Silicone Rubber Matrix Research Articles

Preparation and analysis of conductive and superhydrophobic silicone rubber

Conductive and superhydrophobic rubber products are of great significance to the safety and long-term use of outdoor equipment. However, the preparation of low-cost conductive, superhydrophobic rubber products with good extensibility, durability, stability, and environmental adaptability remains a challenge. In this paper, conductive and superhydrophobic silicone rubber composites with uniform concave-convex structure were prepared on the surface of silicone rubber by filling carbon nanotubes (CNTs) in the silicone rubber matrix and using 2000 mesh screen template replication method and spraying technology. Using the self-made conductive circuit, the good electrical conductivity of the silicone rubber composite was verified at 200% elongation and after 500 times of torsion. In addition, the silicone rubber composite had good droplet bounce, anti-icing and self-cleaning properties.

Ultrasmall SnFe2O4 nanoparticles anchored on N-doped carbon nanofibers for ultralight and high-performance microwave absorption.

One-dimensional (1D) N-doped carbon nanofibers decorated with ultrafine (∼4.5 nm) SnFe2O4 nanoparticles (denoted as SFO/N-CNFs) are successfully synthesized by a combination of electrospinning and solvothermal process, and their microwave absorption (MA) properties are reported for the first time. With only 5 wt% filler loading in a silicone rubber matrix, the optimum reflection loss (RL) could reach -46.5 dB and the qualified frequency bandwidth (RL < -10 dB) can be capable of 4.8 GHz at 1.6 mm, exhibiting better comprehensive absorption performance relative to other analogous absorbers. The lightweight and highly efficient MA of SFO/N-CNFs is largely ascribed to the improved impedance matching and satisfactory attenuation ability caused by the synergistic effect between the ultrasmall-sized SFO nanoparticles (NPs) and 1D N-CNF matrix. This work not only offers a novel and promising high-performance microwave absorber, but also offers a general approach to designing and fabricating ultrasmall transition metal oxide nanoparticle decorated carbon-based composite nanostructures for multifunctional applications.

Lewis acidic molten salts etching route driven construction of double-layered MXene-Fe/carbon nanotube/silicone rubber composites for high-performance microwave absorption

Transition metal carbide/nitride (MXene) materials have triggered intensive research interest in the field of microwave absorption (MA). However, the complicated fabrication process and monotonous loss mechanism of MXene materials seriously hinder their practical applications. Here, we first developed a green and facile synthesis of dielectric-magnetic MXene-Fe nanocomposites via one-step Lewis acidic molten salts etching, which were combined with carbon nanotube (CNT) filler and silicone rubber (SR) matrix to fabricate double-layered MXene-Fe/CNT/SR composites by casting and curing. The in-situ growth magnetic Fe nanoparticles on MXene and unique double-layered structure composed of MXene-Fe/SR as the upper absorption layer and CNT/SR as the bottom reflection layer imparted the composites with excellent MA properties by offering appropriate impedance matching, strengthened internal reflection, polarization, magnetic loss, and conductive loss. Accordingly, the proposed double-layered composites showed superior MA properties compared with other MXene-based composites. The MXene-Fe-45%/CNT-5%/SR sample showed a reflection loss value of −65.9 dB at 12 GHz and an effective absorption bandwidth up to 8.24 GHz at 2.86 mm thickness. The double-layered composites exhibited tunable absorption frequency between the whole Ku-band and X-band by simply regulating the sample thicknesses and filler contents. These features indicate that the developed double-layered MXene-Fe/CNT/SR composites have great potential for high-performance MA applications. This study offers a novel and simple strategy to develop high-efficiency and broadband MA materials.

