Anti-Fog Coatings for Spacesuit Helmets

The purpose of this Phase-II project is to continue optimizing the anti-fogging coating developed in Phase-I and begin commercializing the coating for use on NASA spacesuit helmets and other applications, such as consumer eyewear. In Phase-I a permanent and robust anti-fog coating was developed that is applied to the interior of polycarbonate spacesuit helmets. The coating is a mechanically resilient and permanent superhydrophilic layer produced by a two-step process consisting of a plasma processing pre-treatment followed by the deposition of an optically transparent diamond like carbon coating to achieve an anti-fog layer with Water Contact Angle 10 degrees. The all-dry vacuum process consists of an oxygen plasma etching to engineer the surface of the polycarbonate, creating a well-controlled nanotextured morphology, which is key to the superhydrophilic properties, followed by plasma enhanced chemical vapor deposition of the diamond like carbon coating with high surface energy. The process is carried out at low temperatures compatible with polycarbonate materials and the two steps are performed back-to-back without breaking vacuum between steps. The process is readily scalable and compatible with large scale production volumes. The anti-fogging coating was tested for 200 hours exposure using a breath simulator with no detrimental effect on the coating performance. The coating was also tested for exposure to cleaning fluids, IPA chemical exposure, adhesion testing per ASTM D3359, and abrasion resistance per MIL-C-48497 with no detrimental effects. Anti-fog coatings are commonly used in spacesuit helmets to eliminate fogging on the interior of the face shield due to the astronaut’s breathing. Currently for the Extravehicular Mobility Unit (EMU) spacesuit an astronaut applies an anti-fog liquid to the interior of the helmet bubble before each extravehicular activity. However, the anti-fog solutions can causes eye discomfort, irritation and has even caused temporary blindness during a spacewalk. In addition wipe-on solutions are not a desirable because they are not permanent, must be applied before each use, are easily compromised by cleaning and incidental contact, and are a consumable that must be tracked and supplied for each mission. To address these problems a permanent and robust anti-fog coating is desired that can be applied to the interior of polycarbonate spacesuit helmets. In this project Acree developed a robust, permanent, optically transparent superhydrophilic Diamond Like Carbon anti-fogging coating that is applied using a two-step vacuum process. Technical Objectives: 1) Continue optimizing the Phase-I coating for anti-fogging performance, optical transparency, mechanical abrasion resistance, adhesion, and tolerance to chemical exposure and cleaning. 2) Coat at least five curved polycarbonate domes similar in size to the NASA GFE helmet and measure the thickness and uniformity of the coating and subject the coating to all of the durability and exposure testing. Objective: To demonstrate the repeatability and performance of the coating on curved domes. 3) Coat at least one GFE helmet bubble provided by NASA with the anti-fogging coating. Subject the coated helmet to all the durability and exposure testing. Objective: To demonstrate the performance of the coating on an actual GFE helmet. 4) Perform tensile testing on at least 10 coated and 10 uncoated dog-bone samples per ASTM D638-14, type I. Objective: to ensure that the anti-fog coating does not affect the mechanical properties of the polycarbonate. 5) Provide coated polycarbonate samples and work with NASA to perform EMU/xEMU off-gas testing per NASA memorandum TOX-VM-2014-07 Rev B. Objective: To demonstrate no toxicological effects from the coating. 6) Deliverable: Send 30 coated and 30 uncoated samples to JSC at the mid-point and end of the project for their testing. 7) Deliverable: Final Report and technical results.
Benefits: The anti-fogging coating can be used on the inside surface of NASA spacesuit helmets, such as the Extravehicular Mobility Unit (EMU) or the Exploration EMU (xEMU) pressure bubbles, or any other spacesuit helmet used or being developed for NASA. The anti-fogging coating has potential for widespread use on items such as consumer eyewear, ski goggles, face shields, etc., and spacesuit helmets from other companies, such as SpaceX.