Determination of polymer-solvent interaction parameters using piezoelectric crystals,with reference to the sorption of chemical warfare agents

Polymeric materials which show sensitivity to certain classes of organic vapors and give minimal responses from interferents are being sought for use as coatings on piezoelectric mass detection devices. The present work illustrates some simple methods for the determination of fundamental properties such as polymer-solvent interaction parameters and diffusion constants, and relates these to the sensitivity and response time of the sensor. Polymers with a controlled variation in crosslink density were exposed to a variety of common solvents and vapors covering a range of solubility parameters. Seven non-crosslinked amorphous polymeric materials were also assessed for their suitability as selective coatings for the detection of a range of chemical warfare vapors. Gross differences in the response characteristics of coated crystals immersed in liquids can be predicted, and an approximate guide to the relative rates of solvent penetration can also be obtained. More accurate predictions are hampered by the lack of knowledge of the specific interactions which occur within polymer–solvent pairs. Crosslinking the polymer film to enable operation in strongly solvating liquids has the effect of reducing the extent of swelling to a larger degree than expected on the basis of existing theories. The operation of coated crystals in the gas phase at very high vapor concentrations leads to a dual site adsorption process which can be described by the BET equation. At much lower vapor concentrations Henry's law appears to determine the response, and a simple solution model developed from partition theory for stationary phases in gas–liquid chromatography can be used to interpret the sensitivity of three non-crosslinked amorphous polymeric films to DMMP, GA, GB, and GD. While adequately describing the responses of the organophosphorus esters, the model is not as satisfactory in predicting the interactions with HD. © 1993 John Wiley & Sons, Inc.