Double Network Elastomers Research Articles

Visualization of mechanochemical polymer-chain scission in double-network elastomers using a radical-transfer-type fluorescent molecular probe

Sacrificial bond cleavage in double-network elastomers was visualized by adding a diarylacetonitrile derivative as a radical-transfer-type fluorescent molecular probe.

Poly(Ionic Liquid) Double-Network Elastomers with High-Impact Resistance Enhanced by Cation-π Interactions.

With the continuous development of impact protection materials, lightweight, high-impact resistance, flexibility, and controllable toughness are required. Here, tough and impact-resistant poly(ionic liquid) (PIL)/poly(hydroxyethyl acrylate) (PHEA) double-network (DN) elastomers are constructed via multiple cross-linking of polymer networks and cation-π interactions of PIL chains. Benefiting from the strong noncovalent cohesion achieved by the cation-π interactions in PIL chains, the prepared PIL DN elastomers exhibit extraordinary compressive strength (95.24 ± 2.49MPa) and toughness (55.98 ± 0.66MJ m-3) under high-velocity impact load (5000 s-1). The synthesized PIL DN elastomer combines strength and flexibility to protect fragile items from impact. This strategy provides a new research idea in the field of the next generation of safety and protective materials.

Elastomer Nanocomposites: Effect of Filler-Matrix and Filler-Filler Interactions.

The reinforcement of elastomers is essential in the rubber industry in order to obtain the properties required for commercial applications. The addition of active fillers in an elastomer usually leads to an improvement in the mechanical properties such as the elastic modulus and the rupture properties. Filled rubbers are also characterized by two specific behaviors related to energy dissipation known as the Payne and the Mullins effects. The Payne effect is related to non-linear viscoelastic behavior of the storage modulus while the Mullins or stress-softening effect is characterized by a lowering in the stress when the vulcanizate is extended a second time. Both effects are shown to strongly depend on the interfacial adhesion and filler dispersion. The basic mechanisms of reinforcement are first discussed in the case of conventional rubber composites filled with carbon black or silica usually present in the host matrix in the form of aggregates and agglomerates. The use of nanoscale fillers with isotropic or anisotropic morphologies is expected to yield much more improvement than that imparted by micron-scale fillers owing to the very large polymer-filler interface. This work reports some results obtained with three types of nanoparticles that can reinforce rubbery matrices: spherical, rod-shaped and layered fillers. Each type of particle is shown to impart to the host medium a specific reinforcement on account of its own structure and geometry. The novelty of this work is to emphasize the particular mechanical behavior of some systems filled with nanospherical particles such as in situ silica-filled poly(dimethylsiloxane) networks that display a strong polymer-filler interface and whose mechanical response is typical of double network elastomers. Additionally, the potential of carbon dots as a reinforcing filler for elastomeric materials is highlighted. Different results are reported on the reinforcement imparted by carbon nanotubes and graphenic materials that is far below their expected capability despite the development of various techniques intended to reduce particle aggregation and improve interfacial bonding with the host matrix.

Constrained shape-memory behaviors of multiple network elastomers

Most existing shape-memory polymers (SMPs) only generate low recovery stress, which restricts the applications of SMPs. To address this issue, here we investigate the shape-memory behaviors of multiple network elastomers (MNEs), a type of novel tough soft materials. The dynamic mechanical tests and uniaxial compression tests are used to characterize the mechanical behaviors of MNEs across the glass transition region. The constrained recovery tests show that the recovery stress depends on the deformation temperature, applied strain, and the number of networks. For double network elastomers with an 85 % programmed strain, the peak recovery stress and the final recovery stress are both larger than 20 MPa, which is significantly larger than the values reported in the literature.

An Ogden-like formulation incorporating phase-field fracture in elastomers: from brittle to pseudo-ductile failures.

Over the past 50 years the Ogden model has been widely used in material modelling owing to its ability to match accurately the experimental data on elastomers at large strain, as well as its mathematical properties, such as polyconvexity. In this paper, these characteristics are exploited to formulate a finite-strain model that incorporates, through the phase-field approach recently proposed by Wu (Wu 2017 J. Mech. Phys. Solids 103, 72-99) for small strains, a cohesive damage mechanism which leads to the progressive degradation of the material stiffness and to failure under tension. By properly tailoring the constitutive parameters, the model is capable of encompassing a wide range of effects, from brittle to pseudo-ductile failure modes. A plane stress problem is formulated to test the model against experiments on double-network elastomers, which display a pseudo-ductile damage behaviour at large strain, and on conventional rubber compounds with brittle failure. The results show that the proposed model is applicable to fracture coalescence and propagation in a wide range of materials. This article is part of the theme issue 'The Ogden model of rubber mechanics: Fifty years of impact on nonlinear elasticity'.

