Molecular Chain Network Research Articles

Experimental study and mathematical modeling of magnetorheological elastomers considering molecular chain network and temperature influence

Experimental study and mathematical modeling of magnetorheological elastomers considering molecular chain network and temperature influence

Mechanical property tests and physics-informed data-driven modeling of viscoelastic materials subjected to thermal-oxidative aging

The purpose of this paper is to investigate and characterize the performance changes of viscoelastic materials (VEMs) in viscoelastic (VE) devices used for structure vibration control due to the influence of aggressive environmental conditions during long-term service. To this end, a series of thermal-oxidative (TO) aging experiments are conducted on the developed VEMs, variation of microstructure and macroscopic mechanical behaviors of TO aged VEMs are tested and analyzed. The molecular chain network of VEMs that can be simplified into elastic chain network and free chain network is described by the architecture of microsphere model, a physics-informed data-driven model is proposed to reflect the mechanical properties of TO aged VEMs, in which the physics-informed neural network (PINN) theory is incorporated to describe the statistical characteristics of molecular chains and the reaction rate of TO aging. Based on the experimental data, implementation and validation of the proposed model are conducted on the mechanical properties of VEMs under varying aging levels. The experimental results suggest that TO aging could alter molecular chain structure of VEMs from the microscopic level, leading to an increase in crosslinking degree and modulus, and the degeneration of deformation ability and energy-dissipation capacity for VEMs. The verifications reveal that the proposed model possesses high accuracy in characterizing the mechanical properties and energy-dissipation capability of VEMs under different aging levels, which preliminarily proofs the potential of PINN theory in reflecting the complex mechanical behaviors of VEMs.

Flexible Capacitive Sensors Based on Liquid Crystal Elastomer.

The disordered transformation of the ordered aligned polar liquid crystal molecules in liquid crystal elastomers (LCEs) under the influence of an external field imbues them with the unique property of thermally reversible shape memory, making them highly valuable for various applications, particularly in actuators. In this study, we examined the high dielectric constant exhibited by the orientation polarization of polar liquid crystal molecules in RM257-LCE films, which holds significant potential for developing flexible capacitive sensors. By manipulating the flexibility of the molecular chain network and introducing hydrogen bonds and metal ions into the main chain, we were able to enhance the relative dielectric constant of LCEs to an impressive value of 62 (at 100 Hz), which is approximately 23 times higher than for polydimethylsiloxane (PDMS). This elevated dielectric constant displays a noteworthy positive temperature coefficient within a specific temperature range, starting from room temperature and extending to the clearing point. Using this property, we fabricated highly sensitive capacitive, flexible temperature sensors. Moreover, we successfully engineered a flexible pressure sensor with an excellent pressure-sensing range of 0-2 MPa by combining the porous structure of the prepared LCEs with mushroom electrodes. Additionally, the sensor showcases a remarkable capacitance recovery time of 0.8 s at 90 °C. These outstanding features collectively contribute to the excellent pressure-sensing characteristics of our sensor. The findings of this study offer valuable insights and serve as a reference for the design of innovative flexible sensors, enabling advancements in sensor technology.

Study on properties of copolymers based on different types of benzoxazines and branched epoxy resins

Previous studies on linear epoxy (bisphenol A epoxy) resin/benzoxazine composites showed that with the addition of epoxy (EP) resin, the resulting copolymers exhibited an increased glass transition temperature ( Tg) ( Tg reached a maximum value at a specific content), improved flexural strength, lower heat resistance, and reduced tensile strength. Herein, branched EP resin (AG-80)/benzoxazine copolymers featuring novolac (N-box) and siloxane (Si-box) chains were prepared without any external curing agent. In both systems, the EP resin endowed the copolymers with an increased crosslinking density; however, Tg continued to increase with increasing EP content. In addition, the heat resistance of the copolymers gradually enhanced. Different types of benzoxazines have various effects on the properties of copolymers. In terms of mechanical properties, AG-80/N-box copolymers exhibited brittle fracture characteristics; with increasing EP content, the flexural strength of the copolymer decreased while the tensile strength increased. AG-80/Si-box copolymers exhibited ductile fracture characteristics, with gradual increases in flexural and tensile strengths. Furthermore, with increasing EP content, the molecular chain migration ability and network homogeneity of the AG-80/N-box copolymers decreased gradually. Alternatively, in the case of the AG-80/Si-box copolymers, the molecular chain migration ability remained unchanged and network homogeneity improved. Hence, the developed copolymers can be used as resin matrices for the fabrication of advanced composites.

