Conductive Silicone Rubber Research Articles

Multifunctional elastomer-organohydrogel hybrid patch for durable skin epidermal strain-sensing and antibacterial applications

A multifunctional elastomer-organohydrogel hybrid patch for skin surface strain sensors, denoted as MSR-PO, composed of a modified conductive silicone rubber (MSR) and PAA-based organohydrogel (PO), is fabricated by surface radical polymerization of the PO layer on MSR film, the two layers are linked together with the strong chemical bonding, thereby amalgamating their distinct functionalities. The MSR layer endows the patch with great wear-resisting, anti-freezing, and durable sensing properties. The gel layer coated on conductive silicone rubber imparts the patch with excellent adhesive capability to match the modulus of the skin, which is in favor of monitoring large and small movements of the human body, showing great potential in the field of wearable flexible electronic sensing. Importantly, the rubber layer and gel layer of MSR-PO patch exhibit outstanding synergistic antibacterial effects. This work will inspire the design and fabrication of novel rubber-gel asymmetric patch for multifunctional applications.

Simulation-Directed Construction of Bamboo-Forest-Like Heat Conduction Networks to Enhance Silicon Rubber Composites' Heat Conduction Properties.

Highly vertically thermally conductive silicon rubber (SiR) composites are widely used as thermal interface materials (TIMs) for chip cooling. Herein, inspired by water transport and transpiration of Moso bamboo-forests extensively existing in south China, and guided by filler self-assembly simulation, bamboo-forest-like heat conduction networks, with bamboo-stems-like vertically aligned polydopamine-coated carbon fibers (VA-PCFs), and bamboo-leaves-like horizontally layered Al2O3(HL-Al2O3), are rationally designed and constructed. VA-PCF/HL-Al2O3/SiR composites demonstrated enhanced heat conduction properties, and their through-plane thermal conductivity and thermal diffusivity reached 6.47W(mK)-1 and 3.98mm2s-1 at 12vol% PCF and 4vol% Al2O3 loadings, which are 32% and 38% higher than those of VA-PCF (12vol%) /SiR composites, respectively. The heat conduction enhancement mechanisms of VA-PCF/HL-Al2O3 networks on their SiR composites are revealed by multiscale simulation: HL-Al2O3 bridges the separate VA-PCF heat flow channels, and transfers more heat to the matrix, thereby increasing the vertical heat flux in composites. Along with high volume resistivity, low compression modulus, and coefficient of thermal expansion, VA-PCF/HL-Al2O3/SiR composites demonstrate great application potential as TIMs, which is proven using multiphysics simulation. This work not only makes a meaningful attempt at simulation-driven biomimetic material structure design but also provides inspiration for the preparation of TIMs.

Facile preparation of conductive silicone rubber composite foams with tunable cell morphologies and absorption-dominant characteristics

Flexible silicone rubber (SR) foams with tunable cellular morphologies were fabricated via supercritical CO2 foaming. Conductive carbon black (CB) modified at a low cost and with high complex viscosity was preferentially selected. The effects of the pore size and void fraction on the electrical conductivity and dielectric permittivity of the SR/CB composite foams were carefully investigated. The pore size of the foams affected the specific shielding effectiveness (SSE) and absorption coefficient (A), whereas the variation in the void fraction did not generate evident changes. In comparison with its solid counterpart, a foam with a pore diameter of 59.9 μm showed a 50 % decrease in density, 31.6 % increase in absorptivity, and 95.7 % increase in SSE, demonstrating a considerable electromagnetic interference shielding effectiveness (EMI SE). Decreases in the pore size and void fraction of the foams improved compression modulus and strength. In addition, sample preparation process was simplified, making industrial production easier.

