Recovery behaviour of shape memory polymer with laser-inscribed hierarchical micro/nanoscale features

Abstract

This report studies the recovery behaviour of a shape memory polymer (SMP) with femtosecond laser-machined hierarchical micro- and nano-scale surface structures over the course of multiple deformation and recovery cycles. In an effort to identify the respective contributions of the nano and microscale texture, we investigate samples with a typical laser-induced porous network of nanostructures in comparison to microstructures such as pillars and holes of square and triangular shape covered in alike laser-induced nanostructures. Square microstructures recovered fully even after multiple cycles. In contrast, triangular shaped microstructures, which exhibited good recovery after one cycle, lost their structural integrity after multiple deformations. The difference in recovery between the different geometries is explained by the respective elongation of the geometrical features under deformation. The porous nanostructure showed poor recovery over the course of repeated deformations, which we attribute to surface energy minimization during the squeezed deformation stage. Contact angle measurements on all surfaces before and after deformations correlated well with the detailed topographical analysis. The observations of this SMP on these small scales shed some light on the limitations of these materials and of laser micromachining as an industrially versatile processing method.