Impact of the electrostatic interaction on the diffusion of small polyelectrolytes in charged colloidal suspensions

Abstract : This work investigates the impact of the presence of charged obstacles, consisting of charged silica nanoparticles, on the diffusion of short polyelectrolytes, from the simple propanoate to longer polyacrylate. In the range of volume fraction studied (φ < 0.2), the increase of the volume fraction of the obstacles leads to a linear decrease of the diffusion coefficient. The data show that the decrease is significantly larger than what is expected for a diffusion only restricted by the pure obstruction of the obstacles. The electrostatic origin of this reduced diffusion is confirmed by the study of the system with the addition of salt and the change of pH, since the addition of salt screens the interaction between obstacles and diffusers, and the change of pH modifies their charge. To further investigate the phenomenon, the diffusion coefficient is computed using a cell-model to solve Smoluchowski equation of diffusion in the presence of a screened Coulomb potential between the diffuser and the obstacles. A semi-quantitative agreement is found between the cell-model and the experimental data. Finally, the perspectives and limitations of the model are discussed.
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Caterina Dolce, Guillaume Mériguet. Impact of the electrostatic interaction on the diffusion of small polyelectrolytes in charged colloidal suspensions. Journal of Molecular Liquids, Elsevier, 2018, 272, pp.821-827. ⟨10.1016/j.molliq.2018.10.07⟩. ⟨hal-01992063⟩

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