Surface Engineering of Nanomaterials for Biomimetic and Hybrid Applications

This thesis is devoted to surface engineering of nanomaterials. Surface engineering involves all types of surface modifications of materials, which provides new properties or improves the current properties. It opens great opportunities both in the field of nanocomposites through enhancement of compatibility of their components and in the field of functional nanomaterials by development of various topographies and obtaining of new physical and chemical properties of nanoobjects. The first focus of this thesis is exploration of possibilities and limitations of surface-initiated atom transfer radical polymerization (SI-ATRP) from cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) for the surface engineering. CNCs and CNFs are very promising nanomaterials due to their sustainability and outstanding mechanical properties. Surface engineering of CNCs and CNFs using polymer-grafting provides new opportunities for utilization of these materials. The second focus of the thesis is preparation and characterization of bulk nacre-mimetic clay-polymer nanocomposites. In recent decades, many attempts have been made to create nacre-mimetic materials due to exceptional mechanical properties of nacre. However, nacre-mimetic clay-polymer nanocomposites were limited to nanocomposite films, which do not allow studying of fracture mechanics. In this thesis we fill this gap by fabricating and studying bulk nacre-mimetic nanocomposites. The Publication I explores possibilities of interpolyelectrolyte complex (IPEC) self-assembly for the formation of CNCs 3D surface topography. Self-assembly of IPEC shell on the surface of polymer-grafted CNC allows formation of stable helical and tentacle-like topographies. The suggested technique is a potential tool for the preparation of various 3D topographies on the surfaces of different nanoobjects. The Publication II discusses formation of microporous silicon dioxide capsules by the template-directed synthesis of silica on the surface of polymer-grafted CNCs. Uniform silica coating is formed within the poly(2-dimethylaminoethyl methacrylate) shell grafted from the CNC surface. In addition to the template function, polymer brushes provide formation of micropores after calcination of the CNC/silica hybrids. The Publication III addresses issues related to conventional SI-ATRP polymerization from CNFs and reveals unexpected degradation caused by this process. SI-ATRP is a potentially powerful tool of CNFs surface modification and Publication III represents the first steps of optimization of this method. The Publication IV discusses preparation and mechanical properties of nacre-mimetic bulk nanocomposites. It is shown theat the fracture toughness of KIc of aligned clays separated by nanometric polyvinyl alcohol layers approaches that of red abalone.