Physik-Department, Physik weicher Materie, Technische Universität München , James-Franck-Strasse 1, 85748 Garching, Germany.
IMFUFA, Department of Science and Environment, Roskilde University , P. O. Box 260, 4000 Roskilde, Denmark.
ACS Appl Mater Interfaces. 2017 Sep 20;9(37):31291-31301. doi: 10.1021/acsami.6b16563. Epub 2017 Mar 20.
Mixtures of two diblock copolymers of very different lengths may feature both macro- and microphase separation; however, not much is known about the mechanisms of separation in diblock copolymer thin films. In the present work, we study thin films of mixtures of two compositionally symmetric block copolymers, both in the one-phase and in the two-phase state, combining coarse-grained molecular simulations (dissipative particle dynamics, DPD) with scattering experiments (grazing-incidence small-angle X-ray scattering, GISAXS). We reveal that the film thickness and selective adsorption of different blocks to the substrate control the distribution of macrophases within the film as well as the orientation of the lamellae therein. In thick films, the mixtures separate in the vertical direction into three layers: Two layers being rich in short copolymers are formed near the film interfaces, whereas a layer being rich in long copolymers is located in the film core. The lamellar orientation in the layers rich in short copolymers is dictated by the surface selectivity, and this orientation only weakly affects the vertical orientation of lamellae in the film core. This provides the opportunity to control the domain orientation in the copolymer films by mixing block copolymers with low-molecular additives instead of relying on a more complicated chemical modification of the substrate. In thinner films, a lateral phase separation appears.
两种长度差异非常大的两嵌段共聚物的混合物可能具有宏观相和微观相分离；然而，对于两嵌段共聚物薄膜中的分离机制，我们知之甚少。在本工作中，我们结合粗粒化分子模拟（耗散粒子动力学，DPD）和散射实验（掠入射小角 X 射线散射，GISAXS），研究了两种组成对称嵌段共聚物混合物的薄膜，包括单相和两相状态。我们揭示了薄膜厚度和不同嵌段对基底的选择性吸附控制了薄膜内大相的分布以及其中层片的取向。在厚膜中，混合物沿垂直方向分离成三层：靠近薄膜界面形成两层富含短共聚物，而富含长共聚物的层位于薄膜芯部。富含短共聚物的层中的层片取向由表面选择性决定，这种取向仅对薄膜芯部层片的垂直取向产生微弱影响。这为通过混合嵌段共聚物和低分子添加剂来控制共聚物薄膜中的畴取向提供了机会，而无需依赖于更复杂的基底化学修饰。在更薄的薄膜中，出现了横向相分离。
