Interactions of ionic liquids with hydration layer of poly(N-isopropylacrylamide): comprehensive analysis of biophysical techniques results

Abstract

Here, we report comprehensive analysis of biophysical technique results for the influence of ionic liquids (ILs) containing the same cation, 1-butyl-3-methylimidazolium (Bmim⁺), and commonly used anions such as SCN⁻, BF₄⁻, I⁻, Br⁻, Cl⁻, CH₃COO⁻ and HSO₄⁻ on the phase transition temperature of poly(N-isopropylacrylamide) (PNIPAM) aqueous solution. Further, the effect of these ILs on bovine serum albumin (BSA) has also been studied. The modulations in UV-visible (UV-vis) absorption spectra, fluorescence intensity spectra, viscosity (η), hydrodynamic diameter (d_H), Fourier transform infrared (FTIR) spectra and scanning electron microscopy (SEM) micrographs clearly reflect the change in the hydration state of PNIPAM in the presence of ILs. The observed single phase transition of PNIPAM aqueous solution at higher concentration of IL is the result of weak ion–ion pair interactions in IL.