Elastomeric Systems Research Articles

Fundamental Aspects of Stretchable Mechanochromic Materials: Fabrication and Characterization.

Mechanochromic materials provide optical changes in response to mechanical stress and are of interest in a wide range of potential applications such as strain sensing, structural health monitoring, and encryption. Advanced manufacturing such as 3D printing enables the fabrication of complex patterns and geometries. In this work, classes of stretchable mechanochromic materials that provide visual color changes when tension is applied, namely, dyes, polymer dispersed liquid crystals, liquid crystal elastomers, cellulose nanocrystals, photonic nanostructures, hydrogels, and hybrid systems (combinations of other classes) are reviewed. For each class, synthesis and processing, as well as the mechanism of color change are discussed. To enable materials selection across the classes, the mechanochromic sensitivity of the different classes of materials are compared. Photonic systems demonstrate high mechanochromic sensitivity (Δnm/% strain), large dynamic color range, and rapid reversibility. Further, the mechanochromic behavior can be predicted using a simple mechanical model. Photonic systems with a wide range of mechanical properties (elastic modulus) have been achieved. The addition of dyes to photonic systems has broadened the dynamic range, i.e., the strain over which there is an optical change. For applications in which irreversible color change is desired, dye-based systems or liquid crystal elastomer systems can be formulated. While many promising applications have been demonstrated, manufacturing uniform color on a large scale remains a challenge. Standardized characterization methods are needed to translate materials to practical applications. The sustainability of mechanochromic materials is also an important consideration.

Influence of different Reynolds numbers and new geometries on water jacket cooling performance in a CI engine

Physical damage and emission increases that may occur in the engine due to uncontrolled temperature increases are prevented by cooling systems. In this study, the water jacket (WJ) of the F-Type F8Q706 engine was examined for different Reynolds numbers and geometries. With a combined examination approach, engine tests, 1D engine model, 3D in-cylinder combustion (ICC) model, and 3D WJ CFD studies are presented together, for the first time. Accordingly, a 3D WJ CFD model was developed using in-cylinder parameters calculated from 1D and 3D ICC which were verified by tests. Engine powers in 1D and 3D models, heat transfer, liner temperature, and heat flux in WJ models were compared. The engine powers at 2500 rpm with wide-open throttle are as follows: 1D (33.610 kW), 3D ICC (32.075 kW), engine catalog test (30.890 kW), and a literature test (29 kW). In the WJ model, instead of the Reynolds number 22,128.97, values of 18,440.81–15,367.34–12,806.11–1067.76–8893.14–7410.95–6175.79 were used. In this case, heat transfer decreased by 11.224%–20.844%–29.940%–38.168%–45.723%–52.874%–59.340%. Liner temperature increased by 3.962%–7.505%–10.879%–13.958%–16.800%–19.470%–21.822%. As the Reynolds number decreased, heat transfer decreased, and liner temperature increased. In the WJ, uncontrolled temperature increases were seen in areas farthest from the water inflow. Unlike studies using nanofluids, a new WJ geometry with 169 fins was developed for cooling performance. Nanoparticles cause damage to elastomeric system elements, clogging, and corrosion in lines. This geometry increased heat transfer by 42.01% and reduced liner surface temperatures by 48.28% for 22,128.966 Re. Repeated analyses showed that the fins increased heat transfer.

Research on the Thermal Aging Performance of a GAP-Based Polyurethane Elastomer.

