April 3-7, 2016
Microencapsulation of small volatile chemicals remains an unsolved challenge for both industry and academia as most capsule walls tend to be permeable to such species. Metal coated capsules are of particular interest as they offer much reduced diffusion coefficient for this same species. A continuous metal shell can provide reduced permeability compared to a standard a polymer shell and can prevent the escape of volatile encapsulated compounds. The permeability of continuous metal films is much lower than that of polymer shells due to their crystalline structure. Additionally, there is potential opportunity to exploit electrical, mechanical, optical and magnetic properties of the metallic shell for additional capsule functionality. Metal encapsulated compounds can have improved shelf life, potentially including those with high sensitivity to water and oxygen.
Metallic encapsulation of small species has successfully been demonstrated within our research group1; however the process developed so far has used a solvent evaporation method to form a polymeric capsule on which the metallic film is deposited. This technique tends to start with an oil phase mixture where the oil to be encapsulated is only present up to ~15% and is only suitable for a number of oils and stabilisers due to limiting wetting characteristics. Additionally harmful solvents which require adequate ventilation such as dichloromethane are often used. Other methods exist to produce polymer shells encapsulating an emulsion core, however these also often suffer from initial loss of a small, volatile core via diffusion through the polymer shell during processing.
In the method proposed here the metallic film is deposited directly onto a Pickering emulsion droplet stabilised with the catalytic nanoparticles, hence allowing 100% of the active material to be encapsulated. It removes the need for a polymer shell all together. In the method we developed, polymer stabilised platinum nanoparticles act as both the emulsifier by adsorbing to the oil-water interface and the catalyst for the growth of a secondary metallic gold film via electroless deposition. In this presentation we will show the effect of gold salt concentration on the resulting metal film thickness and oil release rates.
Please click Additional Files below to see the full abstract.
Kirsty Stark, Olivier Cayre, and Simon Biggs, "Facile two-step encapsulation of small species in a metallic shell" in "Design and Manufacture of Functional Microcapsules and Engineered Products", Chair: Simon Biggs, University of Queensland (Aus) Co-Chairs: Olivier Cayre, University of Leeds, UK Orlin D. Velev, North Carolina State University, USA Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/microcapsules/32