High resolution self-assembled patterns on flexible nanocellulose film

The demand for bionanomaterial architectures to be used in next generation material solns. e.g. in optoelectronics, biosensors and nanoporous membranes is intense and topical. Besides the requirements deriving from the high-resoln. nanoarchitecture, materials should possess several beneficial features such as flexibility, transparency and strength. Here we present an elegant bottom-up approach where a carbohydrate-based diblock copolymer, polystyrene-bmaltoheptaose (PS-b-MH) is organized on a flexible self-standing film of cellulose nanofibrils (CNF) via effortless selfassembly. During solvent annealing the PS-b-MH undergoes spontaneous rearrangement into high-resoln. patterns. AFM imaging revealed that the domains formed by PS-b-MH are in the range of 10-15 nm. It is remarkable to find that they were able to self-assemble directly on CNF films with a surface roughness of 100-400 nm which is a significantly higher unit distance compared to the dimension of the domain unit of the block copolymer. The pattern resoln. of the horizontal assemblies is comparable to the patterns detected on smooth and inert surfaces. Interestingly, patterns seem to follow the macroscale topog. features of the nanocellulose film. The ideal conditions for block copolymer selfassembly require weak surface interactions between the block copolymer and the substrate, in order to increase the chain mobility and enable rearrangements of the block copolymer to take place during annealing. This is exactly how our carbohydrate-based diblock copolymer system behaves. The adsorption of PS-b-MH on CNF surfaces monitored by QCM-D revealed weak interactions between CNF and PS-b-MH, and the formed PS-b-MH layer was soft and mobile. The use of plant-derived carbohydrates as building blocks to create complex structures is a recognizable nanotechnol. that will enable the bioeconomy transition.