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Interactions in concentrated colloidal dispersions by scattering and force measurement

Final Activity Report Summary - CONCSCATTER (Interactions in concentrated colloidal dispersions by scattering and force measurement)

The properties of surfaces can be modified extensively by coating them with polymers and surfactants. Examples of this are abundant from the Teflon coating on a frying pan to the sunscreen we wear at the beach. Another familiar aspect of polymers at surfaces is lubrication in an engine that would seize up without its protective coating. The new surfaces we produce through these modifications can, for example, be made strongly adhesive, non-stick, biologically active, anti-bacterial, etc depending on the coatings used and these can be tailored for each application. In industrial processes, particles such as pigments, paint bases and pharmaceuticals are frequently coated with molecules to control either their processing or end-user properties. While the behaviour of small molecules such as soaps and detergents at these surfaces is well-understood, the role of larger molecules such as polymers is not.

When two coated surfaces come together (say when a cell adheres to a filtration membrane or when two drops of ink coalesce), what happens at the interface is quite unclear. In this project, we studied the molecular structures that form in these confined spaces. To do so, we constructed a compression device where a flexible membrane is pushed against a very flat 10 cm diameter quartz or silicon block. These two surfaces coming together mimic the two small particles coming together (such as the cell and membrane or two ink drops we mentioned earlier) but at a larger scale so that we can see what is going on in the solution between them. At the same time as we compressed the surfaces, we shone a neutron beam through the interfaces to measure the structures near the interface. Neutrons are similar in some respects to X-rays in that they can measure structures with sub-nanometre precision and can pass through many materials allowing us to see inside.

We were able to see water being squeezed out of the gap between the two surfaces and have started to develop a more detailed picture of the surface structures involved in polymeric stabilisation and flocculation. With this knowledge, we hope to be able to design novel materials to fulfil these functions.