The inﬂuence of various alkylammonium-based ionic liquids on the hydration state of temperature-responsive polymer
Mhkize, Thandeka Yvonne
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The inﬂuence of different alkylammonium-based ionic liquids (ILs) on the temperature-dependent aqueous poly(N-isopropylacrylamide) (PNIPAM) solution is explored by the comprehensive experimental analysis. The co-solvents investigated in the present study included a series of ILs with a ﬁxed (triﬂuromethylsulfonyl)imide [NTf2]− anion and variable ammonium cations such as butyltrimethylammonium (IL-1), methyl-trioctylammonium (IL-2), diethylmethyl(2-methoxyethyl)ammonium (IL-3) and ethyldimethylpropyla mmonium (IL-4). The thermal phase transitions of aqueous solution of thermo-responsive polymer (TRP) in ammonium-based ILs were studied by various experimental techniques such as ﬂuorescence spectroscopy, dy-namic light scattering (DLS) and viscosity (η). We further employed ﬁeld emission scanning electron microscope (FESEM) to reveal the distinct morphological changes of various self-assembled morphologies. Our results reveal that the lower critical solution temperature (LCST) of the TRP can be signiﬁcantly altered by the ILs. The phase transition state of aqueous TRP decreases as the concentration of IL increased. We ﬁnd that IL-4 lowers the LCST of TRP signiﬁcantly more as compared to the other ILs. Our experimental results reveal that the hydrophobic interactions are predominant between the monomers of PNIPAM and ions of the ILs. This research work high-lights new opportunities for the wide applications in engineering of the bio-responsive smart PNIPAM-based de-vices and appropriate selection of ILs, which should allow for increasing the usage of thermo-responsive phase behaviour of polymers.
Umapathi, R. et al. 2016. The inﬂuence of various alkylammonium-based ionic liquids on the hydration state of temperature-responsive polymer. 225: 186-194.