New research showing how droplets move

A group of researchers including Trinity fellow Ian Hewitt have created a new mechanism by which liquid droplets placed in channels with flexible walls can whisk themselves though tiny ducts – without any help from external forces.

The mechanism could be exploited in a range of applications from targeted drug delivery to self-cleaning surfaces or pipes that clear themselves.

Liquid droplets are normally propelled through narrow channels using driving forces created by things such as temperature gradients, electric fields or chemical gradients – but taking away these forces means droplets will no longer move. Hewitt and his colleagues have now created a channel in which no external driving force is needed to transport droplets. To do this, they formed a channel from two thin glass coverslips, coated in a material that attracts oil but repels water. The coverslips are clamped at one end and are held apart by a glass spacer just few hundred microns thick. This creates a channel with walls that are able to move together or apart.

The researchers have coined the term ‘bendotaxis’ to describe the motions they observed, since the droplets propel themselves – a behaviour called ‘taxis’– by bending their surroundings. This new mechanism of motion could be applied to technologies such as labs-on-a-chip and tiny devices that deliver drugs to targeted parts of the body.

Ian Hewitt, Fellow and Tutor in Applied Mathematics at Trinity, said of the research: ‘The exciting thing about this mechanism is that it causes drops to move the same way along the channel regardless of whether they wet the walls or not – that potentially makes it a very versatile method for driving droplet motion.’

The research is described in Physical Review Letters.

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