Design of particulate composites for optical applications

Abstract This paper reviews the basic theoretical approach to describing light scattering in filled materials with nearly matching refractive indices (Rayleigh‐Gans‐Debye Theory). The modifications necessary to handle high filler concentrations (interparticle interference and multiple scattering) are included empirically. The primary result of this analysis is an expression for the optical transmission of a polymer composite as a function of particle size, volume fraction, composite thickness, and refractive index difference between the components. The angular dependence of the scattering is included so that scattered light which falls within the aperture of the transmission detector can be accounted for, Particular attention is given to including the temperature dependence of the refractive index and the effect of fillers on the thermal expansion properties of the polymer matrix in order to predict the temperature range over which the composite will be optically useful. Similarity to analyses of the Christiansen filter is discussed.