Hybrid supracolloidal structures through interface driven assembly

Abstract

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