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Research Publications (Applied Sciences)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/213

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Subject: search.filters.subject.Ionic liquids

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    The influence of various alkylammonium-based ionic liquids on the hydration state of temperature-responsive polymer
    (Elsevier, 2016-11-19) Umapathi, Reddicherla; Mhkize, Thandeka Yvonne; Venkatesu, Pannuru; Deenadayalu, Nirmala
    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.
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    Excess molar volumes of binary mixtures (an ionic liquid + water) : A review
    (Elsevier, 2015-03) Bahadur, Indra; Singh, Sangeeta; Redhi, Gan G.; Venkatesu, Pannuru; Letcher, Trevor M.
    This review covers recent developments in the area of excess molar volumes for mixtures of {ILs (1) + H2O (2)} where ILs refers to ionic liquids involving cations: imidazolium, pyridinium, pyrrolidinium, piperidinium, morpholinium and ammonium groups; and anions: tetraborate, triflate, hydrogensulphate, methylsulphate, ethylsulphate, thiocyanate, dicyanamide, octanate, acetate, nitrate, chloride, bromide, and iodine. The excess molar volumes of aqueous ILs were found to cover a wide range of values for the different ILs (ranging from −1.7 cm3 · mol−1 to 1.2 cm3 · mol−1). The excess molar volumes increased with increasing temperature for all systems studied in this review. The magnitude and in some cases the sign of the excess molar volumes for all the aqueous ILs mixtures, apart from the ammonium ILs, were very dependent on temperature. This was particularly important in the dilute IL concentration region. It was found that the sign and magnitude of the excess molar volumes of aqueous ILs (for ILs with hydrophobic cations), was more dependent on the nature of the anion than on the cation.
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    Densities, speeds of sound, and refractive indices for binary mixtures of 1-butyl-3-methylimidazolium methyl sulphate ionic liquid with alcohols at T = (298.15, 303.15, 308.15, and 313.15) K
    (Elsevier, 2012-09-24) Singh, Sangeeta; Aznar, Martin; Deenadayalu, Nirmala
    Experimental densities, speeds of sound, and refractive indices of the binary mixtures {1-butyl-3-methylimidazolium methylsulphate ([BMIM]+[MeSO4]−) + methanol, or 1-propanol, or 2-propanol, or 1-butanol} were measured over the whole range of composition at T = (298.15, 303.15, 308.15, and 313.15) K. From the experimental data, excess molar volumes, excess isentropic compressibilities, deviation in refractive indices and molar refractions were calculated. The excess molar volumes, change in isentropic compressibilities, and deviation in refractive indices were fitted by the Redlich–Kister smoothing polynomial. The Lorentz–Lorenz equation was applied to correlate the volumetric properties and predict the density or the refractive index of the binary mixtures. Results for these quantities have been discussed in terms of intermolecular interactions between the components of the mixtures. For all the systems studied, the excess molar volume and excess isentropic compressibility are negative, while the change in refractive index on mixing is always positive over the entire composition range and at all temperatures.