ORGANIC VAPOR DETECTION BY QUARTZ-CRYSTAL MICROBALANCE MODIFIED WITH MIXED MULTILAYER LANGMUIR-BLODGETT-FILMS

Mixed chloroform solution of Polysiloxane PS-264 and stearic acid was made into multilayer Langmuir-Blodgett (LB) films on the surface of qu artz crystal microbalance (QCM). The condition for forming mixed multi layer LB films is discussed in this paper. In addition, PS-264, steari c acid and their mixture (molar ratio 1:1) were coated on the surface of QCM sensors by a spin coating method. The above modified crystals w ere exposed to different concentrations of various organic vapors, inc luding related chlorinated hydrocarbons and alcohol vapors. The result s of frequency changes corresponding to concentration change of the ab ove vapors were compared. The linear regression coefficients of the QC M with LB film had better values (0.9881 < R < 0.9981) than QCM with s pin-coated films. The sensitivity between analytes/coating was interpr eted in terms of solubility interactions. For the more polar organic v apors investigated, even at the same concentration, frequency changes of the QCM with LB films were somewhat larger, especially for chlorofo rm and dichloromethane. However, the sensitivity of many organic vapor s investigated on the mixed multilayer LB films is similar to the spin -coated films of mixture and PS-264, except that chloroform and dichlo romethane only were sensed with much higher sensitivity on the mixed m onolayer. The sensitivity of the QCM spin-coated with the mixture of P S-264 and stearic acid was between mixed LB films and PS-264 for many organic vapors investigated. In this study, the surface morphologies o f the uncoated and coated QCM were characterized by atom force microsc opy (AFM). (C) 1998 Elsevier Science B.V.