WO1994018551A1 - Gas sensing devices - Google Patents

Gas sensing devices Download PDF

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Publication number
WO1994018551A1
WO1994018551A1 PCT/GB1994/000233 GB9400233W WO9418551A1 WO 1994018551 A1 WO1994018551 A1 WO 1994018551A1 GB 9400233 W GB9400233 W GB 9400233W WO 9418551 A1 WO9418551 A1 WO 9418551A1
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WO
WIPO (PCT)
Prior art keywords
alkyl
gas sensing
mesogenic
hal
dioxanyl
Prior art date
Application number
PCT/GB1994/000233
Other languages
French (fr)
Inventor
Neville John Freeman
Iain Peter May
Donald James Weir
Original Assignee
Gec-Marconi Limited
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 Gec-Marconi Limited filed Critical Gec-Marconi Limited
Priority to EP94905806A priority Critical patent/EP0636245A1/en
Priority to JP6517802A priority patent/JPH07506191A/en
Publication of WO1994018551A1 publication Critical patent/WO1994018551A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/036—Analysing fluids by measuring frequency or resonance of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N5/00—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid
    • G01N5/02—Analysing materials by weighing, e.g. weighing small particles separated from a gas or liquid by absorbing or adsorbing components of a material and determining change of weight of the adsorbent, e.g. determining moisture content
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/025—Change of phase or condition
    • G01N2291/0256—Adsorption, desorption, surface mass change, e.g. on biosensors

Definitions

  • This invention relates to gas sensing devices, "gas” in this specification being taken to include vapour.
  • Gas sensing devices are known, of a kind in which a piezo-electric component is coated with a sensor material having characteristics of mass, stiffness and viscosity.
  • the sensor material interacts with gaseous materials, in this context analytes, selectively, to produce a change in one or other of the characteristics such as to affect the oscillation frequency of the piezo-electric component when incorporated in an oscillator circuit.
  • Some sensor materials are relatively non-discriminating, causing a similar reaction to a wide range of gases, while others are fairly selective.
  • Other problems with known sensor materials include inadequate repeatability of response, insufficiently rapid response to stimulation, and limited 'designability' of response to suit specific gases.
  • An object of the present invention is to provide a sensor material for a gas sensing device which at least partly overcomes one or more of these disadvantages.
  • a gas sensing device comprises a piezo-electric component connected in an oscillator circuit to oscillate at the component resonant frequency, the piezo-electric component being loaded with a polysiloxane sensor material which interacts with a range of gaseous analyte materials so as to alter the oscillation frequency response resulting from such interaction being indicative of the analyte material, and the sensor material being a polysiloxane having the general formula:
  • M is a mesogenic group having a general structure:
  • Me is methyl
  • D and E are either alkyl, typically methyl or ethyl, or alkyl cyanides, (CH 2 ) n CN, the rings P & Q are selected from phenyl, trans-cyclo hexyl, pyridyl, pyrimidyl, dioxanyl, and bicyclo (2.2.2) octyle;
  • n 0 or 1 ;
  • R 1 is alkyl, open chain or branched, containing 1-12 carbon atoms
  • A is COO, OOC or CH 2 .CH 2 ;
  • X and Z are selected independently from H, methyl and Hal such that one at least of
  • X, Y and Z contains fluorine
  • the ratio b:a is less than 3:1 and > 0.
  • the piezo-electric oscillating component is coated with a polymer selected from the following polymers described in GB Patent Specification Numbers: 2195646,
