RU1102258C - Method of manufacturing thermal-sensitive material - Google Patents

Description

 The invention relates to methods for producing thermosensitive materials based on cholesteric liquid crystals used to measure temperatures and visualize temperature fields in infrared and microwave radiation devices, aerodynamics and other fields of science and technology.

 There is a method of producing thermal indicator films based on cholesteric liquid crystals, which consists in introducing cholesteric liquid crystals into a polymer binder, applying the resulting emulsion to a substrate, drying and illuminating in the form of strips through a stencil with a UV lamp. Each strip is illuminated for a different time, which determines its color and temperature characteristics [1].

 The disadvantage of this method is the low sensitivity of the obtained thermal indicator film. Under the influence of UV radiation, simultaneously with a change in the color and temperature characteristics, the intensity of selective light reflection is significantly reduced.

 Closest to the proposed method is a method of producing a thermosensitive material based on cholesteric liquid crystals, which consists in introducing a liquid crystal thermal indicator including cholesteryl benzoate into a hydrophobic polymer binder, applying the resulting emulsion to a substrate, drying with placing the material in a preheated chamber and then cooling to room temperature [2].

The specified method is characterized by a low temperature sensitivity (Δt / Δλ, ^about C / nm) with an insufficiently wide operating temperature range of the obtained material (see comparative example).

 The aim of the invention is to expand the operating temperature range and increase temperature sensitivity.

This is achieved by the fact that according to the proposed method for producing a thermosensitive material based on cholesteric liquid crystals, which consists in introducing a liquid crystal thermal indicator, including cholesteryl benzoate, into a hydrophobic polymer binder, applying the resulting emulsion to a substrate, drying, placing the material in a preheated chamber and then cooling to room temperature temperature, use a liquid crystal thermal indicator, optionally containing cholesteryl-n-octyloxyben enoate or cholesteryl-n-nonyloxybenzoate the following component ratio, wt. %: Cholesteryl benzoate 18-27
Cholesteryl-n-alkoxy benzoate 73-82, and drying is carried out by placing the substrate with the emulsion in a heat insulating pedestal having a room temperature, which was then placed in a preheated to 70-75 ^{° C} followed by gradual cell with increasing temperature up to ^about 145-150 C for 40-45 minutes

In carrying out the known method [2] in a hydrophobic polymer binder used polyvinyl acetate, polyvinyl chloride, as the cholesteric liquid crystals using various haraktericheskie nematikoholestericheskie liquid crystals or a mixture with an interval of existence of a cholesteric phase of (-) 10 to (+) 100 ° ^C. The substrate is mylar film 10 microns thick, whose thermal conductivity is close to the thermal conductivity of a thermosensitive material. In the process of drying and heating the thermo-indicator film, the thickness of the heat-sensitive layer varies from 240 to 30 microns. The resulting temperature-indicating film changes color once with a change in temperature (from red to blue).

In this invention, in contrast to the prototype, to create a temperature gradient over the cross section of the heat-sensitive layer during the film formation, it is placed on a massive heat-insulating stand made of asbestos with a thickness of 10 cm at room temperature, which is then placed in an oven previously heated to a temperature of 70-75 ^о С. The top layer of the heat-sensitive layer is at a temperature of 70-75 ^о С, and the bottom layer is at the temperature of the insulating stand, i.e. room temperature, since the thermal conductivity of asbestos is small α = 0.21 9 W / (m˙ K), and the thickness of the stand (100 mm) is significant compared to the thickness of the heat-sensitive layer (its thickness, as in the prototype) at the beginning of drying 240 microns, at the end of drying 30 microns).

 A temperature gradient arises in the heat-sensitive layer, which contributes to the formation of a disturbed spiral structure of cholesteric liquid crystals. With gradual warming up, this temperature gradient decreases. As a result of this mode of drying the material, capsules of different sizes are formed in the layers adjacent to the insulating support and in the upper layers with a free surface, and therefore, the spiral pitch of cholesteric liquid crystals in these layers will be different and will change differently with temperature.

