Volatile organic compound sensors

• US 5,756,879 A
• Filed: 07/25/1996
• Issued: 05/26/1998
• Est. Priority Date: 07/25/1996
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Inventors: Stanford, Thomas B., Miller, Leroy J., van Ast, Camille I., Yamagishi, Frederick G.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): WIGGINS, JOHN DAVID
• Application Number:
  US08/685,997
• Time in Patent Office: 670 Days
• Field of Search: 73/28.01, 73/24.04, 73/23.34, 73/23.31, 73/31.02, 73/31.03, 204/424, 324/439, 324/446, 324/691, 324/693, 428/421, 428/426, 422/90, 422/94, 422/98
• US Class Current: 73/28.01
• CPC Class Codes: G01N 27/126 comprising organic polymers
• CPC Class Codes: Y10T 428/3154 Of fluorinated addition polymer from unsaturated monomers

Abstract

A novel, inexpensive sensor and method for detecting volatile compounds in the gas phase at concentrations of less than about 500 ppm in ambient air are provided. The sensor comprises (a) a dielectric substrate having a major surface; (b) a pair of electrically conductive electrodes disposed on the major surface of the substrate; and (c) a conductive polymer covering the pair of electrically conductive electrodes, with the conductive polymer doped with appropriate dopants in measurable excess of that stoichiometrically required to change the conductive polymer from a neutral state to a charged state to provide requisite conductivity. A method for making the sensor is provided, as is a method of use of the sensor which relates to its use in a monitoring system comprising a means for measuring the conductivity of the sensor connected to a warning means for providing an indication when the conductivity reaches a predetermined level. Contemplated specific methods of use include the detection of fugitive emissions in chemical plant environments; the detection of certain pollutants in vehicle exhaust; and the detection of certain pollutants near chemical handling operations, such as painting operations.

Claims

1. The invention claimed is a sensor for reversibly detecting target volatile material in the gas phase comprising:

(a) a dielectric substrate having a major surface;

(b) a pair of electrically conductive electrodes disposed on said major surface of said substrate; and

(c) a conductive polymer covering said pair of electrically conductive electrodes, said conductive polymer doped with appropriate dopants, said dopants present in said conductive polymer in measurable excess of that stoichiometrically required to change said conductive polymer from a neutral state to a charged state to provide requisite conductivity,

said sensor being capable of detecting the presence of said target volatile material at a concentration of less than about 500 ppm.

wherein said dielectric substrate is deactivated by a surface treatment means that enhances the hydrophobicity of surface on said substrate.

2. The invention claimed is the sensor of claim 1 wherein said conductive polymer is prepared by spin-casting from dilute organic solutions having a concentration of less than about 10% and wherein said dilute organic solutions are substantially free of agglomeration.

3. The invention claimed is the sensor of claim 2 wherein said sensor is capable of detecting the presence of said target volatile material at a concentration of less than about 1 00 ppm.

4. The invention claimed is the sensor of claim 1 wherein said electrically conductive electrodes comprise a material selected from the group consisting of gold, platinum, palladium, and carbon.

5. The invention claimed is the sensor of claim 4 wherein said electrically conductive electrodes consist essentially of gold.

6. The invention claimed is the sensor of claim 5 wherein said gold electrodes are formed on an adhering layer that adheres said gold electrodes to said substrate.

7. The invention claimed is the sensor of claim 1 wherein said conductive polymer is selected from the group consisting of polyaniline, polythiophene, polypyrrole, poly(p-phenylene vinylene), derivatives of these polymers, and mixtures of these materials.

8. The invention claimed is the sensor of claim 7 wherein conductive polymer is polyaniline and said dopants are selected from the group consisting of p-toluenesulfonate, copper phthalocyanine-tetrasulfonate, poly(styrenesulfonate), camphorsulfonate, dodecylbenzenesulfonate, butanesulfonate, octanesulfonate, hexadecanesulfonate, octadecanesulfonate, and bisulfate.