  • a liquid crystal polymer having a general Formula 1 having a general Formula 1 :
  • Y is COO, OOC or CH 2 CH 2 , C is 0 or 1;
  • n is an integer between 4 and 9 inclusive
  • the polymer being random or substantially random polymer
  • Liquid crystal polymers of the general formula:
  • rings P and Q are phenyl, trans-cyclohexyl, pyridyl, pyrimidinyl, dioxanyl, or bicyclo (2,2,2) octyl;
  • A is COO, OOC, CH 2 CH 2 ;
  • m is 0 or 1;
  • X, Z are H, Me hal; and
  • Y is alkyl, alkoxy, hal, CF 3 ,CN or CO 2 alkyl.
  • rings P and Q are selected from phenyl, trans-cyclohexyl, pyridyl, pyrimidinyl, dioxanyl, and bicyclo (2,2,2) octyle, A, x, y and z are standard mesogenic substitutuents and b/a ⁇ 3 and > 0.
  • rings P and Q are selected from phenyl, trans-cyclohexyl, pyridyl, pyrimidinyl, dioxanyl, and bicyclo (2,2,2) octyl;
  • X, Y, Z, A and m are standard mesogenic groups.
  • the device includes a piezo-electric element incorporated in an oscillator circuit in known manner, the element resonant frequency determining the oscillation frequency, e.g. 10MHz.
  • the frequency will depend upon the type of piezo-electric device, whether piezo- electric crystal, surface or bulk acoustic wave or other mass-balace device. Means are provided for monitoring the oscillation frequency.
  • the piezo-electric element is coated with a sensor material which interacts selectively with gaseous analytes to which it is exposed, the characteristics - mass, stiffness or viscosity - of the sensor material being modified by this interaction to cause a frequency response which is characteristic of the combination of piezo- electric element, sensor material and analytes. Means are then provided for recording the response and identifying it with predetermined analyte responses.
  • the present invention is based on the appreciation that materials, at least some of which were previously known in connection with electro-optic liquid crystal display technology, are admirably suited for use as sensor materials in piezo-electric gas sensing devices. Such materials, in their function as liquid crystal polymers, are described in GB Patent Specification Numbers: 2195646, 2221690, 2249794 and 2249795 to which attention is directed for an explanation of the structure and preparation of such materials.
  • polysiloxanes suitable for use as sensor materials in gas sensing devices are the following:
  • a piezo-electric element coated with polysiloxane (A) is subjected to toluene vapour at time zero, the toluene being purged at time 1600 seconds by replacement with an unreactive gas. It can be seen that the frequency response undergoes an almost step change by 700 Hz, both rising and falling edges being very steep.
  • Figure 2 shows the result of similar tests using toluene and polysiloxane (B), and it may be seen that there is very little difference between the results for (A) and (B), (B) giving a slightly smaller frequency shift.
  • Figures 4, 5 and 6 show the response of the three example to di-butylsulphide analyte. Again, there is very little difference between the results for polysiloxanes (A) and (B) but a much larger frequency shift for (C).
  • Figures 7 and 8 show responses to iso-amyl acetate for polysiloxanes (B) and (C) and again there is a considerable difference of frequency shift.
  • M is a mesogenic group having a general structure:
  • Me is methyl
  • K is alkyl, typically methyl or ethyl
  • the rings P & Q are selected from phenyl, trans-cyclo hexyl, pyridyl, pyrimidyl, dioxanyl, and bicyclo (2,2,2) octyl;
  • n 0 or 1 ;
  • R 1 is alkyl, open chain or branched, containing 1-12 carbon atoms
  • A is COO, OOC or CH 2 .CH 2 ;
  • X and Z are selected independently form H and F such that one at least of X, Y and Z contains fluorine
  • the above mesogenic group M may be selected from the following structures (a) to (i):

