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.

No abstract

Olive oil-gas partition coefficients, Lo,,, have been determined for 80 solutes at 310 K using a gas chromatographic method in which olive oil is used as the stationary phase. Combination with other literature values has enabled a list of 140 log L o i , values at 31 0 K to be constructed. Hexadecane-gas partition coefficients, Lhex, have similarly been determined for 140 solutes at 298 K, and used to obtain a reasonably comprehensive list of log Lhex values for ca. 240 solutes at 298 K. It is shown that olive oilwater partition coefficients, Poi,, calculated indirectly from Loir and Cwater partition coefficients agree quite well with directly determined Poi,. values. Similarly, hexadecane-water partition coefficients, Phex, obtained from Lhex and Lwater agree with directly determined values. It is suggested that in the case of the t w o particular solvents, olive oil and hexadecane, mutual miscibility of the two phases is of little consequence, and that Po,, and Phex values can conveniently be obtained by combining the respective solventgas and water-gas partition coefficients.

Surface acoustic wave (SAW) devices coated with a thin film of a stationary phase sense chemical vapors In the gas phase by detecting the mass of the vapor that distributes Into the stationary phase. This distribution can be described by the partition coefficient. An equation is presented that allows partition coefficients to be calculated from SAW vapor sensor frequency shifts. The experimental responses of fluoropolyd-coated 158-MHz dual delay line SAW vapor sensors are converted to partition coefficients by this method, and these results are compared with partition coefficients determined by gas-liquid chromatography. These two methods rank the vapors In the same order of Increasing sorption, but Individual partition coefficient values are not always In precise agreement. The Influence of temperature and gas-phase vapor concentration on vapor sorption Is also examined.

Paper 4/03649B