Publications

Abstract The specific heat capacity of the poly(ethylene glycol)-water system has been determined using a drop calorimeter over the full range of composition at 25 °C. The system heat capacity responds linearly to change in composition in the dilute solution regime up to 30% (w/w) and is an irregular function at lower water content. The breakpoint in solubility corresponds to a minimal content of 2.5 water molecules per ethylene oxide to complete hydration. We have difficulty in explaining the large excess heat capacity by the presence of a stoichiometrically defined hydrogen-bonded complex between each ethylene oxide group and water molecules. It seems possible that the water of hydration also interacts with bulk water and/or the rest of the polymer chain. © 1990.

Abstract The binding of a series of alkanediols, HO(CH2)NOH, n = 3 to 10, to α-cyclodextrin was studied by microcalorimetric titration at 288.15 K, 298.15 K, and 308.15 K. For n = 3 to 7, the results agreed well with a 1-1 binding model but for n = 8 to 10, a more complex stepwise-association model had to be assumed: the formation of both 1-1 and 1-2 (1 diol + 2 α-CD) complexes. Apparent values for the binding constants, and changes in the standard molar Gibbs energies, enthalpies, entropies, and heat capacities, were derived for the binding process. At all temperatures, enthalpy and entropy values show an initial zig-zag pattern as a function of the number of CH2 groups whereas the CH2 increment in the standard molar Gibbs energy change is regular up to C8. The heat-capacity increments are regular up to C6, after which they level off. The results are interpreted in terms of the expected "driving forces" leading to the binding and the observed pattern in the thermodynamic properties. © 1990.

Abstract The minimum in the differential capacity of (111), (100), (110), (210) and (311) single-crystal gold faces in contact with dilute solutions of HClO4 as a function of the temperature was used to estimate the temperature coefficient of the potential of zero charge of these interfaces. The results are discussed in terms of the interaction of water with the metallic surfaces and the role played by the surface atomic arrangement. The strength of Au (hkl)-water interactions are proposed to be in the order Au (111) > Au (311) > Au (100) > Au (110) > Au (210) ≈ Hg. © 1990.

Abstract The origin of experimental high frequency artifacts in the measurement of the ac impedance of the interface between immiscible electrolytes is discussed. Different cell designs have been tried and it is concluded that the main origin of the observed high frequency dispersion is the high value of the resistance of the Luggin capillary in the organic phase. The use of a Ag/AgTPB reference electrode appears to obviate these problems. © 1990.

Abstract The effect of temperature on the differential capacity versus potential curve and the potential of zero charge was measured for a gold (100) face electrode in contact with solutions of HClO4. A small shift of the potential of the capacity minimum with concentration was observed, pointing to slight adsorption of perchlorate ions at zero charge. The sign of the temperature coefficient of the potential of zero charge and the variation of the entropy of formation of the interface with charge density are interpreted in terms of the interactions of the gold surface with the solvent. The sign of the temperature coefficient of the inner layer capacity at zero charge was found to be positive. © 1990.

Abstract The standard (po = 0.1 MPa) molar enthalpies of combustion, in oxygen, at 298.15 K, were measured by static bomb calorimetry for three 8-hydroxyquinolines; the vapour pressures of the crystals were measured as functions of temperature by the Knudsen-effusion technique, and the standard molar enthalpies of sublimation, at 298.15 K, were derived by the Clausius-Clapeyron equation. Direct measurements of the standard molar enthalpies of sublimation using micro-calorimetry confirmed the values from the Knudsen technique. {A table is presented}. © 1989.

Abstract The standard (po = 0.1 MPa) molar enthalpies of combustion in oxygen at 298.15 K were measured by static-bomb calorimetry for some quinones and dihydroxyquinones. The standard molar enthalpies of sublimation at 298.15 K were measured by microcalorimetry for 1,4-naphthoquinone and 9,10-phenanthraquinone; values were selected from the literature for the remaining compounds in order to derive the standard molar enthalpies of formation in the gaseous state. {A table is presented}. The energies of the intramolecular hydrogen bonds in the dihydroxyquinones were assessed as (25 ± 3) kJ·mol-1. 1,4,9,10-Anthradiquinone is apparently considerably strained, and although its reaction with water produces 1,4-dihydroxy-9,10-anthraquinone, a concomitant formation of hydrogen peroxide is shown to be thermodynamically improbable. © 1989.

Abstract The standard (po = 0.1 MPa) molar enthalpies of combustion in oxygen at 298.15 K of crystalline thiobenzamide, N, N-dimethylthiobenzamide, and N, N-diethylthiobenzamide to produce CO2(g), N2(g), and H2SO4·115H2O(l) were measured by rotating-bomb calorimetry. The standard molar enthalpies of sublimation at 298.15 K were measured by microcalorimetry. {A table is presented}. These results form the basis of a bond-energy scheme to estimate ΔfHmo(C6H5CSNr2, g). © 1989.