阅读说明：本技术 用于制备共聚物包裹的纳米管纤维的方法和装置 (Method and apparatus for preparing copolymer-wrapped nanotube fibers ) 是由 周剑 徐雪珠 吉勒斯·吕比诺 于 2018-10-10 设计创作，主要内容包括：一种制备共聚物包裹的纳米管同轴纤维的方法。该方法包括将第一纺液供应至纺丝喷嘴；将第二纺液供应至纺丝喷嘴；将第一纺液和第二纺液作为同轴纤维纺丝至第一湿浴中；以及将同轴纤维置于不同于第一浴的第二湿浴中。同轴纤维具有包括第一纺液的部分的芯和包括第二纺液的部分的护套。第二湿浴的溶剂分子穿透护套并且从芯中除去酸。(A method for preparing a copolymer-coated nanotube coaxial fiber. The method includes supplying a first dope to a spinning nozzle; supplying the second dope to the spinning nozzle; spinning the first dope and the second dope as coaxial fibers into a first wet bath; and placing the coaxial fibers in a second wet bath different from the first bath. The coaxial fiber has a core comprising a portion of the first dope and a sheath comprising a portion of the second dope. The solvent molecules of the second wet bath penetrate the sheath and remove the acid from the core.)

1. A method for making a copolymer-wrapped nanotube coaxial fiber, the method comprising:

supplying a first dope to a spinning nozzle;

supplying the second dope to the spinning nozzle;

spinning the first dope and the second dope as coaxial fibers into a first wet bath; and

the coaxial fibers are placed in a second wet bath different from the first bath,

wherein the coaxial fiber has a core comprising a portion of the first dope and a sheath comprising a portion of the second dope, and

wherein molecules of the second wet bath penetrate the sheath and remove acid from the core.

2. The method of claim 1, wherein the wick is fluid before the second wet bath and becomes solid after the second wet bath.

3. The method of claim 1, wherein the first dope comprises single-walled carbon nanotubes (SWCNTs).

4. The method of claim 3, wherein the first dope further comprises a dispersant.

5. The method of claim 4, wherein the dispersant is CH₃SO₃H。

6. The method of claim 5, wherein the second bath is extracting CH from a core₃SO₃Acetone bath of H.

7. The method of claim 3, wherein the first dope comprises 2 wt% SWCNT and CH₃SO₃H。

8. The method of claim 3, wherein the second dope comprises a thermoplastic elastomer.

9. The method of claim 8, wherein the second dope further comprises CH₂Cl₂。

10. The method of claim 9, wherein the first bath is an ethanol coagulation bath.

11. The method of claim 10, wherein the ethanol bath extracts CH from the sheath₂Cl₂。

12. The method of claim 1, wherein the core is electrically conductive and the sheath is an insulator.

13. The method of claim 1, further comprising:

the coaxial fibers are flattened.

14. An apparatus for making a copolymer-wrapped nanotube coaxial fiber, the apparatus comprising:

a spinning nozzle having an inner channel and an outer channel;

a first container holding a first dope and configured to supply the first dope to an inner passage of the spinning nozzle;

a second container holding a second dope and configured to supply the second dope to an outer channel of the spinning nozzle;

a third vessel holding the first wet bath and configured to receive spun coaxial fibers from the spinning nozzle; and

a fourth vessel holding a second wet bath and configured to receive the spun coaxial fibers from the third vessel.

15. The apparatus of claim 14, wherein the spun coaxial fibers comprise a first dope as a core and a second dope as a sheath.

16. The device of claim 15, wherein molecules of the second wet bath penetrate the sheath and remove acid from the core.

17. The apparatus of claim 14, wherein the first dope comprises single-walled carbon nanotubes (SWCNTs) and CH₃SO₃H。

18. The apparatus of claim 17, wherein the second dope comprises a thermoplastic elastomer and CH₂Cl₂。

19. The apparatus of claim 14, wherein the first bath comprises ethanol and the second bath comprises acetone.

20. A method for making a copolymer-wrapped nanotube coaxial fiber, the method comprising:

spinning the first dope and the second dope as coaxial fibers into a first wet bath;

placing the coaxial fibers in a second wet bath to extract acid from the core of the coaxial fibers; and

the coaxial fibers are flattened.

