A study of recognition coating response for quartz crystal microbalances
Computerized molecular modeling methods supplemented with chemometric methods may be used to provide information regarding sensitivity, selectivity, and other properties of solid/vapor sorption interactions for chemically coated Quartz Crystal Microbalances (QCMs). When exposed to the individual vapors of a homologous series of carboxylic acid vapors, a QCM coated with varying thicknesses of poly(ethylenimine) (PEI) coating, produces a linear response that is sensitive and selective. The selectivity of the PEI coating toward analytes increases with aliphatic chain length probably due to dispersive interactions. A linear relationship between calculated van der Waals force values and experimental dispersion force values may exist. BET isotherm plots indicate that heats of adsorption values for the interactions fall within the range of physical adsorption. At high analyte concentrations, PEI coated sensors may behave differently because multilayering interactions increase. At low concentrations, monolayer adsorption appears to predominate and the values of the coating coefficients become constant.