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Adhesion with a Cassie-Wenzel-like Transition for Textured Elastic Contacts
When a smooth sphere of elastomer is pressed against a substrate micropatterned with a regular hexagonal array of pillars, a transition between a contact only established at the top of the pillars (Cassie-like state) and a mixed contact with a central zone of full contact (Wenzel-like state) surrounded by a top contact corona has been reported to appear when increasing the applied load. The full contact always nucleates with a finite radius, even very close to the threshold, giving to the transition a first order like character. This jump in the radius of full contact decreases when increasing the height or the surface density of pillars, indicating a competition between adhesion energy gained in forming inter-pillar contacts inside the full contact zone and elastic energy associated to the corresponding additional deformations of the pillars and the inter-pillar substrate and lens. We have developed a model in order to described the effect of the inter-pillar adhesion to produce a realistic treatment of the mechanics of these complex contacts.