Polydimethylsiloxane Composites Research Articles

Flexible electrically conductive biomass-based aerogels for piezoresistive pressure/strain sensors

Flexible, compressible and conductive aerogels were fabricated by incorporating polyaniline (PANI) into bacterial cellulose/chitosan (BC/CH) composites through facile freeze-drying technique. The PANI/BC/CH aerogel fabricated with the BC:CH weight ratio of 1:1 displayed the highest resistance response and showed extremely high sensitivity (1.41 kPa−1), low pressure detection (32 Pa), wide range of pressure deformation and extraordinary stability as a piezoresistive sensor. Polydimethylsiloxane (PDMS) was embedded into PANI/BC/CH aerogels to form PANI/BC/CH PDMS composites that displayed good stability under large mechanical deformation. Furthermore, applications of PANI/BC/CH aerogels and PANI/BC/CH/PDMS composites in piezoresistive sensors for wearable devices were also reported, which could detect human motions, ranging from joint movement to speech recognition, thus suggesting feasibility in health monitoring systems.

Synergistic Effects of BaTiO3/Multiwall Carbon Nanotube as Fillers on the Electrical Performance of Triboelectric Nanogenerator Based on Polydimethylsiloxane Composite Films

Herein, polydimethylsiloxane (PDMS) composite films containing BaTiO3 particles with an average size of 70 and 500 nm are prepared and characterized, respectively. Then, triboelectric nanogenerators (TENG) based on the composite films are designed at different BaTiO3 sizes and mass ratios. In addition, multiwall carbon nanotubes (MWCNTs) are also used for uniform dispersion of BaTiO3 particles in composite films for the TENG device. With the synergistic effects of BaTiO3/MWCNT fillers, discrete conductive micronetworks surrounded by BaTiO3 particles form, and then, the effective filler–matrix interface effect in the three‐phase composite is enhanced, leading to superior triboelectric output performance, supported by much higher dielectric permittivity and COMSOL simulation. Moreover, the triboelectric output performance of TENG changes with different‐sized BaTiO3 particles. As to BT‐70‐MWCNT/PDMS composites, with the same mass ratio of BT, the peak output current is always higher than that of BT‐500‐MWCNT/PDMS. Furthermore, the optimum BT mass ratio of BT‐70‐MWCNT/PDMS composites is also higher than that of BT‐500. With BaTiO3 of size 70 nm, the maximum surface charge density is about 160 μC m−2 under an optimized mass ratio, whereas it is about 110 μC m−2 for BaTiO3 of size 500 nm.

Achieving highly electrical conductivity and piezoresistive sensitivity in polydimethylsiloxane/multi-walled carbon nanotube composites via the incorporation of silicon dioxide micro-particles

Conductive polydimethylsiloxane (PDMS) composites have attracted extensive attention worldwide due to its potential application on wearable electronics and strain sensors. In this work, silicon dioxide micro-particles (μ-SiO2) were added into the flexible PDMS/multi-walled carbon nanotubes (MWCNT) composites to improve their electrical conductivity and piezoresistive sensitivity. First, the μ-SiO2 particles can exhibit volume exclusion effect to dense MWCNT fillers in PDMS matrix, which leads to the high electrical conductivity and low percolation threshold. Furthermore, the larger μ-SiO2 particles could give higher electrical conductivity and lower percolation threshold. For examples, the electrical conductivity and percolation threshold of the PDMS/MWCNT composites with 0.3 vol% MWCNT increased from 3.5 × 10−9 to 2.2 × 10−4 S/m and decreased from 0.44 to 0.08 vol%, respectively, by the incorporation of 30 vol% 85 μm-SiO2 particles. Second, the piezoresistive sensitivity of PDMS/MWCNT composites was abruptly enhanced by the addition of μ-SiO2 particles because of the high modulus of μ-SiO2 particles, which resulted in the asymmetric deformation in the composites. The deformation of PDMS/MWCNT phase was higher in the PDMS/MWCNT/μ-SiO2 composites than that of the PDMS/MWCNT composites, which leaded to high piezoresistive sensitivity. For example, the gauge factor (GF) of the PDMS/MWCNT composites increased from 1.3 to 62.9 at 30% compression strain by the addition of 30 vol% 1 μm-SiO2 particles. The highest piezoresistive sensitivity was found in the PDMS/MWCNT/μ-SiO2 composites with lowest size of μ-SiO2 particles due to the highest deformation of PDMS/MWCNT phase.

