Force-induced fluorescent polymer film and preparation and use condition determination method thereof

Abstract

The invention relates to a force-induced fluorescent polymer film and a preparation and use condition determination method thereof, and the method comprises the following steps: preparing mixed solutions with different luminous molecule contents by taking tetranitro-tetraphenylethylene as a solute and a polyurethane solution as a solvent; pouring the mixed solution into a round glass mold, and drying in a drying oven to prepare a polymer film; shooting microscopic images of the films with different luminous molecule contents by using an optical microscope; carrying out a friction experiment by adopting a pin disc type rotary friction device; exciting a friction area of the thin film by using an ultraviolet light source, and capturing a fluorescence image through a CCD camera; and positioning a light-emitting area based on image cutting and boundary extraction algorithms, calculating an average gray value to quantify the light-emitting intensity, and drawing a light-emitting intensity change curve. The polymer film provided by the invention has the characteristic of continuous luminescence, and has more excellent mechanical stimulation luminescence response performance; when the applied acting force is 3N, the frictional contact reaches the best, and the frictional luminous intensity reaches the maximum value at the moment, so that tiny contact force can be detected.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and in particular relates to a mechanoluminescent polymer film and a method for preparing and determining a working condition of the film. Background Art

[0002] As a new type of intelligent response material, mechanoluminescent materials can produce fluorescent responses under the action of external mechanical forces (including stretching, compression, friction, etc.). In recent years, they have shown important application value in stress sensing, structural health monitoring, anti-counterfeiting and encryption. Especially in scenarios such as flexible electronic skin tactile perception, biomechanical monitoring and dynamic handwriting recognition, traditional piezoresistive sensors are limited by defects such as wiring complexity, electromagnetic interference sensitivity and signal hysteresis, making it difficult to achieve non-contact, high-spatial-resolution visualization of global stress distribution. In contrast, optical detection technology based on mechanoluminescent materials has become a potential alternative solution due to its advantages such as no need for external power supply, high response sensitivity and strong spatial resolution.

[0003] At present, although typical mechanoluminescent materials represented by transition metal-doped sulfides (such as ZnS:Mn) and metal-organic complexes have high initial luminescence intensity, they generally have the problem of rapid attenuation of the luminescence signal, resulting in insufficient signal stability under long-term continuous monitoring or complex working conditions, making it difficult to achieve reliable quantitative analysis. Tetranitro-tetraphenylethylene (TPE-4N) is an organic mechanoluminescent material. After being dissolved in chloroform or acetone, it can form a thin film when applied to the surface of the structural device. When stimulated by external mechanical force, it emits continuous visible green fluorescence under ultraviolet excitation. However, this thin film coating method still has limitations. On the one hand, organic solvents must be used to dissolve the TPE-4N molecules, which will also dissolve the anti-rust coating on the surface of the structural device. On the other hand, the high surface roughness will also reduce the film-forming ability, thereby affecting the accurate detection of contact force.

[0004] Current research still faces two core challenges: first, the dispersion uniformity of luminescent molecules in the organic matrix and their aggregation morphology will also significantly affect the luminescence efficiency and luminescence intensity of the material, but there is currently a lack of research on the correlation between the luminescent molecule content of the material and the mechanical response characteristics; second, in the scenario of small contact force detection, the detection sensitivity and linear response range of existing luminescent materials are difficult to match the actual technical indicator requirements. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology, provide a mechanoluminescent polymer film and its preparation method, and determine its operating conditions. The present invention combines the advantages of controllability of material preparation process and detection sensitivity, and provides a new solution for the field of mechanical sensing.

[0006] The present invention solves the technical problem by the following technical solutions:

[0007] A method for preparing a mechanoluminescent polymer film, comprising the following steps:

[0008] S1. Preparation of mechanoluminescent polymer solution: Tetranitro-tetraphenylethylene (TPE-4N) powder is used as a solute and polyurethane solution is used as a solvent to prepare mixed solutions with different TPE-4N contents;

[0009] S2. Preparation of induced fluorescent polymer film: The mixed solution is ultrasonically oscillated for 1 to 2 minutes to remove bubbles and then poured into a circular mold to allow the mixed solution to soak the bottom of the circular mold. The circular mold is placed in an oven and heated until the mixed solution is completely evaporated and a uniform and smooth film is formed on the bottom of the circular mold. The film is peeled off the circular mold to obtain a induced fluorescent polymer film.

[0010] Moreover, the content of tetranitro-tetraphenylethylene (TPE-4N) in the mixed solution of S1 is 5% to 20%.

[0011] Moreover, the circular mold of S2 is a circular glass culture dish of different sizes.

[0012] Moreover, the heating temperature of S2 is 80±5° C., and the heating time is 4 to 5 hours.

[0013] A mechanoluminescent polymer film is prepared by adopting the method.

