Method for producing a dimensionally graded conductive foam

• US 5,523,119 A
• Filed: 03/16/1995
• Issued: 06/04/1996
• Est. Priority Date: 05/14/1993
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Wettermark, Urszula G., Worrell, Gregory H.
• Primary Examiner(s): SCHOFER, JOSEPH
• Application Number:
  US08/405,524
• Time in Patent Office: 446 Days
• Field of Search: 427/58, 427/244, 427/256, 427/261, 427/430, 427/1, 427/341
• US Class Current: 427/244
• CPC Class Codes: C08J 2375/04 Polyurethanes
• CPC Class Codes: C08J 9/405 with polymerisable compounds
• CPC Class Codes: H01B 1/127 comprising five-membered aromatic rings in the main chain, e.g. polypyrroles, polythiophenes
• CPC Class Codes: Y10T 428/249953 Composite having voids in a component [e.g., porous, cellular, etc.]
• CPC Class Codes: Y10T 428/249961 With gradual property change within a component
• CPC Class Codes: Y10T 428/249987 With nonvoid component of specified composition

Abstract

A dimensionally graded electroconductive and electromagnetically responsive composite material is produced by contacting a polyurethane open cell foam substrate with a solution of an oxidatively polymerizable compound, such as pyrrole, that is polymerized to form a thin electroconductive polymer coating on the foam'"'"'s surfaces. The reaction, wherein the compound is oxidized and polymerized to form a conductive polymer occurs over time. By varying the amount of time the porous foam substrate is in contact with the reacting solution a graded amount of electroconductive polymer is deposited on the foam substrate. The electrical activity of the resultant electrically conducting polyurethane/polypyrrole composite foam is measured as a Free Field Transmission loss at the microwave frequency of 10 GHz and expressed in "-dB". The polyurethane/polypyrrole composite foam with dimensionally graded electrical conductivity/activity constitutes a new bulk absorber.

Claims

1. A method for making a dimensionally graded electroconductive composite material from a polyurethane foam substrate, the method comprising the steps of:

preparing a solution of a polymerizable monomer that can be polymerized to form an electroconductive polymer;

contacting at least a portion of the substrate in the solution of polymerizable monomer;

initiating the polymerization reaction of the polymerizable monomer in the solution, whereby the electroconductive polymer is deposited on a surface of the substrate over time; and

then

varying the contact time of the substrate with the solution of polymerizable monomer, thereby producing a dimensionally graded deposit of electroconductive polymer on the substrate.

2. The method of claim 1, wherein:

the polymerizable monomer is polymerized by an oxidation reaction; and

the reaction is initiated by adding an oxidant to the solution.

3. The method of claim 1, wherein:

the contact time is varied by immersing the substrate into the solution; and

then

gradually removing the substrate from the solution.

4. The method of claim 1, wherein:

the contact time is varied by immersing the substrate into the solution; and

then

incrementally removing the substrate from the solution.

5. The method of claim 1, wherein:

the substrate is a dielectric.

6. The method of claim 1, wherein:

the substrate is an open cell polyurethane foam.

7. A method for making a dimensionally graded electroconductive composite material from a polyurethane foam substrate in a chemical reaction, which occurs over time, the method comprising the steps of:

preparing a solution of an oxidatively polymerizable compound;

adding an oxidant to the solution, wherein the compound is oxidized by the oxidant to form an electroconductive polymer that is deposited on the surface of the substrate over time; and

then

moving the substrate through the solution, where in portions of the substrate are in contact with the reacting solution for different periods of time so that a dimensionally graded deposit of the electroconductive polymer is produced on the substrate.

8. The method of claim 7, wherein:

the substrate is moved through the solution by immersing the substrate in the solution; and

then

gradually removing the substrate from the solution.

9. The method of claim 7, wherein:

the substrate is moved through the solution by immersing the substrate into the solution; and

then

incrementally removing the substrate from the solution.

10. The method of claim 7, wherein:

the solution is an aqueous solution.

11. The method of claim 7, wherein:

the oxidant is provided by a ferric chloride salt.

12. The method of claim 7, further comprising:

adding a stabilizing dopant to the solution.

13. The method of claim 12, wherein:

the stabilizing dopant is provided from an organic sulfonate.

14. The method of claim 12, wherein:

the stabilizing dopant is supplied by a p-toluene sulfonate sodium salt.

15. The method of claim 7, wherein:

the substrate is an open cell polyurethane foam.

16. The method of claim 7, wherein:

the polymerizable compound is pyrrole.

17. A method for making a dimensionally graded electroconductive composite material from a polyurethane foam substrate in a chemical reaction which occurs over time, the electrical activity of the composite material being measurable as a degree of transmission loss measured in decibels at the frequency of 10 GHz, the method comprising the steps of:

preparing an aqueous solution of pyrrole;

adding a stabilizing dopant provided from an organic sulfonate;

adding an oxidant to the solution, wherein the pyrrole is oxidized by the oxidant to form a pyrrole polymer that is deposited on the surface of the substrate over time; and

then

moving the substrate through the solution, wherein portions of the substrate are in contact with the solution for different periods of time so that a dimensionally graded deposit of the pyrrole polymer is produced on the substrate.

18. The method of claim 17, wherein:

the substrate is moved through the solution by immersing the substrate in the solution; and

then

gradually removing the substrate from the solution.

19. The method of claim 17, wherein:

the substrate is moved through the solution by immersing the substrate into the solution; and

then

incrementally removing the substrate from the solution.

20. The method of claim 17, wherein:

the substrate is an open cell polyurethane foam.

21. The method of claim 17, wherein:

the oxidant is provided by a ferric chloride salt.

22. The method of claim 17, wherein:

the stabilizing dopant is supplied by a p-toluene sulfonate sodium salt.

23. A method for making a dimensionally graded electroconductive composite material from an open cell polyurethane foam substrate in a chemical reaction which occurs over time the electrical activity of the composite material being measurable as a degree of transmission loss measured in decibels at the frequency of 10 GHz, the method comprising the steps of:

preparing an aqueous solution of pyrrole;

adding a p-toluene sulfonate sodium salt to act as a stabilizing dopant;

adding a ferric chloride salt to the solution to act as an oxidant, wherein the pyrrole is oxidized by the oxidant to form a pyrrole polymer that is deposited on the surface of the substrate over time; and

then

moving the substrate through the solution, wherein portions of the substrate are in contact with the solution for different periods of time, the periods of time increasing along a given dimension of the substrate causing more of the polymer to be deposited on the portions as the periods of time increase.

24. The method of claim 23, wherein:

the substrate is moved through the solution by immersing the substrate in the solution; and

then

gradually removing the substrate from the solution.

25. The method of claim 23, wherein:

the substrate is moved through the solution by immersing the substrate into the solution; and

then

incrementally removing the substrate from the solution.