Showing papers in "The Journal of Physical Chemistry in 1974"

Dependence of the glass transition temperature on heating and cooling rate

Abstract: It is shown that under certain conditions the dependence of the glass transition temperature Tg on heating or cooling rate |q| is given to a high degree of approximation by d In \\q\\/ATg = Ah*/RTr2 or alternatively by d In | q | /d(l/Tg) = — Ah */R, where Tr is a temperature in the middle of the transition range and Ah * is the activation enthalpy for the relaxation times controlling the structural enthalpy or volume relaxation. The conditions necessary for the validity of these relations are that the structural relaxation be describable by a temperature-independent distribution of relaxation times and that the glass be cooled from a starting temperature well above the transition region and subsequently reheated at the same rate starting from a temperature well below the transition region. Experimental measurements of Tg vs. |q| are presented for As2Ses, B2O3, potassium silicate, and borosilicate crown glasses. Ah* is found to be equal within experimental error to the activation enthalpy for the shear viscosity.

Thermal electron transfer reactions in polar solvents

Abstract: (13) G. W. Robinson and V. E. Di Giorgio, Can. J. Chem., 36, 31 (1958); J. Chem. Phys., 31, 1678 (1959); V. A. Job, V. Sethuraman, and K. K. Innes, J. Mol. Spectrosc., 30, 365 (1969). (14) E. B. Fleischer, N. Sung, and S. Hawkinson, J. fhys. Chem., 72, 4311 (1968). (15) When consid(ering the two rings rotated by different angles around the minimum, the calculated energies are always higher than that corresponding to the costrained conformation at 22’. (16) F. A. L. Anet and M. Ahmad, J. Amer. Chem. Soc., 86, 119 (1964); H. G. Silver and J. L. Wood, Trans. faraday Soc., 60, 5 (1964); F. A. Miller, W. G. Fately, and R. E. Witkowski, Specfrochian. Acta, Part A, 23, 891 (1967). (17) This failure is probably due to the inadequacy of the 4-31G basis set near the nucleus. See, for example, H. Konishi and K. Morokuma. J. Amer. Chem. SOC., 94, 5604 (1972); and references therein. (18) K. Eiben and R. W. Fessenden, J. fhys. Chem., 75, 1186 (1971). (19) G. A. RussellandG. R . Underwood, J. fhys. Chem., 72, 1074 (1968). (20) A. Hudson and J. W. E. Lewis, Tetrahedron, 4413 (1970); L. Lunazzi, G. F. Pedulli, M. Tiecco, C. A. Veracini, and C. Vincenzi, J. Chem. SOC., ferkin Trans. 2, 751 (1972).

Kinetics of step-wise micelle association

Abstract: During the last few years, the kinetics of micelle association and dissociation in surfactant solutions have been studied experimentally with various techniques. The degree of association is typically of the order of 100, which requires either that drastically simplified assumptions be made in treating the kinetics, or, that a perspicuous method be found for its handling. First, the kinetic equation is put into a form which suggests an analogy with heat conduction (diffusion, etc.) and identifies the proper rate-limiting quantities. A treatment of the relaxation process at very small deviations from equilibrium is given and the results compared with existing experimental results. The treatment is then extended to larger deviations from equilibrium and a plausible explanation given of the apparent linearity still exhibited by the process. Finally, the process of rearrangement among the abundant micelles is treated by approximating the kinetic equations by a partial differential equation. (30 refs.)

Luminescence decay of hydrophobic molecules solubilized in aqueous micellar systems. Kinetic model

Abstract: A phenomenological model describing the kinetics of quenching reactions in micelles is presented. Its validity is tested by laser photolyste experiments with aqueous solutions containing micellized sodium lauryl suifate (NaLS) solubilized pyrene as a fluorescent probe and methylene iodide or nitromethane as quenchers. The constants of the distribution equilibrium of these quenchers between NaLS micelles and water were determined as K(CH/sub 3/NO/sub 2/) = 1.64x 10/sup 2/ M/sup -1/ and K(CH/sub 2/I/sub 2/) = 2.5 x 10/sup 3/ M/sup -1/ u sing the (296 deg K) using the pulse radiolysis method. From the kinetic evaluation we obtain for the specific rates of association and dissociation of methylene iodide and NaLS micelles n = 2.5 x 10/sup 10/ M/sup -1/ sec/sup -1/ and K' = 9.5 x 10/sup 6/ sec/sup -1/ (296 deg K) Triplet lifetime measuremente with solutions containing micellized cetyltrimethylammoninm bromide (CTAB), for the exit of anthracene from the CTAB micelle into the aqueous phase is as low as 2 x 10/sup 2/ sec/sup -1/ (296 deg K). (auth)

