Reshapable bio-based thiol-ene vitrimers for nanoimprint lithography: Advanced covalent adaptability for tunable surface properties

Abstract

Taking inspiration from natural surfaces known for their ability to adaptively remodel their shape, we fabricated stimuli-responsive microstructures by using UV-induced nanoimprint lithography. For this, a fully bio-based dynamic thiol-ene photopolymer was synthetized by the radical mediated addition of a trifunctional eugenol-based thiol (SH3E) crosslinker across an allylated linseed oil (ALELO). To catalyze the bond exchange reactions between the hydroxyl and ester groups within the network, a bio-based eugenol phosphate ester was introduced as a transesterification catalyst. Pure eugenol was further added as a reactive diluent to increase the number of hydroxyl groups and thus, accelerate the thermo-activated bond exchange reactions. Once cured by UV exposure, the dynamic photopolymer is thermally stable up to 250 °C and is able to relax 63% of the original stress within 62 min at 160 °C. Subsequently, films with micropillars, having an aspect ratio of 1:2.5 were prepared by using nanoimprint lithography. The macroscopic reflow capability of the dynamic network enabled a reorientation of the imprinted structures during a thermal reshaping step. The imprints were characterized by 2D/3D optical microscopy, μCT imaging and static water contact angle measurements. Based on the orientation of the micropillars, the water contact angle was varied between 118° and 95°, giving rise to a possible application in microfluidic devices.