Evolution of the isotropic to nematic phase transition in octyloxycyanobiphenyl+aerosil dispersions

Details Evolution of the isotropic to nematic phase transition in octyloxycyanobiphenyl+aerosil dispersions Evolution of the isotropic to nematic phase transition in octyloxycyanobiphenyl+aerosil dispersions

2003-10-03

arxiv.org/abs/cond-mat/0310070v1

Physics

Condensed Matter

Soft Condensed Matter

30 total pages, 8 figures, 1 table submitted to Physical Review E 1 October 2003

Scientific paper

10.1103/PhysRevE.69.031703

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.

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