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Why does soil sometimes absorb water, while repelling it at other times? Two researchers from the University of Amsterdam (UvA) hope to find the answer, not by conducting fieldwork in the desert or the dunes, but in microgravity conditions aboard an aircraft.

Why does soil sometimes absorb water, while repelling it at other times? Two researchers from the University of Amsterdam (UvA) hope to find the answer, not by conducting fieldwork in the desert or the dunes, but in microgravity conditions aboard an aircraft.

Researchers Sebastiaan de Vet and Lieke Mulder from the Institute for Biodiversity and Ecosystem Dynamics (IBED) of the UvA have been selected for the Fly Your Thesis project of the European Space Agency. Supported by the Netherlands Space Office (NSO), they will conduct experiments during parabolic flights at the end of May. This involves flying in an Airbus A300, which makes a series of dives providing 30 minutes of weightlessness in total during which time experiments can be performed by the scientists.

Mini raincoat

The research will focus on terrestrial phenomena of enormous proportions, such as desertification, mudslides and wildfires. However, the actual data will be collected at the level of a single grain of sand, as this is where it all begins, according to De Vet. ‘If it rains, you put on a raincoat. That raincoat is waterproof, so your body stays dry. Something similar happens with sand grains. Plant remains can form a coating around a single grain of sand; a mini raincoat, so to speak. This grain of sand thus repels water. If a whole area has this repellent characteristic, water will not be absorbed into the ground, but will flow across the surface. This can lead to erosion of the landscape or dangerous mudslides.’

Lost Energy

In three days (24, 25 and 26 May), the researchers will fly ninety parabolas for their project entitled Advancing Repellency and Innovating Detection (ARID). During each parabola, everything aboard the aircraft is weightless for 22 seconds. In the test set-up, three types of grains will collide with each other: grains stripped of their ‘raincoat’, grains with an inactive coating and grains with an active coating. Christina Giannopapa from Eindhoven University of Technology (TU/e) will record this in meticulous detail using two high-speed cameras.

De Vet described the reason for conditions of weightlessness: ‘We are going to collide individual sand grains with each other. If you do this research in a laboratory, the earth's gravity causes friction with the sand in the test setup and therefore leads to unusable test results. In weightless conditions you do not have this friction, because the grains of sand can move in all directions.’

The energy lost during the collisions will tell the researchers more about the characteristics of the ‘mini raincoats’. De Vet: ‘With this data we hope to bridge the gap between the properties of a grain of sand and the large-scale effects that water repellency can have on nature.’ Sand from the Dutch coast is being used for the experiment, as water repellency could also have great consequences for the Netherlands: ‘In addition to wind erosion and sand dispersion, water repellence also has a great influence on the shape and erosion of our dunes.’

In addition to TU/e, the primary research partner, other collaborators in this projects include: Bradford Engineering (design and electronics experiment), Electro Abi (launchpad experiment), Bruel & Kjaer Benelux (vibration measurement), RIMAS (frame parts).

Sebastiaan de Vet will be reporting on the parabolic flight campaign using a blog published by Kennislink. The blog can be followed via the link below.