Crystallization temperature-dependent crystal orientations within nanoscale confined lamellae of a self-assembled crystalline-amorphous diblock copolymer

For a lamella-forning poly(ethylene oxide)-block-polystyrene (PEO-b-PS) dib lock copolymer ((M) over bar(n)(PEO) = 8.7K and (M) over bar(n)(PS) = 9.2K) , the glass transition temperature of the PS blocks is 62 degrees C, and th e melting temperature of the PEO crystals is around 51 degrees C when the s ample is crystallized below 40 degrees C. The PEO blocks thus crystallize i n a one-dimensionally confined lamellar space of 8.8 nm, as studied recentl y by one-dimensional small-angle X-ray scattering (SAXS) and transmission e lectron 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 experim ents. 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 crystalli zation temperature (T-c). Detailed crystallographic analyses indicate that the c-axis orientation at each T-c corresponds to a uniform orientation rat her than a mixture of different crystal orientations.