Comprehensive investigation of the viscoelastic properties of PMMA by nanoindentation

Instrumented nanoindentation (NI) was used to examine the viscoelastic properties of poly(methyl methacrylate) (PMMA) as an amorphous polymer model. An evaluation combining adhesive contact and empiric spring–dashpot models has been applied to obtain the instantaneous elastic modulus E ₀ and the infinitely elastic modulus E _∞ from nanoindentation creep curves. The value of E ₀ has been compared to moduli obtained with atomic force microscopy-based nanoindentation (AFM-NI) and compression tests. Furthermore, the elastic modulus has been evaluated by the method introduced by Oliver and Pharr (O&P) for the NI and AFM-NI results. Comparison of the elastic modulus E ₀ from the creep measurements of NI and AFM-NI to compression tests reveals good agreement of the results. However, only the O&P based AFM-NI results yield to lower values.