Structure-property relationship of nanostructured functionally graded epoxy adhesives

Abstract Adhesives with a variation of properties along the bondline are appealing to the joining industry, yet few developments give easy, versatile implementations and at the same time a control over the toughness of the joints. We herein present an original methodology to control the variation of properties in functionally graded epoxy adhesives (FGAs). The FGAs are obtained by putting into contact two plots of compatible adhesives, where the two plots occupy each half of the aluminum substrates. Diffusion of thermoplastic, triblock copolymers in the epoxy-amine adhesive within the joint provokes a gradient of copolymers, inducing in turn a variation of properties along the overlap. We use a driven wedge test (DWT) to assess the variation of properties within the FGAs, by continuously inserting a wedge in the unbonded part of the sample. We discuss on the contribution of the ductility and resilience of the FGAs to the overall energy dissipated, which is found to be superior for FGAs, compared to homogenously filled adhesives. We infer this result to the heterogeneous spatial distribution of the copolymers in the FGAs, due to the diffusion.