Flexible Conductive Composites Research Articles

Construction of polyurethane composites incorporating borate ester and B-N coordinative bonds: Achieving ultra-high fracture energy, self-healing property, and facile recyclability for wearable sensors

In recent years, there has been a notable surge in research focusing on the utilization of polyurethane (PU) in flexible wearable electronic devices. Consequently, it is essential to incorporate attributes such as high stretch, self-healing, and easy recyclability into PU. However, the suboptimal compatibility of PU with conductive fillers poses a significant challenge. This paper details the synthesis of a highly stretchable, self-healing, and easily recyclable PU elastomer, utilizing borate ester bonds and B-N mating bonds as the composite matrix. Highly conductive flexible composites were fabricated, employing multi-walled carbon nanotubes (CNTs) and graphene nanosheets (GNSs) as fillers. These composites exhibit excellent fracture energy, self-healing ability, and tensile strength due to the synergistic interaction of borate bonds, B-N ligand bonds, and hydrogen bonds. The fracture energy achieves an impressive 109.4 KJ·m−2, with a noteworthy 79% self-healing efficiency. Furthermore, the materials demonstrate mechanical properties, including a tensile strength of 66.5 MPa and an exceptionally high elongation at break of 2792%. The flexible conductive composites present high electrical conductivity (6.86 S/m) and sensitivity (GF：9.45). In its capacity as a flexible conductive composite, it can accurately detect human behaviors, such as finger flexion, facial expressions, throat articulation tests, and more. Therefore, it has potential applications in various fields, including wearables, robotic skin, and health monitoring.

Ternary Liquid Metal Polymer Composite for Stretchable Electronics

AbstractThe small strain characteristics of the traditional flexible conductive composites hinder their realization of skin‐like properties and multi‐scenario applications. The value of liquid metal (LM)‐based elastomers is demonstrated in flexible electronics. Attempts in this area include the development of multifunctional LM‐based elastomers with controllable morphology, superior mechanical performances, and excellent stability. In this work, an efficient strategy is proposed to achieve the fast preparation of the LM patch by uniformly distributing eutectic gallium–indium–tin alloy in deionized water and by constructing the LM‐iron particles‐Ecoflex (LMIE) ternary composite system. In this study, the fabricated LMIE large strain sensor exhibits high sensitivity (the gage factor (GF) = 0.98 when strain ranges from 0% to 60%; GF = 1.91 when strain ranges from 60% to 100%), high linearity (correlation coefficient (R2) = 0.96 when strain ranges from 0% to 60%; R2 = 0.99 when strain ranges from 60% to 100%), a wide strain range of detection (e.g., 1%–100%) and breaking elongation (e.g., 450%), a fast response time (80 ms), excellent repeatability and stability. This work exhibits the excellent potential of multifunctional liquid metal composites in wearable electronics and prediction devices of structural collapse.

A synergistic effect of MXene/MWCNT enables self-healable and low percolation elastomer sensor: A combined experiment and all-atom molecular dynamics simulation

