Globally anisotropic high porosity silica aerogels |
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Authors: | J Pollanen KR Shirer S Blinstein JP Davis H Choi TM Lippman WP Halperin LB Lurio |
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Institution: | 1. Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA;2. Department of Physics, Northern Illinois University, DeKalb, IL 60115, USA |
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Abstract: | We discuss two methods by which high porosity silica aerogels can be engineered to exhibit global anisotropy. First, anisotropy can be introduced with axial strain (i.e. axial compression). In addition, intrinsic anisotropy can result during growth and drying stages and, suitably controlled, it can be correlated with preferential radial shrinkage in cylindrical samples. We have performed small angle X-ray scattering (SAXS) to characterize these two types of anisotropy. We show that global anisotropy originating from either strain or shrinkage leads to optical birefringence and that optical cross-polarization studies are a useful characterization of the uniformity of the imposed global anisotropy. |
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