Utilization of polymer viscoelastic properties in acoustic wave sensor applications

Acoustic wave responses arising from changing viscoelastic properties of polymer film overlays are investigated when induced by a photo-cross-linking reaction and vapor absorption. When a polymer film is present on the surface of an acoustic wave device, changes in the viscoelastic properties of the film induce changes in wave propagation velocity and attenuation, providing two sensor responses. Film changes which occur during polymer cross-linking allow photopolymerization to be monitored in real time using acoustic devices. A photoaction spectrum of photoresist reveals the cross-linking wavelength with maximum quantum yield. Changes in the viscoelastic properties of a polysiloxane film induced by vapor absorption are found to be unique for each of several species, making differentiation of species with a single film possible. A Maxwell model for polymer viscoelasticity, in combination with mass loading effects, provides a sound theoretical basis for explaining observed results for both polysiloxane and polybutadiene/polystyrene copolymer films.<>