TRANSITION PHENOMENA IN THE THIOPHENE CRYSTAL

Heat capacities of thiophene-benzene binary solutions [(1-x)C4H4S+xC6H6] with x = 0.199, 0.404 and 0.601 were measured by an adiabatic calorimeter in the temperature range 13-300 K. The results are presented in the form of phase diagrams in the thiophene-rich region and over the whole concentration range. The change in temperature, size, and shape of the heat capacity anomalies occasioned by the composition variation indicated that, for this system, changes in molecular environment exerted considerable effects on the phase and glass transitions of pure thiophene. Calculated solidus and liquidus lines based on Raoult's law showed that a considerable deviation from ideal mixing occurred in either or both of the solid and liquid solutions. The calorimetric entropy of each solid solution was calculated to derive a possible residual entropy arising from frozen-in processes in the system. © 1990.