Flexible conductive composites have garnered significant interest as wearable strain sensors due to their potential in diverse application fields, such as next-generation robotics automation, electronic skin, and human body detection. Nevertheless, the practical usage scenarios often entail tear and fracture, posing a persistent challenge to their performance stability. Consequently, there exists a pressing demand to engineer conductive composites that not only exhibit flexibility, stretchability, and sensing capabilities but also demonstrate effective self-healing properties. This pursuit presents a formidable task, considering the complex requirements imposed on the materials. This study presents a novel methodology for fabricating a conductive silicone elastomer composite. The approach involves the initial utilization of an excess of amino-capped Polydimethylsiloxane (PDMS) to undergo a reaction with Toluene diisocyanate (TDI) and Isoflurane diisocyanate (IPDI), leading to the formation of amino-capped polyurea (TPU). Subsequently, the self-healing elastomer IPDI/TDI/TA (ITT) is synthesized through chain expansion with Terephthalaldehyde (TA) in tetrahydrofuran (THF). To complement the experimental investigations, all-atom molecular dynamics (AAMD) simulations are employed to develop a comprehensive model elucidating the mechanical characteristics and self-healing capabilities of the elastomers. To introduce hybrid fillers into the elastomer composite, MXenes are electrostatically modified with L-glutamine (negatively charged), while multi-walled carbon nanotubes (MWCNTs) are modified with cetyltrimethylammonium bromide (positively charged). These modified fillers self-assemble in water and are subsequently combined with the aforementioned rubber THF solution after drying. Through ultrasonication and drying, the ITT elastomers/MXene/MWCNT composite is successfully prepared. The formation of hydrogen bonds and dynamic imine bonds is verified using FT-IR and AAMD simulations. By maintaining a fixed ratio of TA to PDMS, we observe a positive correlation between TDI concentration and the fracture strength of the ITT elastomer, while the elongation at break decreases with increasing TDI. Furthermore, the successful modification of MXene and MWCNT is confirmed through FT-IR, XRD, and zeta potential measurements, and the resulting composites exhibit significant electrical conductivity and self-healing properties. Tensile and electrochemical measurements demonstrate that the composite possesses promising characteristics suitable for sensor applications, and its mechanical and electrical properties can recover after self-healing. Notably, the resulting composites exhibit a very low conductivity threshold (3.5 wt%). The composite system exhibits desirable tensile properties and efficient self-healing ability due to the reversibility of multiple hydrogen and imine bonds. Overall, this study aims to introduce a novel elastomer-based composite that possesses excellent properties in terms of self-healing, stretchability, sensing capability and flexibility.

Flexible Perfluoropolyethers-Functionalized CNTs-Based UHMWPE Composites: A Study on Hydrogen Evolution, Conductivity and Thermal Stability.

Flexible conductive composites based on ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNTs) modified by perfluoropolyethers (PFPEs) were produced. The bonding of PFPE chains, added in 1:1 and 2:1 weight ratios, on CNTs influences the dispersion of nanotubes in the UHMWPE matrix due to the non-polar nature of the polymer, facilitating the formation of nanofillers-rich conductive pathways and improving composites’ electrical conductivity (two to five orders of magnitude more) in comparison to UHMWPE-based nanocomposites obtained with pristine CNTs. Electrochemical atomic force microscopy (EC-AFM) was used to evaluate the morphological changes during cyclic voltammetry (CV). The decrease of the overpotential for hydrogen oxidation peaks in samples containing PFPE-functionalized CNTs and hydrogen production (approximately −1.0 V vs. SHE) suggests that these samples could find application in fuel cell technology as well as in hydrogen storage devices. Carbon black-containing composites were prepared for comparative study with CNTs containing nanocomposites.

Green Manufacturing of Flexible Sensors with a Giant Gauge Factor: Bridging Effect of CNT and Electric Field Enhancement at the Percolation Threshold.

Toxic organic solvents are commonly used to disperse nanomaterials in the manufacturing of flexible conductive composites (e.g., graphene-PDMS). The dry-blended method avoids toxic organic solvent usage but leads to poor performance. Here, we proposed an innovative manufacturing method by adapting the traditional dry-blended method, including two key steps: minor CNT bridging and high-frequency electric field enhancement at the percolation threshold of graphene-PDMS. Significant improvement was achieved in the electrical conductivity (1528 times), the giant gauge factor (>8767.54), and the piezoresistive strain range (30 times) over the traditional dry-blended method. Further applications in measurements of culturing rat neonatal cardiomyocytes and mouse hearts proved that the proposed method has great potential for the manufacturing of nontoxic flexible sensors.

