Ultrasound‐Induced Adsorption of Acousto‐Responsive Microgels at Water–Oil Interface

Abstract

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.

Dynamic light scattering for particle characterization subjected to ultrasound: a study on compact particles and acousto-responsive microgels

“…One of the external fields that have drawn attention in recent decades is the US which is employed to manipulate the physical or chemical properties of particles and molecules with applications in drug delivery 14 , catalysis 15 and materials synthesis 16 . Recently, we showed that the high-frequency US, in its non-destructive condition (low amplitude), can be used as a stimulus to induce a phase transition in solutions of linear poly(N-Isopropylacrylamide)(PNIPAM) 17,18 and also PNIPAM microgels at an oil-water interface 19 . The dehydration of PNIPAM which is usually triggered by increasing the temperature above the lower critical solution temperature (LCST), is then induced by the US.…”