WO2001029547A1 - Detecteurs - Google Patents

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Publication number
WO2001029547A1
WO2001029547A1 PCT/GB2000/004012 GB0004012W WO0129547A1 WO 2001029547 A1 WO2001029547 A1 WO 2001029547A1 GB 0004012 W GB0004012 W GB 0004012W WO 0129547 A1 WO0129547 A1 WO 0129547A1
Authority
WO
WIPO (PCT)
Prior art keywords
chemiresistor
film
pyrrole
substrate
process according
Prior art date
Application number
PCT/GB2000/004012
Other languages
English (en)
Inventor
Norman Ratcliffe
Geoffrey Clive Teare
Original Assignee
University Of The West Of England, Bristol
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University Of The West Of England, Bristol filed Critical University Of The West Of England, Bristol
Priority to AU79337/00A priority Critical patent/AU7933700A/en
Publication of WO2001029547A1 publication Critical patent/WO2001029547A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G01N27/125—Composition of the body, e.g. the composition of its sensitive layer
    • G01N27/126—Composition of the body, e.g. the composition of its sensitive layer comprising organic polymers

Definitions

  • the present invention relates to a gas sensor and to a process for preparing such a sensor.
  • sensors comprise a gas sensitive-film coated on to a substrate.
  • sensors have been developed which employ conducting polymers capable of reversibly changing their electrical resistance in response to organic vapours.
  • conducting polymer is a polypyrrole.
  • GB-A-2234515 describes a process for preparing an electrically-conductive polypyrrole film on a nonconducting substrate which comprises contacting the substrate with pyrrole and an organic oxidising agent in a solvent (or with the colloidal polypyrrole that is the reaction product thereof) and removing the substrate while the film is at least substantially transparent .
  • the substrate may be brought into contact with the polymerising solution (or the resulting polypyrrole) by, for example dipping the substrate into a bath comprising the polymerising solution.
  • Known substrates include, glass, acrylic and polyester. Hitherto, low melting point thermoplastic materials, such as perspex have been preferred since the bonding of the polypyrrole film to the substrate can be enhanced by heating the substrate to the temperature at which it softens, followed by cooling.
  • sensors based on a perspex substrate are usually sensitive to water and are therefore less sensitive at high humidities. They also tend to be unsuitable for use in conditions of variable humidity, and they can be unstable in air, causing the gas- sensitive film to degrade, known as "drift".
  • thermoplastic polymers selected from polyetherketone, polyethersulphone, polyetherimide, polyimide and polyamide are used as the substrate with a conducting polymer film such as polypyrrole
  • the sensor has enhanced stability in air at room temperature, a reduced sensitivity to water, and an increased sensitivity for the target volatile, such as ammonia.
  • these materials as a result of their low permeability to water, low temperature coefficient of expansion and high glass transition temperature, are able to form a rigid platform for the conducting polymer film.
  • the inventors have also found that the stability in air can be increased further by the addition of an alcohol such as a lower alkyl alcohol, for example ethanol, to the polymerising medium used to prepare the substrate. This has also been found to increase the sensitivity of the sensor to alcohols.
  • an alcohol such as a lower alkyl alcohol, for example ethanol
  • a chemiresistor which comprises a non-conducting substrate at least partially coated with an electrically-conductive polypyrrole film, characterised in that the said substrate is a high melting-point, thermoplastic polymer selected from: an aromatic polyetherketone, a polyethersulphone, a polyetherimide, a polyimide and a polyamide.
  • the substrate is preferably a thermoplastic aromatic polyetherketone substrate and may be crystalline or amorphous.
  • a presently preferred substrate is polyetheretherketone (PEEK) as described, for example, in EP-A-0001879 which has been found to be very effective as a substrate for polypyrrole in ammonia sensors .
  • the polypyrrole film is that prepared by or obtainable by polymerization of a pyrrole monomer, which includes pyrrole and substituted pyrroles, such as 3-substituted pyrroles.
  • a pyrrole monomer which includes pyrrole and substituted pyrroles, such as 3-substituted pyrroles.
  • suitable 3- substituted monomers are those in which the 3- substituent is a an alkyl group, for example a substituted or unsubstituted alkyl group having up to 16 carbon atoms where the substituent is a carbonyl group, an ester group, an acid group or an amide group.
  • suitable 3-substituted polypyrrole monomers are :
  • R and R 1 are R C0 2 R' independently hydrogen or lower alkyl.
  • the chemiresistor of the invention may be produced by adding the pyrrole, or an aqueous solution of the pyrrole, with stirring, to an oxidising agent, for example, ferric ions.
