Structure Of Elastomers Research Articles

Tuning of the Stretchability and Charge Transport of Bis‐Diketopyrrolopyrrole and Carbazole‐Based Thermoplastic Soft Semiconductors by Modulating Soft Segment Contents

AbstractPolymer semiconductors are promising materials for stretchable, wearable, and implantable devices due to their intrinsic flexibility, facile functionalization, and solution processability at low temperatures. However, the crystalline domain of the conjugated structure for high charge carrier mobility in semiconducting polymers exhibits lower stretchability than that of the semi‐crystalline or amorphous domains. Herein, a set of thermoplastic soft semiconductors is synthesized with different ratios of diketopyrrolopyrrole–carbazole–diketopyrrolopyrrole (DPP‐Cz‐DPP)‐based hard segments and thiophene‐based aliphatic soft segments, having the similar structure of thermoplastic elastomers. The polymers exhibit decreased glassy temperatures with the increased content of the soft segments. The polymers show high crystallinity after copolymerization with a large‐sized DPP‐Cz‐DPP core and non‐conjugated segments due to an aggregation property of the conjugated core, still possessing a semi‐crystalline domain after annealing. The polymer films exhibit stretchability under strains of up to 60%. Organic field‐effect transistors fabricated using stretchable polymers show a mobility range of 0.125–0.005 cm2 V−1 s−1 with different proportions of the soft segment. The stretchability is improved significantly and the mobilities are decreased less when the content of the soft segment is increased. Therefore, this study presents a design principle for the development of a high‐performance stretchable semiconducting polymer.

Study of the Structure and Elastic Properties of Ethylene‒Propylene‒Diene Elastomers by Atomic Force Microscopy

Study of the Structure and Elastic Properties of Ethylene‒Propylene‒Diene Elastomers by Atomic Force Microscopy

High-Resolution, Transparent, and Flexible Printing of Polydimethylsiloxane via Electrohydrodynamic Jet Printing for Conductive Electronic Device Applications.

In the field of soft electronics, high-resolution and transparent structures based on various flexible materials constructed via various printing techniques are gaining attention. With the support of electrical stress-induced conductive inks, the electrohydrodynamic (EHD) jet printing technique enables us to build high-resolution structures compared with conventional inkjet printing techniques. Here, EHD jet printing was used to fabricate a high-resolution, transparent, and flexible strain sensor using a polydimethylsiloxane (PDMS)/xylene elastomer, where repetitive and controllable high-resolution printed mesh structures were obtained. The parametric effects of voltage, flow rate, nozzle distance from the substrate, and speed were experimentally investigated to achieve a high-resolution (5 µm) printed mesh structure. Plasma treatment was performed to enhance the adhesion between the AgNWs and the elastomer structure. The plasma-treated functional structure exhibited stable and long strain-sensing cycles during stretching and bending. This simple printing technique resulted in high-resolution, transparent, flexible, and stable strain sensing. The gauge factor of the strain sensor was significantly increased, owing to the high resolution and sensitivity of the printed mesh structures, demonstrating that EHD technology can be applied to high-resolution microchannels, 3D printing, and electronic devices.

Novel electromagnetic interference shield developed by gamma irradiation of strengthened WPE/WEPDM thermoplastic elastomer With carbon nanotubes

