Conductive Silicone Research Articles

Conductive, sensing stable and mechanical robust silicone rubber composites for large‐strain sensors

AbstractConductive polymer composites (CPCs) with carbon nanotubes (CNTs) have exhibited desirable sensing capacities to external stimuli. In this study, it is found that poor dispersion of single‐wall CNTs gives rise to low mechanical strength and unsteady responsive signal outputs of CPCs as strain sensing materials. With attempt to solve this problem, we prepare the conductive silicone rubber composites with hybrid CNT masterbatch and carbon black (CB) fillers (CNT/CB composites) by drying mixing method. Hybrid CBs separate and loosen the entanglement of CNTs in CNT/CB composites which forms more conductive paths and better dispersion of CNTs than those only with single CNTs (CNT‐composites). CNT/CB composite achieves a good conductivity, sufficient mechanical strength and high elasticity. In contrast with CNT‐composite, its reproducibility of resistance responsivity was remarkably improved at strain cycles, which display stable sensing properties for mechanically strain sensor applications. Importantly, CNT/CB composites show outdoor usage robustness, including excellent salt‐spray resistance, hot‐humidity stability and a wide operation temperature range of −40 to +50°C. It is believed that our work offers a simple approach to fabricate stable and flexible strain sensing materials, which is useful for sensor products.

A Novel Waterproof sEMG Electrode Based on Conductive Silicone for Underwater Signal Recognition

Current prosthetic hands remain challenging to use in water conditions for amputees, such as bathing, swimming, and washing. In order to improve the living conditions of amputees, we developed a waterproof conductive silicone electrode and proposed a corresponding signal recognition method. To evaluate the signal acquisition performance of the electrode, we designed two experiments to compare the conductive silicone electrode with the Ag/AgCl electrode according to acquired surface electromyography (sEMG) signals. For the first experiment, we acquired sEMG signals simultaneously by two kinds of the electrode on flexor carpi radialis, and the correlation coefficient of signals is 0.8752. In the second experiment, we used two kinds of electrodes to record sEMG signals, and the recognition accuracy has no significant difference. The results of the two experiments can show that the proposed electrode can be used for sEMG signal acquisition. Further, we developed an experiment to prove the feasibility of underwater signal acquisition by the proposed electrode. We acquired two-channel signals using the conductive silicone electrode in the water condition, and the recognition accuracy can still reach 93.41%. After sEMG signals were performed high-pass filtering, the accuracy is 94.44%. The experimental results demonstrate that we can use the electrode to acquire sEMG signals in the water condition. Based on the developed waterproof sEMG electrode and signal recognition system, it is now possible for amputees to use prosthetic hands in water conditions.

Silicone Solutions

Heat dissipation in EV batteries can be improved with highly engineered thermal interface materials such as gap fillers made of conductive silicone

Machinability improvement of Inconel 718 through mechanochemical and heat transfer effects of coated surface-active thermal conductive mediums

Low thermal conductivity usually leads to workpiece materials machine poorly and difficultly. Surface-active media has been proven to improve the machinability of workpiece materials. However, the non-thermal-conductive films have been selected in previous research as the surface-active medias, which are hard to improve machinability of workpiece materials with low thermal conductivity such as Inconel 718. This paper presents a novel technique to improve the machinability of Inconel 718 by applying surface-active thermal conductive medium (SACM) on the surface of workpiece before machining. The SACM can improve the heat dissipation and reduce the cutting temperature. Three SACMs including thermal conductive silicone grease (SG), glue (GL) and liquid graphene (GR) are recommended and applied on Inconel 718 surface. The effects of SACMs on the Inconel 718 machinability improvement are verified through machining experiments. The cutting temperature, surface roughness, and cutting force with and without SACMs are measured and analyzed. The results show that the minimum cutting force, cutting temperature and machined surface roughness under using GR SACM, which are reduced by 11%, 12% and 23% respectively compared with that without SACM. It is found that the improvement of Inconel 718 machinability is attributed to the coupling effect of mechanochemical and heat transfer effects of GR SACM.

