Volume Measurements and Transitions of MBBA at High Pressures

The volumes of MBBA in expansion at constant pressure and compression at constant temperature to about 180°C and 7 kbar were measured. Expansion and compression curves and the P-T phase diagram for the crystal-nematic and nematic-isotropic equilibria are presented. The first two sets of curves display the volume changes associated with phase transformations. Optical observations in a diamond cell to about 8 kbar and 200° failed to indicate any new liquid crystal phase. The enthalpies and entropies estimated for C-N, N-I transformations were respectively about 3500 and 12 cal/mol for C-N and about 100 and 0.3 cal/mol for N-I.