Technical Field

Embodiments of the subject matter disclosed herein relate generally to methods of generating copolymer-wrapped nanotube fibers, and more particularly, to methods and coaxial fibers for deformable and wearable strain sensors.

Background

Stretchable conductors are a major component of wearable electronics, flexible displays, transistors, mechanical sensors, and energy devices. Stretchable fiber conductors are very promising for next generation wearable electronics because they can be easily mass produced and woven into fabrics. Recently, stretchable fibers have been developed towards high stretchability and high sensitivity, which is suitable for applications such as electronic skin and health monitoring systems.

Some of the parameters responsible for strain sensor performance are (1) sensitivity, (2) stretchability, and (3) linearity. Sensitivity (defined herein by the strain sensitivity coefficient, GF, or gage factor) is defined by (a) the relative change in resistance (Δ R/R)₀) Ratio between (a) and (b) applied strainAnd (4) showing. Stretchability is the maximum uniaxial tensile strain of the sensor before breaking. The linearity quantifies how constant GF is over the measurement range. Good linearity makes the calibration process of the strain sensor easier and ensures accurate measurements over the entire range of applied strain.

However, conventional fiber-based strain sensors fail to combine high sensitivity (GF > 100), high stretchability (strain > 100%), and high linearity. For example, carbonized silk fibers are used as components in wearable strain sensors with good stretchability. However, the sensitivity of the sensor was low and as the strain increased from 250% to 500%, the GF increased from 9.6 to 37.5, indicating a large change in the strain measurement range. The graphene-based composite fiber having the "compressed ring" structure increases the stretchability of the sensor, but the structure of the sensor is very complicated and the GF thereof is low (GF 1.5 at 200% strain). Electronic fabrics based on electrodes wrapped with piezoresistive rubber simultaneously (a) map and (b) quantify mechanical strain, but the manufacturing process is complex and time consuming.

Therefore, a new generation of conductive and stretchable fibers is needed to design high performance strain sensors.

Disclosure of Invention

According to an embodiment, a method for making a copolymer-wrapped nanotube coaxial fiber is provided. The method includes supplying a first dope to a spinning nozzle; supplying the second dope to the spinning nozzle; spinning the first dope and the second dope as coaxial fibers into a first wet bath; and placing the coaxial fibers in a second wet bath different from the first bath. The coaxial fiber has a core comprising a portion of the first dope and a sheath comprising a portion of the second dope. Molecules of the solvent (e.g., acetone) of the second wet bath penetrate the sheath and remove the acid from the core.

According to another embodiment, an apparatus for making copolymer-wrapped nanotube coaxial fibers is provided. The device includes: a spinning nozzle having an inner channel and an outer channel; a first container holding a first dope and configured to supply the first dope to an inner passage of the spinning nozzle; a second container holding a second dope and configured to supply the second dope to an outer channel of the spinning nozzle; a third vessel holding the first wet bath and configured to receive spun coaxial fibers from the spinning nozzle; and a fourth vessel holding a second wet bath and configured to receive spun coaxial fibers from the third vessel.

According to another embodiment, a method of making a copolymer-wrapped nanotube coaxial fiber is provided. The method includes spinning a first dope and a second dope as coaxial fibers into a first wet bath; placing the coaxial fibers in a second wet bath to extract acid from the core of the coaxial fibers; and flattening the coaxial fibers.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:

FIG. 1A shows an apparatus 100 for making copolymer-wrapped nanostructured fibers, FIG. 1B shows a bath into which spun fibers are placed, FIG. 1C shows the process of flattening the fibers, and FIG. 1D shows the final fibers;

FIG. 2 shows a copolymer-encased nanostructured fiber;

FIG. 3 is a flow diagram of a process for making copolymer-encased nanostructured fibers;

