CONTROLLED MODIFICATION OF SILOXANE OR HYDROCARBON INTERFACES USING ORGANOSILANES

Abstract

Surfaces/interfaces are considered as one of the key factors that determine performance, and ultimately the application, of materials. In many cases, surface/interface modifications are required for desired properties, such as adhesion and wettability. Organosilanes have been widely used to alter surface/interfacial properties for many materials including metals, glass, and polymers, etc. However, controllable processes for surface/interfacial modification are desired. This thesis aims to explore controllable paths for surface/interfacial modifications on siloxane or hydrocarbon-based materials using organosilanes. Further understanding about the methodologies for quantification of functional groups located at surfaces/interfaces is also within the scope of this thesis. In this thesis, a comprehensive study of PDMS surface modification using thioalkylsilane coupling agents is described. An equilibrium silanization allowed the introduction of thiols on silicone elastomer surfaces under control and without damaging the surface. Two different titration methods for testing thiols in solution were developed and improved for quantification of thiol groups located at air-solid interfaces. The thiol-functionalized silicone could be further modified with maleic anhydride and/or with a variety of polymers and surfactants in a single step or two steps. A long term, stable hydrophilic surface was obtained after these modifications. In this thesis, the modification of hydrocarbon-based materials is also described. A method based on the Piers-Rubinsztajn reaction was used to convert lignin into value-added chemicals, including monomeric/oligomeric aromatics and lignin composites. For the hard wood lignin, reduction of the ether bonds and silylation with hydrosilanes led to nearly complete fragmentation. The monomeric/oligomeric aromatics decomposed from hard wood lignin are easy to process as demonstrated by their excellent solubility in various solvents. Alternatively, softwood, which does not have an ideal structure for fragmentation, is effectively employed as “green filler” in silicones for lignin-based elastomer/foams. The partial (interfacial) reduction of hydrosilanes at lignin interfaces results in covalent linkage sbetween lignin and siloxane network, improving the interfacial miscibility. The softwood lignin, thus plays dual roles as a crosslinking and reinforcing agent. Formulations were readily developed to prepare silicone foams/elastomers by controlling processing parameters and methods. Lignin-based silicone elastomers could be obtained with additional solvent and casting in an open mold; lignin-based silicone foams could be molded in a volume-confined mold after extrusion.