Convex Arrhenius behaviour in a nematic-isotropic phase transition
Surface Physics and Material Science Divison, Saha Institute of Nuclear Physics - 1/AF Bidhannagar Block, Sector-1, Kolkata-700064, India
Received: 24 July 2014
Accepted: 19 October 2014
Convex Arrhenius behaviour, rare in transitions between equilibrium phases of pure systems, is observed in the plot of heating rate vs. temperature for Nematic-Isotropic (N-I) transition of liquid crystalline MBBA through Differential Scanning Calorimetry (DSC). The plot is best fit by a monomolecular growth function, using which an entropy-driven activation barrier, increasing non-linearly with temperature, is obtained. Fourier Transform Infrared (FTIR) studies of MBBA around the N-I transition temperature show increase in out-of-plane benzene ring distortions and decrease in order along the C=N-C axis, consistent with DSC results of conformational entropy-driven barrier.
PACS: 64.70.M- – Transitions in liquid crystals / 07.20.Fw – Calorimeters / 78.30.cb – Organic liquids
© EPLA, 2014