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. 2023 Sep 11;3(5):394–405. doi: 10.1021/acspolymersau.3c00010

Highly Stretchable Stress–Strain Sensor from Elastomer Nanocomposites with Movable Cross-links and Ketjenblack

Ryohei Ikura †,‡, Kota Kajimoto †, Junsu Park †,‡, Shunsuke Murayama ⊥, Yusei Fujiwara #, Motofumi Osaki †,‡, Tomohiro Suzuki 7, Hidenori Shirakawa 7, Yujiro Kitamura 7, Hiroaki Takahashi 7, Yasumasa Ohashi 7, Seiji Obata ■, Akira Harada ∥, Yuka Ikemoto ↔, Yuta Nishina ■,▽,*, Yasutomo Uetsuji #,*, Go Matsuba ⊥,*, Yoshinori Takashima †,‡,§,*
PMCID: PMC10571104  PMID: 37841949

Abstract

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Practical applications like very thin stress–strain sensors require high strength, stretchability, and conductivity, simultaneously. One of the approaches is improving the toughness of the stress–strain sensing materials. Polymeric materials with movable cross-links in which the polymer chain penetrates the cavity of cyclodextrin (CD) demonstrate enhanced strength and stretchability, simultaneously. We designed two approaches that utilize elastomer nanocomposites with movable cross-links and carbon filler (ketjenblack, KB). One approach is mixing SC (a single movable cross-network material), a linear polymer (poly(ethyl acrylate), PEA), and KB to obtain their composite. The electrical resistance increases proportionally with tensile strain, leading to the application of this composite as a stress–strain sensor. The responses of this material are stable for over 100 loading and unloading cycles. The other approach is a composite made with KB and a movable cross-network elastomer for knitting dissimilar polymers (KP), where movable cross-links connect the CD-modified polystyrene (PSCD) and PEA. The obtained composite acts as a highly sensitive stress–strain sensor that exhibits an exponential increase in resistance with increasing tensile strain due to the polymer dethreading from the CD rings. The designed preparations of highly repeatable or highly responsive stress–strain sensors with good mechanical properties can help broaden their application in electrical devices.

Keywords: stress−strain sensor, carbon composite, movable cross-link, supramolecular materials, polymeric materials, tough materials, upcycling

Flexible stress–strain sensors have attracted considerable attention due to increasing demands for their application in wearable electronic devices,1−3 for structural health monitoring4,5 and human motion detection,6 and in soft robotics.7,8 The main strain sensing outputs are mechanochromism5,9−18 and electrical signals. The methods to transduce mechanical deformation into electrical signals include resistive change,19 piezoelectricity,20−24 triboelectricity,6,25 capacitive response,26−29 transistor,24,30,31 and macroscopic shape change.32−36 Traditional metallic and semiconducting stress–strain sensors show excellent sensitivity but low flexibility due to low fracture strain (<5%).37,38 Compositing polymeric and conductive materials (e.g., carbon black,39−44 carbon nanotubes,45−54 graphene,55−62 metal nanofillers,63−71 liquid metals,8,72 conductive polymers,73−75 MXenes,76 and ionic liquids77−79) is an effective method to achieve high stretchability. The types of stress–strain sensors that utilize the above composites mainly employ the resistive change caused by the disconnection of conductive paths. Practical applications like very thin stress–strain sensors require high strength, stretchability, and conductivity, simultaneously. To achieve them, one of the important approaches is improving the toughness of stress–strain sensing materials. However, it is usually difficult to improve the strength and stretchability of the general polymeric materials simultaneously.

Recently, a lot of effort has been put into overcoming issues mentioned above. Polymeric materials with high strength and stretchability have been designed via three approaches. One approach is the use of interpenetrating brittle and ductile networks.14,80−83 Another approach is the use of a reversible cross-linked network. Notably, these approaches are based on sacrificial bonds, which dissipate stress to prevent catastrophic crack propagation.84−96 The final approach is the use of a movable cross-linked network that disperses stress based on the mobility of cross-links along the axis of the polymers.97−110 This stress dispersion strategy results in high toughness.