Glycidyl azide polymer (GAP)-based polyurethane is an ideal elastomeric matrix for high-energy, low-smoke, and insensitive solid propellants. As the skeleton structure of GAP propellants, changes in the structure and properties of GAP elastomers during aging lead to the deterioration of propellant performance (especially in relation to mechanical properties), which causes safety risks. A high-temperature-accelerated aging experiment (70 °C) on a GAP elastomer was conducted. The evolution of the microstructure of the GAP elastomer system was analyzed by Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR), and variations in the macroscopic properties were analyzed by the hardness test and the uniaxial tensile test. The experimental results showed that thermal aging of the GAP elastomer is a coupled process of multiple chemical reactions. The azide groups, urethane groups, and ether bonds were the weak links in the network structure, breaking during the aging process, and the crosslinking density rose and then decreased. Macroscopic properties also showed segmented changes. The aging process was divided into three stages: post-curing (stage one); when the crosslinked network began to break (stage two), and when the crosslinked network was destroyed (stage three). Changes in the microstructure and macroscopic properties were consistent. This work is of great significance for exploring the aging mechanism of GAP propellants and extending their storage life.

Flexing with lignin: lignin-based elastomers synthesised from untreated kraft black liquor.

The synthesis and characterisation of a lignin-based elastomer system using lignin-epoxy-resins is presented. Untreated kraft black liquor was used to synthesise glycidyl lignin or black liquor-based epoxy resin (BLER), following a published procedure. A flexible, elastomeric thermoset was produced by cross-linking BLER with succinic anhydride (SA). The produced material was characterised in respect to its chemical, thermal, mechanical and swelling characteristics. In addition, vertical burning tests were performed. The obtained lignin-based elastomeric thermoset had a tensile strength of 1.0 ± 0.20 MPa and elastic moduli of 1.6 ± 1.4 and 0.44 ± 0.35 MPa at 5% and 50% elongation, respectively. A maximum elongation of 151 ± 49% was found.

A super-tough plant oil based elastomer for UV-light assisted 3D printed soft robotics and shape-memory

Herein we introduce a plant oil-based elastomer system for 3D-printable soft robotics, offering high flexibility and resolution. Systems with varied mechanical properties in printed parts enable fast, delicate movements and the shape memory effect.

The Use of Seismic Isolators to Improve Building Performance

Abstract The use of seismic isolators is a design method that involves inserting a flexible element at the base of the structure to decouple its movement from that of the ground to reduce vulnerability to earthquakes. They also make it possible to reduce the demand for force and deformation on the various structural elements. The aim of this research is to evaluate the contribution of HDRB high damping elastomeric seismic isolators in the reduction of seismic forces. It also consists in comparing the results of the dynamic analysis of the two fixed base structures in frames or frames braced by shear walls with the isolated structure mounted on an HDRB elastomer system and subjected to the same seismic excitation using the SAP 2000 calculation software. The results obtained showed an attenuation in the accelerations, a lengthening of the period, strong reduction in displacements and a reduction in the shearing force at the base of the isolated structure compared to fixed base structures.

Simultaneous polymerization constructing Hydrogel-Elastomer composites with ultra-tough interface for robust epidermal mechanoreceptor

Seamlessly integrating responsive hydrogel with antagonistic elastomer is paramount and desired for developing multi-layered architectures with high complexity, which shows predominating potentials in biomimetic electronic mechanoreceptor. Here, we introduce a facile yet universal simultaneous polymerization (STP) strategy achieved by the synergy of simultaneous self-polymerization of hydrogel and elastomer systems, and competitive copolymerization at interface region. Such a strategy forges an ultra-tough and durable interface with an interfacial toughness up to ∼ 1100 J/m2 for hydrogel-elastomer composites (HEC), while avoiding the complex stepwise polymerization process of both layers. The STP strategy universally exercises on toughening the interfaces between a wide range of interior hydrogels (e.g., PAAm, PAA, PDMAA and PAMPS based) and exterior elastomers (e.g., PEA, PHFEA, and PMEA based). Such a robust interface fulfills the delocalization of interfacial stress and high-fidelity transfer to interior hydrogel during deformation, leading to exceptional responsiveness and cyclic stability. The quantitative correlations between interfacial toughness and sensing properties guide the design of mechano-receptor with high sensitivity, sparking promising prospects in epidermal signals monitoring.

