JPS5848851B2 - Organic vapor detection device and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical device for detecting organic vapors and a method of using the device.

Aerospace Medicine in January 1969
Tolive on pages 35 to 39 of e.
r ), Roach, Roundy
There is a paper entitled "Liquid Crystals" by J.D. and Hoffmann.

This article specifically describes liquid crystals that change color when exposed to organic vapors.

A technical report on liquid crystals by EM Chemicals, page 7, also describes the use of liquid crystals for gas analysis of vapors such as acetone, benzene, chloroform, petroleum ether, etc. at lppm levels.

In U.S. Patent No. 3,050,982,
A dew point measuring device is described in which moisture adhering to an elongated waveguide changes the light transmission capacity of the waveguide, and the rate of change indicates the dew point.

This does not include the LCD. U.S. Patent Nos. 3 and 4
No. 09,404 describes an analytical method and apparatus using cholesteric liquid crystal materials,
This relates to the qualitative or quantitative detection and analysis of substances such as gases.

It is stated that reversible effects on the optical properties of liquid crystals are observed for common organic solvents, amines, simple alcohols, organic acids, etc.

U.S. Pat. No. 3,704,060 describes an electrically controllable light guiding device,
It is stated that the coating material on the waveguide can be a liquid crystal coating.

In U.S. Patent No. 3,802,760,
A device is described for changing the properties of a thin film waveguide by means of a liquid crystal member lining a portion of the waveguide.

An apparatus for detecting organic vapors according to the invention comprises (a) a sufficient amount of organic vapors sensitive to the organic vapors to measurably change the optical transmission ability of the waveguide when the waveguide is brought into contact with the organic vapors; an elongated waveguide having a liquid crystal material on its surface;
) a light source disposed at a position that transmits light in the longitudinal direction of the waveguide; and (C) means for measuring light exiting from the waveguide.

The apparatus comprises: (a) exposing the waveguide to a gas that may include organic vapors to which the liquid crystal is sensitive; and (b) transmitting light through the waveguide; )
It is also useful in a method for measuring organic vapors in which the light transmitted in the previous step (b) is detected as a measure of the organic vapors.

A waveguide, including any void space within the waveguide,
It is coated or impregnated with a liquid crystal material that is sensitive to organic vapor substances.

However, the condition is that the waveguide loaded with liquid crystal material is sufficiently transparent to the light; in some cases, the liquid crystal material may consist of reactive groups attached to the waveguide. .

In the case of a coated waveguide, the waveguide may be solid or hollow, e.g., hollow cylindrical or solid cylindrical; in the case of a hollow cylinder, the coating covers the inner surface. It may be located on the outer surface, on the outer surface, or on both surfaces.

However, usually only the outer peripheral area is coated, and the ends of the solid rod are uncoated unless it is desired that the coating at both ends allows light to pass through and absorb light at a particular wavelength.

Obviously, the amount of liquid crystal material in the waveguide must be sufficient to cause a measurable change in optical transmission over the range of concentrations of organic vapors that the waveguide is intended to detect. There is.

The waveguides may be in the form of ronds or fibers and may be made of transparent materials such as sapphire, glass, pyrex or other transparent inorganic materials, or of polystyrene, polyalpha-methylstyrene, polymethylmethacrylate or other transparent plastic materials. It can be made from transparent plastic such as

The waveguide is elongated in the direction of light flow.

Cylindrical waveguides, sometimes called optical fibers, are usually used, but fibers or ronds with square, rectangular, oval or other cross-sectional shapes are also used, and the light is shown in Figures 1 and 3. As shown in the figure, it can be transmitted while being reflected many times in the vertical direction.

The first article presenting the prior art from Aerospace Medicine describes various liquid crystals and their use for detecting organic vapors.

Liquid crystal, cholesteryl chloride and 6 0/4 0
A mixture of oleyl cholesteryl carbonate and cholesteryl nanonate was used to detect chloroform, benzene and cyclohexane.

Also, a mixture of liquid crystals, cholesteryl butyrate, nanonate and erucate was used to detect the same organic vapor.

The light source may be a commercially available light source that is a substantially white light source, or it may be colored, i.e., infrared,
It may be of substantially monochromatic light in the ultraviolet, yellow, orange, green, blue or other color ranges.

However, filters can be used to obtain colored light.

Monochromatic light of various colors can be provided by light emitting diodes (LEDs).

Certain colors, such as green, may be most desirable depending on the color or composition of the coating appearing on the waveguide.

Next, the present invention will be described in detail with reference to embodiments of the present invention based on the accompanying drawings.

The combination of the waveguide and the cladding is selected to provide the cladding with a refractive index that is either higher or lower than the refractive index of the waveguide.

Lower refractive index conditions are commonly used in optical waveguide applications, resulting in a mechanism such as that illustrated in FIG. 1A.

