Interactions between crystalline and amorphous domains in semicrystalline polymers: Small-angle X-ray scattering studies of the Brill transition in nylon 6,6

The lamellar structures in nylon 6,6 were characterized at several temperat ures using synchrotron small-angle X-ray scattering (SAXS) to monitor the c hanges during the Brill transition at similar to 160 degrees C (T-B) The in tegrated intensity and the coherence length of the lamellar stacks increase during heating above T-B. In contrast, during cooling, the intensity incre ases below T-B whereas the coherence length increases up to T-B and remains unchanged upon further cooling. The increase in SAXS intensity observed ab ove T-B during heating is attributed to the enhanced contrast resulting fro m a decrease in the packing density of the amorphous chain segments. It is suggested that the changes in the packing of the crystalline stems, as they do occur during crystalline phase transitions, provoke a proportionate res ponse in the packing of the amorphous chain segments in the interlamellar r egions. The thermal expansion coefficient of the amorphous segments calcula ted from the X-ray diffraction data above T-B is 5.9 x 10(-4)/K (molar ther mal expansion coefficient, 854 x 10(-10) m(3)/(mol K)), and this is in reas onable agreement with the published values.