Bioinspired Photodetachable Dry Self-Cleaning Surface.

Geckos have adapted to the complicated natural environment with its excellent climbing ability. Current artificial gecko-inspired synthetic adhesives (GSAs) mimic gecko's attach-detach mechanism by creating anisotropic and hierarchical structures. Easy detachment and high self-cleaning capability are still the unsolved problems in GSAs. This study presents an unprecedented photodetachable mechanism of making bioinspired smart surfaces utilizing carbon dot (CD)-doped polydimethylsiloxane (PDMS) composites. Under ultraviolet (UV) irradiation, it could be triggered up to 80.46% reduction of adhesion force between PDMS-CDs bioinspired surfaces and contaminating particles. A load-drag-pull (i.e., LDP) test mimicking gecko's locomotion was adopted to test the dry self-cleaning capabilities of these bioinspired surfaces, where the falling rate of the model contaminates (PS micropellets; average size in diameter ∼8 μm) can reach up to 54.83% after seven repeated steps under UV irradiation. The significantly improved dry self-cleaning capability is attributed to the photothermal effect of CDs inside the PDMS matrix. The mechanism proposed in this work will find its applications in the realms of climbing robots, space adhesive devices, and self-cleaning, advanced gripping technologies for pick and place or assembly.

A conductive cell-imprinted substrate based on CNT-PDMS composite.

Cell function regulation is influenced by continuous biochemical and biophysical signal exchange within the body. Substrates with nano/micro-scaled topographies that mimic the physiological niche are widely applied for tissue engineering applications. As the cartilage niche is composed of several stimulating factors, a multifunctional substrate providing topographical features while having the capability of electrical stimulation is presented. Herein, we demonstrate a biocompatible and conductive chondrocyte cell-imprinted substrate using polydimethylsiloxane (PDMS) and carbon nanotubes (CNTs) as conductive fillers. Unlike the conventional silicon wafers or structural photoresist masters used for molding, cell surface topographical replication is challenging as biological cells showed extremely sensitive to chemical solvent residues during molding. The composite showed no significant difference compared with PDMS with regard to cytotoxicity, whereas an enhanced cell adhesion was observed on the conductive composite's surface. Integration of nanomaterials into the cell seeding scaffolds can make tissue regeneration process more efficient.

A directional fibre optic ultrasound transmitter based on a reduced graphene oxide and polydimethylsiloxane composite.

Strongly directional ultrasound sources are desirable for many minimally invasive applications, as they enable high-quality imaging in the presence of positioning uncertainty. All-optical ultrasound is an emerging paradigm that exhibits high frequencies, large bandwidths, and a strong miniaturisation potential. Here, we report the design, modelling, and fabrication of a highly directional fibre-optic ultrasound transmitter that uses a composite of reduced graphene oxide and polydimethylsiloxane as the optical ultrasound generator. The ultrasound transmitter, which had an outer diameter of just 630 μm, generated ultrasound with a pressure exceeding 0.4 MPa for axial distances up to 16 mm, at a large bandwidth of 24.3 MHz. The ultrasound beam exhibited low divergence, with a beam diameter ranging between 0.6 and 2.1 mm for distances between 0 and 16 mm. The presented directional optical ultrasound source is hence well-suited to high-resolution interventional imaging.

All-Printed Human Activity Monitoring and Energy Harvesting Device for Internet of Thing Applications.

