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The sorption of vapors by fluoropotyol, poly(epichlorohydrln), and poly(lsobutytene) Is examined by gas-liquid chromatography (GLC), and these results are compared with the responses of surface acoustic wave (SAW) vapor sensors coated with the same polymers. The sensor responses exceed those which can be attributed to gravimetric effects, Indicating that the SAW devices are responding to some other change In the coating properties. A model Is developed to estimate the effect of polymer swelling on SAW sensor responses. The model Is based on the use of partition coefficients determined by GLC as an Independent measure of polymer mass loading, and polymer thermal expansion on SAW surfaces as a measure of volume change effects which Is Independent of mass loading effects. Both experimental comparisons and the model Indicate that swelling effects can be ca. 4 times greater than mass-loading effects. The likely mechanism by which swelling Influences the SAW sensor response Is via reductions In the modulus of the polymer overlayer.

Paper 4/03649B

Ostwald solubility coefficients, L, have been determined for 37 gases and vapours in methylene iodide at 298 K, and have been correlated through equation (i). where the solute explanatory log L = -0.74 + 0.32R2 + 1.34~: + 0.83@ + 1.1 9 B + 0.87 log L"variables are R, an excess molar refraction, . n: the solute dipolarity/polarisability, a: and fl the solute hydrogen-bond acidity and basicity, and log L16 where L" is the solute Ostwald solubility coefficient on hexadecane at 298 K. Similar equations have been constructed for solvation of solutes in tetrachloromethane, trichloromethane and 1.2-dichloroethane using literature data. It is shown that polarisability effects favour solvation in methylene iodide, through the R, term, but that such effects enhance the solubility of polarisable solutes only moderately: thus the R, term contributes 0.4 log units more in methylene iodide than in trichloromethane for the solute benzene.

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