[0014] A method for determining the operating conditions of a mechanoluminescent polymer film, using a mechanoluminescent polymer film prepared by the method, the method comprising the following steps:

[0015] S1. Microstructure characterization: Place the mechanoluminescent polymer films with different luminescent molecule contents under an optical microscope to photograph the dispersion uniformity and aggregation morphology of the luminescent molecules;

[0016] S2. Friction experiment: A friction experiment was conducted on a mechanoluminescent polymer film using a pin-on-disk rotating friction test apparatus. The friction area was excited with an ultraviolet light source, and the fluorescence response image was captured.

[0017] S3. Fluorescence image processing and analysis: The fluorescence response image is cropped, the luminescent area is extracted, the average grayscale value is calculated, and pseudo-color mapping is performed. The triboluminescence intensity change curve is drawn to determine its optimal application range.

[0018] Moreover, the force range of the friction experiment is 1 to 5N, the friction linear speed is 1mm / s, and the friction time is 1min; the wavelength of the ultraviolet light source is 365nm, the power is 10W, the excitation time is 5 to 10 seconds, and the fluorescence response image is captured using a CCD camera equipped with a filter, and the exposure time of the CCD camera is 0.2 seconds.

[0019] Moreover, the S3 is specifically:

[0020] (1) The fluorescence response image was cropped into a square image with the luminescent area centered and the luminescent area was marked with a red circle;

[0021] (2) The average grayscale value in the marked area is calculated to characterize the luminescence intensity, and the triboluminescence intensity change curve is drawn according to the experimental parameters. At the same time, the fluorescence image is converted into a grayscale pseudo-color image for visual output.

[0022] The advantages and beneficial effects of the present invention are:

[0023] 1. The present invention is based on the light response characteristics of tetranitro-tetraphenylethylene materials to prepare mechanoluminescent polymer films. After being stimulated by external mechanical force and then excited by ultraviolet light, its fluorescence signal can be sustained for a long time, breaking through the technical bottleneck of short luminescence time of traditional fluorescent materials. It is suitable for scenarios that require long-term dynamic tracking or continuous detection.

[0024] 2. This invention systematically controls the luminescent molecule content in the film and, combined with microstructural characterization, clearly demonstrates its influence on luminescence intensity. Specifically, when the luminescent molecule content is 10%, it exists as evenly distributed fine particles, while at 20%, it forms large-area aggregates. The resulting polymer film exhibits superior mechanically stimulated luminescence performance.

[0025] 3. The present invention reveals the relationship between the applied force and the luminous intensity of the film, and determines that the force threshold for reaching the maximum luminous intensity of the film is 3N, which can be used to detect small contact forces. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The preparation route of the mechanoluminescent polymer film of the present invention is as follows;

[0027] Figure 2 Schematic diagram of the friction experiment of the present invention;

[0028] Figure 3 is a flow chart of fluorescence image processing of the present invention;

[0029] Figure 4 This is a graph showing the change in triboluminescence intensity of films with different luminescent molecule contents under a force of 3N according to the present invention;

[0030] Figure 5 This is a curve diagram of the triboluminescence intensity change of the film with 10% luminescent molecule content under different forces of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0032] A method for preparing a mechanoluminescent polymer film and determining its use conditions is innovative in that it comprises the following steps:

[0033] (1) Preparation routes of polymer films such as Figure 1 As shown, the mechanochromic luminescent material tetranitro-tetraphenylethylene (TPE-4N) was selected as the solute, and polyurethane was selected as the solvent. The fluorescent material was prepared according to the method described in the Chinese invention patent "Preparation and Application of Polynitro-Substituted Tetraphenylethylene Compounds" (Invention Patent Application No.: CN201310057959, Publication No.: CN104003886A). In this example, a total of four films with luminescent molecule contents (5%, 10%, 15%, and 20%) were prepared. Since the preparation methods of films with different contents are the same, the preparation of a polymer film with a 15% TPE-4N content is taken as an example. First, TPE-4N powder and polyurethane solution are poured into a small beaker at a ratio of 1:3 and stirred evenly with a glass rod.

[0034] (2) Pour the mixed solution in the small beaker into a round glass Petri dish, allowing the solution to soak the bottom of the mold. Place the mold in an ultrasonic oscillator and vibrate for 1-2 minutes to ensure that the solution is evenly mixed and to remove any bubbles in the solution. Place the mold in an oven (in this example, 80°C is selected for heating for 4-5 hours until the solution is completely evaporated). After ensuring that a uniform, smooth film has formed on the bottom of the mold, peel the film off the Petri dish and set aside for testing.

[0035] (3) Place polymer films with different luminescent molecule contents under an optical microscope and photograph the dispersion uniformity and aggregation morphology of the luminescent molecules in the films one by one.

[0036] (4) Schematic diagram of pin-disc rotating friction experiment Figure 2 As shown, before the experiment, the film was mounted on a rotating platform. Multiple friction tests were conducted on films with varying luminescent molecule contents by varying the applied force (1 to 5 N). All experiments were conducted at a linear speed of 1 mm / s and for a duration of 1 minute. After the experiment, the rubbed film was excited for 5 to 10 seconds using a UV light source with an emission wavelength of 365 nm and a power of 10 W. Fluorescence images were captured using a CCD camera equipped with a filter, with an exposure time of 0.2 seconds.

