The central aim of this work is the detailed investigation of the self-organization of colloidal cadmium selenide (CdSe) nanoparticles at liquid-liquid and liquid-air interfaces. To prevent the coagulation of the nanoparticles in solution, the CdSe cores were covered with stabilizing tri-n-octylphosphine oxide (TOPO) ligands. The adsorption behaviors of spherical CdSe nanoparticles with diameters of 2.3 nm, 4.6 nm and 6.0 nm as well as rod-like particles with dimensions of (7 x 30) nm, (4 x 34) nm und (4 x 25) nm were considered. The kinetics of the self-assembly and the formation of the nanoparticle monolayer were experimentally followed and described on the basis of adsorption theory. The experimental part of this work includes the synthesis and characterization of the CdSe-TOPO-nanoparticles with different size and shape and the investigation of the adsorption process and kinetics at the liquid-liquid and liquid-air interfaces of nanoparticles of variable size, shape, ligand coverage, etc. Here the dependence of the adsorption kinetics on the size and shape of the nanoparticles, their concentration in bulk, and temperature reveals the key parameters. The detailed con-sideration of all factors promotes the development of a theoretical model based on the dif-fusion theory, which was suggested to describe the adsorption and co-adsorption kinetics at the liquid-liquid interface. According to this theory the effective diffusion coefficients for the early and late stages of nanoparticle adsorption were evaluated. A comparison of the esti-mated coefficients with the coefficients for free diffusion reveals an energy barrier for the particle adsorption at the late stages. In addition, the analysis of the structure and the mechanical properties of the nanoparticle aggregates formed at the liquid interfaces were carried out. The properties of films from self-assembled nanoparticles are strongly dependent on the size and shape of the particles, the temperature and co-adsorption with other particles and were discussed in detail. The interaction between the adsorbed nanoparticles leads to the build up of stable and elas-tic films (membranes) at the liquid-liquid interfaces. In addition, the formation of pores, randomly distributed in the membrane, was shown.
|School:||Universitaet Bayreuth (Germany)|
|Source:||DAI-C 81/1(E), Dissertation Abstracts International|
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