A fluorescent flexible tension sensor, its preparation method and application

Abstract

The present invention provides a fluorescent flexible tensile sensor, a preparation method, and applications thereof. The method comprises: dissolving 1,4-bis-[4-(3-acryloxypropoxy)benzoyloxy]-2-methylbenzene, 2,2′-(1,2-ethylenedioxy)bis-ethanethiol, and pentaerythritol mercaptopropionate in a solvent to obtain a RM mixture; adding an aggregation-induced luminescence material and a catalyst to the RM mixture to carry out a catalytic polymerization reaction to obtain a reaction mixture; curing the reaction mixture in a mold, and drying and removing the solvent to obtain a fluorescent flexible tensile sensor. The present invention combines the aggregation-induced luminescence material with a liquid crystal elastomer through a cross-linking reaction to prepare a wireless force sensor that is flexible, highly stretchable, and wirelessly resistant to electromagnetic interference, and is low in cost and lightweight.

Description

Technical Field

[0001] The present invention relates to the technical field of smart materials, and in particular to a fluorescent flexible tension sensor, a preparation method thereof, and applications thereof. Background Art

[0002] Flexible strain sensors are widely used in human activity tracking, sports rehabilitation, personalized health monitoring, and human-computer interaction. With the development of interactive electronics, several flexible force sensing methods have been proposed, primarily utilizing materials such as polyimide (PI), polyurethane (PU), polyethylene terephthalate (PET), and polydimethylsiloxane (PDMS) and organic transistors to construct flexible sensing elements. The high flexibility of these materials makes the sensors resistant to damage caused by physical shape changes. However, due to their circuit-based electronic design, some flexible sensors are susceptible to electromagnetic (EM) and radio frequency (RF) interference. To overcome EM and RF interference, force sensors have been further improved using soft materials, primarily PET and PDMS. However, these sensors are either wired, making them difficult to operate remotely, or require bulky modules (batteries or wireless communication modules) for remote operation, hindering their portability and widespread application in wireless communications. Furthermore, these flexible sensors lack both good stretchability and resilience.

[0003] Liquid crystal elastomers (LCEs) are promising candidates for wireless, flexible force sensors with high elasticity and resilience. As a popular smart material, LCEs have become the preferred choice for generating bio-inspired electric fields. However, their application in optical strain sensors is relatively uncommon. Due to their excellent hybrid physical properties, including high strain-optical coefficients and high compliance, these materials have the potential to be studied and tested in a wide range of systems, including biological tissues and biomedical devices. Existing research indicates that LCEs exhibit typical isotropy when mechanically strained, with high strain-optical coefficients and high compliance. However, this approach can only distinguish force magnitudes through the different colors of the LCEs, making it insensitive. To further their application, existing technologies combine certain functional materials with LCEs to form LCE-based composites. For example, some fluorescent materials are physically dispersed within the LCEs, but this physical dispersion does not guarantee uniform distribution of the fluorescent material within the elastomer. Summary of the Invention

[0004] The problem solved by the present invention is that existing flexible tensile sensors based on PET and PDMS are usually wired or difficult to operate remotely, and their stretchability and resilience need to be improved. Liquid crystal elastomers with high elasticity and high resilience can be combined with functional materials to form composite materials, but there are problems such as uneven mixing and dispersion and low sensitivity.

[0005] In order to solve at least one aspect of the above problems, the present invention provides a method for preparing a fluorescent flexible tension sensor, comprising:

[0006] Dissolving 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, 2,2′-(1,2-ethylenedioxy)bis(ethanediol) and pentaerythritol-mercaptopropionate in a solvent to obtain an RM mixture;

[0007] adding an aggregation-induced emission material and a catalyst to the RM mixture to carry out a catalytic polymerization reaction to obtain a reaction mixture;

[0008] The reaction mixture is placed in a mold for solidification, and dried to remove the solvent, thereby obtaining a fluorescent flexible tensile sensor.

