Patent Application
20220018766
This application is a national phase entry under 35 U.S.C. § 371 of International Patent Application PCT/FR2019/052736, filed Nov. 18, 2019, designating the United States of America and published as International Patent Publication WO 2020/104746 A1 on May 28, 2020, which claims the benefit under Article 8 of the Patent Cooperation Treaty to French Patent Application Serial No. 1871648, filed Nov. 21, 2018.
The present disclosure relates to the field of sensors, and more particularly of sensors of volatile compounds, such as gases for example, and to the field of the use of such sensors.
At the present time, many pollutants may be present in an atmosphere, such as, for example, the interior of a room, or even the interior of a motor-vehicle passenger compartment. These pollutants are generally in gaseous form. These gases may be colorless and odorless, or even present at levels that are too low to be directly detected by a user as he breathes. However, such gases may be harmful to health in case of regular, repeated or extended exposure.
Sensors configured to detect a particular element and to determine its concentration in an atmosphere to be tested are known in the prior art, such as, for example, that which is described in document WO 2014/189758.
Furthermore, for example from document WO 2007/019517, a detector of pollutants in a gas is known that employs a gas chromatograph oven in order to allow thermal desorption of compounds adsorbed on a selective layer. The device described in this document also employs a concentrator upstream of the measuring device, which is configured to concentrate the gas to be analyzed before it enters into the measuring device. In addition, the various desorbed elements are then analyzed. However, the pollutant detector described in this document employs elements that consume large amounts of power and requires an analyzing device in order to determine the presence of a pollutant in this gas. Thus, the pollutant detector described in this document could be improved.
Gas detectors employing a sensitive layer on which volatile compounds may adsorb are also known from documents US 2016/0084786 and FR 2871573, and from the article “Planar indium tin oxide heater for improved thermal distribution for metal oxide micromachined gas sensors,” Sensors, 2016, 16, 1612. These adsorbed compounds are then thermally desorbed and the desorption of these compounds is detected via modification of a physical property of this sensitive layer, and notably its resistance. However, detecting the modification of resistance may be complicated to do. In addition, detecting the modification of the resistance of this sensitive layer does not allow the chemical nature of the desorbed compound to be determined and it is therefore necessary to subsequently carry out complementary analyses. The various detectors described in these documents would therefore appear to require quite a long time to determine the chemical nature of the desorbed volatile compounds. In addition, the use of an ITO layer as heating element and of an electrically transduced sensitive layer requires that these two elements be separated by a non-conductive element. Such a gas detector therefore has a complex and expensive structure.
Moreover, a gas detector comprising a fixed or movable sensitive layer on which volatile compounds may adsorb is known from document FR 3046244. The adsorption or desorption of volatile compounds on or from this sensitive layer is detected via the variation in a physicochemical property of this sensitive layer. In this document, the volatile compounds are desorbed thermally. However, this document indicates that the composition of the sensitive layer may be tailored to the nature of the volatile compound that it is desired to detect. However, this document neither discloses nor suggests the way in which the chemical nature of the volatile compounds, once desorbed, may be determined or even their concentration evaluated.
The objective of the present disclosure is to provide a detector that allows at least one volatile compound in an atmosphere to be tested to be detected and quantified that is simple to use and that delivers results in a time that is improved with respect to the detectors of the prior art.
Another objective of the present disclosure, which objective is different from the preceding one, is to provide a detector of volatile compounds that is inexpensive.
Another objective of the present disclosure, which objective is different from the preceding ones, is to provide a detector of volatile compounds that is effective even at low concentrations of volatile compounds in the atmosphere to be tested.
Another objective of the present disclosure, which objective is different from the preceding ones, is to provide a method for detecting and quantifying volatile compounds in an atmosphere to be tested that provides rapid results.
Another objective of the present disclosure, which objective is different from the preceding ones, is to provide a sensitive reflecting element that may be heated optimally without disrupting the optical transduction.