Enhancing Tensile Strength and Toughness via Moderate Orientation of Amorphous Molecular Chains in Biobased Biodegradable Poly(lactic acid)

The preparation of high-toughness and high-strength poly(lactic acid) (PLA) is of great significance for promoting its application in packing, construction, and medical fields. Compared to blending with polymeric elastomers, hot stretching is an effective method to improve the toughness of PLA without sacrificing its strength. However, it is still unclear which part of the structural change after hot stretching is responsible for the increased toughness of PLA. In this work, the semicrystalline structure and mechanical properties of the PLA samples stretched at different temperatures were studied. First, the semicrystalline structure of the PLA samples was studied by combining differential scanning calorimetry and wide-angle X-ray diffraction analyses. When the stretching temperature was relatively low (e.g., 65 °C), the mesophase, an intermediate phase between crystal and amorphous, was formed. Furthermore, significant stretch-induced crystallization was observed due to the enhanced chain mobility when the stretching temperature was 65–75 °C. With further increasing the stretching temperature, the crystallinity of the PLA samples decreased sharply to nearly 0 due to the rapid chain relaxation. Intriguingly, the PLA samples stretched at 85 °C showed the highest elongation at break 238.4% and high strength 75.8 MPa, which was attributed to its moderate molecular chain orientation not only hindering physical aging but also retaining the entanglement network of PLA molecular chains. The findings in this work provide an insightful understanding of the improved toughness of PLA, which will facilitate the large-scale practical application of PLA.

Design of a genetically programmed barnacle-curli inspired living-cell bioadhesive.

In nature, barnacles and bacterial biofilms utilize self-assembly amyloid to achieve strong and robust interface adhesion. However, there is still a lack of sufficient research on the construction of macroscopic adhesives based on amyloid-like nanostructures through reasonable molecular design. Here, we report a genetically programmed self-assembly living-cell bioadhesive inspired by barnacle and curli system. Firstly, the encoding genes of two natural adhesion proteins (CsgA and cp19k) derived from E. coli curli and barnacle cement were fused and expressed as a fundamental building block of the bioadhesive. Utilizing the natural curli system of E. coli, fusion protein can be delivered to cell surface and self-assemble into an amyloid nanofibrous network. Then, the E. coli cells were incorporated into the molecular chain network of xanthan gum (XG) through covalent conjugation to produce a living-cell bioadhesive. The shear adhesive strength of the bioadhesive to the surface of the aluminum sheet reaches 278 ​kPa. Benefiting from living cells encapsulated inside, the bioadhesive can self-regenerate with adequate nutrients. This adhesive has low toxicity to organisms, strong resistance to the liquid environment in vivo, easy to pump, exhibiting potential application prospects in biomedical fields such as intestinal soft tissue repair.

