Prof Alex Routh

Colloidal Dispersions group

Film Formation and dispersion drying

When a dispersion of stable colloidal particles is dried the particles pack and form a solid network. If the particles are weak enough they deform and a continuous film, with a particle volume fraction of unity is formed. For polymeric particles, interdiffusion of polymer chains blurs out the existence of the original particles and a continuous polymer film is created. This process is called film formation.

An EU project is examining film formation using composite particles, where a hard component such as clay or silica is embedded within the polymer particles. We have modelled the deformation of such particles and followed the stress development in a film using a beam bending technique. 

For harder particles the film is weak and displays cracks. The crack pattern and spacing has been the subject of much work and we have shown how flow of solvent away from defects in the film set the spacing and lead to a stick-slip motion of the crack through the drying film. A current project in collaboration with Dr Bill Clegg in Materials Science is examining the forces at play as the cracks develop.

As a film dries the particles will distribute themselves. Using a distribution in particle sizes it is possible to create gradients in particle concentraions and hence film properties. This is a self assembly type mechanism for stratification. 

Aggregation

When colloidal particles attract each other they will form macroscopic clumps, called flocs and the process by which this happens is called aggregation. We are studying this in two separate systems

Engine oil additives

Engine oil contains 5 nm calcium carbonate particles and these are stabilised by the use of surfactants. Under certain circumstances the particles become unstable and we are elucidating the mechanism using light scattering, rheology and small angle neutron scattering. We are also using thermodynamics to predict the phase diagram in systems containing free polymer and comparing our theoretical results with experiment.

Encapsulation

We make a number of encapsulated systems: In one project we are seeking to encapsulate enzymes in an aqueous core surrounded by a polymeric shell. The shell is responsive, allowing the biological reaction to be externally controlled. Encapsulation is carried out in colloidosomes with a self - assembly approach used.

In a different project we are seeking to make organic core capsules with a shell that slowly dissolves. This enables controlled release of active for a number of application.

Microgels

Microgels are latex particles that respond to their external environment by sewlling. An example is particles based on poly(N-isopropylacrylamide) which are swollen at temperatures below 32oC and collapsed at higher temperatures. We have examined the thermodynamics of the collapse as well as the fluid mechanics of solvent flow around and through such particles.