UK scientists have used light to separate complex chemical mixtures. The method can be used to recover high value products and catalytic nanoparticles from reaction mixtures, they claim.

When UV light is shined on the emulsion, the surfactant causes the oil and water phases to separate

Julian Eastoe, at the University of Bristol, and colleagues added light-sensitive surfactants to microemulsions. When they shone UV light on the mixtures, the surfactants caused the oil and water phases in the emulsions to separate.

Previously researchers have relied on heat, pH changes or salt addition to separate the phases in microemulsions. The new method does not change the chemical composition of the microemulsion or use as much energy as heat-induced separation.

'We are fascinated by the opportunities offered by light-activated particles, colloids and interfaces. It adds another dimension to the chemical engineering tool box,' says Eastoe.

Importantly, adds Eastoe, these separations are reversible. A sample can be cycled between dispersed and separated states using only light. 'The research shows the dream of light-triggered colloids is becoming reality,' he says.

'What is particularly exciting about this work is that through the simple and elegant addition of a small amount of a photoresponsive surfactant, the authors have transformed the conventional microemulsion into a photoresponsive system,' says Ted Lee, an expert in responsive surfactant systems at the University of Southern California, Los Angeles, US.

The new method could be used in light-activated release and delivery systems for pharmaceuticals and agrochemicals, explains Eastoe. But he says their next challenge is to develop photosensitive surfactants that are cheap, safe and environmentally friendly.

Sarah Dixon

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