Disclaimer: This summary is provided for informational purposes and is based on publicly available source material. It is based on a Science X Dialog article written by Alessio Zaccone of the University of Milan about the scientific article “Atomistic framework for glassy polymer viscoelasticity across twenty frequency decades,” published in The Journal of Chemical Physics under DOI 10.1063/5.0332872.
Researchers have developed a theoretical framework that predicts how a glassy polymer responds to deformation across more than 20 orders of magnitude in frequency. The approach links ultrafast atomic vibrations with the much slower mechanical behaviour measured in conventional laboratory experiments.
The researchers studied poly(methyl methacrylate), or PMMA, using an atomistic model containing 9,920 atoms. Rather than directly simulating the polymer over every relevant timescale, they analysed its vibrational modes and how individual atomic motions respond to an imposed deformation.
The framework is based on non-affine lattice dynamics. In structurally disordered materials such as polymer glasses, atoms do not move uniformly when the material is deformed. Instead, they undergo additional local rearrangements that collectively reduce the material’s stiffness. The model uses this microscopic information to calculate the frequency-dependent shear modulus, a measure of resistance to shear deformation.
To represent the long-lasting influence of earlier molecular movements, the researchers incorporated a power-law memory kernel into the model. This non-Markovian component allowed the theory to reproduce the broad range of relaxation processes found in glassy polymers, including the secondary β relaxation observed around one hertz.
The resulting predictions covered frequencies extending from hundreds of terahertz to the millihertz range. They were consistent with results obtained through molecular-dynamics simulations, Brillouin light scattering, ultrasonic measurements, high-strain-rate testing and dynamic mechanical analysis.
The findings demonstrate that information derived from atomic structure can be used to predict material behaviour at engineering timescales. The approach could reduce reliance on multiple separate testing methods and support the development of better predictive models for polymer glasses. Further work will be required to extend the framework toward the glass-transition region and to polymers with more complex molecular architectures.