Mukherji Debashish, Marques Carlos M, Stuehn Torsten, Kremer Kurt
Max-Planck Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany.
J Chem Phys. 2015 Mar 21;142(11):114903. doi: 10.1063/1.4914870.
Smart polymers are a modern class of polymeric materials that often exhibit unpredictable behavior in mixtures of solvents. One such phenomenon is co-non-solvency. Co-non-solvency occurs when two (perfectly) miscible and competing good solvents, for a given polymer, are mixed together. As a result, the same polymer collapses into a compact globule within intermediate mixing ratios. More interestingly, polymer collapses when the solvent quality remains good and even gets increasingly better by the addition of the better cosolvent. This is a puzzling phenomenon that is driven by strong local concentration fluctuations. Because of the discrete particle based nature of the interactions, Flory-Huggins type mean field arguments become unsuitable. In this work, we extend the analysis of the co-non-solvency effect presented earlier [D. Mukherji et al., Nat. Commun. 5, 4882 (2014)]. We explain why co-non-solvency is a generic phenomenon, which can only be understood by the thermodynamic treatment of the competitive displacement of (co)solvent components. This competition can result in a polymer collapse upon improvement of the solvent quality. Specific chemical details are not required to understand these complex conformational transitions. Therefore, a broad range of polymers are expected to exhibit similar reentrant coil-globule-coil transitions in competing good solvents.
智能聚合物是一类现代高分子材料，在溶剂混合物中常常表现出不可预测的行为。共非溶剂化就是这样一种现象。当两种（完全）互溶且相互竞争的良溶剂混合在一起时，对于给定的聚合物就会发生共非溶剂化。结果，在中间混合比例范围内，同一聚合物会坍缩成紧密小球状。更有趣的是，当溶剂质量保持良好甚至通过添加更好的共溶剂而变得越来越好时，聚合物却会坍缩。这是一个由强烈的局部浓度涨落驱动的令人困惑的现象。由于相互作用基于离散粒子性质，弗洛里 - 哈金斯型平均场理论变得不适用。在这项工作中，我们扩展了之前[D. 穆克吉等人，《自然通讯》5, 4882 (2014)]对共非溶剂化效应的分析。我们解释了为什么共非溶剂化是一种普遍现象，只有通过对（共）溶剂组分竞争取代的热力学处理才能理解它。这种竞争会导致在溶剂质量改善时聚合物坍缩。理解这些复杂的构象转变不需要具体化学细节。因此，可以预期在相互竞争的良溶剂中广泛种类的聚合物会表现出类似的折返性线团 - 小球 - 线团转变。
