Elastomeric Matrices Research Articles

Магнетит как функциональный наполнитель эластомерных композитов: эффекты размерности и структурирования

Samples of composite materials based on Fe3O4 magnetite with different particle sizes (natural and crushed in a planetary mill) and various elastomeric matrices (chloroprene rubber of sulfur regulation – PCP, styrene butadiene rubber - BSK and cold-cured polydimethylsiloxane – SKTN-A) in the concentration range of 10...200 weight parts per 100 weight parts of elastomeric matrices. The kinetics of curing of the elastomeric compositions under consideration has been studied, on the basis of which optimal molding modes have been proposed. The samples were formed both in the presence of a magnetic field up to 0.3 T and without it. The functional (electrophysical and magnetic) properties of the samples were studied and it was shown that these properties in a wide range of values can be regulated by changing the size of magnetite particles and/or structuring them by means of a magnetic field during the molding of elastomeric composites.

Kinetics of Formation and Degradation of Elastomeric Matrices by a New Generation of Non-ASTM Carbon Blacks

Kinetics of Formation and Degradation of Elastomeric Matrices by a New Generation of Non-ASTM Carbon Blacks

An Investigation into Sheet-Inconel 718 Forming with Flexible and Metal Tools-Simulation and Experiment.

The article presents the results of numerical simulations and experimental tests of plastic forming sheets made from the difficult-to-deform nickel alloy Inconel 718 with a thickness of 1 mm, using punches made from elastomeric materials with hardness 50-90 Shore A and steel dies. Elastomeric stamps were created in the form of five layers with a diameter of 160 mm. The influence of the hardness of the elastomeric punches on the geometry of the elements obtained was determined. The dies were made from 90MnCrV8 steel with a hardness of over 60 HRC. Their task was to obtain the expected shape of the element while generating various stress states in specific areas of the semi-finished product. The research was carried out using an original device whose operating principle was based on the Guerin method. The shape and dimensions of the elements made from Inconel 718 nickel alloy were determined by optical 3D scanning. The geometry of the drawpiece showed a significant impact of the hardness of the layered elastomer matrices on the degree of shape reproduction. The results obtained from numerical modeling were confirmed by the results of experimental tests. It has been shown that the hardness of the elastomeric material used for punches for plastic forming Inconel 718 nickel alloy sheets should be adapted to the shape of the drawpiece. It was also found that one of the important aspects of plastic forming sheets using the Guerin method is the tendency to obtain a diversified shape of the final elements.

Investigation of Macroscopic Mechanical Behavior of Magnetorheological Elastomers under Shear Deformation Using Microscale Representative Volume Element Approach.

Magnetorheological elastomers (MREs) are a class of smart materials with rubber-like qualities, demonstrating revertible magnetic field-dependent viscoelastic properties, which makes them an ideal candidate for development of the next generation of adaptive vibration absorbers. This research study aims at the development of a finite element model using microscale representative volume element (RVE) approach to predict the field-dependent shear behavior of MREs. MREs with different elastomeric matrices, including silicone rubber Ecoflex 30 and Ecoflex 50, and carbonyl iron particles (CIPs) have been considered as magnetic particles. The stress-strain characteristic of the pure silicon rubbers was evaluated experimentally to formulate the nonlinear Ogden strain energy function to describe hyper-elastic behavior of the rubbery matrix. The obtained mechanical and magnetic properties of the matrix and inclusions were integrated into COMSOL Multiphysics to develop the RVE for the MREs, in 2D and 3D configurations, with CIP volume fraction varying from 5% to 40%. Periodic boundary condition (PBC) was imposed on the RVE boundaries, while undergoing shear deformation subjected to magnetic flux densities of 0-0.4 T. Comparing the results from 2D and 3D modeling of isotropic MRE-RVE with the experimental results from the literature suggests that the 3D MRE-RVE can be effectively used to accurately predict the influence of varying factors including matrix type, volume fraction of magnetic particles, and applied magnetic field on the mechanical behavior of MREs.

Next-Generation Cardiac Interfacing Technologies Using Nanomaterial-Based Soft Bioelectronics.