Conductive Silicone Vocal Folds Reproducing Electroglottographic Signal in Pathophysiological Conditions

The development of larynx simulators as platforms for clinical investigations has been identified as a useful tool for understanding the pathophysiology of vocal folds. The primary goal of this study was the realization of electrically conductive silicone vocal folds able to replicate an electroglottography (EGG) signal under pathophysiological conditions, in order to provide a quantitative method for monitoring the vocal folds vibratory characteristics. Both simulators showed an oscillatory behavior similar to human counterpart, thanks to the materials used for their realization. In addition, the synthetic simulators are made conductive by a silicone-based conductive solution applied to the surface of the synthetic vocal folds, in order to acquire an electrical signal to be compared to an EGG signal. Results showed a direct correlation between conductance variation and the occurrence of vocal folds contact, as it happens for the real EGG signal. In addition, results suggested that both simulators are able to replicate the vibratory characteristics of healthy and pathological vocal folds and to reproduce an electrical signal that is comparable to a real EGG. This will represent a powerful tool to characterize and cluster different vocal folds pathologies, which can lead to a significant improvement of prevention programs and an early diagnosis for laryngeal diseases.

Custom-Fitted In- and Around-the-Ear Sensors for Unobtrusive and On-the-Go EEG Acquisitions: Development and Validation.

Objectives: This paper aims to validate the performance and physical design of a wearable, unobtrusive ear-centered electroencephalography (EEG) device, dubbed “EARtrodes”, using early and late auditory evoked responses. Results would also offer a proof-of-concept for the device to be used as a concealed brain–computer interface (BCI). Design: The device is composed of a custom-fitted earpiece and an ergonomic behind-the-ear piece with embedded electrodes made of a soft and flexible combination of silicone rubber and carbon fibers. The location of the conductive silicone electrodes inside the ear canal and the optimal geometry of the behind-the-ear piece were obtained through morphological and geometrical analysis of the human ear canal and the region around-the-ear. An entirely conductive generic earpiece was also developed to assess the potential of a universal, more affordable solution. Results: Early latency results illustrate the conductive silicone electrodes’ capability to record quality EEG signals, comparable to those obtained with traditional gold-plated electrodes. Additionally, late latency results demonstrate EARtrodes’ capacity to reliably detect decision-making processes from the ear. Conclusions: EEG results validate the performance of EARtrodes as a circum-aural and intra-aural EEG recording system adapted for a wide range of applications in audiology, neuroscience, clinical research, and as an unobtrusive BCI.

Conducting Silicone-Based Polymers and Their Application.

Over the past two decades, both fundamental and applied research in conducting polymers have grown rapidly. Conducting polymers (CPs) are unique due to their ease of synthesis, environmental stability, and simple doping/dedoping chemistry. Electrically conductive silicone polymers are the current state-of-the-art for, e.g., optoelectronic materials. The combination of inorganic elements and organic polymers leads to a highly electrically conductive composite with improved thermal stability. Silicone-based materials have a set of extremely interesting properties, i.e., very low surface energy, excellent gas and moisture permeability, good heat stability, low-temperature flexibility, and biocompatibility. The most effective parameters constructing the physical properties of CPs are conjugation length, degree of crystallinity, and intra- and inter-chain interactions. Conducting polymers, owing to their ease of synthesis, remarkable environmental stability, and high conductivity in the doped form, have remained thoroughly studied due to their varied applications in fields like biological activity, drug release systems, rechargeable batteries, and sensors. For this reason, this review provides an overview of organosilicon polymers that have been reported over the past two decades.

Highly Conductive Silicone Elastomers via Environment‐Friendly Swelling and In Situ Synthesis of Silver Nanoparticles

AbstractFlexible and stretchable conductors are crucial components for next‐generation flexible devices. Wrinkled structures often have been created on such conductors by depositing conductive materials on the pre‐stretched or organic solvent swollen samples. Herein, water swelling is first proposed to generate the wrinkled structures on silicone elastomers. By immersing silicone/sugar hybrid in water, a significant amount of swelling occurs as a result of osmosis and capillary interactions with the sugar and silicone matrix. Considering the drastic swelling effect and controllable swelling ratio, water swelling is used to replace the conventional pre‐stretching and organic solvent swelling to fabricate stretchable conductors. In situ growing of silver nanoparticles (AgNPs) is carried out on the swollen silicone elastomers. Wrinkled conductive silicone elastomers are successfully constructed after removing the residual water. The conductive elastomer has a sheet resistance of less than 1 Ω sq‐1 at zero strain and also shows high sensitivity when subjected to external deformation up to 100% strain. The silicone/sugar composite also possesses good 3D printability with the desired shear‐thinning property. Human motion detection is demonstrated using the 3D printed sensors. This work provides a facile and environment‐friendly strategy to fabricate superior flexible and stretchable sensing devices.

