Pickering emulsions stabilized by surface-modified Fe3O4 nanoparticles

Tuning the Wettability of Halloysite Clay Nanotubes by Surface Carbonization for Optimal Emulsion Stabilization

The carbonization of hydrophilic particle surfaces provides an effective route for tuning particle wettability in the preparation of particle-stabilized emulsions. The wettability of naturally occurring halloysite clay nanotubes (HNT) is successfully tuned by the selective carbonization of the negatively charged external HNT surface. The positively charge chitosan biopolymer binds to the negatively charged external HNT surface by electrostatic attraction and hydrogen bonding, yielding carbonized halloysite nanotubes (CHNT) on pyrolysis in an inert atmosphere. Relative to the native HNT, the oil emulsification ability of the CHNT at intermediate levels of carbonization is significantly enhanced due to the thermodynamically more favorable attachment of the particles at the oil-water interface. Cryogenic scanning electron microscopy (cryo-SEM) imaging reveals that networks of CHNT attach to the oil-water interface with the particles in a side-on orientation. The concepts advanced here can be extended to other inorganic solids and carbon sources for the optimal design of particle-stabilized emulsions.

Self-assembled micelles based on branched poly(styrene-alt-maleic anhydride) as particulate emulsifiers

The self-assembled micelles of branched poly(styrene-alt-maleic anhydride) (BPSMA) are prepared and exhibit much superior emulsifying performance over the corresponding linear copolymer micelles as particulate emulsifiers.

Two-way effects of surfactants on Pickering emulsions stabilized by the self-assembled microcrystals of α-cyclodextrin and oil

Two way effects of Tween 80 and soybean lecithin (PL) on the stability of cyclodextrin (CD) Pickering emulsions.

Stability and viscoelasticity of magneto-Pickering foams

We have developed a new class of bistable Pickering foams, which can remain intact for weeks at room temperature but can be destroyed rapidly and on-demand with the use of a magnetic field. Such responsive foam systems can find application in various industrial and environmental processes that require controlled defoaming. These foams are stabilized by particles of hypromellose phthalate (HP-55) and contain oleic acid-coated carbonyl iron particles embedded in the HP-55 matrix. The complex behavior of these foams arises from several factors: a robust anisotropic particle matrix, the capacity to retain a high amount of water, as well as an age-dependent response to an external field. We report how the structure and viscoelastic properties of the foams change with time and affect their collapse characteristics. The evolution of foam properties is quantified by measuring the rate of liquid drainage from the foam as well as the rate of bubble growth in the foam with respect to time elapsed (in the absence of a magnetic field). We also evaluate the time necessary for foam collapse in magnetic fields as a function of magnetic particle content. A decreasing liquid volume fraction in the foam during aging leads to an increase in the elasticity and rigidity of the foam structure. These data allow us to identify a transition time separating two distinct stages of foam development in the absence of field. We propose different mechanisms which control foam collapse for each stage in a magnetic field. The stiffening of foam films between air bubbles with age plays a key role in distinguishing between the two destabilization regimes.

Versatile fabrication of nanocomposite microcapsules with controlled shell thickness and low permeability

Novel ethyl phenylacetate (EPA)-loaded nanocomposite microcapsules with polyurea (PU) /poly (melamine formaldehyde) (PMF) shells were facilely and fabricated: by using silica nanoparticle-stabilized oil-in-water (o/w) emulsion template and subsequent interfacial reaction and in situ polymerization. SiO2 nanoparticles absorbed at the interface between oil and water to stabilize the o/w emulsions. The oil droplets containing EPA, isophorone diisocyanate (IPDI) and tolylene 2,4-diisocyanate-terminated poly (propylene glycol) (PPG-TDI) were subsequently reacted with MF prepolymer (pre-MF) dissolved in water phases. The interfacial reaction between pre-MF and IPDI produced interior PU walls. Meanwhile, the in situ polymerization of pre-MF generated exterior PMF walls. It was found that these in/out double walls were compact together. The resulting capsules had spherical shapes and rough exterior surfaces, and could be easily isolated, dried, and redispersed in epoxy resins. The size of the produced microcapsules was dependent on the concentration of SiO2 nanoparticles. The dynamic thermal gravimetric analysis (TGA) demonstrated that the capsules showed excellent thermal stability with little weight loss when exposed at 150 °C for 2 h. Interestingly, with a double PU/PMF shell, these capsules exhibited an extra-low permeability. Moreover, these microcapsules can also demonstrate exceelent magnetic responsiveness after introducing magnetic nanoparticles inside. We believe our microcapsules could be potential candidates in microcapsule engineering, self-healing composites, and drug-carrying systems.

Pickering emulsions stabilized by nanoparticle surfactants

Amphiphilic gold nanoparticles are demonstrated to effectively stabilize emulsions of hexadecane in water. Nanoparticle surfactants are synthesized using a simple and scalable one-pot method that involves the sequential functionalization of particle surfaces with thiol-terminated polyethylene glycol (PEG) chains and short alkane-thiol molecules. The resulting nanoparticles are shown to be highly effective emulsifying agents due to their strong adsorption at oil-water and air-water interfaces. The original nonfunctionalized gold nanoparticles are unable to effectively stabilize oil-water emulsions due to their small size and low adsorption energy. Small-angle X-ray scattering and electron microscopy are used to demonstrate the formation of nanoparticle-stabilized colloidosomes that are stable against coalescence and show significant shifts in plasmon resonance enhancing the near-infrared optical absorption.