Previously, we prepared elastomers with movable cross-links as stress dispersion units by the copolymerization of cyclodextrin (CD) and vinyl monomers.108,109 The vinyl chain polymers penetrated into the CD cavities to form movable cross-links, and the obtained elastomers showed a higher fracture stress and strain than those of covalently cross-linked elastomers.

We hypothesize that compositing these movable cross-linked elastomers and conductive materials by suitable methods will realize innovative stress–strain sensors with high strength, stretchability, electrical conductivity, and sensitivity. The stress–strain sensors constructed by a combination of hard and soft domains are expected to have excellent mechanical and electrical properties. On the basis of our hypothesis, we focus on the mechanical and electrical properties of composite materials with a carbon filler (ketjenblack, KB) and two types of movable cross-linked elastomers to realize high repeatability or sensitivity of strain sensing (Figure 1). One composite consists of SCP (single movable cross-network (SC) elastomer with a penetrating polymer) elastomers with KB and is obtained by ball-milling methods. The SCP composites consist of soft SC elastomer particles and hard networks of linear polymers with KB, abbreviated SC/PEA/KB. The other composite consists of movable cross-network elastomers for knitting dissimilar polymers (KP) with KB (PSCD⊃PEA/KB), where PEA polymers penetrate the CD-modified polystyrene, acting as the movable cross-links. The movable cross-links connect the hard and soft polymers to achieve high strength and stretchability.

Figure 1.

Figure 1

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Routes for two different material designs: KB-composited SCP elastomer (SC/PEA/KB) and KB-composited KP elastomer (PSCD⊃PEA/KB).

Experiment and Methods

Preparative details of the polymers and KB composites can be found in the Supporting Information. Methodological details of characterization of the polymers and KB composites by nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR), and Raman spectra, gel permeation chromatography (GPC), mechanical properties measurements, and electrical conductivity measurements (ultrasmall angle X-ray scattering (USAXS) measurement, small-angle X-ray scattering (SAXS) measurement, scanning electron microscopy (SEM)) can be found in the Supporting Information.

Results and Discussions

Preparation of the KB Composites (SC/PEA/KB(w) and PSCD⊃PEA/KB(w))

Figures 2a, 3a, and S3 show the chemical structures of the vinyl monomers, primary polymers, KP elastomers, SC elastomers, and polymer blends. Ethyl acrylate (EA), styrene (S), and N,N-dimethylacrylamide (DMAA) were employed as liquid vinyl monomers. The peracetylated γCD monomer (mono-6O-acrylamidomethyl-triicosaacetyl-γ-cyclodextrin, TAcγCDAAmMe) was solubilized in hydrophobic solvents. Ketjenblack (KB) was composited as a carbon filler.

Figure 2.

Figure 2

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(a) Chemical structures of SC/PEA(x), SC/PEA/KB(w), SC/KB(w), and PEA/KB(w). (b) Stress–strain curves of SC/PEA(x) (x = 0, 33, 50, and 63). (c) Plots of the energy at break and Young’s modulus values of SC/PEA/KB(10), PEA/KB(10), and SC/KB(10). (d) Stress–strain curves and (e) plots of the energy at break and wt % values of KB. (f) Cross-section SEM images of SC/PEA/KB(w) (w = 0, 2.5, 5.0, 7.5, 10, 12.5, and 15 wt %) at 1,000× magnification. (g) Plots of the conductivity and wt % of the KB in SC/PEA/KB(w) (w = 0, 2.5, 5.0, 7.5, 10, 12.5, and 15 wt %), PEA/KB(10), and SC/KB(10).

Figure 3.

Figure 3

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(a) Chemical structures of PSCD⊃PEA, PSCD⊃PEA/KB(w), PSCD/PEA/KB(w), and PEACD⊃PEA/KB(w). (b) Stress–strain curves of pristine and recycled PSCD⊃PEA. (c) Plots of the energy at break and Young’s modulus of PSCD⊃PEA/KB(10), PSCD/PEA/KB(10), and PEACD⊃PEA/KB(10). (d) Stress–strain curves of PSCD⊃PEA/KB(w) (w = 0, 5.0, 10, and 15 wt %). (e) Plots of the energy at break and wt % of KB. (f) SEM images at 10,000× magnification. (g) Plots of the conductivity and wt % of PSCD⊃PEA/KB(w) (w = 0, 5.0, 10, and 15 wt %).

