For soft materials with Young's moduli below 100 kPa, quantifying mechanical and interfacial properties by small scale indentation is challenging because in addition to adhesion and elasticity, surface tension plays a critical role. Until now, microscale contact of very soft materials has only been studied by static experiments under zero external loading. Here we introduce a combination of the colloidal probe technique and confocal microscopy to characterize the force-indentation and force-contact radius relationships during microindentation of soft silicones. We confirm that the widespread Johnson-Kendall-Roberts theory must be extended to predict the mechanical contact for soft materials. Typically a liquid component is found within very soft materials. With a simple analytical model, we illustrate that accounting for this liquid surface tension can capture the contact behavior. Our results highlight the importance of considering liquid that is often associated with soft materials during small scale contact.
|Physical Review Materials
|Published - Jun 19 2017
Bibliographical noteFunding Information:
We thank Doris Vollmer for stimulating discussions and Sebastian Stappert for kindly providing the dye. We acknowledge support from an Alexander von Humboldt Fellowship (J.T.P.) and an ERC Advanced Grant No. SUPRO 340391 (H.J.B.).
© 2017 American Physical Society.
ASJC Scopus subject areas
- Materials Science (all)
- Physics and Astronomy (miscellaneous)