Cardiac interfacing devices are essential components for the management of cardiovascular diseases, particularly in terms of electrophysiological monitoring and implementation of therapies. However, conventional cardiac devices are typically composed of rigid and bulky materials and thus pose significant challenges for effective long-term interfacing with the curvilinear surface of a dynamically beating heart. In this regard, the recent development of intrinsically soft bioelectronic devices using nanocomposites, which are fabricated by blending conductive nanofillers in polymeric and elastomeric matrices, has shown great promise. The intrinsically soft bioelectronics not only endure the dynamic beating motion of the heart and maintain stable performance but also enable conformal, reliable, and large-area interfacing with the target cardiac tissue, allowing for high-quality electrophysiological mapping, feedback electrical stimulations, and even mechanical assistance. Here, we explore next-generation cardiac interfacing strategies based on soft bioelectronic devices that utilize elastic conductive nanocomposites. We first discuss the conventional cardiac devices used to manage cardiovascular diseases and explain their undesired limitations. Then, we introduce intrinsically soft polymeric materials and mechanical restraint devices utilizing soft polymeric materials. After the discussion of the fabrication and functionalization of conductive nanomaterials, the introduction of intrinsically soft bioelectronics using nanocomposites and their application to cardiac monitoring and feedback therapy follow. Finally, comments on the future prospects of soft bioelectronics for cardiac interfacing technologies are discussed.

Verifying the seating of a 3D-printed removable die using elastomeric matrices: A dental technique.

Computer-aided design and computer-aided manufacturing systems enable digital designing and 3-dimensional (3D) printing of definitive casts with removable dies. However, the fit of the removable dies should be without interferences for their accurate positioning in the cast. Given that the accuracy of additive manufacturing depends on design- and manufacturing-related factors, verifying the accuracy of the position of 3D-printed removable dies in their cast is essential to fabricate positionally accurate definitive prostheses, which would enable minimal or no laboratory and clinical adjustments. This dental technique article presents a straightforward approach to verify the seating of a 3D-printed removable die by using verification matrices made of a polyvinylsiloxane interocclusal registration material.

Quasi-Static Modeling Framework for Soft Bellow-Based Biomimetic Actuators.

Soft robots that incorporate elastomeric matrices and flexible materials have gained attention for their unique capabilities, surpassing those of rigid robots, with increased degrees of freedom and movement. Research has highlighted the adaptability, agility, and sensitivity of soft robotic actuators in various applications, including industrial grippers, locomotive robots, wearable assistive devices, and more. It has been demonstrated that bellow-shaped actuators exhibit greater efficiency compared to uniformly shaped fiber-reinforced actuators as they require less input pressure to achieve a comparable range of motion (ROM). Nevertheless, the mathematical quantification of the performance of bellow-based soft fluidic actuators is not well established due to their inherent non-uniform and complex structure, particularly when compared to fiber-reinforced actuators. Furthermore, the design of bellow dimensions is mostly based on intuition without standardized guidance and criteria. This article presents a comprehensive description of the quasi-static analytical modeling process used to analyze bellow-based soft actuators with linear extension. The results of the models are validated through finite element method (FEM) simulations and experimental testing, considering elongation in free space under fluidic pressurization. This study facilitates the determination of optimal geometrical parameters for bellow-based actuators, allowing for effective biomimetic robot design optimization and performance prediction.

Tunable structure and linear viscoelastic properties of poly(glycerol adipate urethane)-based elastomeric composites for tissue regeneration

Elastomeric biocomposites based on poly(glycerol adipate urethane) and hydroxyapatite were fabricated for tissue regeneration. The poly(glycerol adipate urethane) (PGAU) elastomeric composite matrices were obtained by chemical crosslinking of the poly(glycerol adipate) prepolymer (pPGA) with diisocyanate derivative of L-lysine. Two series of composites varying in the amount of L-lysine diisocyanate ethyl ester (LDI) used as a crosslinking agent were manufactured. As a ceramic filler both unmodified and L-lysine surface-modified hydroxyapatite (HAP) particles were used. The novelty of our research consists in the manufactured elastomeric materials and characterization of their linear viscoelastic (LVE) properties. The LVE properties of the composites were investigated by means of dynamic thermomechanical analysis. Frequency sweep and amplitude sweep measurements were performed in shear mode. The influence of the crosslinking agent (LDI) amount, HAP content and surface modification of HAP on the LVE properties of the composites was determined based on the analysis of the master curves of storage (G′) and loss (G″) moduli and of tanδ of the composites. Depending on the amount of LDI, HAP and surface modification, the materials differ in the values of rubber elasticity plateau modulus (G0) and G′ and G″ determined at selected shear frequencies and at the glassy state. G0 ranges from 278 kPa to 3.98 MPa, G′ in the glassy state is within the range of 219 MPa–459 MPa. The G0 values of the PGAU-based composites are within the stiffness range of soft tissue. In view of the choice of HAP as the ceramic component and the G0 values, elastomeric composites have the potential to be used as filling materials in small bone defects (due to their mechanical similarity to osteoid) as well as materials for cartilage tissue regeneration.

