Polydimethylsiloxane Structures Research Articles

Viscoelastic particle focusing and separation in a microfluidic channel with a cruciform section.

Considerable attention has been given to elasto-inertial microfluidics, which are widely applied for the focusing, sorting, and separation of particles/cells. In this work, we propose a novel yet simple fabrication process for a microchannel with a cruciform section, where elasto-inertial particle focusing is explored in a viscoelastic fluid. SU-8 master molds for polydimethylsiloxane (PDMS) structures were fabricated via standard photolithography, and then plasma bonding, following self-alignment between two PDMS structures, was performed for the formation of a microchannel with a cruciform section. The particle behaviors inside the fabricated microchannel were experimentally investigated for various flow rates and particle sizes and compared with those inside a microchannel with a square cross section. The experimental results revealed that 3D particle focusing was achieved in the center under viscoelastic fluid flow over a wide range of flow rates without any shear thinning. Even for small particles (∼2 μm), single-line particle focusing was observed in the microchannel with a cruciform section but not in a square microchannel with the same hydraulic diameter (Dh = 75 μm). The effects of four reflex angles (270°) on particle focusing were quantitatively evaluated through numerical simulation. The simulation revealed that the migration pattern of particles is governed by the combined effect of the reflex angles and fluid inertia, leading to characteristic particle focusing behavior within the cross section of the cruciform microchannel. These findings agree well with the experimental results, which highlight the superior capability of the cruciform microchannel for inertial particle focusing across a wide range of particle sizes.

Stacked hydrogel-based brain-on-chips utilizing capillary force flow pinning

Cellular processes in brain tissue such as migration, proliferation, morphology, and differentiation are influenced by mechanical cues, demonstrating the interplay between the structure and function. Given the complexity, it remains a substantial challenge to establish a reliable in vitro model mimicking structural properties as brain tissue. To address this challenge, we propose an innovative approach to create vertical hydrogel stacks based on microfluidic technology. 3D-printed microfluidic features in the sidewall profile of our chip designs allowed us to faithfully replicate these capillary force flow pinning structures in polydimethylsiloxane. After the successful application of hydrogel of a defined height, thanks to the pinning process and plating of stem-cell-derived neurons, the results demonstrated the potential of our BoC platform, providing a valuable tool for neuroscience research.

Reliable plasmonic biosensing with atmospheric pressure dielectric barrier discharge oxygen plasma treated polydimethylsiloxane microfluidic channels

Polydimethylsiloxane (PDMS) has emerged as a popular choice of material for many microfluidic and flexible sensing devices despite its inherent hydrophobic nature. Here, we report on the use of atmospheric pressure dielectric barrier discharge (APDBD) oxygen (O2) plasma in the development of hydrophilic and protein repulsive PDMS microchannels for plasmonic sensing application. The effect of plasma treatment on the wettability, surface energy and hydrophilicity retention capacity of PDMS was determined using contact angle measurements. The PDMS sample exposed to low-power DBD O2 plasma for 6 min demonstrated lowest contact angle of 35.15˚, surface energy of 62.83 mN/m and hydrophilicity retention capacity of more than 50 days in Phosphate Buffered Saline (PBS). The treatment of PDMS with plasma induces surface hydrophilicity due to the introduction of polar functional groups as evinced by Fourier Transform Infrared (FTIR) analysis without compromising the bulk structure and optical properties of PDMS which were confirmed by X-Ray Diffraction (XRD) and Ultraviolet-visible (UV-Vis) Spectroscopic measurements. The plasma treated PDMS was used in the construction of a microfluidic Surface Plasmon Resonance (SPR) biosensor which demonstrated very low detection limits of 7.13 ng/ml, 5.91 ng/ml and 1.47 ng/ml and high sensitivities of 16.8˚/(µg/ml), 13.5˚/(µg/ml) and 16.65˚/(µg/ml) against anti-Human Immunoglobulin-G protein raised in mouse, goat and rabbit respectively. The obtained results infer that APDBD O2 plasma is a promising technique to render PDMS hydrophilic suited for reliable microfluidic based plasmonic biosensing applications.