A self-powered device for human activity monitoring and energy harvesting for Internet of Things (IoT) devices is proposed. The self-powered device utilizes flexible Nano-generators (NGs), flexible diodes and off-the-shelf capacitors. During footsteps the NGs generate an AC voltage then it is converted into DC using rectifiers and the DC power is stored in a capacitor for powering the IoT devices. Polydimethylsiloxane (PDMS) and zinc stannate (ZnSnO3) composite is utilized for the NG active layer, indium tin oxide (ITO) and aluminum (Al) are used as the bottom and top electrodes, respectively. Four diodes are fabricated on the bottom electrode of the NG and connected in bridge rectifier configuration. A generated voltage of 18 Vpeak was achieved with a human footstep. The self-powered smart device also showed excellent robustness and stable energy scavenger from human footsteps. As an application we demonstrate human activity detection and energy harvesting for IoT devices.

Preparation and properties of flexible conductive polydimethylsiloxane composites containing hybrid fillers

Aiming to fabricate highly flexible conductors via a facile method, hybrid fillers of carbon nanotubes (CNTs) and carbon fiber (CF) were incorporated with polydimethylsiloxane (PDMS) using a solution blending method. The results showed that the hybrid fillers evidently decreased the composite resistivity and the lowest resistivity was achieved with the composite that had 6:4 CNT/CF ratio when the total filler content was 1 wt%. Due to the low filler content, the stretching strains of the composites reached greater than 200%, and the conductive network which was formed by flexible CNT and rigid CF was sensitive to strain and the related resistance change of resulted composites reached 2480.5% with a gauge factor of 50. The alternating current electrical, rheological and morphological property measurements were performed, and the results presented the existence of synergistic effect between the hybrid fillers in the conductive networks which decreased resistivity of composites. Therefore, the PDMS/CNT/CF nanocomposites are good candidates for application as inflexible sensors.

Evaluation of nanosilica emission in polydimethylsiloxane composite during incineration.

At the end of their life cycle, it is expected that many industrial silicone components end up in incineration waste plants. Hence, the issue concerning the risks resulting from the generation of fumes (combustion gas and aerosol) has to be addressed. The aim of our work was to investigate the behavior and fate of nanosilicas from filled polydimethylsiloxane nanocomposites burnt under two different scenarios of incineration. Combustion tests have been performed at lab-scale using a particular tubular furnace and a specific cone calorimeter. The collected fumes (particulate matter and gas phase) have been characterized using various techniques. The results show persistent nanosilica particles, newly produced nanosilica particles in the fumes and in the residues, as well as silicon oxycarbide SixOyCz particles which seem to originate from polysiloxane matrix decomposition.

Stabilization of formaldehyde into polydimethylsiloxane composite: application to the in situ determination of illicit drugs.

The Marquis test is the most frequently used spot color assay for the screening of unknown drugs such as amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, 3,4-metilenedioxymethamphetamine, and morphine. However, this test involves the use of the toxic reagent formaldehyde, as well as the manipulation of concentrated sulfuric acid. Here, we report a new format of this test that improves the sustainability and safety for the operator by immobilizing formaldehyde into a polydimetylsiloxane composite. In contact with a solution (or suspension) of the suspected sample in sulfuric acid, the dispositive delivers formaldehyde and the reaction takes place in a few seconds. Under the proposed conditions, only small amounts of the drug (μg) are necessary to produce intense changes of color. In addition, the percentage of the drug in the sample can be established by obtaining pictures of the test vials and subsequent analysis of the digitalized images. The responses were linear for amphetamine-like drugs up to a concentration of 100mgL-1, and the precision achieved was adequate (relative standard deviations, RSDs < 10%). The developed composites were tested for the determination of MDMA in several drug street samples, and a good correlation with the results obtained by a reference method based on liquid chromatography was found. The main advantages of the proposed approach over the traditional Marquis test format are better portability and safety for the operator at a lower cost and the possibility of using it for quantitative analysis.

