MODIFIED POLYMERS FOR RELIABLE DETECTION OF ORGANIC-SOLVENTS - THERMODYNAMICALLY CONTROLLED SELECTIVITIES AND SENSITIVITIES

Thin layers of polydimethylsiloxane, polycyanopropylmethylsiloxane, po lyaminopropylmethylsiloxane, poly(isopropanoic acid)methylsiloxane, an d polyphenylmethylsiloxane were spray-deposited on quartz microbalance oscillators. This preparation leads to very homogeneous layers even f or modified polysiloxanes which cannot be deposited perfectly onto qua rtz substrates by other methods such as spin-on coating. We measured f requency changes DELTAf upon exposure of the quartz oscillators to dif ferent organic solvent molecules such as n-octane, methylcyclohexane, perchloroethylene, chloroform, tetrachloromethane, toluene, diisopropy lether, ethanol, n-propanol and isopropanol. We determined their parti tion coefficients f(p/g) in the modified polysiloxane layers for diffe rent partial pressures at T = 303 K under conditions of perfect reprod ucibility. We determined energies and entropies of polymer/gas interac tions in a thermodynamic approach. The values f(p/g) depend strongly o n the different functional groups in the polysiloxane matrix which is explained by the different molecular interactions between the function al groups and dissolved organic molecules.