FIGS. 4A and 4B illustrate the process of drawing the fiber and the occurrence of cracks;

FIGS. 5A and 5B illustrate the strain applied to TPE fibers and copolymer encapsulated nanostructured fibers;

fig. 6A shows cracks occurring in the copolymer-encased nanostructured fibers, and fig. 6B shows the average crack opening versus strain;

FIG. 7A shows the resistance of a copolymer-encased nanostructured fiber when strain is applied, FIG. 7B compares the strain sensitivity coefficient of a copolymer-encased nanostructured fiber with that of a conventional fiber, FIG. 7C shows the impedance versus frequency of a copolymer-encased nanostructured fiber, and FIG. 7D shows a conduction model of a copolymer-encased nanostructured fiber under strain;

8A-8C illustrate the response when multiple strain sensors are located on a straight cable;

9A-9C illustrate the response of multiple strain sensors when a cable is strained;

10A-10B illustrate the response of multiple strain sensors when the cable is bent into an S-shape; and

fig. 10C to 10D show the response of a plurality of strain sensors when the cable is bent into a circle.

Detailed Description

Embodiments are described below with reference to the drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Rather, the scope of the invention is defined by the appended claims. For simplicity, the following examples are discussed with respect to thermoplastic elastomer (TPE) wrapped single-walled carbon nanotube (SWCNT) microwires. However, the present invention is not limited to TPE materials or carbon nanotubes. Other copolymers and electrical insulators that are stretchable may be used instead of TPE, and other conductive materials such as carbon black, silicon, graphene, and metal nanoparticles may be used instead of carbon to form nanotubes. Those skilled in the art will understand, after reading this description, that other materials may also be used.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

One common method used in the past for the industrial manufacture of continuous fibers is wet spinning. This approach provides a robust approach to engineering high performance conductive fibers. Previously, silver nanoparticle/thermoplastic elastomer mixtures were wet spun to construct microfiber-based strain sensors, but maintaining a continuous conductive path in the fiber and uniform distribution of metal fillers was challenging. Conductive polymer/thermoplastic elastomer fibers are also prepared by wet spinning for highly stretchable sensors, but even with highly loaded conductive polymer fillers, it is difficult to maintain both stretchability and sensitivity. In previous work by the authors of the present disclosure (see, e.g., U.S. patent publication 2017/0370024-a1), conductive poly (3, 4-ethylenedioxythiophene)/poly (styrenesulfonate) (PEDOT/PSS) polymer microfibers were prepared via a hot-stretch-assisted wet spinning process. By combining the vertical thermal stretching process with solvent doping and dedoping of the microfibers, a conductivity of 2804S cm-1 was obtained. Due to the brittleness of PEDOT/PSS, the stretchability of the conductive fibers is limited to 20%, and the GF is only 1.8 at 13% strain (Zhou et al, J.Mater.chem.C.2015,3, 2528-2538). The wet spinning process has also been successfully applied to prepare single-walled carbon nanotube (SWCNT) microfilaments for strain sensors with a high GF of 105 (see, for example, international publication WO2018/092091a1), although the stretchability is limited to 15% (Zhou et al, Nanoscale2017,9,604-.

Most of the above sensors exhibit large non-linearities. Furthermore, in most of these sensors, the conductive surfaces of the fibers are exposed, and therefore they risk being short-circuited when used as a strain sensor. As a result, stability and durability are poor.

According to the examples, a coaxial wet spinning process was combined with a post-treatment process to prepare TPE-wrapped SWCNT fibers for high performance strain sensors. Textile fibers containing SWCNT/acid dope in the core were post-treated in an acetone bath to remove acid residues, and then the SWCNT cores were densified by pressing on the fiber surface to obtain ribbon-like coaxial fibers. When the draw exceeds the fiber's initiation strain, the fiber breaks with a high density of cracks. The tangled network of SWCNTs bridging the fragmented fragments plays a positive role during strain sensing. As discussed next, these new coaxial fibers were found to be suitable for high performance strain sensors due to their ability to act as deformable and wearable electronics.

