Examination of gecko-inspired dry adhesives for heritage conservation as an example of iterative design and testing process for new adhesives

Rarely within the conservation of cultural heritage have conservation professionals been lucky enough to have materials custom-designed to meet their requirements. Most of the time the field must adapt solutions developed for other applications. The research presented here was initiated as part of a long-term aim to develop new adhesives for heritage conservation. Gecko-inspired dry adhesives (GDAs) are polymer tapes with micropatterns that are based on the adhesive properties of the pads of gecko lizard feet: they have strong normal and shear adhesion with low peel adhesion. They present potentially versatile and reversible adhesives for heritage conservation applications; which do not require solvents for activation or for removal, and do not migrate or off-gas. In nature, geckos can adhere with their feet to any surface they walk on. This is possible because of micro- and nanostructures on their feet that attach to surface via van der Waals forces. Practical studies aimed at comprehensively assessing their properties, and biomimetic solutions in heritage conservation are still sparse at present. This research has the objective of assessing GDAs properties by mechanical testing of adhesive joints, as well as physical and chemical characterisation of the materials used. The research has also included a museum case study and a two-year natural ageing test. The testing has shown that the GDAs can perform very well as an adhesive patch on the reverse of gelatine-based photographs, achieving shear forces between 0.80 N and 48.10 N on 8 cm(2) lap joints (depending on the type of the GDA) and peel forces between 0.20 N and 0.47 N over 2 cm of peel front. This is lower than forces exceeding 1 N recorded in widely available pressure-sensitive tapes. This shows that GDAs may have the potential of a sufficiently strong, yet easily removable adhesive that works well on materials widely present in museum collections.