Carbon nanotubes (CNTs) have established wide attention as strengthened fillers because of their excellent several characters. Nano polymers based on thermoplastic elastomer composed of waste polyethylene (WPE)/Waste ethylene propylene diene monomer (WEPDM) blended equally 50/50 wt. % and strengthened with different concentrations of CNT (0.1, 0.3, and 0.5%) were fabricated via melt mixing. The prepared specimens were exposed to various gamma radiation doses, namely 50 and 100 kGy to evaluate the impact of radiation on the Nano polymers structure. FTIR and XRD were used to track the structure and crystallinity changes of thermoplastic elastomer with CNT filling. Mechanical features including tensile strength (TS), elongation at break (E%), modulus of elasticity (EM) and hardness (Shore D) of the unirradiated and irradiated samples were evaluated. Furthermore, the dynamic mechanical properties named storage (E′) and loss modulus as well as tan delta (δ) of the fabricated specimens were measured. TGA and also DSC monitored the thermal decomposition and the melting point alterations caused by CNT reinforcement. Electromagnetic Interference (EMI) was studied for all fabricated samples as an application of shielding for radio frequency signals. In general, all the studied parameters revealed improvements of thermoplastic elastomer properties via CNT interference. Subsequent reinforcement of CNT concentrations into WPE/WEPDM produced higher shielding for radio frequency signals. Furthermore, applied gamma radiation doses improved the shielding properties of the fabricated nanocomposites.

Tuning the Mechanical Behavior of Density-Graded Elastomeric Foam Structures via Interlayer Properties.

The concept of density-graded foams has been proposed to simultaneously enhance strain energy dissipation and the load-bearing capacities at a reduced structural weight. From a practical perspective, the fabrication of density-graded foams is often achieved by stacking different foam densities. Under such conditions, the adhesive interlayer significantly affects the mechanical performance and failure modes of the structure. This work investigates the role of different adhesive layers on the mechanical and energy absorption behaviors of graded flexible foams with distinct density layers. Three adhesive candidates with different chemical, physical, and mechanical characteristics are used to assemble density-graded polyurea foam structures. The mechanical load-bearing and energy absorption performances of the structures are evaluated under quasi-static and dynamic loading conditions. Mechanical tests are accompanied by digital image correlation (DIC) analyses to study the local strain fields developed in the vicinity of the interface. Experimental measurements are also supplemented by model predictions that reveal the interplay between the mechanical properties of an adhesive interlayer and the macroscale mechanical performance of the graded foam structures. The results obtained herein demonstrate that the deformation patterns and macroscale properties of graded foam composites can be tuned by selecting different bonding agents. It is also shown that the proper selection of an adhesive can be a practical way to address the strength–energy dissipation dichotomy in graded structures.

Bio‐Inspired Wrinkled Photonic Elastomer with Superior Controllable and Mechanically Stable Structure for Multi‐Mode Color Display

AbstractColor is an excellent carrier of information between organisms. Photonic elastomers that convert abstract mechanical information into intuitive color information have shown great potential in various application fields. However, angular correlation of structural colors and monotonous color conversion mode affect the accuracy of material information reading and the applicability in diverse application scenarios. Here, inspired by a kind of bright blue spider‐ Poecilotheria metallica, a new wrinkled photonic elastomer structure is reported. Through wrinkling stretchable 1D photonic crystals (1DPCs), photonic elastomers with both one‐directional and omni‐directional angle‐independent brilliant structural colors are realized. It is worth noting that with the hybrid 1DPC and polydimethylsiloxane substrate support, the wrinkled photonic structure and structural color remain stable after 1000 strain cycles, and mechanochromic sensitivity can reach 3.25 nm/%, indicating strong structural stability and sensitive deformation performance under stress. More importantly, by comprehensively manipulating micro‐wrinkle structure and lattice spacing of the photonic films, the structural color can achieve delayed discoloration and invisible‐visible reversible switching performance only through a single strain direction. The proposed wrinkled photonic elastomers have a broad application value in the fields of visual strain sensing, wearable devices, and information encryption. Furthermore, it provides a new strategy for color regulation of photonic materials.

