Nanotailored crystalline morphology in hexagonally perforated layers of a self-assembled PS-b-PEO diblock copolymer

作者：Zhu L; Huang P; Chen WY; Ge Q; Quirk RP; Cheng SZD; Thomas EL; Lotz B; Hsiao BS; Yeh FJ; Liu LZ

来源：Macromolecules, 2002, 35(9): 3553-3562.

DOI：10.1021/ma012184n

Nanoscale tailored polymer crystalline morphology is studied in a polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymer with number-average molecular weights for the PS and PEO blocks being 17 000 and 11 000 g/mol, respectively. The PEO volume fraction is 0.39. After large amplitude planar reciprocating shear, a hexagonally perforated layer (HPL) structure is obtained. Since the glass transition temperature of the PS blocks (72 degreesC) is higher than the PEO crystal melting temperature (similar to51 degreesC when the crystallization temperature, T-c, is lower than 40 degreesC), the PEO block crystallization is confined within the HPL structure. The PEO crystal (the c axis) orientation within this complex confined environment is investigated using simultaneous synchrotron two-dimensional small-angle and wide-angle X-ray scattering (SAYS and WAXS) methods. The PEO crystal orientations with respect to the layer plane (or the 10001}) of the HPL structure have been found to be dependent upon T-c. At very low T(c)s (below -50 degreesC), the PEO crystals have a random orientation. Between -50 degreesC less than or equal to T-c less than or equal to -10 degreesC, the PEO crystal c axes preferentially orient parallel to the layer plane. Above T-c = 0 degreesC, the crystal c axes orient inclined to the layer plane of the HPL structure, and the tilt angle with respect to the layer plane increases with T-c. Contrary to the confined polymer crystallization in nanolamellar structure, however, the c axis orientation perpendicular to the layer plane is not found at least up to T-c = 40 degreesC in this HPL confined environment. Meanwhile, the ribbonlike PEO crystal growth is specifically tailored along the {10 (1) over bar0} planes of the hexagonal PS perforations. Apparent crystallite size analyses using the Scherrer equation confirm the one-dimensional crystal growth at high T(c)s. Using time-resolved WAXS experiments, the crystal orientation is observed to occur in the early stage of crystallization with a crystallinity of similar to7 wt %. Based on the results of specifically designed self-seeding experiment, the crystal orientation is determined by the crystal growth (surface nucleation) in the confined HPL phase rather than the preorientation of primary nuclei.

• 出版日期2002-4-23
• 单位MIT