Development and evaluation of a one-pot self-assembly route to switchable adhesives

The lack of reversibility in traditional adhesives has led to the development of a range of switchable adhesives. However, most switchable adhesives cannot be applied to a substrate, and must be created on the surface using stringent laboratory conditions. In this thesis, a new type of pH switchable adhesive which could be applied directly to a surface was developed and tested for adhesive strength. This material was compared to the ‘grafted-from’ pH switchable adhesives in the literature, and found to have a similar adhesive strength.

A series of synthetic transformations were used to mono-functionalise a calix[4]resorcinarene, which can modify surfaces, with either poly(2-(dimethylamino)ethyl methacrylate) or poly(methacrylic acid) using atom transfer radical polymerisation. This new material was then deposited onto hydrophobic silicon wafers using Langmuir-Schaefer deposition to give densely grafted monolayers of adhesive. Adhesion studies using hydrogels of oppositely charged polyelectrolytes showed that the measured adhesion was due to adhesive failure at the gel-monolayer interface, rather than the monolayer-wafer interface. This deposited material was shown to have a similar adhesive strength to material grafted from the surface, demonstrating that the calixarenes are sufficiently anchoring the polyelectrolytes to the substrate. When the calixarene brush layer was replaced with a polyelectrolyte multilayer deposited by layer-by-layer deposition for comparison, it could be concluded that the strength of the calix[4]resorcinarene binding compensates for any reduction in surface coverage in this system. Variation of the load applied showed that there is a dependency on the observed adhesion due to the onset of plastic deformation of the hydrogel.

Overall, these experiments provide a first step towards creating a reversible adhesive that would be practicable in commercial applications. Although further work needs to be done to improve the quality of this adhesion, this thesis demonstrates that a one-pot route to reversible and repeatable adhesion is viable.