Smart Material Solutions has been working for five years on scaling so-called “functional surface textures.” In May 2021, we partnered with Prof. Chih-Hao Chang of the University of Texas, Austin NASCENT Center and won a NASA-funded Small Business Innovation Research (SBIR) contract to adapt our technology for a new functionality: dust mitigation on spacecraft components on the moon.
If you’re not a fan of dust, the Moon is not the place for you. The moon has no liquid water, wind, weather, or even atmosphere. Everything we see on the surface is the result of meteor impacts, which all at once melt, turn to glass, and then shatter the minerals on the surface. The result is an extremely abrasive, microscopic, electrically charged dust that sticks to everything and is never worn down by the weather - even after billions of years! Lunar dust wreaked havoc during the Apollo Missions, with so much being tracked into the Lunar Module that it created haze in the cabin. With return to the moon via Artemis inevitable, the problem has resurfaced as a NASA priority.
Nanostructures on a surface dramatically affect how that surface interacts with the environment. For instance, texturing a surface with nanoscale features can make the surface self-cleaning via the lotus effect or decrease the adhesion of dust to a surface. This provides an opportunity for a passive solution to the dust problem. Passive solutions require no power or increase in payload mass, unlike, for example, an air spray, windshield wiper, vibrating panel, electrodynamic dust shield, or other proposed “active” solutions.
Nanostructures essentially place the tiny micro-dust particles on a bed of nails, as shown in Figure 1. This reduces the contact area and the microscale adhesion forces, such as Van der Waals forces. The spacing between the nanostructures is important. It determines whether a dust particle will sit on top of multiple features, as desired, or whether it will stick between them, effectively making the problem worse.
Figure 1 - Large dust particles (left) sit on top of the features of a textured surface (desirable), while small dust particles (right) can fall in between the features (undesirable).
Lunar dust consists of a wide array of particles ranging from 1 μm to 100 μm in size. Single-digit micron-scale surface features may help reduce the adhesion of 10 μm particles or larger but become clogged over time with the smaller 1 μm particles. So the first goal of surface design is to reduce the spacing between the surface features as much as possible.
Another factor that impacts adhesion is the radius of curvature and material properties of the two bodies being attracted. In general, softer surface materials with larger features will have a larger contact area and thus larger adhesion force, as shown in Figure 2. So given the option, the goal is to make the individual features as sharp as possible to limit contact area.
Figure 2 - Sharper features (right) have a smaller contact area and thus reduced adhesion.
These geometric properties combine with material properties like hardness, surface energy, and electrical conductivity to determine a surface's passive affinity for dust. Unfortunately, due to the harsh realities of the lunar environment, including unfettered UV exposure and 200 degree temperature swings, the materials available for texturing are limited and typically so robust that they’re hard to pattern through the typical thermal embossing or UV curing processes. Solving this problem, at scale, is the goal of SMS’s NASA-sponsored SBIR Project. Figure 3 shows exciting preliminary results from this project.
Figure 3 - Video comparing the dust-mitigating properties of a smooth and a nanopatterned film. The two films were covered in Lunar dust simulant and tilted so that gravity could remove the bulk of the dust. After tilting, the smooth film remains covered in dust, whereas the nanopatterned film is largely free of dust.
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