Glass transition temperature of a polymer thin film: Statistical and fitting uncertainties

Abstract

The polymer glass transition is an important property in a wide variety of applications. The glass transition temperature of a polymer composite or confined thin film can be significantly different to the pure polymer. Molecular dynamics simulations are useful for providing molecular level insight and prediction, particularly at interfaces, that are not easily observable experimentally. However, there are significant methodological uncertainties in calculating the polymer glass transition temperature using molecular dynamics simulations. In this work we investigate how the cooling method, fitting range and statistical variation affects the calculated glass transition temperature of polyethylene. We found that it is necessary to perform multiple independent simulations to obtain statistically significant results, and that appropriate fitting ranges must be chosen. The methodological findings were used to investigate the difference in glass transition temperature between pure polyethylene and a polyethylene film confined between graphene surfaces. It was found that the glass transition temperature of a 9 nm thick confined film was higher than bulk polyethylene by approximately 15 K.

Critical Thickness of Free-Standing Nanothin Films Made of Melted Polyethylene Chains via Molecular Dynamics

“…We simulated layers at T values of 373. 15, 473.15, 573.15, and 673.15 K, below the bulk T m of linear polyethylene (403.65 K for a molecular weight of 100.5 kg/mol) [20], beyond the highest T g reported (253 K) [23,24], up to T values near the limit of thermal stability (losses of 5% of the weight at 695.55 K, and the maximum loss begins at 747.45 K) [25,26]. The simulation cell consisted of a parallelepiped with A i = 145 A × 145 A, which was large enough to contain a stretched chain in each lateral direction, had a variable length in the inhomogeneous direction (depending on the number of chains simulated), and contained between 93 and 1568 C 200 polyethylene chains.…”

Poly(alkylene 2,5-furanoate)s thin films: Morphology, crystallinity and nanomechanical properties

“…Specifically, a recent review about polymer thin films spotlighted their use in chips, flat panel displays, photovoltaic devices, and coatings [27]. Moreover, polymer thin films have been a subject of academic debates for over the past 20 years [28][29][30][31]. In the particular case of semicrystalline polymers, the confinement imposed by the thin film geometry, and the polymer-substrate adsorption effects, resulted in differences in the crystallization rate [32,33], crystalline morphology [34][35][36], thermal transitions and polymers' molecular dynamics [32,37].…”

Modified Group Contribution Scheme to Predict the Glass-Transition Temperature of Homopolymers through a Limiting Property Dataset

“…As rheological, mechanical, and dielectric properties change dramatically when the operating temperature passes through T g , T g plays a vital role in a wide range of both scientific and industrial processes. To explore the correlation between T g and the chain structure of the polymer, several attempts have been made by experiments, molecular dynamics simulation, , and quantitative structure–property relationship . Undoubtedly, a reliable and quick property prediction of polymers that are not even synthesized is desirable as it saves time and resources for basic research and industrial product development.…”