In order to at least partially achieve at least one of the aforementioned objectives, one subject of the present disclosure is an optical device for detecting volatile compounds, comprising:
Such an optical detecting device is easy to implement because it solely uses a detection of the variation in the refractive index of the sensitive reflecting element in order to identify the desorption of a volatile compound from the sensitive layer. In addition, the thermal desorption allows the chemical nature of the volatile compound to be easily and rapidly determined because each volatile compound has a specific desorption temperature that is dependent on the chemical composition of the sensitive layer. In addition, the presence of the computing and processing unit notably allows the concentration of desorbed volatile compound in the atmosphere to be tested to be determined. Thus, such an optical detecting device allows the presence of volatile compounds in an atmosphere to be tested to be simply and rapidly detected and their concentration to be determined, even at low concentrations, i.e., of the order of one ppm or even of one ppb.
The optical detecting device according to the present disclosure may furthermore comprise one or more of the following features, which may be implemented alone or in combination.
According to one aspect, the presence of one or more desorbed volatile compounds may be detected via comparison of the light intensity reflected by the reflecting sensitive element without any volatile compounds adsorbed at a given temperature with the light intensity reflected by the sensitive reflecting element just after desorption at the same temperature.
The concentration of the one or more volatile compounds detected in the atmosphere to be tested may be determined via integration of the area of peaks in variation of the reflected light intensity corresponding to the desorption of the one or more volatile compounds.
The at least one sensitive layer may have a thickness within a range from 50 nm to 2000 nm, e.g., within a range from 400 nm to 1200 nm, e.g., within a range from 500 nm to 800 nm.
The at least one sensitive layer may have an average pore size smaller than 2 nm.
According to one particular embodiment, the at least one sensitive layer may have a porosity lower than 25%.
According to one variant, the at least one sensitive layer may be made of sol-gel silica.
According to another variant, the at least one sensitive layer may be made of a xerogel.
According to one aspect of this other variant, the xerogel may comprise tetraethyl orthosilicate (TEOS).
According to another aspect of this other variant, the xerogel may comprise triethoxymethylsilane (MTEOS).
According to yet another aspect of this other variant, the xerogel may comprise phenyl-triethoxysilane (Ph-TEOS).
According to one particular embodiment, the xerogel may comprise a mixture of tetraethyl orthosilicate (TEOS), triethoxymethylsilane (MTEOS) and phenyl-triethoxysilane (Ph-TEOS).
According to one aspect, the at least one sensitive layer may have a refractive index within a range from 1.2 to 1.6, e.g., within a range from 1.3 to 1.5, at wavelengths within a range from 400 nm to 1000 nm before its exposure to the atmosphere to be tested.
Alternatively or in addition, the at least one sensitive layer may have a structure configured to increase the variations in the optical signal.
The structure of the at least one sensitive layer may comprise a diffraction grating.
The structure of the at least one sensitive layer may comprise resonant regions.
The structure of the at least one sensitive layer may comprise a photonic crystal.
The structure of the at least one sensitive layer may comprise a stack of layers.
According to a first embodiment, the sensitive reflecting element may comprise a single sensitive layer.
According to this first embodiment, the optical detecting device comprises a single light source and a single light detector.
According to a second embodiment, the sensitive reflecting element may comprise a plurality of sensitive layers.
According to this second embodiment, the optical detecting device comprises as many light sources as sensitive layers.
According to this second embodiment, the optical detecting device may comprise a single light detector when the emission wavelengths of the light sources are different.
Alternatively, the optical detecting device may comprise as many light detectors as light sources.
According to this second embodiment, the sensitive layers of the sensitive reflecting element may have perpendicular chemical affinities in order to allow a more precise chemical identification of the chemical component.
According to a first variant, the sensitive layers having perpendicular chemical affinities may be placed side-by-side.
According to a second variant, the sensitive layers having perpendicular chemical affinities may be separated from one another in the sensitive reflecting element.
