Department of Chemistry, University of Delhi, Delhi, India.
J Phys Chem B. 2011 Apr 28;115(16):4752-7. doi: 10.1021/jp201826v. Epub 2011 Apr 5.
The effect of the imidazolium based ionic liquid (IL) 1-benzyl-3-methylimidazolium tetrafluoroborate ([Bzmim][BF(4)]) was investigated on the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAM) in aqueous solution by using fluorescence, viscometric, and dynamic light scattering (DLS) techniques. The measurements were performed at four different [Bmim][BF(4)] concentrations (1-4 mg/mL) in PNIPAM aqueous solution. Our experimental results elucidate that the IL induces the collapsed globular structure of polymer, facilitated by the weakening of hydrogen bonds between the amide group of the polymer and water molecules; therefore, IL destabilizes the hydrated macromolecule structure. We observed that the phase transition of PNIPAM aqueous solution abruptly shifts down with increasing IL concentration mainly due to hydrophobic collapse and aggregation of a macromolecule. These results unambiguously reveal that the imidazolium based IL significantly affected the phase transition of PNIPAM and ruptured the hydrogen bonding between polymer and water molecules, and eventually the hydrated macromolecule structure was destabilized.
研究了 1-苄基-3-甲基咪唑四氟硼酸盐([Bzmim][BF(4)])离子液体对聚异丙基丙烯酰胺(PNIPAM)水溶液低临界溶解温度(LCST)的影响，采用荧光、黏度和动态光散射(DLS)技术。在 PNIPAM 水溶液中四种不同的[Bmim][BF(4)]浓度(1-4mg/mL)下进行了测量。实验结果表明，离子液体通过削弱聚合物酰胺基团与水分子之间的氢键，诱导聚合物发生塌陷的球状结构，从而使水合大分子结构失稳。我们观察到，随着 IL 浓度的增加，PNIPAM 水溶液的相转变急剧向下移动，主要是由于疏水塌陷和大分子的聚集。这些结果清楚地表明，基于咪唑的离子液体显著影响了 PNIPAM 的相转变，破坏了聚合物与水分子之间的氢键，最终使水合大分子结构失稳。
