AI 中文总结
本文理论证明，完全对称非缔合的多组分液体粗粒化模型可因单体数密度低时的强位置关联，表现出LCST与闭环相行为，该机制或可解释现有聚合物材料的相关相行为。
AI 中文摘要
多组分液体可在加热时发生相分离，表现出较低临界溶液温度（LCST）。此外，少数材料在进一步加热时会发生无序转变，形成闭环相图。此前研究表明，LCST或闭环相行为可出现在组分不对称或相互作用势经过特殊设计吸引的液体模型中。本文从理论上证明，LCST与闭环相行为可在更广泛的模型中出现。具体而言，研究发现，任何多组分液体的最简单且广泛使用的粗粒化（CG）模型都可表现出这些现象，该模型中物种完全对称，所有粒子通过任意排斥势相互作用。此外，研究还发现，这些模型中的LCST与闭环相行为仅源于CG液体模型的基本性质，即单体数密度ρ较低时会出现强单体-单体位置关联。研究对完全对称二元共混物和二嵌段共聚物熔体的模型进行了模拟，其中非键合单体通过通用的与温度（T）无关的纯排斥简谐势相互作用。正如预测，在ρ足够低时，会出现LCST与闭环相行为，该ρ会导致强单体-单体关联，进而引起有效配位数对T的强依赖，这又会诱导Flory-Huggins参数对T的非单调依赖。综上，研究发现，多组分液体的最简单完全对称非缔合CG模型可因任何CG液体模型的基本性质所产生的机制表现出复杂的温度响应，该机制可能促成了许多现有聚合物材料中LCST与闭环相行为的出现。
英文摘要
Multicomponent liquids can phase separate upon heating, exhibiting a lower critical solution temperature (LCST). Moreover, a narrow class of materials can undergo disordering transition upon further heating, yielding closed-loop phase diagrams. Previously, it was shown that LCST or closed-loop phase behavior can appear in the models of liquids in which components are asymmetric or interaction potentials have a specifically designed attraction. Here, we show theoretically that LCST and closed-loop phase behavior can occur in a significantly wider set of models. In particular, we found that these phenomena can be exhibited by the simplest and widely used coarse-grained (CG) models of any multicomponent liquid in which species are fully symmetric and where all particles interact via an arbitrary repulsive potential. In addition, we discovered that LCST and closed-loop phase behavior in these models emerges merely due to the basic property of CG liquid models, namely, the appearance of strong monomer-monomer positional correlations at low monomer number density $ρ$. We simulated the models of fully symmetric binary blends and diblock copolymer melts where nonbonded monomers interacted via a generic T-independent purely repulsive harmonic potential. As predicted, LCST and closed-loop phase behavior emerged at $ρ$ sufficiently low to cause strong monomer-monomer correlations leading to a strong T-dependence of the effective coordination number, which, in turn, induced a nonmonotonic T-dependence of the Flory-Huggins parameter. To summarize, we discovered that the simplest fully symmetric non-associating CG models of multicomponent liquids can exhibit complex temperature response due to a mechanism stemming from the basic nature of any CG liquid model. This mechanism might contribute to the emergence of LCST and closed-loop phase behavior in many existing polymer materials.