Magnetized microcilia-based triboelectric nanogenerators with mechanoluminescence for energy harvesting and signal sensing

Flexible triboelectric nanogenerators with multimodal sensing capabilities have received considerable attention due to their potential for the development of wearable technology. However, the accurate and reliable display of motion trajectories represents a significant challenge. The structure design of the triboelectric nanogenerators yarn with magnetized microcilia and mechanoluminescence (MLY-TENG) was designed, which can be woven into the fabric of display force trajectories. The positive electrode is constructed by the braided yarn with a porous structure, consisting of polyurethane formed by wet spinning. Meanwhile, the flexible negative electrode is designed by the recombination of magnetized microcilia and the mechanoluminescent structure of polydimethylsiloxane, matching with the porous structure of the positive electrode, which enhances the electric transfer. At a compression depth of 100 %, compression frequency of 5 Hz, and magnetized powder of 50 wt%, the proposed MLY-TENG shows the triboelectric properties of 109.2 V and exhibits excellent cyclic stability. Furthermore, the magnetized microcilia on the luminescent magnetized microcilia (LMM) film with the polyurethane-copper-polyurethane (PWP)-based fabric (MLF-TENG) distinguishes the shape and area of object recognition with electrical signals and visual sensing of mechanoluminescence. The MLY-TENG offers the possibility of the development of advanced visualization techniques for wearable electronic devices.

Tuning thermal and structural properties of nano‐filled PDMS elastomer

AbstractIncreasing the thermal stability and thermal conductivity of polydimethylsiloxane (PDMS) is a crucial issue for thermal applications. This paper focuses on enhancing PDMS's thermal and structural properties by incorporating nanocomposite into the PDMS matrix. An investigation of the impact of rGO‐CaCO3 nanocomposite on the thermal and structural properties of PDMS was performed using Field Emission Scanning Electron Microscopy (FESEM), X‐ray diffraction (XRD), the thermogravimetric analysis and differential thermal analysis (TGA‐DTA), and thermal analyzer tests. It was observed that PDMS doped with rGO‐CaCO3 nanocomposite shows better thermal stability, thermal conductivity, and higher crystallinity. The thermal stability was enhanced significantly by adding a 5% rGO‐CaCO3 nanocomposite, and the initial and end degradation temperatures rose to 492°C and 605°C, respectively. The thermal conductivity of pure PDMS is approximately 0.17 W/mK, whereas a conductive elastomer filled with 5% rGO‐CaCO3 nanocomposite exhibits a thermal conductivity of 0.44 W/mK at a temperature of 20°C. In contrast, the thermal diffusivity is enhanced from 0.13 mm2/s to 0.366 mm2/s. Additionally, the Fourier Transform Infra‐Red (FTIR) spectrum at 1411 cm−1 becomes sharp and noisy, and an additional peak arises at 1398 cm−1, corresponding to the vibrational rocking of the CC bond and COC bond in CaCO3 and rGO.Highlights The manuscript focuses on the development of conductive elastomer by incorporating rGO‐CaCO3 doped and its effect on the morphology, structure, and thermal properties of PDMS. The variation in peak intensity observed in XRD attributed to disparities in the crystalline structure of PDMS due to the inclusion of nanocomposite. The thermal degradation range is observed to shift toward the upper end. The degradation temperature at the beginning and end of the process is observed to move to 492°C and 605°C, respectively, upon introducing a 5% rGO‐CaCO3 nanocomposite. The addition of 5% rGO‐CaCO3 filled conductive elastomers shows a significant improvement of approximately 2.6 times in heat conductivity than bare PDMS.

