High Frequency Sonoprocessing: A New Field of Cavitation‐Free Acoustic Materials Synthesis, Processing, and Manipulation

Abstract

Ultrasound constitutes a powerful means for materials processing. Similarly, a new field has emerged demonstrating the possibility for harnessing sound energy sources at considerably higher frequencies (10 MHz to 1 GHz) compared to conventional ultrasound (⩽3 MHz) for synthesizing and manipulating a variety of bulk, nanoscale, and biological materials. At these frequencies and the typical acoustic intensities employed, cavitation-which underpins most sonochemical or, more broadly, ultrasound-mediated processes-is largely absent, suggesting that altogether fundamentally different mechanisms are at play. Examples include the crystallization of novel morphologies or highly oriented structures; exfoliation of 2D quantum dots and nanosheets; polymer nanoparticle synthesis and encapsulation; and the possibility for manipulating the bandgap of 2D semiconducting materials or the lipid structure that makes up the cell membrane, the latter resulting in the ability to enhance intracellular molecular uptake. These fascinating examples reveal how the highly nonlinear electromechanical coupling associated with such high-frequency surface vibration gives rise to a variety of static and dynamic charge generation and transfer effects, in addition to molecular ordering, polarization, and assembly-remarkably, given the vast dimensional separation between the acoustic wavelength and characteristic molecular length scales, or between the MHz-order excitation frequencies and typical THz-order molecular vibration frequencies.

Sonoporation: Past, Present, and Future

“…When acoustic pressures are sufficiently high (e.g., 0.3-1.0 MPa at ≈1 MHz), [89][90][91][92] bubble collapse can be induced by acoustic waves thus generating a strong 'jetting' flow (i.e., fluid streaming), [93,94] which can further rupture the membrane of an adjacent cell as illustrated in Figure 1a. In addition to pressure, the inertial cavitation performance is dependent on acoustic wave frequency, [90][91][92]95,96] pulse repetition rate, [89] pulse duration, [89] initial bubble radius, [91,92] bubble properties, [90,95] temperature, [97] fluid properties, [90,98] wave-type, [99,100] and device energy efficiency. [99,100] Apart from the 'jetting' effect, inertial cavitation is also associated with shock waves generated from the bubble collapse.…”

Jean-Louis Luche and the Interpretation of Sonochemical Reaction Mechanisms

“…It was therefore a pleasure to find that in 2020 Yeo et al from RMIT University in Melbourne Australia published a review article entitled “High Frequency Sonoprocessing: A New Field of Cavitation-Free Acoustic Materials Synthesis, Processing, and Manipulation” [ 37 ]. In this review using much higher frequencies than normally associated with sonochemistry evidence is provided for sonoprocessing in the absence of cavitation.…”

Acoustic Platform for MXene Synthesis and Electrochemical Behaviour of i-MXenes in Aqueous Electrolytes

“…The high pressures build up a high localized energy that can accelerate the solution drop up to ~100 m s -2 . We can implement the input power of the wave to match the required application such as mixing or jetting at moderate powers and nebulization or liquid dissociation at the high powers (40) .…”

“…Generally, the SAW device technology is not new, it has been used intensively in many industrial fields ranging from telecommunication to gas sensing devices (37,39) . Nowadays, millions of the SAW devices are commonly used in electronic circuits, signal filtration, gas sensor, flow measurements, microfluidics and recently in the field of material synthesis (40)(41)(42)(43) . In principle, we will discuss in this chapter the traditional Rayleigh SAW that is widely used in the microfluidic devices.…”