Revitalising high voltage cable: Exploring effective repair methods and influential factors for buffer layer defects using conductive silicone rubber

Revitalising high voltage cable: Exploring effective repair methods and influential factors for buffer layer defects using conductive silicone rubber

Contact detection in a rib-reinforced vacuum driven actuator with an embedded CSR bridge sensor

ABSTRACT Stable control and accurate sensing are necessary for the safe operation of soft robots, and flexible sensors that can follow the flexible movements of soft robots are needed. In this paper, flexible bending sensors are embedded in a rib-reinforced vacuum-driven actuator with no risk of rupture, considering the application of flexible sensors to human cooperative work and wearable devices. The bending sensor is a bridge circuit with conductive silicone rubber (CSR) for variable resistance. The CSR bridge sensor consists of four CSRs that capture deformation and a circuit with a conductive coating spray printed on a laminated sheet. The sensor value is the output voltage divided by the input voltage, and the effects of the drift and input voltage variations are canceled out. The bending sensor embedded in the silicone actuator has a linear relationship, and the rib-reinforced vacuum driven actuator provides angle PID control for continuously changing reference inputs by feeding back sensor estimated angle. Furthermore, contact detection was established by using the pressure estimated from the CSR bridge sensor and the pressure sensor error as the threshold. The algorithm provides reliable contact detection and force estimation with actuator response thresholds and anti-chattering.

Investigating the non‐linear conductivity properties of silicone rubber co‐modified with doped calcium copper titanate @ zinc oxide and grafted glycidyl methacrylate

AbstractIn order to solve the issue of localised electric field concentration in high‐voltage direct current cable accessories, a method for preparing a composite material with high conductivity and nonlinear conductivity properties is proposed. The authors employed homemade calcium copper titanate @ zinc oxide (CCTO@ZnO) as a filler and glycidyl methacrylate (GMA) as a grafted small molecule to co‐regulate the non‐linear conductivity of silicone rubber (SiR). The results indicate that doping CCTO@ZnO can enable SiR to acquire non‐linear conduction properties and grafting GMA can significantly enhance the conductivity of SiR. However, both doping CCTO@ZnO and grafting GMA have a negative impact on the breakdown performance of SiR. Simulation results indicate that reinforced insulators made from doped and grafted co‐modified composites can improve the distribution of electric fields in cable accessories.

Study on electrical, thermal, mechanical and corrosion resistance properties of conductive silicone rubber for polymer-based metal composite grounding electrodes

Study on electrical, thermal, mechanical and corrosion resistance properties of conductive silicone rubber for polymer-based metal composite grounding electrodes

Studies on 8.4 W/m·K thermally conductive silicone rubber with high compressibility, high electrical insulation, high thermal reliability, and low cost

Thermally conductive silicone rubber (TCSR) has been widely used to enhance heat dissipation in electronics and energy storage devices. Currently, it is a challenge to produce TCSR which combines high thermal conductivity, high compressibility, high thermal reliability, high electrical insulation, and low cost. Here, we report a state-of-the-art TCSR which achieves such a combination. Owing to the optimized alumina gradation, the loading level of alumina in the TCSR reaches 96 wt%. The TCSR reaches a high and isotropic thermal conductivity of 8.4 W/m·K, a high compression ratio of 48 % (under a pressure of 6 psi or 42.4 kPa), and a high dielectric strength (>6 kV/mm). After heating at 180 °C for 100 h, little oil bleeding is observed. More importantly, these properties remain stable (variation < 10 %) after 2000 h of thermal aging at 135 °C, indicating high thermal reliability.

Study on the effects of incremental curing on the thermal conductivity, insulation, and mechanical properties of thermal conductive silicone rubber

With the development of fields such as electronics and telecommunications, electronic devices are becoming more integrated and powerful. Therefore, there is an increasing demand for high thermal conductive and insulating flexible materials. Silicone rubber (SR), as an excellent flexible substrate, is often combined with various thermal conductive fillers to enhance its thermal conductivity (TC). Carbon materials are commonly used as thermally conductive fillers. To improve the insulation performance while maintaining the TC of the material, uncured SR filled with boron nitride (BN) is used as an insulating layer on the same substrate. The TC of the once-cured BN/SR composite and the incremental cured BN/SR composite as a coating are 0.492 W/(mK) and 0.484 W/(mK), respectively, with a BN content of 10 vol%. The TC of carbon fiber (CF)/SR composites before and after surface treatment with BN/SR are 1.760 W/(mK) and 1.682 W/(mK), respectively, with a CF content of 20 vol%. The volume resistivity of the former is less than 104 Ω cm, while the latter is greater than 1014 Ω cm.

