A LIGHT-SCATTERING STUDY OF SPINODAL DECOMPOSITION IN SYSTEMS CONTAINING SURFACTANT MOLECULES

We have performed a series of spinodal decomposition measurements on t wo critical systems containing surfactant molecules, i.e. (i) a three- component microemulsion made up of a surfactant (aerosol-OT), water an d decane, and (ii) a water-butoxyethanol (C(4)E(1)) micellar-like mixt ure. The measurements were performed, via a temperature jump crossing the coexistence line along the critical isovolume fraction line, using the time-resolved light scattering intensity technique. All of the th ree stages of the evolution were studied. The time evolution of intens ities for the initial stage closely follows the linearized theory. The time evolution of the characteristic wavevector, the maximum scattere d intensity, and the intensity distribution in the intermediate and la te stages are discussed in the framework of dynamical scaling theories and compared with the findings of recent molecular dynamics simulatio ns. Such a comparison of the data obtained with the numerical analysis carried out for binary mixtures containing surfactant gives a clear i ndication that in the systems investigated the phase-separation proces s occurs through the formation of different structural coalescing doma ins. Whereas in the AOT microemulsion system the separation occurs thr ough the formation of irregular bicontinuous-like domains, in the wate r-C(4)E(1) mixture the separation is dominated by a process of formati on of micellar domains. In addition, in the latter case thermal fluctu ation processes have a significant effect on the coarsening of the dom ain structures.