CN107934908B

CN107934908B - Stress sensor and preparation method thereof

Info

Publication number: CN107934908B
Application number: CN201710337940.3A
Authority: CN
Inventors: 张敏; 张硕; 王焕
Original assignee: Peking University Shenzhen Graduate School
Current assignee: Peking University Shenzhen Graduate School
Priority date: 2017-05-15
Filing date: 2017-05-15
Publication date: 2020-07-14
Anticipated expiration: 2037-05-15
Also published as: CN107934908A

Abstract

The application discloses a synthetic nano material, which comprises an Ecoflex transfer layer and a plurality of nano walls fixed on the Ecoflex transfer layer; each nanometer wall comprises one or more one-dimensional nanometer conductive structures and an Ecoflex material for coating the one or more nanometer conductive structures into the nanometer wall; wherein the one-dimensional nano-conductive is substantially vertically fixed on the Ecoflex transfer layer; wherein, without the Ecoflex transfer layer being stretched, the one-dimensional nano-conductive structures in the outer surface of adjacent nano-walls contact each other at one or more junctions. Methods of making such synthetic nanomaterials and stress sensors including such synthetic nanomaterials are also disclosed.

Description

Stress sensor and preparation method thereof

Technical Field

The application relates to a stress sensor technology, in particular to a stress sensor prepared by using an Ecoflex material and a preparation method thereof.

Background

A stress sensor is a sensor that senses a change in force by converting a mechanical deformation into a change in an electrical characteristic, such as resistance or capacitance. With the development of sensor technology, stress sensors are used to detect small range movements of the human body, such as subtle movements of the face, chest, and neck during emotional fluctuations, breathing, swallowing, and speaking. The detection of these movements plays a very important role in diagnosing vocal cord injuries, respiratory diseases, angina pectoris, assessing bone spacing, determining changes in spinal shape, detecting parkinson's disease, measuring posture and movement, analyzing changes in facial expression and monitoring skin sclerosis.

To achieve the above objects well, the stress sensor is required to have excellent stretchability, flexibility, high sensitivity, high linearity, recoverability, durability, rapid response and recovery speed, biocompatibility, and the like.

The resistance type stress sensor detects stress by detecting the change of resistance when the sensor is mechanically deformed. Compared with a piezoelectric stress sensor and a capacitance stress sensor, the resistance stress sensor has a larger measuring range and higher sensitivity. However, obtaining stress by measuring the resistance value change poses difficulties due to the non-linear dependence of the resistance value change on stress. Secondly, the large measurement range and high sensitivity are difficult to coexist in the same device.

Conventional stress sensors are made of metal and silicon. These sensors have the advantage of low cost and process maturity, but tend to exhibit poor flexibility and stretchability, can only be used to measure stress in a fixed direction, and cannot be embedded in a substrate material. Therefore, a variety of flexible and stretchable stress sensors based on novel materials, such as carbon nanotubes, graphene, metal nanowires, nanoparticles, and semiconducting polymers, have been developed.

Disclosure of Invention

The application provides a synthetic nanomaterial, comprising an Ecoflex transfer layer and a plurality of nanowalls fixed on the Ecoflex transfer layer; each nanometer wall comprises one or more one-dimensional nanometer conductive structures and an Ecoflex material for coating the one or more nanometer conductive structures into the nanometer wall; wherein the one-dimensional nano-conductive is substantially vertically fixed on the Ecoflex transfer layer; wherein, without the Ecoflex transfer layer being stretched, the one-dimensional nano-conductive structures in the outer surface of adjacent nano-walls contact each other at one or more junctions.

In particular, the one-dimensional nano conductive structure comprises a carbon nano tube, a metal nano wire or a nano fiber.

In particular, the length of the one-dimensional nano conductive structure is 5 to 50 micrometers.

In particular, the Ecoflex transfer layer has a thickness of 5 to 50 micrometers.

The present application further provides a stress sensor comprising the synthetic nanomaterial described in any of the preceding.

