Conductive Elastomer Composites Research Articles

Thermally Conductive Elastomer Composites with High Toughness, Softness, and Resilience Enabled by Regulating Interfacial Structure and Dynamics.

The emerging applications of thermally conductive elastomer composites in modern electronic devices for heat dissipation require them to maintain both high toughness and resilience under thermomechanical stresses. However, such a combination of thermal conductivity and desired mechanical characteristics is extremely challenging to achieve in elastomer composites. Here this long-standing mismatch is resolved via regulating interfacial structure and dynamics response. This regulation is realized both by tuning the molecular weight of the dangling chains in the polymer networks and by silane grafting of the fillers, thereby creating a broad dynamic-gradient interfacial region comprising of entanglements. These entanglements can provide the slipping topological constraint that allows for tension equalization between and along the chains, while also tightening into rigid knots to prevent chain disentanglement upon stretching. Combined with ultrahigh loading of aluminum-fillers (90 wt%), this design provides a low Young's modulus (350.0kPa), high fracture toughness (831.5 J m-2), excellent resilience (79%) and enhanced thermal conductivity (3.20 W m-1 k-1). This work presents a generalizable preparation strategy toward engineering soft, tough, and resilient high-filled elastomer composites, suitable for complex environments, such as automotive electronics, and wearable devices.

Linear Strain Sensors via a Spatial Heteromodulus Tricontinuous Structure Design for High-Resolution Recording of Snoring Breath.

Porous conductive elastomer composites are very attractive for designing flexible and air-permeable mechanical sensors for healthcare, while it is challenging to achieve a linear and sensitive electromechanical response over a wide strain range for high-resolution recording of physiological activities and body motions. Here, a scalable strategy is developed to construct porous elastomer composites with a bamboo-shaped heteromodulus microstructure in the pores for the fabrication of linear stretchable strain sensors. Such a spatial heteromodulus microstructure is fabricated via phase separation and selective location of high-modulus phase during melt compounding of elastomers and thermoplastics, together with green etching of the water-soluble plastic in the tricontinuous elastomer composites. The bamboo-shaped heteromodulus microstructure is constructed on the pore struts via the fracture of a high-modulus polymer self-assembled on the pore surface and relaxation recovery of the elastomer matrix after prestretching, which blocks the propagation of cut-through microcracks upon stretching. The composites with super low resistance after in situ growth of silver nanoparticles sustain up to 110% tensile strain with a linear and sensitive electromechanical response, demonstrating potential applications in discriminating respiration status and monitoring snoring breath. This work unveils a new approach to fabricate high-performance air-permeable strain sensors in a simple and scalable way.

A sparse-dense hierarchical structured conductive elastomer composites for highly sensitive and stretchable strain sensor

Flexible strain sensor using conductive elastomer (CE) have fostered hope for the development of healthcare, human–machine interfaces, and soft robotics technologies. However, it is still challenging to obtain CE based strain sensor with excellent stretchability, wide strain range, high sensitivity coupled with outstanding stability via facile preparation process. Herein, combining the advantages of sparse and dense conductive network, a sparse-dense hierarchical structured conductive elastomer composites (CECs) based on natural rubber (NR) and modified MWCNTs (m-MWCNTs) is developed through facile one-pot synthesis. By means of the low cloud point of nonionic surfactant Triton x-100, the thick-sparse and thin-dense conductive layers as well as the excellent interface between hierarchical structure are formed by controlling the content of Triton x-100 and dispersed temperature. The severe slippage of sparse conductive network at small deformation and the avulsion of dense conductive network at large strain could synergistically enhance mechanical property and sensing performance of NR/m-MWCNTs CECs. Consequently, the designed stain sensor can achieve high sensitivity and linearity at a strain range of 0–200 % and 200–423 %, which are superior to most other state-of-the-art CECs strain sensors. Meanwhile, a wide range of detection (1 %-423 %), a fast response time (0.23 s), excellent repeatability, and stability are also obtained. Besides, our developed strain sensor was successfully applied in elbow pad and knee pad for monitoring human motion. In addition, NR/m-MWCNTs CECs exhibit the superior electric heating performance. The above satisfactory results reveal that our developed sparse-dense hierarchical CECs has the potential for applications in smart wearable electronics.

