Publications

Abstract This work explores the n vs. iso isomerization effects on the physicochemical properties of different families of ionic liquids (ILs) with variable aromaticity and ring size. This study comprises the experimental measurements, in a wide temperature range, of the ILs' thermal behaviour, heat capacities, densities, refractive indices, surface tensions, and viscosities. The results here reported show that the presence of the iso-alkyl group leads to an increase of the temperature of the glass transition, T-g. The isopyrrolidinium (5 atoms ring cation core) and iso-piperidinium (6 atoms ring cation core) ILs present a strong differentiation in the enthalpy and entropy of melting. Non-aromatic ILs have higher molar heat capacities due to the increase of the atomic contribution, whereas it was not found any significant differentiation between then and iso-alkyl isomers. A small increase of the surface tension was observed for the non-aromatic Its, which could be related to their higher cohesive energy of the bulk, while the lower surface entropy observed for the iso isomers indicates a structural resemblance between the IL bulk and surface. The significant differentiation between ILs with a 5 and 6 atoms ring cation in the n-alkyl series (where 5 atoms ring cations have higher surface entropy) is an indication of a more efficient arrangement of the non-polar region at the surface in ILs with smaller cation cores. The ILs constituted by non aromatic piperidinium cation, and iso-alkyl isomers were found to be the most viscous among the studied Its due to their higher energy barriers for shear stress. (C) 2016 Published by Elsevier B.V.

Abstract The thermodynamics of molecular self-assembling of an anionic biosurfactant, sodium cholate (NaCA) and its mixtures with sodium dodecyl sulfate (SDS) in aqueous solution have been investigated by isothermal titration calorimetry (ITC), along with fluorescence and conductivity measurements. Different critical concentrations were obtained by these three techniques - critical pre-micelle concentration (cmc(pre)) and critical micelle concentration (cmc) for pure NaCA, and critical micelle concentrations (cmc(mix)) for the mixed systems with differently initial SDS concentrations. Importantly, ITC allowed us to directly measure the enthalpy changes of pre-micelle formation (DHpremic = (-0.28 +/- 0.02) kJ.mol(-1)) and of micelle formation (Delta H-mic = (-1.76 +/- 0.05) kJ.mol(-1)) for pure NaCA as well as the enthalpies for micellization for the mixed systems NaCA/SDS. The non-ideality of the mixed surfactant solution was evaluated in terms of interaction parameters and excess enthalpies that were calculated in the light of Clint's and Rubingh's models. It was found that there is an obvious synergistic effect in the NaCA/SDS mixed system. From all these results we can ascribe the strong interaction between the same charge surfactants NaCA and SDS to the structural difference in their hydrophobic moieties. In fact, the flexible alkyl chains of SDS and the non-planar hydrophobic beta-faces of NaCA tend to have a more compact packing than pure NaCA.

Abstract UV-Vis can be used as an easy and forthright technique to accurately estimate the band gap energy of organic pi-conjugated materials, widely used as thin films/composites in organic and hybrid electronic devices such as OLEDs, OPVs and OFETs. The electronic and optical properties, including HOMO-LUMO energy gaps of pi-conjugated systems were evaluated by UV-Vis spectroscopy in CHCl3 solution for a large number of relevant pi-conjugated systems: tris-8-hydroxyquinolinatos (Alq(3), Gaq(3), Inq(3), Al(qNO(2))(3), Al(qCl)(3), Al(qBr)(3), In(qNO(2))(3), In(qCl)(3) and In(qBr)(3)); triphenylamine derivatives (DDP, p-TTP, TPB, TPD, TDAB, m-MTDAB, NPB, alpha-NPD); oligoacenes (naphthalene, anthracene, tetracene and rubrene); oligothiophenes (alpha-2T, beta-2T, alpha-3T, beta-3T, alpha-4T and alpha-5T). Additionally, some electronic properties were also explored by quantum chemical calculations. The experimental UV-Vis data are in accordance with the DFT predictions and indicate that the band gap energies of the OSCs dissolved in CHCl3 solution are consistent with the values presented for thin films.

Abstract A comprehensive study of the solution and solvation of linear alcohols (propan-1-ol, butan-1-ol and pentan-1-ol) in ionic liquids (ILs) is presented. The effect of the alkyl chain size of both alcohols and ILs (1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(n)C(1)im][NTf2], ionic liquid series) on the thermodynamic properties of solution and solvation was used to obtain insight into the interactions between alcohols and ILs. Alcohols were used as molecular probes to ascertain whether their solvation in ILs would reflect IL nanostructuration. A trend shift was found in the values of enthalpy of solution and solvation for the [C(n)C(1)im][NTf2] series at a critical alkyl size (CAS) of C-6. Further, the effect of the hydrogen bond basicity of the anion in the solvation of alcohols was explored based on the comparative study of the solvation of propan-1-ol in two different IL series, 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C(n)C(1)im][NTf2] and hexafluorophosphate [C(n)C(1)im][PF6]. The results obtained provide experimental support for the strength of hydrogen bonds between the alcohols and the NTf2 and PF6 anions, providing insights into the IL intermolecular interactions, namely by indicating the ability of the alcohols to discriminate the IL anion hydrogen bond basicity.

Abstract Graphene nanoplatelets (GNPs) are 'tagged' with 1-(biphen-4-yl)ferrocene. Chronoamperometry is then utilised to observe single particle impacts when GNPs suspended in solution collide with a carbon fibre micro wire electrode held at an oxidising potential, resulting in current/time transient "spikes". The impacts are associated with two types of charge transfer: Faradaic due to oxidation of the 'tag' and capacitative due to disruption of the double layer. Analysis of the spikes suggests approximate monolayer coverage of 1-(biphen-4-yl)ferrocene on the GNP surfaces, with a surface coverage of (2.2 +/- 0.3) x 10(-10) mol cm(-2). In contrast non-derivatised ferrocene does not exhibit any significant adsorption on the GNP material.

