AFM Peakforce QNM mode for measurement of nanosurface mechanical properties of Pt-cured silicones

Abstract

Sylgard 184 is used for diverse applications including nanoimprinting, micro-electronic and mechanical systems (MEMS), soft robots, ice-phobic coatings and tactile and epidermal sensors. For such applications, understanding effects of processing conditions on nanoscale mechanical properties is essential for performance. It is surprising, then, that little attention has been paid to effects of cure temperature on surface and mechanical properties. The present work adds depth to understanding the complex relationships among hydrosilylation and little recognized autoxidation of SiH to SiOH and secondary network formation by condensation. Peakforce Quantitative Nanomechanical Mapping (PF-QNM), an atomic force microscopy (AFM) mode was used to provide a nanoscale map of deformation, adhesion, dissipation, modulus and morphology as a function of varying cure temperature and base-to-crosslinker ratio. The interaction of the SiOH rich oxide layer of the silicon AFM tip with the outermost Sylgard 184 silicone surface provided modulus and adhesion measurements that revealed important effects of cure conditions and composition. Results were interpreted in terms of a model for the concentration of near surface SiOH from autoxidation and changes due to SiOH condensation at high temperature cure. Moduli were found to be comparable with dynamic mechanical analysis (DMA), supporting PF-QNM as a tool for mechanical property measurements. The dependence of nanosurface mechanical properties on composition and network formation conditions provides guidance for future work using Pt-cured silicones.