Permanent Anti-Fog Coatings Produced Via Aerosol Impact Driven Assembly

The Exploration Extravehicular Mobility Units (xEMU) helmet is a complex assembly designed to accomplish several tasks to protect and enable astronauts. In addition to maintaining a suitable environment for the wearer, it must also allow for appropriate mobility and provide a wide and undistorted view of the surroundings. A critical component of the helmets optical system is the anti-fog coating. While previous versions of the anti-fog coating have provided suitable anti-fog performance, they have been difficult to apply, lacked mechanical or chemical durability, or resulted in unanticipated failures (e.g., outgassing of eye-irritating materials during use). This work describes the use of a new coating technology, aerosol impact-driven assembly (AIDA), to develop a next-generation permanent anti-fog coating for the xEMU helmet. We use AIDAs unique ability to tune both the refractive index and surface roughness of films to deposit a thin, transparent (85% transmittance of visible light), and hydrophilicanti-fog coating. The Exploration Extravehicular Mobility Unit’s (xEMU) helmet is a complex assembly designed to accomplish several tasks to protect and enable astronauts. In addition to maintaining a suitable environment for the wearer, it must also allow for appropriate mobility and provide a wide and undistorted view of the surroundings. A critical component of the helmet’s optical system is the anti-fog coating. While previous versions of the anti-fog coating have provided suitable anti-fog performance, they have been difficult to apply, lacked mechanical or chemical durability, or resulted in unanticipated failures.   This work uses a new coating technology, aerosol impact-driven assembly (AIDA), to develop a next-generation permanent anti-fog coating for the xEMU helmet. We use AIDA’s unique ability to tune both the refractive index and surface roughness of films to deposit a thin, transparent (>85% transmittance of visible light), hydrophilic (contact angle <10°) anti-fog coatings that meet NASA's stringent durability requirements.  Objective #1: Polycarbonate substrate surface is modified such that the water contact angle is reduced to <10° resulting in a reduction/elimination of visible condensation in an xEMU helmet under operational conditions.  Objective #2: The process for accomplishing objective #1 does not reduce transmission of visible light below 70%. Ideally the process results in an increase in transmission. Transmission haze remains below 3%.  Objective #3: Contact angle and transmittance/haze are maintained after the following durability tests: Simulated breathing ≥ 4B Cross hatch test (ASTM 3359) 1000 cycles of simulated cleaning with water 1000 cycles of simulated cleaning using IPA 1000 cycles of simulated cleaning using windex 1000 cycles of simulated cleaning using a 50% water 50% dish soap mixture Exposure to and removal of spit, skin oils, and vomit Facial hair abrasion Intense UV exposure Objective #4: Coating is composed of low-volatility materials such that it passes an off-gassing test conducted by the White Sands Test Facility.  Objective #5: The coating can be applied to the xEMU helmet and meet objectives 1-4 Objective #6: The process used to form the coating that meets objectives 1-5 is reproducible with at least a 90% success rate.   Deliverables: 100 coated 4” x 4” , 25 coated 12” x12”, 1 coated xEMU helmet bubble with the coating applied to the interior

The solicitation identifies anti-fog coatings for use in the xEMU helmet as an immediate need. As the coating and coating method have been shown to be substrate agnostic, there is the opportunity to apply it to other materials (other polycarbonate components, glass, fabrics) that require anti-fog functionality. More generally, the ability to deposit dozens of different materials with tunable porosity onto a variety of substrates will undoubtedly enable new applications not yet considered.  Anti-fog coatings represent a $16B global market with applications in the packaging industry, automotive industry, solar industry, display industry, and the eyewear industry. 

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