Micro-patterns on nanocellulose films and paper by photo-induced thiol-yne click coupling: a facile method toward wetting with spatial resolution

We report a facile approach to tailor the wettability of ligno-cellulosic substrates via photo-induced thiol-yne click coupling. First, cellulosic surfaces were functionalized with 4-pentynoic acid to introduce terminal alkyne moieties for the subsequent photo-induced coupling in heterogeneous phase. Next, the (primed) surfaces were reacted with various thiol-containing molecules to systematically tailor the surface energy. Finally, the method was applied to nanocellulose films and paper to develop micro-patterned surfaces via UV lithography, endowing the substrates with thin hydrophilic channels (similar to 250 mu m thickness) and hydrophobic boundaries between neighboring water droplets, as small as 100 mu m in width. Overall, we propose thiol-click as a facile method toward spatially-resolved wetting that enables paper-based electronics in smart labels and point-of-care bioplatforms.