Nanoscale physics of polymeric liquid on silicon dioxide nanotemplates from block copolymer thin films
A bottom-up approach to generate inorganic-organic hybrid nanotemplates is presented using a surface induced-orientation of poly (methacrylate POSS (isobutyl)-b-methacrylate). Methacrylate-functionalized polyhedral oligomeric silsesquioxane with isobutyl periphery functional groups (MAPOSS (isobutyl)) was polymerized via atom-transfer radical polymerization (ATRP) to give halide-end capped polyMAPOSS (isobutyl) macroinitiators. In the presence of methylmethacrylate (MMA), chain extension of the macroinitiator via the same synthetic mechanism resulted in poly (MAPOSS (isobutyl)- b-methylmethacrylate) block copolymers. Small angle X-ray scattering (SAXS) revealed that these block copolymers microphase separated into microdomains with characteristic periods of 18 to 40 nm. In thin film studies, preferential and non-preferential interactions between the blocks and substrates were achieved by surface modification of silicon wafers with hydroxy-terminated poly (styrene- r-MMA) and poly (styrene-r-bromostyrene) brushes. Like other block copolymers systems, islands and holes formed on the surface when one block preferentially interacted with the substrate and the island area fraction could be tuned by varying the thickness of the block film. Thin films of the block copolymers produced cylindrical microdomains with an orientation that depended on interfacial interactions.
Nanostructured SiO2 surfaces were then prepared from the inorganic-organic hybrid poly (POSS (isobutyl)-b-MMA) nanotemplates by thermal and oxygen plasma treatments. Silicon dioxide nanostructured surfaces were obtained with topographies resembling the starting hybrid structures. The oxide surfaces produced were also modified using monochlorosilanes. The wetting characteristics of thin PS films on the oxide surfaces were found to depend on the surface topography. For surfaces with nanoscopic posts, the dewetting of the PS was pinned; whereas, for surfaces with islands having a step height of several nanometers, dewetting similar to that on a smooth surface was found. If, however, the terraces were interconnected, then the dewetting was accelerated. These studies demonstrate the potential use of hybrid block copolymers as precursors for the fabrication of inorganic nanotemplates with well-defined topographies and interfacial properties.