Polydimethylsiloxane and poly(ether) ether ketone functionally graded composites for biomedical applications

Functionally graded materials (FGMs), with varying spatial, chemical and mechanical gradients (continuous or stepwise), have the potential to mimic heterogenous properties found across biological tissues. They can prevent stress concentrations and retain healthy cellular functions. Here, we show for the first time the fabrication of polydimethylsiloxane and poly(ether) ether ketone (PDMS-PEEK) composites. These were successfully manufactured as a bulk material and functionally graded (stepwise) without the use of hazardous solvents or the need of additives. Chemical, irreversible adhesion between layers (for the FGMs) was achieved without the formation of hard, boundary interfaces. The mechanical properties of PDMS-PEEK FGMs are proven to be further tailorable across the entirety of the build volume, mimicking the transition from soft to harder tissues. The introduction of 20 wt% PEEK particles into the PDMS matrix resulted in significant rises in the elastic modulus under tensile and compressive loading. Biological and thermal screenings suggested that these composites cause no adverse effects to human fibroblast cell lines and can retain physical state and mass at body temperature, which could make the composites suitable for a range of biomedical applications such as maxillofacial prosthetics, artificial blood vessels and articular cartilage replacement.

Enhanced thermal properties of PDMS composites containing vertically aligned graphene tubes

The development of high-power electronics, such as Li-ion batteries for electric cars, demands effective thermal management, because the temperature rise beyond the normal operating range is detrimental to the electronic performance. Due to its high thermal conductivity, graphene would be one of the ideal candidates for thermal management. But in graphene/polymer composites, thermal energy takes far more time to transfer through polymer chains than through graphene due to the vibration of polymer chains and phonon scattering. In this work, vertically aligned graphene tubes /polydimethylsiloxane (PDMS) composites were prepared and their thermal properties were characterized. Graphene loadings were controlled from 1.09 wt% to 4.5 wt% in the composites. The ordered-orientation of graphene in polymer facilitates the heat transfer. The results show that the thermal conductivity reaches 1.7 W m-1 K−1, which is 10.8 times higher than that of pure PDMS. Incorporation of structured graphene can reduce the thermal expansion. It is forecasted that the prepared composites have considerable prospects in encapsulation and heat dissipation of electronic devices.

Tuning the Surface Chemistry of Graphene Oxide for Enhanced Dielectric and Actuated Performance of Silicone Rubber Composites

The influence of reduction temperature on the electromechanical properties and actuation behavior of polydimethylsiloxane (PDMS) dielectric elastomer containing the thermally reduced graphene oxide (rGO) with different surface chemistry has been systematically investigated. A set of rGO nanosheets was prepared by thermal reduction of graphene oxide (GO) at four temperatures (150, 200, 300, and 400 °C). The dielectric permittivity, dielectric loss, and elastic modulus of PDMS composites were increased, while the electrical breakdown strength of composites was decreased with an increase of the reduction temperature of GO. A thermodynamic model applied for studying the electromechanical deformation and stability of PDMS/GO(rGO-x) dielectric elastomer composites showed that the optimum value of the break-point was observed in PDMS/rGO-300. It is shown for the first time that the variation of electromechanical instability and recovery behavior are attributed to the surface chemistry of rGOs. A critical reducti...

Enhancing thermal conductivity of polydimethylsiloxane composites through spatially confined network of hybrid fillers

The thermal conductivity of polydimethylsiloxane (PDMS) composites containing short carbon fiber (SCF) and whisker carbon nanotube (wCNT) were studied by investigating the synergy of both fillers and the dimensions of the conducting filler network.The SCF was more effective in enhancing the thermal conductivity of PDMS than wCNT due to its larger aspect ratio and more homogeneous dispersion, which facilitated the formation of a continuous conducting network. The PDMS composites were further compressed to reduce the sample thickness from 2.0 mm to 0.2 mm by using a Spatial Confining Forced Network Assembly (SCFNA) process. Consequently, the thermal conductivity of the composites was further enhanced as the thickness decreased across the range of filler concentrations. The combination of wCNT and SCF increased the thermal conductivity of the PDMS composites to 2.087 W/(mK) when the sample thickness was 0.2 mm, which is ascribed to the bridging effect of wCNT with SCF network and the densified conducting network. In summary, the hybrid SCF/wCNT filler system facilitates the connections among fillers, and the SCFNA approach further densifies the conducting filler network. Both effects synergistically enhance the thermal conductivity of the composites without increasing the filler concentrations. The PDMS/SCF/wCNT composite was tested as a heat spreader, and it reduced the temperature by 12.23 °C as compared to the pure PDMS counterpart. The SCFNA method offers a facile route to produce higher thermally conductive yet light weighting polymer composites.

