The Effect of Particle Shell on Cooling Rates in Oil-in-Oil Magnetic Pickering Emulsions

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.

Light-driven Pickering interfacial catalysis for the oxidation of alkenes at near-room temperature

“…However, no appreciable temperature change occurs upon further increasing the Au amount to 26 and 40 μg, encompassing a concomitant increase of the amount of Au/SiO 2 –C 3 NPs in the system. This observation indicates a poorer heat transfer to the continuous phase at higher Au/SiO 2 –C 3 NP loading, which can be attributed to two main reasons: (1) a high viscosity of the emulsion system that might hinder heat transfer from the water/toluene interface to the bulk phases 20 and (2) a denser packing of Au/SiO 2 –C 3 NPs at the inner and outer interface of the droplets. As a result, the local temperature of the interfacial shell is expected to be much higher than the bulk temperature, with photon absorption.…”

Pickering Emulsions as Templates for Architecting Composite Structures

“…Molecular brush surfactants have also been reported to stabilize o/o emulsions, even at high internal phase through interfacial jamming of the polymeric brushes . Recently, Pickering surfactants have emerged for the stabilization of o/o emulsions, again imparting steric stabilization to the interface, and not solely relying on decreasing the interfacial tension. , For example, fumed silica particles, with hydrocarbon groups or fluorocarbon chains, fluoro-silicone particles, plate-like fluorinated calcium lauryl taurate particles, Shigaite-like clay, polystyrene particles, silica particles, diblock copolymer particles, , alkylated cellulose, and magnetic particles have been reported to stabilize these nonaqueous interfaces …”

“…26,30 For example, fumed silica particles, with hydrocarbon groups or fluorocarbon chains, fluoro-silicone particles, 31 plate-like fluorinated calcium lauryl taurate particles, 32 Shigaite-like clay, 33 polystyrene particles, 34 silica particles, 35 diblock copolymer particles, 36,37 alkylated cellulose, 38 and magnetic particles have been reported to stabilize these nonaqueous interfaces. 39 The Pentzer lab developed alkylated graphene oxide (GO) nanosheets for the stabilization of o/o emulsions (Figure 2).…”

Nonaqueous Emulsion Polycondensation Enabled by a Self‐Assembled Cage‐like Surfactant

“…O/o emulsions bear potential to realize a larger scope of water‐sensitive applications such as the stabilization of hydrolytically unstable compounds, [66] serving as vehicles in drug delivery,[ 67 , 68 ] finding use in material science,[ 69 , 70 ] and the synthesis of polymer products. [ 58 , 71 , 72 ] In particular, emulsion polymerization is a research topic of high interest because it allows control over the synthesis of polymer‐based functional nano‐objects such as globules or capsules with well‐defined sizes and morphologies.…”