Building Ion-Conductive Supramolecular Elastomeric Protective Layer via Dynamic Hard Domain Design for Stable Zinc Metal Anodes.

The instability of zinc metal anode caused by zinc dendrite growth and severe parasitic reactions has significantly restricted the extensive application of rechargeable aqueous zinc-ion batteries (RAZBs). Herein, based on the strategy of dynamic hard domains, we develop an ion-conductive supramolecular elastomer consisting of Zn salts and the polyurethane-urea-polypropylene glycol polymer skeleton. This elastomer combines high mechanical strength, high ionic conductivity, decent hydrophobicity, and high adhesion to stabilize the electrode-electrolyte interface. In the elastomer system, this elastomer can dynamically adapt to the volume changes of Zn anodes during repeated zinc plating/stripping processes through the reversible dissociation/reassociation of hierarchical hydrogen bonds (H-bonds) formed by the polar groups of urea and urethane moieties. Meanwhile, the coordination of Zn2+ with soft polypropylene glycol (PPG) segments contributes to fast ion transport. This hydrophobic elastomer can also effectively inhibit water-induced corrosion by shielding the active Zn metal from the aqueous electrolyte. Based on the above synergies, the surface-modified anode shows excellent cycling stability above 550 h at a high current density of 5 mA cm-2 and a capacity of 2.5 mAh cm-2. Moreover, the assembled Zn//MnO2 full cell also displayed an enhanced electrochemical performance. This work provides inspiration for the design of solid electrolyte interphase (SEI) layers in aqueous battery chemistry to accelerate the application of RAZBs.

Enhancing the mechanical properties of hydrogels with vinyl-functionalized nanocrystalline cellulose as a green crosslinker

Hydrogels have gained significant attention in scientific communities for their versatile applications, but several challenges need to be addressed to exploit their potential fully. Conventional hydrogels suffer from poor mechanical strength, limiting their use in many applications. Moreover, the crosslinking agents used to produce them are often toxic, carcinogenic, and not bio-friendly. This study presents a novel approach to overcome these limitations by using bio-friendly modified nanocrystalline cellulose as a crosslinker to prepare highly stretchable and tough thermosensitive hydrogels. The surface of nanocrystalline cellulose was modified with 3-methacryloxypropyltrimethoxysilane (MPTS) to obtain modified nanocrystalline cellulose (M-NCC) crosslinker and used during free radical polymerization of thermosensitive N-isopropyl acrylamide (NIPA) monomer to synthesize NIPA/M-NCC hydrogel. The resulting nanocomposite hydrogels exhibit superior mechanical, thermal, and temperature-responsive swelling properties compared to conventional hydrogels prepared with traditional bi-functional N, N′-methylene bis (acrylamide) (MBA) as a crosslinker. The elongation at break, tensile strength, and toughness of the NIPA/M-NCC hydrogels significantly increase and Young’s modulus decrease than conventional hydrogel. The designed M-NCC crosslinker could be utilized to improve the mechanical strength of any polymeric elastomer or hydrogel systems produced through chain polymerization.

Nonlinear dynamics of an artificial muscle with elastomer–electrode inertia: Modelling and analysis