Morphology of poly-3-hexyl-thiophene blends with styrene-isoprene-styrene block-copolymer elastomers from X-ray and neutron scattering.

The nano- and micron scale morphology of poly(3-hexylthiophene) (P3HT) and polystyrene-block-polyisoprene-block-polystyrene (PS-PI-PS) elastomeric blends is investigated through the use of ultra-small and small angle X-ray and neutron scattering (USAXS, SAXS, SANS). It is demonstrated that loading P3HT into elastomer matrices is possible with little distortion of the elastomeric structure up to a loading of ∼5 wt%. Increased loadings of conjugated polymer is found to significantly distort the matrix structure. Changes in processing conditions are also found to affect the blend morphology with especially strong dependence on processing temperature. Processing temperatures above the glass transition temperature (Tg) of polystyrene and the melting temperature (Tm) of the conjugated polymer additive (P3HT) creates significantly more organized mesophase domains. P3HT blends with PS-PI-PS can also be flow-aligned through processing, which results in an anisotropic structure that could be useful for the generation of anisotropic properties (e.g. conductivity). Moreover, the extent of flow alignment is significantly affected by the P3HT loading in the PS-PI-PS matrix. The work adds insight to the morphological understanding of a complex P3HT and PS-PI-PS polymer blend as conjugated polymer is added to the system. We also provide studies isolating the effect of processing changes aiding in the understanding of the structural changes in this elastomeric conjugated polymer blend.

Effects of a liquid metal co‐filler on the properties of epoxy/binary filler composites

AbstractLiquid metals (LMs) with high fluidity and high thermal conductivity (TC) are receiving considerable attention in the research on thermal management polymer composites as alternatives to conventional rigid solid fillers or as co‐fillers to overcome the trade‐off between TC and composite processability at high filler loads. While most previous studies have investigated the effects of LM fillers in soft elastomeric matrices, their effects on the composite properties with rigid matrices, such as epoxy‐based polymers, have not been discussed extensively. Herein, we investigated the effects of LM eutectic Ga‐In (EGaIn) as a co‐filler on the properties of rigid epoxy‐based composites with a binary filler (Al2O3/EGaIn) system. The increase in the volume fraction of LM fillers significantly improves the processability of uncured precursor composites but markedly decreases the mechanical strength of the cured composites at their high loads—the latter effects have rarely been examined in previous studies. However, with adequate LM loads, the composites exhibited superior mechanical properties compared with the all‐solid‐filler system, withstanding a surprisingly high compressive load (~100 kN) under which the all‐solid‐filler system fractured. Furthermore, the epoxy/binary filler composites exhibited reasonably high TC values (~1 W/mK) comparable to that of commercial epoxy molding compounds, suggesting their potential applicability for electronic packaging.

Hair-Reinforced Elastomer Matrix Composites: Formulation, Mechanical Testing, and Advanced Microstructural Characterization.

