JPS60123751A - Liquid cell for detecting optoacoustic signal - Google Patents

Abstract

PURPOSE:To enhance the sensitivity of a detection cell and to mold said cell into an arbitrary shape, by using a vinylidene fluoride/trifluoroethylene copolymer in a high-molecular piezoelectric body as a pressure detecting element. CONSTITUTION:The cylindrical part of a cylindrical cell 1 is made of a vinylidene fluoride/trifluoroethylene copolymer and flat quartz plates are provided to the optical windows of opposed wall surfaces 2a, 2b. A solution or suspension of a specimen is introduced from an inflow port 3a and discharged from an outflow port 3b after measurement. Light energy absorbed with the liquid is converted to heat energy by a non-radiation process and a compressional wave is generated by the risin in the temp. of the liquid and the thermal expansion thereof while piezo-electricity is generated in the vinylidene fluoride/trifluoroethylene copolymer. This piezo-electricity is taken out as an electric signal from electrodes 4a, 4b and detected. Therefore, sensitivity becomes high and moldability is made well by using the vinylidene fluoride/trifluoroethylene copolymer as a detection vibrator and the cell can be molded into an arbitrary shape.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly sensitive photoacoustic signal detection cell made of a polymeric piezoelectric material.

Conventionally, the concentration of a solute dissolved in a solvent or the concentration of a suspended sample can be measured using absorption, transmission, scattering, etc. of infrared light, visible light, or ultraviolet light. A detector that applies this fact is liquid chromatography (L
C), hydrodynamic chromatography (HD
C) etc. However, in these conventional detectors, the amounts of absorption, transmission, and scattering are not necessarily proportional to the concentration, and it is difficult to measure trace amounts.

A photoacoustic signal (PAS) detection method was developed to overcome this drawback. In this detection method, when a sample is intermittently irradiated with light, part of the absorbed light energy is converted into thermal energy by a non-radiative process, the sample temperature rises, and the thermal expansion vibration of the medium It takes advantage of the phenomenon that generates waves. Then, this compression wave is detected by a microphone or a piezoelectric element to detect the concentration of the sample.

Currently, PAS detectors for liquid cells use piezoelectric ceramics such as PZT and polyvinylidene fluoride (hereinafter abbreviated as PVDF) as pressure detection elements, but the former is difficult to mold, and the latter is piezoelectric. There are disadvantages such as low rate.

The present invention attempts to eliminate the above-mentioned drawbacks by using a novel polymeric piezoelectric material as a pressure sensing element. The present invention is a liquid cell for photoacoustic signal detection using a vinylidene fluoride/trifluoroethylene copolymer as a detection vibrator.

The photoacoustic signal measurement cell of the present invention is an LC or HDC cell.
Since vinylidene fluoride/trifluoroethylene copolymer was used as the polymeric piezoelectric material, it has the following advantages.

■Higher sensitivity than when using piezoelectric ceramics.

■ Piezoelectric ceramics have better impedance matching with liquids.

(2) Since piezoelectric ceramics are hard and brittle, it is difficult to mold them into various shapes, but in the present invention, the material can be molded into arbitrary shapes.

■ PVDF requires a stretching operation in order to exhibit sufficient piezoelectricity, making it difficult to form it into any desired shape. However, with the present invention, piezoelectricity can be generated without stretching the material. Therefore, it can be molded into any shape, and its piezoelectric constant is higher than that of PVDF. Therefore, ultra-trace measurements can be made.

The sound wave propagating substance used in the present invention is water.

Examples include aqueous solutions, halogenated hydrocarbons such as chloroform and dichloroethane, aromatic hydrocarbons such as benzene, toluene and xylene, alcohols such as methanol and ethanol, and aliphatic hydrocarbons such as hexane and heptane.

The vinylidene fluoride/trifluoro-engineered tyrene copolymer used in the present invention can be obtained by solution polymerization, emulsion polymerization, @turbidity polymerization, or bulk polymerization in the presence of a conventional radical catalyst. Generally, vinylidene fluoride, trifluoroethylene, a radical catalyst, water or a solvent, and additives such as an emulsifier are placed in a pressure-resistant autoclave and copolymerized at a constant temperature for a certain period of time. A vinylidene/trifluoroethylene copolymer is obtained as a powder.