[0009] Preferably, the molar ratios of the 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, the 2,2′-(1,2-ethylenedioxy)bis(ethanediol) and the pentaerythritol mercaptopropionate are 50-55%, 35-40% and 5-15%, respectively.

[0010] Preferably, the aggregation-induced emission material includes tetraphenylethylene-polypropylene.

[0011] Preferably, the mass ratio of the aggregation-induced emission material to the 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene is less than 1%.

[0012] Preferably, the catalyst comprises dipropylamine.

[0013] Preferably, before adding the catalyst, the method further comprises: dissolving the dipropylamine in N,N-dimethylformamide to form a DPA-DMF solution, wherein the volume ratio of the dipropylamine to the N-dimethylformamide is 1.5%-2%.

[0014] Preferably, the reaction mixture is placed in a mold and solidified at room temperature for 24 hours to 30 hours.

[0015] Preferably, the drying temperature is 85°C-90°C.

[0016] The advantages of the present invention over the prior art are:

[0017] The present invention prepares a liquid crystal elastomer through a cross-linking reaction, and in the process of generating the liquid crystal elastomer through the reaction, an aggregation-induced luminescence material is incorporated into the liquid crystal elastomer. The aggregation-induced luminescence material molecules can be dispersed and arranged along with the liquid crystal molecules, thereby ensuring uniform mixing of the two. Moreover, since the two are combined through a cross-linking reaction, the chemical reaction dispersion uniformity is higher than that of physical mixing dispersion, thereby ultimately preparing a liquid crystal elastomer with fluorescent properties. When the aggregation-induced luminescence material aggregates, it can emit fluorescence under ultraviolet excitation. Moreover, when the polymer elastomer contracts and stretches, the aggregation-induced luminescence material exhibits different fluorescence intensities at different aggregation levels. Therefore, the magnitude of the force applied to the material can be judged according to the fluorescence intensity, and the detection sensitivity is high.

[0018] In addition, compared with traditional flexible mechanical sensors that require wired connections, or need to be loaded with bulky batteries or wireless communication modules for remote operation, the fluorescent flexible tensile sensor made by the present invention only needs to be excited under ultraviolet irradiation, and the fluorescence intensity can be remotely captured by a camera. The fluorescence intensity can be analyzed in a non-contact manner to obtain the magnitude of the force, thereby realizing wireless force measurement.

[0019] The present invention also provides a fluorescent flexible tensile sensor, which is manufactured using the above-mentioned method for preparing the fluorescent flexible tensile sensor.

[0020] The advantages of the fluorescent flexible tensile sensor prepared by the present invention compared with the existing technology are the same as the advantages of the preparation method of the fluorescent flexible tensile sensor compared with the existing technology, which will not be repeated here.

[0021] The present invention also provides an application of a fluorescent flexible tensile sensor in mechanical detection. Based on the fluorescent flexible tensile sensor described above, the application includes mechanical detection in dark, outdoor environments, non-contact remote mechanical detection, and portable mechanical detection.

[0022] The fluorescent flexible tensile sensor of the present invention can be applied to mechanical detection in dark environments, mechanical detection scenarios where contact measurement is difficult in the field, or portable detection that does not require quantitative measurement but only qualitative comparison of the degree of mechanical change, and other non-contact remote mechanical detection that can be observed with the naked eye without the need for wired support. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Flowchart of a method for preparing a fluorescent flexible tension sensor according to an embodiment of the present invention;

[0024] Figure 2 : is the relationship between the fluorescence intensity and the concentration of the aggregation-induced emission material in the embodiment of the present invention;

[0025] Figure 3 Schematic diagram of the preparation process of the fluorescent flexible tension sensor according to an embodiment of the present invention;

[0026] Figure 4 The relationship between stress, strain and force of the fluorescent flexible tensile sensor prepared in Example 1 of the present invention;

[0027] Figure 5 The relationship between strain, fluorescence intensity and force of the fluorescent flexible tensile sensor prepared in Example 1 of the present invention;

