State Key Laboratory of Chemical Engineering and School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China.
J Phys Chem B. 2020 Jun 25;124(25):5292-5300. doi: 10.1021/acs.jpcb.0c02711. Epub 2020 Jun 15.
We study phase behaviors in compressible polymer blends by using an equation of state in the framework of classical density-functional theory. The phase behaviors are explored by decomposing the compressible mixing of polymers into two steps: incompressible mixing as holding the volume and density relaxation at the given pressure. There exists both upper consolute pressure (UCP) and lower consolute pressure (LCP). LCP-type behaviors are driven by the entropy effect of asymmetric size of molecules, while UCP-type behaviors are driven by energetic interactions. The value of LCP follows a scaling of (), which can be improved to () by taking into account the effects of random chain conformation. The volume of LCP-type polymers expands upon mixing, while that of UCP-type polymers contracts. A closed-loop phase coexisting curve may appear because of the interplay between UCP- and LCP-type behaviors. At the UCP/LCP boundary, the mixing free energy of density relaxation is much smaller than that of both UCP- and LCP-type behaviors. The contribution from incompressible mixing step always dominates the phase behaviors, while that from density relaxation step could distinguish UCP-type between LCP-type behaviors.
我们使用经典密度泛函理论框架中的状态方程来研究可压缩聚合物共混物的相行为。通过将聚合物的可压缩混合分解为两个步骤来探索相行为：在给定压力下保持体积和密度弛豫的不可压缩混合。存在上临界共溶压力 (UCP) 和下临界共溶压力 (LCP)。LCP 型行为由分子不对称尺寸的熵效应驱动，而 UCP 型行为由能量相互作用驱动。LCP 的值遵循 () 的标度，通过考虑随机链构象的影响，可以将其改进为 ()。LCP 型聚合物在混合时体积膨胀，而 UCP 型聚合物体积收缩。由于 UCP 和 LCP 型行为的相互作用，可能会出现闭环相共存曲线。在 UCP/LCP 边界处，密度弛豫混合自由能比 UCP 和 LCP 型行为都小得多。不可压缩混合步骤的贡献始终主导着相行为，而密度弛豫步骤的贡献可以区分 UCP 型和 LCP 型行为。