The application also provides a method for preparing the synthetic nano material, which comprises the steps of preparing a basically vertical one-dimensional nano conductive structure network on a first substrate; forming a non-cured Ecoflex transfer layer on a second substrate; transferring the one-dimensional nano-conductive structure network onto the Ecoflex transfer layer and curing the Ecoflex transfer layer; and removing the first and second substrates and forming an electrode on the Ecoflex transfer layer.

In particular, the one-dimensional nano conductive structure comprises a carbon nano tube, a metal nano wire or a nano fiber; the first substrate comprises a silicon substrate.

In particular, the second substrate comprises a PEN or PDMS material; the method also includes forming a cured Ecoflex tie layer between the second substrate and the Ecoflex transfer layer for joining the second substrate to the Ecoflex transfer layer.

Hereinafter, a detailed description of exemplary embodiments of the present application will be given with reference to the accompanying drawings.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and together with the description, serve to explain the principles of the application.

FIGS. 1a-1f are schematic diagrams illustrating a process flow for preparing synthetic nanomaterials according to one embodiment of the present application;

FIG. 2 is a flow diagram of a method for preparing synthetic nanomaterials using the process flow shown in FIGS. 1a-1 f;

FIGS. 3a-3g are schematic process flow diagrams illustrating the preparation of synthetic nanomaterials according to another embodiment of the present application;

FIG. 4 is a flow diagram of a method for preparing synthetic nanomaterials using the process flow shown in FIGS. 3a-3 g;

FIG. 5 illustrates a side cross-sectional and top SEM view of a synthetic nanomaterial according to one embodiment of the present application;

FIG. 6 is a top SEM image of a synthetic nanomaterial according to one embodiment of the present application in the absence of stretching and with stretching;

FIG. 7 is a graph illustrating the rate of change in resistance as a function of degree of stretching for a synthetic nanomaterial fabricated using carbon nanotubes 10 microns and 15 microns long in accordance with one embodiment of the present application;

FIG. 8 is a graph illustrating the rate of change of resistance as a function of degree of stretching for a synthetic nanomaterial fabricated using carbon nanotubes 10 microns and 15 microns long with varying densities according to one embodiment of the present application;

FIG. 9 is a graph showing the ratio of resistance change of a conventional synthetic nanomaterial fabricated using a vertical carbon nanotube network as a function of the degree of stretching;

FIG. 10 is a graph illustrating the rate of change of resistance as a function of the number of stretches for a synthetic nanomaterial according to one embodiment of the present application; and

FIG. 11 is a graph illustrating the rate of change of resistance versus temperature for a synthetic nanomaterial according to one embodiment of the present application.

Detailed Description

Exemplary embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be noted that the relative arrangement of the components and steps, the numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present application unless specifically stated otherwise.

The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the application, its application, or uses.

Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate.

In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values.

It should be noted that like reference numerals and letters refer to like items in the following figures, and thus, once an item is defined in one figure, further discussion thereof is not required in subsequent figures.

Carbon nanotubes are easily embedded in flexible stretchable substrates due to their unique mechanical and electrical properties, and are one of the ideal materials for resistive flexible stress sensors. Most of the carbon nanotube networks constituting the stress sensors in the prior art are planar conductive networks, that is, the carbon nanotubes are often randomly distributed and oriented and are connected with each other by van der waals force. Because the force is weaker, when the external tensile force acts, the carbon nanotubes which are originally connected or contacted mutually slide relatively, and the connection among some carbon nanotubes is broken, so that the connection point density of the carbon nanotubes and the number of conductive paths are reduced, the resistance is increased, and the proportional relation between the resistance and the external tensile deformation is realized. This is the working principle of a typical carbon nanotube based resistive stress sensor.

However, in the structure of the planar carbon nanotube conductive network, the proportion of the number of the carbon nanotube connecting nodes broken under small stretching in the total number of the nodes is much smaller than the proportion of the number of the carbon nanotube connecting nodes broken under large stretching in the remaining nodes, so that the stress sensor prepared based on the planar carbon nanotube conductive network is not sensitive to small stretching. The resulting non-linear dependence of resistance on strain also severely limits the usefulness of the stress sensor.

