  High-resolution ac-calorimetry has been carried out on dispersions of
aerosils in the liquid crystal octyloxycyanobiphenyl (8OCB) as a function of
aerosil concentration and temperature spanning the crystal to isotropic phases.
The liquid-crystal 8OCB is elastically stiffer than the previously well studied
octylcyanobiphenyl (8CB)+aerosil system and so, general quenched random
disorder effects and liquid-crystal specific effects can be distinguished. A
double heat capacity feature is observed at the isotropic to nematic phase
transition with an aerosil independent overlap of the heat capacity wings far
from the transition and having a non-monotonic variation of the transition
temperature. A crossover between low and high aerosil density behavior is
observed for 8OCB+aerosil. These features are generally consistent with those
on the 8CB+aerosil system. Differences between these two systems in the
magnitude of the transition temperature shifts, heat capacity suppression, and
crossover aerosil density between the two regimes of behavior indicate a liquid
crystal specific effect. The low aerosil density regime is apparently more
orientationally disordered than the high aerosil density regime, which is more
translationally disordered. An interpretation of these results based on a
temperature dependent disorder strength is discussed. Finally, a detailed
thermal hysteresis study has found that crystallization of a well homogenized
sample perturbs and increases the disorder for low aerosil density samples but
does not influence high density samples.