Fabrication of ultra-precise flexible electrothermal film by direct-write printing porous graphene-Ag structure

In this study, graphene oxide (GO)‑silver nitrate (AgNO3) composite ink was prepared with stable printability, which could match the direct-write print technique for patterning GO-AgNO3 composite structure. Reduced graphene oxide (rGO)‑silver (Ag) porous structure could be obtained with a freeze-drying and gas phase reduction process. The rGO-Ag porous structure could reach a conductivity of 3.2 × 105 S/m through quantum penetration effect with the bridging action. Subsequently, polydimethylsiloxane (PDMS) encapsulated the rGO-Ag porous structure, and a special composite structure of PDMS/ rGO-Ag/PDMS films could be obtained by adjusting the wetting effect. PDMS provided a good tensile property and excellent bending resistance, and then a relative resistance changes within 5 % could be achieved after the number of 10,000 bending times. With the rGO-Ag porous structure compressed into a thinner film, an ultra-precise flexible electrothermal performance could be realized with the conductive network and flexible package structure. The surface temperature of fabricated composite film could reach 201.3 °C at the voltage of 7 V, within a heating time of 25 s, and maintaining the temperature for 1800 s. Meanwhile, the flexible electrothermal film could keep a stable temperature after 120 power on/power off cycles. Furthermore, the flexible electrothermal film also has a linear temperature control ability, which could carry out the linear temperature control with different temperature regions. At last, the ultra-precise flexible electrothermal film exhibits an excellent applying effect for the wrist hot compress, pipeline heating and window cleaning with uneven ice thickness. Therefore, the direct-write printed porous graphene-Ag structure presents a special property for fabricating ultra-precise flexible electrothermal film, which could provide a great research significance and application value in printing electronic structure and manufacturing electronic device.

Experimental Study on SPR Array Sensing Chip Integrated with Microvalves.

This paper discusses a microfluidic system designed for surface plasmon resonance (SPR) sensing, incorporating integrated microvalves. This system is built from a layered structure of polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA). The functionality of the microvalves is verified through a conductance method involving electrodes positioned at the microfluidic channels' inlets and outlets. These microvalves can fully close at a control pressure of 0.3 MPa, with their operation depending on the duration of the applied pressure. The study further explores the coordinated operation of multiple microvalves to regulate the sequential flow of samples and reagents in the system. In SPR detection experiments, the microfluidic system is integrated with an SPR array sensing system to control the injection of NaCl solutions via the microvalves, and the observation of phase change curves in different chip regions are observed. The findings validate the microvalves' dependability and suitability for use in SPR array sensing.

A Microwave Voyage into Swelling Phenomenon: Investigation of Polydimethylsiloxane and VOCs Interaction.

When exposed to specific gases, polymers undergo swelling, leading to physiochemical changes that can significantly affect their performance. Monitoring this swelling phenomenon requires innovative approaches. This study focuses on investigating the real-time resonant microwave behavior of two polydimethylsiloxane (PDMS) structures (solid and porous) in interaction with tetrahydrofuran (THF) and acetone, which are primary swelling agents. A microwave measurement method is proposed using an 8.63 GHz planar split ring resonator (SRR). The device's resonant frequency downshifts to 7.75 and 8.42 GHz when solid and porous PDMS blocks are placed on the split ring gap. Interaction of the solid PDMS and porous PDMS with target gases caused a change in PDMS structure resulting in alterations in the dielectric properties of the PDMS/gas system, as evidenced by the resonator's transmission amplitude and resonant frequency shifts. The magnitude of these shifts depends on the type and concentration of the solvent gas. The PDMS-integrated SRR exhibits a sensitivity of 25.3 MHz/1 ppt THF and 7 MHz/1 ppt acetone. Additionally, the solid block demonstrates response times of 6800 and 4200 s for swelling and deswelling, respectively, when in exposure to 25 ppt concentrations of THF and acetone. Overall, this study underscores the substantial potential of microwave resonators as versatile tools for investigating the physical changes in polymers during their interaction with gases, contributing to the understanding of polymer-gas interactions and opening avenues for further research and diverse applications.

