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 swollen with methyl methacrylate (MMA) is presented. The electron density of the swollen particles can easily be matched by addition of sucrose to the latex. Also, there is an excellent contrast between the polymer and its monomer. SAXS measurements in conjunction with contrast variation near the match point are therefore well-suited for the detection of even minute changes of the radial concentration profile. Thus, this method is capable of detecting the depletion of the polymer chains near the particle surface due to the wall-repulsion effect. The results point to an outer shell of approximately 2 nm thickness in which the swelling agent is enriched. It is concluded that the present system exhibits a small but non-negligible wall-repulsion effect which is discussed in terms of recent theoretical approaches to the problem.