Browsing by Author "Visak, Zoran P."
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- Electrolytic conductivity of four imidazolium-based ionic liquidsPublication . Calado, Marta; Diogo, João C. F.; Mata, José L. Correia da; Caetano, Fernando J. P.; Visak, Zoran P.; Fareleira, João M. N. A.In this article, electrolytic (ionic) conductivity measurements of four ionic liquids (ILs), namely, 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide ([C2mim][NTf2]), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([C2mim][OTf]), 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C6mim][NTf2]), and 1-ethyl-3-methylimidazolium ethyl sulfate ([C2mim][EtSO4]) (ECOENG212 ), were performed in a temperature range of (288.15 to 333.15) K. [C6mim][NTf2] was chosen to be a reference ionic liquid for several properties, including the electrolytic conductivity by the IUPAC Project 2002-005-1-100. For that reason, the measurements performed with that ionic liquid primarily serve the purpose to validate the instrumentation and the experimental procedure used in this work. The measurements were carried out using a complex impedance method, applying a novel electronic device designed and constructed for this purpose. The complete setup includes a Schott Instruments LF 913 T, used as a four-electrode conductivity cell, and a lock-in amplifier. The cell was calibrated using standard reference KCl aqueous solutions. The measurements of the impedance of the conductivity cell were carried out along a range of frequencies from (0.2 to 30) kHz, and the results were extrapolated to infinite frequency, in order to determine the electrolytic conductivity of the liquid samples. The results obtained for the ionic liquid [C6mim][NTf2] were compared to reference data, and it was estimated that the overall uncertainty of the present results is better than 2%. All the data obtained were compared with available literature data, and were analyzed and discussed in respect to the effect of temperature, cation alkyl chain length, and anion.
- Volumetric properties and spectroscopic studies of pyridine or nicotine solutions in liquid polyethylene glycolsPublication . Visak, Zoran P.; Ilharco, Laura; Garcia, Ana Rosa; Najdanovic-Visak, Vesna; Fareleira, João M. N. A.; Caetano, Fernando J. P.; Kijevcanin, Mirjana; Serbanovic, SlobodanDensities and molar excess volumes of the solutions of pyridine or nicotine in liquid polyethylene glycol, PEG200 and PEG400, have been determined at several temperatures. The experimental molar excess volumes are negative, thus indicating strong attractive interactions between the components, as could be expected considering their highly polar nature and good hydrogen bond abilities. For the pyridine systems, this negativity is slightly increased as the temperature rises, while the opposite tendency is observed for the nicotine mixtures. When pyridine and nicotine solutions are compared, the former—particularly those with PEG400—exhibit substantially more negative molar excess volumes than the latter. The effect of the polymer chain length on the results for the nicotine solutions is almost negligible. However, this is not the case when pyridine is one of the components: a longer chain induced considerably higher compression on mixing. The Fourier-transform infrared analysis allowed interpretation of the negative experimental molar excess volumes in terms of specific inter- and intramolecular interactions.