The material used for the detection vibrator of the present invention needs to have a high piezoelectric constant. Vinylidene fluoride/
The composition ratio of the trifluoroethylene copolymer is 94/6 ~
25/75 (molch), preferably 90/10-40
/6 (1 (molty)).The piezoelectric constant of the above copolymer having a composition in which the amount of trifluoroethylene is less than 6 molti and 75 molti or more is low.In the present invention, the structural material of the cell other than the detection vibrator is A vinylidene fluoride/trifluoroethylene copolymer may also be used as the solvent.

When manufacturing a cell using the above-mentioned copolymer as a material, any method may be used and there are no particular limitations. For example, a mold may be made to obtain a molded article as shown in FIGS. 1 and 2, and the copolymer may be injection molded using this mold. It is also possible to create sheets or films of the required thickness by melt molding, casting, or other methods, and use them to assemble molded products as shown in FIGS. 1 and 2.

Hereinafter, the present invention will be specifically explained with reference to the drawings.

FIG. 1 and FIG. 2 show an embodiment of a liquid cell for photoacoustic signal detection of the present invention.

A pair of optical windows (for example, a quartz flat plate, a glass flat plate, etc.) 2a, 2 are provided on opposing walls of a cylindrical cell 1 (the material is vinylidene fluoride/trifluoroethylene copolymer).
b is provided to allow light to pass through the optical windows 2a, 2b. The cylindrical cell 1 is provided with a liquid inlet 3a (made of vinylidene fluoride/trifluoroethylene copolymer, a polymeric material that can adhere to the copolymer, etc.) and a liquid outlet 3b (made of the same material as 3a). A liquid, for example a liquid sound propagation substance, can be introduced into and discharged from the space. Band-shaped electrodes 4a, 4b are attached to the inner and outer walls of the cylindrical cell 1, and lead wires 5a, 5b are attached to each electrode.

Now, a liquid in which a sample to be measured is dissolved or suspended is introduced into the cylindrical cell 1 from the liquid inlet 3a, and light is intermittently irradiated from the optical window or 2b. A part of the optical energy absorbed by the sample in the liquid is converted into thermal energy by a non-radiative process, increasing the sample temperature and generating compression waves from thermal expansion vibration of the sample.

The pressure changes caused by the compression waves cause the vinylidene fluoride/polymer piezoelectric material forming the cylindrical cell 1 to
Piezoelectricity occurs in trifluoroethylene copolymers. This piezoelectricity is extracted as an electric signal by electrodes 4a, 4b attached in strips on the inner and outer surfaces of the cylindrical cell 1, and sent to an amplifier (not shown) via leads @5a, 5b. The output level of the electrical signal depends on the sample concentration. In this way, the concentration of the sample in the liquid can be measured.

The copolymer used in the present invention generates piezoelectricity even when unstretched, so the cell itself can be integrally molded as shown in Figure 1, and can be used for electrode attachment, poling, and window material attachment. Therefore, the liquid cell for photoacoustic signal detection of the present invention can be manufactured.

Examples 1 and 2 and Comparative Example 1 A cell shown in FIG. 1 was manufactured using vinylidene fluoride/trifluoroethylene copolymer. The electrical response constant gs+ and processability of this cell were compared with those of a cell made of PVDF. The results are shown in Table-1.

Table-1

[Brief explanation of the drawing]

1 and 2 show an embodiment of a liquid cell for photoacoustic signal detection according to the present invention, with FIG. 1 showing a longitudinal cross-sectional view thereof, and FIG. 2 showing a cross-sectional view thereof. 1... Cylindrical cell, 2a, 2b... Optical window, 3a... Liquid inlet, 3b...
Liquid outlet, 4a, 4b... Electrode, 5a, 5
b...Lead wire.

Claims (1)

[Claims] A device for detecting photoacoustic signals that can contain or continuously flow a liquid sound wave propagation substance, and uses vinylidene fluoride/trifluoroethylene copolymer as a detection vibrator. liquid cell.