Modulus Of Polymer Research Articles

Advantages of a 3-parameter reduced constitutive model for the measurement of polymers elastic modulus using tensile tests

Exact measurements of the rheological parameters of time-dependent materials are crucial to improve our understanding of their intimate relation to the internal bulk microstructure. Concerning solid polymers and the apparently simple determination of Young’s modulus in tensile tests, international standards rely on basic protocols that are known to lead to erroneous values. This paper describes an approach allowing a correct measurement of the instantaneous elastic modulus of polymers by a tensile test. It is based on the use of an appropriate reduced model to describe the behavior of the material up to great strains, together with well-established principles of parameter estimation in engineering science. These principles are objective tools that are used to determine which parameters of a model can be correctly identified according to the informational content of a given data set. The assessment of the methodology and of the measurements is accomplished by comparing the results with those obtained from two other physical experiments, probing the material response at small temporal and length scales, namely, ultrasound measurements with excitation at 5 MHz and modulated nanoindentation tests over a few nanometers of amplitude.

Electrochemical and mechanical properties of polyolefin hard segment with polyethylene oxide conductive phase block copolymers

A high lithium ion conductivity polymer electrolyte with excellent mechanical properties was developed in a polyolefin hard segment with a polyethylene oxide conducting phase block copolymer (OEO) and tetraethylene glycol dimethyl ether (G4) composite polymer with lithium bis(fluorosulfonyl)imide (LiFSI). The effect of the modulus of polymers on the ionic conductivity is generally controversial; high ion conducting polymer electrolyte typically exhibit poor mechanical properties. The composite polymer electrolytes developed in this study have ion conductivities in the range of 10−5 to 4×10−4Scm−1 and tensile strengths in the range of 1 to 12MPa at room temperature. 10OEO-1.4LiFSI-2.5G4, where OEO is based on ethylene oxide (EO) units, has ionic conductivity of 1.3×10−4Scm−1 and tensile strength of 5.1MPa at room temperature. The high G4 content composite of 10OEO-3.0LiFSI-4.0G4 has a high ion conductivity of 4.0×10−4Scm−1, but a low tensile strength of 1.0MPa at room temperature. The OEO-LiFSI-G4 composite polymer with high conductivity and high tensile strength is an attractive candidate for the electrolyte in lithium polymer batteries.

The variation in elastic modulus throughout the compression of foam materials

We present a comprehensive experimental study of the variation in apparent unloading elastic modulus of polymer (largely elastic), aluminium (largely plastic) and fibre-reinforced cement (quasi-brittle) closed-cell foams throughout uniaxial compression. The results show a characteristic “zero-yield-stress” response and thereafter a rapid increase in unloading modulus during the supposedly “elastic” regime of the compressive stress–strain curve. The unloading modulus then falls with strain due to the localised cell-wall yielding or failure in the pre-collapse stage and the progressive cell crushing in the plateau stage, before rising sharply during the densification stage which is associated with global cell crushing and foam compaction. A finite element model based on the actual 3D cell structure of the aluminium foam imaged by X-ray computed tomography (CT) predicts an approximately linear fall of elastic modulus from zero strain until a band of collapsed cells forms. It shows that the subsequent gradual decrease in modulus is caused by the progressive collapse of cells. The elastic modulus rises sharply after the densification initiation strain has been reached. However, the elastic modulus is still well below that of the constituent material even when the “fully” dense state is approached. This work highlights the fact that the unloading elastic modulus varies throughout compression and challenges the idea that a constant elastic modulus can be applied in a homogenised foam model. It is suggested that the most representative value of elastic modulus may be obtained by extrapolating the measured unloading modulus to zero strain.

