Shape-specific Patterning of Polymer-functionalized Nanoparticles

It has been shown that polymers end-tethered to a two-dimensional substrate will collapse into so-called “pinned micelles” upon exposure to poor solvency conditions. These structures consist of polymer-dense cores surrounded by stretched polymer “legs” as a result of constrained de-wetting. This thesis transfers this known phenomenon to a three-dimensional system: nanoparticles end-grafted with polymer ligands, as a unique strategy to surface pattern nanoparticles with polymer patches. Using spherical gold nanoparticles functionalized with thiol-terminated ligands (mainly polystyrene), the quality of the solvent was reduced and as a response, the uniformly thick polymer brush layer collapsed. In this process, polymer patches are formed to reduce unfavorable interactions at the polymer-solvent interface. The size, distribution, and number of pinned micelles were controlled by three factors: (i) polymer molecular weight, (ii) polymer grafting density, and (iii) nanoparticle diameter. Each factor played a role in the resulting surface free-energy of the system, based on the gain in energy from the polymer-polymer interaction within the micelle core and the energetic cost of stretching the polymer tethers required to form the pinned micelles. The nanoparticle shape played a role in controlling or directing the patches onto specific regions of the nanoparticle surface. For nanoparticles which have various regions of local curvature (e.g. nanocubes, triangular prisms, nanodumbbells, and nanorods), the patches were found to be more stable in regions of higher curvature such as edges, vertices, and tips of various nanoparticle geometries (i.e. predicable localization of polymer patches). Interestingly for nanorods, which exhibit different curvatures along their longitudinal and transverse axes, there is an asymmetric polymer stretching, yielding a unique helicoidal wrapping of the polymer patches. Finally, the stability of the polymer patches was studied for various temperature conditions. The patches are stable over several days at 23 and 40 degrees Celsius, however at 80 degrees Celsius, the patches merge and as a result, the number of patches per nanoparticle decreases. Eventually, the thiol-terminated polymer detaches from the nanoparticle surface. These effects emphasize the lability of the thiol-terminated polymer ligands, given that sufficient energy is applied to the system.Ph.D.2020-11-13 00:00:0