus ** gamma and alpha //p degree plus Z prime vertical T minus T//c* vertical ** minus ** alpha in both above and below the phase transition points, and 1. 18 (T less than T//c*), 1. 31 (T greater than T*//c), 1. 31 (T greater than T//c*) for the critical exponent gamma and 0. 59 (T less than T//c*), 0. 53 (T greater than T//c*) for alpha were found. The pretransitional phenomena in both the nematic phase and also in the isotropic phase were observed. By the Clausius-Clapeyron equation, the transition enthalpy ( DELTA H//N//-//I equals 0. 92 J/cm**3) and the transition entropy ( DELTA S//N//-//I equals 0. 72 J/mole. K) accompanied by the nematic-isotropic phase transition were obtained, and the specific heat (C//p) was calculated from the experimental results of K//T and alpha //p using the method proposed by Chin and Neff.