Particles adsorbed at various non-aqueous liquid-liquid interfaces

Particles adsorbed at liquid interfaces are commonly used to stabilise water-oil Pickering emulsions and water-air foams. The fundamental understanding of the physics of particles adsorbed at water-air and water-oil interfaces is improving significantly due to novel techniques that enable the measurement of the contact angle of individual particles at a given interface. The case of non-aqueous interfaces and emulsions is less studied in the literature. Non-aqueous liquid-liquid interfaces in which water is replaced by other polar solvents have properties similar to those of water-oil interfaces. Nanocomposites of non-aqueous immiscible polymer blends containing inorganic particles at the interface are of great interest industrially and consequently more work has been devoted to them. By contrast, the behaviour of particles adsorbed at oil-oil interfaces in which both oils are immiscible and of low dielectric constant (ε < 3) is scarcely studied. Hydrophobic particles are required to stabilise these oil-oil emulsions due to their irreversible adsorption, high interfacial activity and elastic shell behaviour

Rough and Hollow Spherical Magnetite Microparticles: Revealing the Morphology, Internal Structure, and Growth Mechanism

We report the fabrication, characterization, and a tentative growth mechanism of spherical microparticles with a rough surface fabricated by oxidative aging of ferrous hydroxide. The aging involves the transformation of ferrous hydroxide into Fe₃O₄ and the growth of the magnetite particles. Scanning electron microscopy, focused ion beam, and transmission electron microscopy studies of the spherical microparticles show that they have a small void in the center and that they are polycrystalline with a typical grain size of 150 nm. The crystallites are oriented along the radial direction of the spheres, stretching themselves from the central cavity to the particle surface, and their crystalline orientations do not keep any obvious relationship. The collected data and the structure suggest that the microparticles’ growth mechanism has four main stages: (1) initial nucleation of small magnetite nanoparticles, (2) aggregation to form spherical polycrystalline clusters, (3) direct crystal growth from species in solution, and (4) development of the outer facets. Magnetization measurements are in agreement with the observed crystalline structure. Both X-ray powder diffraction and magnetization measurements indicate that the stoichiometry of these particles is slightly oxidized with respect to Fe₃O₄

Interfacial Activity of Gold Nanoparticles Coated with a Polymeric Patchy Shell and the Role of Spreading Agents

Gold patchy nanoparticles (PPs) were prepared under surfactant-free conditions by functionalization with a binary ligand mixture of polystyrene and poly­(ethylene glycol) (PEG) as hydrophobic and hydrophilic ligands, respectively. The interfacial activity of PPs was compared to that of homogeneous hydrophilic nanoparticles (HPs), fully functionalized with PEG, by means of pendant drop tensiometry at water/air and water/decane interfaces. We compared interfacial activities in three different spreading agents: water, water/chloroform, and pure chloroform. We found that the interfacial activity of PPs was close to zero (∼2 mN/m) when the spreading agent was water and increased to ∼14 mN/m when the spreading agent was water/chloroform. When the nanoparticles were deposited with pure chloroform, the interfacial activity reached up to 60 mN/m by compression. In all cases, PPs exhibited higher interfacial activity than HPs, which were not interfacially active, regardless of the spreading agent. The interfacial activity at the water/decane interface was found to be significantly lower than that at the water/air interface because PPs aggregate in decane. Interfacial dilatational rheology showed that PPs form a stronger elastic shell at the pendant drop interface, compared to HPs. The significantly high interfacial activity obtained with PPs in this study highlights the importance of the polymeric patchy shell and the spreading agent