In addition, since the stretchability of the carbon nanotubes themselves is only 40% smaller than that of conventional substrate materials such as PDMS, the carbon nanotubes may be broken or slip relative to the substrate under a large stretching. The rupture of the carbon nanotubes can cause an irreversible increase in the resistance of the device, and the relative sliding of the carbon nanotubes with respect to the substrate can cause the carbon nanotubes to buckle or bend after the tensile force is released, thereby also preventing the resistance from returning to its original value. Therefore, the main challenges for stress sensors made with carbon nanotubes are the recoverability of the device resistance and sensitivity at small tensions.

The vertical carbon nanotube network can solve the above problems to some extent. By a vertical carbon nanotube network is meant that the carbon nanotubes are fixed to the substrate in a substantially vertical manner. It is of course understood by those skilled in the art that since the growth of carbon nanotubes is accomplished through a series of physicochemical processes, it is not possible to expect each carbon nanotube to grow on the substrate in an absolutely vertical manner, and therefore the description of being substantially vertical is appropriate here.

In a vertical carbon nanotube network, carbon nanotubes are fixed on a substrate in a nearly vertical manner or are fixed on the substrate at a small angle in an inclined manner, and form a carbon nanotube conductive network with surrounding carbon nanotubes. Therefore, even under the condition of small stretching, the carbon nanotubes move along with the flexible substrate, so that a large number of nodes are disconnected, and the carbon nanotubes are thinned along with the stretching of the substrate such as PDMS, so that the number of the disconnected nodes caused by the stretching of the same length is reduced, but the number of the residual nodes is reduced, and the ratio of the number of the disconnected nodes to the number of the residual nodes is relatively stable.

But such vertical carbon nanotube network structures are also problematic. Due to the interaction between the adjacent carbon nanotubes, such as friction and van der waals force, the carbon nanotubes are restricted from moving along with the substrate during stretching and releasing, so that the sensitivity (GF) during stretching cannot reach the ideal level of GF ═ 7, but can only reach GF ═ 2. In addition, the resistance does not return to its initial value after the release of the tension.

To address this problem, researchers in the field have tried many different substrates, but none have found a good alternative material.

Ecoflex is a platinum catalyzed silicone manufactured by Smooth-On corporation, a simple and versatile silica gel material. Are commonly used to prepare prostheses or masks. The inventor of the application has found that Ecoflex is a very soft polymer material, and the young modulus of the Ecoflex is 125kPa, and the Ecoflex is similar to the softness of human skin. Compared with other existing materials such as PDMS, the Ecoflex and the carbon nanotube can achieve high adhesion. Ecoflex also has very good ductility, which can be as high as 900%, and is therefore very suitable for the preparation of synthetic nanomaterials for use in, for example, stress or pressure sensors, or even triboelectric, optical signal transmission, or flexible solar structures. Furthermore, as described above, Ecoflex is a polymer that is stable with respect to the surrounding environment, has good water resistance, and is suitable for long-term sensing applications. More importantly, the inventor of the present application has obtained a special material synthesized by Ecoflex and one-dimensional conductive nano-material such as carbon nano-tube, which is very suitable for preparing devices such as stress sensor or pressure sensor.

The present application will be described in detail with reference to the accompanying drawings and examples.

FIG. 1 is a schematic process flow diagram for preparing synthetic nanomaterials according to one embodiment of the present application.

FIG. 2 is a flow diagram of a method for preparing a synthetic nanomaterial according to the process flow described in FIG. 1.

At step 202, as shown in FIG. 1a, a vertical carbon nanotube network 102 is prepared. According to one embodiment, a catalyst may be utilized to synthesize a vertical carbon nanotube network on the substrate 104 using a PECVD process. According to one embodiment, the catalyst may be iron or another material and the substrate 104 may be a silicon substrate. The producer can control the density of the grown carbon nanotubes by controlling the amount of the catalyst. The relationship between the density of the carbon nanotubes and the performance of the sensor will be described in detail later in this application.