According to the embodiment shown in fig. 1A and 1B, the apparatus 100 for making TPE-wrapped SWCNT fibers includes a spinning nozzle 110 having an inner channel 112 and an outer channel 114. The inner passage 112 is located inside and concentric with the outer passage 114. Each of these channels contains a different dope. The two dopes do not mix within the spinning nozzle 110. In fact, the two dopes do not contact each other within the spinning nozzle 110. As shown in fig. 1A, when two kinds of dope are spun from the spinning nozzle 110, the dope 113 of the inner passage 112 contacts the dope 115 of the outer passage 114 only at the tip 116 of the spinning nozzle 110.

The first dope 113 is supplied, for example, from a first storage vessel 118 in fluid communication with the inner passage 112 and the second dope 115 is supplied, for example, from a second storage vessel 120 in fluid communication with the outer passage 114.

Fig. 1A shows that the first dope 113 is spun in the second dope 115 and this structure is maintained throughout the spinning process. In part because of the chemical composition of the dope. For this example, the first dope 113 was 2 wt% SWCNT/CH₃SO₃H。CH₃SO₃H is used as a dispersant for the highly concentrated SWCNTs so that the first dope 113 can be spun into continuous microfilaments. The second dope 115 is TPE in CH₂Cl₂The solution of (1). This solution was chosen as the external spinning solution because TPE is an electrically insulating elastomer. This copolymer creates an outer sheath 122 (see fig. 2) for spinning the fiber 123 that protects the fiber electrode 124(SWCNT core) from short circuits and environmental degradation. Further, as an ultra-stretchable substrate, the outer sheath 122 introduces a desired stretchability to the conductive coaxial fiber 123.

After being spun, the first SWCNT/CH from the inner channel 112₃SO₃H dope 113 and a second TPE/CH from outer channel 114₂Cl₂The solution 115 is simultaneously introduced into an ethanol coagulation bath 130 held in a container 132. The ethanol bath 130 extracts CH2Cl2 from the second TPE/CH2Cl2 dope, and CH₃SO₃H remains in SWCNT core 124.

As a result of this process, a single TPE-wrapped SWCNT coaxial fiber 123 (see FIGS. 1A and 2)Are wet spun and collected at lengths exceeding 5m, which shows the potential of these fibers for large scale production. Due to CH₃SO₃The high boiling point of H (167 ℃) and the rapid curing of TPE in the ethanol bath, even after collection of the fibers 123, mostly CH₃SO₃The H acid remains inside the core 124.

Then, a post-treatment process as shown in fig. 1B is performed. During the post-treatment process, CH is removed from the still-fluid SWCNT core 124 by immersing the fiber 123 in an acetone bath 140₃SO₃H acid, as shown in FIG. 1B. FIG. 1B shows CH₃SO₃H acid is removed from core 124 and acetone enters. The extraction was monitored by observing the diameter of the fibers, and the diameter of the fibers decreased with the increase of the extraction time. The pH of the dried fiber also depends on the extraction time.

After the fibers 123 are removed from the acetone bath 140 held in the container 142, the acetone residue has evaporated, which results in an uneven surface. Thus, for example, the fibers 123 are pressed into a ribbon shape as shown in FIG. 1C with the glass slide 144. In one application, the resulting thickness T and width W of the spun fiber are 200 μm and 1050 μm, respectively. The resulting fiber 143 shown in fig. 1D now has both a solid core 124 and a sheath 122, while the fiber 123 in fig. 1B has a liquid core 124.

To study the morphology of SWCNTs 113 in core 124, TPE layer 122 was dissolved in CH₂Cl₂In (1). The porous structure of SWCNT core 124 with a randomly distributed network of SWCNTs has been observed in SEM images. Some SWCNTs join together and form larger bundles, which play a positive role in reducing the overall resistance of the fiber 143. Experiments with this fiber have shown that the coaxial fiber acts as an insulator when measured on the surface of the coaxial fiber 143 due to the protection of the insulating TPE jacket 122. After connecting a 2cm long SWCNT core 124 with silver paste and copper wire, the fiber was measured to have a low resistance of 142.6 Ω. Experiments confirmed that conductive coaxial fibers made of TPE-wrapped SWCNT cores were obtained by wet spinning and post-treatment processes. Successful production of these coaxial fibers would make them suitable for use in wearable electronicsIn the equipment.

