Glow discharge method for producing a bondable Room Temperature Vulcanizing (RTV) silicone is described. Mechanical and chemical properties of silicone specimens are described. Theory concerning the relationship between surface characteristics and bondability is examined with respect to the polymer specimen

Delollis, N. J.

Montoya, O.

English

NASA Technical Reports Server

June 1972	 B72-10367 
say C
AEC-NASA TECH BRIEF  
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Office, NASA, Code KT, Washington, D.C. 20546. 
Bondability of RTV Silicone Rubber 
Cured two-part Room Temperature Vulcanizing 
(RTV) silicones are not bondable with common organic 
adhesives such as epoxies or neoprene. Attempts to 
develop bondable surfaces on cured RTV have primarily 
involved various silicate or silane primers. These have 
met with only marginal success. 
A new glow discharge method renders the vinyl 
addition RTV silicone rubber surface bondable. An 
activated oxygen plasma acts on both sides of the RTV 
specimens in a glow discharge chamber for 10 minutes. 
The power level is set at 250 watts and the oxygen pres-
sure at 1 millimeter mercury. 
This treatment provides the RTV silicone spec-
imens with adhesive bond strength in excess of 500 psi. 
In contrast, untreated specimens exhibited adhesive 
bond strengths of less than 10 psi. 
The glow discharge treatment challenges the pre-
vailing theory concerning the relationship between sur-
face characteristics and bondability. According to this 
theory the presence of a "weak boundary layer" (WBL), 
related to low molecular weight polysiloxane fractions 
on the surface, contributed to the unbondability of 
silicone rubber. Therefore, most attempts to produce a 
bondable surface of silicone rubber were directed 
toward removal of the WBL. 
The glow discharge treatment creates a bondable 
surface of silicone rubber without removing the WBL. 
The activated oxygen reacts preferentially with the 
vinyl groups rather than the ring structured poly-
siloxanes leaving the WBL virtually unchanged. This
implies that the presence or absence of WBL or low 
molecular weight inclusions is a secondary or negligible 
factor in the bonding process, and that treatment of the 
polymer substrate is the primary factor. 
Note:
Requests for further information may be directed 
to:
Mr. Glenn K. Ellis 
Technology Utilization Officer 
Office of Information Services 
U.S. Atomic Energy Commission 
Washington, D.C. 20545 
Reference: TSP72-10367 
Patent status: 
Inquiries concerning rights for commerical use of 
this information may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Source: Nicholas J. DeLollis, and 
Orelio Montoya
Sandia Laboratories 
under contract to
Atomic Energy Commission
(AEC-10026) 
Category 04 
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This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son acting on behalf of the United States Goverr'ment assumes any
liability resulting from the use of the information contained in this 
document, or warrants that the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
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Bondability of RTV silicon rubber

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