Synthese ultradünner Polymerfilme durch Adsorption reaktiver Monomere aus der Gasphase
Creators: name: Pieper, Fabian
Publisher: name: Technische Universität Dortmund
Year: 2019
Subjects: subject: Ultradünne Filme
subject: Rheologie
subject: Polymerisation
subject: 540
subject: Rheologie
subject: Polymerisation

description: The aim of the present work was the preparation of ultrathin silane films from the gas phase. For this purpose, a system analogous to the chemical thin-film process was developed in which silane monomers were evaporated and subsequently adsorbed on a water surface. Subsequent autopolymerization at the boundary phase allowed the creation of the ultrathin, permanently cross-linked films. Octadecyltrichlorosilane was used as the standard monomer. The resulting networks, as well as the course of adsorption and network formation, were subsequently investigated by rheological and microscopic methods. The aim of investigations and optimization was the synthesis of an ideal, monomolecular polymer layer. It could be shown that the network formation on the water surface was diffusion-controlled at the beginning of the synthesis. As the degree of coverage increased, the occupation probability of the vacancies decreased, whereby the speed of film formation became increasingly dependent on the adsorption of new particles. The experiment also showed that after the formation of a nearly monomolecular base layer, the synthesis proceeded beyond the base layer, as water molecules from the subphase were able to diffuse through the hexagonal structure of the polymer network. The polymolecular layer structure was circumvented by the constant monitoring of the reaction progress by rheological time tests and timely cancellation of the silane feed. The material properties of the films thus produced were investigated as a function of ligands, the chain length of the organic rest and their layer thickness. In this way, by progressively optimizing monomer selection and reaction conditions, an ultrathin silane layer with a thickness of 2.93 nm could be obtained. It has been shown that by adjusting various apparatus parameters silane films with adjustable layer thickness and material properties can be produced without much effort. In addition to the actual synthesis of the films, a functionalization of the polymer networks was achieved by the addition of surface-active molecules and magnetic nanoparticles. The actual goal of an ideal monomolecular layer could not be achieved during this work due to the liquid subphase. In addition to the generation of two-dimensional layers, capsules with a liquid or gaseous core could also be synthesized by adsorption of reactive monomers from the gas phase. Methods were developed in which a variety of spheres could be produced quickly. Overall, the capsule production methods look promising and versatile, but still need some optimization. Generally, the synthesis of ultrathin films by adsorption of reactive monomers from the gas phase shows good and reproducible results. Of great interest is not only the layer thickness but also the almost freely selectable material properties of the films produced. Full understanding of the surface structure of the films, space requirements of the monomers and alignment of the chains could allow further interventions in the network structure and would be another step in the path of desingable films. Specific functionalizations could also open up new areas of application. Also, the direct synthesis of an ultrathin film on a solid surface would be conceivable and probably the last step to achieve the desired monomolecular layer. An alternative to this step would also be to modify the organic rests with large hydrophobic groups blocking the water from the subphase. The presented capsule synthesis also shows promising possibilities. For example, microballoons with an oxygen core would have potential applications in diagnostics. Here, too, the almost arbitrary composition of the core of the spheres is what promises a high range of applications for the still immature methodology. Important for these and other applications would be the knowledge of the noted limitation in the smallest possible size of the previously obtained capsules. In general, with all the capsule systems presented here, another scale-down would probably be the next sensible step.