Mutual capacitance of liquid conductors in deformable tactile sensing arrays

Advances in highly deformable electronics are needed in order to enable emerging categories of soft computing devices ranging from wearable electronics, to medical devices, and soft robotic components. The combination of highly elastic substrates with intrinsically stretchable conductors holds the promise of enabling electronic sensors that can conform to curved objects, reconfigurable displays, or soft biological tissues, including the skin. Here, we contribute sensing principles for tactile (mechanical image) sensors based on very low modulus polymer substrates with embedded liquid metal microfluidic arrays. The sensors are fabricated using a single-step casting method that utilizes fine nylon filaments to produce arrays of cylindrical channels on two layers. The liquid metal (gallium indium alloy) conductors that fill these channels readily adopt the shape of the embedding membrane, yielding levels of deformability greater than 400%, due to the use of soft polymer substrates. We modeled the sensor performance using electrostatic theory and continuum mechanics, yielding excellent agreement with experiments. Using a matrix-addressed capacitance measurement technique, we are able to resolve strain distributions with millimeter resolution over areas of several square centimeters.

Hydrolytically Stable Thiol-ene Networks for Flexible Bioelectronics.

Hydrolytically stable, tunable modulus polymer networks are demonstrated to survive harsh alkaline environments and offer promise for use in long-term implantable bioelectronic medicines known as electroceuticals. Today's polymer networks (such as polyimides or polysiloxanes) succeed in providing either stiff or soft substrates for bioelectronics devices; however, the capability to significantly tune the modulus of such materials is lacking. Within the space of materials with easily modified elastic moduli, thiol-ene copolymers are a subset of materials that offer a promising solution to build next generation flexible bioelectronics but have typically been susceptible to hydrolytic degradation chronically. In this inquiry, we demonstrate a materials space capable of tuning the substrate modulus and explore the mechanical behavior of such networks. Furthermore, we fabricate an array of microelectrodes that can withstand accelerated aging environments shown to destroy conventional flexible bioelectronics.

Dynamic viscoelastic properties of polyvinyl chloride with physical aging

The experimental research of dynamic viscoelastic properties of polyvinyl chloride was conducted by the dynamic mechanical analysis method in this paper. And the fitting equation of dynamic modulus of polymers has been presented. Based on the time-aging time equivalent principle, horizontal shift factor and vertical shift factor of aging time are carried out, which proposes a novel method for the research on time-aging time equivalent analysis of dynamic mechanical properties of polymers during physical aging.

Field-Cycling Relaxometry as a Molecular Rheology Technique: Common Analysis of NMR, Shear Modulus and Dielectric Loss Data of Polymers vs Dendrimers

Linear poly(propylene glycol) (PPG) as well as a poly(propyleneimine) (PPI) dendrimer with different molar masses (M) are investigated by field-cycling (FC) 1H NMR, shear rheology (G) and dielectric spectroscopy (DS). The results are compared in a reduced spectral density representation: the quantity R1(ωτα)/R1α(0), where R1(ωτα) is the master curve of the frequency dependent spin–lattice relaxation rate with τα denoting the local correlation time, is compared to the rescaled dynamic viscosity η′(ωτα)/η′α(0). The quantities R1α(0) and η′α(0), respectively, are the zero-frequency limits of a simple liquid reference system. Analogously, the dielectric loss data can be included in the methodological comparison. This representation allows quantifying the sensitivity of each method with respect to the polymer-specific relaxation contribution. Introducing a “cumulative mode ratio” Fi(M) for each technique i, which measures the zero-frequency plateau of the rescaled spectral density, characteristic power-law beh...

Variable Chain Confinement in Polymers With Nanosized Pores and Its Impact on Instability

Recent experiments and molecular dynamics simulations have proven that polymer chains are less confined in layers near the free surfaces of submicron-nanosized pores. A recent model has incorporated this observed variable chain confinement at void surfaces in a mechanism-based hyperelastic model. This work employs that model to do two things: explain the large discrepancy between classical homogenization theories and physical experiments measuring the modulus of nanoporous polymers, and describe the instability behavior (onset and postinstability deformation) of this class of materials. The analysis demonstrates that less confinement of polymer chains near free surfaces of voids inhibits tilting buckling while promoting pattern transformation. The sensitivity of geometric instability modes to void size is also studied in depth, helping lay the foundation for fabricating solids with tunable acoustic and optical properties. The simulation approach outlined provides experimentalists with a practical route to estimate the thickness of the interfacial layer in nanoporous polymers.