Preparation and Performances of Polyether Polytriazole Elastomers Based on Click Chemistry

Since the polyurethane elastomer synthesis process is susceptible to moisture, polytriazole polyethylene oxide-tetrahydrofuran (PTPET) elastomer was used as a replacement owing to its mild production environment. In contrast to the conventional flask-synthesis method, the twin-screw reactor instrument could provide more meaningful data in the synthesis. In this study, PTPET elastomer was prepared by the MiniLab twin-screw reactor method for the first time, and the activation energy of the PTPET elastomer was calculated using the torque variation obtained from the MiniLab twin-screw reactor during the synthesis process at two different temperatures. The addition of flame retardants could endow the composites with more useful properties. The PTPET composites poly (phenylsilsesquioxane) (PTPET-PPSQ), octaphenyl polyhedral oligomeric silsesquioxane (PTPET-OPS) and PTPET-PhVPOSS (phenyl/vinyl polysilsesquioxane) were synthesized by using the MiniLab twin-screw reactor. The prepared PTPET elastomer and composites were fully characterized by FT-IR, TG, DSC, swelling test, mechanical test, SEM and combustion test. The characterization results show that the addition of the flame retardants has little influence on the original structure and properties of PTPET elastomer. The flame retardancy was characterized by the combustion test showing that all PTPET composites form a certain thickness of char layer during the burning process. These results indicate that the addition of flame retardants maintains the outstanding properties of PTPET elastomer and also endows the materials with a certain extent of flame retardancy; thus, it is believed to be a good engineering material that could be applied in many realms.

Nonprestretching double-network enabled by physical interaction-induced aggregation

The design of double-network (DN) improves the properties of matrix effectively, which has attracted wide attention. The recently reported construction of DN structure usually involves the prestretching process (swelling process). However, such complicated multistep swelling processes become more difficult in high molecular weight matrix, which are not suitable for constructing DN structure in the universal elastomers (for example, natural rubber and polyisoprene rubber). To expand the application fields of DN, this work designs the dense crosslinking domain and the sparse crosslinking domain to construct nonprestretching DN structure through physical interaction-induced aggregation. We find that physical interaction induced-aggregation form the dense crosslinking domain and the sparse crosslinking domain, which builds the two contrasting DN structures. Double-quantum nuclear magnetic resonance, dynamic mechanical analyzer, and mechanical property characterization demonstrate that the dense crosslinking domain as the brittle first network is preferentially ruptured upon deformation, leading to a large energy dissipation. This design concept represents a general approach to develop the nonprestretching DN structure, which expands the application fields of DN structure in the elastomer matrix.

Encapsulations of Magnetorheological Fluids Within 3-D Printed Elastomeric Cellular Structures

In this study, magnetorheological fluid (MRF) was successfully encapsulated in a 3-D printed elastomeric cellular structure. To this end, an MRF, which was composed of (40% volume fraction) carbonyl iron particles (6– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~\mu \text{m}$ </tex-math></inline-formula> in diameter) suspended in silicone oil, was encapsulated in a thermoplastic polyurethane (TPU) elastomeric cellular structure. A 3-D printer was used to print a TPU elastomer with a rectangular cellular structure in the shape of a circular cylinder. The MRF was injected into the rectangular voids within the TPU cellular structure (hereinafter MRF-TPU elastomeric composite), and then sealed into the composite by 3-D printing a capping or sealing layer on top. The mechanical stiffness and damping properties of the MRF-TPU elastomeric composite with respect to external magnetic fields (0, 2, and 7 kG) and excitation frequencies (1, 5, and 10 Hz) were measured via uniaxial dynamic mechanical testing. Also, the effects of excitation and prestrain amplitude on the mechanical properties of the MRF-TPU elastomeric composite were investigated in these experiments. The complex stiffness and dissipated energy measured via dynamic mechanical testing were used as the performance index.

Topological, Micromolecular, and Supramolecular Structure of Ethylene-Propylenediene Elastomers and Patterns of their Combination with Nitrile Butadiene Rubbers

Topological, Micromolecular, and Supramolecular Structure of Ethylene-Propylenediene Elastomers and Patterns of their Combination with Nitrile Butadiene Rubbers

Responsive friction modulation of 3D printed elastomeric bioinspired structures

Elastomeric bioinspired structures with desirable friction performances are attractive for engineering applications. However, friction-tuning mechanisms through hybrid designs and shape fabrication techniques remain challenging. Herein, we developed a scalable elastomeric bioinspired structure using 3D printing inspired by claws, toe pads and overhang granules found in nature. Friction modulations are demonstrated with pillar and dimple hybrid structures in dry and wet conditions, including different structure arrangements, mechanical properties (strength ~13.8 MPa, elongation ~410%) and numerical simulations. We identified pillar hybrid design has strong friction features (~2.5 times higher than smooth) on wet surfaces, by evaluating through strong edge boundary and spontaneous liquid splitting effects. Pillar structures are used to mimic grip experiments and simulations to determine gripping strategies.

