| Abstract
| - We present a comprehensive investigation of the spatial dimensions of colloidal spherical polyelectrolytebrushes in solutions. The particles studied here consist of a solid polystyrene core of 50−100 nm radiusonto which linear poly(acrylic acid) (PAA) chains are chemically grafted. The grafting is achieved throughphoto-emulsionpolymerization in which radicals are generated on the surface of the core particles. Thisprocedure leads to a dense brush of PAA chains chemically fixed on the surface of the core particles. Thehydrodynamic radius RH of these particles is studied by dynamic light scattering as function of saltconcentration. The chemical grafting leads to an extreme colloidal stability, and RH can be studied in KClsolutions which concentrations varying between 10-3 and 3 M. The resulting RH decreased monotonicallywith ionic strength. The data of RH as function of ionic strength were compared with the theory of Hariharan,Biver and Russel (Macromolecules, 1998, 31, 7514). This theory, which is based on the Daoud−Cottonmodel of uncharged curved brushes, describes the spherical polyelectrolyte brushes, in terms of an excludedvolume parameter v and the Kuhn length lK. The local ionic strength of the brush cs is predicted to differwidely from the bulk value ca. Both v and lK depend on the local ionic strength cs as expressed throughthe Debye length κ-1 within the brush. Quantitative agreement of theory and experiment is achieved whenthe following assumptions are made: v ∝ lK2κ-1, and lK ∝ lB-1κ-2, where lB denotes the Bjerrum-length.
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