Yu Jingying, Liu Faqiang, Tang Ping, Qiu Feng, Zhang Hongdong, Yang Yuliang
State Key Laboratory of Molecular Engineering of Polymers, Collaborative Innovation Center of Polymers and Polymer Composite Materials, Department of Macromolecular Science, Fudan University, Shanghai 200433, China.
Polymers (Basel). 2016 May 11;8(5):184. doi: 10.3390/polym8050184.
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 . This suggests that non-lamellae structures can be obtained by tuning β, besides . 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 = 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.
通过在三维（3D）位置空间中应用自洽场理论（SCFT），并考虑棒状分子在球面上的取向，研究了几何不对称参数β（由棒状分子的长径比描述）对棒-线圈二嵌段共聚物相行为的影响。不同几何不对称情况下的相图表明，棒状分子的长径比β不仅影响有序-无序转变（ODT），还影响有序-有序转变（OOT）。通过绘制棒状分子与线圈之间相互作用的相图，并将其与β进行对比，发现β对相图的影响类似于共聚物组成。这表明，除了通过调整共聚物组成外，还可以通过调节β来获得非层状结构。当棒状分子比各向同性的线圈链段更细长时（β相对较大），相行为与线圈-线圈二嵌段共聚物有很大不同。在这种情况下，即使在棒状分子之间不存在取向相互作用时，只有线圈位于界面凸侧的六方柱相和层状相是稳定的。相图不再关于对称共聚物组成对称，并且柱相占据相图的大面积。ODT远低于线圈-线圈二嵌段共聚物体系，无序、柱相和层状相在平衡中共存的三相点位于棒状分子组成为0.66处。相反，当棒状分子短而粗时（β较小），线圈的拉伸熵成本可以得到缓解，相行为类似于线圈-线圈二嵌段共聚物。因此，在前两种结构旁边还发现了由线圈形成的六方柱相。此外，由于短粗棒状分子提供的每条链的大界面面积，ODT甚至可能比线圈-线圈二嵌段共聚物的ODT略高，从而补偿了线圈的拉伸熵损失。
