Wavelength Dependent Haze of Transparent Glass-Particle Filled Poly(Methyl Methacrylate) Composites

Glass particles as filler were incorporated in a poly(methyl methacrylate) matrix. The refractive indexes of both materials match at a wavelength of about 400？nm. The effect of particle volume fraction on the light transmittance and light scattering (haze) in dependence of the refractive index difference was studied. The curve shape of the haze in dependence of the wavelength is comparable to that of the refractive index difference, but the base line of the haze increases with the filling grade. This indicates that there are other scattering or absorbing mechanisms, like defects in the filler binding. 1. Introduction Particle-filled polymers are normally nontransparent. By the use of a transparent polymer as a matrix and an optical glass with a matching refractive index as filler particles, transparency can be achieved for at least one temperature and wavelength of light. These transparent composites are expected to have, compared to the bulk material, increased mechanical properties (higher stiffness, increased strengths by the use of fibers) a lower expansion coefficient and an increased thermal conductivity. In the event the particle size is one order of magnitude greaterthan the wavelength in the visible range ( ), the light scattering theories of Rayleigh and Mie cannot be applied. [1] First experiments on this subject have been done by Breuer and Grzesitza [2]. They analyzed a mixture between two polymers to adapt the refractive index to that of the used glass fibers. Specimens show a wavelength- (because of the different dispersion) and temperature-dependent extinction curve of the indecent light. Significant work on this subject has been carried out in Japan by the group of Kagawa. They studied the influence on light transmittance, mechanical, and thermal properties of many parameters, such as refractive index difference, particle size, particle surface area, and filler content [3–8]. The materials that have been investigated are an epoxy resin as a matrix and different optical glasses as filler particles. The light transmittance clearly shows the dependence of the refractive index difference because of the different dispersions of the materials. Nevertheless, the light transmittance of the compound is always less than that of the pure matrix. Waver et al. [9] investigated glass-fiber reinforced PMMA. They used optical glass as fiber material and studied the optical properties in dependence of the temperature among others. Experiments show that the temperature dependence of the polymer changes with the filling grade due to the reduced thermal