Adhesion (stickyness) of a set of related siloxane rubbers is compared with a theoretical model

What is it about?

We directly measure adhesion between a smooth spherical glass probe and several related polydimethylsiloxane elastomers. We take data at several temperatures to show the time-temperature superposition principle works with adhesion data (as has been shown in the past) and run experiments at several different probe speeds. All materials showed a strong speed dependence, which is expected for polymeric materials. We find that a bottlebrush elastomer has much lower adhesion than does more conventional elastomers, and that an extracted network has a much higher adhesion than the conventional elastomers. We also show how some materials (Sylgard) show a modulus dependence to their adhesion (or in greater detail a cross-link density dependence), whereas other materials do not show a strong correlation (Zhermacks). Following suggestions of recent theoretical work, we measure the dynamic modulus of all materials over a broad range of frequency. We see many of the siloxane elastomers crystalize, whereas the Sylgard materials do not seem to crystalize strongly showing instead a smooth increase of modulus as temperature is reduced. We normalize by the low speed adhesion and find that the data collapses into two different functions of speed. Sylgard shows a stronger speed dependence, which is suggested to be related to its slow change in dynamic modulus. The adhesion of materials showing crystalization all followed a more slowly increasing function of speed. We go on to compare the measured values with several approximations of the Persson-Brenner adhesion model without finding much success. However, a rigorous application of the model does show good correlation with experiments at low speeds. We suggest that the discrepancy at high speed may only be due to failures of a linear-elastic model.

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Photo by Osman Rana on Unsplash

Photo by Osman Rana on Unsplash

Why is it important?

This work is important because it points to various mechanisms that may lead to reduced adhesion forces between solids like ice and modern elastomeric coatings.