Self-Cleaning Coatings for Space or Earth

The following methods can be used individually or in combination to generate superhydrophobic surfaces: Synthesis of novel copolyimide oxetanes with unique surface properties The technology is the synthesis of a polyimide coating or film with a modified surface chemistry shown in Figure 1. A minor amount of an oxetane reactant containing fluorine is added to the polyimide, and the oxetane preferentially migrates to the surface, enabling relatively high concentrations of fluorine at the surface, without compromising the functional performance of the bulk of the polymide coating/film. The copolymers exhibit mitigation of particle adhesion and fouling from exposure to various particulate and biological contaminants and exhibit reduced surface energy and increased surface fluorine content at extremely low oxetane loadings relative to the imide matrix (see Figure 2). Additionally, the short fluorinated carbon chains do not bioaccumulate, reducing the environmental impact of these materials. Modifying surface energy via laser ablative surface patterning This method uses a laser to create nanoscale patterns in the surface of a material to increase the hydrophobicity of the surface (see Figure 2). The benefits of hydrophobic surfaces include decreases in friction and increases in self-cleaning properties. This is an advantageous method of surface modification because it is fast and single-step, promises to be scalable, requires no chemicals, could be applied to a variety of materials, and does not require a planar surface for patterning.

Previous techniques for measuring dust accumulation, mostly de-pendent on solar cell output, were limited by their inability to distin-guish dust effects from other factors like incident radiation and radiation damage. These techniques were less effective in environ-ments with inconsistent solar flux and future missions, such as the Lunar South Pole, and lacked versatility in adapting to diverse envi-ronmental conditions. The PADS device embraces success over these challenges, and reflects enhanced features over prior iterations to also allow for space environments. Key design features begin with the customizable mechanical design of the PADS device for use in space environments, heaters with imbedded precision temperature sensors, a selected optical coating for the device coupons that are calibrated on high-fidelity thermal modeling and validated with ground-based testing to simulate the space environment of interest (including dusting with simulants representative of the planetary-body soil/regolith), and a control circuit for precision control/matching of the thermal inputs to the sensor via the heaters. Retainers with mount isolators are implemented to ensure the stacked layers within the device do not dislodge during high vibration or gravitational loads during launch. For operation, the PADS device is installed at the point of interest (e.g., space vehicle surface, extraterrestrial equipment) to quantify dust accumulation. Power and data transfer are done through cabling to the space vehicle system or can be provided standalone. A control circuit/algorithm adjusts the power to the heaters to precisely match the temperature setpoints. Ground testing in the simulated space environment conditions of interest creates a calibration plot of effec-tive emittance versus dust density, and allows determination of the degradation in emittance as the dust increases on the surface. Testing on the PADS device has been completed in a simulated lunar environment and data has been collected to enable sensor calibration for its use on the Moon. It is currently poised for integration into a lander for flight testing. Although the PADS device is intended for use in a burgeoning space industry and requisite environments – but given that the PADS device is partially comprised of programmable sensors in conjunction with optically coated coupons that can be tailored for custom use - it or its constituent components could be modified for terrestrial applications such as surface dust monitoring on photovoltaic panels or potentially combustible dust on various industrial surfaces.

State-of-the-art (SOTA) EDS technology includes the addition of a dielectric substrate, the EDS electrodes, and a dielectric cover layer. Typically, this multilayer stack-up for thermal radiator EDSs are built as a stand-alone and placed directly on top of the thermal radiator base and covered with the thermal control material. This new coating system represents an alternative EDS approach that integrates with the thermal radiator's thermal control coating system. The approach involves utilizing the thermal control coating in multiple functional capacities within the EDS configuration. The thermal control coating properties are leveraged to provide electrical insulation characteristics suitable for EDS operation while maintaining thermal performance requirements. The EDS configuration incorporates conductive elements positioned within the thermal control coating structure. The thermal control coating is applied using processes compatible with standard thermal radiator construction methods. The conductive elements are integrated during the coating application sequence. This integrated EDS approach incorporated into a thermal radiator system reduces certain components compared to SOTA EDS systems. The reduction in components offers potential benefits in system mass, thermal performance characteristics, and manufacturing complexity. The approach may reduce certain failure modes associated with interface layers and thermal expansion effects. This EDS configuration allows for enhanced flexibility in thermal radiator design parameters.

This durable, transparent, nano-textured coating can be applied via a wet chemistry process to variety of rigid and flexible surfaces by spin coating, brush application, or spray application, making it applicable for many purposes beyond space flight and aeronautical applications. The coatings unique nano-textured surface and overcoat reduces surface energy and contact surface area, giving the coating anti-contamination and self cleaning properties that minimize dust, liquid, and ice accumulation on its surface, similar to a leaf on the Lotus plant. The coating is low outgassing, stable in vacuum, and can survive harsh spaceflight environments. Depending on requirements, the Lotus Coating can be tailored to fit the specific needs of a project or customer. This customization makes the Lotus system far more adaptive, allowing for a more diverse range of applications.

WaveRider is a form of EDS technology that uses wires or insulated metal rods held a few millimeters above a substrate that is laden with dust. The wires carry a high-voltage AC square-wave signal. As the wires are moved across the surface, the dust is repelled and moves away from the wires until the whole surface is cleaned. The benefit of WaveRider over traditional EDS is that it can work on any surface, whereas traditional EDS only works with an insulating top coat. This would be a concern to any spacecraft that uses a statically dissipative surface as it's exterior top coat, and would require something like WaveRider to remove dust. Additionally, It may be beneficial to have moving wires as opposed to just having stationary electrodes for optically reliant surfaces (such as mirrors, solar panels, and helmets), as stationary wires can affect visibility. Also, because it uses wires, it can conform to irregularly shaped surfaces such as astronaut helmets or curved radiator surfaces. Moving electrodes may also offer fewer integration complexities compared with embedding stationary electrodes above the surface, since it may save weight and is structurally less complex. Electrodes on top of a surface don't place any burden on integrating it within a system (e.g., traditional EDS needs to be embedded inside cover glass for solar panels, inside O-rings/gaskets, or beneath the surface of a thermal control coating for radiators). It won't affect the properties of a coating, and there are no issues with how well it adheres to a surface like there are with traditional EDSs. Due to the nature of the technology, WaveRider could be adapted into a handheld tool that would allow much more ease of use, which is a freedom that astronauts wouldn't have if the system was built into a spacesuit or built into a machine.