Abstract

The invention consists in a gas sensing device employing a piezo-electric element coated with a sensor material which interacts with a range of gases selectively, the oscillation frequency of the piezo-electric element varying with the degree of interaction with an analyte gas and thus with the particular gas. It has been found that polymers previously known in liquid crystal applications, and in particular polysiloxanes, are highly suited for use as sensor materials, giving advantages which have no relevance to liquid crystals.

Description

GAS SENSING DEVICES
This invention relates to gas sensing devices, "gas" in this specification being taken to include vapour.
Gas sensing devices are known, of a kind in which a piezo-electric component is coated with a sensor material having characteristics of mass, stiffness and viscosity. The sensor material interacts with gaseous materials, in this context analytes, selectively, to produce a change in one or other of the characteristics such as to affect the oscillation frequency of the piezo-electric component when incorporated in an oscillator circuit.
Some sensor materials are relatively non-discriminating, causing a similar reaction to a wide range of gases, while others are fairly selective. Other problems with known sensor materials include inadequate repeatability of response, insufficiently rapid response to stimulation, and limited 'designability' of response to suit specific gases.
An object of the present invention is to provide a sensor material for a gas sensing device which at least partly overcomes one or more of these disadvantages.
According to one aspect of the present invention a gas sensing device comprises a piezo-electric component connected in an oscillator circuit to oscillate at the component resonant frequency, the piezo-electric component being loaded with a polysiloxane sensor material which interacts with a range of gaseous analyte materials so as to alter the oscillation frequency response resulting from such interaction being indicative of the analyte material, and the sensor material being a polysiloxane having the general formula:
Figure imgf000004_0001
wherein M is a mesogenic group having a general structure:
Figure imgf000004_0002
and wherein:
Me is methyl;
D and E are either alkyl, typically methyl or ethyl, or alkyl cyanides, (CH2)n CN, the rings P & Q are selected from phenyl, trans-cyclo hexyl, pyridyl, pyrimidyl, dioxanyl, and bicyclo (2.2.2) octyle;
m is 0 or 1 ;
Y is R1, OR1, Hal (F,Cl,Br,I), CF3, CO2R, or CN when m = 1
and R1, OR1, Hal (F,Cl,Br,I), CO2R, or CN when m = 0;
where R1 is alkyl, open chain or branched, containing 1-12 carbon atoms;
A is COO, OOC or CH2.CH2;
X and Z are selected independently from H, methyl and Hal such that one at least of
X, Y and Z contains fluorine;
the ratio b:a is less than 3:1 and > 0.
Preferably the piezo-electric oscillating component is coated with a polymer selected from the following polymers described in GB Patent Specification Numbers: 2195646,
2221690, 2249794 and 2249795:
a. A liquid crystal polymer having a general Formula 1 :
Figure imgf000005_0001
wherein X is mesogenic group having a general structure
wherein
Figure imgf000005_0002
may carry lateral methyl, fluoro or chloro substituents, and are selected from phenyl, trans-cyclohexyl, pyridyl, pyri midyl, dioxanyl and bicyclo-(2,2,2)-octyl;
wherein Y is COO, OOC or CH2CH2, C is 0 or 1;
wherein n is an integer between 4 and 9 inclusive;
wherein R is F, CF3, CN, R1, OR1 or COOR1 where R1 is alkyl, and (L) indicates that a lateral methyl or fluorosubstituent may be present; in cases other than when R is CN and Y is COO and n=5 and C=1, L=CH3: wherein the ratio bra is less than 3 and greater than 0; The polymer being random or substantially random polymer,
b. Liquid crystal polymers, of the general formula:
Figure imgf000006_0001
wherein the mesogenic grouping M has a general structure
Figure imgf000006_0002
wherein the rings P and Q are phenyl, trans-cyclohexyl, pyridyl, pyrimidinyl, dioxanyl, or bicyclo (2,2,2) octyl; A is COO, OOC, CH2CH2; m is 0 or 1; X, Z are H, Me hal; and Y is alkyl, alkoxy, hal, CF3,CN or CO2 alkyl.
Homopolymers wherein b=0 and at least one of x, y and z is F or CF3 or wherein b=0 and R is CH2Me, and copolymers wherein R4 is (CH2)3CN are preferred materials, c. Liquid crystal polymers of the general formula:
Figure imgf000006_0003
wherein the mesogenic grouping M has a general structure
Figure imgf000007_0001
wherein the rings P and Q are selected from phenyl, trans-cyclohexyl, pyridyl, pyrimidinyl, dioxanyl, and bicyclo (2,2,2) octyle, A, x, y and z are standard mesogenic substitutuents and b/a < 3 and > 0.
d. Liquid crystal polymers of the general formula:
Figure imgf000007_0002
wherein the mesogenic grouping M has a general structure
Figure imgf000007_0003
wherein the rings P and Q are selected from phenyl, trans-cyclohexyl, pyridyl, pyrimidinyl, dioxanyl, and bicyclo (2,2,2) octyl;
and X, Y, Z, A and m are standard mesogenic groups.