Soft, Tough, and Thermally Conductive Elastomer Composites by Constructing a Curled Conformation

Soft, Tough, and Thermally Conductive Elastomer Composites by Constructing a Curled Conformation

Piezoresistive behavior of elastomer composites with segregated network of carbon nanostructures and alumina

Electrically conductive elastomer composites (CECs) with segregated networks of conductive nanofillers show high potential in stretchable strain sensors due to balanced mechanical and electrical properties, yet the sensitivity at low strain is generally insufficient for practical application. Herein, we report an easy and effective way to improve the resistive response to low strain for CECs with segregated network structure via adding stiff alumina into carbon nanostructures (CNS). The CEC containing 0.7 ​wt% CNS and 5 ​wt% Al 2 O 3 almost sustains the same elasticity (elongation at break of ∼900%) and conductivity (0.8 ​S/m) as the control, while the piezoresistive sensitivity is significantly improved. Thermoplastic polyurethane (TPU) composites with a segregated network of hybrid nanofillers (CNS and Al 2 O 3 ) show much higher strain sensitivity (Gauge factor, GF ​= ​566) at low strain (45% strain) due to a local stress concentration effect, this sensitivity is superior to that of TPU/CNS composites (GF ​= ​11). Such a local stress concentration effect depends on alumina content and its distribution at the TPU particle interface. In addition, CECs with hybrid fillers show better reproducibility in cyclic piezoresistive behavior testing than the control. This work offers an easy method for fabricating CECs with a segregated filler network offering stretchable strain sensors with a high strain sensitivity.

Highly Stretchable and Patternable Conductive Elastomer Composites Based on Direct Cut‐Patterning Technique for Stretchable Circuit Board Applications

Stretchable interconnects, essential to the versatility of stretchable circuit boards (SCBs) in the emerging field of wearable electronic systems, are commonly made from conductive elastomer composites. However, the simultaneous realization of exceptional performance and a simple and reproducible fabrication has proven to be a challenge. In this study, high‐performance stretchable interconnects are introduced. These interconnects, constructed from highly patternable conductive composites, are produced using a straightforward, reproducible, and potentially scalable method termed as direct cut‐patterning (DCP). The DCP process enables the creation of distinctive conductive composite patterns and SCBs in a customizable manner, achieving a minimum feature size of 200 µm. The unique architecture of the proposed stretchable interconnects, featuring a fully embedded meander‐patterned composite conductor with periodic secondary cuts, enables the device to endure stretches exceeding 300%, while displaying a minimal gauge factor of ≈0.19 at 100% strain. Importantly, it fully reverts to its original form upon release. The proposed DCP‐based SCB approach is successfully applied in designing a highly stretchable and stable single‐layer light‐emitting diode array circuit, showcasing its potential for use in stretchable display panels.

Recyclable and super-stretchable conductive elastomeric composites with a carbon nanostructure interconnected network structure for effective thermal management and excellent electromagnetic wave suppressor

ABSTRACT The increasing demand for flexible electronics and portable gadgets has resulted in an increase in the amount of emitted EM radiation in recent years. Conductive carbon black (VCB XC 72) is a quasi-graphitic structure of clustered carbon particles that was deemed an ideal material for the development of extremely flexible electromagnetic interference (EMI) shielding materials. The sequential solution and melt mixing process has been used to generate a flexible and recyclable zinc oxide cross-linked, and VCB XC 72 nanofiller reinforced EMI shielding material. The ionic cross-linked network, created by other self-clustering ion duplets of Zn2+ ions, gave rise to the amazing recycling and reprocessing abilities of carboxylated acrylonitrile butadiene rubber (XNBR). The cross-linked XNBR and conductive black combination formed a tunable inferential framework that provided absorption, reflection, and multiple reflection shielding mechanisms. Based on the findings of the morphological study, it has been determined that the scattered and distributed carbon black clusters included inside XNBR rubber are creating the pathway for electrical hopping. As a result, the electrical percolation threshold has been lowered, and EMI shielding has significantly improved. The rubber composites had improved thermal characteristics in addition to having outstanding mechanical performances. Hopefully, these findings will pave the way forward for the development of smart electronic devices and environmentally friendly EMI shielding materials.