Schemes S1 and S6 show the preparation of SC elastomers and linear polymer PEA. SC elastomers with permanent cross-links are not dissolved into solvents but are swollen to form organogels. SC/PEA/KB(w) (w is the wt % of KB) was obtained by mixing SC, linear polymer PEA, and KB with N-methyl pyrrolidone (NMP) using a ball-milling method (Schemes S7, S9, and S10; Tables S3 and S9). This method kinetically mixes the samples and zirconia balls through the use of severe shear stress during planetary movement. These balls crush the SC organogels, resulting in well-mixed slurries. After the NMP is removed, the obtained KB composites are abbreviated SC/PEA/KB(w). As control samples to investigate the properties derived from network structures, SC/PEA without KB, PEA/KB(w), and SC/KB(w) were also prepared by the ball-milling methods.

Schemes S2–S5 and Tables S1–S2 show the preparation of PSCD⊃PEA (KP elastomers) and PS/PEA (polymer blends as control samples). PSCD⊃PEA elastomers were dissolved into tetrahydrofuran (THF) to dethread the after-polymerized PEA chain (secondary polymer). Casting a THF suspension of KP elastomers and KB resulted in PSCD⊃PEA/KB(w), where w is wt % of KB (Scheme S8; Tables S4–S6). PSCD⊃PEA without KB and PS/PEA/KB(w) were also prepared in the same manner. The obtained materials were characterized by 1H NMR, 13C NMR, FT-IR, and Raman spectra (Figures S4–S33).

Mechanical Properties of SC/PEA

Prior to KB compositing, the mechanical properties of SC/PEA(x) elastomers were optimized by investigating polymer network structures with various wt % of PEA (x = 0, 33, 50, and 63 wt %). The mechanical properties of the SC/PEA(x) elastomers were evaluated by tensile tests (Figures 2b and S35), and energy at break was calculated from the integral of the stress–strain curve. As a result, the fracture strain increased with increasing x values. SC/PEA(33) and SC/PEA(50) showed clear fracture points, suggesting a network structure with physical cross-links based on entanglements with linear polymers penetrating the SC networks. The stress of SC/PEA(63) started decreasing over approximately 2,000% strain, indicating that the necking by the disentanglements of linear polymers dispersed the stress at high strain. SC/PEA(50) also showed the necking around 2,000% strain. Notably, SC/PEA(50) had a good balance between elasticity and stress dispersion to achieve the highest energy at break (17 ± 6 MJ·m–3). The cyclic tensile test of SC/PEA(50) shows the elasticity in low strain and stress-dispersion in high strain, allowing for improving the fracture strain and stress simultaneously (Figure S36). Hereinafter, the KB composite materials for stress–strain sensors were optimally prepared with 50 wt % linear polymers.

Mechanical Properties of SC/PEA/KB(w)

Figure 2c shows plots of the relation between the energy at break and Young’s modulus of SC/PEA/KB(10) and the control samples. PEA/KB(10) showed plastic deformation and low fracture stress due to the absence of cross-links (Figure S37 and S38). SC/KB(10) was not well mixed between the SC network and KB, leading to the lowest energy at break. On the other hand, SC/PEA/KB(10) exhibited clear fracture points and the highest energy at break (44 ± 5 MJ·m–3). These results indicated the presence of a network structure in SC/PEA/KB(10), resulting from entanglements between the SC networks and linear polymer. These structures contributed to improving the mechanical properties and mixabilities. This presumption was also supported by the plastic deformation and low energy at break of SC/PS/KB(10), where entanglements between the immiscible main chains (PEA and PS) could not form due to their low miscibility (<0.01 wt % of PEA in PS)111 (Figure S39).

Figure 2d shows the stress–strain curves of the SC/PEA/KB(w) composites with various KB content (w = 0, 2.5, 5.0, 7.5, 10, 12.5, and 15 wt %). The results can be divided into two tendencies. (i) At low wt % of KB (w = 0, 2.5, and 5.0), an increase in w resulted in higher fracture stresses and lower fracture strains. (ii) The other composites (w = 7.5, 10, 12.5, and 15 wt %) showed similar fracture stresses, whereas their fracture strains decreased with increasing w. The fracture stress of SC/PEA/KB(7.5) significantly increased to 2.4 ± 0.3 times that of SC/PEA/KB(5), yielding the highest energy at break (61 ± 9 MJ·m–3) (Figure 2e). These results suggested structural changes of KB aggregates around w = 7.5 wt %.

