The Adhesion and Mechanical Behaviour of Different Elastomers

This work was focused on the physical removal of small particles from plastic surfaces, in collaboration with Teknek, a company that develops cleaning solutions and that provided some of the materials like reference surfaces and some elastomers (cleaning materials). Atomic force microscopy was used to find the adhesion force between colloidal probes made of different materials and different types of surfaces to verify which surface has the greatest or lowest adhesion. Colloidal probes were chosen as example of contaminant particles to be removed: the surface that shows the greatest adhesion toward a colloidal probe is the one that would retain the contaminant. Adhesion test was done on samples provided by Teknek: it was found that, for these samples, roughness is the main factor that modifies adhesion. Qualitative explanation of how roughness could influence adhesion is provided considering the different scales of roughness and surface features. Characterization of samples hydrophobicity/hydrophilicity cannot exclude a contribution of the capillary force in enhancing adhesion. Some laboratory made samples made of polydimethylsiloxane were synthesised to verify if bulk properties can influence adhesion. Adhesion test revealed that the Young's modulus and the crosslinking density do not change adhesion in the studied conditions. Viscoelasticity was seen only in two samples and it is known that it allows adhesion to be dependent on the crack speed and a new strategy is proposed for crack speed calculation from experimental data. It was found that calculated crack speeds follow the expected behaviour toward the energy release rate, however this method also allowed to have a look at the microscale detachment process letting the conclusion that also at this scale, polydimethylsiloxane behaviour is comparable to that seen at the macroscale, with mainly polymer elongation and 'regular' movement of the contact line before the minimum of the force-indentation curve, and fingering detachment processes after it.