Polarization Effects of Dielectric Nanoparticles inAqueous Charge-Asymmetric Electrolytes.

Small nanoparticles, globular proteins,viral capsids, and othernanoscopic biomolecules usually display dielectric properties thatare different from those of the medium in which they are dispersed.These dielectric heterogeneities can significantly influence the surroundingion distribution, which determines the self-assembly and colloidalstability of these nanoparticles in solution. Here, we study the impactof a dielectric discontinuity in the structural and thermodynamicproperties of a spherical nanoparticle made of different dielectricmaterials when it is immersed in a charge-asymmetric 1:zsupporting electrolyte. The mean electrostatic potential, integratedcharge, and ionic profiles are analyzed as a function of both thesalt concentration and the nanoparticle’s valence via MonteCarlo simulations and the nonlinear Poisson–Boltzmann theory.We observe that the electrostatic screening and charge neutralizationnear the surface of a nanoparticle increase when the nanoparticle’sdielectric permittivity increases in all instances. For 1:1 salts,this effect is small and the nonlinear Poisson–Boltzmann theorydisplays a good agreement with simulation results. Nevertheless, significantdeviations are displayed by the mean field scheme regarding simulationresults in the presence of multivalent ions. In particular, for trivalentcounterions we observe that increasing the dielectric permittivityor the valence of the nanoparticle decreases the critical salt concentrationat which occurs a sign inversion of the mean electrostatic potentialat the Helmholtz plane, which is closely related to the behavior ofthe ζ potential and the electrophoretic mobility. Moreover,we observe that the phenomenon of surface charge amplification, orthe augmenting of the net charge of a nanoparticle by the adsorptionof like-charged ions on its surface, can be promoted by polarizationeffects in weakly charged spherical nanoparticles with low dielectricpermittivity. [ABSTRACT FROM AUTHOR]