According to one aspect, the substrate layer may be made of a semiconductor, e.g., of silicon, of glass, of sapphire, or of a metal.
According to one particular embodiment, the substrate layer may possess a refractive index higher than 2.5, e.g., higher than 3, at wavelengths within a range from 250 nm to 1500 nm.
The incident angle and the detection angle may be, respectively, within a range from 30° to 75° with respect to a normal to the sensitive layer.
According to one particular embodiment, the wavelength emitted by the light source is within a range from 400 nm to 1000 nm.
According to one aspect of this particular embodiment, the wavelength emitted by the light source may be monochromatic and chosen with the angle of incidence so as to coincide with the wavelength position of an inflection between two constructive and destructive interference peaks of the reflection spectrum of the sensitive reflecting element.
The electrically conductive layer may have a thickness smaller than or equal to 150 nm, e.g., within a range from 70 nm to 90 nm.
According to one aspect, the electrically conductive layer may have a resistivity within a range from 10−4 Ω·m to 10−7 Ω·m so as to allow the sensitive layer to be heated by Joule heating.
According to one aspect, the resistance of the material from which the electrically conductive layer is made is within a range from 2Ω to 200Ω, e.g., within a range from 20Ω to 50Ω.
The electrically conductive layer may be made of a transparent conductive oxide, e.g., of indium-doped tin oxide (ITO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), or fluorine-doped tin oxide (FTO).
According to one particular embodiment, the optical device may comprise an enclosure in which the sensitive reflecting element is placed.
The enclosure may comprise at least one aperture configured to allow the atmosphere to be tested to enter and/or exit.
Another subject of the present disclosure is a method for detecting and quantifying volatile compounds in an atmosphere to be tested implementing an optical detecting device such as described above. The detecting and quantifying method comprises the following steps:
The detecting and quantifying method, according to embodiments of the present disclosure, allows, inter alia, an adsorption of volatile compounds on the sensitive layer at room temperature. Subsequently, the adsorbed volatile compounds are detected and quantified via simple detection of a variation in the refractive index of the sensitive reflecting element, this notably allowing a rapid response to be obtained as regards the identification of the detected volatile compound or even the concentration of this volatile compound in the atmosphere to be tested.
The method for detecting and quantifying volatile compounds in an atmosphere to be tested, according to embodiments of the present disclosure, may furthermore comprise one or more of the following features, which may be implemented alone or in combination.
According to one alternative, the steps of illuminating the sensitive layer and of exposing the sensitive reflecting element to the atmosphere to be tested may be interchanged.
According to one aspect, the step of heating the sensitive layer may be carried out via controlled heating at a heating rate within a range from 1° C./s to 20° C./s.
According to one particular embodiment, the nature of the volatile compound desorbed during the heating step is determined via comparison of the refractive index of the reflecting sensitive element at a given temperature with respect to the refractive index of this sensitive reflecting element without any adsorbed compound at the same temperature.
According to one alternative, the nature of the desorbed volatile compound is determined by plotting the curve of variation in refractive index of the sensitive reflecting element as a function of the temperature of the electrically conductive layer and by determining the desorption temperature, which corresponds to the temperature at which the value of the derivative of this curve is zero, by solving the equation:
According to another alternative, the amount of volatile compound desorbed is determined by comparing the variation in refractive index before and after heating.
According to this other alternative, the amount of volatile compound desorbed is proportional to the equation:
N2−N1
According to one aspect, the step of measuring the light intensity reflected by the sensitive layer may be carried out at a time interval within a range from 0.2 seconds to 5 seconds.
The desorbed volatile compounds may be quantified via integration of an area of a peak of variation in the refractive index of the sensitive reflecting element corresponding to the desorption of the corresponding volatile compound.
According to one variant, the volatile compound, in the case where there is a mixture of volatile compounds, may be identified via deconvolution of the refractive index of the sensitive reflecting element during the desorption of this volatile compound.