According to one embodiment, the silicon substrate 104 may be first placed in a chamber in a high vacuum state, and hydrogen gas may be introduced at a flow rate of 30sccm and nitrogen gas may be introduced at a flow rate of 10sccm, and the chamber temperature may be heated to 850 ℃; then, the reaction gas CH was introduced at a flow rate of 35sccm₄And the power of the plasma was fixed at 200 watts. According to various embodiments, the reaction time may vary from 40 seconds to 120 seconds in order to control the length of the vertical carbon nanotubes. The relationship between the length of the carbon nanotube and the performance of the sensor will be described in detail later in this application.

The carbon nanotubes 102 formed at this step may have a single-layered sidewall or may have a multi-layered sidewall. Methods for producing vertical carbon nanotube networks with single or multiple sidewalls are well established. The transparency of the composite material of the present application can be further improved if carbon nanotubes with single-layer sidewalls are used, thereby providing more desirable application effects. Of course, other one-dimensional vertical conductive materials such as metal nanowires like zinc oxide nanowires, silver nanowires, or conductive nanofibers can also be used as an alternative to carbon nanotubes.

At step 204, the substrate 106 is prepared. According to one embodiment, the substrate may employ a cured Ecoflex layer. As shown in fig. 1b, Ecoflex is injected in the mold 108 without curing and then cured into a film by heating for, e.g., 15 minutes or standing for, e.g., 12 hours. According to one embodiment, the Ecoflex thin film layer 106 as a substrate may have a thickness of several millimeters.

At step 206, a non-cured Ecoflex transfer layer 110 is spin coated on the substrate 106, as shown in fig. 1 c. According to one embodiment, the amount of Ecoflex spun in this step may be approximately equivalent to 5-50 microns, e.g., 15 microns thick. According to one embodiment, the amount of material of the Ecoflex transfer layer 110 can be adjusted according to the carbon tube length. According to one embodiment, the thickness of the Ecoflex transfer layer 110 may be similar to the length of the vertical carbon nanotubes.

At step 208, the vertical carbon nanotube network 102 is transferred to the uncured Ecoflex transfer layer 110, as shown in fig. 1d, and the Ecoflex transfer layer 110 is cured after the transfer. According to one embodiment, no external force is applied during the placement of the vertical carbon nanotubes in the Ecoflex transfer layer 110, but the weight of the silicon substrate 104 alone is relied upon to trap the carbon nanotube network 102 into the uncured Ecoflex transfer layer 110. According to one embodiment, the time for curing after the transfer is complete may be 2 hours, and the curing temperature may be 70 ℃, although various other curing temperatures and times may be used. Since Ecoflex polymers have high viscosity, carbon nanotubes are coated with Ecoflex during curing to form a plurality of nanowalls.

It should be noted that the coating mentioned here may be that the carbon nanotube 102 is completely or partially coated by the Ecoflex transferred layer 110, for example, the upper end of part of the carbon nanotube may protrude out of the Ecoflex transferred layer 110.

In step 210, the silicon substrate 104 is removed, the effect being shown in fig. 1 e. Due to the strong adhesion between the carbon nanotubes 102 and the Ecoflex transfer layer 108 during the curing process of step 208, the silicon substrate 104 can be smoothly removed from the carbon nanotubes or from the nanowalls during this step.

At step 212, electrodes 112 are formed across the Ecoflex transfer layer 108, as shown in fig. 1 f. According to one embodiment, copper wires may be fixed as electrodes at both ends of the Ecoflex transfer layer 108 by silver paste. Other known methods of forming the electrodes may of course be used.

Of course, those skilled in the art will appreciate that there may be conventional steps, such as packaging, etc., that follow. Since it is not the focus of the present application, it will not be described herein in detail.

FIG. 3 is a schematic process flow diagram for preparing synthetic nanomaterials according to one embodiment of the present application.

FIG. 4 is a flow diagram of a method for preparing a synthetic nanomaterial according to the process flow described in FIG. 3.

At step 402, as shown in FIG. 3a, a vertical carbon nanotube network 302 is prepared. According to one embodiment, a catalyst may be utilized to synthesize a vertical carbon nanotube network on the substrate 304 using a PECVD process. According to one embodiment, the catalyst may be iron or another material and the substrate 304 may be a silicon substrate. The producer can control the density of the grown carbon nanotubes by controlling the amount of the catalyst. The relationship between the density of the carbon nanotubes and the properties of the synthesized nanomaterial will be described in detail later in this application.

