Droplets covered by adsorbed particles are used in a wide range of research studies and applications, including stabilising emulsions used in the food or cosmetic industries, and fabricating new materials, such as microcapsules or multi-cavity structures. Pickering emulsions are commonly prepared by bulk emulsification techniques, for instance, by ultrasonic homogenisation or mechanical stirring, by membrane emulsification, or with the use of microfluidics. The latter two methods typically allow for more precise control of the droplet size distribution, whereas the bulk techniques guarantee high throughput. Here we propose a new bulk approach to fabricating Pickering emulsions by utilising electric fields. We prepare oil-in-oil emulsions stabilised by microparticles and control the mean size of the Pickering droplets. In our approach we take advantage of total surface area reduction of emulsion droplets by electrocoalescence. This leads to an increase in particle coverage, and eventually to formation of densely packed particle shells on Pickering droplets. First, we prepare an unstable pre-emulsion with droplets having small sizes and low particle coverages, from which the final Pickering emulsion is formed via consecutive coalescence events speeded up by application of electric fields. We monitor the development of the emulsions with optical microscopy imaging. The results demonstrate that the utilisation of electric fields goes beyond the mere role of enhancing coalescence; it plays an important role in surface particle manipulation and droplet rotation that further promote formation of stable particle-covered drops.

During hyperthermia, magnetite nanoparticles placed in an AC magnetic field become a source of heat. It has been shown that in fluid suspensions, magnetic particles move freely and generate heat easily. However, in tissues of different mechanical properties, nanoparticle movement is limited and leads to a small temperature rise in tissue. Therefore, it is crucial to conduct magnetic hyperthermia experiments in similar conditions to the human body. The effect of tissue-mimicking phantom compressibility on the effectiveness of magnetic hyperthermia was investigated on agar phantoms. Single and cluster nanoparticles were synthesized and used as magnetic materials. The prepared magnetic materials were characterized by transmission electron microscopy (TEM), and zeta potential measurements. Results show that tissue-mimicking phantom compressibility decreases with the concentration of agar. Moreover, the lower the compressibility, the lower the thermal effect of magnetic hyperthermia. Specific absorption rate (SAR) values also proved our assumption that tissue-mimicking phantom compressibility affects magnetic losses in the alternating magnetic field (AMF).

Hyperthermia treatment is the heating of tumor tissue up to temperatures between 41 ¥ C and 45 ¥ C, which trigger several physiological reactions in the body. Hyperthermia within tissue can be applied through various mechanisms. One of them is magnetic hyperthermia which uses superparamagnetic iron oxide nanoparticles (SPIONs) heated by an externally applied magnetic field. SPIONs can also be used as sonosensitizers in ultrasound hyperthermia increasing acoustic wave attenuation. The impact of SPION concentration on thermal effect during ultrasonic and magnetic hyperthermia was investigated in agar-gel phantom with added magnetite nanoparticles. The presence of nanoparticles in the tissue-mimicking phantom increases the thermal losses of ultrasound energy and temperature of the phantom.

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Pickering emulsions (particle-stabilized emulsions) are usually considered because of their unique properties compared to surfactant-stabilized emulsions including better stability against emulsion aging. However, the interesting feature of particle-stabilized emulsions could be revealed during their magnetic heating. When magnetic particles constitute a shell around droplets and the sample is placed in an alternating magnetic field, a temperature increase appears due to energy dissipation from magnetic relaxation and hysteresis within magnetic particles. We hypothesize that the solidity of the magnetic particle shell around droplets can influence the process of heat transfer from inside the droplet to the surrounding medium. In this way, particle-stabilized emulsions can be considered as materials with changeable heat transfer. We investigated macroscopically heating and cooling of oil-in-oil magnetic Pickering emulsions with merely packed particle layers and these with a stable particle shell. The change in stability of the shell was obtained here by using the coalescence of droplets under the electric field. The results from calorimetric measurements show that the presence of a stable particle shell caused a slower temperature decrease in samples, especially for lower intensities of the magnetic field. The retarded heat transfer from magnetic Pickering droplets can be utilized in further potential applications where delayed heat transfer is desirable.

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Particle-stabilised emulsions are of interest to many scientists in both academia and industry as they hold promise for numerous applications. There is a lot of research effort put into developing new methods for their fabrication. Often, different experimental techniques are used for monitoring the process of the emulsion formation. However, the control of the emulsion fabrication and its real-time characterisation is generally challenging. In this work, we propose a convenient method to control fabrication of Pickering emulsions using ultrasound. The benefit of acoustical measurements compared to other techniques is their ability to test the medium in a non-destructive way, without requiring special sample preparation (e.g. dilution like in the case of DLS or NMR) nor a usage of thin sample cells (e.g. in the case of optical microscopy). Here, ultrasonic measurements are able to follow droplets growth during the emulsion development using the limited coalescence approach. We found that ultrasonic attenuation increased with the droplet size within the time frame of droplet stabilisation. Following these changes in ultrasonic attenuation enabled the study of macroscopic behaviour—for example, estimation of a time when droplets achieve their final size and become fully covered by solid particles. These results are compared with the results obtained from the optical measurements. We also make an attempt to theoretically describe ultrasound propagation in particle-stabilised emulsions by comparing our experimental results with the scattering theory ECAH for emulsions.