InkFusion3D: 3D Printing Flexible Sensors with Silicone Rubber and Conductive Ink Materials

With the continuous advancement in current sensor design research, most design schemes still rely on rigid or semi-flexible materials for sensor usage. These interactive devices are increasingly unable to meet the demands of users for adaptability, durability, and biocompatibility, limiting their use in dynamic environments. This paper introduces a novel flexible sensor, InkFusion3D, which is fabricated using a combination of low-cost conductive ink and silicone rubber through 3D printing technology. Due to the significant advantages of InkFusion3D material, such as low cost, durability, good biocompatibility, and wide applicability, it can be customized for various applications to address challenges. The paper elaborates on the manufacturing method of InkFusion3D and its sensing principle upon force application. It also proposes applications in medical and gaming scenarios, such as joysticks, buttons, tangible interaction models, and smart filler materials.

Preparation of continuous PBO fiber-filled silicone rubber with high thermal conductivity through simple Wrapping

With the development of the electronics, the demand for flexible thermal materials with high thermal conductivity continues to rise. Here, we report a type of thermally conductive silicone rubber (SR) prepared using continuous poly (p-phenylene benzobisoxazole) fiber (PBO). Through a process consistent with the layer stacking principle, continuous fibers are first immersed with SR or boron nitride (BN)/SR and then wound layer by layer onto a mold. Then, PBO/SR and PBO/BN/SR composites were prepared in the laboratory. In these composites, PBO fibers can directly form numerous thermal paths. Additionally, due to the traction and compression between fibers during the winding process, BN is distributed along the fibers. It allows BN to better form independent thermal paths and, together with PBO fibers, create a thermal network in SR. The thermal conductivity of PBO/SR and PBO/BN/SR composites can reach 5.656 W m−1 K−1 and 7.853 W m−1 K−1, respectively, with PBO and BN contents of 20 vol% and 10 vol%, respectively.

Thermally conductive silicone rubber used as insulation coating through incremental curing and the effects of thermal filler on its mechanical and thermal properties

Thermally conductive silicone rubber used as insulation coating through incremental curing and the effects of thermal filler on its mechanical and thermal properties

Effect of the cross-linking of polyorganosiloxane on highly thermally conductive silicone rubber's mechanical, dielectric, and thermally conductive properties and thermal reliability

With the rapid development of thermal management techniques, there is an urgent need for thermally conductive silicone rubber (TCSR) which has high softness, high electrical insulation, high thermal conductivity, and high reliability. Currently, the reliability problem has received little attention in the academic reports. Herein, the effect of the cross-linking of polyorganosiloxane on TCSR's mechanical, dielectric, and thermal properties and thermal reliability has been studied. It is found that the cross-linking has great impacts on the thermal reliability of mechanical and oil bleeding properties, and slight impacts on the thermal reliability of dielectric and thermally conductive properties. When the content of hydrogen-terminated silicone oil is 2–4 phr and the content of hydrogen-side silicone oil is 1.5–1.8 phr, the resultant TCSR has high properties, including high softness (Shore OO hardness 55−68), high compression ratio (20−40 % @ 20 psi), high dielectric strength (5.3−5.7 kV/mm), high thermal conductivity (4.3−4.8 W/mK), and high thermal reliability (less than 10 % variation for most properties after thermal aging). Possible mechanisms have been discussed.

Fast Degradable and Thermally Conductive Silicone Rubber Vitrimer with Low Dielectric and UV‐Shielding Properties

AbstractSilicone rubbers are widely employed in various fields such as electronics, electrical engineering, mobile communications, aerospace, and automotive industries. However, silicone rubbers are typically challenging to reprocess and degrade. Moreover, with the advancement of technology, higher demands are placed on its thermal conductivity and dielectric properties. In this study, diglycidyl ether terminated polydimethylsiloxane is cured by 4,4′‐dithiodibutyric acid which contains dual dynamic covalent disulfide and ester bonds with triazobicyclodecene as the ester exchange catalyst to prepare silicone rubber vitrimers (SRVs) through a casting method. The SRVs demonstrate a relatively higher intrinsic thermal conductivity of 0.26 W (m⁻1 K⁻1) compared to ≈0.20 W (m⁻1 K⁻1) of conventional silicone rubber. Besides, the SRVs exhibit very low and stable dielectric constant and dielectric loss at both low and high frequencies (X‐band). The lowest dielectric constant and dielectric loss tangent at 10 GHz are 2.75 and 0.0650, respectively. Besides, the dual dynamic covalent bonds enable the SRVs to have excellent reprocessability and fast degradability. Moreover, the SRVs reveal UV‐shielding capability, as the transmittance of the SRVs is 0% from 200 to 400 nm of UV light.