According to one particular embodiment, the wavelength of the light source may be chosen so as to coincide with the wavelength position of an inflection between two constructive and destructive interference peaks of the reflection spectrum of the sensitive reflecting element.
Other features and advantages of embodiments of the present disclosure will become more clearly apparent on reading the following nonlimiting description, which is given by way of illustration, and the accompanying drawings in which:
Identical elements in the various figures have been designated with the same references.
The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Single features of various embodiments may also be combined and/or interchanged to form other embodiments.
In the present description, certain elements or parameters may be indexed (e.g., first element or second element and first parameter and second parameter or even first criterion and second criterion, etc.). In this case, it is simply a question of an indexation that is used to differentiate and denote elements, parameters or criteria that are similar but not identical. This indexation does not imply a priority of one element, parameter or criterion with respect to another and such denominations could easily be interchanged without departing from the scope of the present description. This indexation also does not imply, for example, an order in time that such or such criteria must be estimated.
In the present description, by “volatile compound” what is meant is a compound that vaporizes or evaporates easily under standard temperature and pressure conditions (i.e., 25° C. and 1 bar) such as defined by the International Union of Pure and Applied Chemistry. In the present description, a volatile compound may be of organic nature; it may be, for example, a question of a volatile organic compound (also known by the acronym VOC), or even of a volatile compound of inorganic nature, such as water, for example.
In addition, in the following description, by “transparent” what is meant is a material that is preferably colorless, through which light may pass with a maximum intensity absorption of 10% at wavelengths, in particular, within a range from 280 nm to 1300 nm.
Moreover, in the following description, by “xerogel” what is meant is a material comprising a macromolecular network of vitreous oxides that is manufactured using a sol-gel process.
Below, in the following description, by “quasi-monochromatic” what is meant is a wave the spectrum of which occupies only a very narrow wavelength band; the spectrum of this wave may occupy, for example, a wavelength band narrower than 2 nm.
In
The sensitive reflecting element 3 is intended to be placed in an atmosphere to be tested so that at least some of the volatile compounds present in this atmosphere to be tested are adsorbed by this sensitive reflecting element 3, in order to make it possible to detect their presence and to determine their concentration on their desorption. Thus, the intensity of the reflection of the sensitive reflecting element 3 is intended to vary as a function of the volatile compounds A, B, C contained in the atmosphere to be tested that are adsorbed by this sensitive reflecting element 3 and of their concentration. The sensitive reflecting element 3 comprises a substrate layer 31, at least one sensitive layer 33, and an electrically conductive layer 35 sandwiched between the substrate layer 31 and the sensitive layer 33. Moreover, the electrically conductive layer 35 is configured to heat the sensitive layer 33 by Joule heating.
The substrate layer 31 may be made of a semiconductor, e.g., silicon, of glass, of sapphire, or of a metal. Furthermore, the substrate layer 31 possesses a refractive index higher than 2.5, e.g., higher than 3, at wavelengths within a range from 250 nm to 1500 nm. In addition, the substrate layer 31 may be reflective for example because of a mirror-type metal coating on one of its faces, which face is placed facing the electrically conductive layer 35.
Moreover, the at least one sensitive layer 33 is porous and transparent. This sensitive layer 33 is configured to allow at least some of the volatile compounds A, B, C (shown in
The at least one sensitive layer 33 may be made of sol-gel silica, or even be a xerogel. By virtue of the use of sol-gel processes, it is possible to easily control the formation of this sensitive layer 33 and, e.g., its thickness e (shown in
Moreover, the at least one sensitive layer 33 does not comprise any structuring agents, i.e., chemical species of mineral or organic nature about which the material from which the sensitive layer 33 is made could organize.
Furthermore, in the case where the sensitive layer 33 is formed by a xerogel, this xerogel may comprise tetraethyl orthosilicate (TEOS), triethoxymethyisilane (MTEOS), or even phenyl-triethoxysilane (Ph-TEOS). According to one particular embodiment described in more detail below, the xerogel may comprise a mixture of tetraethyl orthosilicate (TEOS), triethoxymethylsilane (MTEOS) and phenyl-triethoxysilane (Ph-TEOS).
