Nanoscale mechanical characterization of polymers by atomic force microscopy (AFM) nanoindentations: viscoelastic characterization of a model material

Abstract

The atomic force microscope (AFM), apart from its conventional use as a microscope, is also used for the characterization of the local mechanical properties of polymers. In fact, the elastic characterization of purely elastic materials using this instrument can be considered as a well-assessed technique while the characterization of the viscoelastic mechanical properties remains the challenge. In particular, one finds the mechanical behavior changing when performing indentations at different loading rates, i.e. on different time scales. Moreover, this apparent viscoelastic behavior can also be due to complex contact mechanics phenomena, with the onset of plasticity and long-term viscoelastic features which cannot be identified by the force curve alone. For this reason, a viscoelastic characterization, and thus the study of the effects of indentation rate and temperature, was done on model materials where such additional phenomena are not observed. Another time dependence originating from the instrument itself has also been identified and decoupled. In fact, the viscoelastic behavior has been found to be reproducible even if one changes the experimental set-up as far as the preliminary determinations concerning AFM nanoindentations are well performed. The effects of temperature and time scales on the mechanical behavior have also been undertaken. A check on time–temperature superposition is also attempted through the WLF equation and the apparent activation energies for the elementary motions in the rubbery and in the glass transition regions are in good agreement with the expected values.

Characterization of human ovarian teratoma hair by using AFM, FT‐IR, and Raman spectroscopy

“…While teratoma hair has no chance to meet the environmental changes, therefore it may maintain the intrinsic properties, namely the hydrophobic cuticles that result in a smaller adhesive force. As expected, the adhesive force of wet hair was larger than dry hair, showing a good agreement in the report results (Tranchida et al, 2009). The direct characterization of the keratin protein can be performed by FT-IR and Raman spectroscopy.…”

Surface characterisation and biomechanical analysis of the sclera by atomic force microscopy

“…AFM force-indentation plots were then taken on each of the layers, at 1 µm distance from the previous indentation. Use of the closed loop mode eliminated non-linear piezo hysteresis effects during nanoindentation experimentation (Tranchida and Kiflie et al, 2009). Plots are then fitted to the Hertzian based contact theory for a cone,…”

Nano-scale temperature dependent visco-elastic properties of polyethylene terephthalate (PET) using atomic force microscope (AFM)

“…Further, as the cantilever probe assembly can be treated as a spring, it can be used to measure surface stiffness and adhesive properties. Previous studies have explored the visco-elastic and nano-mechanical properties of polymer films (Bliznyuk et al, 2002;Cappella et al, 2005;Kaliappan and Cappella, 2005;Torres et al, 2009;Tsui et al, 2000;Yang et al, 2006), polymer electrospun fibres (Wang and Barber, 2012) and rubber (Tranchida et al, 2009) using AFM with increasing temperature. However, AFM based nanoindentation analysis on polymeric materials can become problematic * Corresponding author.…”