  • an oxidising agent for example, ferric ions.
  • a colloidal suspension of polypyrrole results which may the be deposited or coated on the substrate when the substrate is contacted with the suspension. After a period which may be less than 3 hours, e.g. about 30 minutes, the coated substrate is removed, washed with water and dried, for example at ambient temperature.
  • a cosolvent such as ethanol
  • Contacts can be provided to the polypyrrole film by any of various methods, for example by the application of conducting paint. Alternatively, suitable contacts (for example gold) may be formed on the substrate prior to coating.
  • the resultant chemiresistor conducts electricity and the resistance changes reversibly in the presence of low concentrations of ammonia as well as other inorganic and organic species in the vapour phase.
  • a crystalline thermoplastic aromatic polyetherketone as the substrate resulted in a conducting polymer film with significantly enhanced stability in air at room temperature and under a range of humidities .
  • the films exhibit a high sensitivity to ammonia, with a lower response to water vapour than films prepared on perspex.
  • a method of polymerizing a pyrrole monomer comprising the step of contacting said pyrrole monomer with an oxidising agent in an aqueous solution, wherein the aqueous solution comprises an organic co-solvent which is at least partially miscible with water.
  • the solution may be stirred.
  • the organic co-solvent should ideally not be oxidisible by, or otherwise interfere with the oxidising agent, should not be attacked by high concentrations of hydrogen ions ' and should not interfere with the pyrrole monomer or polypyrrole product.
  • suitable co-solvents are water soluble ethers, water soluble ketones such as lower (Cl-6) alkyl ketones for example acetone, and water soluble alcohols (which are presently preferred) such as a lower (Cl-6) alkyl alcohol, for example ethanol, as well as other water miscible solvents such as acetonitrile which have good solvent properties.
  • the proportion of co-solvent can be determined empirically.
  • an amount up to about 80% by volume may be used, although it is presently preferred to employ an aqueous ethanol solution containing from 10-30% v/v ethanol.
  • an amount up to 90% by volume may be used.
  • the oxidising agent is typically ferric ions and is typically used at a molar ratio of pyrrole to ferric ions of l:n, where n is 2 or more.
  • a co-solvent unexpectedly makes it possible to prepare conducting polymers from substituted pyrrole monomers, such as 3-substituted pyrroles, which are insoluble in water alone, and so opens up a range of new polypyrrole films with potentially valuable sensing properties.
  • substituted pyrrole monomers such as 3-substituted pyrroles
  • the following 3-substituted pyrroles may be used in this aspect of the invention to prepare new polypyrrole sensors :
  • a chemiresistor may then be formed by contacting the suspension with a suitable non- conducting substrate which is preferably a crystalline thermoplastic aromatic polyetherketone, such as PEEK, as described above, although the other substrates mentioned above as well as other known substrates, such as glass, acrylic, polyester or perspex may be employed. After a period which may be less than 3 hours, e.g. about 30 minutes, the coated substrate is removed, washed with water and dried, for example at ambient temperature. Reference is again made here to GB-A-2234515.
  • an ethanol co-solvent results in a sensor having increased sensitivity to ethanol and also to methanol. It is theorised that the use of an alcohol co-solvent leads to the formation of "pores" or "channels" in the film which are so-shaped as to absorb the same alcohol molecule (or ones smaller than it) from the vapour phase in use as a sensor, leading to an enhanced response .
  • a process for treating a chemiresistor comprising a non-conducting substrate at least partially coated with an electrically-conductive polypyrrole film, wherein an oxidising agent or an acidic agent is contacted with the surface of the said film.
  • the polypyrrole film may be one prepared in accordance with the methods described herein or by other methods which may be known per se.
  • the polypyrrole film may be one prepared by polymerising a pyrrole monomer or a substituted pyrrole monomer.
  • the treated chemiresistor prepared in accordance with this aspect of the invention exhibits significantly superior electrical resistance changes to ammonia, while maintaining low degradation/drift in air.
  • the acidic agent may be an aqueous solution of a mineral acid such as hydrochloric acid, nitric acid or sulphuric acid, with hydrochloric acid being presently preferred.
  • a mineral acid such as hydrochloric acid, nitric acid or sulphuric acid
  • strong organic acids are also suitable, such as CF 3 COOH or HCOOH.
