Compositions – Electrically conductive or emissive compositions
Patent
1997-09-12
2000-03-07
Kopec, Mark
Compositions
Electrically conductive or emissive compositions
73 3106, 528423, H01B 100, G01N 700, G01N 2700, C08G 7306
Patent
active
060336013
DESCRIPTION:
BRIEF SUMMARY
This invention relates to semiconducting organic polymers which may be used in gas sensors.
It is known that certain electrochemically prepared semiconducting polymers such as polypyrrole may be employed in sensors in order to detect gases, vapours and odours. Such a sensor may comprise a pair of electrodes mounted on a substrate, with a layer of the semiconducting organic polymer deposited on and between the electrodes in order to produce an electrical connection between the electrodes. The semiconducting organic polymer may be sensitive to the presence of a gas or, more likely, to a range of gases, to the extent that adsorption of the gas onto the polymer surface affects the physical and electrical properties of the polymer. Hence the presence of gas may be detected by monitoring, for example, the change in DC resistance of the sensor on exposure to the gas. For instance, Miasik et al (Miasik, J J, Hooper, A and Tofield, B C) J C S Faraday Trans. 1, 1986, 82, 1117-26 demonstrated a polypyrrole gas sensor displaying a DC resistance which was sensitive to the presence of nitrous oxide and hydrogen sulphide. GB-2, 203, 553-B discloses an improved method of detection wherein various AC impedance characteristics are measured at different AC frequencies.
A given semiconducting organic polymer will typically be sensitive to a range of compounds. Clearly this lack of selectivity is a major problem if one wishes to develop a sensor which is specific to a particular gas. Conversely, a sensor which employs a given semiconducting organic polymer will not be sufficiently sensitive to such a broad range of gases that it may be considered a general purpose device.
A solution to these problems is a device which employs a plurality of sensors, wherein each sensor incorporates a different polymer and each polymer possesses differing gas response profiles. Thus a suite of polymers may be selected which possess broadly overlapping responses, but which are individually chemically tailored to enhance differences in response to certain molecules or classes of molecules. Often the variation of a substituent group on the monomer unit is sufficient to enable such "fine tuning" of response. A multi-sensor device detects gases and odours as a characteristic pattern of individual responses across the array of sensors.
The present invention relates to a class of semiconducting organic polymers based on 1-substituted, 3-substituted and 1,3 substituted indole monomer units which display high sensitivity towards a number of important species.
According to a first aspect of the invention there is provided a semiconducting organic polymer polymerised from a 3-substituted or 1,3-substituted indole monomer.
According to a second aspect of the invention there is provided a semiconducting organic polymer polymerised from a 1-substituted, 3-substituted or 1,3-substituted indole monomer for use in a gas sensor.
A substituent at the 3 position may be an alkyl or aromatic acetyl group.
A substituent at the 1 position may be an alkyl group.
Alternatively, a substituent at the 1 position may contain an aromatic group. Said substituent may be tosyl or benzyl.
The substituted indole monomer may be polymerised electrochemically from a solution containing said monomer and a counter-ion. The counter-ion may be BF.sub.4.sup.-, PF.sub.6.sup.-, ClO.sub.4.sup.-, C.sub.8 H.sub.17 SO.sub.3.sup.-,[Fe(CN).sub.6 ].sup.3- or CH.sub.3 C.sub.6 H.sub.4 SO.sub.3.sup.-.
The semiconducting organic polymer may be polymerised from a monomer selected from the group comprising:
1-octylindole; 1-benzylindole; 1-tosylindole; 1-tosylindole; 3-hexanoxyl-1-tosylindole; 3-hexanoylindole; 3-hexylindole; 3-dodecanoyl-1-tosylindole; 3-dodecanoylindole and 3-dodecylindole.
According to a third aspect of the invention there is provided a gas sensor comprising: polymerised according to the first aspect of the invention, deposited between the pair of electrodes in such manner as to effect a semiconducting electrical connection between said electrodes; of a gas.
Semiconducting organic p
REFERENCES:
patent: 4443615 (1984-04-01), Matsuoka et al.
patent: 4488943 (1984-12-01), Skotheim
patent: 4887455 (1989-12-01), Payne et al.
patent: 5107308 (1992-04-01), Koezuka et al.
patent: 5436167 (1995-07-01), Robillard
B.A. Gregory, "An Introduction to Electrical Instrumentation and Measurement Systems", pp. 215 and 220-221.
J.J. Miasik et al., "Conducting Polymer Gas Sensors", J. Chem. Soc., Faraday Trans. 1, 1986, pp. 1117-1126.
R. Waltman et al., "Substituent Effects in the Electropolymerization of Aromatic Heterocyclic Compounds", 1984, pp. 4343-4346.
Mohialdin-Khaffaf Soad
Persaud Krishna Chandra
Aromascan PLC
Kopec Mark
Petruncio John M.
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