Modified polymers for reliable detection of organic solvents: Thermodynamically controlled selectivities and sensitivities

Abstract Thin layers of polydimethylsiloxane, polycyanopropylmethylsiloxane, polyaminopropylmethylsiloxane, poly(iso-propanoic acid)methylsiloxane, and polyphenylmethylsiloxane were spray-deposited on quartz microbalance oscillators. This preparation leads to very homogeneous layers even for modified polysiloxanes which cannot be deposited perfectly onto quartz substrates by other methods such as spin-on coating. We measured frequency changes Δ f upon exposure of the quartz oscillators to different organic solvent molecules such as n-octane, methylcyclohexane, perchloroethylene, chloroform, tetrachloromethane, toluene, diisopropylether, ethanol, n-propanol and isopropanol. We determined their partition coefficients f p/g in the modified polysiloxane layers for different partial pressures at T =303 K under conditions of perfect reproducibility. We determined energies and entropies of polymer/gas interactions in a thermodynamic approach. The values f p/g depend strongly on the different functional groups in the polysiloxane matrix which is explained by the different molecular interactions between the functional groups and dissolved organic molecules.