A method for producing the above-described coaxial fiber will now be discussed with reference to fig. 3. In step 300, the first dope 113 is supplied from the first storage container 118 to the inner passage 112 of the spinning nozzle 110. In step 302, the second dope 115 is supplied from the second storage container 120 to the outer passage 114 of the spinning nozzle 110. In step 304, the two dope solutions are wet spun from the spinning nozzle 110 into the ethanol bath 130. In step 306, the fiber 123 formed with the spinning nozzle 110 is placed in the acetone bath 140 to remove the acid from the first dope. In optional step 308, the fibers 123 are flattened. The dope may be the first dope and the second dope discussed above. Other dope may be used as long as the outer sheath is an insulator and the core comprises nanostructures and is electrically conductive. Those skilled in the art will appreciate that other baths may be used, for example, any bath capable of extracting acid from the core of the fiber may be used in place of the acetone bath. The final step of flattening the fibers is optional.

In a specific embodiment, the following materials are used to generate the fibers. The materials used for the first dope were: SWCNTs functionalized with 2.7% carboxyl groups, purchased from CheapTubes, having a purity of over 90 wt% and containing over 5 wt% MWCNTs. The true density of these SWCNTs was 2.1g cm^-3. The materials used for the second dope were: polystyrene-block-polyisoprene-block-polystyrene (TPE) (styrene, 22 wt%), methanesulfonic acid (CH) purchased from Sigma Aldrich₃SO₃H) Ethanol and dichloromethane (CH)₂Cl₂)。

The preparation of SWCNT dope and TPE solution comprises: by adding 0.2g of SWCNT to 9.8g of CH₃SO₃H and stirred for 2 minutes, followed by sonication for 60 minutes using a Brason 8510 bath sonicator (250W) (Thomas Scientific) to prepare a 2 wt% SWCNT dope. The mixture was further stirred for 24 hours and then passed through a 30 μm syringe filter (Pall corporation) to remove aggregates. By mixing 9g of TPE with 21g of CH₂Cl₂The solvent was mixed at 200rpm for 10 hours to make a 30 wt% TPE solution.

Wet spinning of coaxial fibers is performed as follows: the SWCNT dope was charged to 10mI syringe and spun into an ethanol bath through an internal stainless steel needle (21G). The flow rate of the ink was fixed at 150. mu.l/min by using a Fusion 200 syringe pump (Chemyx Co.). The TPE solution in a 10ml syringe was spun into an ethanol bath through an external stainless steel needle (15G). The flow rate of the ink was 200. mu.l/min. The fiber length is 2m min^-1To 4m min^-1Is continuously collected on a 50mm spool. The fibers were then soaked in an acetone bath for 6 hours to remove acid residues. The resulting fibers were removed from the acetone and densified by flattening with a glass slide as shown in fig. 1C. For comparison of mechanical properties, pure TPE fibers were prepared by wet spinning a 20 wt% TPE/DCM solution into an ethanol bath with a stainless steel needle (21G) at an injection rate of 200. mu.l/min.

The resulting fibers were characterized as follows: scanning electron microscope observation (SEM) was performed on the fibers using a Quanta3D machine (FEI corporation). The stretching and relaxation of the coaxial fibers was captured by a BX61 material microscope (Olympus corporation). The loading and unloading of the samples was controlled by 5944 mechanical testing machine (Instron corporation). Then, both ends of the 2cm long fiber were immersed in colloidal silver ink, connected to copper wires and coated with conductive silver epoxy. The resistance change of the fibers was monitored by a 34461A digital multimeter. Incremental, cyclic stretching and relaxation procedures were applied to break the SWCNT core within the coaxial fiber. The program was set to 50% incremental strain, starting at 0% and at 5mmmin^-1Continues to 250% then a cyclic stretch and relaxation process is applied to the fiber at the same speed with a maximum strain of 100%, for five cycles₀) V. where R is₀Is the initial resistance, Δ R/R₀Is the relative change in resistance and is the applied strain.

