Construction and utilisation of the adhesion test platform for the development of novel adaptive interfacial adhesives

Abstract

Smart adhesives are widely used in both nature and human industries. Even though there are many breakthroughs and innovations in this field, many challenges such as requiring a releasable adhesion interface for 3D printing, possessing selective and controllable attachment and detachment for transfer printing, and having a strong, reversible, and fast adhesion response for soft robotics still exist. To overcome such challenges, new adhesive materials and novel adhesive designs are needed. In this paper, an adhesion test platform that can measure both theoretical interfacial adhesion strength, σth, and critical energy release rate, Gc, simultaneously was constructed. To construct the platform, typical adhesion test methods were reviewed and a newly developed theory for Pull Test was incorporated into the design. The components were either purchased or self-fabricated, then assembled onto an Instron 5566 Universal Testing Machine, to complete the platform. The adhesion test platform was then utilised to characterise a new adhesive material, epoxy shape memory polymer (SMP). The measured adhesion parameters, σth and Gc, provided guidelines for the design of an SMP adhesive fibril, by finding the range of fibril radii where the adhesion exhibits DMT-like behaviour with strong adhesion in the glassy state and JKR-like behaviour with weak adhesion in the rubbery state. To validate the SMP adhesive fibril design, adhesion tests with different radii were conducted with the same adhesion test platform. It was found that SMP adhesive fibrils within the range provided by the guidelines can attain the theoretical adhesion strength of 1.893 MPa, and good switchability with a switching ratio of 22.9, even when the radius is scaled to macro-scale, up to 2.7 mm. Existing reports of fibrillar adhesive were compiled and compared with this design. By utilising the JKR-DMT transition, the designed SMP adhesive fibril outperforming former reports in many aspects, such as strong adhesion strength in macro-scale and weak adhesion strength for controllable detachment. These characterisations and measurements demonstrated the utility of the adhesion test platform.