Monolayer properties of fatty acids : III. Thermodynamics of mixing

The thermodynamic properties of mixed fatty acids have been studied in the region of the surface vapor pressure. Using myristic acid as a common component various saturated and unsaturated fatty acid mixtures have been compared with regard to their tendency to be miscible or immiscible. Deviations from expected ideal behavior have allowed estimation of activity coefficients. Measurement of surface heats of vaporization has led to the determination of solubility parameters for each fatty acid. Applying regular solution theory or using activity coefficients allows independent estimation of , the partial molar enthalpy of mixing, and the two approaches are in good agreement. Therefore, it is possible to predict mixing tendencies for any combination of fatty acids used in this study.     

Temperature dependence of the permittivity of water

In a previous work the temperature dependence of the permittivity of some pure normal alcohols was analyzed. The experimental values were fitted to a modification of Onsager’s equation. In this work, the static permittivity of water at different temperatures was measured and its values were fitted to the same equation used for alcohols. One parameter of the fittings agrees with the tendency observed for the alcohols and the other tends to the square of the refractive index. A good agreement was obtained between the experimental values and the fittings, this fact showing that water behaves, under this point of view, like an alcohol.     

Thermodynamic properties of alkali halides. V. Temperature and pressure dependence of excess free energies in water

A simple equation has been derived relating the temperature dependence of activity functions with excess enthalpies and excess heat capacities. Using experimentally determined parameters at 298.15°K, it is possible to predict osmotic coefficients and mean activity coefficients of alkali halides in water up to 1 m from 273°K to about 350°K. In general, the predicted functions agree with the measured values within the uncertainty of the activity data. An equation is also given for the pressure dependence of the excess free energies, but it was not possible to check the limitation of this equation due to lack of activity data at various pressures.To whom correspondence should be addressed.     

Temperature dependence of the crystal structures of nylon 11

Careful examination of x-ray diffraction patterns from melt-crystallized nylon 11 films show significant discrepancies with the proposed α-form structure. These discrepancies do not disappear after the samples have been annealed. The temperature dependence of the d spacings of the two strongest peaks show further evidence that the melt-crystallized and solution-cast films (α form) possess different crystal structures. These results suggest a different crystal structure for the melt-crystallized films; this would help explain the rather low piezoelectric response of these films and also the failure to observe a rapid decrease in polarization at the transition temperature.     

Temperature dependence of the general spectrum for water

Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 1, pp. 89–97, January–February, 1990.     

Temperature dependence of the fluorescence properties of curcumin

Steady-state and time-resolved techniques were employed to study the nonradiative process of curcumin dissolved in ethanol and 1-propanol in a wide range of temperatures. We found that the nonradiative rate constants at temperatures between 175-250 K qualitatively follow the same trend as the dielectric relaxation times of both neat solvents. We attribute the nonradiative process to solvent-controlled proton transfer. We also found a kinetic isotope effect on the nonradiative process rate constant of ~2. We propose a model in which the excited-state proton transfer breaks the planar hexagonal structure of the keto-enol center of the molecule. This, in turn, enhances the nonradiative process driven by the twist angle between the two phenol moieties.     

Monte Carlo calculation of the thermodynamic properties of water

The Monte Carlo method and parallel computing are used to calculate the thermodynamic properties of water (density, heat capacity, compressibility, thermal expansion coefficient, and static dielectric constant) in a wide range of temperatures (from 70 K to 530 K) at constant (atmospheric) pressure. Four groups of computational experiments are carried out, each for its own model of the water molecule: TIP3P (Jorgensen et al., 1983), SPC/E (Berendsen et al., 1987), TIP4P/2005 (Abascal&Vega, 2005), and TIP5P-E (Rick, 2004). An additional calculation based on the replica exchange method is conducted for the TIP4P/2005 model. A comparison of the calculated properties of water with experimental data suggests that the TIP4P/2005 model can provide highly realistic computer simulation results for water and aqueous solutions.