Optimization of conductive elastomeric composites for directly printed intrinsically stretchable conductors

Intrinsically stretchable solid-state conductors can shed light on the realization of further biocompatible and reliable wearable electronics. However, their material composition should be optimized considering the compatibility of target stretchable platforms. In this paper, we report directly printable conductive elastomeric composites for intrinsically stretchable conductors. A pneumatic direct ink writing system is employed to deposit well-defined patterns. Polydimethylsiloxane (PDMS), Ag particles, and multi-walled carbon nanotubes were used as the elastomeric matrix, conductive fillers, and auxiliary fillers, respectively. Because there is a critical trade-off between the conductivity and stretchability depending on the concentration of conductive fillers, we optimize the Ag concentration to 77.5 wt% to fulfill these requirements. In particular, we introduce multi-solvent Ag composite inks to simultaneously deliver excellent printability and enhanced conductivity. We further investigated the electromechanical reliability of the encapsulated conductors undergoing cyclic strains, finding that they exhibited stable R/R O values over 50% strain.

Thermally conductive and compliant polyurethane elastomer composites by constructing a tri-branched polymer network.

Most elastomers suffer from poor thermal conductivity, which limits their further applications in various fields, especially for electronic devices. A common method to enhance thermal conductivity is to introduce thermally conductive fillers into elastomers. Unfortunately, thermal conductivity and compliance are often correlated and coupled: large amounts of fillers are required to increase thermal conductivity while damaging the compliance dramatically. In this study, we report thermally conductive and compliant polyurethane elastomer composites by constructing a tri-branched polymer network. The resultant polyurethane elastomer composites exhibit excellent superhigh stretchability (2000%), low Young's modulus (640 kPa), and low thermal resistance (0.11 K cm2 W-1). Experimental rheology and a theoretical tube model are employed to study the nature of the high compliant tri-branched polymer network. Furthermore, the remarkable flexibility of our elastomer composite and heat dissipation act as thermal interface materials in the thermal management of flexible electronics. These findings advance our understanding on the rational design of the polymer frameworks of thermal composites, improving our ability to predict, design, and leverage their unique properties for future applications.

Breadcrumb-inspired construction of liquid metal@BN core-shell microparticles for highly thermal conductive elastomeric composites with excellent flexibility and stability

The rapid development of wearable electronics urges for flexible thermal management materials with higher service performance and stability of operation under high-complexity environmental stresses. A liquid metal embedded elastomer (LMEE) offers a combined solution with both high flexibility and thermal conductivity to heat dissipation of wearable electronics. But the potential leakage risk of the liquid metal (LM) in LMEE under external force severely limits the application of LMEE in the field of flexible thermal management. Inspired by a traditional Chinese snack, “fried milk”, we herein modify the two-dimensional boron nitride (BN) by thiolation, so as to develop LM@BN core-shell particles through the formation of a protective layer around micron-sized LM particles using thiol-metal interactions, before the flexible thermal management material with high stability is finally prepared by the combination between the LM@BN particles and a silicone rubber elastomer. The results demonstrated that the LM@BN core-shell structure can effectively maintain the balance between the tensile property, the thermal conductivity, and the stability of the material, thereby facilitating the future application of LM-elastomer composites with regard to flexible thermal management and thermal interface materials.