A gas sensing device in accordance with the invention will now be described by way of example with reference to the accompanying drawings, Figure 1-8, showing frequency response characteristics for a number of specific sensor materials and analytes. The device includes a piezo-electric element incorporated in an oscillator circuit in known manner, the element resonant frequency determining the oscillation frequency, e.g. 10MHz. The frequency will depend upon the type of piezo-electric device, whether piezo- electric crystal, surface or bulk acoustic wave or other mass-balace device. Means are provided for monitoring the oscillation frequency. The piezo-electric element is coated with a sensor material which interacts selectively with gaseous analytes to which it is exposed, the characteristics - mass, stiffness or viscosity - of the sensor material being modified by this interaction to cause a frequency response which is characteristic of the combination of piezo- electric element, sensor material and analytes. Means are then provided for recording the response and identifying it with predetermined analyte responses.
The present invention is based on the appreciation that materials, at least some of which were previously known in connection with electro-optic liquid crystal display technology, are admirably suited for use as sensor materials in piezo-electric gas sensing devices. Such materials, in their function as liquid crystal polymers, are described in GB Patent Specification Numbers: 2195646, 2221690, 2249794 and 2249795 to which attention is directed for an explanation of the structure and preparation of such materials.
Particular examples of polysiloxanes suitable for use as sensor materials in gas sensing devices are the following:
Figure imgf000009_0001
Examples of frequency response obtained using the three polysiloxane examples (A), (B) and (C) with analytes toluene, di-butylsulphide and iso-amyl acetate are shown in Figures 1 to 8.
In Figure 1, a piezo-electric element coated with polysiloxane (A) is subjected to toluene vapour at time zero, the toluene being purged at time 1600 seconds by replacement with an unreactive gas. It can be seen that the frequency response undergoes an almost step change by 700 Hz, both rising and falling edges being very steep.
The test was repeated three times, the three graphs being superimposed to show the degree of repeatability.
Figure 2 shows the result of similar tests using toluene and polysiloxane (B), and it may be seen that there is very little difference between the results for (A) and (B), (B) giving a slightly smaller frequency shift.
In Figure 3 however, using polysiloxane (C) and again toluene as the analyte, there is a much greater frequency shift, of about 3200 Hz, although with a 100% instead of 50% analyte concentration.
Figures 4, 5 and 6 show the response of the three example to di-butylsulphide analyte. Again, there is very little difference between the results for polysiloxanes (A) and (B) but a much larger frequency shift for (C).
Figures 7 and 8 show responses to iso-amyl acetate for polysiloxanes (B) and (C) and again there is a considerable difference of frequency shift.
Many variations may be made to the polysiloxane examples given, particularly to the pendant side chains, making the polymers effectively 'designable', the selectivity and sensitivity being tunable to suit the particular analyte gas/vapour. The polymer examples given above fall within the general formula:
Figure imgf000011_0001
wherein M is a mesogenic group having a general structure:
Figure imgf000011_0002
In the above formula:
Me is methyl;
K is alkyl, typically methyl or ethyl;
the rings P & Q are selected from phenyl, trans-cyclo hexyl, pyridyl, pyrimidyl, dioxanyl, and bicyclo (2,2,2) octyl;
m is 0 or 1 ;
y is R, OR1, Hal, CF3, CO2R, or Cn when m = 1
and R, OR1, Hal, CO2R, or CN when m = 0;
R1 is alkyl, open chain or branched, containing 1-12 carbon atoms;
A is COO, OOC or CH2.CH2;
X and Z are selected independently form H and F such that one at least of X, Y and Z contains fluorine
the ratio b:a is less than 3:1. The above mesogenic group M may be selected from the following structures (a) to (i):
/ C V
V
Figure imgf000012_0001
Advantages arising from the use of polymers described above are:
1) These materials demonstrate little visco-elastic change as a consequence of vapour sorption yielding highly reproducible responses on exposure to gases and vapours;
2) Rapid sorption and desorption of gases and vapours from these materials lead to rapid responses upon stimulation;
3) Sensitivity of specific materials to specific vapours or gases is extremely high as a result of considerable partitioning between the material and the gaseous phase;
4) Selectivity for specific gases and vapours varies significantly between materials;
5) Designability of the materials for specific uses allows control of both the sensitivity and selectivity for specific gases and vapours.

