Unravelling the Time-dependent Viscoelasticity of Polymers: The Dual Role of Temperature and Nanoindentation Depth

Understanding the nanoscale viscoelastic response of polymers is essential for applications requiring long-term dimensional stability. This study investigates the viscoelastic creep behaviour of PMMA and epoxy using nanoindentation at two distinct depths (300 nm and 700 nm) across different temperatures (30°C − 55°C). A load-controlled nanoindentation test, combined with holding at maximum load, is used to analyse the time dependent deformation. The mechanical properties, such as elastic modulus and hardness, show significant depth and temperature dependent softening, with epoxy demonstrating superior mechanical strength below its glass transition temperature (T _g − 45°C), while PMMA exhibits greater stability above this threshold. Burgers model analysis of creep displacement reveals fundamental differences in molecular mechanisms through the key parameters like instantaneous creep deformation (h ₀ ), the time-dependent creep deformation (h ₁ ), retardation time (τ ₁ ) and viscosity coefficient (η ₀ ). Epoxy’s viscosity exceeds that of PMMA at low temperatures but drops significantly near its T _g , reflecting enhanced viscous flow due to crosslink network mobility. In contrast, PMMA’s amorphous structure maintains more consistent viscoelastic parameters. At greater depths, viscosity decreases for both the materials. These findings highlight the influence of molecular architecture on governing time dependent deformation, offering actionable insights for optimizing polymer performance in structural, aerospace, and biomedical applications.