Effects of crosslinking reaction and extension strain on the electrical properties of silicone rubber/carbon nanofiller composites

AbstractStretchable conductive silicone rubber (SR) composites are important in wearable electronic devices and the crosslinking of SR composites is necessary for their applications. But the effect of the crosslinking reaction on the electrical conductivity of SR composites is rarely reported. In this article, the effect of crosslinking reaction on the electrical conductivity of SR composites filled with conductive carbon black, carbon nanotubes, and graphene are studied. The crosslink density of SR composites increases with increasing curing time, but the electrical conductivity decreases sharply at the early stage of crosslinking, especially for SR/conductive carbon black composite, which is ascribed to the reaggregation of conductive nanofillers in SR during the crosslinking process. The elastic modulus of the three SR composites gradually increases while the elongation at break decreases with increasing curing time, and the SR/carbon black composite shows ultra‐high elongation at break (1578%). In addition, SR/graphene composite is more sensitive to the extension strain than SR/carbon black and SR/carbon nanotubes composites, and its gauge factor is 414 at the strain ranges of 3–25%. This research work brings a new method to optimize the crosslinking structure of conductive SR composites.

Effect of Micro-Scale and Nano-Scale Boron Nitride on Thermal Property of Silicone Rubber Via Experimental and Simulation Method

With the development of electronic integration, excellent insulation and high thermal conductivity thermal interface materials (TIMs) are needed to be used. Most of currently reported TIMs have high thermal conductivity, but their processing is complex and not suitable for industrial application. In this work, a simple method is provided to prepare thermally conductive silicone rubber (SR) composites. Effects of size and ratios of micro-scale boron nitride (BN) and nano- scale BN on mechanical properties, thermal conductivity and thermal stability of SR/BN composites are investigated. Results show that when the ratio of micro-scale BN loading to nano-scale BN loading is equal and the loading of BN are 60 phr, the thermal conductivity of SR/BN composites reaches to 2.632 W/(m·K), which is 18 times higher than that of SR. Meanwhile, when the loading of micro-scale BN is twice than that of nano-scale BN, the SR/BN composites maintain good mechanical properties (the tensile strength reaches to 6.2 MPa). In addition, the SR/BN composites exhibit excellent thermal stability and the heat loss of all samples are nearly 45%. This can provide a new idea for a simple and effective preparation of the SR/BN composites with a high thermal conductivity and insulating.

Thermally conductive silicone composites modified by graphene-oxide aerogel beads loaded with phase change materials as efficient heat sinks

Electrically insulating phase change composite materials (PCCMs) with lightweight, good thermal management performance, high stability and high mechanical strength are strongly desired for lithium-ion battery (LIB) thermal management. This research study presents a group of PCCMs based on the integration of reduced graphene-oxide aerogel beads (rGOAB), phase change materials (PCMs) and thermally conductive silicone rubbers (SRs). To demonstrate the thermal management performance, a 3 × 3 square 18650 LIB module was inserted into a SR pack. The temperature reduction (temperature reduction of the battery cells at the hottest point in the SR pack compared with in air) reached 8.6 °C, 13.0 °C and 14.7 °C at 1C, 2C and 3C discharge rate, respectively, at a concentration of 20 wt% PCM beads in SR with thermal conductivity of 0.5 W/mK. The specific energy reduction of above-mentioned pack is only 15.8%, substantially lower than the commercial level (above 30% to 40%). The lowest specific energy reduction in SR pack with thermal conductivity of 0.3 W/mK goes down to 13.4%, indicating its remarkable lightweight and high energy density features. The effects of PCM-encapsulant type, SR matrix thermal conductivity and bead size on LIB temperature reduction were also discussed. The heat transfer mechanism between the matrixes and rGOAB/PCM was thoroughly explained. Mechanical properties and battery thermal management performance of the composites were systematically examined. The rGOAB/PCM@SR composites exhibited more than 10 times of impact strength compared with expanded graphite-based PCCMs and higher compressive toughness above the phase transition point.

