Tunnelling the structural insights between poly(N-isopropylacrylamide) and imidazolium sulfate ionic liquids

Abstract

The integration of polymers and ionic liquids (ILs) leads to the substantial development and establishment of sustainable technologies to fabricate novel polymeric composites and polymeric materials. In this regard, poly(N-isopropylacrylamide) (PNIPAM), a classic biomedical thermoresponsive polymer (TRP), has attracted wide attention in the scientific, technological, and industrial fields owing to its characteristic tuning ability with the surrounding environment. ILs have been regarded as potential candidates as green solvents that can function as reaction and solvent media. Owing to the wide-ranging importance of these materials in diverse fields, it is imperative to study the interactions between TRPs and ILs to fabricate polymeric-IL-based materials. In this paper, we study the comparative effect of imidazolium-based ILs such as 1-ethyl-3-methylimidazolium methyl sulfate [Emim][MtSO4] and 1-butyl-3-methylimidazolium ethyl sulfate [Bmim][EtSO4] on the phase transition behavior of biomedically renowned thermoresponsive PNIPAM. To probe into these changes, we conduct various experimental studies such as temperature-dependent dynamic light scattering, thermal fluorescence spectroscopy, steady-state fluorescence spectroscopy, and UV–visible absorption spectroscopy. Our experimental results explicitly elucidate the phenomenological changes in the molecular interactions, variations in absorbance, and agglomeration behavior of PNIPAM and ILs aqueous mixtures. The temperature-dependent dynamic light scattering studies demonstrate the alterations in the phase transition behavior of PNIPAM with the addition of ILs. Both the added ILs decreased the lower critical solution temperature of PNIPAM towards different extents. The current work will contribute to the design of polymeric ionic liquid-based materials.