Abstract
Metal nanoparticles are receiving increased scientific attention owing to their unique physical and chemical properties that make them suitable for a wide range of applications in diverse fields, such as electrochemistry, biochemistry, and nanomedicine. Their high metallic polarizability is a crucial determinant that defines their electrostatic character in various electrolyte solutions. Here, we introduce a continuum-based model of a metal nanoparticle with explicit polarizability in the presence of different kinds of electrolytes. We employ several, variously sophisticated, theoretical approaches, corroborated by Monte Carlo simulations in order to elucidate the basic electrostatics principles of the model. We investigate how different kinds of asymmetries between the ions result in non-trivial phenomena, such as charge separation and a build-up of a so-called zero surface-charge double layer.
Highlights
In the case of a planar dielectric discontinuity, the electrostatic potential can be expressed as the electrostatic potential arising from a fictive ‘‘image charge’’ residing on the other side of the discontinuity
The image-charge concepts have been adapted to spherical symmetry by Linse.[1,11,12]. He showed that approximating the exact mathematical expressions for the spherical geometry leads to a simplified picture in which the polarization is described by image charges as in planar cases
The image charges in the spherical geometry are of paramount importance, since a vast majority of the soft-matter electrostatics research in the recent decades has focused on colloidal and biological systems, where various macromolecular structures in water can be modeled as spherical entities with a lower dielectric interior e0 than the surrounding water environment (e0 { e).[1,13,14,15,16,17,18,19,20,21,22,23,24]
Summary
In the case of a planar dielectric discontinuity, the electrostatic potential can be expressed as the electrostatic potential arising from a fictive ‘‘image charge’’ residing on the other side of the discontinuity. Prominent discoveries was that gold nanoparticles (of a size 1–10 nm) are active catalysts for oxidation reactions.[27] This has triggered a tremendous research activity in nanocatalysis, which presently remains one of the fastest growing areas of nanoscience.[28,29,30] applications involving metal nanoparticles can for instance be found in electrochemistry for nanoelectrodes,[31] photovoltaic cells[32] electro-osmosis,[33] or in biochemistry and nanomedicine for drug delivery, therapeutics, diagnostics, and bioimaging.[34,35,36,37,38] At the same time, experimental findings pointed out cytotoxic features of some metal nanoparticles.[39,40] Several studies suggested that metal nanoparticles interact with cell membranes in a complex way,[41,42,43,44] governed by electrochemical potentials and ion distributions around the membrane and a nanoparticle These achievements emphasize the importance of a deeper theoretical understanding of the interface between a nanoparticle and the solvent, which acts as a determining factor for many properties of the nanoparticle and its complexes in aqueous environments.[45]. We show how different kinds of asymmetries between ions result in non-trivial phenomena, such as charge separation and a build-up of net electrostatic potential and effective surface charge
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