Publications

Abstract While cationic/anionic surfactant mixtures have been reported to form strongly non-ideal mixed aggregates in aqueous solution the micellization of true catanionic surfactants i e the salt free ion paired compounds obtained from the mixtures has been much less investigated However if there is a significant solubility mismatch between the paired chains these surfactants may show less conventional aggregation features in water such as a temperature driven vesicle-micelle transition and the coexistence of two lamellar phases in equilibrium In this work we carry out micellization studies for a catanionic surfactant of the type C(16)(+)C(8)(-) cetyltrimethylammonium octylsulfonate (TASo) by surface tension and conductivity measurements For comparison purposes the catanionic mixture cetyltrimethylammonium bromide (CTAB)/sodium octylsulfonate (SOSo) at different mixing ratios and the neat SOSo have also been studied For the non ideal CTAB/SOSo mixture Rubingh s model has been applied to determine the beta interaction parameter and the mixed micelle composition The cmc of TASo has been investigated as a function of temperature salt and excess ionic surfactant displaying some differences with respect to conventional ionic and nonionic surfactants The trends in the thermodynamic parameters of micellization of the three types of systems are comparatively rationalized

Abstract The thermal behavior for three homologous series of cationic geminis surfactants of the type n-2-n, alkanediyl-alpha,omega-bis(alkyldimethylammonium bromide), with n = 12, 14, 16, and 18, and sodium alkyl sulfates, SC (m) S, with m = 12, 14, and 16, is reported here. The cationic/anionic molar ratio is kept at 1:2 (equicharged mixtures), and salt is also present. Polarizing light microscopy and differential scanning calorimetry show a stepwise fusion for the mixtures with appearance of several mesophases between the crystalline structures and the isotropic liquid. A main endothermic transition is observed, associated with partial chain melting and consequent loss of crystalline order, followed by a transition to a smectic liquid crystal. The phase transition thermodynamics is interpreted in terms of an interplay between van der Waals chain-chain interactions and ionic head group interactions.

Abstract Salt-free ion-paired catanionic amphiphiles of the C(m)(+) C(n)(-) type, with a high solubility mismatch (n >> m or m >> n) display a remarkable phase behavior in water. A temperature-driven vesicle-to-micelle transition in the dilute side together with a coexistence of two lamellar phases oil the concentrated side is one of the peculiar effects that have been reported for the hexadecyltrimethylammonium octylsulfonate surfactant, C(16)C(8) or TA(16)So(8) (extensive to C(14)C(8) and C(12)C(8)). In this work, with TA(16)So(8) as a reference, the cationic trimethylammonium (TA(+)) and pyridinium (P(+)) headgroups are combined with the anionic sulfate (S(-)) and sulfonate (So(-)) headgroups to yield other C(16)C(8) compounds: hexadecyltrimethylammonium octylsulfate (TA(16)S(8)) 1-hexadecylpyridinium octylsulfonate (P(16)So(8)), and 1-hexadecylpyridinium octylsulfate (P(16)So(8)). We show that, if the asymmetry of the chain lengths is kept constant at C(16)C(8) and the headgroup chemistry is changed, most of the unusual self-assembly properties are still observed, indicating that they are not system-specific but extensive to other combinations of headgroups and mainly dictated by the ion-pair solubility mismatch. Thus, all the compounds in water quite remarkably show a lamellar-lamellar phase coexistence and spontaneously form vesicles upon solubilization. Moreover, P(16)So(8) undergoes at temperature-driven vesicle-to-micelle transition that involves an intermediate planar lamellar state, similar to TA(16)So(8). Some interesting effects on the global phase behavior, however, do arise when the headgroups are changed, Geometric packing effects are shown to be important, but the differences in phase behavior seem to be mainly dictated by (i) the charge density of the headgroups, which tunes the solubility mismatch of the ion-pair, and (ii) specific interactions between headgroups, which affect the short-range repulsive force that controls the swelling of the concentrated lamellar phase,

Abstract The synthesis and functionalization of carbon nanoparticles with PEG(200) and mercaptosuccinic acid, rendering fluorescent carbon dots, is described. Fluorescent carbon dots (maximum excitation and emission at 320 and 430 nm, respectively) with average dimension 267 nm were obtained. The lifetime decay of the functionalized carbon dots is complex and a three component decay time model originated a good fit with the following lifetimes: tau (1) = 2.71 ns; tau (2) = 7.36 ns; tau (3) = 0.38 ns. The fluorescence intensity of the carbon dots is affected by the solvent, pH (apparent pK (a) of 7.4 +/- 0.2) and iodide (Stern-Volmer constant of 78 +/- 2 M-1).

