Diffraction Line-Shape Analysis of Poly(3-dodecylthiophene):  A Study of Layer Disorder through the Liquid Crystalline Polymer Transition

The nature of the structural ordering within semicrystalline poly(3-dodecylthiophene) films has been analyzed using a Warren−Averbach line-shape analysis which includes up to five orders of the (h00) lattice reflections. This analysis yields a semiquantitative measure of the volume averaged crystallite sizes, the lattice parameter variations, and the disorder fluctuations. The progression of these quantities has been followed through a liquid crystal polymer (LCP) phase transition which occurs in the vicinity of 60 °C. The pronounced peak width narrowing of the low-order (h00) reflections, observed on heating, is found to be essentially uncorrelated with a theorized annealing-induced increase in average crystallite size. The major contribution to this narrowing arises from systematic variations in the microscopic heterogeneities and fluctuations. Moreover, we observe an anomalously large increase in the higher-order (h00) (h = 3−5) peak widths at temperatures spanning that of the thermotropic LCP transition. This effect is found to be strongly correlated with a maximum in the disorder fluctuations, and this relationship suggests an underlying mechanism for the nature of the LCP transition.