Mechanical modeling and testing of different polyamides considering molecular chain structure, crystallinity, and large strains

Polyamide (PA) is a semi-crystalline polymer in which the main chain is configured by the repeating units of amide bonds (-NHCO-). The strength of PA is achieved by intermolecular hydrogen bonding between the hydrogen and oxygen atoms of the amide bonds. In this study, the effects of the density of the amide group and crystallinity were evaluated by uniaxial tensile tests of commercial PA11, PA610, PA6, and PA-MXD10. The maximum stress was proportional to the tensile rate, and the stress-strain curves of the PAs with small crystallinity showed a sharp drop after the maximum stress. In contrast, a gradual change in the stress was observed around the maximum stress of the PAs with high crystallinity. Subsequently, a time-dependent nonlinear mechanical model based on the unfixed molecular chain network (MCN) model is proposed to predict the mechanical behavior of PAs. Because this model was proposed for amorphous epoxies, we modified the unfixed MCN model to reproduce the mechanical response of semi-crystalline PAs. In this study, a constant resistance to debonding in the original unfixed MCN model was replaced by the function of the viscoplastic strain. The modified version of the unfixed MCN model reproduced the gradual softening at a large strain range and the effects of the crystallinity on the mechanical response of the PA.

Deformation of Molecular Chain's Network Structure of Spherical Gel under Quasi-static Compressive Loading Condition

Elastomeric gels are soft-elastic materials consisting of a three-dimensional crosslinked polymer network and liquid filling the space among such network. To take advantage of the swelling-deformation behavior of elastomeric gel and explore its possibility for applications in engineering as a structural member, investigations on the swelling-deformation behavior under various loading conditions are indispensable. Therefore, in this study, we at first proposed a nonaffine model for the elastomeric gel to account for the change of the entangling structure of polymer chains during the swelling-deformation process, in which the change of the number of polymer chains per unit volume N is depending on the first invariant of right Cauchy-Green deformation tensor I1. And then, to investigate the effect of the nonaffine movement of the polymer chain on the mechanical behavior of the elastomeric gel, we performed a FEM simulation for a spherical gel under quasi-static compressive loading condition. The results show that the swelling-deformation behavior of the spherical gel is quite different at the positions such as the polar, the equator or the center of the sphere.

Mathematical modeling and test verification of viscoelastic materials considering microstructures and ambient temperature influence

Micro structures of viscoelastic materials (VEM) play an important role in their mechanical properties and energy dissipation capacities. This work shows a mathematical modeling of VEMs considering molecular chain-network configurations, and the temperature effects on mechanical properties of VEMs can also be characterized based on the equivalent relationship between temperature and frequency. The Dynamic Thermomechanical Analyzer (DMA) test is carried out to observe dynamic behaviors of the VEM and prove the accuracy of the proposed new mathematical model. The experimental data of viscoelastic damper (VED) are utilized to further verify the correctness of the proposed model with different ambient temperatures.

Multiscale analysis of elastic waves in soft materials: From molecular chain networks to fiber composites

We provide a multiscale analysis of elastic waves in soft microstructured materials including the underlying molecular chain network mechanisms and micromechanics of hyperelastic fiber composites. First, we examine the interplay between the crosslinked and entangled polymer chains and elastic wave characteristics in finitely deformed materials. Next, we study the shear wave propagation in a class of heterogeneous hyperelastic composites. In particular, we consider the transversely isotropic fiber composites with phases characterized by the stiffening behavior stemming from the non-Gaussian statistics of polymer chains. By employing a micromechanics-based approach, we derive explicit expressions for phase velocities in terms of material properties and volume fraction of the phases. Our results indicate the significant influence of the variety of length-scales mechanisms on the elastic wave characteristics. We provide examples to illustrate the influence of the mechanisms under different loading conditions, wave propagation directionality, and material microstructure parameters.

Water-Tree Resistant Characteristics of Crosslinker-Modified-SiO2/XLPE Nanocomposites.

