Simulated Glass Transition of Poly(ethylene oxide) Bulk and Film: A Comparative Study

Abstract

Stepwise cooling molecular dynamics (MD) simulations have been carried out on the bulk and film models for poly(ethylene oxide) (PEO) to understand glass transition of amorphous polymer films. Three types of properties--density, energy, and dynamics--are computed and plotted against the temperature for the two systems. It has been confirmed that all these properties can reveal glass transition in both PEO bulk and film systems. All the determined glass transition temperatures (T(g)'s) drop in the same order of magnitude to the experimental data available. Among various methods, the T(g)'s obtained from the density and energy data are close to each other if the same space regions are defined, which can suggest the same free volume theory, and dynamic T(g)'s obtained from mean-squared displacements (MSDs) are highest, which can suggest the kinetic theory for structural relaxation. Consistently, all these T(g)'s obtained using different methods show that the T(g)'s of PEO film are lower than those of PEO bulk. The free surface layers of polymer films dictate this offset.

Glass transition in single poly(ethylene oxide) chain: A molecular dynamics simulation study

“…As in our previous work, the poly(ethylene oxide) (PEO) was studied as one typical example for its simple structure and technical importance. A single PEO chain comprised of 250 monomers was first built and optimized.…”

“…Different from the previous ones, our method does not need to calculate the relaxation time that depends upon the definition, and it depends upon less assumption, that is, no MCT or VFT relation is required. This work is further motivated by the facts: despite numerous studies, glass transition of amorphous polymers remains to be poorly understood; during the past decade or earlier, the hot points of such studies have been shifted from bulks to confined films because of the realization of their technical importance; how the T g of a polymer is varied under the confined conditions has a long debate, and the ultimate objective is to isolated chains in comparison to bulks . In this work, to address this issue on the confinement effects, the newly proposed method for locating the polymer T g is applied to simulate single‐chains in various environments (namely, bulk, film, and isolated systems) using the all‐atomistic simulation method.…”

Identification of relaxation processes in pure polyethylene oxide (PEO) films by the dielectric permittivity and electric modulus formalisms

“…Polyethylene oxide is a nontoxic semiconducting polymer of complex molecular structure {H − [O − CH 2 − CH 2 ] n − OH} with molecular weight M w =18.02 + 44.05 n >10 5 g/mol, where n is the number of repeated molecular chain‐like units of identical monomers. The pure PEO has melting point T m <72 ° C (345 K), crystallization temperature T c ≲60 ° C (333 K), and low glass transition temperature T g (≳ − 58 ° C ≅ 215 K), depending on its molecular weight, and possesses strong solvating ability for many metal ions, including Li . Besides its ability to dissolve inorganic lithium‐ion salts, PEO polymer is highly soluble in water and organic solvents (ethanol, methanol, and toluene), so it can be fabricated in the form of solid films by various solvent‐evaporation coating methods .…”

Polymer Dynamics in a Polymer-Solid Interphase: Molecular Dynamics Simulations of 1,4-Polybutadiene At a Graphite Surface

“…In fact, computer simulation of a coarse-grained model of short polymers between two equivalent attractive walls revealed an enhancement of T g (18,19); whereas, repulsive walls lead to a decrease of T g (18)(19)(20). However, several works also address structural and dynamical properties for different polymer-solid contacts using chemically realistic simulations (39)(40)(41)(42)(43). Lastly, when ξ < D/2, where the film shows bulk behavior in its center, it can be that certain experimental techniques still are dominated by this bulk behavior and do not pick up significant effects from the interfacial regions with modified physical behavior.…”