Thermal study of the influence of aerosils on the phase transitions of heptyloxybenzylidene butylaniline

Bulk heptyloxybenzylidene butylaniline (70.4) undergoes first order nematic (N)-isotropic (I), nematic-smectic A (SmA), and smectic C (SmC)-crystal G(CrG) transitions as well as a mean-field second order SmA-SmC transition. The dispersion of 70 Angstrom diameter hydrophobic silica aerosil particles in 70.4 leads to doubling and significant temperature shifts for all three first order transitions, as determined with a.c. calorimetry. The SmA-SmC heat capacity peak merely shifts in position while remaining a single sharp Landau feature with an amplitude that decreases as the aerosil density increases. The behaviour of three 7O.4 + hydrophobic aerosil samples is discussed and compared to that of one 70.4 hydrophilic aerosil and previously reported results for 7O.4 + aerogel and 4O.8 + aerosil samples.