According to one embodiment, the silicon substrate 304 may be first placed in a chamber in a high vacuum state and hydrogen gas at a flow rate of 30sccm and nitrogen gas at a flow rate of 10sccm, and the chamber temperature is heated to 850 ℃; then, the reaction gas CH was introduced at a flow rate of 35sccm₄And the power of the plasma was fixed at 200 watts.According to various embodiments, the reaction time may vary from 40 seconds to 120 seconds in order to control the length of the vertical carbon nanotubes. The relationship between the length of the carbon nanotubes and the properties of the synthesized nanomaterial will be described in detail later in this application.

The carbon nanotubes 302 formed at this step may have a single-layered sidewall or may have a multi-layered sidewall. Of course, other one-dimensional vertical conductive materials such as zinc oxide nanowires, silver nanowires, etc. may also be employed as an alternative to carbon nanotubes.

In step 404, a first layer of Ecoflex is formed on the substrate 306 as a tie layer 308, as shown in fig. 3b, and cured. According to one embodiment, the substrate 306 may be a PEN or PDMS material. According to one embodiment, the curing time may be 30 minutes and the curing temperature may be 70 ℃. According to one embodiment, the cured thickness of the Ecoflex tie layer 308 may be 50-150 microns, particularly, for example, 100 microns.

In step 406, a layer of uncured Ecoflex polymer is spin coated onto the tie layer 308 as the transfer layer 310, as shown in fig. 3 c. According to one embodiment, the amount of Ecoflex spun in this step can be up to about 15 microns thick after curing. Due to poor wettability between the Ecoflex and the substrate 306 material, such as PEN or PDMS, the Ecoflex tie layer 308 is employed to improve the wettability between the substrate 306 and the Ecoflex transfer layer 310 and to act as a support for the Ecoflex transfer layer 310.

At step 408, the vertical carbon nanotube network 302 is transferred to the uncured Ecoflex transfer layer 310, as shown in fig. 3 d. According to one embodiment, no external force is applied during the placement of the carbon nanotube network 302 in the Ecoflex transfer layer 310, and the weight of the silicon substrate 304 alone is relied upon to trap the carbon nanotube network 302 in the Ecoflex transfer layer 310. According to one embodiment, the time for curing after the transfer is complete may be 2 hours, and the curing temperature may be 70 ℃, although various other curing temperatures and times may be used. Since Ecoflex polymers have high viscosity, carbon nanotubes are coated with Ecoflex during curing to form a plurality of nanowalls.

At step 410, the substrate 304 is removed, the effect being shown in FIG. 3 e. Due to the strong adhesion between the carbon nanotubes 302 and the Ecoflex transfer layer 308 during the curing process of step 308, the silicon substrate 304 can be smoothly removed from the carbon nanotubes or nanowalls during this step.

At step 412, the substrate 306 is removed, the effect being shown in FIG. 3 f. At this step the substrate 306, which may be comprised of PEN or PDMS, is removed from the Ecoflex adapter layer 308.

At step 414, electrodes 312 are formed across the Ecoflex transfer layer 310, as shown in fig. 3 g. According to one embodiment, copper wires may be fixed as electrodes at both ends of the Ecoflex transfer layer 310 by silver paste.

FIG. 5 illustrates a side cross-sectional and top SEM view of a synthetic nanomaterial according to one embodiment of the present application. As can be seen, during the curing process the carbon nanotubes are coated by Ecoflex to form individual composite structures, which we call nanowalls in this application.

The synthetic nanomaterials provided by the present application can have various applications, such as stress sensors, pressure sensors (e.g., two layers of synthetic nanomaterials are stacked together) or triboelectric devices, among others. The following description will be given by taking the application of the stress sensor as an example.

