Surface acoustic wave-based generation and transfer of droplets onto wettable substrates

Abstract

Investigation of surface acoustic wave-based generation and transfer of droplets onto wettable substrates is carried out and explained in terms of polydispersity index. Transfer of biomolecules is demonstrated to highlight the technique.

Deicing of Sessile Droplets Using Surface Acoustic Waves

“…The IDTs are etched and patterned onto the LiNbO 3 substrate using standard photolithography and wet etching techniques. 24 The width and interelectrode spacing are kept fixed at 20 μm which gives a resonant frequency of 49.98 MHz. To avoid direct electrical connections between the ice and the IDTs, thin polydimethylsiloxane (PDMS) film of 20 μm thickness is fabricated 38 and placed over the IDTs and the lead wires.…”

“…18,19 Upon application of high frequency (MHz) electrical signals to interdigitated electrodes (IDTs) patterned on a piezoelectric substrate, surface vibrations are generated due to the inverse piezoelectric effect. 20,21 Depending on the IDT design, the resonance frequency of the SAW device can be controlled, 22 and thus, SAW-based systems have found various applications in acoustofluidics, 23,24 sensors, 25 wireless communications, 26 biology, 27−30 and droplet microfluidics. 31−33 In addition to the surface vibrations, Joule heating of the IDTs as well as dielectric loss of the piezoelectric substrate leads to heat generation in the substrate.…”

“…SAW devices are prepared using conventional microfabrication techniques. 24 A 128°rotated Y-cut X propagating lithium niobate (LiNbO 3 ) wafer of thickness 0.5 mm is used as the piezoelectric substrate. Cr/Au of thickness 10/100 nm is sputter coated onto the LiNbO 3 substrate and patterned to prepare the IDTs.…”

“…Deicing using surface acoustic waves (SAWs) is a promising approach due to the various advantages it offers over the existing methods. , Upon application of high frequency (MHz) electrical signals to interdigitated electrodes (IDTs) patterned on a piezoelectric substrate, surface vibrations are generated due to the inverse piezoelectric effect. , Depending on the IDT design, the resonance frequency of the SAW device can be controlled, and thus, SAW-based systems have found various applications in acoustofluidics, , sensors, wireless communications, biology, − and droplet microfluidics. − In addition to the surface vibrations, Joule heating of the IDTs as well as dielectric loss of the piezoelectric substrate leads to heat generation in the substrate. , When a drop is exposed to SAWs, the energy leaks into the drop at the Rayleigh angle θ R = sin –1 ( C l / C s ) where C l and C s refer to speed of sound in the liquid medium and the substrate, respectively. Depending on the input energy and droplet volume, the drop can undergo vibration, translation, and atomization into submicron sized droplets. , Apart from this, the leaky acoustic energy gets converted into thermal energy due to viscous dissipation inside the drop which is known as acoustothermal heating.…”

Advances in Microscale Droplet Generation and Manipulation

“…Such forces were activated by scanning a hot tip or an infrared laser over a lithium niobate substrate. Owing to low power requirements and robust fabrication methods, surface acoustic wave (SAW)-based techniques are preferred for atomizing micrometer-sized (picoliter) droplets. , Nevertheless, this technique is expensive due to the necessity of a piezoelectric substrate such as lithium niobate (LiNbO3) or thin-film zinc oxide (ZnO) …”