Colloidal Aggregation in Mixtures of Partially Miscible Liquids by Shear-Induced Capillary Bridges

We have studied shear-induced aggregation of colloidal silica particles suspended in a variety of partially miscible liquid mixtures. The shared characteristic of the investigated systems is that after liquid–liquid phase separation of the binary liquid mixtures one phase completely wets the particles. We have explored compositions where there are insufficient quantities of the particle wetting component to induce phase separation. As the proportion of the wetting component is increased, we find a significant concentration range where shear-induced aggregation takes place. The macroscopic characteristics of this phenomenon are demonstrated, for which observations were greatly facilitated by mostly using liquid pairs partially miscible at room temperature. Measurements revealing the adsorption of the minority component to colloidal particles show that capillary condensation between particles causes the observed aggregation. The likely microscopic features underlying this aggregation behavior are then discussed. Finally, the overall picture of these systems is sketched as a nonequilibrium liquid–liquid phase diagram, in which outside the binodal there is a region of shear-induced aggregation

Making Non-aqueous High Internal Phase Pickering Emulsions: Influence of Added Polymer and Selective Drying

We report the first example of a non-aqueous (oil-in-oil) Pickering high internal phase emulsion (HIPE) stabilized by chemically modified fumed silica. In this case, a 75 vol % ethylene carbonate (EC)-rich internal phase is emulsified in 25 vol % <i>p</i>-xylene (xylene)-rich continuous phase using interfacial nanoparticles. It is revealed that no phase inversion takes place during the HIPE formation process when using the appropriate wettability of solid particles. Incorporating polystyrene (PS) into xylene enables one-step formation of PS-filled HIPEs in place of a multi-step polymerization of the continuous phase. We observe that the size of droplets changes with the addition of PS, and we associate this with the change in the viscosity of the continuous xylene-rich phase. Drying the pure HIPE results in the selective removal of xylene and coalescence of EC-rich droplets. With the PS in the xylene-rich continuous phase, we show that EC-rich droplets can be retained even though the xylene is evaporated off, and a new semi-solid composite containing both liquid phase and solid phase is formed via this non-aqueous Pickering-HIPE template

Temperature- and pH-Dependent Shattering: Insoluble Fatty Ammonium Phosphate Films at Water–Oil Interfaces

We study the films formed by tetradecylamine (TDA) at the water–dodecane interface in the presence of hydrogen phosphate ions. Using Fourier transform infrared spectroscopy (FTIR), interfacial shear rheology, confocal fluorescence microscopy, cryo-scanning electron microscopy (cryo-SEM), and small-angle neutron scattering (SANS), we find that between pH 5 and 8 tetradecylammonium cations bind to hydrogen phosphate anions to form needle-shaped crystallites of tetradecylammonium hydrogen phosphate (TAHP). These crystallites self-assemble into films with a range of morphologies; below pH 7, they form brittle, continuous sheets, and at pH 8, they form lace-like networks that deform plastically under shear. They are also temperature-responsive: when the system is heated, the film thins and its rheological moduli drop. We find that the temperature response is caused by dissolution of the film in to the bulk fluid phases. Finally, we show that these films can be used to stabilize temperature-responsive water-in-oil emulsions with potential applications in controlled release of active molecules