Monte Carlo Simulation of Uniaxial Deformation of Polyethylene‐Like Polymer Glass: Role of Constraints and Deformation Protocol

Abstract

The deformation of a glassy amorphous polymer has been simulated by Monte Carlo. A molecular model with constrained chemical bonds (rigid‐bond model) and one with chemical bonds represented by Gaussian springs (flexible‐bond model) have been compared. Furthermore, two different deformation protocols have been tested. Comparisons on the basis of stress–strain behavior, contributions of various interactions to stress and energy, evolution of density and distribution of dihedral angles, and of pair correlation functions show that both the introduction of constrained bonds and the deformation protocol influence the results dramatically. The results obtained using the flexible‐bond model, employing a deformation protocol in which all the monomers are displaced affinely with the box size, show the best agreement with experimental facts.magnified image

Deforming glassy polystyrene: Influence of pressure, thermal history, and deformation mode on yielding and hardening

“…24,[26][27][28] Also other simulation techniques are applied to study the deformation of polymers, such as Monte Carlo algorithms or variants of energyminimization methods for PE-alike, 29 polypropylene, 30,31 poly͑oxypropylene͒, 32 PC, [33][34][35] and PE. 36,37 As the simulation studies are limited to only small time and length scales, numerical agreement is often only possible by means of extrapolation over orders of magnitude.…”

Influence of ensemble boundary conditions (thermostat and barostat) on the deformation of amorphous polyethylene by molecular dynamics

“…Coarse grain techniques [2][3][4][5], such as united atom models [6][7][8][9][10], have been widely used to simulate polymer systems at various length and time scales. For instance, previous work has used Monte Carlo methods and molecular dynamics (MD) simulations to study deformation mechanisms during uniaxial tensile deformation of amorphous polyethylene-like glassy polymers [8][9][10]. The stress-strain curves qualitatively show agreement with experimental results on amorphous polymers.…”

“…For instance, Hoy and Robbins [17][18][19] have used such coarse-grained bead-spring models to interrogate strain hardening in glassy polymers as a function of both microstructure and deformation conditions; they found that the plastic flow stress correlated with the strain hardening modulus, indicating that entropic network models used for rubber elasticity theory may not accurately capture the nanoscale physics of strain hardening in polymer glasses. Additionally, other simulations have used more chemically-realistic potential formulations for studying properties in specific systems (e.g., polyethylene [20][21][22][23][24]) as well as different numerical schemes for molecular deformation, such as Monte Carlo [8,9,25]. However, although several groups have studied the static, dynamic, and mechanical properties of glassy polymer systems, there is still much that is not understood with respect to polymer deformation simulations.…”

“…Here, we have chosen to investigate one aspect of uncertainty pertaining to how the thermostat and barostat conditions affect the deformation response. Several studies have focused on uniaxial and triaxial states of stress associated with how pressure is dissipated at the boundary conditions [15,28] or even different deformation protocols [9]. For instance, Rottler and Robbins [15] used a bead-spring model with three stress states (uniaxial tension, biaxial compression, and biaxial shear) to examine yield and yield criteria for amorphous polymers.…”

“…More recently, Makke et al [28] used a bead-spring model with both uniaxial and triaxial tensile stress states to examine the effect of boundary-driven deformation. Additionally, Mulder et al [9] used Monte Carlo simulations to investigate different deformation conditions in a polyethylene-like polymer system: (i) rigid vs. flexible bonds and (ii) affinely displacing all atoms vs. displacing the center-of-mass of entire molecules. However, the role of the thermostat in dissipating heat generated during deformation and how this affects deformation of glassy polymers has not been extensively discussed in the literature.…”