[0037] (5) Fluorescence image processing.

[0038] The fluorescence image processing process is as follows Figure 4 As shown in the figure, the original image captured by the CCD camera was first cropped into a square image centered on the luminescent area using ImageJ, resulting in a 300×300 operation area. Next, a boundary extraction algorithm was used in Matlab to extract the bright annular area in the image by setting an appropriate threshold and marking its boundary with a red ring. The average grayscale value was then calculated to represent the fluorescence response intensity. All data were processed using Origin software, and triboluminescence intensity curves were plotted based on different parameter settings. An example is shown in the figure below. Figure 4 and Figure 5 Finally, Matlab was used to convert the cropped fluorescence image into a grayscale image and mapped into a pseudo-color image output in Jet mode, where the color from blue to red corresponds to the luminescence intensity from weak to strong.

[0039] (6) Determine the operating conditions of the polymer film.

[0040] like Figure 5 As shown in Figure 2, with the increase of the content of luminescent molecules, the triboluminescence intensity shows a complex non-monotonic change trend. When the content is 10%, the luminescent molecules exist in the form of uniformly distributed fine particles or form large-area agglomerates when the content is 20%. The polymer film has better mechanical stimulation luminescence response performance. In addition, as Figure 4 As shown in the figure, as the applied force increases, the triboluminescence intensity of the film shows a characteristic pattern of first increasing and then decreasing. When the applied force is 3N, the frictional contact reaches its optimal state, and the triboluminescence intensity reaches its maximum value, which can be used to detect small contact forces.

[0041] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for preparing a mechanoluminescent polymer film, characterized in that: The steps of the method are: S1. Preparation of mechanoluminescent polymer solution: Tetranitro-tetraphenylethylene (TPE-4N) powder is used as a solute and polyurethane solution is used as a solvent to prepare mixed solutions with different TPE-4N contents; S2. Preparation of induced fluorescent polymer film: The mixed solution is ultrasonically oscillated for 1 to 2 minutes to remove bubbles and then poured into a circular mold to allow the mixed solution to soak the bottom of the circular mold. The circular mold is placed in an oven and heated until the mixed solution is completely evaporated and a uniform and smooth film is formed on the bottom of the circular mold. The film is peeled off the circular mold to obtain a induced fluorescent polymer film.

2. The method for preparing a mechanoluminescent polymer film according to claim 1, wherein: The content of tetranitro-tetraphenylethylene (TPE-4N) in the mixed solution of S1 is 5% to 20%.

3. The method for preparing a mechanoluminescent polymer film according to claim 1, wherein: The circular molds of S2 are circular glass culture dishes of different sizes.

4. The method for preparing a mechanoluminescent polymer film according to claim 1, wherein: The heating temperature of S2 is 80±5° C., and the heating time is 4 to 5 hours.

5. A mechanoluminescent polymer film, characterized in that: The method is prepared by the method according to any one of claims 1 to 4.

6. A method for determining the operating conditions of a mechanoluminescent polymer film, characterized by: A mechanoluminescent polymer film prepared by the method according to any one of claims 1 to 4, wherein the method comprises the following steps: S1. Microstructure characterization: Place the mechanoluminescent polymer films with different luminescent molecule contents under an optical microscope to photograph the dispersion uniformity and aggregation morphology of the luminescent molecules; S2. Friction experiment: A friction experiment was conducted on a mechanoluminescent polymer film using a pin-on-disk rotating friction test apparatus. The friction area was excited with an ultraviolet light source, and the fluorescence response image was captured. S3. Fluorescence image processing and analysis: The fluorescence response image is cropped, the luminescent area is extracted, the average grayscale value is calculated, and pseudo-color mapping is performed. The triboluminescence intensity change curve is drawn to determine its optimal application range.

7. The method for determining the operating condition of a mechanoluminescent polymer film according to claim 6, wherein: The force range of the friction experiment is 1 to 5 N, the friction linear speed is 1 mm / s, and the friction time is 1 min; the wavelength of the ultraviolet light source is 365 nm, the power is 10 W, the excitation time is 5 to 10 seconds, and the fluorescence response image is captured using a CCD camera equipped with a filter, and the exposure time of the CCD camera is 0.2 seconds.

8. The method for determining the operating condition of a mechanoluminescent polymer film according to claim 6, wherein: The S3 is specifically: (1) The fluorescence response image was cropped into a square image with the luminescent area centered and the luminescent area was marked with a red circle; (2) The average grayscale value in the marked area is calculated to characterize the luminescence intensity, and the triboluminescence intensity change curve is drawn according to the experimental parameters. At the same time, the fluorescence image is converted into a grayscale pseudo-color image for visual output.

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