A. Tunell, D. Cordon, L. Kirsch, A. Lizaola, L. Micklow, N. Scott, S. Furst, F. Mangolini, C. Chang
University of Texas,
United States
Keywords: anti-dust, nanostructures, electrostatic forces, humidity
Summary:
Low adhesive surfaces have applications in a variety of industries such as for solar panels, optics, and dust mitigation on extraterrestrial environments. The Apollo missions discovered a need for these surfaces when seals clogged, and mechanical components quickly degraded due to the highly abrasive lunar dust. In addition, particle contamination causes many problems for terrestrial applications, including for optics, automobile, aerospace, and healthcare industries. Existing approaches to passive dust mitigating surfaces center around reducing the short range van der Waal forces through the addition of surface structures that separate dust particles from the bulk substrate. However, recent works within our group have revealed that this performance is highly sensitive to environmental conditions including relative humidity and charge buildup from photoelectric charging. In a high humidity environment, water vapor condenses on the surface and forms a liquid meniscus between a particle creating capillary forces. On the other hand, in a low humidity environment the conductivity of the air decreases and surfaces accumulate charge, introducing strong electrostatic forces. In this work, we investigate the effects environmental effects on the performance of dust mitigating nanostructured surfaces. The nanostructure’s effect on the electrostatic force is approximated using a modified form of Coulomb’s law and compared to numerical COMSOL simulations allowing for greater insight into the more complicated interactions of insulators. These predictions are confirmed by experimental studies using planar and 500 nm periodic nanostructured polycarbonate samples coated with 30 nm of Al2O3, Pt, or TiO2 to vary the surface conductivity. The surfaces are contaminated with a layer of lunar dust simulant and a scanning electron microscope (SEM) is used to apply charge, causing particle removal by the electrostatic force which is quantified and evaluated. The addition of nanostructures is found to either a decrease or an increase in the electrostatic force depending on the ratio of surface charge to particle charge. This is reflected in experimental results where insulating nanostructured surfaces have an increase rate of particle remove when charge is applied compared to a planar reference. Conversely, a conductive nanostructured surface has a decreased rate of particle removal when charge is applied compared to a planar reference. Through this work, several insights into the design of a nanostructured surface to tune the electrostatic response have been discovered. A broad evaluation on the effects of nanostructures on the electrostatic force using direct AFM measurements and dust adhesion testing, proposed models to evaluate these forces, and proposed geometry will be presented. Insights into these forces have a wide range of applications in a variety of industries ranging from dust mitigation to electrostatic wafer carriers in semiconductor fabrication.