Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
Soft Matter. 2016 May 7;12(17):3849-53. doi: 10.1039/c6sm00627b. Epub 2016 Apr 14.
We investigated the phase behavior of thin film, thickness h≈ 100 nm, mixtures of a polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer with star-shaped polystyrene (SPS) molecules of varying functionalities f, where 4 ≤f≤ 64, and molecular weights per arm Marm. The miscibility of the system and the surface composition varied appreciably with Marm and f. For large values of Marm, regardless of f, the miscibility of the system was qualitatively similar to that of linear chain PS/PS-b-P2VP mixtures - the copolymer chains aggregate to form micelles, each composed of an inner P2VP core and PS corona, which preferentially segregate to the free surface. On the other hand, for large f and small Marm, SPS molecules preferentially resided at the free surface. Moreover, blends containing SPS molecules with the highest values of f and lowest values of Marm were phase separated. These observations are rationalized in terms of competing entropic interactions and the dependence of the surface tension of the star-shaped molecules on Marm and f.
我们研究了厚度约为 100nm 的薄膜中，不同功能化程度 f（4≤f≤64）和臂数均方根分子量 Marm 的星形聚苯乙烯（SPS）分子与聚苯乙烯-b-聚（2-乙烯基吡啶）（PS-b-P2VP）嵌段共聚物的混合物的相行为。该体系的混溶性和表面组成随 Marm 和 f 显著变化。对于 Marm 的较大值，无论 f 如何，体系的混溶性与线性链 PS/PS-b-P2VP 混合物的混溶性定性相似——共聚物链聚集形成胶束，每个胶束由一个内 P2VP 核和 PS 冠组成，优先分离到自由表面。另一方面，对于大 f 和小 Marm，SPS 分子优先位于自由表面。此外，含有具有最高 f 值和最低 Marm 值的 SPS 分子的混合物发生了相分离。这些观察结果可以用竞争的熵相互作用和星形分子的表面张力对 Marm 和 f 的依赖性来解释。
