Sculpting and Aerosolizing Pinned Liquid Films With Localized Acoustic Pressures of Surface Acoustic Waves

2012 ◽  
Author(s):  
Daniel Taller ◽  
Hsueh-Chia Chang ◽  
David B. Go
Keyword(s):  
Contact Angle ◽  
Numerical Modeling ◽  
Contact Line ◽  
Acoustic Waves ◽  
Acoustic Pressure ◽  
Surface Acoustic Waves ◽  
Liquid Films ◽  
Solid Substrate ◽  
Planar Surface ◽  
Bulk Film

Due to viscous decay, a planar surface acoustic wave (SAW) diffracting from a solid substrate into a liquid film produces a time-averaged, exponentially decaying acoustic pressure in the film. We show that if the film is pinned against a bounding wall, the localized acoustic pressure generates a sequence of surface drops at the contact line, whose dimensions decay in the same exponential manner as the localized acoustic pressure. The undulating interfacial profile near the contact line also inherits this exponential decay, such that the averaged contact angle is exponentially small. The bulk film topology and the aerosolization mechanism are hence insensitive to the wettability of the surface but are controlled only by the localized acoustic pressure and the decaying undulations it produces at the contact line. The size distribution of surface drops is collapsed under the exponential scaling that depends only on the SAW decay rate and amplitude. Numerical modeling based on the Young-Laplace equation is used to model the liquid profile and to predict two aerosolization regimes.

scholarly journals Visualization of Surface Acoustic Waves in Thin Liquid Films

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
R. W. Rambach ◽  
J. Taiber ◽  
C. M. L. Scheck ◽  
C. Meyer ◽  
J. Reboud ◽  
...  
Keyword(s):  
Liquid Film ◽  
Acoustic Waves ◽  
Low Cost ◽  
Thin Liquid Film ◽  
Surface Acoustic Waves ◽  
Liquid Films ◽  
Theoretical Description ◽  
Propagation Path ◽  
Microfluidic Channels ◽  
Potential Applications

Abstract We demonstrate that the propagation path of a surface acoustic wave (SAW), excited with an interdigitated transducer (IDT), can be visualized using a thin liquid film dispensed onto a lithium niobate (LiNbO3) substrate. The practical advantages of this visualization method are its rapid and simple implementation, with many potential applications including in characterising acoustic pumping within microfluidic channels. It also enables low-cost characterisation of IDT designs thereby allowing the determination of anisotropy and orientation of the piezoelectric substrate without the requirement for sophisticated and expensive equipment. Here, we show that the optical visibility of the sound path critically depends on the physical properties of the liquid film and identify heptane and methanol as most contrast rich solvents for visualization of SAW. We also provide a detailed theoretical description of this effect.

scholarly journals Double flow reversal in thin liquid films driven by megahertz-order surface vibration

2014 ◽  
Vol 470 (2169) ◽  
pp. 20130765 ◽  
Author(s):  
Amgad R. Rezk ◽  
Ofer Manor ◽  
Leslie Y. Yeo ◽  
James R. Friend
Keyword(s):  
Thin Films ◽  
Acoustic Waves ◽  
Surface Acoustic Waves ◽  
Intermolecular Forces ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Propagation Direction ◽  
Flow Reversal ◽  
Order Surface ◽  
Over Time

Arising from an interplay between capillary, acoustic and intermolecular forces, surface acoustic waves (SAWs) are observed to drive a unique and curious double flow reversal in the spreading of thin films. With a thickness at or less than the submicrometre viscous penetration depth, the film is seen to advance along the SAW propagation direction, and self-similarly over time t 1/4 in the inertial limit. At intermediate film thicknesses, beyond one-fourth the sound wavelength λ ℓ in the liquid, the spreading direction reverses, and the film propagates against the direction of the SAW propagation. The film reverses yet again, once its depth is further increased beyond one SAW wavelength. An unstable thickness region, between λ ℓ /8 and λ ℓ /4, exists from which regions of the film either rapidly grow in thickness to exceed λ ℓ /4 and move against the SAW propagation, consistent with the intermediate thickness films, whereas other regions decrease in thickness below λ ℓ /8 to conserve mass and move along the SAW propagation direction, consistent with the thin submicrometre films.

