Crystal orientation changes in two-dimensionally confined nanocylinders ina poly(ethylene oxide)-b-polystyrene/polystyrene blend

A lamella-forming poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock cop olymer has been blended with a low molecular weight polystyrene (PS) homopo lymer to form a miscible polymer blend. The PEO volume fraction is 0.32, an d the order-disorder transition temperature (T-ODT) of this blend is 175 de greesC. Therefore, the PEO blocks form nanocylinders surrounded by a PS mat rix below the TODT. Since the glass transition temperature of the PS is 64 degreesC and the PEO crystal melting occurs at similar to 50 degreesC, the PEO-block crystallization takes place in a two-dimensionally confined glass y environment. The cylinder diameter is determined to be 13.7 nm, based on small-angle X-ray scattering (SAXS) and transmission electron microscopy re sults. Using simultaneous two-dimensional SAXS and wide-angle X-ray scatter ing techniques, the crystal orientation (the c-axes of the PEO crystals) wi thin the nanocylinders is found to change simply depending upon the crystal lization temperature (T-c). At very low T-c (< -30 <degrees>C), PEO crystal s are randomly oriented within the confined cylinders. Starting at T-c = -3 0 degreesC, the crystal orientation changes to be inclined with respect to the cylinder axis, (a) over cap. The tilt angle from (a) over cap continuou sly increases with increasing T-c, and finally it becomes 90 degrees when T -c greater than or equal to 2 degreesC. Crystallographic analysis indicates that the crystal c-axis orientation at each T-c corresponds to a uniform c rystal orientation.