Highly Stretchable, Responsive Flexible Dual‐Mode Magnetic Strain Sensor

AbstractStretchable strain sensors with high stability, high responsiveness, and low detection limit provide the broad potential for intelligent robots and electronic skin. However, developing low‐cost strain sensors with contact and non‐contact sensing modes remains a significant challenge. In this study, a flexible magnetic strain sensor based on a sandwich structure is proposed to address this challenge. The proposed structure utilizes the coordination between carbon black and Fe3O4 microparticles in the silicone rubber matrix to enhance the sensor's sensitivity to external strain and magnetic stimuli. The sensor exhibits excellent tensile properties with a strain range of up to 180%, fast response/recovery time (78 ms/65 ms), high stability, and durability after 9000 cycles. Moreover, the flexible magnetic strain sensors can detect micro‐vibration and micro‐strain signals. It can also be performed as electronic skin to precisely sense human movements. Furthermore, the newly developed sensor can accurately sense oncoming objects and bicycle riding speed/distance, and a flexible magnetic keyboard is conceived. Consequently, the dual‐modal magnetic strain sensor exhibits an excellent ability to identify contact and non‐contact states and has broad application prospects in next‐generation intelligent products.

Research on the Use of Silicon-Ethanol Composite in Actuators

Silicon-ethanol is a relatively new smart composite in the category of phase-change materials (PCM). It consists of liquid ethanol entrapped in bubbles spread into a silicone rubber matrix, i.e., during cooling. The composite is able to expand significantly when heat is applied and shrink when it is removed. The properties of this material can be used in a new type of actuator. In this paper, the basic equations that describe the properties of actuators with a silicon-ethanol composite are given. Using them, two solutions of unidirectional actuators with a composite inserted into polycarbonate tubes and metal bellows are designed and investigated. In the study, actuators with different geometric dimensions and applied composite volumes are investigated. The elongations of the actuators and the blocking forces are measured. The theoretical relationships given at the beginning of the paper that describe the properties of the composite are validated using the performed experimental results of the built actuators. The tube actuators achieved elongation between 32% and 35% at a temperature of 75 degrees Celsius, that is, less than that predicted according to equations from earlier publications. Due to this, a modified equation that includes the influence of friction was proposed and compared with experimental results. The performance of the tube actuator deteriorates rapidly. In the case of bellow actuators, they stabilize after a few cycles of heating and cooling.

Characterization and optimization of 3D-printed, flexible vibration strain sensors with triply periodic minimal surfaces

Flexible piezoresistive strain sensors have promising applications in wearables and soft robotics. For sensing dynamic strains, such as a runner’s gait or a slipping object held by a robotic gripper, the sensor must be capable of vibration strain sensing for a range of amplitudes and frequencies. This article presents the characterization and design optimization of a flexible sensor using Schwarz P-type triply periodic minimal surface (TPMS) structures for vibration strain sensing. Sensors are fabricated using a 3D-printing process, coating a silicone rubber (SR) matrix with graphene nanoplatelets (GNP). Sensors are characterized under uniaxial compressive strain amplitudes from 0% to 10% and frequencies of 10–110 Hz. Frequency and time-domain analyses demonstrate sensor performance and explain the unique deformation mechanisms of the TPMS structure. Low sensor delays of less than 6.3 ms demonstrate its capability for high-frequency sensing. The frequency independence of the sensor is demonstrated, as the mean frequency dependence error is only ±3.89%. In addition, the TPMS sensor was parametrized, and a size optimization was performed on it using a multi-objective adaptive firefly algorithm (MOAFA). The MOAFA converged within 1618 unique function evaluations, a reduction of 85.5% compared to the entire set of feasible solutions. The optimized sensor was fabricated and characterized, displaying a reduced mean frequency dependence error of only ±2.18%.

A facile fabricating method for smart soft robotic hand

AbstractA facile fabricating method was proposed for a smart soft robotic hand (SSRH) composed of shape memory alloy (SMA) wires, stainless‐steel springs, and silicon rubber matrix by one‐step curing technology. The SMA wires were embedded into a flexible matrix by pouring silicon rubber into a 3D‐printed hand‐like polylactic acid mold. The good demoulding property was verified after curing at room temperature for 6 h. In addition, the reversible bending behaviors of SSRH were demonstrated by Joule heating actuation. Moreover, the high load‐bearing capability was evaluated by suspending the weight experiment. All the results can provide a new guide for soft robotic hands in future medicinal applications.