Synthesize and characterization of sustainable natural fibers/ conductive polymer composites

This work aims to obtain reinforced composites of natural fibers that obtained from their agricultural wastes of and conductive polymers to develop an innovation and alternative materials. By the use of natural fibers contributes to the recycle of agricultural wastes, sustainability and further the resulting composite becomes alternative to the metals. Here, flexible conductive composites were obtained from artichoke(A), banana(B) and luffa(L) stem waste fibers(F) by the in-situ polymerization of 3,4-ethylene dioxythiophene (EDOT), pyrrole, and carbazole in the presence of cerium ammonium nitrate, iron nitrate, and iron chloride. Fibers were coated with the conductive polymers mentioned above by the in-situ chemical(C) polymerization and optimum coating conditions were investigated. Effect of EDOT concentration, oxidant concentration was performed to determine the optimum conditions for AF/PEDOT(C). FT-IR, SEM, thermal analysis supported the formation of composite and from the mechanical measurements, modulus of AF/PEDOT(C) was obtained. The highest conductivity of 12.8 S/cm was obtained from AF/PEDOT(C) composite using FeCl3 as an oxidant. Further polymerization of EDOT by electrochemical(E) method was continued on the AF/PEDOT(C) and the electroactivity of resulting electrochemical composite, AF/PEDOT(C)/PEDOT(E) was characterized accordingly. Detailed characterization showed that to use of this composite as a capacitor, one should use 0.03 M EDOT and 0.9 M FeCl3 for chemical polymerization and then continued by electropolymerization by applying 10 cycles in 0.03 M EDOT. All results showed that AF waste could be converted to the valuable AF/PEDOT(C)/PEDOT(E) conductive composites which is potentially suitable material for several electronic applications as charge storage, biosensor, electronic devices.

Improved Sensitivity of Flexible Conductive Composites Throughout the Working Strain Range Based on Bioinspired Strain Redistribution

Improved Sensitivity of Flexible Conductive Composites Throughout the Working Strain Range Based on Bioinspired Strain Redistribution

Fabrication of Conductive Polymer Composites from Turkish Hemp-Derived Carbon Fibers and Thermoplastic Elastomers

In this study, carbon fibers filled flexible conductive polymer composites were fabricated. Turkish hemp was used to produce conductive carbon fibers. In order to do this, hemp fibers were carbonized under different conditions. After this step, flexible conductive composites were fabricated by using poly[styrene-b-(ethylene-co-butylene)-b-styrene] matrix and hemp-based carbon fibers. Composite films were produced by combination of solvent casting and hot pressing. Various levels of carbon fibers were used in order to determine the percolation behavior of the composites. Morphological and electrical properties of the composite films were analyzed. Electrical resistivity of the samples decreased by increasing the filler ratio.

Self-Healing Ti3C2 MXene/PDMS Supramolecular Elastomers Based on Small Biomolecules Modification for Wearable Sensors.

Flexible conductive composites can be used as wearable strain sensors, which are widely used in the fields of new-generation robotics, electronic skin, and human detection. However, how to make conductive composites that simultaneously possess flexibility, stretchability, self-healing, and sensing capability is challenging research. In this work, we innovatively designed and prepared a silicone polymer conductive composite. MXenes and amino poly(dimethylsiloxane) were modified by small biomolecules via an esterification reaction and a Schiff base reaction, respectively. The modified MXenes are uniformly dispersed, which endows the composite with good electrical conductivity. The reversibility of multiple hydrogen bonds and imine bonds in the composite system makes it have ideal tensile properties and high-efficiency self-healing ability without external stimulation. The conductive composite containing 10 wt % A-MXenes showed an elongation of 81%, and its mechanical strength could reach 1.81 MPa. After repair, the tensile properties and the electrical conductivity could be restored to 98.4 and 97.6%, respectively. In addition, the conductive composite is further evaluated for the value of wearable strain sensors. Even after cut-healed processes, the conductive composite can still accurately detect tiny human movements (including speaking, swallowing, and pressing). This kind of self-healing MXene/PDMS elastomers based on the modification of small biomolecules has great potential as wearable strain sensors. This simple preparation method provides guidance for future multifunctional flexible electronic materials.

