Hygromorphic nanocomposites elaborated by filtration and ultraviolet curing of cellulose nanocrystal suspensions

Recent developments in the processing of cellulose nanocrystals (CNCs) and polyethylene glycol diacrylate (PEGDA) suspensions into nanocomposites opened new avenues for producing biosourced materials with attractive functional properties. A recently developed processing method using frontal filtration, followed by UV crosslinking, enabled the fabrication of nanocomposite films with tunable anisotropic textures ranging from nanometric to micrometric scale. This method has been further developed in this work and used to highlight, in manufactured nanocomposite films, an original, highly cohesive bilayer-like structure composed of oriented CNCs with very different concentrations between two nearby regions, inducing original hygromorphic properties. Combined SAXS, WAXD, and SEM characterizations on these nanocomposites revealed a highly organized structure of CNCs oriented parallel to the membrane surface with the presence of an interparticle distance gradient evidenced by SAXS. An improvement of this method consisting in relaxation step (relaxation time of 24 and 66 h) after filtration and before UV crosslinking, has allowed to achieve a more continuous concentration gradient in the prepared nanocomposite films, with cholesteric organizations revealed by WAXD and SEM. This more continuous structuring reduced the hygromorphism but increased the tensile mechanical properties. These results pave the way for developing biobased, humidity-responsive actuators for future emerging technological applications.