Mechanical property and dielectric spectra analysis of solvent-free poly(ionic liquid)/poly(ethyl acrylate) double network elastomers under tensile deformation

Solvent-free double network elastomers have excellent mechanical properties and stability. However, there are few studies on ion transport in solvent-free double network elastomers. In this paper, we prepared a kind of poly(ionic liquid) (PIL)-based solvent-free elastomer with double network structure by using crosslinked poly[2-(methacryloyloxy)ethyl] trimethyl ammonium bis(trifluoromethanesulfonyl) imine (P[VBTMA][TFSI]) network as brittle network and crosslinked poly(ethyl acrylate) (PEA) as stretchable network. The mechanical properties and the ion transport of samples as a function of elongation strain were investigated by stress-strain curves and broadband dielectric spectroscopy, respectively. The results show the double network elastomer has medium elastic modulus of 0.4–0.9 MPa, high elongation strain of 1700–2300% and ionic conductivity of 1.04 × 10−7 S·m−1 at room temperature. When the sample does not yield, stretching almost does not affect the ion transport in the network. As the strain exceeds the yield point, the conductivity relaxation time of the samples with low crosslinking degree of PIL network increases little, while the conductivity relaxation time of the samples with high crosslinking degree increases significantly. This is because the former network breaks uniformly, while the latter appears phase separation when yielding. The result improves the understanding of ion transport in double network polyelectrolyte elastomers.

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 multiscale tensile failure model for double network elastomer composites

Double network elastomer is a class of molecular composites consisting of a brittle filler network and a ductile matrix network. Upon deformation, progressive scission of the filler network dissipates strain energy while the matrix network resists the micro defect propagation, thus enhancing both stiffness and toughness of the composites. Over the past few years, several types of constitutive models have been developed to capture the nonlinear stress-strain relation of double network elastomers, most of which were formulated by taking consideration of network interaction, chain scission and damage evolution. In parallel, despite the abundant macroscopic experiments and microscopic characterizations on the multiscale failure mechanism of double network elastomers, a theoretical prediction for the ultimate strength of the composites is yet to be built up. In this paper, we develop a multiscale model which describes the deformation and tensile failure of double network elastomer composites at the same time. The progressive damage at molecular level is captured by the stretch-induced scission of randomly distributed polymer chains; the propagation of chain-scission-induced defects at microscale is modeled with analogy to cavitation; finally, the macroscopic necking failure is predicted by tracking the stress softening phenomenon. Our model is validated through the comparison between theoretical calculations and experiments, as well as the predictions and analysis of empirical design principles for double network elastomer composites.

Nanophase Separation in Immiscible Double Network Elastomers Induces Synergetic Strengthening, Toughening, and Fatigue Resistance

High modulus, toughness, and fatigue resistance are usually difficult to be obtained simultaneously in rubbery materials. Here, we report that by superimposing the nanophase separation structure in...

Self‐Healable and Transparent Elastomers Based on Dual Reversible Networks

AbstractThe fabrication of silicon elastomer with good mechanical properties and self‐healing ability is still a challenge. Herein, a facile method to fabricate a transparent healable double‐network (DN) elastomer by introducing polyborosiloxane (PBS) into self‐healing polydimethylsiloxane (HPDMS) networks is demonstrated. Tensile testing shows that the mechanical properties of PBS and HPDMS are both improved. The DN elastomer shows high transparency across the visible spectrum with an average transmittance of 75%. Because of the breakage and reconstruction of reversible imine bonds and BO dative bonds, the elastomer exhibits excellent self‐healing properties with a maximum healing efficiency of 98% at room temperature. Meanwhile, the elastomer can be repeatedly reprocessed with a recovery of 85% of virgin mechanical strengths. This work provides a new insight to design transparent, self‐healing silicone elastomers with a simple and eco‐friendly method.