Artificial muscles are dielectric elastomeric system that mimic the response of the natural muscle and are helpful in many bio-mimicking applications. The existing literature is based on the assumption that electrodes are compliant and are focused on materials with greater extensibility than biological matter. The present work deals with the modelling and nonlinear dynamic analysis of dielectric elastomers considering the elastomer–electrode inertia and damping effect for bio-mimicking. The distinguishing point of the proposed work is the appearance of terms related to the elastomer–electrode inertia effect in the governing equation. Further, the biological muscle’s nonlinear elastic behaviour is incorporated using the Fung material model. Equilibrium stretch variation with parameter exhibits cusp catastrophe. The effect of electrode inertia on the equilibria is examined. Single-well and double-well potential energy characteristics are obtained for constant voltage. The basin of attraction illustrates the sensitiveness of system dynamics on the initial state and damping. The system response, when subjected to time-varying voltage, is explored. Multi-frequency response exists due to harmonic, sub-harmonic, and super-harmonic resonance condition. The resonant frequency variation with geometry and inertia is presented. Time-varying voltage may lead to chaotic behaviour illustrated through the bifurcation diagram. The presence of a strange attractor and positive Lyapunov exponent in the chaotic region further justify the existence of chaos. Additionally, chaotic behaviour is obtained in the case of single-well and double-well potential. Also, the existence of similar attractors with same fractal dimension is shown. The inertia effect significantly changes the dynamic characteristic from chaotic to non-chaotic or vice-versa. The mechanical and electrical load may lead to chaotic or non-chaotic behaviour depending on the geometry of the elastomer. The chaotic region’s dependence on the damping value is also obtained. Our results show that electrode inertia significantly impacts the elastomer under quasi-static and dynamic conditions. The proposed work gives a foundation for precisely designing artificial muscle for practical applications like soft robotics, artificial arms, and different prosthetic implants.

Room temperature healable elastomer composite based on light induced supramolecular chemistry

The incorporation of the self-healing feature into commercial elastomers encourages the creation of high-end elastomeric products that have an increased lifetime and maintain their economic viability. Various approaches of self-healing mechanisms are introduced in this elastomeric system. Herein, carboxylated nitrile rubber (XNBR) has been chemically modified with light-sensitive benzylimine-functionalized anthracene (BIFA) moiety. BIFA-modified XNBR composites undergo crosslinking via dimerization of anthracene moiety through π-π interactions in the presence of blue LED light. Again, amine-modified nano-silica was mixed with the BIFA-modified XNBR for tuning the tailored mechanical properties of the composite material. The crosslinked composite film exhibited a desirable self-healing property (healing efficiency of 75%) after keeping it under a blue LED for 8 h at ambient temperature, exhibiting tensile stress of ∼4 MPa. Interestingly, the modified XNBR composite showed different 3D structural shapes. Thus, the visible-light-induced dynamic molecular design strategy of reinforcing silica filler could provide a path for healing at ambient temperature with a good balance of mechanical properties, which could be suitable for next-generation smart elastomeric materials.

Developing sustainable and recyclable high-efficiency electromagnetic interference shielding nanocomposite foams from the upcycling of recycled poly(ethylene terephthalate)

The demand for high-performance electromagnetic interference (EMI) shielding composite foams with satisfactory environmental friendliness and high sustainability has increased considerably. However, considerable obstacles are frequently encountered in the practical development of incorporating upcycling of plastic wastes and environmentally friendly foaming technologies into the manufacture of such EMI shielding systems. In this research, we developed a lightweight sustainable nanocomposite foam system with outstanding EMI shielding performance from the integration of chemical upcycling of recycled poly(ethylene terephthalate) (PET) and supercritical carbon dioxide (sc-CO2) microcellular foaming. First, a green thermoplastic polyamide elastomer (TPAE) system was synthesized using a renewable bis(6-aminohexyl)terephthalamide (BAHT) monomer derived through the aminolysis of recycled PET, followed by adding single-walled carbon nanotubes (SWCNTs) into the TPAE system for the manufacture of TPAE/SWCNT nanocomposites. The π–π stacking of BAHT efficiently enhanced the melt strength of the material system, which was conducive for microcellular foaming process. After sc-CO2 foaming, a series of highly expanded nanocomposite foams with uniform microporous structure that could enable multiple reflections of electromagnetic waves were fabricated. Upon adding only 2 wt% SWCNTs, the foam system achieved a favorable conductivity of 0.15 S/cm and an extremely high specific shielding effectiveness (SSE) of 213.26 (dB cm3/g). Furthermore, the green nanocomposite foam possessed excellent durability. After being bent or twisted 1000 times, the foam maintained EMI shielding effectiveness of > 90% of the original value. Moreover, the foam could be easily recycled, reprocessed, and refoamed. For developing sustainable EMI shielding products, we believe that this study provides a promising direction with benefits of alleviating waste accumulation and reducing the use of virgin plastics in manufacture of foams, showing potential for advanced sustainable electronic applications.

