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.
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References
R. P. Her. The Chemistry of Silica (John Wiley and Sons, New York, 1979), pp. 537–539, 637.
J. Fricke. Sci. Am. 256, 92 (1988).
J. Fricke and A. Emmerling, in Chemistry, Spectroscopy, and Applications of Sol-Gel Glasses, edited by R. Reisfeld and C. K. Jorgensen. Springer Series Structure and Bonding (Springer-Verlag. Heidelberg, Germany, 1991), Vol. 77, p. 37.
G.V. Chandrashekhar and M.W. Shafer, in Better Ceramics Through Chemistry II. edited by C.J. Brinker, D. E. Clark, and D. R. Ulrich (Mater. Res. Soc. Symp. Proc. 73, Pittsburgh, PA, 1986), p. 705.
A. A. daSilva, D.I. dos Santos, and M.A. Aegcrter, J. Non-Cryst. Solids 96, 1159 (1988).
G. Birnbaum and J. Franeau, J. Appl. Phys. 20, 48 (1949).
H. M. Altschuler, in Handbook of Microwave Measurements. edited bv M. Sucher and J. Fox (John Wiley and Sons, New York, 1963). Vol. II, p. 518.
C. J. Brinker and G. W. Scherer, Sol-Gel Science (Academic Press, Inc., San Diego, CA, 1990), p. 620.
W. B. Westphal, in Dielectric Materials and Applications, edited by A. von Hippel (The M.I.T. Press, Cambridge, MA, 1961), p. 63.
A. von Hippel, in Dielectric Materials and Applications, edited by A. von Hippel (The M.I.T. Press, Cambridge, MA, 1961), pp. 3–138.
T.M. Tillotson, L.W. Hrubesh, and I.M. Thomas, in Better Ceramics Through Chemistry III, edited by C. J. Brinker, D. E. Clark, and D.R. Ulrich (Mater. Res. Soc. Symp. Proc. 121, Pittsburgh, PA, 1988), p. 685.
R.W. Pekala, J. Mater. Sci. 24, 3221 (1989).
R.W. Pekala and C.T. Alviso, in Better Ceramics Through Chemistry IV, edited by B.J.J. Zelinski, C.J. Brinker, D.E. Clark, and D.R. Ulrich (Mater. Res. Soc. Symp. Proc. 180, Pittsburgh, PA. 1990), p. 791.
L. W. Hrubesh, T. M. Tillotson, and J. F. Poco, in Better Ceramics Through Chemistry IV, edited by B.J.J. Zelinski, C.J. Brinker, D. E. Clark, and D. R. Ulrich (Mater. Res. Soc. Symp. Proc. 180, Pittsburgh, PA, 1990), p. 315.
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Hrubesh, L.W., Keene, L.E. & Latorre, V.R. Dielectric properties of aerogels. Journal of Materials Research 8, 1736–1741 (1993). https://doi.org/10.1557/JMR.1993.1736
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DOI: https://doi.org/10.1557/JMR.1993.1736