The kinetics of micelle formation for a range of ionic surfactants in aqueous solution have been investigated using the ultrasonic relaxation technique. In order to understand the concentration dependance of both the relaxation time and the relaxation strength, and other aspects of the relaxation data, it was necessary to modify our previous two state kinetic model describing micellisation. In this new theoretical treatment the interchange of the monomers to and from the micelles is assumed to be an adsorption mechanism governed by the fundamental kinetic principles introduced by Langmuir in his adsorption theory. Finally we have reconsidered the origin of the chemical relaxation observed in detergent solutions resulting from temperature-and pressure-jump experiments.Chemical relaxation techniques including u l t r a ~o n i c s , ~-~ temperature-jump ''-I3 and pressure-jump 14* l 5 as well as stopped flow methods 1 6 -1 8 have been used to investigate the kinetics of micelle formation in surfactants. From these experiments relaxation times ranging from to lO-'s have been reported. The interpretation of experimental relaxation data in terms of rate constants connected with micelle formation has been discussed by several authors.6* 7 * l o Recently we proposed a successful two state kinetic model which was primarily used with ultrasonic data ; this model was also found to be consistent with temperature-jump measurements. The conclusion from a recent report l9 based on n.m.r. data indicates that whereas the rates of micellization found from ultrasonic experiments are consistent with n.m.r. considerations the rates found from temperature-jump data are too low. In an attempt to gain more information about the rates and also more details about the mechanism of micelle formation we have carried out ultrasonic relaxation measurements on a variety of detergents of the anionic and cationic variety. These results are discussed in terms of a modified version of the two state model and an attempt is also made to clarify the discrepancies concerning relaxation times and hence rate constants in monomer-micelle equilibria. EXPERIMENTALThe ultrasonic absorption data for all the solutions studied were measured over the frequency range 1-100 MHz with a resonator 2 o (1-25 MHz) and pulse (15-100 MHz) apparatus 21 described previously. The relaxation data were displayed in terms of the frequency dependence of a'il where a' is the excess absorption of the solution over solvent at c
The partition coefficients of the alcohols butan-1-01 -+ hexan-1-01 between water and cetyltrimethylammonium bromide micelles have been obtained from solubility experiments. These results have been combined with previously obtained ultrasonic relaxation data to derive the kinetic and thermodynamic parameters associated with the exchange process involving alcohol molecules and cetyltrimethyl ammonium bromide micelles. Bearing in mind the simplicity of the approaches taken to interpret the equilibrium and kinetic measurements, there is remarkable self-consistency in the data.
and 'Hoechst-Perstorp AB, S-284 80 Perstorp, Sweden SYNOPSIS Film-forming polystyrene/poly(n-butyl acrylate-co-glycidyl methacrylate) [PS/P(BA-co-GMA)] core-shell latex particles were prepared via a two-stage emulsion polymerization procedure using a polystyrene latex seed. Delayed addition of GMA was used in order to locate functional epoxy groups close to the particle surfaces. It was found t h a t a temperature of 25°C a t the second-stage polymerization, in combination with a redox initiator system, was essential for the formation of' a uniform shell of BA-GMA copolymer around the PS core. T h e latex particle morphology was investigated by transmission electron microscopy (TEM). Reactive double bonds were introduced into the particle shells in order t o produce a film-forming latex system t h a t could be cured by ultraviolet (UV)-radiation without any need t o use reactive multifunctional monomers or oligomers as crosslinkers.T h e surface-bound epoxy groups were used as grafting sites for amine or carboxyl functional unsaturated monomers, respectively. T h e grafting was demonstrated by Fourier transform infrared (FTIR) spectroscopy. Films prepared from modified and unmodified latexes were exposed to UV radiation in the presence of a photoinitiator. Crosslinking was tested by thermal mechanical analysis (TMA) and by determination of swelling a n d gel content of exposed films. It was demonstrated t h a t films from the modified latexes after irradiation had significantly higher stiffness and gel content and showed lower swelling than unmodified ones. (As compared to organic-based coating systems, water-based systems have the advantage of low emission of organic compounds to the atmo-Different radiation-curing water-borne coatings have been reported, e.g., w a t e r -~o l u b l e ,~ water-thinnable,' water-dispersible, and latexbased' systems. Some of these systems contain multifunctional acrylates. The main disadvantage of water-based UV curable coatings are essentially the same as for conventional water-borne coatings, i.e., the need to evaporate water before UV curing.'Reduction of the amount of polluting solvents and monomers in radiation curable coatings may be achieved by incorporating the functionality needed for radiation curing into the film-forming latex particles. Therefore, the objectives of our work were to investigate methods for the preparation of radiation curable latexes suitable for coating applications.Emulsion polymerization is a well-known technique for producing dispersions of polymer particles."' The latex is film-forming, provided the poly-435
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