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Nigel Wilding
Nigel Wilding

Internal News - 06 March 2008

New research could improve everything from mayonnaise to drug delivery systems

Dr Nigel Wilding of the Department of Physics has been awarded £297,000 by the Engineering & Physical Sciences Research Council.

The grant is for theoretical studies of the effects of adding nanoparticles to colloidal dispersions.

Colloidal dispersions are a type of fluid in which “colloid” particles of micron size are dispersed in a liquid solvent.

Examples arise in a host of everyday household products including detergents, cosmetics and paints, as well as many foodstuffs like mayonnaise and ice cream.

They also find technological applications, for instance as lubricants and drug delivery systems.

One issue is key to the material properties of all such systems, namely the stability of the suspension, or more generally its “phase behaviour”.

Specifically, one wants to be able to predict whether under prescribed external conditions of, for example, temperature and pressure, a certain type of colloidal dispersion remains stable – that is the particles are evenly dispersed throughout the solvent – or instead separate off to form a dense “phase” or aggregate.

If a dense phase does form, one should like to be able to predict and (ultimately) even control its structural properties.

The project will employ computer simulation to study the properties of colloidal dispersions to which much smaller “nanoparticles” have been added.

Such additives are known to dramatically change the physical properties of a dispersion, including the tendency of the colloid particles to phase separate. This happens because the additive modifies the effective interaction between colloids.

However, a complete understanding of just how this happens, and the generic consequences for phase behaviour, is presently lacking.

Until recently, simulation studies of colloid-nanoparticle mixtures were technically too difficult to perform due to a problem known as "jamming" in which the nanoparticles severely hinder the motion of the colloids on accessible simulation timescales.

However a new simulation method jointly developed by Dr Wilding and collaborators at the University of Illinois at Urbana-Champaign, circumvents jamming and offers the first direct access to problems of real practical interest.

One focus of the work will be to discover the conditions under which exotic self-assembled inhomogeneous phases occur, such as modulated structures and cluster phases.

Structured phases potentially offer great utility as templates for nanolithography, nanoelectronics, photonic crystals and protein crystallisation.

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