While rain has always been believed to play a part in the spread of disease among crops, the mechanism by which it would act has never been fully explained. Research by Tristan Gilet, an assistant professor at the Faculty of Applied Science at the University of Liege and Lydia Bourouiba, the Esther and Harold E. Edgerton Assistant Professor at the Massachusetts Institute of Technology (MIT), has examined in a novel way, the first step in answering the question.  Two main mechanisms seem to be at play. In the first instance, one drop directly collides with another drop that has previously landed on a leaf and in which the pathogens had enough time to spread. The impact of the second drop then projects the pathogen onto another leaf or neighboring plant. The second mechanism is that of the catapult: the raindrop impacts and bends the leaf, transforming it into a catapult which then ejects contaminated drops onto other plants. These findings could ultimately lead to a reduction in the use of pesticides and GMOs.

The Microfluidics Lab was created in 2012 by Tristan Gilet, an assistant professor at the Faculty of Applied Sciences. This laboratory is part of GRASP, which combines several departments involved in the study of soft matter. The Microfluidics Lab is currently active on four lines of research, all of which have surface tension as their focal point. , which is also called surface energy, describes a force that is responsible for such varied phenomena as the ability of insects to walk on water, the spreading of a drop on a glass surface… or the dispersal of grease by “washing-up liquid”!

One laboratory and four avenues of research

These examples show how small facts can have large implications at the industrial scale. This is the basis for the four lines of research developed by Tristan Gilet and his team of young researchers.  “The first line of research is microfluidics”, explains Tristan Gilet; “it involves the concept of lab-on-a-chip technology: we are working on procedures that make it possible to automatize and miniaturize biochemical reactions. These are carried out by mixing drops that have a diameter of one-tenth of a milimeter. One of the advantages of this system is the speed of operation because it is possible to manipulate up to 1,000 drops per second in a single unit. That yields as many individual reactions.

Our second research direction involves microrobotics. Current robots can succeed in grasping very small objects but only up to one-tenth of a milimeter; smaller objects stick to the robot’s claws. This is why we are turning to insects that walk on walls by lifting and dropping their legs several dozen times per second. Their secret is down to the fact that they have micrometric hairs at the tip of their legs, which contain tiny drops of an oily liquid.

The third avenue of research relates to quantum physics: we are studying the way in which milimetric drops bouncing off the surface of a bath behave like quantum particles. Finally, we are also conducting research on plants”!