High-Resolution Mapping of Quantitative Elastic Modulus of Polymers

High-Resolution Mapping of Quantitative Elastic Modulus of Polymers

A new approach for prediction of elastic modulus of polymer/nanoclay composites by considering interfacial debonding: Experimental and numerical investigations

Abstract In this study, experimental and numerical investigations of the elastic modulus of polymers reinforced with nanoclay are presented. First, finite element modeling of elastic modulus is employed, without considering interfacial debonding between the matrix and nanoclay. A high degree of difference between the finite element and experimental results reveals that the assumption of perfect bonding may be incomplete for nanocomposites. Because interfacial debonding has been recognized as a probable source of damage nucleation in nanocomposites, finite element modeling, accounting for interfacial debonding, is utilized secondly. Using Weibull's distribution function, the probability of debonding at the interface and the consequent, volume fraction of the debonded particles is determined. Next, these values are written into a Python based code, which is executed using ABAQUS®. The comparative results of this study indicate that the presented numerical method exhibits a good agreement with experimental data when interfacial debonding between the matrix and nanoclay is considered. Finally, to further validation of the presented method, finite element modeling with/without considering interfacial deboning has been compared with the experimental results of published studies.

Thermomechanical properties of styrene‐butyl acrylate/organo‐silica nanocomposite films prepared by seed emulsion polymerization

Organo‐silica nanoparticles were prepared by sol–gel technique of triethoxyvinylsilane (VTES) in aqueous solution. The vinyl groups located on the surface of organo‐silica were used to induce the polymerization process and the encapsulation into styrene‐butyl acrylate copolymer emulsion. The prepared latex samples were characterized using FTIR, 1HNMR, UV–visible, thermal analysis, field emission‐SEM and TEM. Results of TGA revealed that nanosilica has retarded the decomposition of nanocomposite polymers with at least 10°C higher than that of pure emulsions. DSC has shown an increase in the nanosilica ratio up to 5% which leads to a dramatic decrease in the glass transition (Tg) of nanocomposite polymer due to the formation of silica nanoparticles homopolymer. DMTA results indicated that the storage modulus of pure polymer is less than nanocomposite, which proves the reinforcing role of nanosilica in the matrix of polymer. Water resistance and UV‐blocking ability have improved by introducing the nanosilica into the matrix of prepared polymer. POLYM. COMPOS., 38:61–67, 2017. © 2015 Society of Plastics Engineers

Estimation of Relaxation Modulus of Polymer Melts by Molecular Dynamics Simulations: Application of Relaxation Mode Analysis

A framework for estimating the linear relaxation modulus of polymer melts by molecular dynamics (MD) simulations is presented on the basis of relaxation mode analysis (RMA). Conventional calculations of the relaxation modulus based on the Green–Kubo formula are computationally very expensive owing to long relaxation times and poor convergence of stress autocorrelation functions: In practice, reliable calculations usually require a time average over \(\mathcal{O}(10\tau _{1}{\text{--}}100\tau _{1})\), where τ1 is the longest relaxation time of a chain in the melt. RMA is a method that systematically extracts relaxation modes and rates of a polymer chain from the time correlation functions of coordinates of polymer segments. In the present method, the relaxation modulus is evaluated by fitting the data of the stress autocorrelation functions to the generalized Maxwell model whose relaxation times are determined from the relaxation rate spectrum obtained by RMA. It is demonstrated that the stress relaxation modulus of a polymer melt is well estimated by the present method over a wide range of time scales from MD simulations of length \(\mathcal{O}(1\tau _{1}{\text{--}}10\tau _{1})\).