Effect of CeO2 on UV aging of composite insulators prepared by template‐spraying method

AbstractWhen the silicone rubber composite insulator is exposed outdoors for a long time, it will be affected by high‐temperature ultraviolet environments. In order to ensure the operation of silicone rubber composite insulators, a super‐hydrophobic composite insulator with antiaging characteristics was prepared by mixing cerium dioxide (CeO2) with silicone rubber and spraying CeO2 on the surface of silicone rubber. This article studied the aging characteristics of the base and surface of silicone rubber composite insulator by CeO2 in ultraviolet environment. The properties of silicone rubber composite insulators before and after aging were tested by mechanics, contact Angle, rolling Angle, bounce, and icing experiments. The aging mechanism of silicone rubber was analyzed by Fourier transform infrared spectroscopy and search engine marketing. This study prepared composite insulators with excellent mechanical, hydrophobic, and antiicing properties. The aging resistance of silicone rubber composite insulators is improved by adding CeO2 into silicone rubber matrix and spraying CeO2 on the surface, which also ensure the use of composite insulators in high‐temperature ultraviolet environment.

Electrical Conductivity Modeling and Fabrication of Carbon Nanotubes/Silicone Rubber Composites for High Voltage Insulators in Regions With a Polluted Atmosphere

The condensation mechanism of the insulators’ surface, increase the surface electrical conductivity. The electrical conductivity of the insulator creates a high level of leakage current and causes the failure. Difference between the dew point and the surface temperature of the insulator which occur due to radiative cooling mechanism, is the major reason of the moisture condensation on the polluted insulator surface. To compensate for the temperature difference, carbon nanotubes (CNTs) are being added to the silicone rubber housing material. The main idea of this research is based on generating joule heating by reducing the surface resistance of high voltage insulators. For this purpose, a developed model based on Halpin–Tsai formulation for tensile modulus of nanocomposites is joined with the conventional power-law model for the effective electrical conductivity of silicone rubber matrix carbon nanotube composite (SMCNT). SMCNT samples are prepared with the addition of various CNT volume fractions to high temperature vulcanizing (HTV) silicone rubber by melt-blending method. The developed model reveals that the high fraction of thinner and longer CNT, thicker interphase, higher concentration of percolated CNT, lower waviness of CNT, and higher conductivity of CNT can make a higher effective conductivity for SMCNT.

An embedded printed flexible strain resistance sensor via micro-structure design on graphene-filled conductive silicon rubber

Flexible strain sensors have been improved in sensing performance with the assistance of materials design, novel manufacturing, and microstructure fabrication. In this study, graphene was efficiently dispersed in ethanol and then re-dispersed into silicon rubber (SR) matrix, functioning as a flexible strain resistance sensor (FSRS) with functional macrostructure and modified microstructure to further improve the sensitivity. A stable dispersion of graphene was obtained in an ultrasound-aided ball milling process, where absolute ethanol was selected as the solvent and sodium dodecyl sulfonate as the surfactant. Graphene-filled conductive SR was embedded in the polydimethylsiloxane matrix as a conductive sensing layer, and the high sensing performance (GF = 25 ± 2) was achieved using a spiral printed. Micropores with an optimized interspacing of 10 mm were further introduced into the spiral CSM, and the results presented a significant improved sensitivity (GF = 51 ± 4) of the fabricated FSRS under a working strain (20%–30%) and cyclic test (>104 cycles). The FRSR was sensitive enough to monitor various movements of single and multi-joints of human body and identify the rhythm of music sound, which exhibited its potential application as a wearable flexible sensor.

Development of novel hydrophilic and antibacterial silicone rubber impression material for dental application.