Extremely Soft, Stretchable, and Self-Adhesive Silicone Conductive Elastomer Composites Enabled by a Molecular Lubricating Effect

Softness, adhesion, stretchability, and fast recovery from large deformations are essential properties for conductive elastomers that play an important role in the development of high-performance soft electronics. However, it remains an ongoing challenge to obtain conductive elastomers that combine these properties. We have fabricated a super soft (Young's modulus 2.3-12 kPa), highly stretchable (up to 1500% strain), and underwater adhesive silicone conductive elastomer composite (SF-C-PDMS) by incorporating dimethyl silicone oil as a lubricating agent in a cross-linked molecular network. The resultant SF-C-PDMS not only exhibits superior softness but also can readily recover after a strain of 1000%. The initial resistance only decreases by 8% after 100000 cycles of tensile fatigue test (100% strain, 0.5 Hz, 15 mm/s). This multifunctional silicone conductive elastomer composite is obtained in a one-step preparation at room temperature using commercially available materials. Moreover, we illustrate the capabilities of this composite in motion sensing.

Adaptable thermal conductive, high toughness and compliant Poly(dimethylsiloxane) elastomer composites based on interfacial coordination bonds

Compliant elastomers have been widely used in industry and daily life benefited from their large reversible deformability. But poor thermal conductivity and toughness of unfilled elastomers usually limit their use in thermal management. The most common method to increase these properties is to incorporate thermally conductive fillers to polymeric materials. However, thermally conductive network formed by the large of fillers not only decreases the elastomeric compliance, but may also damages the toughness. Herein, to study the effect of polymer/filler interfacial interaction on thermal and mechanical properties, we choose shorter poly(dimethylsiloxane) without entanglement to construct elastomer composites by non-covalent interfacial carboxyl/aluminum and carboxyl/zinc oxide coordination bonds. Time-domain thermoreflectance technique demonstrates that the strong interfacial interaction leads to reduced interfacial thermal resistance between polymeric materials and fillers, resulting in enhanced thermal conductivity of the elastomer composites. Otherwise, two independent dynamic coordination bonds have been investigated on temperature- and frequency-sweep rheometer. The results reveal that the elastomer composites can counteract the negative effect of high filler content on toughness and compliance according to energy-dissipation of dissociation and generation of dynamic coordination bonds. Thanks to the enhanced interfacial interaction, our material shows high toughness (1073 J/m2), thermally conductive (2.37 W/(m·K)), compliant (stress is 0.11 MPa and elongation break is 910%) and fully reprocess. For the application as thermal interface materials, we demonstrate effective heat dissipation on chip and LED. Our present work suggests that the design principles based on interfacial coordination interaction can be applied to the development of new classes of elastomer composites.

Bis(2-hydroxyethyl) terephthalate from depolymerized waste polyester modified graphene as a novel functional crosslinker for electrical and thermal conductive polyurethane composites

Bis(2-hydroxyethyl) terephthalate (BHET) with active hydroxyl group derived from waste polyester can be applied as a polyurethane chain extender and an organic modifier for graphene oxide (GO). Herein, functionalized reduced GO (BHET-rGO) with single-layer was obtained by modifying GO with BHET, and then reduced by hydrazine hydrate. Waterborne polyurethane (WPU) nanocomposites with excellent mechanical performance, electrical and thermal conductivities were prepared via in-situ polymerization using the novel functional crosslinker BHET-rGO. Compared with the same content of rGO (7.41 wt%), WPU/BHET-rGO composites exhibit better properties containing equivalent BHET content. For example, BHET-rGO endows the WPU composites with higher tensile strength of 39.1 MPa (enhanced by 454.6%), electrical conductivity of 8×10−3 S/m (improved by 15 times), and thermal conductivity of 0.551 W m−1 K−1 (increased by 21.1%). Meanwhile, the sensitivity of WPU/BHET-rGO composite is well recovered during a large-strain stretching/shrinking cycle, and its resistance is stable under complex deformation. Besides, significant thermal stability ensures the durable of polyurethane to resist high-temperature. Hence, BHET-rGO have greater potential for fabricating high-performance elastomer composites, especially for conductive elastomer composites.