9. The invention claimed is the sensor of claim 1 wherein said measurable excess is about one part over that stoichiometrically required to change one part of said conductive polymer from a neutral state to a charged state to provide requisite conductivity.

10. The invention claimed is the sensor of claim 1 wherein said dielectric substrate comprises a material selected from the group consisting of glass, ceramics and dielectric polymers.

11. The invention claimed is the sensor of claim 10 wherein said dielectric substrate comprises a glass selected from the group consisting of silica, phosphate, and borate glasses and mixtures thereof.

12. The invention claimed is the sensor of claim 10 wherein said dielectric substrate comprises a ceramic selected from the group consisting of alumina, magnesia, calcia, quartz, and mixtures thereof.

13. The invention claimed is the sensor of claim 10 wherein said dielectric substrate comprises a dielectric polymer selected from the group consisting of polyethylene terephthalate, poly(tetrafluoroethylene), poly(methyl methacrylate), and polyimides.

14. The invention claimed is a method of making a sensor for reversibly detecting target volatile material in the gas phase comprising:

(a) providing a dielectric substrate having a major surface;

(b) disposing a pair of electrically conductive electrodes on said major surface of said substrate; and

(c) preparing a conductive polymer for disposition on said electrically conductive electrodes by doping said conductive polymer with an excess of appropriate dopants, said dopants present in said conductive polymer in measurable excess of that stoichiometrically required to change said conductive polymer from a neutral state to a charged state to provide requisite conductivity; and

(d) covering said pair of electrically conductive electrodes with said doped conductive polymer,

said sensor being capable of detecting the presence of said target volatile material at a concentration of less than about 500 ppm,

further comprising step (a'"'"',) following step (a);

(a'"'"') deactivating said dielectric substrate by a surface treatment means that enhances the hydrophobicity of surface on said substrate.

15. The invention claimed is the method of claim 14 wherein said dielectric substrate is deactivated by silation with a silating agent selected from the group consisting of hexamethyidisilazane, N-phenylaminopropyltrimethoxysilane, octyltrishlorosilane, octyltrimethoxysilane, octadecyltrichlorosilane and octadecyltrimethoxysilane.

16. The invention claimed is the method of claim 14 wherein said electrically conductive electrodes comprise a material selected from the group consisting of gold, platinum, palladium, and carbon.

17. The invention claimed is the method of claim 14 wherein said dielectric substrate comprises a material selected from the group consisting of glass, ceramics, and dielectric polymers.

19. The invention claimed is the method of claim 14 wherein said conductive polymer is selected from the group consisting of polyaniline, polythiophene, polypyrrole, poly(p-phenylene vinylene), derivatives of these polymers, and mixtures of these materials.

20. The invention claimed is the method of claim 19 wherein said conductive polymer is polyaniline and said dopants are selected from the group consisting of p-toluenesulfonate, copper phthalocyaninetetrasulfonate, poly(styrenesulfonate), camphorsulfonate, dodecylbenzenesulfonate, butanesulfonate, octanesulfonate, hexadecanesulfonate, octadecanesulfonate, and bisulfate.

21. The invention claimed is the method of claim 14 wherein step (c) further comprises spin-casting said conductive polymer from a dilute organic solution having a concentration of less than about 10%.

22. The invention claimed is the method of claim 21 wherein step (c) further comprises minimizing agglomeration in said dilute organic solution.

23. The invention claimed is the method of claim 22 wherein said agglomeration is minimized by ultrasonication.

24. The invention claimed is the method of claim 22 wherein said sensor is capable of detecting the presence of said target volatile material at a concentration of less than about 100 ppm.

25. The invention claimed is the method of claim 14 wherein said measurable excess is about one part over that stoichiometrically required to change one part of said conductive polymer from a neutral state to a charged state to provide requisite conductivity.

26. The invention claimed is the method of claim 14 further comprising step (d):

(d) drying said doped conductive polymer prior to exposing said sensor to said target volatile material.