Abstract The morphology of micro-and nanodroplets and thin films of ionic liquids (ILs) prepared through physical vapor deposition is presented. The morphology of droplets deposited on indium-tin-oxide-coated glass is presented for the extended 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(n)C(1)im][Ntf(2)]; n = 1-8) series, and the results show the nanostructuration of ILs. The use of in-vacuum energetic particles enhances/increases the nanodroplets mobility/coalescence mechanisms and can be a pathway to the fabrication of thin IL films.

Abstract Tris(8-hydroxyquinolinate) metallic complexes, Mq(3), are one of the most important classes of organic semiconductor materials. Herein, the nature of the chemical bond in Mq(3) complexes and its implications on their molecular properties were investigated by a combined experimental and computational approach. Various Mq(3) complexes, resulting from the alteration of the metal and substitution of the 8-hydroxyquinoline ligand in different positions, were prepared. The mer-/fac-isomerism in Mq(3) was explored by FTIR and NMR spectroscopy, evidencing that, irrespective of the substituent, mer- and fac-are the most stable molecular configurations of Al(III) and In(III) complexes, respectively. The relative M-ligand bond dissociation energies were evaluated experimentally by electrospray ionization tandem mass spectrometry (ESI-MS-MS), showing a non-monotonous variation along the group (Al > In > Ga). The results reveal a strong covalent character in M-ligand bonding, which allows for through-ligand electron delocalization, and explain the preferred molecular structures of Mq3 complexes as resulting from the interplay between bonding and steric factors. The mer-isomer reduces intraligand repulsions, being preferred for smaller metals, while the fac-isomer is favoured for larger metals where stronger covalent M-ligand bonds can be formed due to more extensive through-ligand conjugation mediated by metal "d" orbitals.

Abstract Herein, solubility experimental data for six monosaccharides, viz. D-(+)-glucose, D-(+)-mannose, D-(-)-fructose, D-(+)-galactose, D-(+)-xylose and L-(+)-arabinose, in four ionic liquids (ILs), at temperatures ranging from 288.2 to 348.2 K, were obtained aimed at gathering a better understanding of their solvation ability and molecular-level mechanisms which rule the dissolution process. To ascertain the chemical features that enhance the solubility of monosaccharides, ILs composed of dialkylimidazolium or tetra-alkylphosphonium cations combined with the dicyanamide, dimethylphosphate or chloride anions were investigated. It was found that the ranking of the solubility of monosaccharides depends on the IL; yet, D-(+)-xylose is always the most soluble while D-(-)-fructose is the least soluble monosaccharide. The results obtained show that both the IL cation and the anion play a major role in the solubility of monosaccharides. Finally, from the determination of the respective thermodynamic properties of solution, it was found that enthalpic contributions are dominant in the solubilization process. However, the observed differences in the solubilities of monosaccharides in 1-butyl-3-methylimidazolium dicyanamide are ruled by a change in the entropy of solution.

Abstract Structural and thermodynamic insights are reported for the series of fluorinated alcohols {oFTOH; CF3(CF2)(n)CH2OH, with n = 5-12}, with the objective of comparing the phase behaviour of perfluorinated compounds with the analogous linear alkanes and alcohols. As expected the higher vibrational contribution of the -CF2- groups contributes for the higher heat capacities of the perfluorinated compounds. Concerning the fusion/sublimation equilibria, fluorination of the alcohols decreases Delta H and Delta S of phase transitions. Compared to the regular -CH2- alkyl chain structure, the less symmetric -CF2- spiral conformation is characterized by a less efficient molecular alignment in crystal packing, thus explaining the lower Delta H. The lower internal rotational barrier associated with the -CH2- alkyl chains of n-alkanes/alcohols, when compared to -CF2- chains, contributes to the larger values of Delta S observed. Regarding the vaporization equilibria, fluorination leads to greater values of Delta S, which are explained by the larger translational entropy of the heavier perfluoroalcohols, an effect that is more important in the gas than in the liquid phase. (C) 2016 Elsevier Ltd.

Abstract This work shows how the nanostructuration of ionic liquids (ILs) governs the glass and melting transitions of the bistriflimide imidazolium-based [C(n)C(1)im][NTf2] and [C(n)C(n)im][NTf2] series, which highlights the trend shift that occurs at the critical alkyl size (CAS) of n=6. An initial increase in the glass temperature (T-g) with an increase in the alkyl side chain was observed due to the intensification of the dispersive interactions (van der Waals). Above the CAS, the -CH2- increment has the same effect in both glass and liquid states, which leads to a plateau in the glass transition after nanostructuration. The melting temperature (T-m) of the [C(n)C(1)im][NTf2] and [C(n)C(n)im][NTf2] series presents a V-shaped profile. For the short-alkyl ILs, the -CH2- increment affects the electrostatic ion pair interactions, which leads to an increase in the conformational entropy. The -CH2- increment disturbs the packing ability of the ILs and leads to a higher entropy value (Delta(s)dagger S-m degrees) and consequently a decrease in T-m. Above the CAS, the -CH2- contribution to the melting temperature becomes more regular, as a consequence of the nanostructuration of the IL into polar and nonpolar domains. The dependence of the alkyl chain on the temperature, enthalpy, and entropy of melting in the ILs above the CAS is very similar to the one observed for the alkane series, which highlights the importance of the nonpolar alkyl domains on the ILs thermal behavior.