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-dodecyl thiophene) films has been analyzed using a Warren-Averbach Line-shape analy sis which includes up to five orders of the (h00) lattice reflections. This analysis yields a semiquantitative measure of the volume averaged crystall ite sizes, the lattice parameter variations, and the disorder fluctuations. The progression of these quantities has been followed through a liquid cry stal polymer (LCP) phase transition which occurs in the vicinity of 60 degr ees C. The pronounced peak width narrowing of the low-order (h00) reflectio ns, observed on heating, is found to be essentially uncorrelated with a the orized annealing-induced increase in average crystallite size. The major co ntribution to this narrowing arises from systematic variations in the micro scopic heterogeneities and fluctuations. Moreover, Re observe an anomalousl y large increase in the higher-order (h00) (h = 3-5) peak widths at tempera tures spanning that of the thermotropic LCP transition. This effect is foun d to be strongly correlated with a maximum in the disorder fluctuations, an d this relationship suggests an underlying mechanism for the nature of the LCP transition.