Emulsions stabilized with solid nanoparticles: Pickering emulsions

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ev...

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

Stable Pickering emulsions were prepared using only graphene oxide (GO) as a stabilizer, and the effects of the type of oil, the sonication time, the GO concentration, the oil/water ratio, and the pH value on the stability, type, and morphology of these emulsions were investigated. In addition, the effects of salt and the extent of GO reduction on emulsion formation and stability were studied and discussed. The average droplet size decreased with sonication time and with GO concentration, and the emulsions tended to achieve good stability at intermediate oil/water ratios and at low pH values. In all solvents, the emulsions were of the oil-in-water type, but interestingly, some water-in-oil-in-water (w/o/w) multiple emulsion droplets were also observed with low GO concentrations, low pH values, high oil/water ratios, high salt concentrations, or moderately reduced GO in the benzyl chloride-water system. A Pickering emulsion stabilized by Ag/GO was also prepared, and its catalytic performance for the reduction of 4-nitrophenol was investigated. This research paves the way for the fabrication of graphene-based functional materials with novel nanostructures and microstructures.

Factors that Affect Pickering Emulsions Stabilized by Graphene Oxide

ConspectusThe assembly of complex structures from simpler, individual units is a hallmark of biology. Examples include the pairing of DNA strands, the assembly of protein chains into quaternary structures, the formation of tissues and organs from cells, and the self-organization of bacterial colonies, flocks of birds, and human beings in cities. While the individual behaviors of biomolecules, bacteria, birds, and humans are governed by relatively simple rules, groups assembled from many individuals exhibit complex collective behaviors and functions that do not exist in the absence of the hierarchically organized structure.Self-assembly is a familiar concept to chemists who study the formation and properties of monolayers, crystals, and supramolecular structures. In chemical self-assembly, disorder evolves to order as the system approaches equilibrium. In contrast, living assemblies are typically characterized by two additional features: (1) the system constantly dissipates energy and is not at thermodynam...

From one to many: dynamic assembly and collective behavior of self-propelled colloidal motors.

Mimicking the Cell: Bio-Inspired Functions of Supramolecular Assemblies

The fabrication of “soft” nanocomposite clay armored polymer latexes is described. Laponite clay XLS is used as stabilizer in the Pickering emulsion polymerization of a variety of monomer mixtures, that is, methyl methacrylate and n-butyl acrylate, styrene and n-butyl acrylate, and styrene and 2-ethylhexyl acrylate. Overall solids contents of the hybrid latexes in complete absence of coagulation of up to 24 wt % are reported under batch conditions. Key mechanistic aspects of the Pickering emulsion polymerization process are discussed. The use of monomers that have high water solubility and are prone to hydrolyze under basic conditions, for example methyl methacrylate, should be restricted. The use of small amounts of methacrylic acid as auxiliary monomer promotes clay adhesion to the surface of the particles in the Pickering emulsion (co)polymerization of hydrophobic monomers. Detailed kinetic studies at both 60 and 80 °C of the Pickering emulsion copolymerization of styrene and n-butyl acrylate (Sty:BA =...

Pickering Emulsion Polymerization Using Laponite Clay as Stabilizer To Prepare Armored “Soft” Polymer Latexes

Particles that can undergo directed self-propulsion are desirable for colloidal cargo delivery and self-assembly. Herein we describe the synthesis of silica–manganese oxide “matchstick” colloids that undergo catalytic self-propulsion by consumption of hydrogen peroxide. Chemotaxis is observed when particles are placed in a fuel gradient. Movement opposes convective flow which is tracked by following inert polymer microspheres simultaneously.

Holly S. McKenzie

Papers

Pickering Emulsion Polymerization Using Laponite Clay as Stabilizer To Prepare Armored “Soft” Polymer Latexes

Chemotaxis of catalytic silica–manganese oxide “matchstick” particles

Nanoscale hybrid silica/polymer Janus particles with a double-responsive hemicorona