Ionic liquid modulation of swelling and LCST behavior of N-isopropylacrylamide polymer gelsElectronic supplementary information (ESI) available: Analytical techniques, NMR purification data, density, viscosity, DSC data, SEM imaging, ionogel rheometry and vibrational spectroscopy results. See DOI: 10.1039/c3cp53397b

• Main Authors: Gallagher, Simon, Kavanagh, Andrew, Zío kowski, Bartosz, Florea, Larisa, MacFarlane, Douglas R, Fraser, Kevin, Diamond, Dermot
• Format: Journal Article
• Language: English
• Published: 29.01.2014
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c3cp53397b

The physicochemical properties of free-standing cross-linked poly( N -isopropylacrylamide) (pNIPAAM) gels, generated in the presence of the Ionic liquids (ILs), 1-ethyl-3-methylimidazolium [C 2 mIm] + salts of ethylsulfate [EtSO 4 ] − , dicyanamide [DCA] − , bis(trifluoromethylsulfonyl)imide [NTf 2 ] − , and trihexyltetradecylphosphonium dicyanamide ([P 6,6,6,14 ][DCA]) are described. The Lower Critical Solution Temperature (LCST) of the resulting ionogel was found to vary between 24-31 °C. The behaviour of swelling is found to be as high as 31.55% (±0.47, n = 3) from the initial dehydrated state, while 28.04% (±0.42, n = 3) shrinking from the hydrated swollen state is observed. For ionogels based on the [DCA] − anion an unexpected complete loss of the shrinking behaviour occurs, attributed to water interactions with the nitrile group of the [DCA] − anion. Scanning Electron Microscopy also reveals distinct morphological changes, for example [C 2 mIm][EtSO 4 ] displays a highly porous, nodule type morphology, efficiently pre-disposed for water uptake. The LCST behaviour of cross-linked ionogels based on [C 2 mIm] + and [P 6,6,6,14 ] + with [EtSO 4 ], [NTf 2 ] and [DCA] has been investigated. [C 2 mIm][DCA] ionogels display loss of LCST while SEM analysis shows that distinct morphological changes occur in the ionogels before and after hydration.