Study of sorption/desorption of water and organic vapors on poly(ethylene maleate)‐based sensor‐coating materials using an automated gravimetric analyzer

Abstract

Hydrophobic comonomers bisphenol-A and hexafluorobisphenol-A were incorporated as diol components in the sensor-coating material poly(ethylene maleate) (PEM), resulting in modified polymers, HCPEM and HFPEM, respectively. To assess the suitability of these polymers as sensor interfaces, the sorption/desorption isotherms and kinetics of water and a range of volatile organic vapors were obtained over the entire relative pressure range of 0.1 to 1.0, using an automated intelligent gravimetric sorption analyzer. The extent and rate of sorption of organic vapors were higher in the modified polymers compared to those of the parent polymer. Sorption hysteresis was observed at high relative pressures, especially with water and other hydrogen-bonded polar organic vapors. Polarizable vapors like toluene and benzene were sorbed more than nonpolarizable cyclohexane vapors. The sorption results were interpreted in terms of semiempirical models based on concepts of thermodynamic interaction parameter, partition coefficient, and linear solvation energy relationship. The study reveals the potential of sorption/desorption isotherms and kinetics in characterizing the sorption properties of coating materials that are used as an interface in acoustic wave sensors.

A novel approach for evaluation of polymeric interface materials for chemical sensors using alternate indirect methods

“…Because of the π electron cloud, toluene shows a comparatively higher interaction than cyclohexane with PEM. The magnitude and dynamics of sorption obtained from such isotherms for PEM and its derivatives was reported recently4 in our earlier work.…”

“…The extent of polymer–vapor interaction can also be determined from the sorption isotherms and kinetics, as explained in our earlier work 4. A representative isotherm for the sorption of water and organic vapors on PEM is depicted in Figure 2.…”

“…χ ≥ 1 represents limited sorption, whereas χ < 0.5 implies a high sorption; namely, a lower value of χ implies a higher vapor–polymer interaction, leading to a higher partition coefficient K , and thus a higher convexity of the sorption isotherm. χ was calculated, as reported earlier,4–6 using the standard equations. As seen from Figure 3 for the sorption of organic vapors on PEM, the trend in the experimentally determined values of K is in good agreement with the calculated values of χ.…”

“…A microprocessor‐controlled intelligent gravimetric analyzer (Hiden Analytical, UK) was used to obtain the sorption–desorption kinetics and isotherms of various vapors on the polymers, as reported recently 4…”

“…If a polymer exhibits a high sorption of analyte, it is deemed to be sensitive; the reversibility is attained if the analyte is only physisorbed, so that the desorption occurs with ease. A large hysteresis in the sorption–desorption isotherms adversely affects the reversibility 4. Faster kinetics of sorption help in achieving the desired low response time.…”