Transition-temperature differences on cooling for a monotropic liquid-crystal polyester observed in DSCs of different design

Most commercial differential scanning calorimeters (DSC) belong to two types of design, namely the power-compensation DSC and the heat-flux DSC. There have been some reports in the literature indicating differences in response between these two types of instrument. Most of these differences have been observed on heating, and it is often assumed that the response on cooling is symmetrical. In this work, we report on differences observed on cooling a monotropic liquid-crystal polyester in several DSCs of the two designs. The monotropic liquid-crystal polyester used here had two exothermic transitions under moderate cooling rates. It was found that the heat-flux instruments tended to give overlapping exothermic peaks, suggesting that the second transition started before the first was complete. The power-compensation instruments, on the other hand, showed completely separated peaks at the same cooling rates. A monotropic liquid-crystal polymer with appropriate crystallisation kinetics may be a good material to evaluate the DSC response on cooling. (C) 1998 Elsevier Science B.V.