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Complex fluid interfaces and nanofluidics

Understanding the dynamics of interfaces is important to effectively miniaturise lab on a chip devices. EU-funded researchers have developed tools to facilitate such investigations.
Complex fluid interfaces and nanofluidics
Nanofluidics, the study of dynamics and flow behaviour of liquids at nanometre scales, has emerged in the footsteps of microfluidics. Biotechnological applications like labs on chips have motivated this development. By decreasing the size of these devices to such small length scales, the importance of the dynamics of interfaces increases proportionally. For researchers working on the EU-funded project OPTMANDROPS (Optical manipulation of droplets and interfaces in colloid-polymer mixtures), colloid-polymer mixtures provided a very convenient model system to explore interface dynamics in great detail.

The addition of non-absorbing polymers to colloidal suspensions gives rise to an attractive interaction between the colloidal particles, which can lead to phase separation in a ‘colloidal liquid’ and a ‘colloidal gas’ phase, as has been described theoretically. In such systems, interfacial phenomena like droplet snap-off have also been studied. However, active control over these interfacial phenomena has not been achieved so far.

Within OPTMANDROPS, the researchers used optical trapping to deform the fluid-fluid interface in aqueous colloid-polymer mixtures. They used a laser beam that entered the sample parallel to the interface and allowed them to manipulate the interface parallel to the direction of gravity. Using the gradient forces of the laser beam, droplets consisting of thousands of colloidal particles could also be pinched off.

After switching off the optical trap, the interface was monitored by means of fluorescence microscopy. Thermal fluctuations of the unperturbed interface were imaged by confocal microscopy. Both the static structure and dynamic relaxation of the deformed interface could be related to the thermal fluctuations of the unperturbed interface, suggesting that the fluctuation dissipation theorem holds for even large deformations.

The results of the OPTMANDROPS project have been published in the high-impact peer-reviewed journal Soft Matter.

Related information


Nanofluidics, lab on chip, colloid-polymer mixtures, laser beam, fluorescence microscopy
Record Number: 181117 / Last updated on: 2016-04-26
Domain: Industrial Technologies