This investigation aimed to develop a novel hydrophilic and antibacterial silicone rubber impression material for dental application. The basic formula of the new silicone rubber was determined on a preliminary study, and 6% polyether modified silicone oil was added as wetting agent to provide the hydrophilicity. No-vel nano-antibacterial inorganic fillers containing quaternary ammonium salt with long chain alkyl were incorporated into the hydrophilic silicone rubber impression materials at a mass fraction of 0%, 1%, 2%, 3%, 4%, or 5%. A commercial silicone rubber impression material was used as control. The mechanical properties, wettability, detail reproducibility, dimensional stability, and mixing time of silicone rubber materials were measured. Thin-film adhesion method and cell counting kit-8 method were used to detect the antibacterial property and cytotoxicity. Scanning electron microscopy (SEM) was chosen to observe the micromorphology of the novel silicone rubber. When the content of antibacterial filler exceeded 4%, the mechanical properties of the new silicone rubber decreased significantly (P<0.05). Compared with those of the control group, the contact angle and linear size change rate of different groups had no significant change at different time nodes, and the detail reproducibility was intact (P>0.05). The addition of antibacterial fillers had no significant effect on the mixing time (P>0.05). Adding 4% antibacterial fillers could result in the antibacterial rate of 95.26%, showing good antibacterial properties. No significant difference was found in the cytotoxicity of all groups (P>0.05). The SEM pictures of the cross section of the silicone rubber sample showed that the fillers had good compatibility with the silicone rubber matrix and distributed in the matrix evenly. A novel silicone rubber impression material containing 6% polyether modified silicone oil could obtain promising hydrophilic and antibacterial properties after being added with 4% antibacterial inorganic fillers.

Ti3C2Tx MXene-Ag/silicone rubber composites with enhanced dielectric properties and improved mechanical properties

Conductive filler/polymer composites were widely used in dielectric devices, but high dielectric constant was accompanied by high loss tangent. Incorporating highly conductive fillers into silicone rubber (SR) matrix may be a feasible way, since the loss tangent of SR is extremely low. In this paper, to improve the dielectric properties of polymer composites, SR composites were fabricated with Ag decorated Ti3C2Tx MXene (Ti3C2Tx MXene-Ag) as the fillers. The thermal stabilities, dielectric and mechanical behaviors of the Ti3C2Tx MXene-Ag/SR composites were investigated. Compared with Ti3C2Tx MXene/SR composites, Ti3C2Tx MXene-Ag/SR composites exhibit higher dielectric constants, due to the deposition of Ag particles on the surfaces of Ti3C2Tx MXene nanosheets. The dielectric constant of Ti3C2Tx MXene-3.2Ag/SR composites is 7.29 (17.8% higher than MXene/SR composite and 162% higher than SR), and the loss tangent is as low as 0.00114 at 1 kHz. The enhanced interfacial polarization and micro-capacitor model can be used to explain the improved dielectric properties of the composites. Furthermore, the prepared SR composites have excellent mechanical properties, with a tensile stress of 554 kPa and an elongation at break of 257%. This work illustrates a method to obtain polymer-based composites with high dielectric and mechanical performances, which can be used as dielectric elastomers in actuators, sensors, biomedicine, energy collector and so on.

Silicone rubber matrix composites with shear thickening fluid microcapsules realizing intelligent adaptation to impact loadings

In this paper, silicone rubber matrix composites with shear thickening fluid microcapsules (SR-STF) with intelligent adaptation to impact loadings are fabricated for advanced impact protective structure. The composites exhibit more flexibility at low strain rates but higher stiffness at high loading rates, indicating significant strain-rate sensitivity. In addition, the initial flexibility and the strain-rate sensitivity of the composite increase with increasing the mass fraction of the STF microcapsules, which should be ascribed to the shear thickening and compressive jamming of the STF microcapsules in the composite during impulse loadings. Based on experimental results, a hyper-viscoelastic constitutive model is developed, in which the influence of the mass fraction of STF microcapsules, the strain-rate sensitivity, and the strain-hardening effect are taken into account. The paper develops a practical strategy for applications of STF in soft protective structures and provides a reliable prediction of the dynamic mechanical behavior of the SR-STF composites.

Enhancing the thermal stability and mechanical properties of phenyl silicone rubbers by controlling BN addition and phenyl content

Silicone rubber matrix composites with high thermal stability and flexibility are widely used in electronics and aerospace industries. In this work, boron nitride (BN) was added into the phenyl silicone rubber matrix as the reinforcement, and the influence of both the BN content and phenyl content on the thermal stability and mechanical properties of as-prepared composites was studied. The results showed that the thermal stability and mechanical properties were efficiently enhanced by BN addition, regardless of the phenyl content in the matrix. When the filler content was fixed at 40 wt%, the composite with 20 mol% phenyl showed the highest initial decomposition temperature (T5%) of 454 °C and good flexibility (tensile strength, elongation at break and hardness reached 3.10 MPa, 145% and 56 A). However, the decomposition temperature of 30% weight loss, mass retention rate at 800 °C and mechanical properties were improved for the composite with 50 mol% phenyl. The enhancement in thermal stability and mechanical properties was ascribed to the coupled effects of the interfacial force between the matrix and BN particles as well as the pores inside the composite, which was verified by Fourier transform infrared spectroscopy and scanning electron microscopy.

