COLLOIDAL DISPERSIONS GROUP

Colloids are small particles dispersed in a liquid, such as milk. We use our knowledge of their properties to engineer new particles, and make bespoke structures by assembling the particles. Potential applications include washing liquids, paint, solar panels and vaccines.

The challengeManmade materials do not do everything we want them to: paint cracks, so that it no longer protects from things like UV light; enzymes in washing liquids stop working, and drugs have expiry dates. Improving the performance of materials, and designing new ones, is key in technological innovation. Materials science has an enormous potential to tackle all kinds of problems and make technical processes cheaper or faster – and to do new things we do not currently imagine are possible.

Our work in tackling thisWe are focused on a domain of material science called colloids. A colloidal dispersion consists of particles dispersed in a liquid, where the particles are sufficiently small for Brownian motion to operate and keep the particles evenly dispersed, and stop them settling. Every day examples are milk and paint. The colloidal particles we work with can be anything from polystyrene to gold. We look for applications that our specialist technologies may bring benefits to.

Applications we are working on1. Improving ‘bio’ washing liquids Enzymes break down grease and are an important ingredient in the

washing liquids used to clean the billions of tonnes of clothes we wash globally every day. Researchers worldwide are trying to find more efficient ways to stabilise enzymes in liquid soap, which is currently difficult and therefore expensive to do. The difficulties arise because the soap itself is a corrosive environment for the enzymes.

A colloid capsule being heated – shown at five, 30 and 60 minutes – to make a fused polymer coating for use in improved washing liquids.

Our unique method involves protecting the enzyme inside a specially ‘packaged’ colloidal structure. We place the enzyme in water with a colloidal dispersion and emulsify it with oil. The colloidal particles form a ‘packaging’ layer around the enzyme and water capsule. We then place a layer of calcium carbonate around the entire structure to seal it, protecting the enzyme from the soap. The motion of the washing cycle cracks open the capsule and releases the enzyme, to break down the grease on the clothes. This is a simple and cheap process that creates a benign environment for the enzymes. It has the potential to be used for other biological encapsulants such as manufacturing vaccines.

2. Drying and cracking of dispersions If paint on a ship’s hull cracks, water will penetrate and lead

to corrosion. Paint manufacturers are therefore keen to understand the cracking process in order to prevent it. Conversely manufacturers sometimes want paint to crack, for example to produce a craquelure finish. Paint manufacturers are also interested in controlling the composition of coatings: for example to place active biocides in the surface of paint used in damp areas such as bathrooms, to prevent bacteria developing. We are building an understanding of the arrangement of particles within the coating as it dries. This will lead to a control over both the topology and composition of the film and improvements in paint formulations to meet manufacturers’ potential needs.

MethodologyWe use a range of experimental methods, including magnetic resonance to image multi-phase mixtures, laser light scattering to measure particle size distributions and atomic force microscopy to measure surface roughness at the nanometer scale. We also use neutron scattering at central facilities to study individual components in dispersions. We back up these experimental measurements with fluid mechanical modelling to understand the physical processes occurring.

Potential applications• Drug delivery • Active coatings

Current industrial partnershipsWe are working with a large domestic products company on trials of bio-encapsulation. No licences have yet been granted and we are interested in collaborating with other companies.

Our techniques and skills• Dynamic light scattering• Rheology• Neutron scattering

Dr Alex Routh, University of Cambridge, Department of Chemical Engineering and Biotechnology, Pembroke Street, Cambridge, CB2 3RA Tel: 0044 1223 334789 Email: afr10@cam.ac.uk Web: http://www.ceb.cam.ac.uk/directory/alex-routh http://www.bpi.cam.ac.uk/user/alex

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A dried colloid such as paint: the top surface is shown left, and the larger particles of the inner ‘bulk’, right.

• Static light scattering• Fluid mechanics

• Smart materials• More efficient engine oils

An array of aqueous core microcapsules.

Diagram showing the stages of drying in a colloidal film. Useful for applications such as sunscreens where active materials might be needed only on the surface.