Wetting under chemical equilibrium and nonequilibrium conditions

Abstract: The thermodynamics of a solid-liquid-vapor system both under chemical equilibrium and nonequilibrium conditions, based on the model of Gibbs, is discussed. Under chemical equilibrium conditions, the degree of wetting or nonwetting of a flat and nondeformable solid by the liquid is defined by Young's equation in terms of the static interfacial tensions. Under chemical nonequilibrium conditions, mass transfer across an interface results in a transient decrease in the corresponding specific interfacial free energy and the interfacial tension by an amount equal to the free energy of the effective chemical reaction per area at that interface. When the reaction is between the solid and the liquid, this transient lowering of the interfacial tension can cause the liquid drop to spread on the solid substrate if the interfacial energy reduction is large enough and also if the diffusion rates of the reacting components in the solid phase are slow enough relative to the flow rate of the liquid to cause the liquid at the periphery of the drop to be in dynamic contact with unreacted solid.

Effect of pressure on the surface tension of water. Adsorption of low molecular weight gases on water at 25.deg.

Abstract: In recent years, there has been a resurgence in interest concerning bulk and surface properties of water. One area of research that has received comparatively little attention concerns the effect of pressure on the surface tension of water. This paper reports results obtained in measuring interfacial tension as a function of pressure for a number of gas-water systems at 25/sup 0/ using a capillary-rise method. The systems involving water with carbon dioxide and nitrous oxide were of particular interest, since it is known that on the one hand these gases are more soluble than expected in bulk water while on the other hand water is abnormally soluble in compressed CO2 and N2O, leading to the question of whether a corresponding anomaly is to be found with respect to adsorption at the interface of water with these 2 gases. (36 refs.)

Chemical reaction rates of quasi free electrons in nonpolar liquids

Abstract: A method is described for determining reaction rates of molecules dissolved in nonpolar liquids with electrons produced by ionization of the solvent. It is based on modification by the added substance of the current- growth curve which is seen when the liquid, in an electric field, is suddenly exposed to X-rays, and uhich is used for mobility determination by the Hudson method. The rate constants for recombination of electrons with positive ions, determined by the Langevin method in n-pentane, n-hexane, and tetramethylsilane, are diffusion controlled and hence proportional to the electron mobilities; this rate constant in tetramethylsilane is 5 x 10/sup 16/ M/sup -1/ sec/sup -1/. The electron reactions wit h CCl/sub 4/, CH/sub 3/I, and O/sub 2/ are not diffusion controlled; the rates are generally higher in solvents which show higher electron mobilities, but the increase is less than proportional. Different behavior is shown with C/sub 2/H/sub 5/Br; the electron reaction rate is lower in the highelectron-mobility solvents neopentane and tetramethylsilane than in hexane or 2,2,4-trimethylpentane, and its temperature coefficient, which is positive in hexane, becomes unexpectedly negative in the former solvents, and amounts to -- 1.7% per degree in neopentane. New electron mobility determinations are reported for methylcyclohexane,more » n-hexane, n-pentane, cyclohexane, neopentane, and tetramethylsilane.« less

Estimating microsecond rotational correlation times from lifetime broadening of nitroxide electron spin resonance spectra near the rigid limit

Abstract: (48) Although Hayaf and Silver (ref 12) calculate B = 17’, using their .Procedure and data we obtain B = 12” which corresponds to 4 = 36” and q N N N (36”) = 24.4 G . (49) (a)# L. J. Berliner, Acta Crystallogr., Sect. 6, 26, 1198 (1970); (b) A. Capiomon, ibid., 28, 2298 (1972); (c) P. J. Lajzerowicz-Benneteau, ibid., 24, ?96 (1968). (50) 8. Anderson and P. Anderson, Acta Chem. Scand.. 20, 2728 (1966). (51) R. Poupko, B. L. Silver, and M. Rubenstein, J . Amer. Chem. Soc., 92, 4512 (1970). (52) H. M. McConnell and J. Strathdee, Mol. Phys., 2, 129 (1959). (53) M. Barfield, J. Chem. Phys., 53, 3836 (1970)