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Abstract
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.
Highlights
Emulsions are ubiquitous systems utilized in a very broad range of industrial branches, in medicine, and in our daily life
The dynamics were affected by the type of magnetic particles and the intensity of the magnetic field, i.e., the size of particles influences the heating efficiency owing to the increasing effect of hysteresis losses on the overall heat generation
We evaluated the process of cooling in emulsion systems stabilized with magnetic particles
Summary
Emulsions are ubiquitous systems utilized in a very broad range of industrial branches, in medicine, and in our daily life. Emulsions stabilized with surfactants have been gradually replaced by Pickering emulsions, i.e., emulsions stabilized with particles rather than surface-active chemicals Such systems are indicated as more eco-friendly promising materials for food processing [1,2], industrial applications such as oil recovery [3,4] or protection of wood [5], and formulation of new pharmaceutics [6,7]. The alternating magnetic field can induce relaxation processes (namely Néel and Brown) or magnetic hysteresis in magnetic particles that lead to losses of magnetic energy [9] This energy dissipation is converted into heat, which is a well-known fact utilized, among others, in magnetic hyperthermia therapies [10,11] and magnetically-induced catalysis to perform reactions such as CO2 methanation [12]. This fact makes the heating generated in magnetic Pickering emulsions the potential object of interest
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