Claims

1. A gas sensing device comprising a piezo-electric component connected in an oscillator circuit to oscillate at the component resonant frequency, the piezo-electric component being load with a polysiloxane sensor material which interacts with a range of gaseous analyte materials so as to alter the oscillation frequency, the frequency response resulting from such interaction being indicative of the analyte material, wherein the sensor material is a polysiloxane having the general formula:
Figure imgf000014_0001
wherein M is a mesogenic group having a general structure:
Figure imgf000014_0002
and wherein:
Me is methyl;
D and E are either alkyl, typically methyl or ethyl, or alkyl cyanides, (CH2)nCN; the rings P & Q are selected from phenyl, trans-cyclo hexyl, pyridyl, pyrimidyl, dioxanyl, and bicyclo (2.2.2) octyle;
m is O or 1; Y is R1, OR1, Hal (F,Cl,Br,I), CF3, CO2R, or CN when m = 1
and R1, OR1, Hal (F,Cl, Br, I), CO2R, or CN when m = 0;
where R1 is alkyl, open chain or branched, containing 1-12 carbon atoms;
A is COO, OOC or CH2.CH2;
X and Z are selected independently from H, methyl and Hal such that one at least of X, Y and Z contains fluorine;
the ratio b:a is less than 3:1 and > 0.
2. A gas sensing device according to Claim 1, wherein the sensor material is of the said formula and M is selected from the following structures (a) to (i):
/ /
V Y
Figure imgf000016_0001
3. A gas sensing device according to Claim 1, wherein said sensor material comprises one of the following polysiloxanes:
Figure imgf000017_0001
4. A gas sensing device according to Claim 1, wherein said sensor material comprises one of the following polysiloxanes:
a. A liquid crystal polymer having a general Formula 1 :
Figure imgf000018_0001
wherein X is a mesogenic group having a general structure
wherein
Figure imgf000018_0002
may carry lateral methyl, fluoro or chloro substituents, and are selected from phenyl, transcyclohexyl, pyridyl, pyri midyl, dioxanyl and bicyclo-(2,2,2)-octyl;
wherein Y is COO, OOC or CH2CH2, C is 0 or 1;
wherein n is an integer between 4 and 9 inclusive;
wherein R is F, CF3, CN, R1, OR1 or COOR1 where R1 is alkyl, and (L) indicates that a lateral methyl or fluoro substituent may be present; in cases other than when R is CN and Y is COO and n = 5 and C = 1, L =CH3: wherein the ration b:a is less than 3 and greater than 0: the polymer being random or substantially random polymer,
b. Liquid crystal polymers of the general formula:
Figure imgf000019_0001
wherein the mesogenic grouping M has a general structure
Figure imgf000019_0002
wherein the rings P and Q are phenyl, trans-cyclohexyl, pyridyl, pyrimidinyl, dioxanyl, or bicyclo (2.2.2) octyl; A is COO, OOC, CH2CH2; m is 0 or 1; X, Z are H, Me, hal; and Y is alkyl, alkoxy, hal, CF3, CN or CO2 alkyl.
Homopolymers wherein b = 0 and at least one of x, y and z is F or CF3 or wherein b = 0 and R is CH2 Me, and copolymers wherein R4 is (CH2)3 CN are preferred materials, c. Liquid crystal polymers of the general formula;
Figure imgf000019_0003
wherein the mesogenic grouping M has a general structure
Figure imgf000020_0001
wherein the rings P and Q are selected from phenyl, trans-cyclohexyl, pyridyl, pyrimidinyl, dioxanyl, and bicyclo (2.2.2) octyle, A, x, y and z are standard mesogenic substituents and b/a < 3 and > 0.
d. Liquid crystal polymers of the general formula:
O
Figure imgf000020_0002
wherein the mesogenic grouping M has a general structure
Figure imgf000020_0003
wherein the rings P and Q are selected from phenyl, trans-cyclohexyl, pyridyl, pyrimidinyl, dioxanyl, and bicyclo (2.2.2) octyl;
and X, Y, Z, A and m are standard mesogenic groups.
5. A gas sensing device substantially as hereinbefore described with reference to Figure
1 and 4; 2, 5 and 7; or 3, 6 and 8 of the accompanying drawings.
PCT/GB1994/000233 1993-02-12 1994-02-08 Gas sensing devices WO1994018551A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP94905806A EP0636245A1 (en) 1993-02-12 1994-02-08 Gas sensing devices
JP6517802A JPH07506191A (en) 1993-02-12 1994-02-08 gas detection device

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9302782.9 1993-02-12
GB939302782A GB9302782D0 (en) 1993-02-12 1993-02-12 Gas sensing devices

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5866798A (en) * 1995-04-05 1999-02-02 Hoechst Aktiengesellschaft Crystal oscillator sensor

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2071323A (en) * 1980-02-21 1981-09-16 Engstrom Medical Ab Gas detector
GB2195646A (en) * 1986-06-25 1988-04-13 Gen Electric Plc Liquid crystal siloxane polymers
GB2221690A (en) * 1988-08-12 1990-02-14 Gen Electric Co Plc Liquid crystal siloxane polymers
US5076094A (en) * 1990-10-03 1991-12-31 The United States Of America As Represented By The United States Department Of Energy Dual output acoustic wave sensor for molecular identification

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2249794B (en) * 1988-08-12 1993-03-17 Gen Electric Co Plc Liquid crystal materials
GB2249795B (en) * 1988-08-12 1993-01-20 Gen Electric Co Plc Liquid crystal materials

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2071323A (en) * 1980-02-21 1981-09-16 Engstrom Medical Ab Gas detector
GB2195646A (en) * 1986-06-25 1988-04-13 Gen Electric Plc Liquid crystal siloxane polymers
GB2221690A (en) * 1988-08-12 1990-02-14 Gen Electric Co Plc Liquid crystal siloxane polymers
US5076094A (en) * 1990-10-03 1991-12-31 The United States Of America As Represented By The United States Department Of Energy Dual output acoustic wave sensor for molecular identification

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5866798A (en) * 1995-04-05 1999-02-02 Hoechst Aktiengesellschaft Crystal oscillator sensor

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Publication number Publication date
JPH07506191A (en) 1995-07-06
GB9402488D0 (en) 1994-03-30
GB2275111A (en) 1994-08-17
GB9302782D0 (en) 1993-03-31
EP0636245A1 (en) 1995-02-01

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