| Abstract
| - A series of poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymers were usedto generate nucleation sites for the crystal growth of a homo-PEO fraction in solution. The number-average molecular weights of the PEO blocks (MnPEO) were similar, and the number-average molecularweights of the PS blocks (MnPS) ranged from 4.6K to 17K g/mol. In PEO-b-PS/(chlorobenzene/octane)solutions, square-shaped single crystals bounded by four {120} planes were isothermally grown andobserved with transmission electron and atomic force microscopy. A “sandwich” lamellar structure,constructed by a PEO single crystal layer covered by two tethered PS block layers on the top and bottomcrystal basal surfaces, was found. These diblock copolymer single crystals were used as seeds to growhomo-PEO (MnPEO = 56K g/mol) single crystals in amyl acetate. When the MnPS in the block copolymerwas 4.6K g/mol, the edges and corners of the {120} bounded PEO-b-PS single crystals served as nucleationsites to initiate the further growth of the homo-PEO single crystal. As the MnPS of the block copolymersincreased, the homo-PEO crystal growth was increasingly hampered along the {120} edges of the PEO-b-PS single crystals. When the MnPS of the block copolymer was 17K g/mol, only the four corners of thePEO-b-PS single crystal could still act as nucleation sites. The four edges were chemically “shielded” bythe tethered PS blocks. This indicates that increasing the MnPS led to a higher reduced tethering densityof the PS blocks on both the basal surfaces of the PEO-b-PS single crystals. The repulsion generatedamong the tethered PS blocks caused the PS blocks located near and at the edges to advance along the[120] direction. Interestingly, this local environment only accepted the PEO-b-PS molecules but rejectedthe homo-PEO molecules from further growth. As a direct result of this study, novel channel-wire arrayson a submicrometer length scale having chemical and geometric recognitions could be fabricated viaalternating crystal growth of PEO-b-PS and homo-PEO. This fabrication provided robustly controlledarrays with spacing down to 50 nm.
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