Bioinspired design of flexible strain sensor with high performance based on gradient filler distributions

Inspired by nature, nanocarbon black (nCB) was diffused into swollen polydimethylsiloxane (PDMS) to obtain flexible conductive composites, forming a gradient distribution morphology. The nCB was enriched in the surface layers and its loading decreased in the inner region and the distribution process was theoretically calculated. The mechanical properties of PDMS/nCB composites were close to those of pure PDMS due to the gradient nCB distribution, and the surface of PDMS/nCB presented super-hydrophobicity resulted from the rough surface, even under strains. The composite started to be conductive at only 0.8 wt% nCB and it could work at a strain of 355% and had gauge factor of 343 with 6.2 wt% CB loading. The resistance of the composites against strain was explained theoretically using models based on the constriction and tunneling effects. These results indicate that composites with gradient filler distribution are excellent candidates for use as flexible strain sensors with high performance.

Influence of the filler dimensionality on the electrical, mechanical and electromagnetic shielding properties of isoprene rubber-based flexible conductive composites

Rubber-based conductive polymer composites are deformable and flexible, which have been demonstrated tremendous applications in electromagnetic interference (EMI) shielding materials. Here, we filled different dimensional carbonaceous fillers, including zero-dimensional carbon black (0D CB), one-dimensional carbon nanotubes (1D CNTs), two-dimensional graphene (2D GP), and their combinations, into isoprene rubber (IR) to fabricate the flexible EMI shielding composites. Both the electrical, mechanical, and EMI shielding properties were investigated. It was found that the EMI shielding properties of IR-based composites mainly dominated by the microwave absorption consumption. Since 1D CNTs possess the highest EMI shielding effectiveness for absorption, IR/CNTs composites exhibit the best electromagnetic interference shielding properties compared to other carbonaceous nanoparticles filled composites. Moreover, partially replacing CNTs with CB particles to fabricate hybrid IR/CB/CNTs composite is an effective route to improve the electrical properties and lower the cost of the composites. However, it is found that hybrid IR/CB/CNTs composite has a lower EMI shielding effectiveness than IR/CNTs composites, indicating that EMI shielding properties depend on a lot more than just the electrical conductivity of the resulting composites. Nevertheless, based on comprehensive consideration of cost, electrical, mechanical and EMI shielding properties of the composites, it is still an effective way to design the high-performance EMI shielding materials via the combination of different dimensional fillers.

Highly Conductive and Stretchable Ag Nanodendrite-Based Composites for Application in Nanoelectronics

Stretchable flexible conductive composites have received considerable attention recently. In this study, highly conductive and stretchable composites were synthesized using Ag microflakes (AgMFs), ...

Preparation and Research Progress of Polymer-based Flexible Conductive Composites

The development of flexible wearable electronic devices is one of the future directions of technology development. Flexible conductive materials are important supporting materials for wearable electronic devices. Polymer has excellent flexibility, it is an important way to prepare flexible conductor from polymer-based conductive composites. In this paper, the research progress of polymer-based flexible conductive composites is summarized from the aspects of preparation and characterization methods. The key factors to realize flexible conductor are put forward, namely, the maintenance of excellent polymer elasticity and the realization of stable. The design and preparation of the extensible conductor with high elasticity matrix and nanofiller are introduced in detail, and the problems in the current research are summarized.

