Polymer-Induced Modification of Cellulose Nanocrystal Assemblies in Aqueous Suspensions

The effect of adsorbing, nonionic polymers on the phase behavior of cellulose nanocrystals (CNCs) is of interest for design and preparation of functional hybrids. CNC assembly into a chiral nematic phase (N*) was investigated in the presence of highly hydrated poly(vinyl alcohol) (HPVA), low hydrated PVA (LPVA), and poly(vinylpyrrolidone) (PVP). Mapping of the nano-to-micro structure via small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), and polarized light microscopy (POM) reveals the presence of nematic islands already at very low CNC concentrations. While the polymer-decorated CNCs preserve the structure of the native N∗ phase, solvated PVA at concentrations above the semidilute regime disrupt the CNCs' self-organization into the liquid-crystalline phase, whereas PVP does not. It is suggested that the specific structure of the polymers rather than their physical properties or depletion interactions dominates the nanostructure and phase behavior of the polymer-CNC mixtures.