Conducting and stretchable emulsion styrene butadiene rubber composites using SiO2@Ag core-shell particles and polydopamine coated carbon nanotubes

In the present scenario of development in technology, the applications of stretchable conductive elastomers in modern electronic equipments have aroused great interest. Non-covalent bonding modification of carbon nanotubes (CNTs) using dopamine has improved the dispersion of CNT@PDA and interfacial interaction with the rubber matrix. The SiO2@Ag core-shell particles were prepared by coated with silver nanoparticles (AgNPs) on the surface of SiO2 using dopamine oxidation self-polymerization and electroless plating process. ESBR composites were prepared by latex co-coagulation method, where CNT@PDA and SiO2@Ag were used to develop an 1D-3D synergistic conductive network in ESBR composites. One-dimensional (1D) CNT@PDA were incorporated in three-dimensional (3D) spherical SiO2@Ag core-shell particles, which effectively prevented the agglomeration of SiO2@Ag and CNT@PDA. Again, 1D CNT@PDA could also be used as bridges to interact with 3D SiO2@Ag to develop the charge transfer more effectively in ESBR composites. The optimum electrical conductivity of the ESBR/CNT@PDA/SiO2@Ag composites was 0.2 S/cm, which was found to be higher than that of single filler. Moreover, the high electrical conductivity can be controlled at low tensile strain. The mechanical property of ESBR/CNT@PDA/SiO2@Ag composite was also improved by 105.4% as compared by ESBR/CNTs. This work provides a new idea for the fabrication of stretchable conductive elastomer composites with high performance.

PDMS-based conductive elastomeric composite with 3D reduced graphene oxide conductive network for flexible strain sensor

In this work, a novel flexible strain sensor based on reduced graphene oxide/ polydimethylsiloxane (rGO/PDMS) conductive elastomeric composites with a 3D conductive network was developed by latex assembly technique for the first time. Herein, benefiting from the excluded volume of the latex particles, the rGO selectively located in the interstitial space between them, which leading to formation of a 3D conductive network with ultralow amount of rGO (0.44 vol%), thereby enabled the rGO/PDMS composites to be mechanically robust and flexible. Noteworthy, each PDMS latex particle is analogous to a “elastic balloon”, and thus assisting the destruction and reconstruction of the conductive network under external stimulus, which endow the sensor with excellent sensitivity. Specially, the strain sensors showed superior sensitivity (44.01), a wide strain range (300%) and good stability (2500 cycles). Owing to these advantages, the sensor works effectively in detecting human’s finger movements, facial muscles, voice recognition and physiological signals.

Interfacial Coordination Interaction Enables Soft Elastomer Composites High Thermal Conductivity and High Toughness.

Soft elastomers have attracted wide applications, such as soft electronic devices and soft robotics, due to their ability to undergo large deformation with a small external force. Most elastomers suffer from poor toughness and thermal conductivity, which limits their use. The addition of inorganic fillers can enhance the thermal conductivity and toughness, but it deteriorates the softness (low Young's modulus and high stretchability). Integrating thermal conductivity, toughness, and softness into one elastomer is still a challenge. Here, we report a strategy of interfacial coordination interaction to achieve soft elastomer composites with high thermal conductivity and high toughness. We demonstrate the strategy by using poly(lipoic acid) elastomer and silver-coated aluminum filler as model, where silver-sulfur coordination cross-links are formed at the interface. The resultant elastomer composite shows high streachability (450%), high thermal conductivity (2.35 W m-1 K-1), low modulus (321 kPa), and high toughness (3496 J m-2), which cannot be achieve in existing elastomers. The time domain thermoreflectance technique demonstrates that the silver-sulfur coordination interaction lowers the interfacial thermal resistance, resulting in enhanced thermal conductivity of the elastomer composites. The excellent softness stems from lower bonding energy of the silver-sulfur coordination cross-links compared with covalent chemical cross-links. The high toughness also benefits from the interfacial silver-sulfur coordination interaction that can dissipate more energy upon deformation. We further demonstrate the potential application of the thermally conductive, tough, and soft elastomer composites for thermal management of chip and soft electronic devices.

