John R. Hollahan

Combination Moisture Resistant and Antireflection Plasma Polymerized Thin Films for Optical Coatings

The technique of plasma polymerization under vacuum conditions at ~0.1 Torr has been employed to produce highly moisture resistant, thin polymer films on hygroscopic alkali metal halide crystal materials. The polymer film is fluorocarbon in nature. In addition to the moisture resistance, the films also exhibit antireflection properties and have only one absorption band over the range 25,000-250 cm(-1) centered at 1200 cm(-1).

Synthesis of Reverse Osmosis Membranes by Plasma Polymerization of Allylamine

The polymerization of allylamine in a radio-frequency electrodeless plasma to form thin polymer films on microporous filter media provides very effective dry composite membranes for reverse osmosis. Salt and urea rejections as high as 98 percent and 46 percent, respectively, have been achieved from a solution containing 10 grams of sodium chloride per liter and 10 grams of urea per liter. The plasma conditions and polymerization technique are discussed.

Moisture resistant and anti-reflection optical coatings produced by plasma polymerization of organic compounds

The need for protective coatings on critical optical surfaces, such as halide crystal windows or lenses used in spectroscopy, has long been recognized. Many widely used halide materials are extremely moisture sensitive, such as sodium chloride and cesium iodide, and a number of approaches have been taken to protect such optics. These approaches, often crude, have not always been reliable or particularly convenient. It has been demonstrated that thin, one micron, organic coatings produced by polymerization of flourinated monomers in low temperature gas discharge (plasma) exhibit very high degrees of moisture resistence, e.g., hundreds of hours protection for cesium iodide vs. minutes before degradation sets in for untreated surfaces. Moreover, the index of refraction of these coatings is intermediate between that of the halide substrate and air, a condition for anti-reflection, another desirable property of optical coatings. Thus, the organic coatings not only offer protection, but improved transmittance as well. Further, the polymer coating is non-absorbing over the range 0.4 to 40 μ with an exception at 8.0 μ, the expected absorption for C-F bonds.