We introduce a lattice framework that incorporates elements of Flory–Huggins solution theory and the q-state Potts model to study the phase behavior of polymer solutions and single-chain conformational characteristics. Without empirically introducing temperature-dependent interaction parameters, standard Flory–Huggins theory describes systems that are either homogeneous across temperatures or exhibit upper critical solution temperatures. The proposed Flory–Huggins–Potts framework extends these capabilities by predicting lower critical solution temperatures, miscibility loops, and hourglass-shaped spinodal curves. We particularly show that including orientation-dependent interactions, specifically between monomer segments and solvent particles, is alone sufficient to observe such phase behavior. Signatures of emergent phase behavior are found in single-chain Monte Carlo simulations, which display heating- and cooling-induced coil–globule transitions linked to energy fluctuations. The framework also capably describes a range of experimental systems. Importantly, and by contrast to many prior theoretical approaches, the framework does not employ any temperature- or composition-dependent parameters. This work provides new insights regarding the microscopic physics that underpin complex thermoresponsive behavior in polymers.

中文翻译：

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聚合物-溶剂相互作用的不对称性产生复杂的热响应行为


我们引入了一个晶格框架，该框架结合了 Flory-Huggins 溶液理论和 q 态 Potts 模型的元素，以研究聚合物溶液的相行为和单链构象特征。在不凭经验引入与温度相关的相互作用参数的情况下，标准弗洛里-哈金斯理论描述了在温度范围内均匀或表现出上限临界溶液温度的系统。提出的弗洛里-哈金斯-波茨框架通过预测较低的临界溶液温度、混溶环和沙漏形旋节线曲线来扩展这些功能。我们特别表明，包括方向依赖的相互作用，特别是单体链段和溶剂颗粒之间的相互作用，足以观察这种相行为。在单链蒙特卡罗模拟中发现了涌现相行为的特征，该模拟显示了与能量波动相关的加热和冷却引起的线圈-球体转变。该框架还能够描述一系列实验系统。重要的是，与许多先前的理论方法相比，该框架不采用任何与温度或成分相关的参数。这项工作提供了关于支撑聚合物复杂热响应行为的微观物理的新见解。