[0028] Figure 6 : This is the fitting relationship between the applied force and the change in fluorescence intensity of the fluorescent flexible tension sensor prepared in Example 1 of the present invention;

[0029] Figure 7 Images taken during mechanical testing of the fluorescent flexible tensile sensor prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0031] See also Figure 1 As shown, a method for preparing a fluorescent flexible tension sensor according to an embodiment of the present invention includes:

[0032] 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257), 2,2′-(1,2-ethylenedioxy)bis(ethyl mercaptan) (EDDET), and pentaerythritol mercaptopropionate (PETMP) were dissolved in a solvent to obtain an RM mixture;

[0033] adding an aggregation-induced emission (AIE) material and a catalyst to the RM mixture to perform a catalytic polymerization reaction to obtain a reaction mixture;

[0034] The reaction mixture is placed in a mold for solidification, and dried to remove the solvent, thereby obtaining a fluorescent flexible tensile sensor.

[0035] Aggregation-induced emission (AIE) is a phenomenon completely opposite to the fluorescence quenching effect (ACQ). Specifically, organic active substances exhibit very weak fluorescence in single-molecule form or dilute solutions, but emit strong fluorescence when highly aggregated. In this example, a liquid crystal elastomer (LCE) was prepared through a crosslinking reaction and combined with an ACE material. RM257 served as the backbone of the polymer network, EDDET served as a chain extender, and PETMP served as a crosslinker. The AIE material molecules were dispersed and aligned with the LC molecules, ensuring uniform mixing of the two. Furthermore, due to the restriction of intramolecular rotation, the ACE material, when added to the LC system, could emit fluorescence upon UV excitation when aggregated. Furthermore, the ACE material exhibited varying fluorescence intensities at varying degrees of aggregation as the polymer elastomer contracted and stretched. Therefore, the magnitude of the force acting on the material could be determined based on the fluorescence intensity.

[0036] In some embodiments, the RM mixture comprises 50-55% by mole of 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, 35-40% by mole of 2,2′-(1,2-ethylenedioxy)bis(ethylenethiol), and 5-15% by mole of pentaerythritol mercaptopropionate. This ratio ensures a consistent number of double bonds for molecular cross-linking, allowing for complete polymerization to form a polymer network. In a preferred embodiment, the molar ratio of 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, 2,2′-(1,2-ethylenedioxy)bis(ethylenethiol), and pentaerythritol mercaptopropionate is 2.1:1.52:0.24, representing molar proportions of 54.4%, 39.4%, and 6.2%, respectively.

[0037] The aggregation-induced luminescence material is tetraphenylethylene-polypropylene (TPE-PPE). When the content of the aggregation-induced luminescence material is too high, saturation will occur, causing the aggregation-induced luminescence material to precipitate. Therefore, in this embodiment, the mass ratio of TPE-PPE to the RM257 is less than 1%. Here, this mass ratio is referred to as the concentration of TPE-PPE. In addition, since the lower the content of the aggregation-induced luminescence material, the lower the intensity of the fluorescence generated by subsequent laser excitation, therefore, under the premise of ensuring that the concentration of the aggregation-induced luminescence material is less than 1%, the content of the aggregation-induced luminescence material should be increased as much as possible to facilitate the capture of fluorescence and the comparison of the change in fluorescence intensity before and after stretching. In one embodiment, a mixture with TPE-PPE concentrations of 0.1wt%, 0.05wt%, 0.04wt%, 0.03wt%, 0.02wt%, 0.01wt% and 0.005wt% is selected, and the fluorescence intensity changes with the concentration of TPE-PPE as shown in the figure. Figure 2 As shown, Figure 2The horizontal axis concentration represents the concentration of TPE-PPE, and the vertical axis fluorescence intensity represents the fluorescence intensity. Figure 2 It can be seen that as the concentration of TPE-PPE increases, the fluorescence intensity of the mixture under ultraviolet excitation becomes stronger. Among them, the change in fluorescence intensity between 0.01wt% and 0.005wt% is too small to be distinguished by the naked eye. Therefore, considering the material cost and sufficient before-after fluorescence intensity comparison, the preferred TPE-PPE concentration is 0.05wt%. In addition, since the RM257 main chain, chain extender EDDET, and cross-linker PETMP are basically powdered, a solvent needs to be added for dissolution. Therefore, the RM mixture should strictly be a mixed liquid. In this embodiment, the solvent is preferably an organic solvent, such as N,N-dimethylformamide (DMF). The organic solvent is mainly used to dissolve the powdered raw materials. Therefore, the content of the organic solvent should not be too little, otherwise the raw materials cannot be completely dissolved. Of course, the content of the organic solvent should not be too much, otherwise it will be difficult to evaporate and remove the solvent later, resulting in waste and increased cost.