Scanning electron microscopy (SEM) was used to observe the morphology of KB in the composites (Figure 2f). As a result, fibril-like structures were observed from the composites with a high wt % of KB (w = 7.5, 10, 12.5, and 15 wt %). Considering the fibrillar structures increase with wt % of KB, the fibrillar structures seem to be the KB-rich domains with PEA. During the ball-milling, the KB-rich domains may be stretched to form the fibrillar structures. These results confirmed the structural change around w = 7.5 wt %, leading to a high fracture stress. In addition, long fibril-like structures (>3 μm) were observed from SC/PEA/KB(12.5) and SC/PEA/KB(15). This would contribute to the drastic increase in their Young’s moduli (Figure S38).112

Electrical Properties of SC/PEA/KB(w)

Figure 2g shows the relation between the electrical conductivity and w of SC/PEA/KB(w), SC/KB(10), and PEA/KB(10) by the four-point probe method. The conductivity of SC/PEA/KB(2.5) was too low to be measured (σ < 10–5 S·m–1), while the conductivity of SC/PEA/KB(5) suddenly increased to 0.05 S·m–1. Furthermore, the conductivities of SC/PEA/KB(w) (w = 5.0, 7.5, 10, 12.5, and 15 wt %) exponentially increased with w, indicating that the formation of conductive paths started at 2.5 < w < 5. The SEM images showed that the increase in w resulted in the growth of fibril-like structures rather than sea–island structures, allowing the exponential increase in conductivity. SC/PEA/KB(10) exhibited a 1.7 × 104-fold increase in the conductivity of SC/KB(10). Considering the conductivity of PEA/KB(10) is higher than that of SC/PEA/KB(10), the linear polymer in SC/PEA/KB(10) resulted in good mixing and high conductivity. USAXS profiles show the similar size of KB aggregations (30–300 nm) in SC/PEA/KB(10) and PEA/KB(10), indicating that PEA domains in SC/PEA/KB(10) give good mixability to achieve a high conductivity (Figure S43a). Consequently, the network structure with linear polymers penetrating the SC networks leads to materials for stress–strain sensors with high toughness and conductivity.

Recyclability of PSCD⊃PEA

PSCD⊃PEA/KB(w) composites were prepared by a casting method. When KP elastomers are dissolved in solvents, movable cross-links dissociate via the dethreading of secondary polymers from the TAcγCD unit. Notably, the GPC profiles of the PSCD⊃PEA solutions showed two peaks with a molecular weight order comparable to that of the (i) PS-CD primary polymers and (ii) PEA obtained by bulk polymerization (Figure S34; Tables S7 and S8). Therefore, it is necessary to ensure the reformation of movable cross-links through the removal of THF in casting methods.

Figure 3b shows the stress–strain curves of the pristine PSCD⊃PEA elastomers and recycled elastomers obtained by casting methods using THF. The pristine and recycled samples showed similar stress–strain curves, indicating the high recyclability of PSCD⊃PEA. The recycled PSCD⊃PEA showed a Young’s modulus of 87 ± 10% of that of pristine PSCD⊃PEA, showing the effective restoration of the cross-links. The 1H–1H Nuclear Overhauser effect spectroscopy (NOESY) NMR results of the recycled films revealed the reformation of movable cross-links (Figure S44). These results demonstrate the recyclability of PSCD⊃PEA based on the reformation of movable cross-links via the rethreading of secondary polymers. The recyclability enables the acquisition of KB composite materials by casting methods without impairing their cross-links and Young’s moduli.

Mechanical and Electrical Properties of PSCD⊃PEA/KB(w)

Figure 3c shows plots of the relation between the energy at break and Young’s modulus of PSCD⊃PEA/KB(10) and the control samples. The composite without cross-linked PS/PEA/KB(10) showed plastic deformation, low energy at break, and a rough surface due to phase separation based on the low miscibility of the PS and PEA main chains (Figure S38). The phase separation brings the heterogeneous distribution of KB, resulting in the rough surface. In contrast, PSCD⊃PEA/KB(10) showed clear fracture points, a smooth surface, a 30 ± 5-fold increase in energy at break, and a 2.4 ± 0.6-fold increase in the Young’s modulus of PS/PEA/KB(10), showing that the reformation of movable cross-links improved the mechanical properties and mixability.

