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Mobility of Small Molecules in Interlayers of Hectorite Gels: ESR Study with an Uncharged Spin Probe

Published online by Cambridge University Press:  28 February 2024

M. B. McBride
M. B. McBride*
Affiliation:
Cornell University, College of Agriculture and Life Sciences, Department of Soil, Crop and Atmospheric Sciences, 910 Bradfield Hall, Ithaca, New York 14853
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Abstract

Electron spin resonance (ESR) spectroscopy was used to measure the rotational mobility of an uncharged nitroxide spin probe (4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy) in hectorite gels of variable water content. Physical adsorption segregated the probe molecules into two populations: probes in the solution or a solution-like phase, and motionally restricted probes in the adsorbed phase. Although the spectra of these two populations were discrete, indicating that exchange between them was slow on the time scale relevant to ESR, their overlap prevented a straightforward determination of mobility of the adsorbed probes. Even though adsorption was weak, effects of the adsorbed population on the spectral lineshape were detectable for suspensions containing as little as 20 grams clay per liter of water. Orientation of the adsorbed probes on the fully hydrated hectorite surfaces was similar to that of a positively charged nitroxide probe, suggesting that steric factors rather than electrostatic forces control short-range organic molecule interaction with the silicate. The possibility of reaching false conclusions about probe mobility and interlamellar water viscosity when using a weakly adsorbing probe is discussed.

Keywords

ESRHectoriteMolecular mobility
Type
Research Article
Information
Clays and Clay Minerals , Volume 42 , Issue 4 , August 1994 , pp. 455 - 461
Copyright
Copyright © 1994, Clay Minerals Society

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