Viscoelastic Response Of Polymer Research Articles

A Study of Viscoelastic Model of Polymers in Shear Flow Based on Molecular Dynamic Simulations

In this study, the rheological properties and physical significations of an incompressible viscoelastic (inCVE) the inCVE model was investigated by employing molecular dynamics calculations. Polypropylene (PP) and polystyrene (PS) polymers were selected as candidate materials, the corresponding cell models consisting of five chains of 80 (PP) and 30 (PS) units were built successively. The energy minimization and anneal treatment were launched to optimize the unfavorable structures. The periodic boundary condition, COMPASS force field and the Velocity-Verlet algorithm were employed to calculate the shear flow behavior of chains. The sample data were collected and fitted based on the Matlab platform, and the analysis of the variance (ANOVA) method was performed to determine the validity of the model. Experimental results reveal that the inCVE model matches well with the pseudo-plastic fluids. Compared with the Ostwald-de Waele power law model and Cross model, it is effective and robust, and exhibits a three-stage rheological characteristic. Moreover, it characterizes the stress yield, activation energy, temperature dependence and viscoelastic response of polymers.

The Time Dependent Behavior of Linear Viscoelastic Polymers

Polymers have been proved to have attractive mechanical characteristics, which made it desirable to choose these materials over traditional materials for numerous types of applications. As the uses of polymers increase, a thorough understanding of the mechanical behavior of these materials becomes vital in order to perform innovative and economical designs of various components. The main objective of this paper is to develop an effective method with the use of the Laplace inverse transform to describe the time dependent mechanical response of viscoelastic polymers. This general methodology is based on differential constitutive relations for viscoelastic polymers, avoiding the use of relaxation integral functions. As its application, the creep and relaxation properties of the materials are exhibited in the numerical examples.

Creep model on the internal stress calculation of injection molded polymer

In the light of viscoelastic theories of polymer and relevant experimental results,a creep model for calculating the internal stress of injection molded parts is constructed.Based on the creep experimental results and theoretical analysis on the non-linear viscoelastic response of polymer,the formulas are presented to evaluate elastic modulus and viscosity of injection molding polymer. Furthermore,the internal stresses of an injection molded ABS plate are predicted by finite element method.To verify the reliability of the model,the results are compared with relevant experimental data and the data simulated by Moldflow.The results show that the calculating precision with new model is improved.And the calculating steps are simplified.It is tested that the model is an effective approach to predict the internal stresses of injection molded parts.

A Method for Modelling the Nonlinear Viscoelastic Response of Polymers

An explicit mechanical model with multiple units which each comprise an activated viscous element and an elastic element is applied to model the nonlinear response of polymers below and up to the glass transition temperature. Considerations of molecular mechanisms in the context of the energy landscape lead to extensions to the properties of the elements, which produce a stress related slowing and a yield peak, a stress dependent reduction in tangent modulus, and a stress related increase in the recovery rate. The response of the model to strain and stress input deformations is visualised by approximate analytical techniques, which show it to be more appropriate than a stress-time shift. They further provide the basis for the construction of models which quantitatively reproduce the response of polymers, under a range of stresses, deformation histories and temperatures. Successful comparisons of model response and experimental data are made for 22 sets of data on six materials, drawn from the reports of 13 investigations available in the literature.

New Approach in the Synthesis of Hybrid Polymers Grafted with Polyhedral Oligomeric Silsesquioxane and Their Physical and Viscoelastic Properties

Synthesis, chain characteristics, and time-dependent viscoelastic response of polyhedral oligomeric silsesquioxanes (POSS)-containing hybrid polymers were investigated. Unlike many other reported POSS hybrid copolymers works, the POSS-grafted copolymers used in this study, although having different amounts of POSS attachments, have the same degrees of polymerization and molecular weight distribution. This was accomplished by grafting different amounts of aluminosilsesquioxane onto a previously synthesized, random copolymer of styrene and vinyl−diphenylphosphine oxide, PSP. The coordination bonding between aluminum and phosphine oxide is quantitative, which enables the investigation of physical characteristics and viscoelastic response of polymers as influenced only by the POSS attachments. Similar to other hybrid polymers with covalently bonded POSS, we observed a systemic increase in the characteristic relaxation time of polymers at the terminal zone due to the POSS attachment. Linear viscoelastic respon...

The Effects of Nanoscopic Fillers on the Viscoelastic Response of Polymers

ABSTRACTWe have used a technique developed by Brochard (Macromolecules, 2004, 37, 1470) using free standing thin films to study the viscoelastic response of filled-polymer films. Transmission Electron Microscopy (TEM) experiments reported that fillers were well distributed within the films, and therefore no clustering and interfacial segregation occurred. Results from Shear Modulation Force Microscopy (SMFM) measurements revealed that the glass transition temperature of the polymer (Tg) was depressed by 10°C relative to the bulk for Au (10 nm), and bulk like for Au (3 nm). The effects of colloidal fillers on the tracer diffusion coefficient (D) were studied using secondary ion mass spectrometry (SIMS), and results found that D was increased significantly for the Au 10 nm, and constant for the Au 3 nm. Values for zero shear rate viscosity extracted from the diffusion coefficient were compared to the shear strain calculated from the hole growth measurements, and theoretical predictions. Results were attributed to an increase in excluded volume when large particles were introduced into the matrix.

Stress‐dependent dynamic compliance spectra approach to the nonlinear viscoelastic response of polymers

Stress‐dependent dynamic compliance spectra approach to the nonlinear viscoelastic response of polymers

Random walk model for viscoelastic response of glassy polymers

Both theory and experiment suggest that reptation plays a minor role in the viscoelastic response of polymers in the glassy state. The time for reptation is so long that the entanglement network can be considered to be permanent, at least for deformation far below T g. We have developed a network picture of a glassy polymer in which mechanical stresses and strains in the solid are represented in terms of forces and displacement in a harmonic lattice with nearest-neighbor interactions. The intermittent character of segmental motion in the glassy state is modelled in terms of the behavior of a two-state continuous time random walk, one state of which refers to mobilized segments and the second to immobilized segments. The pausing time density for segments in an immobilized state is taken to be negative exponential, and for mobile segments it has an asymptotic stable law form ψ( t)∼ t -( α+1) , where 0<α<1. We show that the quantity needed to calculate the mechanical response of the network is a fourth-order correlation function which is readily found for a harmonic model. A comparison of the theoretical prediction will be made to experimental data on stress relaxation and recovery of glassy polycarbonate.