Epoxy matrix composites reinforced with high-performance fibers, such as carbon, Kevlar, and glass, exhibit excellent specific stiffness and strength in many mechanical applications. However, these composites are disappointingly non-recyclable and are usually disposed of in landfill sites, with no realistic prospect for biodegradation in a reasonable time. In contrast, moldable composites with carbonized elastomeric matrices developed in the last decades possess attractive mechanical properties in final net-shape products and can also be incinerated or recycled. Many carbon and inorganic fillers have recently been evaluated to adjust the properties of carbonized elastomeric composites. Renewable organic fillers, such as human or animal hair, offer an attractive fibrous material with substantial potential for reinforcing composites with elastomeric matrices. Samples of unidirectional fiber composites (with hair volume fractions up to 7%) and quasi-isotropic short fiber composites (with hair volume fractions up to 20%) of human hair-reinforced nitrile butadiene rubbers (HH-NBRs) were produced in the peroxide-cured and carbonized states. The samples were characterized using scanning electron microscopy (SEM), Raman spectroscopy, and photoacoustic microscopy. Mechanical tests were performed under tension using a miniature universal testing machine. The expected effect of fiber reinforcement on the overall mechanical performance was demonstrated for both cured and carbonized composites. Considerable enhancement of the elastic modulus (up to ten times), ultimate tensile strength (up to three times), and damage tolerance was achieved. The evidence of satisfactory interfacial bonding between hair and rubber was confirmed via SEM imaging of fracture surfaces. The suitability of photoacoustic microscopy was assessed for 3D reconstructions of the fiber sub-system's spatial distribution and non-destructive testing.

Additive Manufacturing of Elastomeric Composite Lattices with Thermally Grown Micro‐Architectures for Versatile Applications

AbstractMicroengineering of materials plays an important role in achieving multifunctionality and enhancing performance. However, it is still a major challenge to construct secondary micro‐architectures in composite lattices to date. Herein, a novel microengineering strategy of combining additive manufacturing and thermo‐growth processes is proposed to develop elastomeric composite lattices with micro‐architectures throughout the filaments for versatile applications. The new printing inks are composed of elastomeric matrices, closed‐cell microspheres and carbon nanotubes (CNTs). After printing, microspheres “grow” to form secondary micro‐architectures inside by applying thermal treatment. Such thermo‐growth offers a good opportunity to manufacture objects with exceptional and complex micro‐architectures, and few synthetic materials can “grow” like this. Further investigation shows that the obtained microstructured elastomeric composite lattice has an excellent impact energy dissipation capacity by reducing the impact force by 57% owing to the hierarchical energy dissipation mechanisms, and exhibits a distinctively linear electrical response to impact which endows it a self‐sensing capability. In addition, it also shows a good thermal‐insulation performance endowed by mm‐scale pores and µm‐scale hollow spheres, which is comparable to existing composite foams. This study represents an innovative and effective approach for the development of micro‐engineered composite lattices with excellent multifunctional properties for versatile applications.

Recent trends in thermo‐responsive elastomeric shape memory polymer nanocomposites

AbstractShape memory polymers (SMPs) are polymeric smart materials, a class of stimuli‐responsive polymers that can return to their initial shape from a programmed temporary shape under the application of external stimuli, such as light, heat, magnetism, and electricity. Because of these unique features, SMPs can find applications in many fields, like aerospace, biomedical devices, flexible electronics, soft robotics, shape memory arrays, and 4D printing. The comparatively low density, low cost, easy biodegradability, and biocompatibility make SMPs a better candidate for shape memory applications. Among them, thermo‐responsive SMPs can revert to their permanent shape depending on a temperature greater than their polymer transition temperature. Thermo‐responsive SMPs combine semi‐crystalline or elastomeric polymers with improved mechanical and electrical properties. Integrating nanofillers into the polymer elastomer matrices can further enhance these properties, forming shape‐memory polymer nanocomposites (SMPNCs). This review focuses on the basics, design, and classifications of thermo‐responsive SMPs and the characteristics of elastomers and blends of polymers used. Incorporating various nanofillers to get SMPNCs to have improved properties over SMPs is also presented. The importance of Tg (glass transition temperature) and Tm (melting temperature) based SMPs and SMPNCs, various elastomers used, and the methods for preparation like solution casting, melt compounding, in situ polymerization, and their possible future applications are also discussed.

