Effect of surface on the thermodynamic properties of polar liquids and liquid crystals trapped in a porous medium

The heat capacity of some polar liquids (2,6-lutidine, aniline and nitrobenzene) and liquid crystals (nitrophenyldodecyloxybenzoate and dodecylcyanobiphenyl) trapped in glass and nickel porous matrices have been measured by using a high-resolution adiabatic calorimeter. A decrease in the molar heat capacity of substances trapped in porous media compared with the bulk molar heal capacity was observed. A new phenomenon caused by the effect of the glass surface on the confined fluid was revealed. This phenomenon was manifested as an unusual behaviour of the heat capacity versus temperature curve (a 'crevasse' in a curve). In addition, we observed the nematic phase of dodecylcyanobiphenyl liquid crystal induced by the variable curvature of the glass matrix surface. (C) 1997 Elsevier Science Ltd. All rights reserved.