AFM-nanoSIMS correlative microscopy on multiphase elastomeric systems: Nanomechanical properties and elemental distribution at the nanoscale

AFM-nanoSIMS correlative microscopy on multiphase elastomeric systems: Nanomechanical properties and elemental distribution at the nanoscale

Revisited chaotic vibrations in dielectric elastomer systems with stiffening

Revisited chaotic vibrations in dielectric elastomer systems with stiffening

Compositionally Homogeneous Soft Wrinkles on Elastomeric Substrates: Novel Fabrication Method, Water Collection from Fog, and Triboelectric Charge Generation

AbstractFunctionality and stimuli‐response of natural and artificial elastomeric materials depend significantly on the morphology of their surfaces. Structural transformability and tunable responsiveness of wrinkles on elastomeric materials can enable numerous applications in flexible electronics, optics, and adhesives. Currently existing fabrication techniques rely on sophisticated instrumentation, complex experimental setups, and expensive reagents. These methods are limited in terms of mechanical robustness of the wrinkles produced. Here, a simple, inexpensive, scalable, and reproducible strategy, making use of buckling instability for the creation of soft surface wrinkles on polydimethylsiloxane (PDMS), is presented. PDMS with lower elastic modulus is spin‐coated onto a mechanically stretched film of PDMS with a higher elastic modulus. Thermal curing followed by the release of prestrain resulted in the formation of wrinkles in the top layer of the PDMS. The hydrophobic soft surface wrinkles with compositional homogeneity exhibit efficient fog water collection and triboelectric charge generation useful for the preparation of triboelectric nanogenerator devices. Furthermore, the substrates show high mechanical stability and mechanoresponsive optical behaviors. The simplicity and general applicability of the method presented here is expected to establish a promising pathway toward the formation of soft wrinkles in other elastomeric systems also, facilitating important applications in various fields.

IMPROVED ADHESION IN ELASTOMERIC LAMINATES USING ELASTOMER BLENDS

ABSTRACT Interlayer adhesion between distinct rubber compositions in elastomeric laminates has been pursued by a variety of approaches, including treating surfaces, introducing assistant chemicals, and interposing a “transition layer.” Each approach, however, may be specific to the elastomer chemistries and may not be easily transferred to other rubber composition pairs in laminates. These limitations were overcome by inserting a layer at the interface that is a blend of each of the elastomer compositions of the adjacent layers and that increases the interfacial adhesion strength of the resultant laminates. This approach was demonstrated using three elastomer systems: fluoroelastomer (FKM), acrylonitrile–butadiene rubber (NBR), and isobutylene–isoprene rubber (IIR). The adhesion in the three-layer laminate (FKM/NBR/IIR) was improved with the addition of an FKM-NBR blend layer between the FKM and NBR layers and the addition of an NBR-IIR blend layer between the NBR and IIR layers. The five-layer laminate (FKM/[FKM-NBR blend]/NBR/[NBR-IIR blend]/IIR) was also fabricated. Interfacial adhesion was evaluated using the T-peel test according to ASTM D1876, which showed that the blends provided improved adhesion. Scanning electron microscope images were used to study the interface region. The proposed idea offers a general approach to improve interfacial strength that is widely applicable to other multilayer elastomer laminates.

