Organization Of One-Dimensional Hierarchical Nanostructures

With the growing understanding of nature and the increasing demand for functional materials,hierarchiacal and composite materials have drawn tremendous interest from both scientists and engineers.Hierarchies are present everywhere in our environment.Inspired by nature,strong,tough and flexible synthetic hierarchical materials are constantly being synthesized.These nanocomposite materials hold promising potentials as energy harvesting and storage,biomedical devices,and biological and chemical sensors.One-dimensional materials with varying level of structural hierarchy are important nanomaterial due to its higher aspect ratio and faster charge/mass transport.The insightful understanding of the organization method,structural evolution,formation mechanism,and the relationship between structure and function will be instrumental for the rational design and organization of functional nanocomposite for advanced applications.There are three parts in this thesis.The details are as follows:?1?We demonstrate that strong,tough and flexible polymer nanocomposite fibers can be approached by electrospinning of supramolecular ensemble of dissimilar and complementary components including flexible multiwalled carbon nanotube?CNT?,and stiff cellulose nanocrystals?CNC?in an aqueous poly?vinyl alcohol??PVA?system.CNT and CNC are bridged by a water-soluble aggregation-induced-emission?AIE?molecule that forms?-?stacking with CNT via its conjugated chains,and electrostatic attractions with CNC through its positive charges leading to soluble CNT-AIE-CNC ensemble,which further assembles with PVA through hydrogen bonds.A high level of ordering of the nanoscale building blocks combined with hydrogen bonding leads to more efficient stress transfer path between the reinforcing unit and the polymer.The nanocomposite fiber mat is capable of selective detection of nitroaromatic explosives.?2?We suggest assembling the strong 2D MMT component with high aspect ratio1D PEI-modified CNC.The polymer nanocomposite fibers of MMT-PCNC/PVA was successfully achieved by electrospinning technology.Then the obtained nanofibrous mat is cross-linked by glutaraldehyde at room temperature.The degree of structural organization of MMT-PCNC in the nanocomposite fibers afforded by the electrospinning and GA based chemical crosslinking process enables multiple interactions between the fillers and at the filler-polymer interfaces?electrostatic interactions,hydrogen bonding and covalent bond?leading to effective load transfer between nanosheets and the polymer.?3?We present our interpretation of the structural transformation from solid electrospun fibers to wire-in-tubes?single-and double-layer tubes?in a TiO₂-V_xO_y system.We believe that the structural evolution is the result of delamination of crystalline crust from the underneath amorphous layer due to the different degrees of volume contraction,where the lock-up of the crystalline crust and the fluidity of the remaining organics plays a vital role.By tuning the calcination parameters including atmosphere,temperature and heating rate,the structural features of the hollow product fibers can be modulated.