Crystallization Temperature-Dependent Crystal Orientations within Nanoscale Confined Lamellae of a Self-Assembled Crystalline−Amorphous Diblock Copolymer

For a lamella-forming poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer (M̄ n PEO = 8.7K and M̄ n PS = 9.2K), the glass transition temperature of the PS blocks is 62 °C, and the melting temperature of the PEO crystals is around 51 °C when the sample is crystallized below 40 °C. The PEO blocks thus crystallize in a one-dimensionally confined lamellar space of 8.8 nm, as studied recently by one-dimensional small-angle X-ray scattering (SAXS) and transmission electron microscopy. In this report, the crystal orientation (the c-axis of the PEO crystals) within nanoscale confined lamellae has been investigated using combined two-dimensional SAXS and wide-angle X-ray scattering experiments. The c-axis orientation in the PEO crystals is observed for the first time to change from random to perpendicular, then to inclined, and finally to parallel to the lamellar surface normal, depending only on the crystallization temperature (T c). Detailed crystallographic analyses indicate that the c-axis orientation at each T c corresponds to a uniform orientation rather than a mixture of different crystal orientations.