Interestingly, PSCD⊃PEA/KB(10) exhibited a 7.4 ± 1.3-fold increase in energy at break and a 9.1 ± 2.2-fold increase in the fracture strain of PEACD⊃PEA/KB(10) with PEA as the primary polymer. Contrary to PSCD⊃PEA/KB(10), PEACD⊃PEA/KB(10) showed a rough surface. These results indicated that PS polymers contributed to the improvement in the mechanical properties and mixability. The USAXS profile of PEACD⊃PEA/KB(10) showed high intensity, indicating high heterogeneity due to poor mixability. However, USAXS profiles of PSCD⊃PEA/KB(10) and PS/PEA/KB(10) exhibit the peak of dispersed KB monoparticles (30 nm), supporting that PS polymers give good mixability (Figure S43b).

Figure 3d shows the stress–strain curves of the PSCD⊃PEA/KB(w) composites with various wt % of KB (w = 0, 5.0, 10, and 15 wt %). PSCD⊃PEA/KB(5) and PSCD⊃PEA/KB(10) showed higher fracture stress and lower fracture strain than PSCD⊃PEA without KB. From w = 0–10 wt %, an increase in w resulted in a similar energy at break but higher Young’s modulus (Figures 3e and S39). Notably, PSCD⊃PEA/KB(15) showed a rough surface with the smallest fracture stress and strain. In addition, the Young’s modulus of PSCD⊃PEA/KB(15) was smaller than that of PSCD⊃PEA/KB(10), indicating that the association between the matrix polymers and KB did not work well.

Figure 3g shows the relation between the electrical conductivity and w of PSCD⊃PEA/KB(w). From w = 0–10 wt %, the increase in w resulted in a drastic increase in electrical conductivity. However, PSCD⊃PEA/KB(15) exhibited a moderate increase. These results suggested structural changes between w = 10 and 15 wt %. In the SEM images of PSCD⊃PEA/KB(5) and PSCD⊃PEA/KB(10), many dispersed KB domains were observed on the surface (Figure 3f). These dispersed KB domains improved the fracture stress and Young’s modulus without lowering the energy at break. However, PSCD⊃PEA/KB(15) showed aggregated structures, resulting in poor mechanical properties. Consequently, PSCD⊃PEA/KB(10) is a good candidate for stress–strain sensors with high energy at break, Young’s modulus, and conductivity.

Electrical Properties upon Deformation and Application for Stress–Strain Sensors

To investigate the potential for the application of stress–strain sensors, real-time measurements of the electrical conductivity of each KB composite upon tensile deformation were performed using the circuit shown in Figure 4a and S45. The resistances of the KB composite (R) were measured and calculated with Equation 1, where Vout is the voltage at junction between the 50 kΩ resistor and the KB composites. All the voltage was measured using ground in the circuit as reference (0 V).

graphic file with name lg3c00010_m001.jpg 1

Figure 4.

Figure 4

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(a) Circuit for real-time electrical conductivity measurements of the KB composites upon tensile deformation. ΔR/R0 values of (b) SC/PEA/KB(10) and (c) PSCD⊃PEA/KB(10) upon tensile deformation. ΔR/R0 of (d) SC/PEA/KB(10) and (e) PSCD⊃PEA/KB(10) during 100 stretch-release cycles at 100% strain. (f) Photographs of the stress–strain sensing and remote actuating system are from Movie S1. This system was designed so that the servomotor operated in response to changes in the resistance of PSCD⊃PEA/KB(10) attached to a finger. (g) Changes in the resistance of PSCD⊃PEA/KB(10) by finger movements. The blue ginkgo logo in Figure 4f is the symbol of Osaka University. The logo is a copyright and has been licensed for use by Osaka University.

