Effective medium theory of optical properties of small particle composites

A self-consistent field approach for the calculation of optical properties of a random n-component medium composed of discrete small particles is applied to an insulator-metal mixture for the case of metal formed into small spheres. The real part of the resulting conductivity exhibits broad surface plasmon absorption and a zero-frequency percolation conductivity. This result is contrasted with the Maxwell-Gamett theory for the effective composite conductivity. The effects of an insulating coat on the metal particles' response are examined and shown to produce profound effects at low frequency. Modifications introduced by a distribution of particle sizes are examined, and a completely self-consistent form of the mean field equations for an n-component system, each of whose constituents is distributed in size, is proposed.