Moreover, the electrically conductive layer 35 of the sensitive reflecting element 3 is non-scattering, i.e., it does not scatter light, and transparent at wavelengths within a range from 400 nm to 1000 nm. Specifically, if this electrically conductive layer 35 scattered light, this could potentially be detrimental to the precision of the measurement taken. Specifically, if the electrically conductive layer 35 is scattering, some of the light ray 51 may be scattered, this possibly being detrimental to the intensity of the signal once reflected and making the signal difficult to analyze with the light detector because of the initial signal being subject to masking related to scattering of the signal in the electrically conductive layer 35. In addition, if this electrically conductive layer 35 is opaque, in this case, it is not possible to obtain a reflected ray and therefore to detect the latter with the light detector 7. This electrically conductive layer 35 is placed directly in contact with the substrate layer 31 and with the sensitive layer 33. This electrically conductive layer 35 is configured to allow the sensitive layer 33 to be heated by Joule heating in order to allow desorption of the volatile compounds A, B, C adsorbed on the sensitive layer 33. To this end, the electrically conductive layer 35 may have a resistivity within a range from 10−4 Ω·m to 10−7 Ω·m. Furthermore, the component of this electrically conductive layer 35 may have a resistance within a range from 2Ω to 200Ω, e.g., within a range from 20Ω to 50Ω, so as to allow the sensitive layer 33 to be heated by Joule heating. Placing this electrically conductive layer 35 directly in contact with the sensitive layer 33 allows the latter to be effectively heated and limits the time required to desorb the volatile compounds A, B, C adsorbed on the sensitive layer 33. In addition, the electrically conductive layer 35 may have a thickness s (shown in
Moreover, the electrically conductive layer 35 may, for example, be made of a transparent conductive oxide (TCO), e.g., of tin-doped indium oxide (ITO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), or of fluorine-doped tin oxide (FTO). Such compounds have resistivity properties that are compatible with those required to allow the sensitive layer 33 to be heated by Joule heating. Such a composition of the electrically conductive layer 35 (layer made of a transparent conductive oxide) allows optical transduction via direct reflection of a light beam (e.g., light ray 51) emitted by the light source 5. Furthermore, transparent conductive oxides (TCOs) are good candidates for sol-gel production, and therefore for the formation of the sensitive layer 33. According to this particular embodiment, the substrate layer 31 comprises a mirror-type metal coating on its face placed in contact with the electrically conductive layer 35 in order to improve the intensity of the reflected light ray.
Thus, the sensitive reflecting element 3 has a small thickness, this allowing its placement at measurement sites or even its transport to be facilitated. In addition, the sensitive reflecting element 3 may be placed at measurement sites without requiring other elements of the optical detecting device 1 to be present, the elements being necessary only during the study of the desorption of any volatile compounds A, B, C adsorbed on the sensitive layer 33.
Moreover, the light source 5 is placed to illuminate the sensitive layer 33 at an incident angle α. According to the particular embodiment of
In addition, the light detector 7 is configured to measure the light intensity reflected by the sensitive reflecting element 3 at a detection angle β. This light detector 7 may be, for example, a camera or any other element able to detect the light ray 51 reflected by the sensitive reflecting element 3. According to the particular embodiment of
According to a simplified approach based on fresnel's equations and not taking into account the presence of the substrate layer 31, the following supposition may be made:
Given that in this formula only n2 varies as a function of the adsorption of volatile compounds A, B, C contained in the atmosphere to be tested by the sensitive layer 33, n1, α and β remaining constant, it is possible therefore to deduce therefrom that reflectance decreases linearly with an increase in the refractive index n2. It turns out that the refractive index n2 of the sensitive reflecting element 3 varies linearly with the amount of volatile compounds A, B, C adsorbed by the sensitive layer 33.