Double Network Elastomers: Self‐Assembly Strategy for Double Network Elastomer Nanocomposites with Ultralow Energy Consumption and Ultrahigh Wear Resistance (Adv. Funct. Mater. 34/2020)

Double Network Elastomers: Self‐Assembly Strategy for Double Network Elastomer Nanocomposites with Ultralow Energy Consumption and Ultrahigh Wear Resistance (Adv. Funct. Mater. 34/2020)

Self‐Assembly Strategy for Double Network Elastomer Nanocomposites with Ultralow Energy Consumption and Ultrahigh Wear Resistance

AbstractOne of the environmental crises facing the world is pollution due to rubber auto tire destruction. The use of tires in vehicles consumes 6% of the world's energy and causes 5% of carbon dioxide emissions; it accounts for up to 10% of the microplastic pollution found in oceans. Here, a new rubber nanocomposite self‐assembled from hard and soft elastomer matrixes is designed: polybutadiene with its two hydroxy chain ends reacts with 4,4'‐diphenylmethane diisocyanate to form segmented polyurethane. This system first undergoes self‐assembly, forming well‐defined nanoscale hard domains distributed in the soft matrix. Then, cross‐linking between the soft segments is accomplished by a controlled radiation method, resulting in the double network elastomer (DN‐E). Remarkably, the DN‐E exhibits the lowest reported loss factor value at 60 °C. The index of energy dissipation in the rolling tire demonstrates a prominent reduction of 72%, accomplished with an 88% decrease in energy loss, and 85% less wear loss, as compared with best earlier reported commercial tires. These new double‐network materials open a new prospective for the design and fabrication of ultralow energy‐consumption and strong abrasion‐resistance elastomers, which establishes a milestone for the development of the next generation of green low‐pollution tires causing much less energy dissipation.

3D printing of a biocompatible double network elastomer with digital control of mechanical properties.

The majority of 3D-printed biodegradable biomaterials are brittle, limiting their potential application to compliant tissues. Poly (glycerol sebacate) acrylate (PGSA) is a synthetic biodegradable and biocompatible elastomer, compatible with light-based 3D printing. In this work we employed digital-light-processing (DLP)-based 3D printing to create a complex PGSA network structure. Nature-inspired double network (DN) structures with two geometrically interconnected segments with different mechanical properties were printed from the same material in a single shot. Such capability has not been demonstrated by any other fabrication technique. The biocompatibility of PGSA after 3D printing was confirmed via cell-viability analysis. We used a finite element analysis (FEA) model to predict the failure of the DN structure under uniaxial tension. FEA confirmed the soft segments act as sacrificial elements while the hard segments retain structural integrity. The simulation demonstrated that the DN design absorbs 100% more energy before rupture than the network structure made by single exposure condition (SN), doubling the toughness of the overall structure. Using the FEA-informed design, a new DN structure was printed and the FEA predicted tensile test results agreed with tensile testing of the printed structure. This work demonstrated how geometrically-optimized material design can be easily and rapidly achieved by using DLP-based 3D printing, where well-defined patterns of different stiffnesses can be simultaneously formed using the same elastic biomaterial, and overall mechanical properties can be specifically optimized for different biomedical applications.

RETRACTED: Thermoreversible Structurally Recoverable Dual‐Network Elastomer Hydrogel

AbstractComprising a hydrogen bond crosslinked agarose (Aga) network and a covalently crosslinked hydroxyethyl polyacrylate network, a simple, easily controlled one‐pot construction of agarose/hydroxyethyl polyacrylate (Aga/PHEA) double network (DN) elastomer hydrogel is developed. The Aga/PHEA DN gels combining the strengths of both hydrogel and elastomer indicate excellent fatigue resistance, toughness together with rapid, high recoverable rate. The compression strength, tensile strength, and toughness of DN gels can reach 41 MPa, 1.0 MPa, and 6.7 MJ m−3. Due to the thermoreversible feature of agarose, the gel displays an excellent recoverable ability with the elastic modulus recovery of 93% and the energy loss recovery of 90%, respectively, after heating the compressed and released gels. Interestingly, the gels indicate a typical rubber behavior with a small and almost overlapped hysteresis loop and excellent fatigue resistance by simply regulating the content of the second network HEA. Besides, the in vitro MTT and cell adhesion tests confirm the good biological compatibility of the gels. The active hydroxyl groups in the gel can be bonded with functionalized molecule for different needs. The studies reveal that the DN elastomer hydrogels with excellent mechanical properties, biocompatibility, and functionalization will significantly provide a new road to gel researches and applications.