Crystalline elastomeric block copolymer/ionic liquid membranes with enhanced mechanical strength and gas separation properties

We report a high-performance, three-dimensional (3D) interconnected crystalline elastomeric membrane with enhanced mechanical strength and CO2 separation properties. The membranes were prepared using an amphiphilic crystalline block copolymer, poly(ethylene glycol) monomethyl ether-block-poly(acrylonitrile) (mPEG-b-PAN), synthesized via one-pot free-radical polymerization under environmental-friendly, mild conditions (in water at 50 °C). The strong interaction of the mPEG-b-PAN block copolymer with ionic liquid (IL) resulted in a microphase-separated, interconnected elastomeric structure in which the PAN crystallites acted as crosslinking junctions. Exceptionally high IL loadings of up to 300 wt % were efficiently confined in the crystalline network while maintaining outstanding mechanical properties. The mPEG-b-PAN/IL membrane with 250 wt % IL loading achieved the highest separation performance with a CO2 permeability of 456.4 barrer, CO2/N2 selectivity of 61.4, CO2/CH4 of 18.1 and CO2/H2 of 12.3. The CO2/N2 separation performance exceeds the Robeson upper bound (2008) and approached the upper bound (2019). Both the separation properties and mechanical strength of the mPEG-b-PAN/IL elastomeric membranes outperformed those of homopolymer PAN (H-PAN) and other membranes with ILs. Interestingly, the mPEG-b-PAN/IL membranes were effortlessly prepared regardless of the surface properties of the substrate and IL loading, in contrast to H-PAN/IL, indicating that the amphiphilic property of the polymer plays a pivotal role in turning the interface.

Slidable Cross-Linking Effect on Liquid Crystal Elastomers: Enhancement of Toughness, Shape-Memory, and Self-Healing Properties.

The network structures of liquid crystal elastomers (LCEs) are crucial to impart rubbery behavior to LCEs and enable reversible actuation. Most LCEs developed to date are covalently linked, implying that the cross-links are fixed at a particular position. Herein, we report a new class of LCEs integrating polyrotaxanes (PRs) as slidable cross-links (PR-LCEs). Interestingly, the incorporation of a low loading (0.3-2.0 wt %) of the PR cross-linkers to the LCE causes a significant impact on various properties of the resulting PR-LCEs due to the pulley effect. The optimum PR loading is determined to be 0.5 wt %, at which point the toughness and damping behavior are maximized. The robust mechanical properties of the PR-LCE offers a superior actuation performance to that of the pristine LCE along with an excellent quadruple shape-memory effect. Furthermore, the incorporation of PR is useful to enhance the efficiency of shape-memory-assisted self-healing when heating above the nematic-isotropic transition.

Stretchable and Dynamically Tunable Attenuator Based on Graphene

In this article, a flexible, stretchable, and dynamically tunable attenuator based on coplanar waveguide (CPW) and graphene is proposed. Soft silicone elastomer and serpentine metal structure are used to realize the flexible, stretchable, and biocompatible characteristics of the CPW. A graphene sandwich structure (GSS) is placed on the upper surface of the CPW to dissipate the electromagnetic wave, achieving the dynamically adjustable characteristics of the stretchable attenuator. When the surface impedance of the GSS is tuned by applying a proper bias voltage, the simulated and measured results reveal that the attenuation tuning range is dynamically tuned from 4–11 dB with a low reflection below −10 dB. In addition, the fabricated attenuator is simultaneously optimized to work at conditions of the normal state, 180° bending and 130% stretching, with acceptable changes between insertion loss and return loss up to 6 GHz. The attenuator covers the medical frequency band of 2.4–2.483 GHz and the 5th generation (5G) communication frequency band of 3.5–3.8 GHz, which demonstrates that the attenuator has potential applications in stretchable electronic systems.

