Light scattering for aerogel characterization

Light scattering is a useful tool to evaluate aerogel clarity, study its structure, pore size, mechanical strain, and examine the modes of sol-gel evolution that determine its microstructure. Ultraviolet-visible transmission spectroscopy can be used to study the wavelength dependent scattering to readily compare aerogels of differing origins, thickness, and to evaluate effects of residual contaminants. Infrared reflectance measurements can be used to determine the effective real and imaginary indices of refraction of porous aerogel materials for material property and radiant heat transfer studies. Measurements of scattering at a fixed angle can be used for quality control, to evaluate sources of scattering, and study inhomogeneities. Measurement of the Mueller matrix (describing the 16-element angle-dependent transformation of intensity and polarization of incident to scattered light) provides information about the anisotropy, large pore fraction, induced stresses, microstructure and inhomogeneities in the aerogel. The time evolution of scattering before and after gel formation gives information. (C) 1998 Elsevier Science B.V. All rights reserved.