Ultrasound-Induced Adsorption of Acousto-Responsive Microgels at Water-Oil Interface

Ultrasonic mixing is a well-established method to disperse and mix substances. However, the effects of ultrasound on dispersed soft particles as well as on their adsorption kinetics at interfaces remain unexplored. Ultrasound not only accelerates the movement of particles via acoustic streaming, but recent research indicates that it can also manipulate the interaction of soft particles with the surrounding liquid. In this study, it evaluates the adsorption kinetics of microgel at the water-oil interface under the influence of ultrasound. It quantifies how acoustic streaming accelerates the reduction of interfacial tension. It uses high-frequency and low-amplitude ultrasound, which has no destructive effects. Furthermore, it discusses the ultrasound-induced shrinking and thus interfacial rearrangement of the microgels, which plays a secondary but non-negligible role on interfacial tension reduction. It shows that the decrease in interfacial tension due to the acoustic streaming is stronger for microgels with higher cross-linker density. Moreover, it shows that ultrasound can induce a reversible decrease in interfacial tension due to the shrinkage of microgels at the interface. The presented results may lead to a better understanding in any field where ultrasonic waves meet soft particles, e.g., controlled destabilization in foams and emulsions or systems for drug release. High-frequency ultrasound accelerates the adsorption kinetics of PNIPAM microgels at water-oil interfaces leading to a faster decrease in interfacial tension. This acceleration is attributed to the increased transport velocity of microgels facilitated by acoustic streaming. Additionally, PNIPAM microgels are responsive to high-frequency ultrasound at the interface and thus undergo a volume phase transition, resulting in a reduction in interfacial tension.image

Automated summary

This study investigates the effects of ultrasound on dispersed soft particles and their adsorption kinetics at interfaces. The results show that ultrasound not only accelerates particle movement but also manipulates particle interaction with the surrounding liquid. High-frequency and low-amplitude ultrasound are found to speed up the adsorption kinetics of microgels at water-oil interfaces, leading to a reduction in interfacial tension.