Adhesion Enhancement through Micropatterning at Polydimethylsiloxane−Acrylic Adhesive Interfaces

Abstract

Adhesion at polydimethylsiloxane (PDMS)-acrylic adhesive interfaces is shown to be enhanced through micropatterning of the PDMS substrate. By varying the geometry of the patterns (groves and hexagonal arrays of pillars of micrometer sizes, obtained through soft lithography techniques) and comparing rigid and deformable substrates, the respective roles of the geometry and the size and flexibility of the pattern features on the level of adhesion have been analyzed. For cylindrical pillars, two regimes are clearly identified: for a relatively low aspect ratio (h/r < 3, with h and r, respectively, the height and the radius of the pillars), soft patterned substrates are more efficient than rigid ones at increasing adhesion, pointing out the role of the elastic energy associated with the deformation of the pattern that is lost when the adhesive detaches from the substrate. Using scaling laws, the predominant contribution to that elastic energy can be further identified: deformation of the substrate underlying the pillars for h/r < 1.6 or bending of the pillars for h/r > 1.6.; for a high aspect ratio (h/r > 3), only rigid patterned substrates enhance adhesion, then the only possible contribution to energy dissipation comes from the enhanced viscoelastic losses associated with the pattern that induce modifications of the strain field within the adhesive layer. Soft, high aspect ratio patterns lose their efficiency even if still bent under the effect of the peel forces. This is because when bent, some of the pillars touch each other and remain stuck together, lying flat on the surface after the passage of the peel front. The bending elastic energy of the pillars (which is still lost) is then balanced by the corresponding gain in surface energy of the substrate in the peeled region. These systematic experiments demonstrate that the ability of the patterned surface to be deformed plays a crucial role in enhancing adhesion and allow us to propose a way to fine tune the level of adhesion at PDMS-acrylic adhesive interfaces, independently of the chemistry of the adhesive.

Adhesion mechanisms at soft polymer interfaces

“…Systematic studies do show that producing the equivalent of micrometric connectors by micropatterning the substrate (made of PDMS elastomer) can provide an efficient way of finally controlling adhesion (Ghatak et al 2004;Crosby et al 2005;Lamblet et al 2007). This is another promising route, which could provide adhesion modulation totally driven by the mechanical properties of the substrate and the geometry of the patterns, and only weakly depending on the exact chemical nature of the adhesive.…”

Gecko‐Inspired Surfaces: A Path to Strong and Reversible Dry Adhesives

“…[2,11,12,23,24] The benefit of fibrillar surfaces for adhesion has also been justified by other theoretical approaches. [25] Fibrillar surfaces show smaller effective elastic modulus than planar surfaces. As a result, they deform easily and form contact effectively, especially when adhering to rough substrates.…”

“…[25,38,[46][47][48][49][50][51] The softness and low surface energy of PDMS allow easy demolding of the structures from the masters by peeling-off. Masters were typically fabricated by photolithography using an SU-8 photoresist [25,[46][47][48]52,53] but also by indenting a wax surface with an atomic force microscope (AFM) tip, [49] or by laser ablation of a metallic surface. [50] Arrays of fibers with radii between 1 and 25 mm and lengths between 5 and 80 mm were reported over 25 cm 2 areas.…”

Design of gecko-inspired fibrillar surfaces with strong attachment and easy-removal properties: a numerical analysis of peel-zone

“…Furthermore, antiself-adhesion conditions should also be considered, which is given in §3.2. On the basis of experimental results, Lamblet et al [39] proposed that a correlation existed between the aspect of fibril and the peel strength of the geckoinspired surface. During the peeling process, the elastic bending energy (E b ¼ 2P 2 h 3 /3pER 4 ), the stretching elastic energy (E f ¼ P 2 h/2pER 3 ) and the deformation energy of the substrate (E s ¼ 8pP 2 /27ER) are fully dissipated.…”