For Electrical Impedance Spectroscopy (EIS), the impedance mode Z was measured using an Agilent E4980A Precision LCR instrument using a two probe configuration with a kelvin clamp. The frequency range was 20Hz to 2MHz with a step size of 1000Hz and a scan current of 50 mA. To understand the sensing mechanism of fiber-based sensors, impedance changes over a wide range of frequencies under application of different strains (0%, 5%, 15%, 20%, 40%, 60%, and 100%) were studied.

The good linearity of the fiber 123 obtained with the method discussed above is believed to be the result of the following process. Fig. 4A shows fiber 123 in a relaxed mode (i.e., no strain or stress applied). As the stretch is applied to the fibers 123 in step 400, the length of the fibers increases, as shown in fig. 4B. The sheath 122 is elastic and therefore can be stretched without any problem. The core 124, by virtue of having a plurality of nanostructures (nanowalls and/or nanowires) 125 formed in the method discussed above, is also capable of being stretched while maintaining electrical conductivity. This is because the cracks 150 formed in the core 124 (which include a high density of segments 124A of the core 124) are filled with a network of highly conductive SWCNTs 125. When the fiber is relaxed in step 402, the fiber returns to its relaxed mode as shown in FIG. 4A.

To determine the overall properties of the fiber 123, various stresses are applied as now discussed with respect to fig. 5A and 5B. Figure 5A shows pure TPE fibers with cyclic loading and unloading applied. The Y-axis of the graph shows stress values and the X-axis of the graph shows strain values. Similarly, fig. 5B shows the same cyclic loading and unloading of the coaxial fiber 123 prepared as discussed above. Incremental cyclic loading and unloading at 5min cm^-1Is performed. After the first period (0% to 50% strain), both plot 500 and plot 510 show that there is 10-15% residual strain that remains during subsequent cycles. This indicates that there was some plastic deformation during the first cycle, but that deformation was negligible during subsequent cycles. Figure 5A shows typical mechanical properties of pure TPE, which can be extended far with good elastic recovery properties. The coaxial fiber of fig. 5B experiences a dramatic increase in stress during the first loading period 510 compared to the pure TPE of fig. 5A. The Young's modulus calculated according to the first loading period was 112MPa, 24 times higher than that of pure TPE fiber (4.5 MPa). These results indicate that SWCNT core 124 increases the young's modulus of TPE and that SWCNTs have a conformal interface in the TPE matrix. Thus, the SWCNT core 124 of the coaxial fiber 123 becomes segmented during loading, as shown in fig. 4B.

FIG. 6A depictsThe development of cracks in the coaxial fiber 123 under an optical microscope. Crack opening displacement L when the fiber is stretched_cAlmost linearly correlated with the applied strain (see fig. 6B), demonstrating the overall elastic properties of the fiber 123. As the applied strain increases from 0% to 250%, the resistance of fiber 123 increases from 142 Ω to 2.3M Ω. Cracks appeared perpendicular to the loading direction (< 50%) LD, then multiplied along the quasi-periodic network as the strain became larger (> 50%). The crack density 1/D was found to be 17mm^-1Much higher than previously found in studies on SWCNT cables or thin papers in PDMS substrates. Such a high crack density explains the increased stretchability of the fibers 123 during drawing and the linearity of the resistance response. The crack was almost completely recovered after unloading, with a small but observable opening (see right panel in fig. 6), compared to the initial state at 0% strain. The electrical resistance of the drawn fiber 123 was measured to be 1.5k Ω, ten times that of the original fiber. This is due to the unrecoverable conductive path in the SWCNT core, as shown in fig. 6A.