Multifunctional cementitious composites with integrated self-sensing and hydrophobic capacities toward smart structural health monitoring

In this study, multifunctional cementitious composites with integrated self-sensing and hydrophobicity capacities were developed and investigated using conductive graphene nanoplate (GNP) and silicone hydrophobic powder (SHP). The mechanical properties, permeability, water contact angle, microstructure and piezoresistivity were studied and compared under different contents of GNP and SHP. The highest compressive and flexural strengths with 1% SHP and 2% GNP reached 62.6 MPa and 8.9 MPa, respectively. The water absorption significantly was decreased with the content of SHP, but was minorly affected by GNP. The water contact angle firstly increased but then decreased with the dosages of GNP and SHP. SHP and GNP could reduce the microscale pores and enhance the density of microstructures. The piezoresistivity under compression firstly exhibited low gauge factor, but then gradually increased to a constant value under high-stress magnitude. Moreover, compared to the conventional cement-based sensors, this piezoresistive cementitious composites containing SHP and GNP as novel cement-based sensors are less sensitive to water content and humidity. The outcomes can provide an insight into promoting the application of multifunctional cement-based sensors toward structural health monitoring under various ambient conditions.

Conductive waterborne silicone acrylate emulsion/carbon nanotubes composite coatings: preparation and characterization

Common organic coatings are hardly conductive and seldom applied in electromagnetic shielding fields. Thereby, the thermoplastic conductive nanocomposites, waterborne silicon-acrylic emulsion (SAE) merged with multi-walled carbon nanotubes (MWCNTs) and silica sols (Si), were prepared via co-blending method. Compared with neat SAE, the conductivity of composite latex (5 wt.% MWCNT and 1.5 wt.% Si) was raised nearly seven orders of magnitude, and the tensile strength and Young’s modulus were enhanced to 366% and 177%, respectively. The contact angle was raised from 59° to 84°. The curing temperature was decreased by 12.8 °C. These enhancements proved that the addition of MWCNTs and silica sol could boost the electrical, mechanical, curing, heatproof and waterproof performances of SAE, which will be employed in high-property conductive paint areas, including the flexible and stretchable devices.

High thermal conductive silicone rubber composites constructed by strawberry-structured Al2O3-PCPA-Ag hybrids

Silicone rubber (SR) is commonly used as thermal conductive material due to its high thermal stability, good insulation, and excellent flexibility. However, its low thermal conductivity (λ) limits its wide applications. Here, high thermal conductive SR composites were prepared by incorporating strawberry-structured alumina-poly(catechol-polyamine)-silver (denoted as Al2O3-PCPA-Ag) thermal conductive hybrids. The strawberry-structured Al2O3-PCPA-Ag hybrids were synthesized by modification of Al2O3 with poly(catechol-polyamine) (PCPA) followed by electroless plating of silver (Ag). The PCPA layer decreased the interfacial thermal resistance and Ag nanoparticles benefited the phonon transmission of SR composites. The as-prepared 30 vol% Al2O3-PCPA-Ag/SR composite showed a maximum thermal conductivity of 0.4367 W/mK, which was 3.3-fold higher than that of the SR matrix (0.1320 W/mK). Due to the Coulomb blockage effect of quantum-size Ag nanoparticles, the maximum AC conductivity of Al2O3-PCPA-Ag/SR composites at 100 Hz was 2.14E-12 S/cm. The proposed method provides a new strategy for preparation of high thermal conductive polymeric composites.