Compliant Mechanism-Based Sensor for Large Strain Measurements Employing Fiber Optics.

We propose a sensor design for measurement of large strains where direct application of a fiber optic strain gauge is impossible due to the stiffness mismatch between the optical fiber and the structure under test. The sensor design is based on a rhombus type compliant mechanism, which functions to attenuate input strain and transfer it to the ends of the sensing beam with the mounted optical strain gauge. We developed an analytical model of the sensor, which allows us to relate actuation forces, input displacement/strain, and output strain. The analytical model was verified with the finite element analysis and validated against an experimental prototype. The prototype sensor was able to handle input strains exceeding ±2.5 × 105 µε. Potential application areas of the proposed sensor include compliant elastomeric structures, wearables, and soft robotics.

Nonlinear Vibration and Stability of a Dielectric Elastomer Balloon Based on a Strain-Stiffening Model

Limiting chain extensibility is a characteristic that plays a vital role in the stretching of highly elastic materials. The Gent model has been widely used to capture this behaviour, as it performs very well in fitting stress-stretch data in simple tension, and involves two material parameters only. Recently, Anssari-Benam and Bucchi (Int. J. Non. Linear. Mech. 128:103626, 2021) introduced a different form of generalised neo-Hookean model, focusing on the molecular structure of elastomers, and showed that their model encompasses all ranges of deformations, performing better than the Gent model in many respects, also with only two parameters. Here we investigate the nonlinear vibration and stability of a dielectric elastomer balloon modelled by that strain energy function. We derive the deformation field in spherical coordinates and the governing equations by the Euler-Lagrange method, assuming that the balloon retains its spherical symmetry as it inflates. We consider in turn that the balloon is under two types of voltages, a pure DC voltage and an AC voltage superimposed on a DC voltage. We analyse the dynamic response of the balloon and identify the influential parameters in the model. We find that the molecular structure of the material, as tracked by the number of segments in a single chain, can control the instability and the pull-in/snap-through critical voltage, as well as chaos and quasi-periodicity. The main result is that balloons made of materials exhibiting early strain-stiffening effects are more stable and less prone to generate chaotic nonlinear vibrations than when made of softer materials, such as those modelled by the neo-Hookean strain-energy density function.

Feasibility of elastomeric composites as alternative materials for marine applications: A compendious review on their properties and opportunities

The term elastomer is a curtailment of two words, which are elastic and polymers. Accordingly, elastomers are polymer materials with elasticity. The significant challenges hindering the development of materials for naval applications, similar to other engineering sectors, include achieving a competitive light elastomeric structure. Marine structures are susceptible to various damage responses due to various loads throughout their service life. Being flexible, elastomer has a low modulus of elasticity, exhibits higher values of failure strain and yield strength. In these regards, elastomers are attractive materials for applications that require elasticity because they offer substantial advantages compared to traditional materials. However, the low fire resistance of these elastomeric materials jeopardizes their use in some critical applications. As a result, elastomeric blends and composites containing flame retardant (FR) additives are commonly used. On the other hand, elastomers possess (i) high strength-to-weight ratio, (ii) excellent impact properties, (iii) low infrared, magnetic, and radar signatures, (iv) excellent durability, and (v) high resilience to extreme loads. Hence, the scope of this study focuses on review and awareness regarding the feasibility of marine applications of elastomers/elastomeric composites, their current scientific and technological drawbacks, and future outlooks or prospects to support several applications in the marine industry.

Design, Manufacture, Test and Experiment of Six-Axis Force Torque Sensor for Chinese Experimental Module Manipulator.

