All-polymer flexural plate wave devices for sensing and actuation

Abstract

Polymer based flexural plate wave (FPW) chemical sensors are unique among guided acoustic devices in that they are comprised of components with similar elastic moduli. As a result, they can be very sensitive to stiffness and stress variations in an applied sensing layer. This property may be leveraged to detect the presence of an analyte or to interrogate the mechanical properties of the applied polymer. In this work, polyvinylidene fluoride (PVDF) based, polyethylene dioxythiophene polystyrene sulfonate (PEDOT:PSS) coated FPW devices are fabricated and tested with the purpose of developing an all-polymer VOC sensor. The sensors are coated in polyvinyl acetate (PVAc) and polystyrene (PS) sensing layers and exposed to varying concentrations of toluene during testing. The PS coated sensors show a sensitivity of -80 cm²/g to -200 cm²/g while the PVAc coated devices demonstrate a sensitivity of -240 cm²/g to -490 cm²/g. A performance model is proposed which seeks to describe the sensing layer mechanical properties as a function of analyte vapour concentration in order to predict the sensor resonant frequency. The predictions of this model are compared with experimental results and design modifications are proposed. Along with this, soft material mechanical characterisation is investigated with the purpose of developing a tool for measuring composite resin properties during cure. Finally, it is proposed that these devices may be used to drive acoustic streaming in microfluidic systems. To test the concept, droplets of fluid are applied to the device substrates and acoustically driven flow rates are measured.