Plasma polymerization technique is used to apply thin, adherent, hydrophobic coatings from chlorotrifluoroethylene monomer. Apparently much of the chlorine contained in original monomer is lost during polymerization, and characteristic C-Cl absorption in infrared region is essentially absent

Hollahan, J. R.

Johnson, C. C.

Wydeven, T.

English

NASA Technical Reports Server

December 1973
	
B73-10507 
NASA TECH BRIEF 
Ames Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Moisture-Resistant Coatings for Optical Components 
The problem: 
To protect moisture-sensitive optical components, 
such as the cesium iodide or sodium chloride windows 
used in spectroscopy. The usual techniques of main-
taining critical optics under an atmosphere of dry or 
inert gas, enclosing them in polyethylene envelopes, 
or keeping them in closed compartments with desic-
cants are not always convenient or satisfactory. 
The solution: 
Use a plasma polymerization technique to apply 
thin, adherent, hydrophobic coatings from chiorotri-
fluoroethylene monomer. 
How it's done: 
The optical component is supported on pins inside 
the bell jar of a typical vacuum coating apparatus. 
The bell jar is evacuated to a background pressure of 
less than 0.13 N/rn2 (10-3 torr), and chlorotrifiuro-
ethylene (CTFE) is admitted via a needle valve. 
System pressure, controlled by the flow of CTFE, is 
stabilized at about 0.32 to 0.64 N/rn2, and then argon 
or inert gas is allowed to enter the bell jar through 
a tube which directs the stream substantially onto the' 
upper surface of the optical component. When the 
total pressure (CTFE flow and argon flow) is at 
about 27 N/rn2, rf energy is applied to the gas stream 
until a discharge is initiated and can be maintained at 
30 watts input. The system is operated under these 
conditions for 30 minutes, and then the substrate is 
turned over and exposed to the plasma for an addi-
tional 30 minutes; this assures uniform coating even 
though the plasma pervades all substrate surfaces.
Typically, the film formed on an infrared window 
is thin (0.10 .tm or less), and adheres firmly to the 
entire surface; it is free of pinholes and is moisture re-
sistant. A crystal of cesium iodide coated by plasma 
polymerization is stable for at least 400 hours at 88.8% 
relative humidity. Under the same conditions, an un-
coated crystal etches severely in two minutes. 
As prepared by plasma polymerization, films re-
semble polytetrafluoroethylene; apparently much of 
the chlorine contained in the original monomer is 
lost during polymerization, and the characteristic 
C-Cl absorption in the infrared region is essentially 
absent. The films have transmittances of about 90% 
over the range 1400-400 cm- 1 ; large absorptions at 
1180 cm-1 are inevitable inasmuch as they are caused 
by C-F bond stretching. 
Reference: 
Hollahan, J
.
 R., and Wydeven, T.: Reverse-Osmosis 
Membranes by Plasma Polymerization. NASA Tech 
Brief B72-10710; see also Science, vol. 179, p. 500, 
1973. 
Notes: 
1. It is anticipated that a variety of polymerized 
chloro-, fluoro-, or chiorofluorohydrocarbons would 
have equivalent hydrophobic properties. 
2. No additionl documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B73-10507
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000507 2020-03-17T07:33:38+00:00Z
Patent status:	 Source: John R. Hollahan, Theodore Wydever, 
Inquiries concerning the rights for the commercial 	 and Catherine C. Johnson 
use of this invention should be addressed to: 	 Ames Research Center 
NASA Patent Counsel 	 (ARC-10749)
Mail Code 200-1A 
Ames Research Center 
Moffett Field, California 94035	 - 
B73-10507	 Category 04	
•


Moisture-resistant coatings for optical components

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