Silicone Elastomer Composites Research Articles

Design of High-Temperature Packaging Insulation for Power Modules Using Grafted Nanostructured Silicone Elastomer Composites

Design of High-Temperature Packaging Insulation for Power Modules Using Grafted Nanostructured Silicone Elastomer Composites

Dielectric Behavior of Stretchable Silicone Rubber–Barium Titanate Composites

In this study, elastomer composites, including silicone rubber and barium titanate, were fabricated by mechanical mixing, a low-cost, fast, and easy technique to produce highly dielectric materials. The resulting composites were investigated in terms of their dielectric and mechanical properties in terms of filler percentage in the mixture. Dielectric permittivity measurements were taken using the microwave regime, and uniaxial tensile tests were carried out for the study of the materials’ mechanical properties, while combined experiments were also carried out to investigate potential correlations between them. The experimental results show that barium titanate inclusions in silicone matrix significantly improve the dielectric constant while reducing the mechanical properties of composites. In addition, combined experiments show that the composites exhibit a nearly stable dielectric profile under mechanical deformations. Consequently, mechanically mixed barium titanate–silicone elastomer composites could potentially become a cost-effective alternative in the extensive market for insulating materials and flexible electronics.

Characteristics stability assessment of silica/alumina trihydrate based silicone elastomer composites subjected to long-term weathering under bipolar direct current for industrial electrical insulation

Room temperature vulcanized silicone rubber (RTV-SiR) coatings co-filled with silica (SiO2) and alumina trihydrate (ATH) fillers were subjected to long-term accelerated weathering under bipolar direct current (DC). Experimentations were conducted on fabricated samples of RTV-SiR with 5% nano-silica and RTV-SiR with 20% ATH in a specially designed weathering chamber. An extended aging (10,000 h) was conducted on samples energized equally under both polarity voltages to evaluate the effect of positive and negative voltages on the performance of RTV coating under bipolar high voltage DC. The electrical stability of specimens was assessed using online leakage current measurement, hydrophobicity, volume, and surface resistivity analysis. For mechanical characteristics of test samples hardness shore-A, tensile strength, weight loss, and elongation-at-break were measured and analyzed. Variations in chemical, morphological, and thermal degradation of the samples with aging were assessed using characterization tools like Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Thermal Gravimetric Analyzer (TGA), respectively. Findings explicated that samples with nano SiO2, offer better hydrophobic recovery and hence better leakage current suppression while ATH-filled composites exhibited enhanced thermal stability and better resistance to mechanical alterations. Furthermore, the comparative analysis of voltage polarity elucidates that the impact of positive DC was more profound in aging.

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.

Thermally Stable Silicone Elastomer Composites Based on MoS2@Biomass-Derived Carbon with a High Dielectric Constant and Ultralow Loss for Flexible Microwave Electronics.

With the miniaturization and integration of electronic components in wireless communication and wearable devices, the demand for low-cost flexible composites with temperature-stable high dielectric constant and low loss has substantially increased. However, such comprehensive properties are fundamentally difficult to combine for conventional conductive and ceramic composites. Here, we develop silicone elastomer (SE) composites based on hydrothermally grown MoS2 on tissue paper-derived cellulose carbon (CC). Such design promoted the formation of microcapacitors, multiple interfaces, and defects reinforcing interfacial and defect polarizations and resulting in a high dielectric constant of 9.83 at 10 GHz with low filler loading of 15 wt %. Unlike highly conductive fillers, MoS2@CC with low conductivity ensured a very low loss tangent of 7.6 × 10-3, which was also influenced by the filler dispersion and adhesion to the matrix. Apart from breaking the typical conflict between high dielectric constant and low losses of traditional conductive composites, MoS2@CC SE composites were highly flexible with temperature-stable dielectric properties making them attractive as flexible substrates in microstrip antenna applications and extreme environment electronics. Moreover, recycling from waste tissue paper makes them potential candidates as low-cost and sustainable dielectric composites.

All-Polymer Piezo-Composites for Scalable Energy Harvesting and Sensing Devices.