Washing and Abrasion Resistance of Textile Electrodes for ECG Measurements

Electrocardiogram (ECG) signals are often measured for medical purposes and in sports. While common Ag/AgCl glued gel electrodes enable good electrode skin contact, even during movements, they are not comfortable and can irritate the skin during long-term measurements. A possible alternative is textile electrodes, which have been investigated extensively during the last years. These electrodes, however, are usually not able to provide reliable, constant skin contact, resulting in reduced signal quality. Another important problem is the modification of the electrode surface due to washing or abrasion, which may impede the long-term use of such textile electrodes. Here, we report a study of washing and abrasion resistance of different ECG electrodes based on an isolating woven fabric with conductive embroidery and two conductive coatings, showing unexpectedly high abrasion resistance of the silver-coated yarn and optimum ECG signal quality for an additional coating with a conductive silicone rubber. Sheet resistances of the as-prepared electrodes were in the range of 20–30 Ω, which was increased to the range of 25–40 Ω after five washing cycles and up to approximately 50 Ω after Martindale abrasion tests. ECG measurements during different movements revealed reduced motion artifacts for the electrodes with conductive silicone rubber as compared to glued electrodes, suggesting that electronic filtering of such noise may even be easier for textile electrodes than for commercial electrodes.

Self-Assembly of Multiwalled Carbon Nanotubes on a Silicone Rubber Foam Skeleton for Durable Piezoresistive Sensors.

Conductive nanomaterial/flexible polymer composite foams are of great interest in the field of flexible and wearable piezoresistive pressure sensors. However, the existing composite foam sensors are faced with stability issues from conductive nanomaterials, which tends to decrease their long-term durability. Herein, we developed a solvent evaporation-induced self-assembly strategy, which could significantly improve the stability of multiwalled carbon nanotubes (MWCNTs) on a silicone rubber foam skeleton. The process for self-assembly of MWCNTs was straightforward. Aqueous MWCNT dispersion droplets were first hierarchically enclosed in silicone rubber via water-in-oil (W/O) Pickering high internal phase emulsions (HIPEs). Then, the high pressure generated by fast evaporation of the solvent from the droplets could break the thinnest pore walls to form interconnected pores. As a result, very dense and firm MWCNT layers were self-assembled on the pore wall surface. Due to the excellent stability of MWCNTs and tetramodal interconnected porosity, our MWCNTs/silicone rubber composite foam showed the following "super" properties: low density of 0.26 g/mL, high porosity of 76%, and excellent mechanical strength (the maximum stress loss of 8.3% at 80% strain after 100 compression cycles). In addition, excellent piezoresistive performance, including superior discernibility for different amplitudes of compressive strain (up to 80%), rapid response time (150 ms), and high sensitivity (gauge factor of 1.44), was demonstrated for such foams, together with prominent durability (39,000 compression cycles at 60% strain in air) and excellent stability of resistance response in water and organic solvents (5000 compression cycles at 30% strain in water and ethanol). Regarding its application, a wearable piezoresistive sensor, which was assembled from the as-prepared conductive silicone rubber composite foam, could capture various movements from tiptoeing and finger bending to small deformations resulting from human pulse.

Core-Sheath Fiber-Based Triboelectric Nanogenerators for Energy Harvesting and Self-Powered Straight-Arm Sit-Up Sensing.

Fiber-based triboelectric nanogenerators (F-TENGs), a green and sustainable energy-harvesting and transformation technology, hold great potential in the areas of portable energy harvesters and smart wearable sensors. Herein, the core-sheath structure F-TENGs (CF-TENGs) are developed by using continuous production equipment. The CF-TENGs, consisting of an elastic conductive fiber (core layer) and silicone rubber (sheath layer), can simultaneously accomplish stable reversible strain and excellent electrical output performance. High outputs (an open-circuit voltage of 17.5 V and a short-circuit current of 0.1 μA at a frequency of 1 Hz) can be attained when the CF-TENGs (a length of 5 cm) are contacted with a nylon fabric. The CF-TENGs not only act as self-powered sensors for applications in motion monitoring but also efficiently transfer mechanical energy into electric energy. As self-powered wearable sensors, the CF-TENGs can accurately indicate various human physiological movements. Moreover, they can be applied on straight-arm sit-up sensing to achieve standardized sport testing. Importantly, a CF-TENG-based weaved fabric presents high electrical performance to meet requirements as an energy harvester. These CF-TENGs provide a significant insight to facilitate the development of fiber-based triboelectric applications.