Modulus and adhesion of Sylgard 184, Solaris, and Ecoflex 00‐30 silicone elastomers with varied mixing ratios

AbstractTwo‐part, commercial silicone elastomers are used in a variety of fundamental soft materials research and industrial applications due to their wide availability, ease of use, low cost, and mechanical tunability. This work seeks to create a library of moduli for three common elastomer systems with varied mixing ratios: Sylgard 184, Solaris, and Ecoflex 00–30, as well as provide a comparison of their adhesive properties. Shear storage moduli are quantified using parallel plate oscillatory shear rheology. The work of debonding is measured with spherical probe adhesion testing, and the static, advancing, and receding contact angles are measured via goniometer. Sylgard 184 can have shear moduli ranging from ~0.5 kPa‐620 kPa, Solaris from ~0.6 kPa‐175 kPa, and EF from ~1.3 kPa‐35 kPa measured at a frequency of 0.01 rad/s. In general, increasing mixing ratios creates softer samples. Additionally, softer samples are universally more adhesive, regardless of the material system. When comparing the different material systems, Sylgard 184 is generally the most adhesive, followed closely by Solaris, and then by Ecoflex 00–30. Our study offers a baseline dataset of modulus values and comparative adhesion to help researchers determine an appropriate commercial silicone for their application.

Recent Progress in Double Network Elastomers: One Plus One is Greater Than Two

AbstractHuman beings cannot live without elastomers, which exist almost everywhere in human life nowadays. Although elastomers with a variety of features are developed for specific applications, a timeless topic is how to toughen them, because mechanical properties always determine the reliability and lifespan of the utilized elastomers. Toughening of a soft material has a long history and the main idea is widely accepted, i.e., building energy dissipation into the stretchy networks. Double network (DN) method is the most pioneering and representative practice of materials toughening, which is successfully applied to numerous hydrogel systems. Intensive studies on DN hydrogel systems are implemented and relevant reviews are well documented, whereas important reviews about DN elastomers are absent. In this review, recent progress on toughening elastomers using the DN strategy is reviewed. By reviewing the fabrication methods and relevant extensions, toughening mechanisms at different length scales, functionalities, and applications in sequence, it is shown how one polymer network plus another gives rise to a tough elastomer with superior mechanical properties. It is believed that this review can give some insight into existing DN elastomer systems and inspire the development of next‐generation tough soft materials.

A hyperelastic-damage model based on the strain invariants

We develop a unified framework to describe the hyperelastic and damage behaviors of soft materials. The free energy density consists of both the crosslinked part of Langevin chains and the entanglement part described by a tube model. The micro–macro transition is obtained by using the averaging value over a microsphere. Consequently, the free energy density only depends on the strain invariants. The damage mechanism is then incorporated via the network alteration theory for the crosslinked part, while the deformation can also induce dilation of the tube and subsequent a decrease in the modulus for the entangled part. The hyperelastic model captures the Mooney Rivlin plot with a first decrease in the small deformation regime and then an increase in the large deformation region. The hyperelastic model can also accurately reproduce the stress–strain relationships in the uniaxial and biaxial loading conditions for various elastomer systems. The damage model can describe the stress response of filled rubbers in uniaxial and biaxial loading conditions, which shows a considerable improvement compared with the damage model without the entanglement effect. Since the model only depends on the strain invariants, the model can be easily implemented into the commercial finite element software Abaqus through a UHYPER. The finite element model can accurately reproduce the experimentally measured strain distribution of filled rubbers with complex geometry in the loading process. These results clearly show that the hyperelastic-damage model developed in this work has strong potentials to predict the mechanical responses of soft materials for practical applications.

Binary Silicone Elastomeric Systems with Stepwise Crosslinking as a Tool for Tuning Electromechanical Behavior.

Interpenetrating polymer networks (IPNs) represent an interesting approach for tuning the properties of silicone elastomers due to the possible synergism that may occur between the networks. A new approach is presented, which consists of mixing two silicone-based networks with different crosslinking pathways; the first network being cured by condensation route and the second network by UV curing. The networks were mixed in different ratios and the resulted samples yield good mechanical properties (improved elongations, up to 720%, and Young’s modulus, 1 MPa), thermal properties (one glass transition temperature, ~−123 °C), good dielectric strength (~50 V/μm), and toughness (63 kJ/m3).