In January 2015, the Center for Bio/Molecular Science and Engineering at the Naval Research Laboratory (NRL) began an effort to evaluate and develop top-coat type treatments suitable for application to painted surfaces that would reduce retention of chemical threat agents following standard decontamination approaches. Four commercially available surface treatments were evaluated: NANOskin Hydro Express, Rust-Oleum® NeverWet®, Eagle One Superior NanoWax™, and Rust-Oleum® Wipe New.

Images of a painted coupon (A), a Nanoskin treated coupon (B), a Wipe New treated coupon (C), a NeverWet treated coupon (D), and a NanoWax treated coupon (E).

Aluminum coupons were painted with a polyurethane-based system following the directions for those products. Deposition of the surface treatments onto painted surfaces was completed as advised by manufacturer directions. NANOskin Hydro Express was shaken and sprayed onto a clean, cool surface. The product was spread evenly on the surface and allowed to dry. Eagle One Superior NanoWax™ was similarly applied by spraying and wiping. Rust-Oleum® NeverWet® was applied by simply spraying onto the surface and allowing to dry. Rust-Oleum® Wipe New was applied by wiping it onto the surface with the preloaded microfiber towel provided.

Sessile contact angles for samples evaluated under this effort used three 3 μL droplets per surface with each droplet measured independently three times for each of three targets: water, ethylene glycol, and n-heptane. Geometric surface energy was calculated based on the water and ethylene glycol interactions using software designed for the DROPimage goniometer package.

Sliding angles were determined using 5 μL droplets. The droplet was applied at 0° after which the supporting platform angle was gradually increased up to 60°. Sliding angles for each of the liquids were identified as the angle for which movement of the droplet was identified.

Shedding angles for each liquid were determined using 12 μL droplets initiated 2.5 cm above the coupon surface. Changes in base angle of 10° were utilized to identify the range of droplet shedding angle based on a complete lack of droplet retention by the surface (not sliding). The angle was then reduced in steps of 1° to identify the minimum required angle.

Droplets of 5 mL diameter were applied to the surfaces and images were collected at 30s intervals for 5 minutes followed by images at 5 min. intervals for a total of 30 min. DFP samples were kept covered for the duration of the experiment to minimize evaporation.

Simulant exposure and evaluation methods were based on the tests developed by Edgewood Chemical Biological Center referred to as Chemical Agent Resistance Method (CARM). Standard target exposures utilized a challenge level of 10 g/m2. Here, the coupons were 0.00258 m2; a 5 g/m2 target challenge was applied to the surfaces as two equally sized neat droplets. Following application of the target, coupons were aged 1 hour prior. Decontamination used a gentle stream of air to expel target from the surface prior to rinsing with soapy water (0.59 g/L Al-conox in deionized water). The coupons were then soaked in isopropanol for 30 minutes to extract remaining target; this isopropanol extract was analyzed by the appropriate chromatography method to determine target retention on the surface.

For paraoxon analysis, a Shimadzu High Performance Liquid Chromatography (HPLC) system with dualplunger parallel flow solvent delivery modules (LC-20AD) and an auto-sampler (SIL-20AC; 40 μL injection volume) coupled to a photodiode array detector (SPD-M20A; 277 nm) was used. The stationary phase was a C18 stainless steel analytical column (Luna, 150 mm × 4.6 mm, 3 μm diameter) with an isocratic 45:55 acetonitrile: 1% aqueous acetic acid mobile phase (1.2 mL/min).

For analysis of methyl salicylate (MES), diisopropyl fluorophosphate (DFP), and dimethyl methylphosphonate (DMMP), gas chromatography-mass spectrometry (GC-MS) was accomplished using a Shimadzu GCMS-QP2010 with AOC-20 auto-injector equipped with a Restex Rtx-5 (30 m x 0.25 mm ID x 0.25 μm df) cross bond 5% diphenyl 95% dimethyl polysilox-ane column. A GC injection temperature of 200°C was used with a 1:1 split ratio at a flow rate of 3.6 mL/min at 69.4 kPa. The oven gradient ramped from 50°C (1 min. hold time) to 180°C at 15°C/min. and then to 300°C at 20°C/min. where it was held for 5 min.

This work was done by Brandy J. White, Anthony P. Malanoski, and Martin H. Moore for the Naval Research Laboratory. NRL-0072


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Bioinspired Surface Treatments for Improved Decontamination: Commercial Products

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This article first appeared in the December, 2017 issue of Aerospace & Defense Technology Magazine.

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