Resembling static noise on an old TV, light scatters through a gel in space. But unlike the random pattern on analogue screens late at night, every white and black speckle in this image has meaning in fundamental physics. The blurry background is helping scientists understand the behaviour of microscopic particles when they are free from gravity.
The Colloidal Solids experiment is looking at the dynamics of gels, protein crystals and glasses on the International Space Station. On Earth, heated particles would quickly clump together and then sink to the bottom. This phenomenon can spoil a gel or cream, which are often made with stabilisers to prolong their shelf life.
In space, the agglomeration dance goes on without sedimentation. Studying the process in orbit could lead to longer-lasting products on Earth.
Colloids are liquids with suspended microscopic particles. Milk, paint and aerosols are colloids, for example.
On Earth, gravity dominates how these particles behave, causing them to attract each other and form clusters. In microgravity, however, subtle differences in how particles attract one another become visible, revealing changes in their structure that gravity would normally hide. Even glasses and proteins aggregate in unique ways under microgravity conditions.
NASA astronaut Mike Fincke set up the experiment in ESA’s Microgravity Science Glovebox, a hard-working facility on the International Space Station that provides an enclosed area for manipulating and observing the samples. The glovebox is controlled from Earth by ESA’s User, Support and Operation Centre (E-USOC) in Spain.
These particles in this image are incredibly tiny, measuring about 100 nanometres, or about one thousand times smaller than a human hair.
Mike inserted the sample with the gel mixture. Teams on the ground stirred the sample and heated it up to 35 degrees Celsius. At a higher temperature, the sample began to form a gel.
Images of this detail are impossible to get on the ground, where the gel structure quickly forms a deposit due to gravity. Scientists use them to observe the origin and evolving structure of gels and determine the strength of the forces between particles in liquids.
Understanding the behaviour of gels has great potential in creating stable products made to last, such as medicine, paint, ink and cleaning solutions.
Besides the industrial benefits behind colloidal suspensions in many markets, there is a genuine scientific interest in better understanding the relation between particle shape, symmetry and structure. Scientists are gaining new understanding of fundamental processes and applications.
The Colloidal Solids experiment is an ESA payload developed by Redwire Space in collaboration with the Politecnico of Milano, the Université de Montpellier and Vrije Universiteit Brussel.