Silicone elastomer composites with piezoelectric properties, conferred by incorporated polyimide copolymers, with pressure sensors similar to human skin and kinetic energy harvester capabilities, were developed as thin film (<100 micron thick) layered architecture. They are based on polymer materials which can be produced in industrial amounts and are scalable for large areas (m2). The piezoelectric properties of the tested materials were determined using a dynamic mode of piezoelectric force microscopy. These composite materials bring together polydimethylsiloxane polymers with customized poly(siloxane-imide) copolymers (2−20 wt% relative to siloxanes), with siloxane segments inserted into the structure to ensure the compatibility of the components. The morphology of the materials as free-standing films was studied by SEM and AFM, revealing separated phases for higher polyimide concentration (10, 20 wt%). The composites show dielectric behavior with a low loss (<10−1) and a relative permittivity superior (3−4) to pure siloxane within a 0.1−106 Hz range. The composite in the form of a thin film can generate up to 750 mV under contact with a 30 g steel ball dropped from 10 cm high. This capability to convert a pressure signal into a direct current for the tested device has potential for applications in self-powered sensors and kinetic energy-harvesting applications. Furthermore, the materials preserve the known electromechanical properties of pure polysiloxane, with lateral strain actuation values of up to 6.2% at 28.9 V/μm.

Effect of the support bath on embedded 3D printing of soft elastomeric composites

Soft elastomers have great potentials in advanced materials applications but are difficult to be manipulated by extrusion-based 3D printing due to low viscosity. This study focuses on the embedded 3D printing of silicone elastomer composites and how the support bath influences the physical properties of the composites. Results show the liquid support medium can offer a stable 3D printed structure and higher printing resolution compared to extruding in air. The extensibility and toughness of the elastomeric composites obtained by embedded 3D printing were increased by 66% and 39% by tailoring the formula of the bath material. It shows the embedded 3D printing could be a smart way for achieving next-generation soft materials.

Evaluate the effect of graphene and milled glass fibre on the thermal, flame and dielectric properties of silicone elastomer filled with aluminium hydroxide

In this work, the thermal stability, thermal conductivity, dielectric frequency response, smoke factor (SF), fire performance index (FPI), and fire growth index (FGI) of silicone elastomer composites were studied and compared. TGA/DTG results indicated that the addition of graphene nanoplatelets (GNP)/milled E-glass fibres (MGF) improved the thermal stability of silicone composites by increasing the Tmax2, T20% and T30%, whereas thermal conductivity was improved by 93%–115% compared to RTV1 and 12%–24% compared to RTV2. Based on the GNP/MGF loadings, a low relative permittivity and low dielectric loss were observed. Furthermore, GNP/MGF filled silicone composites exhibited high FPI and low FGI, and microstructure analysis revealed a compact bottom char layer with no crevices on the surface. The most promising silicone composites were RTV4 and RTV5, which had higher thermal stability, improved thermal conductivity, excellent FPI and FGI values, and excellent dielectric properties, making them more suitable for electrical outdoor insulation exposed to fires.

FORC analysis of magnetically soft microparticles embedded in a polymeric elastic environment

First-order reversal curve (FORC) analysis allows one to investigate composite magnetic materials by decomposing the magnetic response of a whole sample into individual responses of the elementary objects comprising the sample. In this work, we apply this technique to analysing silicone elastomer composites reinforced with ferromagnetic microparticles possessing low intrinsic coercivity. Even though the material of such particles does not demonstrate significant magnetic hysteresis, the soft matrix of the elastomers allows for the translational mobility of the particles and enables their magnetomechanical hysteresis which renders into a wasp-waisted major magnetization loop of the whole sample. It is demonstrated that the FORC diagrams of the composites contain characteristic wing features arising from the collective hysteretic magnetization of the magnetically soft (MS) particles. The influence of the matrix elasticity and particle concentration on the shape of the wing feature is investigated, and an approach to interpreting experimental FORC diagrams of the MS magnetoactive elastomers is proposed. The experimental data are in qualitative agreement with the results of the simulation of the particle magnetization process obtained using a model comprised of two MS particles embedded in an elastic environment.

Silicone Elastomer Composites Fabricated with MgO and MgO-Multi-Wall Carbon Nanotubes with Improved Thermal Conductivity.

The effect of multiwall carbon nanotubes (MWCNTs) and magnesium oxide (MgO) on the thermal conductivity of MWCNTs and MgO-reinforced silicone rubber was studied. The increment of thermal conductivity was found to be linear with respect to increased loading of MgO. In order to improve the thermal transportation of phonons 0.3 wt % and 0.5 wt % of MWCNTs were added as filler to MgO-reinforced silicone rubber. The MWCNTs were functionalized by hydrogen peroxide (H2O2) to activate organic groups onto the surface of MWCNTs. These functional groups improved the compatibility and adhesion and act as bridging agents between MWCNTs and silicone elastomer, resulting in the formation of active conductive pathways between MgO and MWCNTs in the silicone elastomer. The surface functionalization was confirmed with XRD and FTIR spectroscopy. Raman spectroscopy confirms the pristine structure of MWCNTs after oxidation with H2O2. The thermal conductivity is improved to 1 W/m·K with the addition of 20 vol% with 0.5 wt % of MWCNTs, which is an ~8-fold increment in comparison to neat elastomer. Improved thermal conductive properties of MgO-MWCNTs elastomer composite will be a potential replacement for conventional thermal interface materials.

