Calorimetric study of phase transitions for butyloxybenzylidene octylaniline in silica aerogels: Static and dynamic behavior

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The quenched randomness and surface effects associated with high-porosity aerogels can have substantial effects on the phase transitions in thermotropic liquid crystals. A high-resolution ac calorimetry and relaxation calorimetry investigation has been carried out on butyloxybenzylidene octylaniline (4O.8) in two silica aerogels with mass densities {ρ}=0.08 and 0.17 g cm^-3. Bulk 4O.8 exhibits weakly first-order nematic-isotropic, second-order nematic--smectic-A, and strongly first-order smectic--A--crystal-B transitions. In both aerogels, all of these transitions become continuous; 4O.8 in the {ρ}=0.17 aerogel exhibits substantial dynamical behavior. Measurements over a range of frequencies from 2.23 to 31.25 mHz allow one to obtain the static specific-heat capacities.