Le site de vulgarisation scientifique de l’Université de Liège. ULg, Université de Liège

Drops on the networks
11/5/15

The device tested by the researcher, which works every time, is as follows: the network is made up of a horizontal fibre and several vertical ones with different diameters. A drop of water is released on every vertical fibre, thus creating several residues and, several water droplets, which can differ because the fibres are different. It is therefore possible to go from one component to another without any contamination or mixing. The device is then turned 90° and a drop of oil is released onto the large horizontal fibre which is now vertical (see animation). The latter will collect all the residues and encapsulate them.


The goal of the study was to manage to create such drops simply and in a very flexible way: if you want internal components for instance, you just have to add as many fibres as you want extra components. This may seem easy but, in fact, it was a question of trial and error and a great many experiments to determine the optimum device. If you don’t use fibres with different diameters, and if you don’t turn the device to invert the symmetry, then encapsulation is impossible. The drop of oil passes the node without taking any of the trapped water with it. That was the trick we had to find.

Drop sliding movement


Applications

The most interesting point is the fact that there are several different droplets within the same drop. “This is what the pharmaceutical industry is looking for”, Floriane Weyer explains. “There are often several active ingredients in a capsule and for the time being, drug manufacturers are obliged to mix them. They are interested in being able to put them in separate compartments so that they can act one after the other, for instance. This is what happens in our system: if you use a component that polymerises (hardens) instead of oil, the capsule is solid and the droplets are separated from each other. And they will remain so whereas if you use oil, they will eventually merge owing to gravity.” A property that has attracted the attention of the chemical industry, which is interested in putting different reagents in the droplets; when they merge, a chemical reaction can occur, making these drops true microreactors.

The production of such drops also offers opportunities in terms of research, for instance in the field of biology. In GRASP, they are being studied in order to examine how they pass through cell membranes. The cells are represented by the water droplets while the membrane is the film of oil separating them. This enables the researchers to study membrane transport by examining how a component passes from one drop to another through the film of oil. We undoubtedly haven’t heard the last of these droplets.

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