Thermal conductivity of silicone elastomer with a porous alumina continuum

Abstract In this paper, porous alumina continuum (PAC) was prepared with alumina powders (APs) by the gel-casting method and was applied to obtain silicone elastomer (SR) composites (PAC/SR) by the impregnating process. The structure was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The influences of PAC on thermal conductivity and dielectric permittivity of PAC/SR composites were studied in comparison with AP/SR composites. When the alumina content was 14 vol%, the thermal conductivity of the PAC/SR composites reached 0.84 W·(m·K)−1, which was 3.1 times higher than that of the AP/SR composites. The thermal conductivity of PAC/SR and AP/SR was simulated by theoretical models, and the interfacial thermal resistance was calculated by effective medium theory, which indicated the advantages of PAC in enhancing the thermal conductivity of SR-based composites and the reduced interfacial thermal resistance between PAC and SR.

Photochromic spiropyrane/silicone composite enabling convenient detection of ultraviolet radiation in the sunlight

It is well-known that exposure to excessive ultraviolet radiation often causes skin erythema, pigmentation and even cancer. Therefore, it is very necessary to timely know UV radiation in the sunlight. Herein, a methacryloxy-functionalized spiropyran (MASP)/silicone elastomer composite (MASP/Si) with controlled photochromic behavior is developed, and thus a colorimetric card consisted of diverse colors caused by various given intensity of UV radiation is established. The photochromic behavior indicates that the photochromic MASP/Si with 0.1 wt% MASP reveals rapid UV radiation response and good fatigue resistance to alternant UV radiation and visible light. Based on the established colorimetric card, the MASP/Si can be used as a UV detector to detect repeatedly the intensity of UV radiation in the sunlight. Even after storage at ambient for nearly one year or 50 times distortion, the MASP/Si still can well detect the UV radiation.

Control of Mullins stress softening in silicone elastomer composites by rational design of fumed silica fillers

The influence of fumed silica as reinforcement filler is investigated on the Mullins stress softening in composite silicone elastomers. Especially, the impact of surface area, loading level, surface chemistry, and structure modification of fumed silica is evaluated on the fatigue behavior of high consistency silicone rubber. It is observed that high loading level and large surface area of fumed silica increase the energy loss during initial loading cycles which is related to disruptions in filler-polymer interactions. Addition of a processing aid or hydrophobization of the silica surface decrease the brittleness and energy loss of the compounds. A close correlation between Shore A hardness and energy loss is found confirming the contribution of the filler-polymer interactions on Mullins stress-softening. At the same time, the permanent set remains almost independent of the surface hydrophobicity of the filler indicating a breakdown of the structured silica agglomerates during initial deformation. To improve the fatigue resistance of the silicone elastomer, a structure modified and hydrophobic silica, AEROSIL® R 8200, was used leading to the lowest permanent set even at high loading levels in combination with good mechanical reinforcement. The reduction in energy loss and permanent set is attributed to the combination of hydrophobic surface and low aggregate structure of the silica preventing agglomerate breakdown and chain disentanglements at the silica surface. This study provides fundamental understanding on the relation between filler-polymer interactions, filler morphology and Mullins stress softening for the rational design of future filler particles in reinforced elastomer composites with improved fatigue resistance.

Mechanical, dielectric and actuated properties of carboxyl grafted silicone elastomer composites containing epoxy-functionalized TiO2 filler

