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.

The effect of magnetic field on the structure formation in an oil-based magnetic fluid with various concentrations of magnetite particles was studied. The evaluation of the experimental data obtained from small-angle X-ray scattering and ultrasonic attenuation indicates the formation of chain-like aggregates composed of magnetite particles. The experimental data obtained from ultrasonic spectroscopy fit well with the recent theoretical model by Shliomis, Mond and Morozov but only for a diluted magnetic fluid. In this model it is assumed that a dimer is the main building block of a B -field-induced chain-like structure, thus the estimation of the nematic order parameter does not depend on the actual length of the structure. The scattering method used reveals information about the aggregated structure size and relative changes in the degree of anisotropy in qualitative terms. The coupling constant $ \lambda$ , concentrations $ \phi$ , average particle size d and its polydispersity $ \sigma$ were initially obtained using the vibrating sample magnetometry and these results were further confirmed by rheometry and scattering methods. Both the particles’ orientational distribution and the nematic order parameter S were inferred from the ultrasonic measurements. The investigation of SAXS patterns reveals the orientation and sizes of aggregated structures under application of different magnetic-field strengths. In addition, the magnetic-field-dependent yield stress was measured, and a relationship between the yield stress and magnetic-field strength up to 0.5T was established.

Ultrasonic hyperthermia is a method of cancer treatment in which tumors are exposed to an elevated cytotoxic temperature using ultrasound (US). In conventional ultrasonic hyperthermia, the ultrasound-induced heating in the tumor is achieved through the absorption of wave energy. However, to obtain appropriate temperature in reasonable time, high US intensities, which can have a negative impact on healthy tissues, are required. The effectiveness of US for medical purposes can be significantly improved by using the so-called sonosensitizers, which can enhance the thermal effect of US on the tissue by increasing US absorption. One possible candidate for such sonosensitizers is magnetic nanoparticles with mean sizes of 10–300 nm, which can be efficiently heated because of additional attenuation and scattering of US. Additionally, magnetic nanoparticles are able to produce heat in the alternating magnetic field (magnetic hyperthermia). The synergetic application of ultrasonic and magnetic hyperthermia can lead to a promising treatment modality.

One-dimensional conductive particle assembly holds promise for a variety of practical applications, in particular for a new generation of electronic devices. However, synthesis of such chains with programmable shapes outside a liquid environment has proven difficult. Here we report a route to simply ‘pull’ flexible granular and colloidal chains out of a dispersion by combining field-directed assembly and capillary effects. These chains are automatically stabilized by liquid bridges formed between adjacent particles, without the need for continuous energy input or special particle functionalization. They can further be deposited onto any surface and form desired conductive patterns, potentially applicable to the manufacturing of simple electronic circuits. Various aspects of our route, including the role of particle size and the voltages needed, are studied in detail. Looking towards practical applications, we also present the possibility of two-dimensional writing, rapid solidification of chains and methods to scale up chain production.