Directing synthetic and bio-nanoparticle self-assembly at liquid and polymer interfaces
Nanoparticles have unique properties, compared with their bulk materials, and potential applications in nanotechnology. To realize this potential, controlled assemblies of nanoparticles into regular patterns on surfaces, at interfaces and in three dimensions are crucial. The assembly of nanoparticles at interfaces is a simple and effective strategy to realize hierarchical assemblies.
In this thesis, the packing of nanorods at the interface between oil and water was investigated. CdSe nanorods were found to assemble at the oil-water interface and the structure was probed in-situ by small angle neutron scattering. When nanorod-covered droplets were dried on a substrate, the decrease in interfacial area produced an in-plane compression, and a range of two-dimensional packings of the nanorods across the droplet surface was observed, from a low-density random packing to a more-dense smectic ordering to a crystalline phase. Different orientation of nanorods at the liquid-liquid interface can be manipulated by controlling concentrations of nanorods in the bulk. For like-charged nanorods, such as TMV, repulsive forces predominate at the oil-water interfaces. The repulsion is strongly affected by the ionic strength of the bulk solution, but not the pH value in the range of pH = 6-8. Subsequent removal of the buffer solution can cause a cleavage of TMV nanorods aligned perpendicular to the oil/water interface.
At polymer interfaces, mixtures of polystyrene-block-poly (2-vinylpyridine) with tri-n-octylphosphine oxide-(TOPO)-covered CdSe nanoparticles were chosen to test the theoretical prediction of synergistic effects between two self-organizing systems. The evolution of the depth-dependent ordering process was revealed by in-situ grazing-incidence small-angle x-ray scattering (GISAXS) during thermal annealing, indicating that the orientation of the microdomains began at the free surface and propagated in the film towards the substrate. Most significantly, this synergistic interaction also applies to different block copolymer morphologies such as lamellar. Further studies on gold nanoparticles show that by varying the ligand functionality of the nanoparticles, as well as the processing conditions, the distribution of gold nanoparticles in the microdomains of the diblock copolymer can be controlled.
Condensed matter physics;
0611: Condensed matter physics
0794: Materials science