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Dielectric properties of aerogels

Published online by Cambridge University Press:  31 January 2011

L.W. Hrubesh ,
L.E. Keene  and
V.R. Latorre
L.W. Hrubesh
Affiliation:
Chemistry and Materials Sciences Department, Lawrence Livermore National Laboratory, Livermore, California 94550
L.E. Keene
Affiliation:
Chemistry and Materials Sciences Department, Lawrence Livermore National Laboratory, Livermore, California 94550
V.R. Latorre
Affiliation:
Chemistry and Materials Sciences Department, Lawrence Livermore National Laboratory, Livermore, California 94550
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Abstract

We have measured the real (dielectric constant) and imaginary (loss factor) components of the complex relative permittivity at 298 K using microwave frequencies (2, 10, and 18–40 GHz) for bulk SiO2-aerogels and for two types of organic aerogels, resorcinol-formaldehyde (RF) and melamine-formaldehyde (MF). Measured dielectric constants are found to vary linearly between values of 1.0 and 2.0 for aerogel densities from 10 to 500 kg/m3. For the same range of densities, the measured loss tangents vary linearly between values of 2 × 10−4 and 7 × 10−2. The observed linearity of the dielectric properties with density in aerogels at microwave frequencies shows that their dielectric behavior is more gas-like than solid-like. The dielectric properties of aerogels are shown to be significantly affected by the adsorbed water internal to the bulk material. For example, water accounts for 70% of the dielectric constant and 70% of the loss at microwave frequencies for silica aerogels. Because of their very high porosity, even with the water content, the aerogels are among the few materials exhibiting such low dielectric properties. Our measurements show that aerogels with greater than 99% porosity have dielectric constants less than 1.03; these are the lowest values ever reported for a bulk solid material.

Type
Articles
Information
Journal of Materials Research , Volume 8 , Issue 7 , July 1993 , pp. 1736 - 1741
Copyright
Copyright © Materials Research Society 1993

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References

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