Trimethylolpropane triacrylate (TMPTA) as a photoactive crosslinker is grafted onto hydrophobic nanosilica surface through click chemical reactions of mercapto double bonds to prepare the functionalized nanoparticles (TMPTA-s-SiO2), which are used to develop TMPTA-s-SiO2/XLPE nanocomposites with improvements in mechanical strength and electrical resistance. The expedited aging experiments of water-tree growth are performed with a water-knife electrode and analyzed in consistence with the mechanical performances evaluated by means of dynamic thermo-mechanical analysis (DMA) and tensile stress–strain characteristics. Due to the dense cross-linking network of polyethylene molecular chains formed on the TMPTA-modified surfaces of SiO2 nanofillers, TMPTA-s-SiO2 nanofillers are chemically introduced into XLPE matrix to acquire higher crosslinking degree and connection strength in the amorphous regions between polyethylene lamellae, accounting for the higher water-tree resistance and ameliorated mechanical performances, compared with pure XLPE and neat-SiO2/XLPE nanocomposite. Hydrophilic TMPTA molecules grafted on the nano-SiO2 surface can inhibit the condensation of water molecules into water micro-beads at insulation defects, thus attenuating the damage of water micro-beads to polyethylene configurations under alternating electric fields and thus restricting water-tree growth in amorphous regions. The intensified interfaces between TMPTA-s-SiO2 nanofillers and XLPE matrix limit the segment motions of polyethylene molecular chains and resist the diffusion of water molecules in XLPE amorphous regions, which further contributes to the excellent water-tree resistance of TMPTA-s-SiO2/XLPE nanocomposites.

Ability of Constitutive Models to Characterize the Temperature Dependence of Rubber Hyperelasticity and to Predict the Stress-Strain Behavior of Filled Rubber under Different Defor Mation States.

In this paper, some representative hyperelastic constitutive models of rubber materials were reviewed from the perspectives of molecular chain network statistical mechanics and continuum mechanics. Based on the advantages of existing models, an improved constitutive model was developed, and the stress–strain relationship was derived. Uniaxial tensile tests were performed on two types of filled tire compounds at different temperatures. The physical phenomena related to rubber deformation were analyzed, and the temperature dependence of the mechanical behavior of filled rubber in a larger deformation range (150% strain) was revealed from multiple angles. Based on the experimental data, the ability of several models to describe the stress–strain mechanical response of carbon black filled compound was studied, and the application limitations of some constitutive models were revealed. Combined with the experimental data, the ability of Yeoh model, Ogden model (n = 3), and improved eight-chain model to characterize the temperature dependence was studied, and the laws of temperature dependence of their parameters were revealed. By fitting the uniaxial tensile test data and comparing it with the Yeoh model, the improved eight-chain model was proved to have a better ability to predict the hyperelastic behavior of rubber materials under different deformation states. Finally, the improved eight-chain model was successfully applied to finite element analysis (FEA) and compared with the experimental data. It was found that the improved eight-chain model can accurately describe the stress–strain characteristics of filled rubber.

Muscle-like Ultratough Hybrid Hydrogel Constructed by Heterogeneous Inorganic Polymerization on an Organic Network.

Inspired by inorganic oligomers and their polymerization, we herein develop a heterogeneous inorganic polymerization tactic that can be used to prepare a muscle-like hybrid hydrogel by inducing the polymerization of calcium phosphate oligomers (CPO) onto a polyvinyl alcohol (PVA) molecular chain network. In this heterogeneous process, the CPO units bond with PVA molecules via assistance from sodium alginate (SA), and then gradually polymerize along the organic chains to form ultrafine hydroxyapatite nanolines with a diameter of ∼1 nm. Because of the well integration of organic and inorganic phases from the heterogeneous polymerization, the hierarchical structured hydrogel can exhibit ultratough mechanical properties of ∼17.84 MPa in strength and ∼8.97 kJ m-2 in fracture energy, which exceed natural muscles and almost synthetic hydrogels. Moreover, the damaged hydrogel can be repaired readily by adding the precursors of CPO, PVA, and SA, which can induce in situ re-polymerization. The hydrogel also exhibits muscle-like rotational motion under aqueous conditions, which can be developed into a water-driven biomimetic motor. This study indicates that inorganic polymerization can achieve a novel organic-inorganic integration rather than conventional organic-inorganic composition, and it provides a novel tactic for design and manufacture of advanced materials.