Silicone rubber (SiR) is one of the most promising dielectric elastomer (DE) materials for DE actuator, but it is still limited by low properties such as mechanical strength, dielectric constant and actuated strain at low electric fields. In this study, we report the design and preparation of SiR DE composite with simultaneously improved tensile strength, dielectric constant and actuated strain at low electric fields by introducing both polar functional group and multifunctional filler. Firstly, carboxyl groups were grafted onto polymethylvinylsiloxane (PMVS) by using a radical-mediated thiol-ene click reaction to improve the dipole polarizability. Meanwhile, epoxy group-functionalized TiO2 (E-TiO2) particles as multifunctional fillers were prepared and filled into carboxyl groups modified PMVS (PMVS-COOH). The esterification reactions between carboxyl groups of PMVS-COOH and epoxy groups of E-TiO2 results in interfacial covalent cross-linking, good interfacial interaction, and strong interfacial polarizability of E-TiO2/PMVS-COOH dielectric composites. As a result, the tensile strength largely increases from 0.33 MPa to 0.89 MPa as the content of E-TiO2 increases from 10 phr to 30 phr. The dielectric constant at 103 Hz of the composite with 30 phr E-TiO2 reaches 8.98, which is 3.3 times as reference SiR due to the simultaneously improved dipole and interfacial polarizability. The actuated strain at low electrical field (15 kV·mm−1) of the composite with 30 phr E-TiO2 reaches 3.7% without any pre-strains, which is 5.2 times than that of reference SiR. Our study provides a simple and effective strategy to simultaneously improve the mechanical, dielectric and actuated properties of SiR DE.

Barium titanate particle filled silicone elastomer composite: Preparation and evaluation of morphology and mechanical behaviour

Barium titanate (BaTiO3) nano particles with different percentage by weight were added in silicone rubber as a filler to develop silicone elastomer composites. The morphology of the fractured surface of the prepared silicone elastomer composite film was investigated to see the distribution of BaTiO3 nano filler in the polymer matrix. The obtained results showed good distribution of BaTiO3 up to 10% by weight in silicon elastomer composite. Beyond this 10% weight percentage, agglomeration of BaTiO3 particles occurs. The mechanical characterizations of silicone elastomer composites with different weight % of BaTiO3 particles were performed through uniaxial tensile testing. Elastic modulus of composite increases when filler content increases up to 10%. However, further increase in the filler content results agglomeration of particles in the composite and decrease in elastic modulus of the silicone elastomer composite. The results show that the optimum value of filler content in the prepared composite is between 5% to 10%.

Design and preparation of carbon black/carbon nanotubes/ silicone elastomer composites with high elasticity and high electrical conductivity stability

Conductive elastomer composites (CECs) with high elasticity, flexibility and sealability of elastomers and the high electrical conductivity of conductive fillers have been widely used in electromagnetic interference shielding, microwave absorpting, stretchable electronics and sensors. To achieve high electrical conductivity, the commonly used fillers are metal powers, metal-coated inorganic particles and carbon black (CB). High filler content is usually required to effectively improve the conductivity, resulting in low elasticity, low flexibility, and poor processability, all of which limit the applications of CECs. Earlier works reported the synergistic effect of two kinds of fillers with different geometrical dimensions, among which CB and carbon nanotubes (CNTs) are two promising candidate that have been widely studied. However, CNTs are easily entangled and aggregated in elastomer matrix with low viscosity, resulting in unsatisfactory conductivity (mostly 104–105 Ω cm). Moreover, little attention has been paid on CECs with high elasticity, high electrical conductivity stability filled with low filler contents (low cost) for stretchable electronics and strain sensors. The relationship between conductive network and electrical conductivity as well as electrical conductivity stability is still not clear. In this study, we designed and prepared CB/CNTs/polymethylvinylsiloxane (PMVS) composites with good elasticity, high electrical conductivity and good electrical conductivity stability by tailoring the filler network structure of the composites with a low content of CB and CNTs in PMVS matrix. The composite with 1.8 vol% of CNTs and 1.2 vol% of CB showed high elasticity, low volume resistivity (271 Ω cm), and high electrical conductivity stability. CNTs used in this study were carbon nanotube arrays (CNTA) that were in situ synthesized on single-layered double hydroxide (LDH) nanosheets by chemical vapor deposition method. The negatively charged CNTs with a loose structure showed no physical entanglement, which can be well dissociated into many single CNTs and dispersed uniformly in PMVS matrix during mechanical shearing. The high aspect ratio of CNTs can help to obtain high conductivity at low filler content, whereas the isotropy of CB helps to rebuild up the new conductive network after tensile strain. On the other hand, these CNTs are curved in the elastomer matrix, become oriented during stretching, and can curve again after recovery, and thus act as nanosprings. The high elasticity of the CNTs nanosprings leads to high elasticity of the PMVS-CB-CNTs composites. We further studied the relationship between conductive network and electrical conductivity as well as electrical conductivity stability of PMVS-CB-CNTs composites. The results showed that CB and CNTs can form a strong dual conductive network at low filler contents, leading to a high conductivity. When stretching, CNTs act as bridges to connect CB and CB aggregations together, maintaining the strong conductive network and thus high electrical conductivity stability under tensile strain. After tensile recovery, CB and CNTs can reform a strong conductive network, leading to high electrical stability during tensile-release cycles.