Design of OMC-Sagnac Loop Using PDMS and Different Package Structures to Improve Sensing Performance and Optimize the Ill-Conditioned Matrix

In the process of ocean exploration, highly accurate and sensitive measurements of seawater temperature and pressure significantly impact the study of seawater’s physical, chemical, and biological processes. In this paper, three different package structures, V-shape, square-shape, and semicircle-shape, are designed and fabricated, and an optical microfiber coupler combined Sagnac loop (OMCSL) is encapsulated in these structures with polydimethylsiloxane (PDMS). Then, the temperature and pressure response characteristics of the OMCSL, under different package structures, are analyzed by simulation and experiment. The experimental results show that structural change hardly affects temperature sensitivity, and square-shape has the highest pressure sensitivity. In addition, with an input error of 1% F.S., temperature and pressure errors were calculated, which shows that a semicircle-shape structure can increase the angle between lines in the sensitivity matrix method (SMM), and reduce the effect of the input error, thus optimizing the ill-conditioned matrix. Finally, this paper shows that using the machine learning method (MLM) effectively improves demodulation accuracy. In conclusion, this paper proposes to optimize the ill-conditioned matrix problem in SMM demodulation by improving sensitivity with structural optimization, which essentially explains the cause of the large errors for multiparameter cross-sensitivity. In addition, this paper proposes to use the MLM to solve the problem of large errors in the SMM, which provides a new method to solve the problem of the ill-conditioned matrix in SMM demodulation. These have practical implications for engineering an all-optical sensor that can be used for detection in the ocean environment.

Casting liquid PDMS on self-assembled bilayer polystyrene nanospheres to prepare a SERS substrate with two layers of nanopits for detection of p-nitrophenol.

p-Nitrophenol (PNP) is widely used in pesticides, pharmaceuticals, and dyestuffs. It is vital to detect trace PNP in the environment, because it poses significant environmental hazards due to its high toxicity. In this paper, a new method was reported for preparing a SERS substrate with excellent SERS activity by combining self-assembly techniques and flexible materials. First, the three-dimensional (3D) polystyrene (PS) photonic crystal (PC) structural master was fabricated by stacking two layers of self-assembled PS nanospheres with different diameters. Polydimethylsiloxane (PDMS) with a complementary structure to the master was obtained by casting, curing and peeling off. Finally, the PDMS-Ag substrate was fabricated by sputtering a thin Ag layer on the PDMS structure. The enhancement factor (EF) of the PDMS-Ag substrate was calculated to be 2.90 × 109 by using 4-amino thiophenol (ATP) as the probe molecule, and the limit of detection (LOD) for ATP can reach 10-11 M. And the RSD of the SERS intensity for the peak at 1078 cm-1 on the PDMS-Ag substrates from batch to batch was within 2%, indicating the high reproducibility of the as-prepared substrate. The quantitative analysis of PNP was achieved with a LOD of 10-8 M. Therefore, the PDMS-Ag substrate exhibits high sensitivity and reproducibility, and it can detect PNP in trace amounts, with great potential for detecting other contaminants.

Bioinspired On-Demand Directional Droplet Manipulation Surfaces

In this study, we exploited the properties of nature-inspired hierarchical structures to propose surfaces capable of on-demand directional droplet manipulation. A microline polydimethylsiloxane structure that simulated a bamboo leaf was fabricated, and silica particles were embedded onto its surface to create hierarchical structures. The as-fabricated multiscale line structures exhibited anisotropic wetting properties along the advancing direction. As the embedded particle size increased, the perpendicular roll-off angle (ROA) decreased and the anisotropic roll-off characteristic disappeared, adopting lotus-leaf characteristics. Consequently, the fabricated surface exhibited characteristics of both bamboo and lotus leaves. The roll off could be controlled through different ROAs by changing the particles size of silica on the same surface.