The relative changes in the resistance (ΔR/R0) were obtained with Equation 2, where R0 is the initial resistance before deformation.

graphic file with name lg3c00010_m002.jpg 2

Figure 4b shows the ΔR/R0 of SC/PEA/KB(10) upon stretching. The ΔR/R0 of SC/PEA/KB(10) proportionally increased with increasing strain. The gauge factor (GF) was 1.6 in the whole sensing range (Figure S46a). Figure 4d shows the ΔR/R0 of SC/PEA/KB(10) during 100 stretch-release cycles at 100% strain for a durability test. After several cycles, SC/PEA/KB(10) showed stable responses and repeatability as a stress–strain sensor. These results suggested that smaller structural changes occurred with tensile deformation. On the other hand, the ΔR/R0 of PSCD⊃PEA/KB(10) showed a large increase when stretched (Figure 4c). PSCD⊃PEA/KB(10) showed a 2.6-fold greater GF of SC/PEA/KB(10) at low strain ε = 0–20% (Figure S46b). Furthermore, GF increased with ε, reaching GF = 180 at ε = 100–120% (Figure S46c–e). After 100 stretch–release cycles, PSCD⊃PEA/KB(10) showed an increase in its ΔR/R0 and approached stable responses. These results suggested that the high sensitivity was caused by stress-induced structural changes (Figure 4e).

The high sensitivity of PSCD⊃PEA/KB(10) allows for its application as a stress–strain sensor and a remote actuator. The stress–strain sensing and remote actuating system was designed so that the servomotor operated in response to changes in the resistance of the KB composites attached to a finger (Figure 4f). When the finger was bent, the KB composite materials were stretched, causing an increase in resistance and lowering of the flag. When the finger was straightened, the strain was released, causing a decrease in the resistance and raising of the flag. Movie S1 demonstrates the successful control of flag movement according to finger movements and subsequent changes in resistance (Figure 4g). The three responses in 1–4 s indicate the small response time (Figure S46f), enabling the stress–strain sensing and remote actuating system.

Investigation of Strain-Sensing Mechanism by SAXS Measurements upon Tensile Deformation

To reveal the strain-sensing mechanism, SAXS measurements were performed upon tensile deformation. The profiles in the tensile and perpendicular directions were obtained from the scattering patterns at various strains (ε = 0%, 40%, 80%, 120%, 160%, and 200% strain). Whereas SC/PEA showed streaklike scattering in its SAXS profile, SC/PEA/KB(10) showed almost no change in its SAXS profile (Figure S47). These results indicated that the stable KB network structures suppressed the orientation of the polymer chain, resulting in stable and repeatable strain sensing of SC/PEA/KB(10) (Figure 5a).

Figure 5.

Figure 5

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Proposed structures of (a) SC/PEA/KB(10) and (b) PSCD⊃PEA/KB(10).

In contrast, the intensities of PSCD⊃PEA/KB(10) in both directions increased through deformation, showing strain-induced phase separation (Figure S48). The orientation of PSCD⊃PEA/KB(10) was also observed from the higher intensity in the perpendicular direction at high ε. PSCD⊃PEA without KB also showed similar tendencies, indicating that the dethreading of the PEA secondary polymer contributed to the phase separation and orientation. Before deformation, PSCD⊃PEA/KB(10) had a peak at 30 nm corresponding to the diameter of the dispersed KB monoparticles. This peak decreased due to deformation and disappeared at ε = 80% strain, thereby showing the aggregation of KB. Consequently, the high sensitivity of PSCD⊃PEA/KB(10) was caused by strain-induced phase separation and KB aggregation (Figure 5b). Consequently, SAXS measurements revealed the relation between stress–strain sensing properties and the dynamics of polymer domains and KB aggregations.

Conclusion

We designed two kinds of nanocomposite materials with KB and movable cross-linked elastomers to achieve high toughness, high conductivity, and strain-sensing functions. One is SC/PEA/KB(w), which is obtained by mixing an SC elastomer, a linear polymer, and KB. The network structure consisting of linear polymers penetrating the SC network results in the high strength, stretchability, and conductivity of the material. The electrical resistance increases proportionally to the tensile strain, allowing for the application of this material as a stress–strain sensor. The responses of this material are stable for over 100 loading and unloading cycles. The other composite material is PSCD⊃PEA/KB(w), which is obtained by casting methods with high recyclability of the KP elastomer. The PS polymer and movable cross-links improve the mixability of KB to obtain a material with high strength, stretchability, and conductivity. PSCD⊃PEA/KB(w) can act as a highly sensitive stress–strain sensor due to its exponential increase in resistance with tensile strain. The high sensitivity of this material is derived from strain-induced phase separation and KB aggregation via dethreading of the polymer from CD rings. These network structures achieve highly stable and sensitive stress–strain sensors with excellent toughness, enabling very thin electrical devices to broaden their applications.