High permittivity ceramics loaded silicone elastomer composites for flexible electronics applications

The dielectric properties of silicone elastomer composites are important in designing flexible electronic devices. The recent explosive growth in wireless communication, automotive and biomedical applications increases the demand for flexible dielectric materials. However, it is very difficult to identify a homogeneous material which possesses these desired properties. Flexible silicone rubber- ceramic composites based BaTiO3 (BT), SrTiO3 (ST) and Ca(1−x)Nd(2x/3)TiO3 (CNT) ceramic fillers have been prepared. The relative permittivity, thermal conductivity and water absorption increase whereas the coefficient of linear thermal expansion decrease as the volume fraction of filler increases. In the case of dielectric loss; a decreasing trend is shown by SR-ST and SR-CNT composites with filler volume fraction whereas SR-BT composites show a reverse trend since BT is a lossy material. The composites have εr in the range 3–14 in the microwave frequency range. The composites with high filler loading are suitable candidates for core of flexible dielectric waveguide and embedded capacitor applications and the composites with ST and CNT are suitable for cladding of flexible dielectric waveguide and also for microwave substrate applications

Synchronously Tailoring Strain Sensitivity and Electrical Stability of Silicone Elastomer Composites by the Synergistic Effect of a Dual Conductive Network.

The use of conductive polymer composites (CPCs) as strain sensors has been widely investigated. A wide range of strain sensitivities and high repeatability are vital for different applications of CPCs. In this study, the relations of the conductive filler network and the strain-sensing behavior and electrical stability under fatigue cycles were studied systematically for the first time based on the conductive polymethylvinylsiloxane (PMVS) composites filled with both carbon nanotubes arrays (CNTAs) and carbon black (CB). It was proved that the composites could be fabricated with large strain-sensing capability and a wide range of strain sensitivities by controlling the volume ratio of CNTA/CB and their amounts. Additionally, the CNTA/CB/PMVS composite with 3 vol % content of fillers showed high sensitivity (GF is 10 at 60% strain), high repeatability (the relative standard deviation (RSD) of the max R/R0 value is 3.58%), and electrical stability under fatigue cycles (value range of R/R0 is 1.62 to 1.82) at the same time due to the synergistic effects of the dual conductive network of CNTAs and CB. This could not be achieved by relying on a single CNTA or CB conductive network. This study may provide guidance for the preparation of high performance CPCs for applications in strain sensors.

Effect of Triclosan on Self‐Assembly of Alkyl Ammonium Surfactants Adsorbed within Montmorillonite Galleries in Silicone Elastomer Composites

SummaryPoly(propylene) homopolymer/fly ash (50% wt) composites have been prepared from two samples of fly ash that differ in terms of the geographic source of coal feedstock, which left one of the samples with a higher group I and II metal content. A screening study indicated that Lubrizol Solplus® C800 (an unsaturated carboxylic acid dimer coupling agent), initiated with dicumyl peroxide, conferred the best strength–toughness balance to the composites. In some cases, however this was related to detachment of the interfacial region due to possible extraction of PP‐C800 adduct‐group I and II ion reaction products. Interfacial adhesion was arguably too high in the case of the fly ash sample bearing a lower level of group I and II ions. These deductions were also supported by DSC data.

Investigation of carbon black/silicone elastomer/dimethylsilicone oil composites for flexible strain sensors

Conductive carbon black (CB) nano-particle filled silicone elastomer (SE) composites with dimethyl silicone oil (SO) as a diluting agent and plasticizer were fabricated for potential strain sensing applications. Heat treatment was used to stabilize the composites, and thermal gravimetric analysis confirmed the good stability of the composites after heat treatment. Effect of CB loading on electrical properties of the composites was studied and a percolation transition range of 0.5–2.5 wt% was observed. I–V characteristics and impedance analysis were used to reveal the conductive mechanisms of the composites. The presence of SO reduced the Young's modulus of the composites without lowering the elongation at break. Characterization of coupled electromechanical properties of the composites demonstrates that, in the post-percolation range, the 9.0CB composite possesses suitable strain sensitivity, good repeatability and linearity as well as slight strain rate dependence, so that it can be used in flexible strain sensors for measuring repeated large deformations.