STUDY OF SPATIAL INHOMOGENEITIES IN SWOLLEN LATEX-PARTICLES BY SMALL-ANGLE X-RAY-SCATTERING - THE WALL-REPULSION EFFECT REVISITED

A small-angle X-ray scattering (SAXS) study of PMMA-latex particles sw ollen with methyl methacrylate (MMA) is presented. The electron densit y of the swollen particles can easily be matched by addition of sucros e to the latex. Also, there is an excellent contrast between the polym er and its monomer. SAXS measurements in conjunction with contrast var iation near the match point are therefore well-suited for the detectio n of even minute changes of the radial concentration profile. Thus, th is method is capable of detecting the depletion of the polymer chains near the particle surface due to the wall-repulsion effect. The result s point to an outer shell of approximately 2 nm thickness in which the swelling agent is enriched. It is concluded that the present system e xhibits a small but non-negligible wall-repulsion effect which is disc ussed in terms of recent theoretical approaches to the problem.