FIG. 6 is a top SEM image of a synthetic nanomaterial according to one embodiment of the present application in the absence of stretching and with stretching. As can be seen, the nanowalls are in close contact with each other in the absence of stretching; under the condition of stretching, at least part of the nanometer walls are separated from each other or the number of contact nodes is reduced. Specifically, the microscopic mechanism of change in stress-sensitivity behavior of the synthetic nanomaterials with the above structures includes two parts: first, stretching of carbon nanotubes coated in Ecoflex. The carbon nano tube has good elasticity and can stretch by 40 percent under the action of tensile stress. Therefore, in the case where the Ecoflex transfer layer is stretched, the carbon nanotubes may be stretched together therewith to cause a reduction in contact junction. However, in any case, the stretching of the carbon nanotubes is limited by the structure of the nano-wall coated outside the carbon nanotubes, so that the mechanism has a relatively limited effect on the increase of the overall resistance of the synthesized nano-material.

The second mechanism of variation is based on the separation or reduction of contact junctions between carbon nanotubes in the outer surface of adjacent nanowalls. That is, the carbon nanotubes in the outer surface of adjacent nanowalls may contact each other at one or more nodes without stretching; but in the case of tension, the contact at the one or more nodes may break or separate. In contrast, the second mechanism has a much greater effect on the electrical resistance of the synthesized nanomaterial than the first mechanism. Because the vertical carbon tubes are embedded in the Ecoflex, the influence of friction among a large number of carbon tubes is eliminated, and therefore, the negative influence caused by the friction is reduced to the minimum by the structure of the nano wall.

The length of the carbon nanotube has an influence on the performance of the synthesized nano material, and certainly, the length of the carbon nanotube can be different according to different applications, but with the structure of the present application, the length of the carbon nanotube cannot be too short, otherwise, the above-mentioned nano wall structure cannot be formed. For example, in the case of using an Ecoflex transfer layer with a thickness of 15 μm, if the length of the carbon nanotube is 5 μm, the surface cannot form a structure of a nanowall after the Ecoflex layer is cured, the carbon nanotube is completely submerged by the Ecoflex polymer, the upper surface of the formed composite is flat, and the sensitivity of the composite is very poor, only about 0.5. This is because the second change mechanism mentioned above is not effective at all because the nano-wall structure is not formed and all the carbon nanotubes are collectively fixed in the Ecoflex transfer layer. In contrast, in the case of using an Ecoflex transfer layer having a thickness of 15 μm, if the length of the carbon nanotube is 10 μm or 15 μm, a nanowall structure can be formed after the Ecoflex layer is cured, and has surface resistances of 3.8k Ω/sq and 2.2k Ω/sq, respectively. Therefore, the relationship between the Ecoflex transfer layer and the length of the carbon nanotube is also important, and generally an Ecoflex transfer layer having a length similar to that of the carbon nanotube may be used.

Fig. 7 is a graph showing the resistance of the synthesized nanomaterial prepared using carbon nanotubes 10 and 15 microns long as a function of the degree of stretching. It can be seen from the figure that the synthesized nanomaterial using the 10 μm carbon nanotube exhibits better sensitivity (GF), i.e., the slope of the curve, which can reach 18 at most. This is because the number of nodes where the nanowalls formed of short nanotubes contact each other is smaller than the number of nodes where the nanowalls formed of relatively long carbon nanotubes contact each other, and thus the rate of change of the junction separation is larger under the same stretching, and thus the sensitivity is higher.

Fig. 8 is a graph showing the rate of change in resistance of synthetic nanomaterials prepared using carbon nanotubes of 10 microns and 15 microns in length having different densities as a function of the degree of stretching. As shown, with carbon nanotubes of the same length, e.g., 10 microns, the greater the amount of catalyst, e.g., iron, the lower the carbon nanotube density, the greater the sensitivity, but the less linear, of the synthesized nanomaterial. This is because the carbon nanotubes have a low density and a relatively small total number of contact nodes, and are therefore sensitive to stretching and therefore sensitive; however, the larger the stretching width, the faster the increase of the number of junctions at a low density of the carbon nanotubes, and thus the higher the ratio of the change in resistance, and thus the worse the linearity of the synthesized nanomaterial.

