Revisiting the electroacoustic phenomenon in the presence of surface acoustic waves

Recently, one observes abundant studies on the application of surface acoustic waves (SAWs) in solid substrates for manipulating liquids and particulates in micron to nanometer thick films and channels and in porous media. At these length scales, contributions of SAWs to the electrical double layer (EDL) of ions and of the latter to particulates and flow may become appreciable. However, the nature of interplay between SAWs and EDLs is unknown. Inert solids support a mechanical wave which translates to acoustic flow in the nearby liquid. Piezoelectric solids, common for generating SAW, further support a voltage signal which travels along the mechanical SAW in the solid. We demonstrate the near equilibrium distortion of the electrical and ion concentration field in the EDL near inert and piezoelectric substrates under SAW excitation. We concentrate on the resulting escape of transient and steady electrical fields from a charged solid surface through the near equilibrium EDL and to the bulk of liquid. The electrical fields far from the solid may be interpreted by different models of EDL to give information about its dynamics and statics and about the zeta potential or properties of the Stern layer and of the intrinsic surface electrical potential at the solid surface.