Light Scattering Studies of Lower Dimensional Colloidal Particle and Critical Fluid Systems. Final Progress Report

摘要

We have completed a program of small angle scattering Rayleigh linewidth measurements on thin films of a 2,6-lutidine + water mixture. No statistically significant departures from three dimensional dynamic response were seen, although the conditions set by the theory of Calvo and Ferrell were met. We have applied digital image processing to evaluate fractal scale invariance in two dimensional particle aggregates arising from the induced coagulation of colloidal particle monolayer crystals. Our system gives us the capability of calculating the pair correlation function for both small and very large (2 x 10 exp 4 particles) particle clusters. We find evidence of an apparent crossover between kinetic clustering aggregation at small distances (about 20 particle diameters) to percolation or gel/sol transition-behavior at large distances. This is evident in both isolated clusters and in final state ''giant'' aggregates. We are carrying through a parallel program of computer calculations whose motivation is to assess the sensitivity of experimental measures of self similarity to cluster size and image resolution, and to generate efficient algorithms which can be applied to calculate fractal ''critical exponents'' other than the Hausdorff dimension. We have succeeded in measuring the surface tension of a water surface covered by a colloidal particle monolayer crystal, in both its repulsive-dipole and close-packed van der Waals phases. (ERA citation 10:053091)