[0038] The catalyst used in the cross-linking reaction is preferably dipropylamine (DPA), which is diluted with a solvent before use. Specifically, dipropylamine (DPA) is dissolved in N,N-dimethylformamide to form a DPA-DMF solution. The catalyst is diluted with a solvent before use to prevent the catalytic reaction from being too intense and causing heterogeneous polymerization, which would result in the reaction mixture polymerizing prematurely before being poured into the mold for finalization. The dosage of the catalyst in this embodiment depends on the intensity of the reaction system. The amount of catalyst content affects the reaction speed. In a preferred embodiment, the concentration of the dipropylamine is 1.5%-2%, that is, the volume ratio (v / v%) of the dipropylamine to the N-dimethylformamide is 1.5%-2%.

[0039] In some embodiments, the reaction mixture is poured into a mold to remove air bubbles and achieve the desired shape for the liquid crystal elastomer. Room temperature curing allows for pre-evaporation of the solvent, resulting in a preliminary solidification of the liquid crystal elastomer. Oven drying allows for complete evaporation of the solvent in the system and promotes cross-linking and polymerization of the liquid crystal elastomer. After cooling to room temperature, the finished product is obtained, the specifications of which are related to the specifications of the mold. The reaction mixture is cured in the mold at room temperature for 24-30 hours, and the drying temperature is 85-90°C.

[0040] In a specific embodiment, Figure 3As shown, RM257 is first dissolved in N,N-dimethylformamide (DMF) and heated to extract water. After cooling to room temperature, the chain extender 2,2′-(1,2-ethylenedioxy)bis(ethylenethiol) (EDDET) and the crosslinker pentaerythritol mercaptopropionate (PETMP) are added.

[0041] The catalyst DPA is dissolved in DMF to form a DPA-DMF solution with a concentration of 1.5%-2%.

[0042] After the RM mixture is completely dissolved, the aggregation-induced emission material (AIE) TPE-PPE is first added to the RM mixture, and then the prepared catalyst DPA-DMF solution is added to catalyze polymerization.

[0043] The reaction mixture is then processed using a mixer to ensure uniform mixing. It is then poured into a rectangular polytetrafluoroethylene mold and allowed to cure for a specified period of time to remove air bubbles. The mixture is then allowed to solidify in the mold at room temperature for a specified period of time. Finally, after evaporating the solvent in an oven and cooling to room temperature, a loosely cross-linked liquid crystal elastomer, or fluorescent flexible tensile sensor, is obtained.

[0044] The fluorescent flexible tensile sensor prepared in this embodiment has a large tensile strength and can be stretched to about 4 times its original length. In the original unstretched state, the width and thickness of the fluorescent flexible tensile sensor are equal to the size of the mold. When exposed to ultraviolet light (wavelength of 365nm, light intensity of 0.84mW / cm 2 ), the fluorescent liquid crystal elastomer (LCE) will exhibit green fluorescence. The excitation intensity of ultraviolet light can be adjusted according to actual needs, and accordingly, the correspondence between fluorescence intensity and force will also be adjusted accordingly. The mechanism of the fluorescent flexible tensile sensor prepared in this embodiment is that the change in fluorescence intensity is caused by the change in the degree of polymerization due to stretching. When an external force acts on the fluorescent liquid crystal elastomer, the fluorescent LCE will be stretched, resulting in a decrease in the degree of aggregation of TPE-PPE, so that the fluorescence intensity of the device is weakened under greater force. The digital single-lens reflex camera can record the change process of the LCE fluorescence intensity into a video, and extract the fluorescence intensity of each stage through a coding program. After reading the fluorescence intensity of each stage, the "strain-force" relationship can be compared with the "strain-fluorescence" relationship to obtain the "force-fluorescence" relationship, and the force applied can be subsequently inferred based on the fluorescence intensity.