Hybrid coating of polydimethylsiloxane with nano-ZrO2 on magnesium alloy for superior corrosion resistance

To enhance the corrosion resistance of magnesium alloys, an organic-inorganic coating of polydimethylsiloxane (PDMS) hybridized with ZrO2 nanoparticles is developed, where the PDMS is selected as the polymeric matrix for superhydrophobic surface, and nano-ZrO2 particles as a physical barrier to strengthen and densify the polymeric matrix. The nanocomposite materials were characterized by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectrophotometry (FT-IR), and X-ray diffraction (XRD). Electrochemical, dropping corrosion, and salt spray tests were carried out to evaluate the effect of the amount of ZrO2 on the corrosion property of the PDMS-ZrO2 coatings. Thermal stability, hydrophobicity, and corrosion resistance of the composite coatings are substantially improved by the introducing ZrO2 modifier into PDMS matrix. Depending on the ZrO2 content, the PDMS-ZrO2 hybrids exhibit superior corrosion resistance, where the corrosion current density of PDMS-ZrO2 coatings containing 10% (wt.%) ZrO2 decreases about five orders of magnitude compared with Mg alloy substrate. Furthermore, it is noteworthy that ZrO2 nanoparticles are filled in the PDMS matrix to provide a long-term protection in the salt spray test up to 210 h. The PDMS-ZrO2 coatings demonstrate an excellent shielding ability for the Mg alloy, which is attributed to the strong hydrophobic surface of PDMS and compact network structure separated by the physical barrier of ZrO2 nanoparticles in the PDMS chains. The proposed mixed matrix membrane guides a design direction for highly water-repellent coating with a long-term corrosion protection performance.

Multifunctional MXene/CNT-based layered film for icing detection, anti-icing, and deicing application

Icing phenomenon usually happens in our daily life, especially in the cold winter or in high altitude areas, which makes us feel inconvenient and greatly threats some fields such as civil aviation or the manufacturing industry. In this study, a multifunctional film with properties of icing detection, anti-icing and deicing was fabricated. One-dimensional material carbon nanotube (CNT) and two-dimensional material Ti3C2Tx MXene were combined by two-step vacuum filtration. Polydimethylsiloxane (PDMS) as the flexible hydrophobic materials was then used to encapsulate layered film. Additionally, PDMS curing process on the sandpaper could make the surface of MXene/CNT layered film possess micro-structures. The low surface energy material PDMS and rough surface structures endow MXene/CNT layered film with good water-repellency. Compared with pure PDMS film (103°), the contact angle of MXene/CNT layered film surface reaches 128°. The result exhibits that a waterdrop(100uL) on the layered film surface takes 1425s to be frozen, which takes longer time than glass and pure PDMS. Additionally, excellent sensibility of the layered film could be used to detect icing phenomenon. The result manifests that gauge factor (GF) of MXene/CNT film reaches 15051 so that different icing stages could be identified by layered film clearly. MXene/CNT layered film possesses good electric heating and photo-thermal properties. The result shows that surface temperature can reach 89 °C with the 2.5 V voltage supply, and temperature reaches 95 °C through the radiation of near-infrared lamp as well. The dual-driven heating of MXene/CNT layered film shows the ability of deicing. 1000 mg ice just takes 223s to be melted entirely by 2.5 V input voltage, and 269s by radiation of 200 mW/cm2, respectively. The multifunctional MXene/CNT based layered film prepared by a simple fabrication method that integrates hydrophobicity, dual-driven heating, and sensibility together, which shows potential application in icing detection, anti-icing, and deicing.

Investigating Mechanical Behaviours of PDMS Films under Cyclic Loading.

Polydimethylsiloxane (PDMS) is widely utilised as a substrate for wearable (stretchable) electronics where high fatigue resistance is required. Cyclic loadings cause the rearrangement of the basic molecular structure of polymer chains, which leads to changes in the mechanical properties of the PDMS structure. Accordingly, it is necessary to investigate reliable mechanical properties of PDMS considering both monotonic and cyclic loading conditions. This study aims to present the mechanical properties of PDMS films against both monotonic and cyclic loading. The effects of certain parameters, such as film thickness and magnitude of tensile strain, on mechanical properties are also investigated. The test results show that PDMS films have a constant monotonic elastic modulus regardless of the influence of thickness and tensile loading, whereas a cyclic elastic modulus changes depending on experimental parameters. Several material parameters, such as neo-Hookean, Mooney–Rivlin, the third-order Ogden model, and Yeoh, are defined to mimic the stress–strain behaviours of the PDMS films. Among them, it is confirmed that the third-order Ogden model is best suited for simulating the PDMS films over the entire tensile test range. This research makes contributions not only to understanding the mechanical behaviour of the PDMS films between the monotonic and the cycle loadings, but also through providing trustworthy hyperelastic material coefficients that enable the evaluation of the structural integrity of the PDMS films using the finite element technique.