Returning to
Thus, the optical detecting device 1 allows the presence of one or more volatile compounds A, B, C in an atmosphere to be tested to be detected easily via a simple variation in the intensity of reflection of a light ray 51 allowing a variation in the refractive index of the sensitive reflecting element 3 to be determined. This detection may therefore be rapid. Specifically, since the transduction is of optical-reflection type, volatile compounds A, B, C are detected by measuring the variation in the intensity reflected at a single wavelength, this variation being induced by the increase in the refractive index associated with the adsorption of the volatile compound A, B, C in the sensitive layer 33. In addition, it is simple and rapid to use thermal desorption to detect and quantify the desorbing volatile compound A, B, C that was initially present in the atmosphere to be tested. In addition, the various components of the sensitive reflecting element 3 are quite inexpensive, this allowing the manufacturing cost of this optical detecting device 1 to be limited.
Moreover, the sensitivity of the optical detecting device 1 may be enhanced by judiciously choosing in particular the thickness e of the sensitive layer 33 on the one hand and the wavelength combined with the angle of incidence α on the other hand. Specifically, above simplified Fresnel's equations were presented with a view to explaining the basis of operation of the optical detecting device 1.
Alternatively or in addition, the at least one sensitive layer 33 may have a structure configured to increase the variations in the optical signal in order to improve the sensitivity of this optical detecting device 1. The structure of the at least one sensitive layer 33 may comprise a diffraction grating, resonant regions, a photonic crystal, or even a stack of layers.
According to the particular embodiment of
In order to mitigate this eventuality, and as shown in
In the particular representation of
In
In
In
The inventors have observed that, depending on the presence and on the configuration of the enclosure 20, the rates of adsorption of the volatile compounds A, B, C are not identical. More particularly, the configuration of the enclosure 20 comprising the first and second apertures 21a, 21b, i.e., the configuration such as shown in
In
The detecting and quantifying method 100 comprises a step E1 of illuminating the sensitive layer 33 at an incident angle α with the monochromatic or quasi-monochromatic light source 5 (these being shown in
The detecting and quantifying method 100 then implements a step E2 of exposing the sensitive reflecting element 3 to the atmosphere to be tested for a predetermined time so as to allow volatile compounds A, B, C contained in this atmosphere to be tested to adsorb on the sensitive layer 33 of the sensitive reflecting element 3. In this exposing step E2, the sensitive layer 33 of the sensitive reflecting element 3 is also illuminated in order to be able to observe any adsorption of volatile compounds A, B, C on this sensitive layer 33. Specifically, the refractive index of the sensitive reflecting element 3 increases or decreases on the adsorption of volatile compounds A, B, C. The illumination of the sensitive layer 33 in this exposing step E2 therefore makes it possible to determine whether volatile compounds A, B, C have been adsorbed by the sensitive layer 33.
According to one alternative, the steps E1 and E2 of illuminating the sensitive layer 33 and of exposing the sensitive reflecting element 3 to the atmosphere to be tested may be inverted. More particularly, the step E2 of exposing the sensitive reflecting element 3 to the atmosphere to be tested may be implemented prior to the step E1 of illuminating the sensitive layer 33.
The detecting and quantifying method 100 then implements a step E3 of heating the sensitive layer 33 via the electrically conductive layer 35 in order to allow the volatile compounds A, B, C to be desorbed from the sensitive layer 33. According to one particular embodiment, the step E3 of heating the sensitive layer 33 is carried out via controlled heating at a heating rate within a range from 1° C./s to 20° C./s.
The detecting and quantifying method 100 comprises a step E4 of measuring the light intensity reflected by the sensitive reflecting element 3 during the heating step E3 in order to determine a variation in the refractive index of this sensitive reflecting element 3. The step E4 of measuring the light intensity reflected by the sensitive reflecting element 3 may, for example, be carried out at time intervals within a range from 0.2 seconds to 5 seconds. Specifically, the modification of the refractive index of the sensitive reflecting element 3 allows the adsorption of volatile compounds A, B, C by the sensitive layer 33 of the latter or even the desorption of volatile compounds A, B, C from the sensitive layer 33 of this sensitive reflecting element 3 to be detected.
