Image Potentials for Multipoles Embedded in a Cavity and Their Applications to the Surface Tension of Aqueous Solutions of Amino Acids

TLDR: In this article, the electrostatictheory for a dielectric spherical or spheroidal cavity, with arbitrary charge distribution within it, is presented, and the results are used to calculate the adsorption potential for a species with specified dipole and quadrupole moments.

Abstract: The electrostatictheory for a dielectric spherical or spheroidal cavity, with arbitrary charge distribution within it, is presented. The cavity is located in a dielectric medium which is separated from another uniform dielectric medium by a planar interface. The use of a cavity avoids the singularities in the image potential for point charges as they approach the interface. It is shown that the adsorption potential is directly related to the resolvent of a matrix whose elements depend on the position and the dimensions of the cavity. The results are used to calculate the adsorption potential for a species with specified dipole and quadrupole moments. The adsorption potential thus calculated is used to analyze the difference between the surface tension of zwitterionic solutions and the pure solvent. We discuss how the diffuseness of the interface diminishes the calculated increase in the surface tension. The calculated changes, arising from electrostatic forces, in the surface tension of aqueous solutions of small amino acids belonging to an homologous series, compare favorably with those derived from the experimental measurements.