Interfacial regions and network dynamics in epoxy/POSS nanocomposites unravelling through their effects on the motion of molecular chains

Interfacial regions formed by incorporating a certain percentage of nanofillers into a polymer matrix can impact on the motion of molecular groups, chain units or chain segments, and alter molecular chain network dynamics, which is regarded as a key factor to achieve a finer degree control of dielectric properties of polymer nanocomposites. It is of interest to investigate the molecular chain motion behavior at interfacial regions with the incorporation of nanofillers. Epoxy resin/polyhedral oligomeric silsesquioxane (EP/POSS) nanocomposites are fabricated and the observations of morphology structure and chemical elements indicate that POSS nanofillers are well dispersed in the matrix. Differential scanning calorimeter, dynamic thermomechanical analysis, and dielectric relaxation spectroscopy are measured to analyze the effect of nanodoping on the motion properties of molecular chain units and chain segments that satisfy the Arrhenius and Vogel-Fulcher-Tammann equations respectively. The thicknesses of interfacial regions between POSS nanofillers and EP matrix are estimated from dielectric spectra and effective relative permittivity simulations, which are around several nanometers and decrease with the increment in the nanofiller content. In addition, the dielectric spectra scaling analysis indicates that the motion of small chain units can be hindered in interfacial regions and be tuned simultaneously by the variations of molecular chain network structure and dynamics. Nevertheless, the thin interfacial regions cannot effectively restrict the orientation of long molecular chain segments during the glass transition process. The variation of chain segment orientation behavior is ascribed to the interactions among molecular chains tuned by the binding effect of POSS nanofillers.

Plasticity and thermally-induced recovery in polycarbonate

In the present paper, we present an approach combining physically-based constitutive modeling and experiments to study the thermo-mechanical response of amorphous thermoplastics whose final objective is the prediction of the thermally-induced strain recovery. The underlying thermo-mechanical mechanisms are described by elastoviscoplastic-viscohyperelastic constitutive relations allowing to account for the variation with temperature of the inter and intramolecular barriers to deformation and their abrupt change when the temperature traverses the glass transition. The model fit shows a good agreement with experimental observations on polycarbonate in terms of temperature and strain-rate dependent stress-strain response. The material kinetics with temperature is designed and introduced into the model to predict the thermally-activated strain recovery process during heating. In our approach, the intramolecular resistance of the entangled molecular chain network orientation/relaxation is used as the driving stress that continuously activates the strain recovery process during zero-stress creep above glass transition. The model predictions are shown under zero-stress creep recovery for different previous loading histories in terms of strain-rate and strain-level. The simulated results are in satisfactory agreement with experimental observations at different heating temperatures showing the relevance of the proposed approach.

A light controlled, reversible, sensitive and highly selective colorimetric sensor for mercuric ions in water

A merocyanine dye as a p-toluenesulfonate salt was synthesized and characterized using spectroscopic techniques. The structure established through single-crystal X-ray crystallography revealed the presence of an extensive H-bond network of dye molecules linked through water molecule and p-toluenesulfonate group. The crystal explorer program was used to estimate the contribution of different intermolecular interactions in the network of molecular chains. The addition of mercuric ions led to the disruption of the molecular chains through complex formation between mercuric ions and the merocyanine form, which produced a change in color visible to the naked eye. The molecule displayed no change in color upon addition of other metal ions. The change in color was used for the detection of mercuric ions. The interaction between the dye molecule and the mercuric ion was further investigated using UV–Visible, DLS and 1H NMR spectroscopy. The interaction between the merocyanine dye and the mercuric ions can be reversibly disrupted by UV light (365 nm). The interaction between mercuric ions and the merocyanine dye was further investigated using density functional theory to corroborate the experimental data. TD-DFT studies indicated a increase in the HOMO-LUMO gap upon addition of mercuric ions.