18. The invention claimed is a method of making a sensor for reversibly detecting target volatile material in the gas phase comprising:

(a) providing a dielectric substrate having a major surface;

(b) disposing a pair of electrically conductive electrodes on said major surface of said substrate; and

(c) preparing a conductive polymer for disposition on said electrically conductive electrodes by doping said conductive polymer with an excess of appropriate dopants, said dopants present in said conductive polymer in measurable excess of that stoichiometrically required to change said conductive polymer from a neutral state to a charged state to provide requisite conductivity; and

(d) covering said pair of electrically conductive electrodes with said doped conductive polymer.

said sensor being capable of detecting the presence of said target volatile material at a concentration of less than about 500 ppm.

wherein said electrically conductive electrodes comprise a material selected from the group consisting of gold, platinum, palladium and carbon, and

wherein said electrically conductive electrodes consist essentially of gold and wherein said method further comprises a step (a") immediately prior to step (b);

(a") depositing an adhering layer on said dielectric substrate comprising a tungsten--titanium alloy.

27. The invention claimed is a method of detecting a target volatile material in ambient air, said method comprising the steps of:

(a) providing a sensor comprising;

(i) a dielectric substrate having a major surface;

(ii) a pair of electrically conductive electrodes disposed on said major surface of said substrate, and

(iii) a conductive polymer covering said pair of electrically conductive electrodes, said conductive polymer doped with appropriate dopants, said dopants present in said conductive polymer in measurable excess of that stoichiometrically required to change said conductive polymer from a neutral state to a charged state to provide requisite conductivity, said conductive polymer having a conductivity that changes as a function of the presence of said target volatile material, said sensor being capable of detecting the presence of said target volatile material at a concentration of less than about 500 ppm;

(b) exposing said sensor to ambient air to generate a signal that is a function of said conductivity; and

(c) monitoring said conductivity of said conductive polymer, said method resulting in the detection of said target volatile material at a concentration of less than about 500 ppm.

wherein said dielectric substrate comprises a material selected from the group consisting of glass, ceramics, and dielectric polymers, and

wherein said dielectric substrate is deactivated by a surface treatment means that enhances the hydrophobicity of surface on said substrate.

28. The invention claimed is the method of claim 27 wherein said conductive polymer is prepared by spin-casting from dilute organic solutions having a concentration of less than about 10% and wherein said dilute organic solutions are substantially free of agglomeration.

29. The invention claimed is the method of claim 28 wherein said sensor is capable of detecting the presence of said volatile material at a concentration of less than about 100 ppm.

30. The invention claimed is the method of claim 27 wherein said electrically conductive electrodes comprise a material selected from the group consisting of gold, platinum, palladium, and carbon.

31. The invention claimed is the method of claim 30 wherein said electrically conductive electrodes consist essentially of gold.

32. The invention claimed is the method of claim 31 wherein said gold electrodes are formed on an adhering layer that adheres said gold electrodes to said substrate.

33. The invention claimed is the method of claim 27 wherein said conductive polymer is selected from the group consisting of polyaniline, polythiophene, polypyrrole, poly(p-phenylene vinylene), derivatives of these polymers, and mixtures of these materials.

34. The invention claimed is the method of claim 27 wherein said conductive polymer is polyaniline and said dopants are selected from the group consisting of p-toluenesulfonate, copper phthalocyaninetetrasulfonate, poly(styrenesulfonate), camphorsulfonate, dodecylbenzenesulfonate, butanesulfonate, octanesulfonate, hexadecanesulfonate, octadecanesulfonate, and bisulfate.

35. The invention claimed is the method of claim 27 wherein said measurable excess is about one part over that stoichiometrically required to change one part of said conductive polymer from a neutral state to a charged state to provide requisite conductivity.

36. The invention claimed is the method of claim 27 wherein said step of exposing comprises placing said sensor in the vicinity of an area of concern regarding the presence of said target volatile material.

37. The invention claimed is the method of claim 27 wherein said step of monitoring comprises measuring the conductivity between said electrodes.

