Polyelectrolyte Conformation at the Particle Surface

When the polyelectrolyte is adsorbed at the particle surface, its conformation is expected to be different from its conformation in solution without the influence of the particle. To get an insight into the extent of change, the mean square radius of gyration <R2g> of the polyelectrolyte is plotted in Fig. 11 as a function of Ci for different op/om values. <R2g> for the isolated chain is also represented for comparison. When op/om < 2, the polyelectrolyte conformation is poorly affected by the presence of a small particle. By increasing the op/om ratio up to 5 and 6, respectively, the particle surface becomes large enough to adsorb a few monomer segments and start producing loops and trains. Maximal deformation is achieved when C = 0. 1 M. Below this concentration the electrostatic repulsion between the monomers is strong enough to limit the adsorption process through the formation of extended tails in solution. When op/om = 8, maximal deformation is achieved whatever the ionic concentration. The surface area is now large enough that the polyelectrolyte can wrap around the sphere to optimize the number of contacts. When op/om > 8, the conformation and size of the polyelectrolyte is now dictated by the size of the particle. By increasing the

FIG. 11 Mean square radius of gyration <Rg> of the polyelectrolyte as a function of C for different op/cm values. <Rg> for the isolated chain is also represented for comparison.

particle size further, a nearly planar surface limit is reached. In this case, the chain can spread fully on the surface with a dimension close to its dimensions in a free solution.

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