Shape memory behavior of novel Ethylene Propylene Diene Monomer (EPDM)/paraffin foams

Ethylene Propylene Diene Monomer (EPDM) rubber foams are widely employed for thermal and acoustic insulation in building construction. However, their installation in confined spaces is often complicated, and the capability of EPDM foams to exhibit shape memory behavior could be a desirable property. In the literature, several works have demonstrated that blending elastomeric matrices with paraffin, a well-known Phase Change Material (PCM), could be an interesting method to obtain shape memory polymers with a tunable switching temperature. In this work, EPDM foams filled with paraffin wax, having a melting temperature of 70°C, were produced and characterized from a microstructural and thermo-mechanical point of view. By melt compounding and hot pressing, samples were produced, and the PCM content in the foams was varied between 0 and 60 wt% (with respect to the EPDM matrix). The results of the shape memory tests evidenced the crucial role played by the PCM in providing excellent shape fixability for the expanded rubber. Even a limited amount of paraffin (i.e., 20 wt%) was able to raise the strain fixity parameter to a value higher than 80%, and it reached 100% when the paraffin content was increased to 60 wt%. On the other hand, an increased PCM fraction caused a slower recovery process. Consequently, a compromise between a fast recovery and optimum shape fixability should be accepted. These results are promising for the development of novel thermal and acoustic EPDM insulating foams easier to be installed.

Study of the influence of Chitosan on selected properties of elastomeric blends

AbstractThe current trend of greening production is increasingly bringing to the fore alternative types of fillers, such as biofillers, which are obtained from renewable sources or waste [1, 2]. Unfortunately, biofillers cannot be used as majority fillers due to their incompatibility with elastomer matrices and high biodegradability susceptibility [3, 4]. Therefore, the way to their efficient industrial use leads through supplementary fillers to the commonly used inorganic fillers and the partial replacement of these fillers in the blend. The influence of Chitosan as the majority filler has been investigated and its combination with carbon black filler on the elastomeric matrix of natural rubber was investigated in the presented work. The results were compared with natural rubber blends filled exclusively with carbon black. Natural rubber blends with different content of Chitosan and carbon black and their various combinations were subjected to the determination of vulcanization parameters, mechanical properties before and after thermo‐oxidative aging, and scanning electron microscopy. Although the scanning electron microscopy analysis confirmed the expected negative impact of Chitosan as the majority filler on the tensile properties of the vulcanizate, its significant impact on the main vulcanization parameters such as scorch time and optimal vulcanization time was also demonstrated. In the case of blends with a combination of carbon black and Chitosan, it has been shown that Chitosan, in addition to the filler function, also acts as an antioxidant agent through its functional groups, limiting the process of degradation of mechanical properties of natural rubber blends due to their thermo‐oxidative aging. It can be concluded that precisely because of its antioxidant and anti‐degradation effects, Chitosan can be, in addition to carbon black filler, an excellent additional filler for elastomeric blends.

Strain- and stress-based parametric optimization of fiber-reinforced elastomers under finite deformations

In this work, a parametric optimization framework is developed to deal with fiber-reinforced elastomeric matrices. The fiber orientations are in a continuous set to obtain the set of angles that minimizes a functional given by the designer. Although this topic has been extensively studied in recent years, the vast majority of works use either gradient-based or global-based methods to define the composite fiber orientation, with the first being very prone to reach poor local minima and the latter increasing the computational burden exponentially with the number of design variables. Besides that, considering finite strain hyperelasticity, the number of works is substantially reduced. The main goal of this research is to study the efficiency of a local-based derivative-free algorithm in the optimization of problems considering finite deformation and material nonlinearity assumptions in fiber composite design. In order to show the proposed methodology efficiency, two optimization problems are studied: strain energy density minimization and mechanical stress minimization, with the latter further divided into a global and a cluster approach. Therefore, the main novelty of this work is to deal with fiber-reinforced elastomers optimization by means of a direct search algorithm in a constrained nonlinear optimization. The methodology can easily be implemented in existing finite element codes and the results show the pros and cons of both types of optimization.

Магнитноструктурированные композиционные материалы на основе эластомерных матриц с различными вязкоупругими свойствами

Composite materials based on elastomeric matrices (sulphur-regulated chloroprene rubber - PCP and cold curing polydimethylsiloxane - SKTN-A) and magnetic fillers: hard magnetic (SmCo, NdFeB) and soft magnetic (natural magnetite Fe3O4, ZnNiCo-ferrite) in the concentration range of 30…100 mass parts per 100 mass parts of the elastomeric matrix have been obtained. The kinetics of curing of the considered elastomeric compositions was studied, on the basis of which the optimal molding modes were proposed. The samples were molded both in the presence of a magnetic field up to 0.3 T and without it. It has been established that the viscosity of the elastomeric matrix at various stages of curing significantly affects the microstructure and properties of the resulting composites. The electrophysical and magnetic properties of the samples have been studied. It is shown that the degree of structuring, which is directly related to the anisotropy of the characteristics under study, depends on the type of matrix used and decreases in the series SKTN-PCP. The studied materials can be used as "smart" materials controlled by an external influence (magnetic or electric field).

