Department of Physics, Faculty of Arts and Sciences, Yildiz Technical University, 34220, Istanbul, Turkey.
Phys Chem Chem Phys. 2018 Jun 6;20(22):15389-15399. doi: 10.1039/c8cp02026d.
The solubility and lower critical solution temperature (LCST) behaviour of poly(oligo(ethylene glycol)methyl ether methacrylate) (POEGMA300) in water were comprehensively investigated by all-atom molecular dynamics (MD) simulations for 5-, 20-, 50- and 75-mer homopolymers. According to various structural and dynamic properties, the water-solubility of POEGMA300 below the LCST is mainly provided by hydrophobic hydration around the side chain carbon atoms, which is achieved by cage-like water formations. The LCST phase transition occurs when these cage-like structures are disrupted by increasing the temperature above the LCST. During this process, significant amounts of water molecules are released and the local water-ordering is reduced. Moreover, the number of hydrogen bonds and hydrogen bond lifetime results indicate that the hydrogen bonding between polymers and water molecules has relatively little effect on the phase transition. Also, the diffusion rates of 50- and 75-mer POEGMA300 decrease with increasing temperature, which may be due to the breakage of cage-like water structures when the polymer exceeds a certain chain length. Our atomistic level findings will enhance the understanding of the LCST phase transition of OEGMA based homopolymers and will be helpful to design homo- and co-polymers of OEGMAs with required properties.
通过全原子分子动力学（MD）模拟，对 5-、20-、50-和 75-mer 均聚物的聚（聚乙二醇甲基醚甲基丙烯酸酯）（POEGMA300）在水中的溶解度和低临界溶液温度（LCST）行为进行了全面研究。根据各种结构和动态特性，低于 LCST 时 POEGMA300 的水溶性主要由侧链碳原子周围的疏水性水合提供，这是通过笼状水形成实现的。当温度升高超过 LCST 时，这些笼状结构被破坏，发生 LCST 相转变。在此过程中，大量水分子被释放，局部水分子有序性降低。此外，氢键数量和氢键寿命的结果表明，聚合物和水分子之间的氢键对相转变的影响相对较小。同样，50-和 75-mer POEGMA300 的扩散速率随温度升高而降低，这可能是由于当聚合物超过一定链长时，笼状水结构被破坏。我们在原子水平上的发现将增强对基于 OEGMA 的均聚物 LCST 相转变的理解，并有助于设计具有所需性能的 OEGMA 均聚物和共聚物。
