Effect of high pressure on the nematic–isotropic transition in aerosil–liquid crystal composites

We report the first high pressure investigations of the nematic–isotropic transition in the composites of a liquid crystal compound with hydrophilic aerosil particles. The low concentrations of the aerosil particles used create soft gels of the composites. As expected TN–Iso, the nematic–isotropic transition at room pressure exhibits a non-monotonic variation with increasing aerosil concentration. This non-monotonic behaviour is seen in the isobaric scans over the wide range of pressures studied, and its “magnitude” is dependent on the pressure applied. The surprising result of the present investigations on these nanocolloidal systems is that the slope of the pressure–temperature boundary also exhibits a non-monotonic dependence with the aerosil concentration, which qualitatively is similar to that of the transition temperature variation. Employing the transition enthalpy values determined at room pressure using differential scanning calorimetric scans collected at low heating rates, we calculate the transition volume dependence on the aerosil concentration. The study adds a new dimension, namely, the influence of pressure on liquid crystalline transitions in restricted geometries.