Stress-sensitive thermally conductive elastic nanocomposite based on interconnected graphite-welded carbon nanotube sponges

Stress-sensitive thermally conductive elastic materials are necessary for designing flexible, thermal-sensitive devices such as sensors or skins. However, combining high thermal conductivity (k) and good cyclic resilience (elastic deformation) is challenging according to the Newton−Laplace equation. This study presents a graphite-welded carbon nanotube (w-CNT) sponges as a three-dimensional skeleton for polydimethylsiloxane (PDMS) composites. Welds of discontinuous CNT with graphite layers promote phonon and stress transfer at the junctions. The interconnected network and uniform closely packed polymers not only enable stress-sensitive heat conduction but also retain excellent cyclic elastic deformability and good resilience. The composite combines a stress-sensitive isotropic k and excellent elastic deformation. The w-CNT/PDMS composite at the content of 4.57 wt% w-CNT exhibits a high k up to 13.1 W m−1 K−1 at 29.2% compressive strain. The composite also retains high k with the loss of 2% after 100000 compression cycles. The stress-sensitive w-CNT/PDMS composite enable it to be used in a flexible thermal-sensitive strain sensor. The bending and stretching of the finger are tracked by thermochromic changes controlled by stress-enhanced heat conduction. The stress-sensitive thermally conductive w-CNT/PDMS composites can be developed for a multitude of flexible sensors by optimizing their microstructures.

Self-Powered Motion-Driven Triboelectric Electroluminescence Textile System.

In recent years, smart light-emitting-type electronic devices for wearable applications have been required to have flexibility and miniaturization, which limits the use of conventional bulk batteries. Therefore, it is important to develop a self-powered light-emitting system. Our study demonstrates the potential of a new self-powered luminescent textile system that emits light driven by random motions. The device is a ZnS:Cu-based textile motion-driven electroluminescent device (TDEL) fabricated onto the woven fibers of a ZnS:Cu-embedded PDMS (polydimethylsiloxane) composite. Triboelectrification, which raises a discontinuous electric field, is generated by the contact separation movement of the friction material. Therefore, light can be generated via triboelectrification by the mechanical deformation of the ZnS:Cu-embedded PDMS composite. This study showed that the TDEL emitted light from the internal triboelectric field during contact and from the external triboelectric field during separation. Light was then emitted twice in a cycle, suggesting that continuous light can be emitted by various movements, which is a key step in developing self-powered systems for wearable applications. Therefore, this technology is a textile motion-driven electroluminescence system based on composite fibers (ZnS:Cu + PDMS) and PTFE fibers, and the proposed self-emitting textile system can be easily fabricated and applied to smart clothes.

Mechanically Enhanced Electrical Conductivity of Polydimethylsiloxane-Based Composites by a Hot Embossing Process.

Electrically conductive polymer composites are in high demand for modern technologies, however, the intrinsic brittleness of conducting conjugated polymers and the moderate electrical conductivity of engineering polymer/carbon composites have highly constrained their applications. In this work, super high electrical conductive polymer composites were produced by a novel hot embossing design. The polydimethylsiloxane (PDMS) composites containing short carbon fiber (SCF) exhibited an electrical percolation threshold at 0.45 wt % and reached a saturated electrical conductivity of 49 S/m at 8 wt % of SCF. When reducing the sample thickness from 1.0 to 0.1 mm by the hot embossing process, a compression-induced percolation threshold occurred at 0.3 wt %, while the electrical conductivity was further enhanced to 378 S/m at 8 wt % SCF. Furthermore, the addition of a second nanofiller of 1 wt %, such as carbon nanotube or conducting carbon black, further increased the electrical conductivity of the PDMS/SCF (8 wt %) composites to 909 S/m and 657 S/m, respectively. The synergy of the densified conducting filler network by the mechanical compression and the hierarchical micro-/nano-scale filler approach has realized super high electrically conductive, yet mechanically flexible, polymer composites for modern flexible electronics applications.