38. The invention claimed is a method of using a sensor for reversibly detecting a target volatile material in the gas phase comprising a dielectric substrate having a major surface:

a pair of electrically conductive electrodes disposed on said major surface of said substrate; and

a coating covering said pair of electrically conductive electrodes, said coating consisting essentially of at least one conductive polymer doped to achieve a requisite conductivity and to have an affinity for said target volatile material, said method comprising the steps of;

(a) connecting said sensor to a mechanism capable of communicating the presence of said target volatile material upon detection thereof by said sensor; and

(b) positioning said sensor such that said sensor is exposed to ambient air in an area of concern regarding the presence of said target volatile material,

wherein said target volatile material is chemical weapon simulant material and said area of concern is selected from the group consisting of the vicinity of a potential chemical weapon deployment and the vicinity of chemical weapon manufacture.

39. The invention claimed is the method of claim 38 wherein said area of concern is in the vicinity of human handling of a material potentially containing said target volatile material.

40. The invention claimed is the method of claim 38 wherein said at least one conductive polymer is doped with appropriate dopants, said dopants present in said at least one conductive polymer in measurable excess of that stoichiometrically required to change said at least one conductive polymer from a neutral state to a charged state to provide requisite conductivity, said at least one conductive polymer having a conductivity that changes as a function of the presence of said target volatile material, said sensor being capable of detecting the presence of said target volatile material at a concentration of less than about 500 ppm.

41. The invention claimed is a method of using a sensor for reversibly detecting a target volatile material in the gas phase comprising a dielectric substrate having a major surface;

a pair of electrically conductive electrodes disposed on said major surface of said substrate; and

a coating covering said pair of electrically conductive electrodes, said coating consisting essentially of at least one conductive polymer doped to achieve a requisite conductivity and to have an affinity for said target volatile material said method comprising the steps of;

(a) connecting said sensor to a mechanism capable of communicating the presence of said target volatile material upon detection thereof by said sensor; and

(b) positioning said sensor such that said sensor is exposed to ambient air in an area of concern regarding the presence of said target volatile material,

wherein said dielectric substrate is deactivated by a surface treatment means that enhances the hydrophobicity of surface on said substrate, wherein said conductive polymer is prepared by spin-casting from dilute organic solutions having a concentration of less than about 10%, and wherein said dilute organic solutions are substantially free of agglomeration, said sensor being capable of detecting the presence of said target volatile material at a concentration of less than about 100 ppm.

42. The invention claimed is a monitoring system for monitoring the content of a target volatile material in ambient air, said monitoring system, comprising:

(a) at least one sensor for reversibly detecting said target volatile material in the gas phase, said at least one sensor positioned to be exposed to said ambient air, said at least one sensor comprising;

(i) a dielectric substrate having a major surface;

(ii) a pair of electrically conductive electrodes disposed on said major surface of said substrate; and

(iii) a conductive polymer covering said pair of electrically conductive electrodes, said conductive polymer doped with appropriate dopants, said dopants present in said conductive polymer in measurable excess of that stoichiometrically required to change said conductive polymer from a neutral state to a charged state to provide requisite conductivity, said conductive polymer having a conductivity that changes as a function of the presence of said target volatile material, said sensor being capable of detecting the presence of said target volatile material at a concentration of less than about 500 ppm, wherein said dielectric substrate is deactivated by a surface treatment means that enhances the hydrophobicity of surface on said substrate;

(b) a conductivity detector for measuring the conductivity of the sensor, said conductivity detector being capable of indicating when said conductivity reaches a predetermined level;

(c) an alarm for providing an indication when said predetermined level is reached; and

(d) interconnectors for interconnecting said sensor and said alarm to said conductivity detector.

43. The invention claimed is the monitoring system of claim 42 wherein said at least one sensor comprises an array of sensors.

44. The invention claimed is the monitoring system of claim 42 wherein said at least one sensor is capable of detecting the presence of said target volatile material at a concentration of less than about 100 ppm.