Dynamic coating of one liquid by another by employing the Acoustowetting phenomenon


  Avital Reizman  
Technion - Israel Institute of Technology

Recent advances in small scale and geographically flexible fabrication are believed to be the beginning of a manufacturing revolution. Some examples are 3D printers and suit-case size photolithography facilities. These advances highlight the necessity for a complementary advance in geographically flexible, small scale, and precise coating technologies. Dynamic wetting of solid substrates by liquid films of distinct thicknesses, called the Acoustowetting phenomenon, was discovered in the last decade and can be used to promote the development of coating technologies. To obtain a complementary advance in the field, we employ MHz-frequency surface acoustic waves, commonly named as SAWs, to power and control the dynamic wetting of objects by a coating liquid.

In our model, a SAW device is activated by an acoustic actuator to form a Rayleigh wave. We designed a coating system of a sessile water drop by an oil film. This system considering the geometrical smoothness and shape of the water drop to achieve a well-defined experiment. To reduce the influence of the gravitational forces on the wetting dynamic marginal, the SAW device was positioned horizontally. Moreover, the thicknesses of the water drop and oil film are below the capillary gravitational length, of approximately 1 mm. In the presence of the SAW, we observe that a thin film of oil dynamically wets the solid substrate of the device along the path of the SAW. At sufficient SAW power, the oil film climbs on top of the water drop to fully cover it. A compound sessile drop, comprised of an oil and water separate phases, is rendered. We thus show that one liquid may coat another in a directional manner under well-defined MHz-frequency acoustic stress.