Publications

Abstract Novel phase diagrams of systems of water and two cosolutes of colloidal size, either macromolecules or surfactant micelles, are presented. For a mixture of two oppositely charged surfactants, a complex phase diagram is obtained with several liquid crystalline phases and equilibrium vesicles. There is a strong tendency for two surfactants to mix and form a range of structures governed by geometrical packing and electrostatic interactions. In recent years, surfactant self-assembly in the presence of different polymers has attracted a great interest, both from fundamental and applied aspects. Attractive or repulsive interactions are observed depending on the system. For the former case, dilute solutions may be analysed in terms of a binding of the surfactant to the polymer or a depression of the critical micelle concentration of the surfactant by the polymer. An important feature of these solutions is thus that the surfactant molecules, also when interacting intimately with a polymer, give micellar-type structures. The phase behavior of polymer-surfactant systems has only recently attracted greater attention but has been shown most significant for the understanding of the interactions involved. Different types of phase separation phenomena are encountered including segregative and associative types. For systems of a polyelectrolyte and an oppositely charged surfactant, an associative interaction is observed leading to phase separation into one solution concentrated in both polymer and surfactant and one very dilute solution. In the presence of an electrolyte, phase separation may be eliminated and, at higher concentrations, a polymer incompatibility type of phase separation may result. It is found fruitful to analyse the phase diagrams of polymer-surfactant systems with those of polymer-polymer and surfactant-surfactant mixtures as a basis. Analogies and differences are discussed and it is found that polymer-surfactant systems show basic similarities to polymer-polymer systems, while surfactant mixtures are different, which is due to the exchange of surfactant molecules between micelles and the formation of mixed micelles and other aggregates. Surfactant mixtures are, therefore, not displaying a segregative type of phase separation.

Abstract The enthalpy of sublimation of diphenylacetylene at 298.15 K, DELTA(cr)g H(m)THETA (C2(C6H5)2] = 95.1 +/- 1.1 kJ mol-1, was derived from vapour pressure-temperature data, obtained with two different Knudsen effusion apparatus, and from heat capacity measurements obtained by differential scanning calorimetry. The molybdenum-diphenylacetylene bond dissociation enthalpy in Mo(eta5-C5H5)2[C2(C6H5)2] was reevaluated as 115 +/- 26 kJ mol-1, on the basis of the new value for DELTA(cr)g H(m)THETA C2(C6H5)2].

Abstract The standard (po = 0.1 MPa) molar enthalpy of formation, at the temperature 298.15 K, of crystalline bis(2,2,6,6-tetramethylheptane-3,5-dionato) dioxouranium(VI) {uranyl(VI) dipivaloylmethanate, UO2(DPM)2}, was determined by solution-reaction calorimetry as -(2169.9±7.6) kJ·mol-1. The vapour pressure of the crystal, as function of the temperature, was measured using the Knudsen mass-loss effusion technique and the standard molar enthalpy of sublimation, at the temperature 298.15 K, was derived as (156.9±1.9) kJ·mol-1. From these results, the standard molar enthalpy of formation of the complex, in the gaseous state, was derived and the mean uranium(VI)-oxygen bond-dissociation enthalpy for the binding of the ligand to the metal, 〈D〉(U-O), was calculated as (223±10) kJ·mol-1.

Abstract The standard (po = 0.1 MPa) molar enthalpies of combustion at the temperature T = 298.15 K were measured by static-bomb calorimetry for crystalline 2,2′,4,4′,6,6′-hexamethylazobenzene-N,N-dioxide (HHMABOO), 2,2′,6,6′-tetramethylazobenzene-N,N-dioxide (TMABOO), 2,4,6-trimethylnitrobenzene (NITME), and liquid 2,6-dimethylnitrobenzene (NITXY). The enthalpies of sublimation at the temperature 298.15 K of HMABOO and TMABOO were assessed from vapour-pressure measurements; the enthalpy of sublimation of NITME and the enthalpy of vaporization of NITXY were measured by microcalorimetry. The standard molar enthalpies of decomposition of the crystalline N,N -dioxides to the corresponding gaseous monomeric nitroso-compounds at T = 298.15 K were measured by microcalorimetry: for HMABOO, (181.1±2.5) kJ·mol-1, and for TMABOO, (179.2±2.2) kJ·mol-1. For HMABOO and TMABOO, D (N=N)/(kJ·mol-1) was derived as (74.1±12.2) and (72.2±12.2), and 〈D(N-O>〉/(kJ·mol-1) as (285.7±6.8) and (287.8±6.6), respectively. D (N-O)/(kJ·mol-1) in NITME and in NITXY was derived as (383.4±2.9) and (380.4±2.3), respectively.

Abstract The standard (po = 0.1 MPa) molar enthalpies of combustion at the temperature 298.15 K were measured by static-bomb calorimetry for p -azoxyanisole and p-azoxyphenetole, and the standard molar enthalpies of sublimation of the temperature 298.15 K were measured by microcalorimetry. [[formula]] From the standard the molar enthalpies of formation of the gaseous compounds, the molar dissociation enthalpies of the N-O bonds were derived: D (N-O)/(kJ·mol-1): p-azoxyanisole, 317.2±5.7; p-azoxyphenetole, 320.4±4.9. Microcalorimetric measurements were made to derive the molar enthalpies of the transitions: crystal-to-liquid: for p-azoxyanisole, (29.3±0.8) kJ·mol-1, (1.0±0.5) kJ·mol-1; and for p-azoxyphenetole, (27.0±0.8) kJ·mol-1, (1.7±0.6) kJ·mol-1, respectively.

Abstract The variations observed in synchronous fluorescence spectra of fulvic acids have been characterised by principal component analysis and evolving factor analysis. Fulvic acids from coastal marine waters (mfua) were examined as a function of pH (between 2 and 7) and Cu(II) concentration. Fulvic acids from soil (sfua) were examined as a function of pH (between 2 and 7) and Cu(II), Co(II) and Ni(II) concentration. Fluorescence properties of sfua are characterised by a constant plus three varying components (defined by three individual spectra), corresponding to three acid-base equilibria with pK(a) values of 3.0, 4.6 and 6.4. For mfua, a constant plus two varying components (defined by three individual spectra) were detected, corresponding to two acid-base equilibria with pK(a) values of 3.1 and 5.3. The influence of the ions on the acid-base equilibrium diagrams is also quantified.

Abstract The standard (p-degrees = 0.1 M Pa) molar enthalpies of formation at 298.15 K in the gaseous state of some beta-ketoimines, RCOCH=C(CH3)NHR1, were determined from their enthalpies of combustion and of sublimation, DELTA(f)H(m)degrees(g)/kJ mol-1: R=CH3, {R1 = C6H5, -66.0 +/- 4.2; R1 = p-C6H4NO2, -98.9 +/- 5.0}: R = C6H5, {R1 = H, -48.7 +/- 3.5; R1 = CH3, -53.7 +/- 4.7; R1 = C6H5, 69.1 +/- 4.2). From these results it is shown that the increase in delocalization energy from R = CH3 to R = C6H5 matches the corresponding increase between acetylacetone and benzoylacetone. Crystal structures are reported for R = CH3, R1 = p-C6H4NO2, and R = C6H5 {R1 = H, R1 = CH3}, and show that those beta-ketoimines with R = C6H5 have a more delocalized structure in the -COCH=C(CH3)NH-moiety than those with R = CH3 in accord with the thermochemical results.