Modulated exponential films generated by surface acoustic waves and their role in liquid wicking and aerosolization at a pinned drop

Abstract

The exponentially decaying acoustic pressure of scattered surface acoustic waves (SAWs) at the contact line of a liquid film pinned to filter paper is shown to sustain a high curvature conic tip with micron-sized modulations whose dimension grows exponentially from the tip. The large negative capillary pressure in the film, necessary for offsetting the large positive acoustic pressure at the contact line, also creates significant negative hydrodynamic pressure and robust wicking action through the paper. An asymptotic analysis of this intricate pressure matching between the quasistatic conic film and bulk drop shows that the necessary SAW power to pump liquid from the filter paper and aerosolize, expressed in terms of the acoustic pressure scaled by the drop capillary pressure, grows exponentially with respect to twice the acoustic decay constant multiplied by the drop length, with a universal preexponential coefficient. Global rapid aerosolization occurs at a SAW power twice as high, beyond which the wicking rate saturates.

Acoustotemplating: rapid synthesis of freestanding quasi-2D MOF/graphene oxide heterostructures for supercapacitor applications

“…Despite the SRBW (or more broadly its surface counterpart, the surface acoustic wave (SAW)) having amplitudes of only a few nanometers, 46 it possesses extraordinarily large surface acceleration (on the order of 10 8 m s −2 ) that has been implicated to give rise to a host of acoustomicrofluidic phenomena. 47–50 These include the phenomenon observed in the current work, namely, the generation and spreading of thin acoustowetting films, 51–53 and their nebulization to produce micron dimension aerosol droplets, 45,54–59 which has also been exploited for the synthesis and manipulation of various nanomaterials, 60 including 2D transition metal dichalcogenides 61–63 and carbides/nitrides (MXenes), 64,65 as well as other bulk crystals, 66 including MOFs. 44,67…”

Surface acoustic wave devices for chemical sensing and microfluidics: a review and perspective

“…Taller et al looked at the atomization from the leached thin film to reveal that the profile of the thin film changes due to the radiated SAW pressure. 111 In addition to showing different atomization regimes as shown in Fig. 9, they also estimated the internal pressure in the thin film for each of these regimes, and importantly it can be negative.…”

“…The film regime figures are adapted with permission from Ref. 111. Copyrighted by the American Physical Society.…”