Using a higher index coating would operate in a mechanism similar to that shown in FIG. 1B.

Either of these methods can be used, but Figure 1A
The mechanism shown in is less sensitive.

This is because mutual interference of vanishing waves occurs only in the area of the rod coating interface.

In either arrangement of FIG. 1B, the radiation is transmitted throughout the sheath so that solid state spectrophotometry can be performed in situ.

To measure light transmittance, a measuring device was designed and manufactured to perform quantitative analytical measurements.

This particular device has a diameter of 0. Accommodates glass rods of 9 mm to 1.3 iH length lOmN or 20 mm.

The basic components are shown schematically in FIG.

These components are as follows: 1 Tungsten filament lamp light source 2 Condensing lens system for producing nearly parallel light rays 3 Wavelength selection filter 4 Annular aperture 5 for blocking axial rays Condensing lens 6 for producing hollow cone rays Wide-angle rays A coupling hemisphere and aperture 7 to couple to the rond; a rond fixture 8 to accurately position the rond relative to the aperture with minimal surface contact; a silicon photodiode detector 9; and an operational amplifier 10 operating as a current-to-voltage converter.
3V 2-Digit Digital Voltmeter for Reading Relative Transmittance An optical diagram with exaggerated rod dimensions is shown in FIG. 3 to illustrate the basic measurement operation.

Light from a tungsten lamp is collimated using both mirrors and lens concentrators.

The light then passes through a heat absorbing glass filter and a variable color selection filter.

The front mirror deflects the light 90' in the vertical direction.

The annular aperture blocks the axial rays and delimits the cone angle for the rays propagating in the quartz rond.

The condensing lens in the next stage converts the parallel light into a strongly converged hollow cone of light.

A hemispherical lens and circular aperture couple the light into the rondo.

After multiple reflections within the rond, the light appears at its upper end face, is scattered by a diffuser, and a portion of the light goes to a silicon photodiode detector.

The photodiode operates in photovoltaic mode and the operational amplifier acts as a current sink to minimize the voltage across the diode.

The amplifier output is a low impedance voltage proportional to the input current ranging from 10-11 amps to 1O-3 amps.

The output voltage suitable for the 200MV full scale digital panel meter is selected by a decimal range switch.

In use, the device first records the amount of light transmitted through the rod after it is coated and before it is exposed.

When the coating is exposed to the organic vapor to be analyzed,
A physical change occurs in the coating, and the transmission of light through the waveguide changes proportionally to the concentration of the organic vapor.

This phenomenon has been described by Kapany (Kapany, N.
．． S. ``Fiber Optics'', Aca
demic Prees, New York, 1
967) is governed by the well-known waveguide management theory described by [967].

The essential requirement is that the critical angle at which the incident ray is no longer transmitted through the Rondo is given by θC=1.

Here, nO, ie, the refractive index of the core, is thicker than n1, ie, the refractive index of the coating.

The coated waveguide thus becomes the electrical equivalent circuit of an amplifier whose electrical equivalent circuit is operated by a vacuum tube or a transistor.

Acting as a light intensifier, small changes in the outer surface of the rod are adjusted as large changes in the light transmitted through the rod.

The composition of the liquid crystal material coated or incorporated into the waveguide is varied to detect different organic vapors and/or to detect changes in different organic vapors.

Therefore, in order to use waveguides in the apparatus of the present invention, a series of waveguides with coatings sensitive to different organic vapors or different amounts of organic vapors may be provided, in order to Within the limits of the liquid crystal material that can be accommodated, the waveguide can be selected to measure the desired vapor or amount of vapor to be detected.

In many cases, the liquid crystal material of the waveguide changes color when exposed to organic vapors, and this color change provides high sensitivity.

However, the device of the invention senses changes in its refractive index, absorption and/or scattering due to physical changes in the liquid crystal material when in contact with organic vapors, and detects any changes that affect its light transmission. Measure optical changes.

Of course, the light-sensing portion of the device can also be modified to detect its own color change upon contact with organic vapors.

When the vapor is removed from contact with the waveguide, the color change returns to its original color.

Its original color may be colorless before contact with steam.

It is often desired to measure the concentration of organic vapors present in the atmosphere.

This is especially true when there is a question of whether safety limits set by OSHA have been exceeded.

There are currently many methods that can be used such as gas chromatography, infrared, etc.

However, all of these methods require complex and expensive equipment for real-time monitoring.

Alternatively, a material such as activated charcoal may be used to capture the vapor, and the container containing the captured vapor may be sent to a laboratory.
There are some things that can then be analyzed using an appropriate method.

Although this method is a simple and inexpensive way to collect vapors, it only provides a temporal average, not a real-time analysis.

