Publication costs assisted by Universitat Bayreuth New developments of the theory of micellar kinetics are reported together with new experimental results obtained in the course of chemical relaxations (T-jump, p-jump, and shock tube) studies of micellar solutions of ionic surfactants. These results as well as those obtained in previous studies are quantitatively interpreted in terms of this theory. Several pieces of information thus far not available on micellar solutions have been obtained: (1) the rate constants k+ and k~for the association/dissociation reactions of one amphiphilic ion to/from micelles. The association reaction is very close to being diffusion controlled. The variation of the dissociation rate constant with the alkyl chain length is in quantitative agreement with what is expected from theory; (2) the width of the distribution curve of stable micelles is found to increase with chain length but the micelle polydispersity is small and decreases for increasing chain length; (3) an approximate value of the average number of amphiphilic ions in the micellar species at the minimum of the distribution curve; (4) the enthalpy and entropy changes associated with the incorporation of one amphiphilic ion into the most stable micelle and into the aggregate at the minimum of the distribution curve. The enthalpy changes for these two processes are of opposite signs. This explains why the overall heat of micellization is very small.

No abstract

Time-resolved laser-induced fluorescence is a unique method for direct uranium speciation at low level in the framework of environmental studies. By varying pH and uranium concentration in the absence of carbonate ions and at fixed ionic strength, it was possible, together with free uranyl UO22+, to identify spectrally and temporally all the uranium-hydroxo complexes, namely, UO2OH+, UO2(OH)2, UO2(OH)3−, (UO2)2(OH)22+, (UO2)3(OH)5+, and (UO2)3(OH)7−.

No abstract

Publication costs assisted by Centre de Recherches sur les Macromolécules Ultrasonic absorption, pressure jump, temperature jump, and shock tube measurements have been performed to investigate the relaxation processes present in solutions of purified sodium lauryl sulfate and laurylpyridinium chloride, bromide, and iodide. The results show the presence of two relaxation processes characterized by the relaxation times and r2 with a ratio 2/ over a hundred. Both relaxation times depend on concentration (C) and ionic strength (µ). The slow process (t2) is more affected by µ than the fast one ( ). The various models presented to account for these two processes are discussed. It is shown that the available experimental data can be qualitatively explained by assigning to the exchange of detergent ions between the micellar phase and the bulk solvent and r2 to the micellization-dissolution equilibrium. The variation of with the chain length of the detergent ion can be quantitatively explained by assuming the exchange reaction to be diffusion controlled. The interpretation of the variation of 2 with C at various ionic strength leads to the conclusion that at concentration only slightly above the critical micelle concentration both the aggregation number and the rate constants for the exchange equilibrium depend on C.

No abstract

Using a precision densimeter, the densities of a series of carefully prepared and purified aqueous solutions of polyelectrolytes of accurately known concentrations have been determined. The following polyelectrolytes have been investigated: poly(methacrylic acid) (PMA) samples of various molecular weights, carboxymethylceliuloses of various substitution degrees (acid form and tetramethylammonium (TMA) salt), poly (acrylic acid) (PA A), poly(maleic acid-methyl vinyl ether), polyphosphate, poly (ethylenesulf onic acid), and poly-(styrenesulfonic acid). Measurements of densities have also been performed on the alkali metal and TMA salts of the last five polyelectrolytes. The densities have been, used for the calculation of the apparent molal volumes .In the concentration range investigated the plots 0 = f(concentration) have been found to be linear and the values of 0 have been extrapolated to zero concentration to give the °'8. For PAA and PMA, 0 °shows practically no dependence on the polymer molecular weight. The ®cp°'s have been found to be nonadditive, in contradistinction to what is observed with simple electrolytes. This result gives an additional experimental evidence to the so-called counterion "site binding." The volume changes associated with this process have been determined for various counterions and found to present large differences, according to the nature of both the polyion and the counterion. Finally for polycarboxylic acids simple assumptions have permitted the determination of the contribution of electrostriction to the apparent molal volume of the polyion at infinite dilution and of the fraction of bound counterions with total dehydration.

No abstract