Direct measurement and modeling of viscoelastic–viscoplastic properties of freely standing thin polystyrene films.

This article focuses on the nonlinear viscoelastic–viscoplastic (VE–VP) mechanical behavior of freely standing thin polystyrene (PS) films under nanoconfinement. Using bubble inflation experiments and constitutive modeling based on Schapery and Perzyna equations, the study reveals that while the glassy compliance remains unchanged with decreasing film thickness (22–113 nm), the rubbery compliance exhibits stiffening that may be influenced by molecular orientation induced by plastic deformation. Additionally, viscoplastic properties such as viscosity and initial yield stress increase exponentially and linearly, respectively, as film thickness decreases, indicating significant nanoconfinement effects on plastic deformation. These findings highlight the importance of integrating nonlinear VE and VP responses to fully understand and predict the mechanical behavior of thin polymer films in nanoscale applications.