A novel six-axis force/torque sensor (F/T sensor) for an Experimental Module Manipulator (EMM) in the Chinese Space Station (CSS) is developed in this paper. First, we designed the elastomer structure of the F/T sensor and used the analytical method and the finite element method to analyze the strain, in order to accomplish the strain gauges’ layout. Then, the electrical system was designed, which mainly realizes the acquisition of force/torque information, temperature and serial communication with the end effector (EE). Following this, we analyzed and designed the adaptability of the F/T sensor to the space environment. After this, the manufacturing process of the sensor was introduced in detail, and the F/T sensor was calibrated by a pulley weight system. Finally, the sensor was tested on the space environment adaptability of mechanical vibration and thermal vacuum on the ground. The test results show that the developed sensor has the ability to accurately measure three-dimensional force and three-dimensional moment information on orbit, which provides necessary conditions for the on-orbit fine operation of EMM.

STUDYING OF THE NANOSTRUCTURIZED POLY(URETHANE-UREA) – POLY(VINYL CHLORIDE) BLEND MODIFIED BY AEROSILS

An influence of surface adsorption-active centers of fine amorphous silica on physical hydrogen bonding (H-bonding) network in polyurethaneurea (PUU) and nanostructurized polymer blend (PUU/30PVC) was studied by FTIR spectroscopy. PUU was synthesized by prepolymer approach in N,N-dimethylformamide (DMF) solution using poly(propylene glycol) of Mn = 1000, 2,4-tolylene diisocyanate and 2,4-tolylene diamin as a chain extender at a molar ratio of 1:2:1. The compositions were obtained by solution-casting technique using DMF as a solvent. It was found introducing fine silica with hydroxylated surface into PUU matrix enhances segregation of hard urethane-urea segments in oligoether matrix. The maximum of strengthening of the filled composites was observed when silica A-300 content reaches 2–3 % (by weight). Oppositely, introducing silica AM-300 with silylated (by (CH3)2SiCl2) surface into PUU initiates degrading domain structure of elastomer due to interactions between polar groups of chemisorbed molecules of chlorine-containing modifier and proton-donor groups of rigid segments. Modified surface of silica has minor destabilization effect on H-bonding network in nanostructurized polymer-polymer blend. As a result, for producing filled composites without weakening interface interactions and, respectively, reducing the strength and optimal filler content (silica AM-300 or A-300) should be selected as high as 1 % (by weight).

Quartz crystal based sensor head design and analysis for robot torque sensor application

Background: In recent years, with the gradual development of robot human-computer interaction, robots need to meet the precise control of more complex motion. Torque sensors play an important role. The traditional strain gauge sensor uses a metal strain gauge as the sensitive element, which means that the sensor has a slow response, low resolution and can easily be affected by external signal noise. Aiming at these deficiencies of strain gauge sensors, a sensor with cutting quartz square sheet as the sensor head is proposed. Methods: In order to study the application of quartz square sensing head in the sensor, firstly, COMSOL (5.6) simulation modeling is used to obtain the stress relationship between square quartz sheet and circular quartz sheet. Then the calculation formula of the force frequency coefficient of the circular quartz sheet is modified to obtain the calculation formula of the force frequency coefficient of the square quartz sheet, and the feasibility of the formula is verified by practical experiments. Next, the theoretical simulation and experimental research on the buckling limit force of quartz wafer are carried out, and the formula of buckling limit force in the process of quartz wafer installation is modified. Finally, the designed sensitive head is installed on the elastomer structure for verification. The frequency signal is collected by SGS-THOMSON Microelectronics 32 with a sampling rate of 1000Hz. Results: The main performances of the sensor are range 150nm, sensitivity 350Hz / nm, linearity 98.14%, hysteresis 0.51%, repeatability 98.44%, resolution 0.02%. Conclusions: As the sensitive unit of the torque sensor, the designed quartz wafer can obtain high response time and high resolution, solve the problems of low resolution and slow response time of the traditional strain gauge torque sensor, and reduce the use cost of the sensor.