Mechanical characterization of polymers on nanometer scale through nanoindentation. A study on pile-up and viscoelasticity

Stefano Piccarolo, Alexander Alexeev, Joachim Loos

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    Abstract

    The analysis of nanoindentation force curves collected on polymers through the common Oliverand Pharr procedure does not lead to a correct evaluation of Young’s modulus. In particular, the estimated elasticmodulus is several times larger than the correct one, thus compromising the possibility of a nanomechanicalcharacterization of polymers. Pile-up or viscoelasticity is usually blamed for this failure, and a deep analysis oftheir influences is attempted in this work. Piling-up can be minimized by indenting on a true nanometer scale,i.e., at penetration depth smaller than 200 nm. On the other side, it is common knowledge that fast indentationsminimize the effect of viscoelasticity. However, changing the indentation time in a broad range of contact time(fractions of second up to hundreds of seconds) did not allow the correct estimation of Young’s modulus for thepolymers used in this work. The final result is that the Oliver and Pharr procedure as well as any other procedureanalyzing the unloading curve with elastic contact mechanics models cannot be employed to measure Young’smodulus of polymers because its application is incorrect from a theoretical point of view, unless the analysis islimited to the very first nanometers of penetration depth when the contact is perfectly elastic. Viscoelastic contactmechanics models should instead be employed to characterize these materials.
    Lingua originaleEnglish
    pagine (da-a)1259-1267
    RivistaMacromolecules
    Volume40
    Stato di pubblicazionePublished - 2007

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    All Science Journal Classification (ASJC) codes

    • Organic Chemistry
    • Polymers and Plastics
    • Inorganic Chemistry
    • Materials Chemistry

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