Properties of thermally conductive silicone rubbers filled with admicellar polymerized polypyrrole‐coatedAl2O3particles

AbstractPolypyrrole (PPy) nanolayers were introduced on the surface of alumina (Al2O3) particles via admicellar polymerization. The properties of silicone rubbers (SRs) filled with PPy‐coated Al2O3and pristine Al2O3as thermally conductive fillers were studied and compared. The results demonstrate that the addition of PPy‐coated Al2O3leads to a better interfacial compatibility but lower cross‐linking density of the composites than pristine Al2O3. The improvement in the compatibility and the decrease in the cross‐linking density are paradoxes in affecting mechanical properties. The improvement in the compatibility shows a slight predominance on the strength at low‐filler contents. Lower cross‐linking density of modified‐Al2O3/SR composites led to a better processing performance and a higher maximum filler loading amount than the pristine Al2O3/SR composites, which is beneficial to increasing the thermal conductivity and maintaining a relatively good strength. The PPy‐coated Al2O3/SR composite with 83 wt% filler content has a thermal conductivity of 1.98 W/(m K) and a tensile strength of 2.9 MPa, and the elongation at break was 63%. Functionalized fillers by admicellar polymerization used in the fabrication of filler/SR composites not only improve the interfacial compatibility but also optimize and expand the functions of the composites, which has great significance for the production and application of thermally conductive SR in some branches of industry (automotive, electrical engineering, etc.) in the future.

P.652 Hypernutrition due to litter reduction induces depressive behavior and decreased GFAP astrocyte expression in prepubertal rats with no oxytocin influence

Simultaneous measurements of glucose, lactate, and neurotransmitters (e.g., glutamate) in cell culture over hours and days can provide a more dynamic and longitudinal perspective on ways neural cells respond to various drugs and environmental cues. Compared with conventional microfabrication techniques, direct writing of conductive ink is cheaper, faster, and customizable, which allows rapid iteration for different applications. Using a simple direct writing technique, we printed biosensor arrays onto cell culture dishes, flexible laminate, and glass to enable multianalyte monitoring. The ink was a composite of PEDOT:PSS conductive polymer, silicone, activated carbon, and Pt microparticles. We applied 0.5% Nafion to the biosensors for selectivity and functionalized them with oxidase enzymes. We characterized biosensors in phosphate-buffered saline and in cell culture medium supplemented with fetal bovine serum. The biosensor arrays measured glucose, lactate, and glutamate simultaneously and continued to function after incubation in cell culture at 37 °C for up to 2 days. We cultured primary human astrocytes on top of the biosensor arrays and placed arrays into astrocyte cultures. The biosensors simultaneously measured glucose, glutamate, and lactate from astrocyte cultures. Direct writing can be integrated with microfluidic organ-on-a-chip platforms or as part of a smart culture dish system. Because we print extrudable and flexible components, sensing elements can be printed on any 3D or flexible substrate.

Preparation of Binary Thermal Silicone Grease and Its Application in Battery Thermal Management.

To improve the problems of large interface thermal resistance and low heat dissipation efficiency in battery thermal management (BTM), this paper uses methyl silicone oil as the matrix, AIN, copper powder (CP), and carbon fiber (CF) as thermally conductive fillers, and acetone and stearic acid as particle surface modification components. A variety of binary thermal silicone greases (TSGs) with different compositions were prepared. Different instruments were used to test the material properties of TSGs, and a better TSG was selected to coat the interface between battery and phase change material (PCM) for battery charging and discharging experiments. Through the analysis of experimental data, it was found that among the TSGs made of three mixed fillers (AIN/CP, AIN/CF, CP/CF), the three TSGs had good thermal stability, and their thermal degradation temperature both exceeded 300 °C. As the ratio of thermally conductive filler was gradually changed from 5:1 to 1:5, the TSG containing CP/CF had higher thermal conductivity and lower volume resistivity, while the TSG containing AIN/CF had the least damage due to interface wear. The acidification treatment of thermally conductive filler can improve the adsorption and compatibility of thermally conductive particles and silicone oil, and reduce the oil separation rate of TSGs. The prepared expanded graphite (EG)/paraffin wax (PW) composite phase change material (CPCM) has a relatively large latent heat of phase change, which can effectively control the temperature of the battery, but coating TSG between the battery and the CPCM can further enhance the heat dissipation effect of the battery.