To use the fiber 123 in a strain sensor, the fiber needs to exhibit high stretchability, high GF, and high sensitivity. The change in resistance of the coaxial fiber 123 with strain of 0% to 250% has been studied. The resistance increases with strain. After unloading from 250% strain, 17mm^-1The segmented structure of coaxial fibers of high crack density can be used as a sensing component in a strain sensor. Repeated cycling tests on fibers at lower strains (0% to 100% strain) may be more representative of the strains encountered in practical applications (e.g., wearable electronics). After the first cycle test (0% to 100% strain), subsequent cycles overlap with minimal signs of hysteresis. FIG. 7A shows five cycles of strain from 0% to 100%, where Δ R/R₀Following a very reversible process, followed by a change in applied strain.

To determine the sensitivity of the fiber, the relative change in resistance with applied strain (Δ R/R) has been determined₀). The change in resistance of the coaxial fiber at 100% strain is Δ R/R₀340. The sensing performance of the fiber-based sensor is characterized byTwo linear regions with two slopes (0% to 5% applied strain, 0.99 linearity, and 20% to 100% applied strain, 0.98 linearity). These values reflect GF at different strain ranges: GF was 48 at 0% to 5% strain and 425 at 20% to 100% strain.

However, conventional metal gauges only have a GF of about 2.0 at strains of less than 5%. The GF was higher than the conventional fiber-based strain sensor, as shown in fig. 7B. Piezoresistive strain sensors are typically capable of achieving high GF or high tensile, but typically have hysteresis and nonlinearity. Experimental measurements show that the sensor using the fiber 123 has good durability and reproducibility, which is important for long-term use. The performance of the strain sensor remained repeatable after 3250 cycles of stretching and relaxation at 20% to 100% strain. Good repeatability of the sensors was confirmed when cycling through 1 to 5, 1000 to 1005, and 3000 to 3005.

To illustrate the sensing mechanism of a strain sensor made with coaxial fibers 123, the electrical impedance response of the fibers was characterized over a wide range of frequencies. Fig. 7C shows the frequency dependence of the modulus of the complex impedance (Z). At low strains (< 20%), the impedance is nearly constant over the tested frequency range, and the conduction mechanism is represented by the resistive properties of the SWCNTs in the core. The contact between the SWCNTs in the crack region ensures macroscopic ohmic behavior. At high strains (> 20%), the impedance Z becomes more frequency dependent. SWCNTs break more and more as strain continues to increase. Thus, conduction of electrons between segments 124A (see fig. 4B) of core 124 becomes impossible and the SWCNT-covered interface in the TPE jacket becomes the only conductive path. As a result, electron tunneling is the dominant conduction mechanism in the fiber 123, as shown by the frequency-dependent impedance curve in fig. 7C.

In fact, the capacitive response at high frequencies is due to this electron tunneling mechanism. These results indicate that the sensing mechanism is similar to that of SWCNT paper embedded in PDMS, where the SWCNT paper between PDMS layers and the CNT interface on PDMS act differently at different strain levels.

Fig. 7D shows an equivalent circuit model of the fiber 123 generated from Electrical Impedance Spectroscopy (EIS) results, which captures the behavior of the coaxial fiber at different strain levels. At low strains (< 20%), only the SWCNT core 124 is connected to the circuit, and its resistance increases with strain during stretching due to the opening of the crack 150 in the fiber 123 (see fig. 4B and 6). The interface 702 is used as a capacitor or an insulator. At high strains (> 20%), crack 150 grew wider until there was no SWCNT network connection between fiber segments 124A. At this stage, the SWCNT cracks 150 are considered open circuits. The resistance increases with strain due to the SWCNT interface 702 attached to the TPE jacket 122. Due to the electron tunneling effect, current flows through the capacitance, allowing greater charge movement. Eventually, the total capacitance of the coaxial fiber 123 is reduced.