Scalable Fabrication of Low Elastic Modulus Polymeric Nanocarriers With Controlled Shapes for Diagnostics and Drug Delivery

A new process, decoupled functional imprint lithography (D-FIL), is presented for fabricating low elastic modulus polymeric nanocarriers possessing Young's modulus of bulk material as low as sub-1 MPa. This method is employed to fabricate sub-50 nm diameter cylinders with >3:1 aspect ratio and other challenging shapes from low elastic modulus polymers such as N-isopropylacrylamide (NIPAM) and poly(ethylene glycol) di-acrylate (PEGDA), possessing Young's modulus of bulk material <10 MPa which is cannot otherwise be imprinted in similar size and pitch using existing imprint techniques. Standard imprint lithography polymers have Young's modulus >1 GPa, and so these polymers used in nanocarrier fabrication in comparison have very low elastic modulus. Monodispersed, shape- and size-specific nanocarriers composed of NIPAM with material elastic modulus of <1 MPa have been fabricated and show thermal responsive behavior at the lower critical solubility temperature (LCST) of ∼32 °C. In addition, re-entrant shaped nanocarriers composed of PEGDA with elastic modulus <10 MPa are also fabricated. Nanocarriers fabricated from PEGDA are shown with model imaging agent and anticancer drug (Doxorubicin) encapsulated in as small as 50 nm cylindrical nanocarriers.

An Analytical Model for Porous Polymer-Ceramic Capacitive Pressure Sensors

An analytical model for pressure sensors is constructed, predicting the capacitive response of a porous, polymer-ceramic composite under an applied pressure. Consisting of mechanical and dielectric counterparts, the iterative model is constructed in detail. The elastic modulus of the three-phase material is approximated by first considering only the polymer-ceramic composite mixture, and then incorporating porosity into the solid composite model. A new model has been developed for approximating the changing elastic modulus of porous polymers undergoing quasi-static compression, which induces the collapsing pores. Necessary material constants were obtained from experimental data published in literature. The permittivity of the paraelectric polymer matrix is modeled, accounting for piezodielectric effects imposed by external pressure and thermally induced stresses caused by substrate pinning. Similarly, the ferroelectric ceramic filler is modeled, considering changes in polarization caused by thermally induced phase transformations in the crystal structure. The final model is evaluated against experimental data, providing insight into composition and microstructure effects on the sensor response.

Micromechanical properties and morphologies of self-healing epoxy nanocomposites with microencapsulated healing agent

The effects of microcapsules and carbon nanotubes (CNTs) on the micromechanical properties (elastic modulus, hardness and plasticity index) of self-healing epoxy polymers were investigated via nanoindentation. A standard Berkovich indenter was used to make indentations under three different normal loads. The surface topographies of the indented regions were monitored via AFM to compare the plasticity of the samples. A nanoscratch test was performed on the self-healing composites, and the healing efficiency was evaluated using AFM. The addition of microcapsules reduced the elastic modulus and hardness of the pure polymer matrix; however, the addition of CNTs significantly improved these mechanical properties. We also used nanoindentation tests in the scratched region to study the mechanical properties of the self-healing composite after healing. Furthermore, the microstructures of both the virgin and healed self-healing composites were determined via SEM. This analysis showed that the microcapsules ruptured during scratch propagation and the healing agent release into the cracks.

Low modulus polymer packaged optical fiber sensor for macrocrack monitoring in ice structures of cold regions

Ice structures provide load-bearing capability for energy exploitation and transportation in cold regions. Meanwhile, staff and facilities take a risk due to large amounts of distributed macrocracks in ice roads, ice bridges, and ice platforms. It is critical to monitor macrocracks for detecting and understanding the fracture process under such a harsh environment. Aiming to obtain real-time, long-term, and quantitative crack opening information for ice structures, this paper presents a feasibility study on monitoring macrocracks with a low modulus polymer packaged optical fiber sensor. Brillouin optical time-domain analysis-based sensing technology is utilized for the distributed strain measurement. According to in situ monitoring requirements, a type of silicone rubber material with appropriate mechanical properties is selected to fabricate the sensor. On this basis, a strain transfer analysis on the packaged and embedded sensor is carried out to derive the relation between the optical measurement and the increment of the crack width. The prototypes have been evaluated by demonstration tests on a tensile device and an ice road model. The experimental results show the sensor can survive in a cold environment and under the large strain resulting from the macrocrack opening. These measured data agree well with the linear calibration. The macrocracks opening in large-scale ice structures can be characterized based on the optical sensor.