Highly Conductive and Compliant Silver Nanowire Nanocomposites by Direct Spray Deposition

The silver nanowire (Ag NW)/elastomer nanocomposite represents a prototypical form of a compliant conductor for flexible and stretchable electronic devices. The widespread implementations are currently hindered by the complicated procedures to effectively disperse Ag NWs into elastomer matrices. In this study, we report a facile and scalable coating process to create Ag NW nanocomposites on various flexible/stretchable substrates. As-synthesized Ag NWs from the high-yield polyol-reduction approach are homogeneously dispersed into a variety of dilute elastomer solutions, thereby enabling direct spray deposition into highly compliant conductors. The as-prepared nanocomposite exhibits excellent conductivity (∼11,000 S/cm) and high deformability to 100% strain. The stable electrical properties are largely retained under repetitive mechanical manipulations including stretching, bending, and folding. The patterned features of conductive nanocomposites are conveniently accessed using shadow masks or selective laser ablation. The practical suitability is demonstrated by the successful implementations of a stretchable sensing patch and a flexible light-emitting diode display.

Surface modification of zirconia by various modifiers to investigate its reinforcing efficiency toward nitrile rubber

AbstractUniform dispersion of metal oxide‐like zirconia in elastomeric matrix is an essential requisite to deliver proper reinforcement. However, inadequate compatibility between the hydrophobic elastomer and the hydrophilic zirconia surface makes this a difficult task. In this work, three different surface modifiers, namely, sodium dodecyl sulfate (SDS: a surfactant), 3‐(trimethoxy silyl) propyl methacrylates (MPS: an organosilane), and tris (hydroxymethyl) aminomethane (Tris: an amine buffer) are employed to modify the surface of sol–gel derived in‐situ generated zirconia. Effect of surface modification of zirconia by these different kinds of surface modifiers on zirconia‐filled nitrile rubber (NBR) composite has been critically investigated in terms of thermal, morphological, mechanical, swelling, rheological, and dielectric properties. Temperature of maximum degradation (Tmax) of the NBR gum (439 °C) is improved upon incorporation of all type of modified zirconia while that is maximum for Tris‐modified zirconia‐filled composite (458 °C). Similar trend is observed in stress–strain study where Tensile strength is enhanced up to six times for the filled composites relative to NBR gum (1.03 MPa) and the highest value is shown by Tris‐modified zirconia‐filled composite (6.35). This study reveals that Tris could be a potential surface modifier for metal oxides like zirconia, as an alternate to organosilane, to reinforce the elastomer matrices.

Nonpatterned Soft Piezoresistive Films with Filamentous Conduction Paths for Mimicking Multiple-Resolution Receptors of Human Skin.

Soft pressure sensors play key roles as input devices of electronic skin (E-skin) to imitate real human skin. For efficient data acquisition according to stimulus types such as detailed pressure images or macroscopic strength of stimuli, soft pressure sensors can have variable spatial resolution, just like the uneven spatial distribution of pressure-sensing receptors on the human body. However, previous methods on soft pressure sensors cannot achieve such tunability of spatial resolution because their sensor materials and read-out electrodes need to be elaborately patterned for a specific sensor density. Here, we report a universal soft pressure-sensitive platform based on anisotropically self-assembled ferromagnetic particles embedded in elastomer matrices whose spatial resolution can be facilely tuned. Various spatial densities of pressure-sensing receptors of human body parts can be implemented by simply sandwiching the film between soft electrodes with different pitches. Since the anisotropically aligned nickel particles form independent filamentous conductive paths, the pressure sensors show spatial sensing ability without crosstalk, whose spatial resolution up to 100 dpi can be achieved from a single platform. The sensor array shows a wide dynamic range capable of detecting various pressure levels, such as liquid drops (∼30 Pa) and plantar (∼300 kPa) pressures. Our universal soft pressure-sensing platform would be a key enabling technology for actually imitating the receptor systems of human skin in robot and biomedical applications.