Propagation of ultrasonic wave in magnetic Pickering emulsion under DC magnetic field

A Pickering emulsion is an emulsion stabilized by solid particles accumulated at the surface of droplets. It is also possible to create a stable Pickering emulsion stabilized by ferromagnetic iron oxide nanoparticles to make it susceptible to magnetic fields. This type of emulsion has received great research interest in recent years because it has generated and holds the promise of a variety of practical applications. One interesting application is magnetic separation in the gradient magnetic field. However, the real-time characterization of magnetic Pickering emulsions, especially under external stimuli such as magnetic fields, is generally challenging. We used a convenient method to control the properties of magnetic particle-stabilized emulsions via the ultrasound technique. In the experiments, we investigated the attenuation of ultrasound using ultrasonic spectroscopy as a function of the magnetic particle concentration and magnetic field intensity. The analysis of ultrasonic waves as a function of frequency provided information about the movement of magnetic Pickering droplets during magnetic separation. The results showed much weaker separation for a low magnetic particles concentration as the magnetic force was not sufficient to induce significant droplets movement, whereas for a high concentration the magnetic separation occurred very dynamically.