Thus, the proposed method allows to obtain material with two intervals of selective reflection of light. In each interval, the color changes from red to blue in a narrow temperature range, i.e., the material has good temperature sensitivity (Δt / Δλ, ^o C / nm is the ratio of the temperature difference to the difference in the wavelengths of selective light reflection corresponding to these temperatures). And due to the existence of two intervals of selective reflection of light, the material has a wide operating temperature range (Δ T). The Δ Т value also includes the temperature range of the transparency zone, since often when studying unsteady thermal processes, the dynamics of the process is studied by the sequence of colors appearing on the surface: the farther one colorization interval is from the other, the fewer experiments will be required to study the unsteady process.

PRI me R 1 (control, prototype). 1 g of a mixture of cholesteric liquid crystals (cholesterylnanoate and cholesteryl valerate, wt.%: 50: 50) is dissolved in 10 g of a 10% (acetone and toluene 1: 1) solution of polyvinyl acetate, the resulting emulsion is applied by irrigation to a 10-micron thick dacron substrate of calculating 1.5 g of the emulsion per 100 cm ² surface, dried at room temperature for 5 minutes, then heated at 130 ^about C for 5 minutes, followed by cooling to room temperature. The resulting material has a selective reflection light interval: red (λ = 630 nm) at 40.4 ^{° C,} blue (λ = 430 nm) at 54.5 ° ^C. Temperatures illumination t _ave initial components: holesterilnonanoat - t _ave 91.5 ^{° C;} cholesteryl valerate - t _pr 100.5 ^about C.

PRI me R 2. 1 g of a mixture of cholesteric liquid crystals (83 wt.% Cholesteryl-n-nonyloxybenzoate and 17 wt.% Cholesteryl benzoate) is dissolved in 10 g of a 10% (acetone and toluene 1: 1) solution of polyvinyl acetate, the emulsion obtained is applied to the curtain mylar substrate 10 microns thick at the rate of 1.5 g emulsion per 100 cm ² surface was placed at room temperature for tablemat asbestos 100 mm thick, then the substrate and the cradle is placed into the heated emulsion to ⁷⁰ ° C chamber and then over 45 minutes gradually increase the temperature o T-70 to 145 ^C. The resulting material has a selective reflection range of light: red (λ = 630 nm) at 126.0 ^{° C,} blue (λ = 430 nm) at 129.0 ° ^C. The bleaching temperature t _ave starting components: cholesteryl-n-nonyloxybenzoate - t _pr 213 ^about C; cholesteryl - t _ave 179.0 ^C.

PRI me R 3. In the conditions of example 2 dissolve a mixture of cholesteric liquid crystals: 82 wt. % cholesteryl-n-nonyloxybenzoate and 18 wt. % cholesteryl benzoate. The material has two intervals of selective reflection of light: I interval - blue color (λ = 430 μm) at 80.0 ^о С, red color (λ = 630 nm) at 84.0 ^о С; II interval - red color at ¹²⁰ ° C, blue at 128.0 ° ^C.

PRI me R 4. In the conditions of example 2 dissolve a mixture of cholesteric liquid crystals: 80 wt. % cholesteryl-n-nonyloxybenzoate and 20 wt. % cholesteryl benzoate. The material has two slots selective reflection of light: I interval - blue (λ = 430 mm) at 75.0 ^{° C,} red (λ = 630 .mu.m) at 80.0 ^{° C;} II interval - red at 115.0 ^{° C,} blue at 125.0 ° ^C.

PRI me R 5. In the conditions of example 2 dissolve the mixture: 73 wt. % cholesterol-n-nonyloxybenzoate and 27 wt. % cholesteryl benzoate. The material has two slots selective reflection of light: I interval - blue (λ = 430 nm) at 68.0 ^C. red (λ = 630 nm) at 75.0 ^{° C;} II interval - red at 108.0 ^about C, blue at 120.0 ^about C.

