Alternative Transparent Coating Lotus Suitable for Optics with Vacuum Deposition Layer
materials and coatings
Alternative Transparent Coating Lotus Suitable for Optics with Vacuum Deposition Layer (GSC-TOPS-262)
A viable dust, water and ice mitigation optical coating for space flight, aeronautical applications, and ground applications
Overview
NASA instrumentation is at risk for contamination from dusty space environments. Additionally, contamination from water and ice buildup can affect instrumentation function. The innovation of the LOTUS coating prevents contamination on sensitive surfaces, like optics, that cannot be cleaned during space missions.
The Technology
In addition to previous LOTUS coating formulations, an additional optical formulation may be applied via vacuum deposition. This coating forms a top layer and may be applied in different thicknesses that serve to enhance its hydrophobic properties. The vacuum deposited material may comprise fluorinated ethylene propylene or a similar material. This coating is transparent and can be used on optical components or any other applications requiring a clear coating.
Benefits
- Adheres to a variety of common materials
- Prevents Dust and water-based contamination
- Optically clear
- Extremely scalable
Applications
- Remote Sensing
- Earth Imaging
- Communications
Similar Results
Lotus Coating
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.
Particle Contamination Mitigation Methods
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.
Smart Coating for Corrosion Detection and Protection
The smart coating is based on the controlled release of corrosion inhibitors and indicators from specially formulated microcapsules and particles pioneered by NASA (patent allowed). The coating detects corrosion in its early stages, inhibits it, and/or repairs the coating. The onset of corrosion triggers the release of compounds that indicate and inhibit corrosion. Mechanical damage to the coating triggers the release of film-forming compounds to repair the damage. In practice, the corrosion-responsive microcapsules detect the chemical changes that occur when corrosion begins and respond by releasing their contents. A corrosion indicator will identify the affected region with a color change, and healing agents and corrosion inhibitors help mitigate the corrosion.
The microcapsules can be tailored for incorporation into different coating systems. This multifunctional coating system will reduce maintenance cost and improve safety by preventing catastrophic corrosion failures. The coating can reduce infrastructure life cycle costs by extending the life of corrosion-susceptible structures and components, reduce inspection times of structures, and reduce the level of repair for corrosion-affected areas.
Self-Cleaning Coatings for Space or Earth
The new transparent EDS technology is lighter, easier to manufacture, and operates at a lower voltage than current transparent EDS technologies. The coating combines an optimized electrode pattern with a vapor deposited protective coating of SiO2 on top of the electrodes, which replaces either polymer layers or manually adhered cover glass (see figure on the right). The new technology has been shown to achieve similar performances (i.e., over 90% dust clearing efficiency) to previous technologies while being operated at half the voltage.
The key improvement of the new EDS coating comes from an innovative method to successfully deposit a protective layer of SiO2 that is much thinner than typical cover glass. Using vapor deposition enables the new EDS to scale more successfully than other technologies that may require more manual manufacturing methods. The EDS here has been proven to reduce dust buildup well under vacuum and may be adapted for terrestrial uses where cleaning is done manually. The coatings could provide a significant improvement for dust removal of solar cells in regions (e.g., deserts) where dust buildup is inevitable, but water access is limited. The EDS may also be applicable for any transparent surface that must remain transparent in a harsh or dirty environment.
The related patent is now available to license. Please note that NASA does not manufacturer products itself for commercial sale.
Self-Cleaning Seals
This NASA innovation applies the concepts of electrodynamic dust shielding (EDS) to develop seals (e.g., O-rings) with active self-cleaning capabilities. NASA’s self-cleaning seals are manufactured in the following manner: A seal with a conductive surface (or otherwise fabricated to be conductive) is generated and an electrical connection, lead or electrode is attached. Next, a dielectric material is coated or placed over the conductive surface of the seal. (NOTE: Using conductive elastomer materials eliminates the need for a conductive cover layer) A high voltage (nominally >1kV) power supply is connected to the conductive layer on the seal and grounded to the metallic groove or gland that houses the seal.
Given the design, dust accumulates on the outer dielectric layer (a high-voltage insulator) of the seal. To clean the seal, a time varying alternating voltage is applied from the power supply, through the high voltage lead and onto the conductive layer of the seal. When this voltage is applied, the resulting electric field produces Coulomb and dielectrophoretic forces that cause the dust to be repelled from the sealing surface. In practice, NASA’s self-cleaning seals could be operated in continuous cleaning mode (actively repelling dust at all times, preventing it from ever contacting the seal surface) or in a periodic cleaning cycle mode (removing dust from the seal surface at regular intervals).
NASA’s self-cleaning seals have been prototyped and demonstrated to be highly effective at dust removal. The invention could serve as the basis of an active, self-cleaning seal product line marketed for in-space and/or terrestrial applications. Additionally, companies developing space assets destined for operation on dusty planetary surfaces (e.g., the Moon) may be interested in leveraging the technology to protect seals from dust/regolith accumulation, ensuring continuous low leakage operations.