| Summary: | 碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 95 === The surface structures of diblock copolymer brushes with various architectures of linear, Y-shaped and comb-like block copolymer brush were investigated by dissipative particle dynamics (DPD). The solvophilic polymer segment is anchored on the surface while that of solvophobic is either at top or side blocks.
In selective solvents, solvophobic blocks tend to form aggregates. The theoretical results suggest that copolymer brush with a rigid rod-like solvophobic block form larger aggregates and surface roughness than those of a soft coil-like solvophobic block. The aggregated size also grows with increasing surface density, especially in horizontal direction. The shapes of the surface aggregates are varied from small isolated islands, large islands, worm-like conformation, even network structures as the surface density increases. The Y-shaped brushes have a similar transformation process as that of the linear brushes but the surface density for the above transition is lower. The surface roughness increases first and then decreases as surface density increase. The copolymer brushes with a longer solvophilic segment possess less surface roughness since the aggregates tend to submerge under the solvophilic polymer domain.
For both linear and Y-shaped block copolymer brushes, the radius of gyration in the direction perpendicular to the surface (RgZ) has a linear relation with the solvophilic chain length, which is the same as that of the homopolymer brush system. However, the RgZ of the solvophobic block exhibits a power exponent of 0.6 to its length, same as free polymer chain in solution. In the case of a high surface density, the shape and length of solvophobic chains have an insignificant effect on the surface structures.
For the comb-like polymer brush systems, aggregates are inclined to the vertical direction rather than the horizontal direction, owing to the size exclusion effect of the main chains. If the free sections on top of the main chains are long enough, only small aggregates would be appeared on the surface. For systems with a high surface density, different layers of aggregates are found in the vertical direction if the gaps between the side chains are large enough. The present study suggests that the polymer architecture, copolymer segment ratio, and surface density play an important role of surface structures of copolymer brushes.
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