Mechanical properties of shape memory polymer composites enhanced by elastic fibers and their application in variable stiffness morphing skins

Shape memory polymers are temperature-controlled variable stiffness materials, which have potential for use as morphing skins. Shape memory polymer skins undergo large strain in their flexible, rubbery state and resist aerodynamic loads in their stiff, glassy state. However, pure shape memory polymers are brittle in their glassy state, and in their rubbery state, they tear rapidly along micro-cracks formed under tension. Due to these disadvantages, the shape memory polymers are not safe and reliable enough for application. In this article, elastic fibers were mixed into pure shape memory polymers to solve these problems. The mechanical properties of the shape memory polymer composites were investigated. The strength and Young’s modulus of pure shape memory polymers at high temperature were improved by elastic fibers, and the toughness of pure shape memory polymers at room temperature (glassy state) was enhanced with acceptable reduction in Young’s modulus. The tear strength of shape memory polymers was significantly improved by elastic fibers, especially at high temperature. Recovery properties and thermal performance were also discussed. Finally, shape memory polymer composite skins were used in a variable camber wing structure to demonstrate their application.

A unified framework for stochastic predictions of mechanical properties of polymeric nanocomposites

We propose a stochastic framework based on sensitivity analysis (SA) methods to quantify the key-input parameters influencing the Young’s modulus of polymer (epoxy) clay nanocomposites (PCNs). The input parameters include the clay volume fraction, clay aspect ratio, clay curvature, clay stiffness and epoxy stiffness. All stochastic methods predict that the key parameters for the Young’s modulus are the epoxy stiffness followed by the clay volume fraction. On the other hand, the clay aspect ratio, clay curvature and the clay stiffness have an insignificant effect on the Young’s modulus of PCNs. Besides the results on the sensitivity of the input parameters, this work includes a comparative study of a series of stochastic methods to predict mechanical properties of PCNs with respect to their performance.

Factors Affecting Electromechanical Properties of Ionic Polymer Actuators Based on Ionic Liquid-Containing Sulfonated Block Copolymers

We investigate the electromechanical properties of ionic polymer actuators based on sulfonated block copolymers and imidazolium ionic liquids (ILs) to unveil key factors affecting the actuation performance. First, the extent of electromechanical deformation of the actuators was proven to be largely affected by the type of anion in the ILs, as understood by the anion-dependent ionic conductivity, charging time, and Young’s modulus of IL-containing polymers. In particular, upon switching the anion from hexafluorophosphate to bis(trifluoromethane)sulfonimide, more than a 2-fold enhancement in the bending strain was observed, which has not been previously reported. Second, we show that the bending strain and durability of the actuators are tunable in a straightforward manner by controlling the block architecture and molecular weight of the polymer, where the use of triblock copolymers was found to be beneficial in enhancing the actuation performance. The high mechanical strength of IL-containing triblock copo...

Shear strengthening of reinforced concrete T‐beams with fully or partially bonded fibre‐reinforced polymer composites

AbstractA series of 10 reinforced concrete T‐beams, designed deficient in shear, were tested in order to investigate the shear performance achieved through externally applied U‐shaped FRP composite strips. Key variables of the study were: type of FRP composite, type of surface bonding and type of end anchorage for the strips. Carbon fibre‐reinforced polymer (CFRP), glass fibre‐reinforced polymer (GFRP) and high modulus of elasticity carbon fibre‐reinforced polymer (Hi‐CFRP) strips were the special composite types with different elastic moduli, full or partial bonding of the strips to the beam surface were the variables for the type of surface bonding. All partially bonded FRP strips were free from surface bonding, whereas epoxy‐bonded FRP anchors were used at their ends close to the slab‐to‐beam connection. Those strips with full surface bonding have either epoxy‐bonded FRP anchors at their ends or the strip ends were without anchorage. The test results revealed that shear‐deficient beams may well be strengthened by the externally applied FRP strips. However, the level of strength enhancement and the failure pattern is closely influenced by the composite's elastic modulus, the type of surface bonding and the type of end anchorage for the FRP strip itself. The enhancement of the Hi‐CFRP strips did not live up to expectations. The use of unbonded FRP for shear strengthening yielded promising results.