Synthetic and Supracolloidal Concepts for Cellulose Nanocrystals

Modern technology requires sustainable solutions for future raw materials and applications. Nanocelluloses, namely cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNF) are of particular interest as renewable, widely available, and highly functionalizable nano-sized raw materials. In this thesis, the fundamental properties of CNCs and their use in synthetic and colloidal self-assembly concepts for novel functional materials were explored. The proper utilization of CNCs for example in films, which reflect color for a selected wavelength, requires understanding of the basic properties for CNCs, both in dry and in liquid state. In publication I the chiral structure of dried CNC films was characterized with scanning electron microscopy (SEM). The method allows direct observation of the left-handed twisting sense and the optical period down to hundreds of nanometres for the self- assembled CNCs. In publication II a controlled polymerization procedure for well-defined polymer brushes tethered from the surface of CNCs was developed. Hydrophobic or hydrophilic brushes could be obtained with high grafting density. This modification route enabled further advanced targeted use for CNCs by exploiting supramolecular ionic complexation of the surface-grafted polyelectrolyte chains toward functionalities and applications.Dendron architecture combined with sugar molecule functionality offers a practical route for self-assembly using multivalent binding with moieties like nanoparticles, block copolymers or surfaces. In publication III strong interactions between maltose-based sugar-functionalized dendronized polymers (DenPols) and CNCs were recognized. The third generation DenPol wrapped around individual CNCs, as directly visualized by cryo high-resolution transmission electron microscopy and electron tomography. The considerable size of the DenPol allowed direct visualization of the wrapping phenomena with cryo-electron microscopy. In publication IV it was demonstrated both experimentally and theoretically, how a chiral plasmonic optical signal could be obtained through interaction between gold nanoparticles and chiral CNCs as dispersed in aqueous phase. This can create new possibilities, for example in sensing chiral molecules with the aid of chiral gold nanoparticle-CNC superstructures. This was the first time that the chiral right-handed twist along individual CNCs was used for a chiral plasmonic response. The results obtained in this thesis contribute to the fundamental understanding of the properties, behavior and manipulation of CNCs as a charged and chiral rod-like nanoparticle towards practical application, like self-healing hydrogels, glue additives, enantiomer separation, and potentially even security paper with structural color.