Interpenetrating network based polymeric sensors with enhanced specificity, sensitivity, and reusability

Cholesteric liquid crystals (CLCs) are widely used as optical sensors against volatile organic compounds (VOCs), whose sensitivity can be increased with the help of strain. However, the specificity and reusability of these structures should be increased to achieve their successful integration into useful applications. For this purpose, we developed an interpenetrating polymeric network (IPN) based on poly(RM257) structure of CLC-templated polymeric films and polydimethylsiloxane (PDMS). Contrary to the generic CLC-hosted IPN sensors that use CLC structures to optically report the changes in the polymeric matrix, we employed the collaborative responsiveness of the constituents of the IPN (both CLC-templated and penetrated polymeric structures) to improve the sensor performance. The elastic swelling of PDMS structure increased the durability and reusability of the poly(RM257) polymeric sensor upon exposure to even high VOC vapor concentrations up to their saturation. The sensor tests of both poly(RM257) and IPN films were carried out against four different VOC vapors namely toluene, hexane, acetone, ethanol and also water vapor. The results showed that the synergistic swelling of PDMS and poly(RM257) polymeric structures against vapors directly affected the sensor performance in terms of earned specificity and enhanced sensitivity. Moreover, the real-time experiments showed that the measurement accuracy, response, and recovery time of the polymeric sensors were also improved significantly by the development of IPN as compared to their non-IPN counterparts. This study shows a promise towards further engineering of sensors against various applications through detailed design of the constituent polymers against targeted species.

Microfluidic device with a carbonate‐rich hydroxyapatite micro‐coating

A contiguous carbonate-rich hydroxyapatite microcoating in a microfluidic device represents a substrate that has chemical and structural similarity to bone mineral. The present work describes a low-temperature method to deposit a carbonate-rich hydroxyapatite microcoating on a glass slide and its incorporation within the microchannels of a microfluidic device. A glass slide is covered/masked with polypropylene-based tape and CaCO3 nanoparticles are deposited on exposed areas by convective self assembly. The precursor CaCO3 is converted to carbonate-rich hydroxyapatite by dissolution-recrystallization in phosphate-buffered saline. The microcoating is aligned/incorporated within a microchannel when the underlying glass is bonded to a polydimethylsiloxane structure with the device layout. X-ray diffraction, laser Raman microspectroscopy, and X-ray photoelectron spectroscopy indicate that the microcoating was comprised of carbonate-rich hydroxyapatite. Scanning electron microscopy and 3D laser confocal microscopy showed that was comprised of nanocrystalline rod-like clusters that collectively exhibit a thickness of ∼20 µm. Monocultures/cocultures of osteoblast-lineage (MC3T3-E1, MG63) and preosteoclast-lineage (RAW 264.7) cells were performed. Osteoblast-lineage cells adhered to the microcoating and deposited an extracellular matrix of collagen fibrils and mineral accretions. Mineralization was detected in/near the inlet wells. The microcoating is analogous to bone mineral and could be applied to various layouts and mineral systems.

Development of a customised 3D printer as a potential tool for direct printing of patient-specific facial prosthesis

This study demonstrates a cost-effective portable fabrication system for 3D printing complex structures from polydimethylsiloxane (PDMS). Material development and characterisation allowed for the design and production of a 3D printer that is capable of fabricating PDMS structures using a photo-initiator and a LED curing process. A 3D model of a participant’s ear was captured using a handheld scanner. These data were used to directly 3D print an ear. Micro-extrusion direct deposition of PDMS at room temperature is demonstrated via a custom designed 3D printer, with in situ UV cross-linking to facilitate curing of the PDMS during the 3D printing process. This 3D printer has great potential to be used as a fast and facile fabrication approach to create facial and other prosthesis. Future developments will also focus on other application areas such as microfluidics, flexible electronics, and other biomedical applications.

