PERCOLATION AND CRITICAL PHENOMENA OF AN ATTRACTIVE MICELLAR SYSTEM

In this work we study an attractive micellar system for which the percolation curve terminates near the critical point. We have studied such an intriguing situation by means of scattering (elastic and dynamical) and viscoelasticity experiments. Obtained data are accounted by considering in a proper way the fractal clustering processes typical of percolating systems and the related scaling concepts. We observe that the main role in the system structure and dynamics it is played by the cluster's partial screening of hydrodynamic interaction. This behaves on approaching the percolation threshold dramatic effects on the system rheological properties and on the density decay relaxations. The measured correlation functions assume a stretched exponential form and the system becomes strongly viscoelastic. The overall behavior of the measured dynamical and structural parameters indicates, that in the present micellar system, the clustering process originates dilute, polydisperse and swelling structures. Finally, this originates an interesting situation observed in the present experiment. As it has been previously, proposed by A. Coniglio et al., percolation clusters can be considered to be "Ising clusters" with the same properties as the Fisher's critical droplets. Therefore at the critical point the percolation connectedness length (ξp) can be assumed as the diverging correlation length (ξp ≡ ξ) and the mean cluster size diverges as the susceptibility.

NUCLEATION AT FIRST-ORDER WETTING TRANSITIONS

A brief review is given of the status of both theory and experiments of nucleation phenomena at first-order wetting transitions, focusing on the early stages of the decay of metastable thin and thick wetting films. Generally, the decay of metastable films is initiated by the formation of critical nuclei, which for a metastable thin film are droplets on the wall of the system, and holes in the wetting layer for a metastable thick film. The shapes of critical droplets and critical holes are characterized in the various regions of the wetting phase diagram. The nucleation rate of critical nuclei is determined, which is a measure of the lifetime of the metastable states. The connection of the theoretical results with recent experiments on nucleated wetting layers is discussed. An outlook on open problems concludes the review.