Abstract The great importance of distinguishing and identifying olive cultivars has been recognized since Roman times. Several classification schemes have been tried based on botanic, ecological, morphological, commercial, and agronomical characteristics. Presently there are a great number of different olive cultivars showing a diversity of morphological and physiological characteristics that result in quite different qualities and uses. However, the olive quality cannot be directly measured, and several indirect measurements, for example fruit and endocarp features, must be correlated with the olive quality and cultivar. This chapter shows that from morphological features of olives (fruit and endocarp) and olive trees (including trees, branches, leaves and flowers) coupled with chemometric multivariate classification techniques, classes of olives from different cultivars are naturally observed. Mixing morphological features from olive fruit and endocarp, classification rules with potential to be applied in the quality control of olives and, consequently, in the Denomination of Protected Origin (DOP) assessment can be developed. Also, it is observed that olive trees can be characterized using classification rules based on leaf and flower features. © 2010 Copyright

Abstract In this work, mutual solubilities of two [PF6]-based ionic liquids (ILs) with water and their thermophysical properties, namely, melting properties of pure ILs and densities and viscosities of both pure and water-saturated ILs, were determined. The selected Its comprise 1-methyl-3-propylimidazolium and 1-methyl-3-propylpyridinium cations combined with the anion hexafluorophosphate. Mutual solubilities with water were measured in the temperature range from (288.15 to 318.15) K. From the experimental solubility data dependence on temperature, the molar thermodynamic functions of solution, such as Gibbs energy, enthalpy, and entropy of the ILs in water were further derived. In addition, a simulation study based on the COSMO-RS methodology was carried out. For both pure ILs and water-equilibrated samples, densities and viscosities were determined in the temperature interval between (303.15 and 373.15) K. The isobaric thermal expansion coefficients for pure and water-saturated ILs were calculated based on the density dependence on temperature.

Abstract A Knudsen mass-loss effusion technique was used for measuring the vapor pressures at different temperatures of the following crystalline compounds: anthraquinone (CAS No. 84-65-1), between (377.06 and 395.03) K; anthrone (CAS No. 90-44-8), between (346.15 and 365.14) K; thianthrene (CAS No. 92-85-3), between (344.27 and 264.06) K; thioxanthone (CAS No. 492-22-8), between (369.12 and 387.20) K; and xanthone (CAS No. 90-47-1), between (342.22 and 362.22) K. From the temperature dependence of the vapor pressure of each crystalline compound, the standard (p degrees = 10(5) Pa) molar enthalpies and Gibbs energies of sublimation, at T = 298.15 K, were derived. The measured thermodynamic properties are compared with literature results for similar compounds, and correlations for estimation of the vapor pressures and enthalpy of sublimation for anthracene-like compounds are presented.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the crystalline state, of 1,5-diaminonaphthalene and 1,8-diaminonaphthalene were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static-bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the dependence of the vapour pressure of the solid isomers of diaminonaphthalene with the temperature, from which the standard molar enthalpies of sublimation were derived using the Clausius-Clapeyron equation. [GRAPHICS] Combining these two experimental values, the gas-phase standard molar enthalpies of formation, at T = 298.15 K, were derived and compared with those estimated using two different empirical methods of Delta fH degrees(m)(g) estimation: the Cox scheme and the Benson's Group Method. Moreover, the standard (p degrees = 0.1 MPa) molar entropies and Gibbs energies of sublimation, at T = 298.15 K, were derived for the two diaminonaphthalene isomers.

Abstract Despite the recent increase in the number of works addressing the effect of water on the thermophysical properties of ionic liquids (ILs), in particular densities and viscosities, the strong effect of the water content in the region of low water content on these properties requires further study for a deeper understanding of the phenomenon. Densities and viscosities of two imidazolium-based ionic liquids, 1-butyl-3-methylimidazolium dicyanamide [C(4)mim][N(CN)(2)] and 1-butyl-3-methylimidazolium tricyanomethane [C(4)mim][C(CN)(3)], and their binaries with water, for mole fractions up to 0.6, at atmospheric pressure and temperatures from (278.15 to 363.15) K were determined. The densities and viscosities of the pure ionic liquids and their binaries with water were described successfully by using several correlations. An extension to the Ye and Shreeve group contribution method shows a good agreement with the density data. An Orrick-Erbar-type approach and the Vogel-Tammann-Fulcher method were also applied to the experimental viscosity data, presenting a good agreement and allowing the estimation of new group contribution parameters, extending the applicability of these methods to new ILs. For mixtures, the one-constant Grunberg and Nissan equation was investigated for the correlation of the experimental viscosity binary mixture data of ILs + H(2)O, providing a good description of the experimental data using a single parameter for each ionic liquid studied.

Abstract The Knudsen mass-loss effusion technique was used for measuring the vapor pressures at different temperatures of the following 4-n-alkyloxybenzoic acids: 4-methoxybenzoic acid, between (340 and 362) K; 4-ethoxybenzoic acid, between (349 and 373) K; 4-propoxybenzoic acid, between (345 and 365) K; 4-butoxybenzoic acid, between (351 and 373) K; 4-pentyloxybenzoic acid, between (355 and 377) K; 4-hexyloxybenzoic acid, between (363 and 379) K; 4-heptyloxybenzoic acid, between (355 and 361) K; and 4-octyloxybenzoic acid, between (363 and 372) K. From the temperature dependence of the vapor pressure of each crystalline compound, the standard (p(0) = 10(5) Pa) molar enthalpies and Gibbs energies of sublimation, at T = 298.15 K, were derived. Differential scanning calorimetry was used in the study of phase transitions between condensed phases. The measured thermodynamic properties are compared with the results obtained on a previous similar study concerning the 4-n-alkylbenzoic acids series.