Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing gas sample
Reexamination Certificate
1999-03-16
2001-11-13
Warden, Jill (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing gas sample
C073S001020, C073S335050, C252S511000, C264S105000, C521S053000
Reexamination Certificate
active
06315956
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electrochemical sensor device for detecting the presence of chemical analytes which are in either a liquid or vapor phase. More specifically, the invention relates to a reversible electrochemical sensor comprised of conductive polymer composite materials and the method of making conductive polymer composite materials for reversible electrochemical sensors.
2. Description of the Prior Art
Chemical sensing, and in particular chemical solvent sensing, has become very important for environmental and loss management concerns. The ability to detect a leak or the presence of a chemical and to identify the chemical in an inexpensive manner is of great interest. Commercial and industrial establishments concerned about gaseous emissions or chemical spills, as well as owners or operators of underground installations or utilities such as fiber optical cables, which can be damaged in the presence of chemical solvents, have a need for reliable and inexpensive chemical sensors.
Conductive polymers and conductive polymer composites have been used for chemical sensing applications because of their ability to be tailored to the chemical(s) to be sensed by a judicious choice of polymer, polymer quantities and constituents. Electrochemical sensors employing conductive polymers and conductive polymer composites often exhibit a change in conductivity in the presence of a target chemical(s). The mechanism effecting the conductivity change is often a swelling of the polymer when it absorbs the chemical or chemical vapors. This swelling alters the volume concentration of the polymer resulting in an increase in the distance between one conductive network branch to the next; therefore changing the conductivity of the polymer.
One such device is illustrated and described in U.S. Pat. No. 5,417,100 (Miller et al.) which discloses a reversible sensor for detecting solvent vapors. The sensor of the '100 patent consists of a dielectric substrate; a pair of interdigitated, electrically conductive electrodes disposed on the surface of the substrate; and a composite coating covering the interdigitated electrodes and comprising a conductive polymer and a dielectric polymer with an affinity for the solvent vapors to be detected. The sensor of the '100 patent relies on physical absorption of the vapor being detected. The absorbed vapor causes the conductive polymer composite to swell, increasing the distance between the conductive polymer chains, and therefore exhibiting a loss in conductivity, or increase of volume resistivity in the composite.
U.S. Pat. No. 5,698,089 (Lewis et al.) discloses a chemical sensor for detecting analytes in fluids. This sensor consists of a pair of conductive elements (electrical leads) coupled to and separated by a chemically sensitive resistor which provides an electrical path between the conductive elements. The resistor comprises a plurality of alternating nonconductive regions of a nonconductive organic polymer and conductive regions comprised of a conductive material. The electrical path length and resistance between the conductive regions changes with the absorption of analytes. The '089 patent also teaches of sensor arrays incorporating combinations of sensors having varied polymer and conductive polymer constituents so as to have sensitivity to a variety of analytes.
The patent to Soane (U.S. Pat. No. 5,672,297) teaches of a gel-matrix whose electrical and/or thermal conductivity undergoes a significant change in response to minor variations in one of several externally controlled thermodynamic parameters such as temperature, pH, ionic strength and solvent composition. The gel-matrix is comprised of three primary components: conductive particles, swellable and deswellable crosslinked particles, and a solvent system. In the de-swollen state, the conductive particles are normally discrete. When the gel-matrix is swollen (in response to a variation in temperature, pH, ionic strength or solvent composition), the interstitial volume between cross-linked gel particles diminishes, forcing conductive particles to come into intimate contact with one another, thus creating a more conductive network.
The heretofore discussed '100 and '089 patents prefer the use of intrinsically conductive polymers, such as polyaniline and polypyrrole, for the conductive polymer regions; while the '297 patent shows a preference for a variety of metallic and other conductive particles, including carbon black powder, for the conductive filler. The application of composite conductive polymers as electrochemical sensors using carbon black as the conductive filler has also been reported on. See for example, Lundberg and Sundqvist (1986) J.Appl.Phys. 60:1074-1079, the contents of which are incorporated by reference, which reports on the resistivity of a polyethylene matrix with a carbon black filler and a poly(tetrafluoroethylene) matrix with a carbon black filler as a function of exposure to various solvents. It was found that the resistivity of these composites increased when exposed to certain solvent vapors or were immersed in certain solvents. The report also suggests combining two or more composites with sensitivities to different analytes in a single detector, thus forming a versatile electronic sensor array.
The ability of polymers to act as electrical insulators is the basis for their widespread use in the electrical and electronic fields. However, material designers have sought to combine the fabrication versatility of polymers with many of the electrical properties of metals. A few select polymers, such as polyacetylene, polyaniline, polypyrrole and others, can be induced to exhibit intrinsic conductivity through doping, although these systems tend to be cost prohibitive and difficult to fabricate into articles. An extrinsic approach of imparting conductivity to a polymer is through the creation of conductive polymer composite (“CPC”) materials. CPC materials require a random distribution of a conductive filler to be dispersed throughout an insulating polymer which results in an infinite network capable of supporting electron flow. Prior art CPC materials have employed metals, intrinsically conductive polymers, or, most often, carbon black as the conductive filler.
A crucial aspect in the production of CPC materials is the quantity of conductive filler content. If the quantity of conductive filler is too high, the processing becomes difficult, the mechanical properties of the composite are poor, and the final cost is high. Therefore, the quantity of conductive filler should be as low as possible while still allowing the composite to fulfill its electrical requirements.
Percolation theory has been successfully used to model the general conductivity characteristics of CPC materials by predicting the convergence of conducting particles to distances at which the transfer of charge carriers between them becomes probable. The percolation threshold (“p
c
”), defined as the lowest concentration of conducting particles at which continuous conducting chains are formed, can be determined from the experimentally determined dependence of conductivity of the CPC material on the filler concentration. For a general discussion on percolation theory, see Kirkpatrick (1975) Review of Modern Physics 45:574-588, the contents of which are herein incorporated by reference. Much work has been done on determining the parameters influencing the p
c
with regard to the conductive filler material. See for example Lux (1993) J. Materials Sci. 28:285-301; Narkis and Vaxman (1984) J.Appl.Poly.Sci. 29:1639-1652; and Sherman and Middleman, et al. (1983) Poly.Egr. & Sci. 23:36-46; the contents of each of which are herein incorporated by reference.
A typical method of optimizing the conductive filler level to conductivity performance ratio of CPC materials is to reduce the content of the conductive filler to a value just above p
c
. More recently, this work has been advanced by developing approaches which exploit aspects
Norris & McLaughlin & Marcus
Pirelli Cables and Systems LLC
Sines Brian
Warden Jill
LandOfFree
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