  • the acidic solution may be applied to the film at a concentration and for a time sufficient to increase the electrical resistance of the film when exposed to ammonia. For example, where the acidic agent is hydrochloric acid, good results were achieved using 6M HC1 treatment for 40 minutes .
  • the acid treatment results in protonation of the polypyrrole resulting in more positive charges on the polymer.
  • the increased concentration in positive charges may produce an increased concentration of binding sites for nucleophiles such as ammonia and other amines.
  • the oxidising agent may be a solution of metal ions, such as a solution of ferric ions and may be applied by way of a solution having a concentration of, for example 0.1M.
  • Other oxidising agents such as hydrogen peroxide are also contemplated.
  • the oxidising agent may be applied to the film at a concentration and for a time sufficient to increase the electrical resistance of the film when exposed to ammonia.
  • the oxidising agent may oxidise the polymer and increase the concentration of positive charges, hence mirroring the effect of acid.
  • the oxidising agent treated films also show an enhanced response to nucleophiles .
  • polymerisation times of between 10 minutes and 1 hours are typical for the preparation of polymer films in aqueous ethanol solutions, and in aqueous solutions of 2-butanol or butane-1, 3-diol, polymerisation times of between 1 and 4 hours are appropriate .
  • the films are rinsed thoroughly with distilled water.
  • Films obtained in aqueous solution, and aqueous ethanol solution are allowed to dry in air for 24 hours, as were films which had been subjected to subsequent oxidation or treatment with acid; films prepared in aqueous 2-butanol and butane- 1,3-diol solutions are dried for 6 hours under vacuum at 70°C to remove residual alcohol from the matrix of the polymer. Films which are to be subjected to further modification with acid or iron (III) salts are not dried prior to the treatment.
  • Sensors are prepared by cutting the polymer coated PEEK strips into 1 cm squares, removing the film from one side of the square with gentle abrasion, and mounting the square, film side uppermost, on a strip of Veriboard. Electrical contacts between the film and the Veroboard mount are made with silver conductive paint. Sensors thus prepared are allowed to stabilise for at least 24 hours prior to exposure to vapours .
  • % response [ (R v - R b ) /R b ] x 100.
  • Sensors are exposed to organic headspace vapours by placing the sensor in a sealed vessel containing a saturated vapour of the analyte.
  • a known mass of the analyte is volatalised in a sealed vessel of known volume, and dilutions of the vapour made to achieve the required vapour concentration.
  • the sensors were placed in a sealed vessel over aqueous solutions of ammonia with known ammonia concentrations in the vapour phase .
  • the film properties may be adjusted by variation of the polymerisation time; similar results may be
  • Example 2 Polypyrrole films on PEEK were prepared using the above method, in aqueous ethanol solutions rather than in de-ionised water (with pyrrole initially dissolved in the appropriate solvent system) .
  • ethanol concentrations of 50 % v/v and less films are obtained at all polymerisation times (1 hour to 4 hour) .
  • films are obtained only at the longer polymerisation times.
  • No films are obtained with ethanol concentrations of 80 % v/v and above.
  • films prepared with ethanol concentrations of 30 % v/v and less are most suitable, owing to their relatively high conductivities .
  • the resistance values for polypyrrole sensors prepared in aqueous ethanol solutions of between 10 and 30 % v/v ethanol are given in Table 2.
  • polypyrrole sensors prepared in aqueous ethanol solution show markedly greater responses to certain analyte vapours than sensors prepared in aqueous solution.
  • the responses of a polypyrrole sensor prepared in aqueous solution (sensorO) and a sensor prepared in 20 % v/v ethanol solution (sensor3) , polymerisation time for both sensors being 1 hour, to D- (+) - ⁇ -methylbenzylamine and ethanol headspace are presented in Table 3.
  • This example relates to the post-treatment of polypyrrole films, on PEEK or perspex.
  • Subsequent acid treatment of the polypyrrole films on PEEK is carried out by placing them in an aqueous solution of hydrochloric acid (18 % wt/v) for 40 minutes, followed by rinsing of the films with de-ionised water and drying in air.
  • the procedure may be adjusted by varying the acid used; the concentration of the acid, and the time of treatment (typically from 15 minutes to 20 hours) .
  • Subsequent treatment of the polypyrrole films on PEEK with oxidising agents may be carried out by placing them in a solution of iron (III) nitrate nonahydrate (30 g) in de-ionised water (300 cm 3 ) for 40 minutes, followed by rinsing the films with de-ionised water and drying in air.
  • the procedure may be adjusted by varying the oxidant used; the concentration of the oxidant, and the time of treatment (typically from 15 minutes to 20 hours) .