To demonstrate the performance of the coaxial fibers 123 as deformable sensors 802, 114 cm long fibers 123 were attached to the back and front sides of a 70cm long deformable hollow cable 800 (see fig. 8A and 8B), which deformable hollow cable 800 may be processed into "strained", "S", and "round" shapes. The sensor 802 is attached to the cable 800 at various locations using tape and the restriction on cable movement is minimal. In the initial state, the metal rod 804 is inserted into the hollow cable 800 such that the strain on the coaxial fibers 123 is 0%. Initial resistance R of all sensors 802₀Is 200-300 omega (see figure 8C). Note that each sensor 802 has been individually connected to a measuring device for measuring current and/or voltage. After removal of the metal rod 804, the cable 800 is extended and the coaxial fibers 123 are in a "strained" state, as shown in fig. 9A and 9B. The electrical resistance of the fiber 123 increases corresponding to a strain of 10% (see fig. 9C). In a uniaxial "strained" state, sensors 802 on the back and front sides of cable 800 have similar Δ R/R₀This indicates that all sensors 802 experience the same level of strain.

By processing the cable 800 into "S" (see FIG. 10A) and "round" (see FIG. 10C) shapes, the fibers 123 on both sides are asymmetrically deformed, resulting in Δ R/R for curved inner and outer surfaces₀The significant difference between them, as shown in fig. 10B and 10D.Based on these measurements, the measurement can be performed by Δ R/R₀The 3D curve of coordinates to distinguish the shape (or state) of the cable 800 demonstrates that the coaxial fiber 123 can be used as a sensor 802 to detect and track complex motions of deformable objects. The same fiber may be attached to another type of object, such as a balloon, a moving part of a machine, or any area of a patient's hand or human body, and the resistance change of the sensor may be measured. A library of such measurements may be generated, and the computer may identify the shape or motion of the object to which the sensor is attached based on a comparison of the measured pattern and patterns stored in the library.

As shown in fig. 8A-10D, coaxial fiber 123 has demonstrated potential for use in wearable electronic devices for sensor/human-machine interface interaction. Thus, a coaxial wet spinning and post-treatment process for preparing coaxial fibers of thermoplastic elastomer-wrapped SWCNTs for high performance strain sensors is achievable and desirable. The method discussed with respect to fig. 3 is industrially feasible and is applicable to conductive nanomaterials that cannot be wet spun using previous methods. Coaxial fibers are highly stretchable and highly conductive. Due to the coating of the electrically insulating and highly stretchable thermoplastic elastomer, the coaxial fibers are strong enough to be used as stretchable interconnects and as deformable and wearable strain sensors. Strain sensors based on coaxial conductive fibres show several advantages: (1) it combines high sensitivity, high stretchability and high linearity; (2) the TPE sheath prevents short circuits and ensures safe operation of the device; (3) the fibers have proven to have potential for large-scale production; and (4) ease of integration into wearable textiles.

The coaxial fibers discussed above can find a wide range of applications in deformable and wearable electronic devices. The examples discussed above can be extended to other conductive materials, such as carbon nanomaterials, metal nanoparticles, and conductive polymers, providing another approach for next generation deformable and wearable devices.

The disclosed embodiments provide methods and mechanisms for generating fibers suitable for use in strain sensors. It should be understood that the description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a thorough understanding of the claimed invention. However, it will be understood by those skilled in the art that the embodiments may be practiced without these specific details.

Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are to be considered within the scope of the claims.

Reference to the literature

Kessens, c.c., Thomas, j., Desai, j.p. and Kumar, v. (2016) Versatile Aeral grading Using Self-Sealing summation. IEEE International Conference on robotics and Automation. IEEE, Stockholm.

Augugliaro, f., Lupashin, s., Hamer, m., Male, c., Hehn, m., Mueller, m.w., Willmann, j.s., Gramazio, f., Kohler, m, and D' Andrea, r. (2014) The flight assisted architecture with flying machines ieeecontrol Systems,34(4), 46-64.

Mellinger, D., Shomin, M., Michael, N. and Kumar, V. (2013). Cooperational and transport using multiple quadrotonic systems, 545-558. Springer.