Mesoporous Highly-Deformable Composite Polymer for a Gapless Triboelectric Nanogenerator via a One-Step Metal Oxidation Process.

The oxidation of metal microparticles (MPs) in a polymer film yields a mesoporous highly-deformable composite polymer for enhancing performance and creating a gapless structure of triboelectric nanogenerators (TENGs). This is a one-step scalable synthesis for developing large-scale, cost-effective, and light-weight mesoporous polymer composites. We demonstrate mesoporous aluminum oxide (Al2O3) polydimethylsiloxane (PDMS) composites with a nano-flake structure on the surface of Al2O3 MPs in pores. The porosity of mesoporous Al2O3-PDMS films reaches 71.35% as the concentration of Al MPs increases to 15%. As a result, the film capacitance is enhanced 1.8 times, and TENG output performance is 6.67-times greater at 33.3 kPa and 4 Hz. The pressure sensitivity of 6.71 V/kPa and 0.18 μA/kPa is determined under the pressure range of 5.5–33.3 kPa. Based on these structures, we apply mesoporous Al2O3-PDMS film to a gapless TENG structure and obtain a linear pressure sensitivity of 1.00 V/kPa and 0.02 μA/kPa, respectively. Finally, we demonstrate self-powered safety cushion sensors for monitoring human sitting position by using gapless TENGs, which are developed with a large-scale and highly-deformable mesoporous Al2O3-PDMS film with dimensions of 6 × 5 pixels (33 × 27 cm2).

Incorporation of carbon nanotubes in polydimethylsiloxane to control Escherichia coli adhesion

Polydimethylsiloxane (PDMS) is widely used as a coating material and in the fabrication of medical implants for the urinary tract and also in biofilm reactors. When this polymer is used in biomedical devices, bacterial adhesion to the surface must be avoided to prevent implant‐related infections, whereas in biofilm reactors, adhesion has to be promoted. In this work, incorporation of carbon nanotubes (CNTs) on PDMS composites was tested to control Escherichia coli adhesion. Pristine and functionalized CNTs were used and the adhesion assays were performed in the hydrodynamic conditions prevailing in the urinary tract. Surfaces were chemically and morphologically characterized by contact angle measurements, scanning electron microscopy, and X‐ray photoelectron microscopy. Incorporation of small amounts (0.1%) of pristine CNTs decreased bacterial adhesion by 20%, whereas functionalized CNTs increased bacterial adhesion also by 20%. This demonstrates that bacterial adhesion can be modulated by incorporating different types of CNTs in the polymer. It is likely that incorporation of higher amounts of CNTs in polymer composites can affect bacterial adhesion by more than 40%. POLYM. COMPOS., 40:E1697–E1704, 2019. © 2018 Society of Plastics Engineers

Development and Characterization of Mechanically Durable Silicone-Polythiourethane Composites Modified with Tetrapodal Shaped ZnO Particles for the Potential Application as Fouling-Release Coating in the Marine Sector.

Ecological considerations strongly necessitate the development of environmentally friendly antifouling paints. A promising alternative to biocide containing antifouling paints are fouling-release coatings, which are non-toxic and designed to prevent permanent attachment of marine organisms to the surface, due to their low surface energy. However, these coatings suffer from insufficient mechanical properties, which make them unsuitable for mechanically stressed surfaces e.g., on ship hulls. To overcome those obstacles, polydimethylsiloxane (PDMS)-polythiourethane (PTU) composites modified with tetrapodal shaped micro-nano ZnO particles (t-ZnO) were produced and characterized by evaluating the surface energy, mechanical properties, and fouling-release performance. Among all variations, PTU/1 wt.% PDMS composites with 1 wt.% t-ZnO particles possess superior properties for applications as fouling-release coatings for maritime purposes.