Lastly, the detecting and quantifying method 100 comprises a step E5 of monitoring the variation in the refractive index of the sensitive reflecting element 3 in order to determine the chemical nature and the amount of volatile compound A, B, C desorbed from the sensitive layer 33 during the heating step E3. This step E5 of monitoring the variation in the refractive index of the sensitive reflecting element 3 is carried out by the computing and processing unit 9. More particularly, in this step E5 of monitoring the variation in the refractive index of the sensitive reflecting element 3, the computing and processing unit determines the nature of the volatile compound A, B, C desorbed during the heating step E3 by taking the derivative of the signal with respect to temperature and by comparing the value of the temperature at which the derivative in question is zero to temperatures present in a database. Furthermore, the desorbed volatile compound A, B, C is quantified via integration of the area of the various peaks of variation in the reflected light intensity corresponding to the desorption of the desorbed volatile compound. This integration may be carried out after calibration of the computing and processing unit 9.
The inventors have determined, in the course of various tests, that all the volatile compounds A, B, C potentially adsorbed on the sensitive layers 33 are completely desorbed when this sensitive layer 33 reaches a temperature higher than or equal to 250° C. If a heating rate within a range from 1° C./s to 20° C./s is used, this detecting and quantifying method 100 is observed to provide short response times.
In
The sensitive layer 33 is then exposed to the atmosphere to be tested, which potentially contains volatile compounds A, B, C at least some of which are intended to adsorb on the sensitive layer 33. The sensitive layer 33 is typically exposed to the atmosphere to be tested at room temperature, i.e., about 25° C. This exposure occurs for a predetermined time in order to allow at least some of the volatile compounds A, B, C to adsorb on this sensitive layer 33. This exposure time may be within a range from a few minutes, typically 10 minutes to 30 minutes, to several days, typically five days or six days. In the example shown in
Specifically, as is illustrated in
In
dN1/dT=0
More particularly, in
Furthermore, the integration of an area S1 placed under the curve 120, corresponding to the area of the peak of variation in the refractive index of the sensitive reflecting element 3 related to the desorption of the volatile compound A, allows the amount of volatile compound A adsorbed on the sensitive layer 33 during its exposure to the atmosphere to be tested to be determined and thus its concentration in this atmosphere to be deduced. Typically, the area S1 corresponds to the portion containing inclined hatching under this curve 120. Furthermore, the quantification of the desorbed volatile compound B is also obtained via integration of an area S2 placed under the curve 130 and corresponding to the area of the peak of variation in the refractive index of the sensitive reflecting element 3 related to the desorption of the volatile compound B. This integration of the area S2 therefore allows the amount of volatile compound B desorbed to be obtained and therefore its concentration in the atmosphere to be tested to be deduced. This area S2 corresponds to the portion containing vertical hatching under this curve 130. Thus, the quantification of the volatile compound desorbed is obtained via differential mathematical processing of the curves of variation in optical response as a function of the temperature of the electrically conductive layer 35 and therefore as a function of the temperature of the sensitive layer 33.
According to one alternative (not shown here) the amount of volatile compounds desorbed is determined by comparing the variation in the refractive index before and after heating the sensitive layer 33. According to this alternative, the amount of volatile compounds desorbed is proportional to the equation:
N2−N1
Desorption temperatures of certain volatile compounds for a given sensitive layer:
In
The sensitive layer 33 used to demonstrate the difference in desorption temperature as a function of the adsorbed volatile compound A, B, C has a composition S3M3P3.
