Hybrid biological spores wrapped in a mesh composed of interpenetrating polymer nanoparticles as “patchy” Pickering stabilizers Nicholas Ballard, and Stefan A. F. Bon, Polym.Chem., 2011, 2(4), 823-827. (HOT ARTICLE DEC 2010, COVER APRIL 2011).

We describe a new method for the decoration of the intricate morphology of spore particles with polymer nanoparticles and investigate their behaviour at liquid–liquid interfaces. We found a large difference in the interfacial activity between spherical microspheres and the anisotropic particles synthesized here and describe this in terms of particle wettability.

Soft polymer and nano-clay supracolloidal particles in adhesives: synergistic effects on mechanical properties Tao Wang, Patrick J. Colver, Stefan A. F. Bon, Joseph L. Keddie, Soft Matter, 2009, 5(20), 3842 - 3849. (COVER ISSUE 20)

Numerous synthesis routes toward nanostructured polymer particles have emerged, but few examples demonstrate the essential need for such complex particle structures to achieve any added benefit in a target application. Here, polymer particles having Laponite clay armor were prepared by the Pickering miniemulsion polymerization of n-lauryl acrylate. The resulting “soft–hard” poly(lauryl acrylate) (PLA)–Laponite hybrid particles were blended at various low concentrations with a standard poly(butyl acrylate-co-acrylic acid) (PBA) latex for application as a waterborne pressure-sensitive adhesive (PSA). The tack adhesion properties of the resulting nanocomposite films were compared with the performance of the PBA when blended with either a conventional non-armored PLA latex, with Laponite RD nanosized clay discs, or a mixture of both. A true synergistic effect was discovered showing that the clay-armored supracolloidal structure of the hybrid particles was essential to achieve a superior balance of viscoelastic properties. The addition of small amounts, e.g. 2.7 wt%, of the “soft–hard” clay-armored PLA particles increased the tack adhesion energy considerably more than found for the two individual components or for the sum of their individual contributions. The soft PLA core ensures that the adhesives are not stiffened too much by the nanosized Laponite clay. Slippage at the interface between the nanoclay platelets and the PBA matrix introduces an additional energy dissipation mechanism during deformation. Through the synergistic effect of the clay and PLA in the supracolloidal armored latex structure, the tack adhesion energy is increased by 45 J m⁻², which is about 70% greater than found for the PBA adhesive alone.

Packing Patterns of Silica Nanoparticles on Surfaces of Armored Polystyrene Latex Particles, Sara Fortuna, Catheline A. L. Colard, Alessandro Troisi, and Stefan A. F. Bon, Langmuir, 2009, 20, 12399-12403. (COVER ISSUE 21)

Fascinating packing patterns of identical spherical and discotic objects on curved surfaces occur readily in nature and science. Examples include C₆₀ fullerenes, 13-atom cuboctahedral metal clusters, and S-layer proteins on outer cell membranes. Numerous situations with surface-arranged objects of variable size also exist, such as the lenses on insect eyes and solid-stabilized emulsion droplets and bubbles. The cover image shows a collection of simulated packing patterns that can be obtained when spherical nanoparticles are assembled onto a central submicrometer-sized sphere. With the aid of Monte Carlo simulations, we are able to rationalize the experimental morphology and the nearest-neighbor distribution of the packing of nanosized silica particles on the surface of polystyrene latex particles fabricated by Pickering miniemulsion polymerization. We demonstrate that broadening of the nanoparticle size distribution has pronounced effects on the self-assembled equilibrium packing structures, with original 12-point dislocations or grain-boundary scars gradually fading out.

Conducting Nanocomposite Polymer Foams from Ice-Crystal Templated Assembly of Mixtures of Colloids Catheline A. L. Colard, Richard A. Cave, Nadia Grossiord, James A. Covington, and Stefan A. F. Bon, Adv.Mater., 2009, 21(28), 2894-2898  (COVER ISSUE 28)

We report a fabrication method to produce conducting nanocomposite reinforced soft polymer foams. The multi-component cellular materials are build from a mixture of colloids dispersed in water by freeze-drying, thereby using ice-crystals as template for the porous structure. We use "soft" (i.e. low glass transition temperature) polymer latexes in combination with considerably smaller "hard" nanoparticles. Upon freezing the colloidal blend, ice crystals act as templates and generate the cellular porous structure. We show that an excluded volume effect armors the "soft" polymer cell walls with "hard" nanoparticles thereby enhancing the mechanical robustness of the foams. Altering the composition of the waterborne mixture of colloids allows fabrication of a range of foams with variable cell sizes and shapes, porosity, and physical and chemical properties, such as potential responsive conductivity. We demonstrate that conducting multi-component foams made from poly(vinyl laurate) latex, silica nanoparticles (Ludox TM-40) and colloidal carbon black, can be used as a promising material for gas sensors.

Pickering Miniemulsion polymerization using Laponite clay as stabilizer Stefan A. F. Bon* and Patrick J. Colver, Langmuir, 2007, 23(16), 8316 - 8322 (COVER ISSUE 16)

Solid particles can adhere strongly to liquid-liquid interfaces. This phenomenon can be used to stabilize emulsions, thereby generating armored droplets. These can be named Pickering emulsions. Nanoparticles can stabilize emulsion droplets of submicron size. The cover image shows an impression of an armored polymer latex particle obtained using Pickering miniemulsion polymerization, whereby discotic Laponite clay nanoparticles were used to stabilize the monomer droplets. The use of the clay discs sets aside the need for conventional surfactants and co-stabilizing monomers. Generation of stable miniemulsions generally involves a high-energy homogenization step, i.e., sonication. This induces reversibility of the assembly process of the nanoparticles onto the surface of the monomer droplets. Control of monomer droplet size is achieved as a result of an equilibrium state of nanoparticle partitioning. A variety of hydrophobic monomers can be used, and subsequent radical polymerization leads to the formation of the armored polymer latexes.