Karimineghlani Parvin, Zheng Jin, Hu Yan-Yan, Sukhishvili Svetlana
Department of Materials Science and Engineering, Texas A&M University, College Station, 77843, TX, USA.
Phys Chem Chem Phys. 2020 Aug 21;22(31):17705-17712. doi: 10.1039/d0cp02679d. Epub 2020 Jul 30.
While the behavior of polyelectrolyte chains in aqueous salt solutions has been extensively studied, little is known about polar polymer chains in solvents with extremely high concentrations of inorganic ions, such as those found in ionic liquids (ILs). Here, we report on expansion, solvation and diffusion of poly(vinyl alcohol), PVA, chains in dilute solutions of a hydrated inorganic IL phase change material (PCM), lithium nitrate trihydrate (LNH). This solvent has an extremely high concentration of inorganic ions (≈18 M) with a low concentration of water molecules largely forming solvation shells of Li and NO ions, as shown using ATR-FTIR spectroscopy. Diffusion and hydrodynamic size of PVA chains of different molecular weights in this unusual solvent were studied using fluorescence correlation spectroscopy (FCS). A higher scaling exponent obtained from the molecular weight dependences of the diffusion coefficients of PVA chains as well as a lower overlap concentration (c*) of PVA in LNH solutions as measured by FCS suggest an expansion of the polymer coils in this solvent. We argue that enhanced solubility of PVA in LNH solutions is likely a result of increased rigidification of polymer chains due to the binding of solvated Li ions, which is demonstrated using Li NMR spectroscopy. We believe that an understanding of solvation and ion-binding capability can offer crucial insight into designing polymer-based shape stabilization matrices for inorganic PCMs.
虽然聚电解质链在盐水溶液中的行为已得到广泛研究，但对于极性聚合物链在无机离子浓度极高的溶剂中的情况却知之甚少，比如在离子液体（ILs）中发现的那些溶剂。在此，我们报告了聚乙烯醇（PVA）链在水合无机离子液体相变材料（PCM）三水合硝酸锂（LNH）的稀溶液中的膨胀、溶剂化和扩散情况。如使用衰减全反射傅里叶变换红外光谱（ATR-FTIR）所示，这种溶剂具有极高的无机离子浓度（约18 M），而水分子浓度较低，且大部分水分子形成了Li⁺和NO₃⁻离子的溶剂化壳层。使用荧光相关光谱（FCS）研究了不同分子量的PVA链在这种特殊溶剂中的扩散和流体力学尺寸。从PVA链扩散系数的分子量依赖性获得的较高标度指数，以及通过FCS测量的PVA在LNH溶液中的较低重叠浓度（c*），表明该溶剂中聚合物线圈发生了膨胀。我们认为，PVA在LNH溶液中溶解度的提高可能是由于溶剂化Li⁺离子的结合导致聚合物链刚性增加的结果，这通过锂核磁共振光谱（Li NMR）得以证明。我们相信，对溶剂化和离子结合能力的理解可为设计用于无机PCM的聚合物基形状稳定基质提供关键见解。