Rheology and structure of Pickering emulsions undergoing transitional phase inversion using a mixture of hydrophilic and hydrophobic silica particles

We investigate the stability and the structure of Polydimethylsiloxane (PDMS)/water emulsions stabilized by a mixture of partially hydrophobic (Aerosil® R816) and hydrophilic silica particles (LUDOX TM 50). Transitional phase inversion from oil-in-water (O/W) to water-in-oil (W/O) is observed by changing the hydrophobic/hydrophilic particles ratio as well as the viscosity of the oil phase. A higher concentration of hydrophilic particles is needed to promote phase inversion for the less viscous oil. Adding gradually hydrophilic silica particles in the water phase leads to the decrease of the fraction of effective emulsified phase i.e. the dispersed phase and the increase of the droplet size which promotes the phase inversion. In addition, all these changes are accompanied by the decrease of the elastic moduli of the emulsions which may be correlated to their complex structure and the interactions of the two types of particles at the interface of the droplets.

Arrayed porous polydimethylsiloxane/barium titanate microstructures for high-sensitivity flexible capacitive pressure sensors

Flexible and wearable devices have been gaining attention in recent years. Compared with other types of pressure sensors, capacitive pressure sensors provide more advantages including simple structure, high stability and reliability, and lower power consumption. This study proposed the flexible capacitive pressure sensors with a double dielectric layer of a porous micro-pillar composite structure of polydimethylsiloxane (PDMS) as the dielectric layer. To further enhance the sensitivity, barium titanate (BT) particles were mixed in the PDMS due to their high relative permittivity. Moreover, finite element analysis (FEA) was utilized to simulate the displacement of the dielectric layer under applying external pressure. The FEA simulation results showed that the proposed structure of the dielectric layer could effectively enhance the sensitivity of the flexible capacitive pressure sensor. Furthermore, the flexible capacitive pressure sensor demonstrates a superb performance with a high sensitivity of 7.847 kPa−1, a low detection limit of 0.21 Pa, and a fast response and release time of 20 ms and 25 ms. The developed sensors have an excellent sensing capability and can be applied widely for monitoring of heartbeat, sensing of the robot arm, measuring of floor height, detecting of weights of objects, and real-time monitoring of healthcare.

Flexible and highly pressure-sensitive ternary composites-wrapped polydimethylsiloxane sponge based on synergy of multi-dimensional components

Flexible pressure sensor becomes increasingly important with the development of ultra-sensitive touch technology, electronic skin, and human health monitoring, which requires higher sensitivity. Here, a novel strategy is proposed by designing conductive polymer composites consisting of four components with different dimensions. Through a simple one-step hydrothermal method, the ternary composites of silver-carbon nanotubes-reduced graphene oxide (Ag-CNTs-rGO) were synthesized. The ternary composites-wrapped polydimethylsiloxane (PDMS) sponges, Ag-CNTs-rGO/PDMS, were fabricated by a dip-drying method. The conductive polymer sponges as pressure sensors showed improved sensitivity of 33 kPa−1 in the range of 0–0.05 kPa, which is twelve times higher than that of the conductive sponge without Ag nanoparticles. The uniform coating of Ag nanoparticles on CNTs and rGO not only enhanced the conductivity of the Ag-CNTs-rGO composites but also reduced the contact resistance between carbon materials. The CNTs-rGO matrix accelerated electron transport throughout the conductive sponge. The good flexible stability of the CNTs-rGO matrix and porous PDMS structures enabled the Ag-CNTs-rGO/PDMS sponge to assemble flexible circuits and act as elastic electric contacts. The combination of zero-dimensional metal nanoparticles, one-dimensional CNTs, and two-dimensional graphene as conductive fillers in three-dimensional porous structures provides new insight into acquiring the ultrahigh-performance flexible pressure sensors.