Tetramethylammonium hydroxide modified MXene as a functional nanofiller for electrical and thermal conductive rubber composites

Ti3C2 MXene with super conductivities can be used in polymer nanocomposites. However, MXene is difficult to disperse uniformly in polymer matrics due to their high surface energy, weakening the filler-rubber interfacial interaction. Herein, functional Ti3C2 (ƒ-Ti3C2) with single-layer and high surface charge loading was prepared by modifying Ti3C2 with tetramethylammonium hydroxide (TMAOH). A novel mechanical mixing and freeze-drying method was provided to fabricate styrene-butadiene rubber (SBR)/ƒ-Ti3C2 nanocomposites. Compared with the same content of Ti3C2 (3.85 wt%), SBR/ƒ-Ti3C2 exhibited better properties. For instance, ƒ-Ti3C2 endows the SBR composites with high tensile strength of 13.7 MPa (enhanced by 479%), electrical conductivity of 3.74 × 10-4 S/m (improved by 116%), and thermal conductivity of 0.659 W m-1·k-1. Besides, the wet skid resistance of SBR/ƒ-Ti3C2 nanocomposites was remarkably enhanced and the rolling resistance was decreased. Hence, ƒ-Ti3C2 has more potential for fabricating high-performance elastomer nanocomposites, especially for conductive elastomer composites.

Solvent-Free Synthesis and Processing of Conductive Elastomer Composites for Green Dielectric Elastomer Transducers.

Stretchable electrodes are more suitable for dielectric elastomer transducers (DET) the closer the mechanical characteristics of the electrodes and elastomer are. Here, a solvent-free synthesis and processing of conductive composites with excellent electrical and mechanical properties for transducers are presented. The composites are prepared by in situ polymerization of cyclosiloxane monomers in the presence of graphene nanoplatelets. The low viscosity of the monomer allows for easy dispersion of the filler, eliminating the need for a solvent. After the polymerization, a cross-linking agent is added at room temperature, the composite is solvent-free screen-printed, and the cross-linking reaction is initiated by heating. The best material shows conductivity σ=8.2Scm-1 , Young's modulus Y10% =167kPa, and strain at break s=305%. The electrode withstands large strains without delamination, shows no conductivity losses during repeated operation for 500000 cycles, and has an excellent recovery of electrical properties upon being stretched at strains of up to 180%. Reliable prototype capacitive sensors and stack actuators are manufactured by screen-printing the conductive composite on the dielectric film. Stack actuators manufactured from dielectric and conductive materials that are synthesized solvent-free are demonstrated. The stack actuators even self-repair after a breakdown event.

Hierarchical Response Network Boosts Solvent-Free Ionic Conductive Elastomers with Extreme Stretchability, Healability, and Recyclability for Ionic Sensors.

The construction of solvent-free ionic conductive elastomers with high mechanical stretchability and large dynamic reversibility of chain segments is highly desired yet challenging. Here, a hierarchical response network strategy is presented for preparing highly stretchable yet mechanical robust ionic conductive elastomer composites (ICECs), among which poly(ethylene oxide) (PEO) microcrystalline serves as a physical cross-linking site providing high mechanical strength and elasticity, while dense hydrogen bonds endow superior mechanical toughness and dynamic reversibility. Due to the formation of the hierarchical response network, the resultant ICECs exhibit intrinsically high stretchability (>1500%), large tensile strength (∼2.1 MPa), and high fracture toughness (∼28 MJ m-3). Intriguingly, due to the high reversibility of hydrogen-bonded networks, the ICECs after being crushed are capable of healing and recycling by simple hot-pressing for multiple cycles. Moreover, the ICECs are dissolvable under an alkaline condition and easily regenerated in an acid solution for manifold cycles. Importantly, the healed, recycled, and regenerated ICECs are capable of maintaining their initial mechanical elasticity and ionic conducting performance. Due to the integration of high stretchability, fatigue resistance, and ionic conductivity, the ICECs can readily work as a stretchable ionic conductor for skin-inspired ionic sensors for real-time and accurately sensing complex human motions. This study thus provides a promising strategy for the development of healable and renewable ionic sensing materials with high stretchability and mechanical robustness, demonstrating great potential in soft ionotronics.

Dataset for "Solvent-free synthesis and processing of conductive elastomer composites for "green" dielectric elastomer transducers"

Dataset for "Solvent-free synthesis and processing of conductive elastomer composites for "green" dielectric elastomer transducers"