High surface area polymer coatings for SAW-based chemical sensor applications

High surface-to-volume ratio coatings consisting of nano-scale polymer particles were applied to surface acoustic wave (SAW) transducers. The resulting sensors were tested upon exposure to analyte vapors and were compared with sensors developed from bulk films of the same polymers. The relative importance of surface adsorption and bulk absorption was investigated and it is shown that high surface area coatings can be used to improve the sensitivity and response time particularly in the case of polymers exhibiting low vapor permeability. Furthermore, because the mean particle diameter is small compared to the spacing of the SAW interdigital electrodes, nano-scale particulate coatings appear acoustically uniform and are therefore, compatible with SAW technology. The high surface-to-volume ratio coatings were deposited using a spray-on technique known as rapid expansion of supercritical solutions (RESS) and both glassy and viscoelastic polymers were studied.