It has been found that organic vapors present in the air can be detected by using a waveguide coated with a liquid crystal mixture.

The invention extends to the use of optical waveguides coated with organic vapor sensitive liquid crystals and/or mixtures.

The principle of this technology is as follows.

Cholesteric materials and (
or) A mixture of cholesteric materials is added to an optical quality glass rond that acts as a waveguide.

The amount of light transmitted is relatively constant prior to exposure to air contaminated with hydrocarbons or other materials, and the signal from a detector such as a photodiode operating in photovoltaic mode is also relatively constant. constant.

By introducing air containing organic vapors, the light transmittance and color properties of the spirally wound cholesteric liquid crystal material are changed.

This changes the refractive index and changes the amount of light exiting the waveguide.

Therefore, a small amount of organic vapor will adjust to a large change in the light transmitted through the rondo.

Many liquid crystal mixtures have been found for use in such applications, with different mixtures producing different colors.

The liquid crystal mixture that gives the best results is manufactured by E.M. of Darmstadt, West Germany. Merck
It is a commercially available mixture (Licrystal 9 1 8 3) manufactured by Licrystal.

This mixture contains a temperature indicator 17/10% glue crystals in 1,1,2-trichlorotrifluoroethane.
It is described as red at 24 and 17°C, green at 21°C, and blue at 24°C, and has a 50m standard package.

Either the waveguide is immersed in a solution of recrystal and the solvent is allowed to evaporate leaving a coating of liquid crystal material, or the solution is brushed or sprayed onto the waveguide.

A waveguide covered with a thin coating of this mixture was exposed to several different vapors.

Methylene chloride and ethanol reacted, but cyclopenkune did not.

The latter two vapors of methylene chloride and ethanol are
It was obtained by simply passing these two liquid Shonin air at room temperature.

The following results were obtained. The temperature monitor and indicator described herein has the following advantages.

(1) The presence of organic vapors and other substances that cause color changes in the liquid crystal mixture coating the waveguide can be monitored in a simple and quick manner.

(2) Small amounts of substances in the gaseous medium that are essentially non-reactive with the coated waveguide can be detected.

(3) Can be easily used to control on-off functions directly by signal output.

(4) Sensitivity can be adjusted by changing the angle at which the light enters the rod or the length of the rod.

(5) It can be used as a portable monitor.

Although the invention has been described in considerable detail with respect to specific embodiments, this is by way of example only and the invention is not necessarily limited to these embodiments.

This is because, in view of this description, various modifications will occur to those skilled in the art.

Accordingly, many modifications may be made without departing from the spirit of the invention.

[Brief explanation of drawings]

FIG. 1 of the accompanying drawings schematically shows the light transmission mechanism of the waveguide of the invention, FIG. 2 is a schematic diagram of the device of the invention, and FIG. 3 shows the device of the invention in optical detail. It is a diagram. 1...Tungsten filament lamp light source, 2...
・Condensing lens system to create almost parallel light rays, 3.
... Wavelength selection filter, 4... Annular aperture that blocks axial rays, 5... Condensing lens that creates hollow cone rays,
6 Coupling hemisphere and aperture to couple the wide-angle beam into the rondo; 7 Rondo fixture to accurately position the rondo relative to the aperture with minimal surface contact; 8 Silicon photodiode detector; 9 . . . operational amplifier operating as a current-to-voltage converter, 10 . . . 31/2 digit digital voltmeter for reading out relative transmissibility.

Claims (1)

[Claims] 1. An elongated waveguide, and a position where light is transmitted from one end of the waveguide in the vertical direction through the waveguide and is internally reflected multiple times. In a detection apparatus comprising a light source and means for measuring light exiting the waveguide from the other end of the waveguide, the elongated waveguide reflects electromagnetic radiation multiple times within the waveguide. The waveguide is in the form of a rod or fiber of transparent material that can be guided in the longitudinal direction and is sensitive to the organic vapor which, when brought into contact with the waveguide, changes the optical transmission capacity of the waveguide to a measurable degree. An organic vapor detection device characterized in that it has a sufficient amount of a liquid crystal material on the outer peripheral surface of the waveguide other than at its ends. 2. An elongated waveguide in the form of a rond or fiber of a transparent material capable of conducting electromagnetic radiation, wherein contacting the waveguide with an organic vapor measurably changes the optical transmission capacity of the waveguide. a waveguide having a sufficient amount of liquid crystal material sensitive to the organic vapor to be altered on its outer peripheral surface other than at both ends of the waveguide, which may contain the organic vapor; exposing the waveguide to an unknown substance, transmitting light from one end of the waveguide through it in a longitudinal direction with multiple reflections within the waveguide; A method for detecting organic vapor, characterized in that light emitted from an end of the organic vapor is detected as a measurement measure of the organic vapor.