High-Precision Particle Arrangement in Gold‒Polymer-Nanocomposites using RAFT Polymerization
von Christian Roßner
Datum der mündl. Prüfung:2016-09-27
Betreuer:Prof. Dr. Philipp Vana
Gutachter:Prof. Dr. Philipp Vana
Gutachter:Prof. Dr. Alec Wodtke
EnglischThis thesis provides a comprehensive analysis of the scientific background on nanocomposites generated via reversible-deactivation radical polymerization (RDRP) techniques. Starting from this basis, nanocomposites with the special combination of a polymeric part from reversible addition-fragmentation chain transfer (RAFT) polymerization and gold nanoparticles were investigated in greater detail. It was shown by means of elemental mapping via scanning transmission electron microscopy and spectrum imaging (STEM-SI) in hybrid gold/RAFT polymer core-shell particles that the RAFT polymers’ sulfur-containing end group is always co-localized with the lateral position of gold cores. This provides, for the first time, microscopic evidence for the claim that the RAFT moiety can be used as an anchoring group for the grafting of polymers to gold nanoparticles. The interaction strength of the trithiocarbonate-type RAFT group used in this work was also investigated employing a specially developed model system and following a literature-known UV/vis-based method for analyzing the Langmuir isotherm of adsorption. For the trithiocarbonate model system studied here, a similar free enthalpy of adsorption (-36 kJ/mol) as compared with phenyl dithioesters studied earlier had been obtained. The characteristic features of RAFT polymerization had been exploited for the fabrication of defined particle arrangements. The discovery was made that RAFT polymers with specific macromolecular design can be used to assemble gold nanoparticles into unique nanohybrid architectures. It was demonstrated the possibility to precisely arrange gold nanoparticles in a controllable fashion by rationally tailoring the polymers used. Specifically, two different systems were realized to illustrate this point: (i) Gold nanoparticles from the two-phase Brust-Schiffrin synthesis were found by means of transmission electron microscopy (TEM) and dynamic light scattering (DLS) to assemble into globular particle network structures, when they are treated ex situ after their synthesis and work-up with linear RAFT oligomers of styrene featuring trithiocarbonate groups at both their termini (telechelic oligomers) or evenly distributed along the backbone (multifunctional oligomers). Here, the density of the primary gold nanoparticles within the network structures can be controlled by adjusting the degree of polymerization of the oligomeric particle linker, as evidenced by TEM. (ii) Higher-order particle assemblies featuring a hierarchical arrangement of two types of gold nanoparticles can be obtained from gold-core-RAFT-star-polymer-shell scaffold architectures. Such nanohybrid particles are shown to provide free star polymer termini (featuring trithiocarbonate groups) in the polymeric shell, which are accessible for further functionalization reactions. Addition of a second type of gold nanoparticles to such scaffold architecture leads to the attachment of these particles on the exterior of the polymer shell, resulting in planet-satellite nanostructures. These unique nanoarchitectures had been thoroughly analyzed by a combination of several analytical techniques, including electron microscopy in the dried state and small-angle X-ray scattering for characterization in the colloidally dispersed state. When the planet-satellite structures are cast on surfaces for TEM characterization, it is found that the planet-satellite distance can be tightly controlled by adjusting the degree of polymerization of the star polymer linker. These nanostructures can also be equipped with functional polymer, illustrating the possibility of combining several distinct building units into one highly functionalized and well-defined nanostructure.
Keywords: Nanoscale Materials; RAFT Polymerization