Acknowledgments

This research was funded by a Grant-in-Aid for Scientific Research on Innovative Area JP19H05714, JP19H05721, JP22H04548, and JP19H05717 from MEXT of Japan, the Kao Foundation for Arts and Sciences, and the Yazaki Memorial Foundation for Science. This work was also supported by JST, CREST Grant Number JPMJCR22L4, Japan. The authors appreciate Prof. Sadahito Aoshima and Prof. Arihiro Kanazawa (Graduate School of Science, Osaka University) for their support with the GPC measurements. The authors would like to thank the Analytical Instrument Faculty of the Graduate School of Science, Osaka University, for their support with the NMR, FT-IR, and TGA measurements. The authors also appreciate Mr. Ryuji Takata (Okayama University) for his support with electrical conductivity measurements. The authors would like to thank Dr. Keiichi Osaka and Dr. Noboru Ohta (SPring-8, JASRI) for the synchrotron radiation scattering measurements. The synchrotron radiation experiments were performed at BL19B2 (Proposal 2022B0578), BL40B2 (Proposal No. 2021A1593), and BL43IR (Proposal No. 2021A1608) of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acspolymersau.3c00010.

  • Additional experimental details, materials, and methods, including photographs of experimental setup (PDF)

  • Movie for the demonstration of stress–strain sensor (MP4)

Author Contributions

Ryohei Ikura: Writing – Original Draft (lead), Investigation (equal), Methodology (supporting); Kota Kajimoto: Investigation (equal), Writing – Original Draft (supporting); Junsu Park Methodology (supporting), Writing – Review & Editing (supporting); Shunsuke Murayama: Formal analysis (supporting); Yusei Fujiwara: Formal analysis (supporting); Motofumi Osaki: Methodology (supporting), Writing – Review & Editing (supporting); Tomohiro Suzuki: Resources (supporting); Hidenori Shirakawa: Resources (supporting); Yujiro Kitamura: Resources (supporting); Hiroaki Takahashi: Resources (supporting); Yasumasa Ohashi: Resources (lead); Seiji Obata: Formal analysis (supporting); Akira Harada: Writing – Review & Editing (supporting); Yuka Ikemoto: Formal analysis (equal), Writing – Review & Editing (supporting); Yuta Nishina: Formal analysis (equal), Writing – Review & Editing (supporting); Yasutomo Uetsuji: Formal analysis (equal), Writing – Review & Editing (supporting); Go Matsuba: Formal analysis (equal), Writing – Review & Editing (supporting); Yoshinori Takashima: Conceptualization (lead), Methodology (lead), Writing – Review & Editing (lead), Supervision (lead), Project administration (lead). CRediT: Ryohei Ikura investigation, methodology, writing-original draft; Kota Kajimoto investigation, methodology, writing-original draft; Junsu Park methodology, writing-review & editing; Shunsuke Murayama formal analysis; Yusei Fujiwara formal analysis; Motofumi Osaki methodology, writing-review & editing; Tomohiro Suzuki resources; Hidenori Shirakawa resources; Yujiro Kitamura resources; Hiroaki Takahashi resources; Yasumasa Ohashi resources; Seiji Obata formal analysis; Akira Harada writing-review & editing; Yuka Ikemoto formal analysis, writing-review & editing; Yuta Nishina formal analysis, writing-review & editing; Yasutomo Uetsuji formal analysis, writing-review & editing; Go Matsuba formal analysis, writing-review & editing; Yoshinori Takashima conceptualization, methodology, project administration, supervision, writing-review & editing.

The authors declare no competing financial interest.

Supplementary Material

lg3c00010_si_001.pdf (9.2MB, pdf)
lg3c00010_si_002.mp4 (9.8MB, mp4)

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