Detection of organic solvent vapours and studies of thermodynamic parameters using quartz crystal microbalance sensors modified with siloxane polymers

Quartz crystal microbalance (QCM) sensors were modified by a series of siloxane polymer coatings, including polydimethyldiphenylsiloxane, polymethylhydrosiloxane and PS-086; These sensors-were exposed to different concentrations of various organic solvent molecules, including related chlorinated hydrocarbons, alcohols and other organic vapours. The results showed that the responses of frequency changes to concentration changes exhibited linear relationships within the concentration range studied. The thickness of the above three coatings was in the range 3.04-4.24 nm. Thermodynamic parameters of polymer-gas interactions were determined. Partition coefficients (K) of the modified polysiloxane layers obtained from frequency changes at different concentrations of the detected solvents showed good reproducibility (about 0.77-5.45% relative standard deviation) at room temperature. The selectivity and sensitivity of the polysiloxane-based sensors mere correlated with the solvent boiling points, Ostwald solubility coefficients and the different molecular interactions between the functional groups of polysiloxanes and organic solvent molecules.