Waffle-inspired thermal conductive silicone rubber composites with excellent electromagnetic shielding performance based on three-dimensional filler networks

Improving the thermal conductivity and electromagnetic shielding performance of silicone rubber composites is crucial for their application in electronic devices. In this work, inspired by the structure of waffle, a novel approach combining ice templating and mechanical vibration was employed to prepare reduced graphene oxide (rGO)/silicon carbide whisker (SiC) filler networks arranged in both horizontal and vertical directions. Silicone rubber composites were prepared by vacuum impregnation of silicone rubber into the three-dimensional filler networks. At the hybrid filler content of 3.88 vol%, the through-plane thermal conductivity reached 5.24 W/(m·K), exhibiting about 31 times higher than that of silicone rubber, and the anisotropy of thermal conductivity of the composite was only 1.35 due to the structural arrangement of the filler network in both vertical and horizontal directions. The total electromagnetic interference (EMI) shielding effectiveness of the composite with 3.88 vol% hybrid filler was 35.2 dB with low electromagnetic reflection, exhibiting good EMI shielding performance.

Preparation Methods and Properties of CNT/CF/G Carbon-Based Nano-Conductive Silicone Rubber

Carbon-based nano-conductive silicone rubber is a kind of composite conductive polymer material that has good electrical and thermal conductivities and high magnetic flux. It has good application prospects for replacing most traditional conductive materials, but its mechanical and tensile strengths are poor, which limit its applications. In this study, carbon fiber (CF), graphene (G) and carbon nanotubes (CNT) are used as fillers to prepare carbon-based nano-conductive silicone rubber via solution blending, and the preparation methods and properties are analyzed. The results show that when the carbon fiber content is 7.5 wt%, the volume resistivity of carbon fiber conductive silicone rubber is 9.5 × 104 Ω·cm, the surface resistance is 2.88 × 105 Ω, and the tensile strength reaches 2.12 Mpa. When the graphene content is 5.5 wt%, the volume resistivity of graphene conductive silicone rubber is 8.7 × 104 Ω·cm, and the surface resistance is 2.4 × 106 Ω. When the carbon nanotube content is 1.25 wt%, the volume resistivity of carbon nanotube conductive silicone rubber is 1.34 × 104 Ω·cm, and the surface resistance is 1.0 × 106 Ω. The three conductive nano-fillers in the blended carbon nano-conductive silicone rubber form a stable three-dimensional composite conductive network, which enhances the conductivity and stability. When the tensile rate is 520%, the resistance of the blended rubber increases from 2.69 × 103 to 9.66 × 104 Ω, and the rubber maintains good resilience and tensile sensitivity under repeated stretching. The results show that the proposed blended carbon nano-conductive silicone rubber has good properties and great application prospects, verifying the employed research method and showing the credibility of the research results.

Preparation of Thermally Conductive Silicone Rubber-Based Ultra-Thin Sheets with Low Thermal Resistance and High Mechanical Properties

Thermally conductive silicone rubber (TCSR)-based thin sheets with low thermal resistance and high electrical insulation properties have been widely used in thermal management applications in the electronic and energy storage fields. The low thermal resistance is mainly attributed to the sheets’ small thickness. In order to further decrease the sheets’ thermal resistance, it is necessary to decrease their thickness. However, the sheets mostly have a thickness of at least 0.20 mm, and it is still a challenge to decrease the thickness to less than 0.10 mm mainly due to the difficulty of smooth calendering through a narrow roll-to-roll gap on calenders. Here, a low-viscosity calendering method has been developed to prepare TCSR-based ultra-thin sheets. The sheets present unprecedentedly small thickness (~0.08 mm), low thermal resistance (0.87 cm2K/W), high tensile strength (~8 MPa), high flexibility, high electrical resistance (&gt;1014 Ω·cm), and high thermal dissipation (&gt;30 °C decrease in LED working temperature). Comparison studies between this new method and the conventional preparation method have been carried out to understand the mechanism of the improvements.