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
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  • Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)

Abstract

Cette invention concerne une chimiorésistance comprenant un substrat non conducteur recouvert au moins en partie d'une pellicule de polypyrrole électriquement conductrice, caractérisée en ce que ledit substrat est constitué par un polymère thermoplastique à point de fusion élevé pris parmi les composés suivants :polyéthercétone aromatique, polyéthersulphone, polyétherimide, polyimide et polyamide. L'invention porte également sur un procédé de polymérisation d'un pyrrole monomère consistant à mettre en contact ledit pyrrole monomère avec un agent oxydant dans une solution aqueuse, laquelle solution aqueuse renferme un co-solvant organique au moins partiellement miscible dans l'eau. L'invention concerne également un procédé de traitement d'une chimiorésistance comprenant un substrat non conducteur recouvert au moins partiellement d'une pellicule électriquement conductrice de polypyrrole, procédé au cours duquel un agent oxydant ou un agent acide est mis en contact avec la surface de ladite pellicule.
PCT/GB2000/004012 1999-10-18 2000-10-18 Detecteurs WO2001029547A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU79337/00A AU7933700A (en) 1999-10-18 2000-10-18 Sensors

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB9924633.2A GB9924633D0 (en) 1999-10-18 1999-10-18 Sensors
GB9924633.2 1999-10-18

Publications (1)

Publication Number Publication Date
WO2001029547A1 true WO2001029547A1 (fr) 2001-04-26

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AU (1) AU7933700A (fr)
GB (1) GB9924633D0 (fr)
WO (1) WO2001029547A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7063978B2 (en) * 2001-11-01 2006-06-20 3M Innovative Properties Company Coated film laminate having an electrically conductive surface

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0267392A1 (fr) * 1986-10-09 1988-05-18 Rockwell International Corporation Synthèse chimique de polypyrrole conducteur
EP0411793A2 (fr) * 1989-08-04 1991-02-06 British Aerospace Public Limited Company Préparation des films conducteurs et leur emploi comme capteurs de gaz
US5504433A (en) * 1992-10-23 1996-04-02 International Fuel Cells Corporation Electrochemical sensor for monitoring electrolyte content
FR2728713A1 (fr) * 1994-12-23 1996-06-28 Neutronic Dispositif detecteur de fumees d'incendie
EP0821228A1 (fr) * 1996-07-25 1998-01-28 HE HOLDINGS, INC. dba HUGHES ELECTRONICS Capteur de composés organiques volatils

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0267392A1 (fr) * 1986-10-09 1988-05-18 Rockwell International Corporation Synthèse chimique de polypyrrole conducteur
EP0411793A2 (fr) * 1989-08-04 1991-02-06 British Aerospace Public Limited Company Préparation des films conducteurs et leur emploi comme capteurs de gaz
US5504433A (en) * 1992-10-23 1996-04-02 International Fuel Cells Corporation Electrochemical sensor for monitoring electrolyte content
FR2728713A1 (fr) * 1994-12-23 1996-06-28 Neutronic Dispositif detecteur de fumees d'incendie
EP0821228A1 (fr) * 1996-07-25 1998-01-28 HE HOLDINGS, INC. dba HUGHES ELECTRONICS Capteur de composés organiques volatils

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
FATMA SELAMPINAR: "a conducting composite of polypyrrole. II. as a gas sensor", SYNTHETIC METALS, vol. 68, 1995, pages 109 - 116, XP000991483 *
PEARCE T C ET AL: "ELECTRONIC NOSE FOR MONITORING THE FLAVOUR OF BEERS", ANALYST,GB,LONDON, vol. 118, no. 4, 1 April 1993 (1993-04-01), pages 371 - 377, XP000196878 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7063978B2 (en) * 2001-11-01 2006-06-20 3M Innovative Properties Company Coated film laminate having an electrically conductive surface

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Publication number Publication date
GB9924633D0 (en) 1999-12-22
AU7933700A (en) 2001-04-30

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