Performance evaluation of thermally aged ATH and BN co‐doped silicone rubber nano‐micro composites for power cable applications

AbstractPower cables are intended to operate at high temperatures over a long period which may change the performance of silicone rubber insulation used in high voltage cable accessories. Therefore, in the current study, to enhance the properties of silicone rubber, alumina try‐hydrate (ATH) and boron nitride (BN) micro and nanoparticles were added to the silicone rubber matrix. The synthesized undoped silicone rubber, silicone rubber with 40 wt% micro ATH, 7 wt% nano BN, and 10 wt% micro ATH + 5 wt% nano BN composites were thermally aged for 600 h at 180ºC. The composite properties were analyzed through electrical, thermal, and physicochemical techniques. To assess the electrical characteristics, water droplet‐initiated corona discharge studies as per IEC 60112 were conducted and leakage current, corona inception voltage, and erosion resistance were evaluated. A deep learning technique also was employed for the prediction of erosion resistance of the samples. Further, to examine the surface texture and chemical changes on the surface of the material, 3‐D microscopy and Fourier transform infrared spectroscopy (FTIR) was adopted. Finally, thermal distribution analysis was performed for all the composites by infrared thermography. The results demonstrated the suitability of nano‐micro co‐doped composites over nanocomposites and micro composites for power cable applications.

SR/GNPs/Pn@SiO2 shape-stabilized phase change composites with low leakage rate and adjustable thermal energy storage

The storage of latent heat using phase change materials (PCM) is an effective method of energy storage. In this study, silicone rubber (SR)/graphene nanoplates (GNPs)/paraffin@SiO2 phase change microcapsules (Pn@SiO2) shape-stabilized phase change materials (SSPCM) with high thermal conductivity, low leakage rate and tunable thermal management capability are prepared by method of add phase change microcapsules and thermal conductivity enhancer graphene nanoplates. The effects of Pn@SiO2 content on properties of the SR/GNPs/Pn@SiO2 (SGP) composites were investigated by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry. The results show that the enthalpy of phase change composites can be adjusted from 25.6 to 78.56 J·g−1 by changing the addition amount of Pn@SiO2 microcapsules. Moreover, the effect of GNPs on the thermal conductivity of SR matrix is greater than that of Pn@SiO2 on SR, as a consequence, the thermal conductivity of SGP composites decreases with the increase of Pn@SiO2. In addition, the thermal conductivity of SGP phase change composites can also reach 0.567 W·m−1K−1 after the addition of microcapsules, which dramatically shortens the response time of the material in the application. In summary, SGP composites have promising applications in the field of thermal storage.

Well-Distributed Polysilsesquioxane-Modified Carbon Nanotubes for Thermal Conductive Insulating Silicone Rubbers

Despite carbon nanotubes (CNTs) have garnered tremendous research interests for enhancing the electrical and thermal conductivity of polymers, it is still a considerable challenge to achieve the uniform dispersion of carbon nanotubes in polymer matrix. Herein, inspired by the mussel-inspired chemistry, we adopted the strategy of coating CNTs with polydopamine. And the polysilsesquioxane-modified CNTs (CNTs-PSQ) were obtained based on the click chemistry reaction. The FT-IR, Raman, XRD, and TGA collectively demonstrated the successful modification of PSQ on the surface of CNTs. The incorporation of PSQ could significantly improve the dispersion of CNTs in the silicon rubbers, and a strong interfacial interaction was formed between CNTs-PSQ and silicon rubber matrix, as observed from TEM images of silicon rubber/CNTs-PSQ nanocomposites. Meanwhile, compared with the nanocomposites with neat CNTs, the ones with CNTs-PSQ exhibited simultaneously improved electrical conductivity and insulating performance. This strategy proposed for the preparation of PSQ-modified CNTs provides insights toward highly insulating and thermal conducting polymers.