[0045] In summary, this embodiment combines aggregation-induced emission materials and liquid crystal elastomers through a cross-linking reaction to prepare a wireless force sensor that can be observed with the naked eye, is flexible, highly stretchable, and wirelessly resistant to electromagnetic interference, and has low cost and light weight.

[0046] An embodiment of the present invention also provides an application of a fluorescent flexible tension sensor in mechanical detection, including mechanical detection in dark, outdoor environments, non-contact remote mechanical detection, and portable mechanical detection.

[0047] Example 1

[0048] 1236.08 mg (2.1 mmol) of RM257 was dissolved in 2 ml of DFM and heated to 85°C for water extraction. After cooling to room temperature, 277.10 mg (1.52 mmol) of EDDET and 117.28 mg (0.24 mmol) of PETMP were added. 5 μl of DPA was dissolved in 250 μl of DFM (i.e., a DPA volume concentration of 2%) and added to the reaction system. 0.6 mg of TPE-PPE (TPE-PPE concentration of 0.05 wt%) was then added to the reaction system to obtain a reaction mixture. The reaction mixture was mixed using a mixer and poured into a rectangular mold (10 mm × 3 mm × 1.33 mm). The mixture was cured for 5 minutes to remove bubbles, then cured at room temperature for 24 hours. After drying in an 85°C oven, a finished product with specifications of 10 mm in length, 3 mm in width, and 1.33 mm in thickness was obtained.

[0049] The fluorescent flexible tensile sensor prepared in this embodiment was tested by applying an external force to the sensor and using a light source with a wavelength of 365 nm and a light intensity of 0.84 Mw / cm 2 The sensor is illuminated by ultraviolet light, and a digital single-lens reflex camera is used to record the change process of the sensor's fluorescence intensity into a video. The fluorescence intensity of each stage is extracted through a coding program, and the relationship between force and fluorescence intensity is obtained, such as Figure 4-Figure 6 shown. Figure 4 In the graph, the horizontal axis is strain, the primary vertical axis is stress, and the secondary vertical axis is force, representing the relationship between stress, strain, and force. The dark curve represents the "strain-stress" relationship (the vertical axis corresponds to the left axis), and the light curve represents the "strain-force" relationship (the vertical axis corresponds to the right axis). Figure 5 In this figure, the horizontal axis is strain, the primary vertical axis is force, and the secondary vertical axis is fluorescence intensity. This graph shows the relationship between strain, fluorescence intensity, and force. Curves with data markers represent the strain-force relationship (vertical axis corresponds to the left axis), while curves without data markers represent the strain-fluorescence relationship (vertical axis corresponds to the right axis). Figure 6 It represents the fitting relationship between the force and the change of fluorescence intensity. Therefore, the magnitude of the force can be reflected according to the fluorescence intensity.

