Biological & Soft Matter Seminar: Dynamic Wetting of Complex Liquids under the influence of MHz Frequency Substrate Vibration

Abstract:

A MHz Substrate vibration is known to excite dynamic wetting of liquid films, a phenomenon usually referred to as Acoustic Spreading. Fully wetting and highly viscous liquids, such as silicon oil, spread spontaneously along or opposite the path of a propagating vibration in the substrate. Partially wetting and low viscosity liquids, such as water on most surfaces, is observed to resist spreading under similar excitation conditions but may be persuaded to spread continuously once vibrational, capillary, and viscous mechanisms are balanced appropriately. 

Using theory and experiment we discuss the spreading of liquid films under the influence of MHz substrate vibration and show opposite contributions from capillary, viscous, and vibrational mechanisms are weighed within one nondimensional number that governs the tendency of a liquid film to spread or avoid spreading. We thus elucidate the discrepancy, observed in earlier studies, between the response of oil and water atop a lithium-niobate substrate to MHz frequency vibrational excitation, and highlight a parametric region where partially wetting liquids may undergo Acoustic Spreading. In this presentation we wish to present the physics associated with the Acoustic Spreading of fully and partially wetting liquids and to further expand these ideas to emulsions and suspensions.

Seminar Organizer: Guy Yaacoby