Ultrasound and Rheological Study of Oil-In-Oil Magnetic Pickering Emulsions

Magnetic Pickering emulsion is a type of heterogeneous system consisting of stabilized immiscible liquid droplets stabilized with insoluble solid particles, such as magnetic nanoparticles. The control of the formation process and stability of such a three-phase system material is important from the application point of view. Moreover, due to its possible biocompatibility and high cargo-loading capacity, magnetic Pickering emulsions hold significant promise in biomedical and pharmaceutical applications, including therapeutic delivery and bioseparation.<br/>This research primarily focused on characterizing magnetic Pickering emulsion stabilized using various volume concentrations of magnetic nanoparticles and with two distinct formation processes involving ultrasound homogenization and electric field. Ultrasound scattering theory, based on a so-called core-shell model, was employed to analyze ultrasound propagation through such a magnetic three-phase system. Additionally, rheological properties were measured to examine changes in the internal structure when subjected to a static magnetic field. The Herschel-Bulkley model was applied to determine the yield stress based on magnetorheology measurements. Optical microscopy was employed to verify optical changes in the system resulting from different formation processes.<br/>The ultrasound spectroscopy results demonstrated variations in attenuation associated with different magnetic shell thicknesses, core radii, and concentrations. Fitting experimental data to the core-shell model revealed the relationship between volume concentrations and both core and shell sizes. Higher particle concentrations were found to result in a greater number of particles at the droplet interface [1], directly affecting the radius of magnetic Pickering droplets, aligning with the findings of another study [2]. Furthermore, higher volume ratios of magnetic nanoparticles exhibited a more pronounced magnetoviscous effect. Additionally, the formation process involving an electric field yielded higher dynamic yield stress [3].<br/>This work was supported by project no. 2019/35/O/ST3/00503 (PRELUDIUM BIS) of the Polish National Science Centre.<br/><br/>Reference<br/>[1] Jameel, B., Bielas, R. and Józefczak, A., 2023. Ultrasound measurements of particle shells in magnetic Pickering emulsions. <i>Measurement</i>, <i>220</i>, p.113409.<br/>[2] Rozynek, Z., Bielas, R. and Józefczak, A., 2018. Efficient formation of oil-in-oil Pickering emulsions with narrow size distributions by using electric fields. Soft Matter, 14(24), pp.5140-5149.<br/>[3] Jameel, B., Paulovičová, K., Tóthová, J., Rajnák, M., Molčan, M., Bielas, R. and Józefczak, A., Magnetorheological characterization of oil-in-oil magnetic Pickering emulsions. <i>Journal of Magnetism and Magnetic Materials</i>, submitted 2023.