Novel Nanostructure Engineering via Self-Assembly of Amphiphilic Hollow Particles

The thesis aims to the preparation of novel nanostructured materials starting from an inexpensive amphiphilic hollow particles. These particles are composed of polyethyleneimine-g-poly(methyl methacrylate) (PEI-g-PMMA) copolymer which is derived from its corresponding PMMA/PEI core-shell particle. A wide range of interesting nanostructured materials have been constructed by simply manipulating assembling conditions such as co-solvent composition, temperature and solution pH.;Surface structure and morphology of the hollow particles as well as the resulting assemblies in both DCM and water were invertible as characterized by X-ray photoelectron spectroscopy and transmission electron microscopy. The hollow particles can deform into ellipsoidal shape with fluid shear at 350 rpm in an appropriate DCM/water (3:7 v/v) mixture. The elongated hollow particles are able to assemble into linear aggregates via tip-to-tip connection, followed by generation of nanotubes with diameters less than 150 nm and the lengths can be extended to micron-scale.;Varying solution temperatures from 15°C to 45°C lead to the formation of hollow particles size ranging from 28 to 225 nm in diameter. The resultant hollow particles could be further developed into snowflake-shape under a controlled heating-cooling process. Increasing solution temperature resulting in the transformation of nanotube to nanofiber with diameter ranging from 17 to 137 nm.;Various novel hierarchical microstructures can also be fabricated using preformed nanotubes as building block through pH tuning. The formation of 3D hierarchical structures in aqueous solution over a pH range are characterized by field-emission scanning electron microscopy, transmission electron microscopy and atomic force microscopy. The hierarchical structures display distinct assembly profiles across three pH regimes. At low pH (pH =3.0), nanotube building blocks appear in random orientation and distribution. At pH between 6 and 8, the nanotube building blocks transform into straw sheaf-like bundle and fractal-like patterns. At pH 9 which is close to isoelectric point of the nanotubular charge density as determined with zeta-potential measurement, nanotubes align into parallel bundles with highly packed columnar structures. When solution pH is above 10, the bundles (in straw sheaf-like morphology) with loosely agglomerated fantail-shaped morphology are further assembled into plate-like morphology with interwoven networks.