Microstructure and tensile properties of injection molded thermoplastic polyurethane with different melt temperatures

ABSTRACTThe use of injection molding technology to prepare heterogeneous interlayer film of laminated glass holds strong applicable potential. This article aims to investigate the effects of melt temperature and melt flow on the microstructure evolution and tensile properties of thermoplastic polyurethane (TPU) specimens during the injection molding process. The tensile properties of the TPU specimens show dependency on the melt temperature and melt flow direction. The results of birefringence indicate that melt flow and lower melt temperature induce higher stretching deformation of the molecular chain network. Small‐angle X‐ray scattering analysis approves that besides the melt temperature and flow direction, the testing position on the cross section of the specimen has great influence on the microstructure of the TPU sheet. Further analysis and conclusions can be made using wide‐angle X‐ray scattering method. The above results demonstrate that both the tensile properties and microstructure of the injection molded TPU specimens tend to be isotropic with the increase of melt temperature. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48891.

Water Effect on the Deformation Behavior of Nafion Membrane

The water channels inside the Nafion membrane are considered as the elastic particles and the effect of the elastic modulus of the particles on the deformation behavior of the membrane is discussed with a particle-contained composite model, which is constituted based on the homogenization method. The results show that the deformation resistance of the membrane is quite dependent on the elastic modulus of the particles, whereas the strain softening behavior after the yielding of the membrane is almost derived from the onset and the propagation of the localized shear band in the matrix, which also leads to the dramatic disappearance of the entanglement points in the molecular chain network of the matrix.

Evaluation and modeling of mechanical behaviors of thermosetting polymer under monotonic and cyclic tensile tests

A nonlinear elastic-inelastic model for a thermosetting polymer is proposed based on the molecular chain network theory. In the proposed model, the bond of the polymer chain is divided into physical and chemical bonds, and the physical bond is allowed to separate and recombine during the deformation. The decrease in the rigidity and increase in the inelastic strain are related to the development of the physical bond density to represent the characteristic deformation behavior of the polymer. A rate-form large deformation constitutive equation is then formulated based on the updated Lagrangian method. Additionally, deformation behaviors of the epoxy under monotonic and cyclic tensile tests were evaluated by experimental and computational studies. The experimental results of the monotonic tensile test displayed a gradual transition from elastic to inelastic deformation, strain softening behavior after the macroscopic yielding stress, and an increase in the initial slope and the macroscopic yielding stresses with an increasing strain rate. The computational model can represent such characteristics by controlling the development of the physical bond density. In a cyclic test, a decrease in the rigidity and an increase in the residual strain with increasing cycles were observed even in a small strain range. Such inelastic deformation depended on the strain rate and the given upper stress in the cyclic test. Further, the proposed model successfully reproduced such nonlinear behavior in the cyclic test.

Constitutive Equations for Rubber under Abrupt Change in Strain Rate Direction

We proposed constitutive equations for the strain rate and temperature-dependent behavior of rubber by employing the nonaffine molecular chain network theory and reptation theory. The finite element homogenization method along with the proposed constitutive equations have the capability of predicting the deformation behaviors of particle-filled rubber under changes in volume fractions, distribution patterns, and size heterogeneity of the particles without additional parameters. The only existing problem is the modest estimation of the stiffness of rubber immediately after the abrupt change in strain rate direction (ACSD) as can be seen in the cyclic deformation behavior. We restricted our attention to the generalization of our nonaffine molecular chain network theory to overcome the problems associated with ACSD. We consider the effect of the delay of deformation in surrounding chains on the elasticity modulus by introducing an amplification parameter dependent on the current chain stretch and direction of strain rate immediately after ACSD. The potential of the proposed constitutive equations is examined against the predictability of the experimentally obtained deformation exhibiting ACSD.