How Does a Smart Polymer Respond to Imidazolium-Based Ionic Liquids?

In this research article, we have explored the changes in the lower critical solution temperature (LCST) of the poly(N-vinylcaprolactam) (PVCL) in the presence of imidazolium-based ionic liquids (ILs) with fixed cation l-butyl-3-methylimidazolium cation [Bmim(+)], and commonly used anions such as SCN-, I-, Br-, Cl-, CH3COO-, and HSO4. The series of anions also reflect the Hofmeister series of ILs. The results reveal that the LCST of the PVCL increases with increasing IL concentration. Interestingly, the results are the reverse of the PNIPAM with the same ILs where the LCST of PNIPAM decreases linearly with increase in the IL concentration following the Hofmeister series. Herein, we observed that the increase in the LCST of PVCL follows the order of ILs as, HSO4- < CH3COO- < Cl- < Br- I- < SCN-. This is the reverse order for Hofmeister series anions effect on the polymer. Furthermore, the different kind of interactions occur between Its and PVCL observed using UV-absorbance, fluorescence, and FTIR spectroscopy. The predicted mechanism suggest that the ILs act as bridge between water and PVCL, because the solvation of the polymers is increased leading to increase in the LCST of the polymer. Moreover, DLS and FESEM techniques were employed to examine the morphological changes in the PVCL at different temperature in the presence of various concentrations of the ILs.