Effects of contact angle hysteresis on drop manipulation using surface acoustic waves

2020 ◽  
Vol 34 (1-2) ◽  
pp. 145-162 ◽  
Author(s):  
Mahdi Sheikholeslam Noori ◽  
Mohammad Taeibi Rahni ◽  
Arash Shams Taleghani
Keyword(s):  
Contact Angle ◽  
Acoustic Waves ◽  
Contact Angle Hysteresis ◽  
Surface Acoustic Waves

scholarly journals Acoustophoretic Control of Microparticle Transport Using Dual-Wavelength Surface Acoustic Wave Devices

Micromachines ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 52 ◽  
Author(s):  
Jin-Chen Hsu ◽  
Chih-Hsun Hsu ◽  
Yeo-Wei Huang
Keyword(s):  
Particle Motion ◽  
Acoustic Waves ◽  
Acoustic Pressure ◽  
Acoustic Radiation ◽  
Surface Acoustic Waves ◽  
Microfluidic Channel ◽  
Radiation Force ◽  
Dual Wavelength ◽  
Single Frequency ◽  
Motion Trajectories

We present a numerical and experimental study of acoustophoretic manipulation in a microfluidic channel using dual-wavelength standing surface acoustic waves (SSAWs) to transport microparticles into different outlets. The SSAW fields were excited by interdigital transducers (IDTs) composed of two different pitches connected in parallel and series on a lithium niobate substrate such that it yielded spatially superimposed and separated dual-wavelength SSAWs, respectively. SSAWs of a singltablee target wavelength can be efficiently excited by giving an RF voltage of frequency determined by the ratio of the velocity of the SAW to the target IDT pitch (i.e., f = cSAW/p). However, the two-pitch IDTs with similar pitches excite, less efficiently, non-target SSAWs with the wavelength associated with the non-target pitch in addition to target SSAWs by giving the target single-frequency RF voltage. As a result, dual-wavelength SSAWs can be formed. Simulated results revealed variations of acoustic pressure fields induced by the dual-wavelength SSAWs and corresponding influences on the particle motion. The acoustic radiation force in the acoustic pressure field was calculated to pinpoint zero-force positions and simulate particle motion trajectories. Then, dual-wavelength SSAW acoustofluidic devices were fabricated in accordance with the simulation results to experimentally demonstrate switching of SSAW fields as a means of transporting particles. The effects of non-target SSAWs on pre-actuating particles were predicted and observed. The study provides the design considerations needed for the fabrication of acoustofluidic devices with IDT-excited multi-wavelength SSAWs for acoustophoresis of microparticles.

Particle Separation inside a Sessile Droplet with Variable Contact Angle Using Surface Acoustic Waves

2016 ◽  
Vol 89 (1) ◽  
pp. 736-744 ◽  
Author(s):  
Ghulam Destgeer ◽  
Jin Ho Jung ◽  
Jinsoo Park ◽  
Husnain Ahmed ◽  
Hyung Jin Sung
Keyword(s):  
Contact Angle ◽  
Acoustic Waves ◽  
Surface Acoustic Waves ◽  
Particle Separation ◽  
Sessile Droplet

Inertial effects in time-dependent motion of thin films and drops

2002 ◽  
Vol 467 ◽  
pp. 1-17 ◽  
Author(s):  
L. M. HOCKING ◽  
S. H. DAVIS
Keyword(s):  
Thin Films ◽  
Contact Angle ◽  
Contact Line ◽  
Evolution Equations ◽  
Liquid Films ◽  
Contact Angles ◽  
Terminal State ◽  
Lubrication Theory ◽  
Plate Motion ◽  
Special Cases

Capillarity is an important feature in controlling the spreading of liquid drops and in the coating of substrates by liquid films. For thin films and small contact angles, lubrication theory enables the analysis of the motion to be reduced to single evolution equations for the heights of the drops or films, provided the inertia of the liquid can be neglected. In general, the presence of inertia destroys the major simplification provided by lubrication theory, but two special cases that can be treated are identified here. In the first example, the approach of a drop to its equilibrium position is studied. For sufficiently low Reynolds numbers, the rate of approach to the terminal state and the contact angle are slightly reduced by inertia, but, above a critical Reynolds number, the approach becomes oscillatory. In the latter case there is no simple relation connecting the dynamic contact angle and contact-line speed. In the second example, the spreading drop is supported by a plate that is forced to oscillate in its own plane. For the parameter range considered, the mean spreading is unaffected by inertia, but the oscillatory motion of the contact line is reduced in magnitude as inertia increases, and the drop lags behind the plate motion. The oscillatory contact angle increases with inertia, but is not in phase with the plate oscillation.

scholarly journals A conservative saint-venant type model to describe the dynamics of thin partially wetting films with regularized forces at the contact line