PRI me R 6. In the conditions of example 2 dissolve the mixture: 72 wt. % cholesteryl-n-nonyloxybenzoate and 28 wt. % cholesteryl benzoate. The material has a spacing of selective reflection of light: red (λ = 630 nm) at 102.0 ^{° C,} blue (λ = 430 nm) at 116.0 ° ^C.

PRI me R 7. In the conditions of example 2 dissolve the mixture: 80 wt. % cholesteryl n-octyloxybenzoate and 20 wt. % Of cholesteryl, massive Tablemat emulsion on a substrate placed in a preheated to 75 ^{° C} and subsequent heating chamber to conduct a temperature of 150 ^{° C} for 40 min. The resulting material has two slots selective light scattering: I interval - blue (λ = 430 nm) at 99.0 ^{° C,} red (λ = 630 nm) at 102.5 ^{° C;} II interval - red at 108.5 ^{° C,} blue at ^about 114.0 C. To cholesteryl-n-oktiloksibenzoata t _ave = 220.5 ° ^C

 The spectral characteristics of the obtained thermosensitive materials were measured on an SF-18 spectrophotometer.

 Other parameters of the drying mode in the process of obtaining a thermosensitive material do not give a positive effect, since in other drying modes the material only changes its color from red to blue once with a change in temperature.

The composition and properties of the obtained heat-sensitive materials are given in the table. The table shows how the temperature sensitivity and the total operating temperature range of the materials obtained by the proposed method (examples 2-7) are compared with the material obtained by the prototype (example 1). The proposed method (examples 3-5, 7) allows to obtain a material with two intervals of selective light scattering with good temperature sensitivity (Δt / Δλ = 0.02-0.06) and a wide operating temperature range (Δ t = 3.0-12 , 0 ^o C, Δ T = 15-52 ^о С). Compared with the prototype (example 1), the temperature sensitivity increased, for example, 2.8 times for the first interval and 1.4 times for the second interval (example 4). The operating temperature range, within which you can estimate the temperature in the dynamics of an unsteady heat process (from 75.0 ^about C to 125.0 ^about C), is 50 ^about C (example 4), and the material obtained by the prototype (example 1), has Δ t = 14.1 ^about C.

The obtained heat-sensitive material has good temperature sensitivity over a wide operating temperature range due to the existence of two intervals of selective light reflection. Such materials find practical application in the study of unsteady processes in heat transfer problems. Their advantage over materials with one interval of selective reflection of light is as follows:
1) when the values of the measured temperatures are not known in advance, a heat-sensitive material with two intervals of selective reflection of light gives information twice as large as material with one interval of selective reflection of light, which means that the number of experiments decreases;
2) a change in the heating rate can be noticed by a change in the arrangement of two color intervals relative to each other (the transparency zone will decrease or increase).

 Thus, the proposed method allows to obtain a qualitatively new materials, with which it is possible to simplify and improve the quality of the experiments by expanding the overall temperature range without reducing the temperature sensitivity.

 (56) 1. USSR Copyright Certificate N 921312, cl. G 01 K 11/12, 1980.

 2. Copyright certificate of the USSR N 630999, cl. G 03 C 1/72, 1976.

Claims (1)

A METHOD FOR PRODUCING A THERMOSENSITIVE MATERIAL based on cholesteric liquid crystals, comprising introducing a liquid crystal thermal indicator including cholesteryl benzoate into a hydrophobic polymer binder, applying the resulting emulsion to a substrate, drying it by placing the material in a preheated chamber and then cooling to room temperature, followed by cooling to room temperature in order to expand the temperature sensitivity, a liquid crystal thermal indicator is used, additionally containing ho lesteryl - p - octyloxybenzoate or cholesteryl p-nonyloxybenzoate in the following ratio, wt. %:
Cholesteryl Benzoate 18 - 27
Cholesteryl p-alkoxybenzoate 73 - 82
and drying is carried out by placing a substrate with an emulsion on a heat-insulating stand having a room temperature, which is then placed in a chamber preheated to 70 - 75 ^o C, followed by a gradual increase in temperature to 145 - 150 ^o C for 40 - 45 minutes

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