Techniken zur Bestimmung von Parametern für die elektrische Personenwarnung

Methods for the determination of parameters for the electrical warning of persons Objectives: The aims of this publication are to present the main findings of research into the development of a wearable system for electrical warning, identify the current challenges and introduce the next research objectives. Methods: A basic study (n = 81) with self-adhesive electrodes on the right upper arm was used to investigate the influence of pulse width, electrode size and electrode position on perceived thresholds as well as qualitative and spatial perception. Varying textile cuff types were developed and tested. The suitability of varying support materials and textile electrodes was investigated with regard to adaptability, comfort, electrical conductivity, DC resistance and traction elastic behaviour. The textile and self-adhesive electrodes were compared with regard to thresholds as well as qualitative and spatial perceptions (n = 30). Results: Practical parameter sets of the thresholds (perception, attention, intolerance) were determined for various pulse widths, electrode sizes and positions. The dominant qualitative perceptions were “Knocking” (perception and attention threshold) and “Muscle twitch” (intolerance threshold). The spatial perception was located at the stimulation area. The resulting textile cuff contains a knitted fabric with electrically conductive surfaces and a layer of an electrically conductive silicone compound. The comparison between textile and self-adhesive electrodes showed no differences regarding thresholds and qualitative and spatial perceptions. The impedance of the textile electrodes was (1.5 to 3 times) higher than that of the self-adhesive electrodes. Conclusions: Future studies will investigate the influences of working conditions, climatic conditions, age, gender and skin properties. The further development of the textile cuffs is focused on the improvement of the contact between electrode and skin to optimise the transition impedance. Keywords: electric stimulation – electrode – TENS – smart textile – wearable

Subcutaneous Ports for Chronic Nerve Cuff and Intramuscular Electrode Stimulation in Animal Models.

Tracking recovery after nerve injury may require many intermittent assessments over long periods, preferably with non- or minimally invasive methods. We developed subcutaneous electrical connection ports (ECPs) for repeated connection to nerve cuff or intramuscular electrodes via transdermal needles and evaluated them during studies of laryngeal reinnervation. Animal experiment. Laboratory. ECPs were designed and 3-dimensionally printed for connection to bipolar electrodes with biocompatible polymers. Dual compartments filled with conductive silicone capped with nonconductive silicone were used to make the connections between electrode leads and transdermally inserted needles. Ten dogs (19-29 kg) were implanted with 22 ECPs. In 7 dogs, 11 electrodes were placed on recurrent laryngeal nerves proximal to transection and suture repair to track laryngeal reinnervation. In 6 dogs, 8 spinal accessory nerve cuff electrodes were used to stimulate neck muscle contraction. In 2 dogs, 3 electrodes were implanted in the thyroarytenoid muscle. Stimulation thresholds, electromyography, and videolaryngoscopic imaging were obtained in 156 tests over survival periods up to 32 months. Stimulation data provided information about ECP performance. ECPs added negligible resistance to electrodes (mean ± SD, 2.14 ± 0.9 Ω). Despite some electrode leads breaking distally, ECPs were reliable and well tolerated at implant sites and enabled periodic assessment of nerve and muscle function over the time course of laryngeal reinnervation. Histology showed ECP encapsulation as thin layers of connective tissue and minimal acute inflammation. Custom ECPs are easily fabricated and cause little tissue reaction over months to years of subcutaneous implantation, facilitating long-term physiologic studies.

All‐Inorganic Ionic Polymer‐Based Memristor for High‐Performance and Flexible Artificial Synapse

AbstractThe implementation of memristors that are wearable and transparent has attracted significant attention. However, the development of high‐performance memristors that simultaneously possess high flexibility and environmental stability has remained a tremendous challenge suffering from limited choice of materials with both good ion‐electron mobility and structural flexibility. Inspired by the unique poly‐ionic nature of ammonium polyphosphate (APP), a novel Au/APP/ITO memristor with favorable flexibility and stability is prepared. Synaptic behaviors can be stimulated by voltage pulses that are 20 ns in width, 0.1 V in amplitude, and repeatable under 104 pulse cycles, thereby outperforming several other benchmark memristors. Further, the device, prepared on conductive silicone, can sustain its synaptic performance even under 360° bending. Furthermore, the device can sustain its synaptic behaviors even after exposure to fire for 60 s and 5.6 kGy of ionic irradiation. Additionally, APP is determined to be nontoxic, biodegradable, and transparent when compared with all the organics and inorganics used in previous memristors. The results of this study will inspire the development of more inorganic polymers for their utilization in future environmentally stable and flexible electronics.