Li-Storage Performances of Liquid-Phase Exfoliated Two-Dimensional Gallium Sulfide Nanosheets/Single-Walled Carbon Nanotubes Composite

The two-dimensional nanosheets (2D NS) of layered metal chalcogenide (MC) evoke huge research attention in lithium-ion battery (LiB). Nevertheless, their undesirable electrical conductivity and complicated synthesis procedures negatively the prospects of these NS as a competive LiB electrode material. To this end, we have developed facile, scalable approach, liquid-phase exfoliation (LPE)/filtration, to produce binder-free GaS NS/SWCNT flexible conductive composite for LiB. The uniform GaS NS/SWCNT composite possesses several advantages at the same time: (i) The open channels in the nanostructure result in faster Li+ diffusion. (ii) The entangled SWCNT network forms developed electron transport paths, lowering the junction resistance. (iii) SWCNT could function as the “conductive binder”, maintaining the structural integrity of the thick electrode without losing electrical contact with the current collector. The resultant GaS NS/SWCNT composite exhibited excellent rate capability, high specific capacity (838 mAh g-1) and a remarkably high utilization of GaS NS (1161 mAh g-1), demonstrating electrochemical performances competitive with those of other reported 2D MC-based electrode systems. This work opens up vast opportunities for other families of MC NS to be scalably processed into porous, binder-free, flexible conductive thin films and composites with a broad range of applications.

Synergistic effects of two types of ionic liquids on the dispersion of multiwalled carbon nanotubes in ethylene-vinyl acetate elastomer: preparation and characterization of flexible conductive composites

Flexible conductive composites based on an elastomer, ethylene-vinyl acetate copolymer (EVM), and multiwalled carbon nanotubes (MWCNTs) were fabricated by melt-blending and subsequent crosslinking. Two types of ionic liquids, tributylmethylammoniu bis(trifluoromethanesulfonyl)imide and 1-ehtyl-3-methylimidazolium tetrafluoroborate, have been used to modify MWCNTs for the purpose to improve the dispersion of MWCNTs in the polymer matrix. It was found that the MWCNTs modified by the individual IL form agglomerates in the EVM matrix, while the MWCNTs modified by the two types of ILs simultaneously disperse in the EVM matrix homogeneously. Moreover, the nanocomposites based the MWCNTs modified by the combination of the two ILs exhibit improved mechanical and electrical properties. The mechanism of such synergistic effects has been investigated. It was found that EVM is miscible with tributylmethylammoniu bis(trifluoromethanesulfonyl)imide and it is immiscible with 1-ehtyl-3-methylimidazolium tetrafluoroborate. On the other hand, MWCNTs show higher interaction with 1-ehtyl-3-methylimidazolium tetrafluoroborate than tributylmethylammoniu bis(trifluoromethanesulfonyl)imide. Therefore, the uniform dispersion of MWCNTs in EVM matrix is attributed to the “bridging” effects by the two ILs due to the different interactions of the two ILs with MWCNTs and EVM. The application by two types of ILs modified MWCNTs in polymer matrix opens a new fabrication strategy for high performance polymer nanocomposites.

The effect of filler dimensionality on the electromechanical performance of polydimethylsiloxane based conductive nanocomposites for flexible strain sensors

Flexible and wearable strain sensors based on conductive polymer composites (CPCs) for human motion detection have been highlighted recently. Herein, two flexible conductive composites were fabricated by mixing matrix polydimethylsiloxane (PDMS) with zero-dimensional conductive filler carbon black (CB) and one-dimensional carbon nanotubes (CNTs), respectively. A low percolation threshold of CB/PDMS (0.48 vol%) was achieved, while this value was higher than that of CNTs/PDMS (0.13 vol%). In strain-dependent response tests, compared with CNTs/PDMS with a gauge factor (GF) of 4.36 (a strain of 10%), CB/PDMS composites showed a higher sensitivity with a larger GF of 15.75 (a strain of 10%). A good reproducibility was obtained in stretching-releasing process for the two composites. In long-term cyclic test, CB/PDMS showed more stable sensing behaviors, while a slight drifting and fluctuation was observed for CNTs/PDMS. Generally, two composites both possessed satisfactory durability. Mathematical models were proposed to explain the mechanism of the distinct strain sensing behaviors. A smart glove was assembled to monitor the finger motion to evaluate the application of the two composites as flexible strain sensors.