STRUCTURAL FEATURES OF THE LIQUID PLASTIC CRYSTAL PHASE-TRANSITION FOR CYCLOHEXANE IN BULK AND CONFINED GEOMETRY

Neutron diffraction measurements have been made for cyclohexane, C6D12 as a function of temperature for bulk samples and also in porous silica with characteristic pore dimensions of approximately 90 angstrom. The results show that the simplifying assumption of cyclohexane as an unhindered rotator are not valid and that complex spatial correlations exist in all phases. The nucleation of the plastic crystal phase is displaced to low temperatures for the confined material and the diffraction pattern of the plastic crystal phase is found to depend on thermal history as well as temperature. The results may be interpreted in terms of defect properties which influence the orientational correlations between neighbouring molecules.