2020 ◽  
Vol 69 ◽  
pp. 79-103
Author(s):  
Pierre Trontin ◽  
Julien Lallement ◽  
Philippe Villedieu
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Driving Forces ◽  
Mesh Size ◽  
Capillary Forces ◽  
Liquid Films ◽  
Industrial Applications ◽  
Type Model ◽  
Finite Volume Scheme ◽  
Mesh Resolution

This paper deals with the numerical simulation of thin liquid films flowing on partially wetting solid substrates. A 2D Saint-Venant like model is proposed. Its originality lies in the conservative formulation of the capillary forces and in the model used for the disjoining pressure that accounts for the contact line capillary forces. A finite volume scheme is proposed for the resolution of the system and various numerical examples are presented and discussed. In particular, when the mesh resolution is fine enough, the model is proved to be able to predict correctly the spreading of a film with the exact contact angle in the vicinity of the contact line. When the mesh size is larger than the film thickness (which could be the case for many industrial applications), it is of course no longer possible to recover the contact angle. However, the model is proved to correctly predict the spreading of the film. This important feature is related to the thermodynamic consistency of the model in the sense that the latter ensures by construction the decrease of the film total free energy in the absence of external driving forces.

Effects of Acoustic Waves on Buried Tunnel Structures Under an Impact Load

2017 ◽  
Vol 17 (01) ◽  
pp. 1750003 ◽  
Author(s):  
S. R. Massah ◽  
M. M. Torabipour
Keyword(s):  
Soil Type ◽  
Acoustic Waves ◽  
Acoustic Pressure ◽  
Impact Load ◽  
Underground Structure ◽  
Surface Acoustic Waves ◽  
Ground Surface ◽  
Sound Waves ◽  
Arbitrary Location ◽  
Two Parameters

In this paper, the transmission and reflection of acoustic waves into and from an underground tunnel are investigated by producing an impact load on the ground and measuring the acoustic pressure levels at different time intervals. For this purpose, a sound detector is placed on the ground and then from an arbitrary location on the surface, acoustic waves are transmitted into the ground from an acoustic source. The pressure levels of acoustic waves transmitted into the tunnel space and reflected back to the ground surface are measured, and the effects of several parameters on the attenuation of acoustic pressure levels of transmitted and reflected sound waves are evaluated. Moreover, the effects of parameters such as soil type, concrete type and thickness, buried depth of the underground structure and also the effect of acoustic absorbers on the transmission, propagation and reflection of acoustic waves into and from the tunnel are investigated. The results obtained indicate that the two parameters of soil type and buried depth have the greatest effect on the transmission of acoustic waves, whereas all the parameters considered are important with regard to the reflection of acoustic waves. In addition, it was observed that the use of acoustic absorbers in tunnel structures has a significant effect on the attenuation of transmitted and reflected acoustic waves.

scholarly journals Effect of the internal pressure on oscillations of a cylindrical gas bubble

2020 ◽  
pp. 51-62
Author(s):  
A. A. Alabuzhev ◽  
Keyword(s):  
Contact Angle ◽  
Finite Volume ◽  
Contact Line ◽  
Incompressible Liquid ◽  
Axial Direction ◽  
Solid Substrate ◽  
Forced Oscillations ◽  
Gas Bubble ◽  
Natural Oscillations ◽  
Round Cylinder

Natural and forced oscillations of a gas bubble are studied. The bubble has the shape of a round cylinder in the state of equilibrium. It is bounded in the axial direction by two parallel solid surfaces and is surrounded by an incompressible liquid of a finite volume with a free outer surface. The entire system is under an alternating pressure field. The velocity of the contact line of three media (gas-liquid-solid substrate) is proportional to the deviation of the contact angle from the equilibrium value. The frequency of eigenmodes of a gas bubble can increase with an increase in the Hocking parameter, in contrast to the frequencies of an incompressible liquid drop, which only decrease. It is shown that radial oscillations of a cylindrical bubble are possible only in a finite volume of liquid. The effect of crossing the modes of natural oscillations is considered for the dissipative case. The amplitude-frequency characteristics are constructed for different values of the internal gas pressure. Resonance phenomena are found. It is shown that the external influence excites, first of all, volumetric oscillations of the bubble. Variations in shape are caused by the movement of the contact line. Expressions are found for the vibration amplitude in the case of a fixed contact line and a fixed contact angle.

scholarly journals Erratum: Corrigendum: Visualization of Surface Acoustic Waves in Thin Liquid Films

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
R. W. Rambach ◽  
J. Taiber ◽  
C. M. L. Scheck ◽  
C. Meyer ◽  
J. Reboud ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Surface Acoustic Waves ◽  
Liquid Films ◽  
Thin Liquid Films
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