[0050] like Figure 7 As shown in FIG, a physical picture of mechanical testing of the fluorescent flexible tensile sensor prepared in this embodiment is shown, wherein: Figure 7 (d) Figure 7 (e) Figure 7 (f) are the weights of the billiard ball, toy, and orange, respectively. It can be seen that the weights of the billiard ball, toy, and orange increase in sequence. Figure 7 (a) Figure 7 (b) Figure 7 (c) Images taken with a digital SLR camera of the fluorescent flexible tensile sensor lifting a billiard ball, a toy, and an orange. It can be seen that under the action of heavy objects such as the billiard ball, the toy, and the orange, the fluorescent flexible tensile sensor is stretched and deformed, and the fluorescence emitted by the sensor gradually weakens and darkens when irradiated with ultraviolet light. This is mainly because the billiard ball is the lightest, so the pulling force of the sensor to lift the billiard ball is relatively small. Figure 6 The relationship between force and fluorescence intensity shows that the smaller the force, the higher the fluorescence intensity. Therefore, the fluorescence generated by the sensor when lifting the billiard ball is the strongest and brightest, that is, the fluorescence intensity is the highest. However, due to the heavy weight of the orange, the pulling force required is greater, so the fluorescence intensity generated by the sensor is smaller, and the fluorescence emitted is darker and weaker. Figure 7 (a) Figure 7 (b) Figure 7 The changes in the fluorescence intensity values ​​in (c) compared with the original fluorescence intensity values ​​are 18.686 (au), 30.047 (au), and 37.645 (au), respectively.

[0051] Example 2

[0052] Dissolve 618.05 mg of RM257 in 1.5 ml of DFM and heat to 85°C for water extraction. After cooling to room temperature, add 138.55 mg of EDDET and 58.64 mg of PETMP. Dissolve 3 μl of DPA in 200 μl of DFM (volume concentration of 1.5%) and add it to the reaction system. Then add 0.6 mg of TPE-PPE (TPE-PPE concentration of 0.1 wt%) to the reaction system. Pour the reaction mixture into a mold (15 mm × 3 mm × 1.32 mm), cure to remove bubbles, and cure at room temperature for 30 hours. After drying in a 90°C oven, a finished product with a length of 15 mm, a width of 3 mm, and a thickness of 1.32 mm is obtained.

[0053] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for preparing a fluorescent flexible tension sensor, characterized in that: include: Dissolving 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, 2,2′-(1,2-ethylenedioxy)bis(ethanediol) and pentaerythritol-mercaptopropionate in a solvent to obtain an RM mixture; Adding an aggregation-induced emission material to the RM mixture and a catalyst to perform a catalytic polymerization reaction to obtain a reaction mixture, wherein the aggregation-induced emission material comprises tetraphenylethylene-polypropylene, and the mass ratio of the tetraphenylethylene-polypropylene to the 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene is less than 1%; The reaction mixture is placed in a mold for solidification, and dried to remove the solvent, thereby obtaining a fluorescent flexible tensile sensor.

2. The method for preparing the fluorescent flexible tension sensor according to claim 1, characterized in that: The molar ratios of the 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene, the 2,2′-(1,2-ethylenedioxy)bis(ethanediol) and the pentaerythritol mercaptopropionate are 50-55%, 35-40% and 5-15% respectively.

3. The method for preparing the fluorescent flexible tension sensor according to claim 1, characterized in that: The catalyst includes dipropylamine.

4. The method for preparing the fluorescent flexible tension sensor according to claim 3, characterized in that: Before adding the catalyst, the method further comprises: dissolving the dipropylamine in N,N-dimethylformamide to form a DPA-DMF solution, wherein the volume ratio of the dipropylamine to the N-dimethylformamide is 1.5%-2%.

5. The method for preparing the fluorescent flexible tension sensor according to claim 1, characterized in that: The reaction mixture is placed in a mold and solidified at room temperature for 24-30 hours.

6. The method for preparing a fluorescent flexible tension sensor according to claim 1, characterized in that: The drying temperature is 85℃-90℃.

7. A fluorescent flexible tension sensor, characterized in that: The fluorescent flexible tension sensor is prepared by the preparation method according to any one of claims 1 to 6.

8. An application of a fluorescent flexible tensile sensor in mechanical detection, characterized in that: Based on the fluorescent flexible tensile sensor as claimed in claim 7, the applications include mechanical detection in dark, outdoor environments, non-contact remote mechanical detection, and portable mechanical detection.

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