CALORIMETRIC STUDY OF PHASE-TRANSITIONS FOR BUTYLOXYBENZYLIDENE OCTYLANILINE IN SILICA AEROGELS - STATIC AND DYNAMIC BEHAVIOR

The quenched randomness and surface effects associated with high-poros ity aerogels can have substantial effects on the phase transitions in thermotropic liquid crystals. A high-resolution ac calorimetry and rel axation calorimetry investigation has been carried out on butyloxybenz ylidene octylaniline (4O.8) in two silica aerogels with mass densities rho=0.08 and 0.17 g cm(-3). Bulk 4O.8 exhibits weakly first-order nem atic-isotropic, second-order nematic-smectic-A, and strongly first-ord er smectic-A-crystal-B transitions. In both aerogels, all of these tra nsitions become continuous; 4O.8 in the rho=0.17 aerogel exhibits subs tantial dynamical behavior. Measurements over a range of frequencies f rom 2.23 to 31.25 mHz allow one to obtain the static specific-heat cap acities.