Surface acoustic wave-liquid drop interactions

Surface acoustic (Rayleigh) waves (SAWs) are highly sensitive to surface ma ss loading. Traditionally SAWs have been considered unsuitable for liquid s ensing applications due to the large attenuation. However if the liquid vol ume is small, SAWs can provide a powerful tool for investigating the dynami cs of viscous liquid spreading. In this work we report experiments in which small droplets of viscous oil were allowed to spread into the path of a SA W device. In all data the SAW signal initially increases while the liquid i s still outside the SAW path. This is followed by a rapid attenuation in SA W amplitude as the liquid spreads across the SAW path. In data for larger v olume drops the SAW amplitude is observed to pass through a minima. For dro ps of smaller volume, small features are observed superimposed on the overa ll attenuation. (C) 1999 Elsevier Science S.A. All rights reserved.