For this composition, the sensitive layer is produced using a sol-gel formulation composed of 0.33 TEOS (tetraethyl orthosilicate); 0.66 Ph-TEOS (phenyl-triethoxysilane); 7.8 H2O; 0.07 HCl; and 6.2 PrOH (isopropanol), the various indicated values corresponding to molar proportions.
More particularly, the curves 700, 710, 720, 730, 740 and 750, shown in
Each of these curves 700 to 750 comprises one (or more than one) more or less marked peak of variation in the refractive index of the sensitive reflecting element 3. In particular, for water, the peak of variation 751 is very small. This peak of variation 751 is detected at a temperature of the sensitive layer 33 of about 40° C. This spectral analysis allows it to be deduced that the sensitive layer 33 of composition S3M3P3 has a hydrophobic character because it collects very little water and the water desorbs very easily (desorption temperature of 40° C.).
For the other volatile compounds A, B, C, which for their part are of organic nature, the variations in refractive index of the sensitive reflecting element 3 are more marked.
In the curve 710 of
In the curve 720 of
In the curve 730 of
In the curve 740 of
The temperatures corresponding to these various peaks correspond to the temperatures at which this curve has a derivative of zero. It is thus possible to easily determine the nature of the desorbed volatile compound depending on its temperature of desorption from the sensitive layer 33. These values may, for example, allow a table to be generated for various volatile compounds A, B, C in order to know their temperature of desorption from the sensitive layer 33 and to facilitate their identification for a sensitive layer 33 of given chemical composition.
The curve 700 of
Returning to the curves 710 and 740 shown in
In order to prove the difference in the desorption temperatures of the volatile compounds A, B, C as a function of the chemical composition of the sensitive layer 33 and to make allowance for a situation in which various volatile compounds desorb from the sensitive layer 33 at the same temperature, as was the case for toluene and ethylene glycol in the preceding example, the inventors have exposed sensitive layers 33 of various chemical compositions to the same atmosphere comprising volatile compounds A, B, C. The results of analyses of thermal desorption are shown in
Composition REF: 1 TEOS (tetraethyl orthosilicate); 4 H2O; 0.17 HCl; 5.8 PrOH (isopropanol);
Composition S3P7: 0.33 TEOS (tetraethyl orthosilicate); 0.33 MTEOS (triethoxymethylsilane); 0.33 Ph-TEOS (phenyl-triethoxysilane); 7.8 H2O; 0.07 HCl; 6.2 PrOH (isopropanol);
Composition S3M3P3: 0.33 TEOS (tetraethyl orthosilicate); 0.66 Ph-TEOS (phenyl-triethoxysilane); 7.8 H2O; 0.07 HCl; 6.2 PrOH (isopropanol).
Furthermore, the atmosphere to which these various sensitive layers 33 were simultaneously exposed, for a time of 5 days, corresponded, in this particular example, to the passenger compartment of a motor vehicle.
More precisely,
In these various figures,
Moreover, the curve 800 of
The various embodiments described above are nonlimiting examples given by way of illustration. Specifically, it will be entirely within the ability of a person skilled in the art to adapt the heating rate of the sensitive layer 33, the thickness e of the sensitive layer 33, the thickness s of the electrically conductive layer 35, and the composition of the substrate layer 31, of the sensitive layer 33, or of the electrically conductive layer 35 as required without departing from the scope of the present description. Furthermore, a person skilled in the art will be able to use light sources having wavelengths different from those described in the present examples without departing from the scope of the present invention. In addition, the refractive indices of the various layers of the sensitive reflecting element 3 may be modified by a person skilled in the art as required without departing from the scope of the present invention.
Thus, a detector of volatile compounds A, B, C that is simple to use, inexpensive, and effective even at low concentrations of volatile compounds A, B, C in the atmosphere to be tested and that delivers measurement results in a short time is obtainable by virtue of the optical detecting device 1 described above and more particularly by virtue of the sensitive reflecting element 3 employed in the detecting and quantifying method 100 described above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1871648 | Nov 2018 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2019/052736 | 11/18/2019 | WO | 00 |
