Structures And Morphologies Of Molecular Assembly At The Interfaces

Currently, nanostructure and nanotechnology are the top research fields. Nanostructured materials composed of nanostructure building blocks are different from the conventional materials due to the size of particles, the ratio of surface and bulk phase atoms and the shape of particles, etc, and are of great current interest for application in electronic, photonics, magnetic and catalytic properties. So that, construction of nanostructured materials based on molecular or atomic scale must be become more attraction for scientists in chemistry, physics, materials, information fields, and so on.Molecular assembly technique at the interfaces is viewed as a main tool for fabrication of new functional nanostructures. In our thesis, structures and morphologies of surfactants (CTAB), polyelectrolytes(PSS, HPAM and AHPAM) and surfactant/polyelectrolyte complexes at the air-liquid interfaces and the solid-liquid interfaces are investigated. At first, for simply, surfactant molecular assemblies at solid-liquid interfaces are systematically studied using atomic force microscopy(AFM), transmission electronic microscopy(TEM), UV, et al. Furthermore, based on these studies we studied structures and morphologies of surfactant/polyelectrolyte complexes at the interfaces. Finally, gold nanoparticles are organized at the interfaces mediated via polyelectrolytes and surfactants. We expect that a combination of gold nanoparticles and surfactant and polyelectrolytes can bring about new results and properties.One of the most widely studied systems is cationic surfactant hexadecyltrimethylammonium bromide (CTAB). The adsorption process of CTAB to mica is a dynamical process. The morphology of CTAB aggregates on solid substrates will show different characteristics at different time. However, the systemically experimental investigations are still lacking so far. In this study, the dynamical adsorption behavior of CTAB on mica was investigated by AFM. We focused on the conformational changes ofthe adsorbed CTAB on mica with the adsorbed time, and the formation mechanism was illustrated. Results show that conformational transitions from globular micelles—^cylindrical micelles—>flat films are observed in the process of the adsorption of CTAB to mica at twice the bulk critical concentration. However, in 0.5 cmc CTAB solution, the adsorbed CTAB molecules to mica form the layered film structures, and apparent conformational transitions do not appear. Meanwhile, the phenomena of the adsorption of CTAB to mica and the dissociation of mica surfaces are periodically observed.We present first visualization of conformations of anionic polyelectrolytes (partially hydrolyzed polyacrylamide) (HPAM) deposited on the mica substrate by AFM. Meanwhile, conformational transition can be investigated in different environment. The conformational transition from network-like aggregate structure to compact globules was imaged. The method offers the possibility of to easily distinguish individual HPAM molecules. In addition, the high enough resolution of the AFM images confirm the existence of necklace-like globules, supporting recently developed theoretical predictions.Atomic force microscopy (FAM) and the surface pressure relaxation technique were employed to characterize the properties of oppositely charged polyelectrolytes/surfactant mixture films formed at the air/water interface. By the observation of AFM, it is shown that partially hydrated polyacrylamide (HPAM) /hexadecyltrimethylammonium (CTAB) complex films appear in the morphology of patch aggregates. Amphoteric HPAM / CTAB complexes are observed to form filbrelike structures. Salts in subphase have impaction on the morphology of interface complexes. Furthermore, the surface pressure relaxation has revealed that the conformational changes of interface complexes are directly related to the stability of films.In our previous research, we have found that the morphology of hexadecyltrimethylammonium bromide (CTAB) / Amphoteric HPAM (AHPAM) complexes transferred on mica substrates was a form of the dendritic fractal aggregates, the nanogold dendritic nanostructure have been organized vis this surfactant/polyelectrolyte complex templating system on mica surface, which is of great current interest forapplication in fabricating nanoscale electronic and optoelectronical devices.