Silicone Rubber Based-Conductive Composites for Stretchable “All-in-One” Microsystems

Wearable electronics with development trends such as miniaturization, multifunction, and smart integration have become an important part of the Internet of Things (IoT) and have penetrated various sectors of modern society. To meet the increasing demands of wearable electronics in terms of deformability and conformability, many efforts have been devoted to overcoming the nonstretchable and poor conformal properties of traditional functional materials and endowing devices with outstanding mechanical properties. One of the promising approaches is composite engineering in which traditional functional materials are incorporated into the various polymer matrices to develop different kinds of functional composites and construct different functions of stretchable electronics. Herein, we focus on the approach of composite engineering and the polymer matrix of silicone rubber (SR), and we summarize the state-of-the-art details of silicone rubber-based conductive composites (SRCCs), including a summary of their conductivity mechanisms and synthesis methods and SRCC applications for stretchable electronics. For conductivity mechanisms, two conductivity mechanisms of SRCC are emphasized: percolation theory and the quantum tunneling mechanism. For synthesis methods of SRCCs, four typical approaches to synthesize different kinds of SRCCs are investigated: mixing/blending, infiltration, ion implantation, and in situ formation. For SRCC applications, different functions of stretchable electronics based on SRCCs for interconnecting, sensing, powering, actuating, and transmitting are summarized, including stretchable interconnects, sensors, nanogenerators, antennas, and transistors. These functions reveal the feasibility of constructing a stretchable all-in-one self-powered microsystem based on SRCC-based stretchable electronics. As a prospect, this microsystem is expected to integrate the functional sensing modulus, the energy harvesting modulus, and the process and response modulus together to sense and respond to environmental stimulations and human physiological signals.

Improvement of tracking resistance of silicone rubber via synergistically promoting ceramization with fluorophlogopite and platinum-nitrogen system

Efficient surface ceramization during the arc discharge is proposed as an efficient strategy to improve the tracking resistance of silicone rubber (SR). Herein, a tracking resistant silicone rubber (FPNs/Pt-NS/SR) with efficient ceramization was fabricated by introducing a small amount of fluorophlogopite nanosheets (FPNs), Karstedt's catalyst (Pt) and aminopropyltriethoxysilane (NS) into SR. FPNs/Pt-NS/SR2 containing 0.50 phr FPNs had excellent tracking resistance and passed 1A4.5 level. After heating treatment at 1000 °C, FPNs/Pt-NS/SR2 transformed into a rigid ceramic with a flexural strength of 7.54 MPa. It was revealed that the radical coupling reaction of SR chains was synergistically catalyzed by FPNs and Pt-NS at high temperature, which promoted the organic-to-inorganic conversion of the SR matrix to form rigid SiOC-like ceramic. When subjected to arc bombardment, the FPNs/Pt-NS/SR2 surface ceramized rapidly and formed a compact ceramic barrier, inhibiting the generation and development of tracking, thus efficiently improved the tracking resistance. This work provides a new strategy for preparing high-performance tracking resistant SR, which has wider application in the field of high-voltage insulation.

Invariable resistance of conductive nanocomposite over 30% strain.

The dependence of the electrical resistance on materials’ geometry determines the performance of conductive nanocomposites. Here, we report the invariable resistance of a conductive nanocomposite over 30% strain. This is enabled by the in situ–generated hierarchically structured silver nanosatellite particles, realizing a short interparticle distance (4.37 nm) in a stretchable silicone rubber matrix. Furthermore, the barrier height is tuned to be negligible by matching the electron affinity of silicone rubber to the work function of silver. The stretching results in the electron flow without additional scattering in the silicone rubber matrix. The transport is changed to quantum tunneling if the barrier height is gradually increased by using different matrix polymers with smaller electron affinities, such as ethyl vinyl acetates and thermoplastic polyurethane. The tunneling current decreases with increasing strain, which is accurately described by the Simmons approximation theory. The tunable transport in nanocomposites provides an advancement in the design of stretchable conductors.