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首页> 美国卫生研究院文献>Polymers >Effect of Geometrical Asymmetry on the Phase Behavior of Rod-Coil Diblock Copolymers
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Effect of Geometrical Asymmetry on the Phase Behavior of Rod-Coil Diblock Copolymers

机译：几何不对称性对棒-油二嵌段共聚物相行为的影响

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摘要

The effect of geometrical asymmetry β (described by the length-diameter ratio of rods) on the rod-coil diblock copolymer phase behavior is studied by implementation of self-consistent field theory (SCFT) in three-dimensional (3D) position space while considering the rod orientation on the spherical surface. The phase diagrams at different geometrical asymmetry show that the aspect ratio of rods β influences not only the order-disorder transition (ODT) but also the order-order transition (OOT). By exploring the phase diagram with interactions between rods and coils plotted against β, the β effect on the phase diagram is similar to the copolymer composition f. This suggests that non-lamellae structures can be obtained by tuning β, besides f. When the rods are slim compared with the isotropic shape of the coil segment (β is relatively large), the phase behavior is quite different from that of coil-coil diblock copolymers. In this case, only hexagonal cylinders with the coil at the convex side of the interface and lamella phases are stable even in the absence of orientational interaction between rods. The phase diagram is no longer symmetrical about the symmetric copolymer composition and cylinder phases occupy the large area of the phase diagram. The ODT is much lower than that of the coil-coil diblock copolymer system and the triple point at which disordered, cylinder and lamella phases coexist in equilibrium is located at rod composition fR = 0.66. In contrast, when the rods are short and stumpy (β is smaller), the stretching entropy cost of coils can be alleviated and the phase behavior is similar to coil-coil diblocks. Therefore, the hexagonal cylinder phase formed by coils is also found beside the former two structures. Moreover, the ODT may even become a little higher than that of the coil-coil diblock copolymers due to the large interfacial area per chain provided by the stumpy rods, thus compensating the stretching entropy loss of the coils.
机译：通过在三维（3D）位置空间中实施自洽场论（SCFT），研究了几何不对称β（由棒的长径比描述）对棒-线圈二嵌段共聚物相行为的影响杆在球面上的定向。不同几何不对称性下的相图表明，棒β的纵横比不仅影响有序无序过渡（ODT），而且还影响有序无序过渡（OOT）。通过探索相对于β绘制的棒和线圈之间的相互作用的相图，β对相图的影响与共聚物组成f相似。这表明除f外，还可以通过调节β来获得非薄片结构。当棒与线圈段的各向同性形状相比较细时（β相对较大），相行为与线圈-线圈二嵌段共聚物的相行为完全不同。在这种情况下，即使在棒之间不存在取向相互作用的情况下，只有在界面和薄片相的凸面处具有线圈的六边形圆柱体才是稳定的。相图不再关于对称共聚物组成对称，并且圆柱相占据了相图的大面积。 ODT远低于线圈-线圈二嵌段共聚物体系的ODT，且无序，圆柱和薄片相共存的三重点位于棒成分fR = 0.66。相反，当棒短且笨拙时（β较小），可以减轻线圈的拉伸熵代价，并且相行为类似于线圈-二嵌段。因此，在前两种结构的旁边也发现了由线圈形成的六角圆柱相。此外，由于由根状棒提供的每链大的界面面积，ODT甚至可能比卷材-线圈二嵌段共聚物的ODT更高，从而补偿了卷材的拉伸熵损失。

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