The sensitivity of the synthesized nanomaterial using carbon nanotubes 10 microns long was higher than that of the synthesized nanomaterial using carbon nanotubes 15 microns long, which is consistent with the previous results and explanations; however, under the condition of large-amplitude stretching, the linearity of the synthesized nano material adopting the carbon nano tube of 15 micrometers is better than that of the carbon nano tube of 10 micrometers. This is because the longer the carbon nanotubes, the more nodes are in contact with each other, and thus the change in the number of nodes generated by stretching the synthetic nanomaterial having longer carbon nanotubes is relatively more stable with respect to the change in the ratio of the number of remaining nodes.

Fig. 9 is a graph showing the ratio of resistance change of a conventional synthetic nanomaterial fabricated using a vertical carbon nanotube network as a function of the degree of stretching. It can be seen from the figure that the resistance change ratio is less than 2.5 in the case of 100% stretching degree, but as shown in fig. 7, the resistance change ratio of the synthetic nanomaterial prepared by using 10 μm carbon nanotubes in the embodiment of the present application can be as high as 8 in the case of 100% stretching degree, which is nearly four times that of the synthetic nanomaterial prepared by using the conventional vertical carbon nanotube network.

FIG. 10 is a graph illustrating the rate of change of resistance as a function of the number of stretches for a synthetic nanomaterial according to one embodiment of the present application. It can be seen from the figure that after four hundred times of stretching, the resistance sensitivity of the synthesized nano material provided by the application is not greatly changed, and the synthesized nano material has good reliability.

FIG. 10 is a graph illustrating the rate of change of resistance versus temperature for a synthetic nanomaterial according to one embodiment of the present application. As can be seen, the resistance of the synthesized nanomaterial decreases with increasing temperature, but the magnitude is very small. This demonstrates the excellent temperature stability of the synthetic nanomaterials provided herein.

In the application, the Ecoflex layer is used as a medium to transfer the vertical carbon nanotubes, and a nano-wall structure formed by mixing the vertical carbon nanotubes and the Ecoflex is formed, so that the sensitivity of the sensor adopting the synthetic nano-material reaches an ideal level of sensitivity (GF-3-18). This is because the two aforementioned mechanisms of variation in the synthesis of nanomaterials work together. On one hand, the carbon nano tube in the nano wall is stretched along with the stretching of the transfer layer, the carbon nano tube at the edge or the outer surface of the micro structure of the nano wall and the carbon nano tube at the edge of the adjacent nano wall form a tunneling junction, and the mechanism in stretching is similar to that of a vertical carbon nano tube network, but the defect of the numerical value carbon nano tube network is overcome. In addition, because the carbon nano tube is coated by the Ecoflex, when an external force acts, the carbon nano tube moves along with the Ecoflex coated with the carbon nano tube, the influence of friction is avoided, and the stability of the sensor is ensured.

Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are for illustrative purposes only and are not intended to limit the scope of the present application. It will be appreciated by those skilled in the art that modifications may be made to the above embodiments without departing from the scope and spirit of the present application. The scope of the application is defined by the appended claims.

Claims

1. A synthetic nanomaterial comprising

The solar cell comprises an Ecoflex transfer layer and a plurality of nano walls fixed on the Ecoflex transfer layer;

each nanometer wall comprises one or more one-dimensional nanometer conductive structures and an Ecoflex material for coating the one or more one-dimensional nanometer conductive structures into the nanometer wall;

wherein the one-dimensional nano conductive structure is substantially vertically fixed on the Ecoflex transfer layer;

wherein, without the Ecoflex transfer layer being stretched, the one-dimensional nano-conductive structures in the outer surface of adjacent nano-walls contact each other at one or more junctions.

2. The synthetic nanomaterial of claim 1, wherein the one-dimensional nano-conductive structure comprises a carbon nanotube, a metal nanowire, or a nanofiber.

3. The synthetic nanomaterial of claim 1, wherein the length of the one-dimensional nano-conductive structure is from 5 to 50 microns.

4. The synthetic nanomaterial of claim 3, wherein the Ecoflex transfer layer has a thickness of 5 to 50 microns.

5. A stress sensor comprising the synthetic nanomaterial of any of claims 1-4.