Hybrid supracolloidal structures through interface driven assembly

We investigated different strategies for the preparation of armoured polymer particles. Inorganic nanoparticles, such as clay platelets and Ludox colloidal silica grades, were used as solids-stabilisers in processes such as miniemulsion, suspension and/or emulsion polymerisations. These nanoparticles were either assembled at liquid-liquid interfaces for the stabilisation of monomer droplets or adsorbed onto solid surfaces in the case of poly(vinyl acetate) latex particles. Colloidal assembly was promoted by modifying the pH and/or the ionic strength of the dispersion medium, thereby tuning the surface properties of the nanoparticles. When prepared in miniemulsion polymerisation, latexes with controlled particle size distributions were obtained. Their diameter was dictated by the amount of solids-stabiliser (Laponite clay) or by the dimensions of the building blocks (Ludox colloidal silica). We developed a versatile emulsion polymerisation process leading to silicaarmoured poly(vinyl acetate) particles and showed that quantitative disc centrifugation analyses throughout the polymerisation process unravelled mechanistic aspects of particle formation and growth. Stability of the armoured particles was studied in dispersion and after spray-drying the hybrid dispersions. The thickness of the silica shell on the polymer particles had an important role in limiting polymer inter-diffusion upon film formation. The obtained powders were tested as additives in cement-based formulations for tile adhesives. However, desired performance characteristics were not obtained in comparison to standard formulations. Soft polymer composite foams were prepared through freeze-drying a mixture of colloids. ‘Large-soft’ particles of poly(vinyl laurate) reinforced by an armouring layer of ‘small-hard’ nanoparticles of colloidal silica led to the formation of highly porous open-cell foams. Upon addition of a third conducting colloidal component, this newly designed material proved promising results as a gas sensor

Physical Methods for the Preparation of Hybrid Nanocomposite Polymer Latex Particles

In this chapter, we will highlight conceptual physical approaches towards the fabrication of nanocomposite polymer latexes in which each individual latex particle contains one or more "hard" nanoparticles, such as clays, silicates, titanates, or other metal(oxides). By "physical approaches" we mean that the "hard" nanoparticles are added as pre-existing entities, and are not synthesized in situ as part of the nanocomposite polymer latex fabrication process. We will narrow our discussion to focus on physical methods that rely on the assembly of nanoparticles onto the latex particles after the latex particles have been formed, or its reciprocal analogue, the adhesion of polymer onto an inorganic nanoparticle. First, will discuss the phenomenon of heterocoagulation and its various driving forces, such as electrostatic interactions, the hydrophobic effect, and secondary molecular interactions. We will then address methods that involve assembly of nanoparticles onto or around the more liquid precursors (i.e., swollen/growing latex particles or monomer droplets). We will focus on the phenomenon of Pickering stabilization. We will then discuss features of particle interaction with soft interfaces, and see how the adhesion of particles onto emulsion droplets can be applied in suspension, miniemulsion, and emulsion polymerization. Finally, we will very briefly mention some interesting methods that make use of interface-driven templating for making well-defined assembled clusters and supracolloidal structures

Conducting nanocomposite polymer foams from ice-crystal-templated assembly of mixtures of colloids

Fabrication of conducting nanocomposite-reinforced soft polymer foams is demonstrated. These multicomponent cellular materials are built from a mixture of colloids dispersed in water by freeze-drying, thereby using ice crystals as template for the porous structure. An excluded-volume effect armors the "soft"-polymer cell walls with "hard" nanoparticles, thereby enhancing the mechanical robustness of the foams