Tough double network elastomers reinforced by the amorphous cellulose network

Amorphous cellulose-based tough double-network (DN) elastomers were successfully fabricated. These elastomers comprise interpenetrated poly(ethyl acrylate) (PEA) network as the soft matrix and the amorphous cellulose network as the brittle component. Unlike carbon-black-filled conventional rubbers, the obtained cellulose/PEA DN elastomers are transparent and can be dyed without any color limitation. Although the cellulose network in the DN elastomer comprises only 2.55 wt%, such cellulose network efficiently reinforces in toughness (10 times), stiffness (28 times), strength (8 times), and durability of the DN elastomer compared to the PEA elastomer. The structure and toughening mechanism of the cellulose/PEA DN elastomers are different from previously reported cellulose composites, in which cellulose nanocrystals were used simply as fillers. Upon deformation, the brittle cellulose network in the DN elastomer is ruptured sacrificially to dissipate energy, which effectively prevents crack propagation. The damaged cellulose network recovers its original structure to show recoverable mechanical properties by thermal annealing.

Tough Self-Healing Elastomers Based on the Host-Guest Interaction of Polycyclodextrin.

Inspired by animal muscles, we developed a kind of tough elastomers combining high strength and high stretchability with autonomous self-healing capability. A key structural feature is the construction of a double network (DN) connected by the hydrogen bond and host-guest interactions. The first network is the classic elastomer polyacrylate matrix cross-linked by strong hydrogen bonding. The second network is formed through the host-guest interactions between polycyclodextrin and the adamantane (Ad) groups on the side of the polyacrylate chain. Supramolecular interactions between two networks make them miscible and interpenetrate in the molecular level and then can share the load as the sample was stretched. The host-guest interactions act not only as sacrificial bonds for energy dissipation but also as self-healing driving forces. The tensile strength of the DN elastomer reaches about 6.7 MPa and the strain is as high as about 950%. The DN elastomer can be easy to repair by touching the damaged surface together at ambient conditions when broken or cut. The recovered tensile strength can reach over 4.5 MPa, which is better than the most pristine strength of existing spontaneous self-healing elastomers.

Autonomous self-healing, self-adhesive, highly conductive composites based on a silver-filled polyborosiloxane/polydimethylsiloxane double-network elastomer

Novel autonomous self-healing, self-adhesive stretchable electrodes were prepared by using PBS/PDMS double-network elastomer with 100% self-healing efficiency in conductivity.

A Physical and Mechanical Study of Prestressed Competitive Double Network Thermoplastic Elastomers

A new approach to prepare and characterize prestressed competitive double network elastomeric systems was investigated. A styrene−butadiene−styrene (SBS) triblock copolymer system containing physical cross-links was used to achieve a double network by additional chemical cross-linking using ultraviolet (UV) light. Properties measured from conventional monotonic tensile tests, stress relaxation, thermomechanical, hysteresis, and swelling analysis were investigated and related to their network structure. These double network elastomers show a transition between competitive and collaborative behavior in their mechanical properties at different strain regimes. These elastomers also show lower permanent set in both low and high strain regimes along with lower hysteresis. These networks exhibit lower modulus along with lower coefficient of thermal expansion, still showing lower swelling ratios, which results from a competition between the networks.

Mechanical and thermo‐mechanical studies of double networks based on thermoplastic elastomers

AbstractA new approach to prepare and characterize double network elastomeric systems was investigated. A styrene‐ethylene‐co‐butylene‐styrene (SEBS) triblock copolymer system containing physical crosslinks was used to achieve a double network by additional crosslinking using ultra‐violet (UV) light. An ethylene–propylene–diene monomer (EPDM) terpolymer system containing chemical crosslinks was used to achieve a conventional double network using UV crosslinking. Properties from conventional monotonic tensile tests, dynamic mechanical analysis, and thermomechanical properties were investigated. These double network elastomers show a transition between competitive and collaborative behavior in their mechanical properties and lower coefficients of thermal expansion arising from a competition of the networks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 778–789, 2010

The Payne Effect in Double Network Elastomers

Abstract Double network elastomers were prepared by curing under strain previously-crosslinked natural rubber or styrene-butadiene copolymer. The rubbers were reinforced with carbon black, so that the conventional (singly-cured) materials exhibited a substantial Payne effect, reflecting agglomeration of the filler particles. This effect was much reduced in the double networks - the storage modulus varied more weakly with strain amplitude, and the mechanical hysteresis was substantially smaller. Comparable results were obtained for dynamic mechanical measurements employing different test geometries; that is, the effect is independent of the direction of the strain relative to the orientation of the double network. These results indicate that deformation during the imposition of a second network disrupts the carbon black agglomerates, and this deflocculated structure is stabilized by the second crosslinking. Thus, double network processing is a general means to lower the hysteresis of filled rubbers.