Polycarbodiimides at interfaces: Polymer adsorption at solution-silica interfaces and thermal decomposition of an adsorbed thin polymer film
Abstract (Summary)Trends in the adsorption of poly(N -methyl-N ' -((Ã?Â±)-Ã?Â±-phenylethyl)carbodiimide), poly-R/S , and poly(N -methyl-N ' -((-)-Ã?Â±-phenylethyl)carbodiimide), poly- S , to native silicon oxide were shown to be influenced by the polymer's conformation in solution (worm-like and rigid, respectively), solvent quality, molecular weight, and process conditions. High affinity adsorption isotherms were measured for poly-R/S adsorbed from toluene to silica and the adsorbed amount increased with molecular weight. The adsorbed amount of poly-R/S and poly-S from THF was influenced by both solvent quality and the conformation of the polymer in solution. For both polymers, adsorbed from THF, the XPS and contact angle data indicated that the adsorbed amount decreased with molecular weight and the adsorbed amount, for equal molecular weights, of poly-S was greater than poly- R/S . Using AFM, the adsorbed films of both polymers were shown to dewet during the evaporation of solvent. The extent of dewetting is shown as a function of solvent quality, temperature, and experimental processes. The size and dimensions of the surface structures after dewetting were shown to increase with molecular weight. Using organosilane chemistry, lyophobic silicon-supported monolayers of tris(trimethylsiloxy)chlorosilane (tris(TMS)), 10-(carbomethoxy)decyldimethylchlorosilane (CMDCS), diphenyldichlorosilane (DPDCS), and mixed binary monolayers of tris(TMS) with CMDCS were prepared; followed by adsorption of poly-R/S and poly-S to the monolayers. Relative to silica, both polymers have little affinity to adsorb to surfaces composed mostly of methyl (tris(TMS)) or methylene (CMDCS) groups. Furthermore, the adsorbed amount increased with molecular weight but decreased with chain rigidity. In addition, the adsorbed films dewetted upon solvent evaporation. Vapor phase modification of silica with DPDCS was shown by AFM to form patchy surface structures. Both polymers were shown to have a higher affinity for the DPDCS modified surfaces compared to adsorptions performed on tris(TMS) and CMDCS surfaces. Adsorption experiments with poly-R/S and poly-S to surfaces composed of hydrolyzed CMDCS (H-CMDCS) indicated an increase in the adsorbed amount with increasing amount of H-CMDCS. Adsorbed films of poly-R/S on native silicon oxide were prepared for studying the effect of thermal decomposition on the adsorbed polymer film. Using real-time FT-IR and TGA, the decomposition rates were measured, but experimental conditions are shown to influence the data. Topography analysis, by tapping mode AFM, of the decomposed adsorbed films indicated changes in the surface structure with thermal exposure. In addition, with thermal exposure the adsorbed film became weakly attached to the substrate. Nonetheless, thermal decomposition can be used to modify an adsorbed film of poly-R/S .
School Location:USA - Massachusetts
Source Type:Master's Thesis
Date of Publication:01/01/2000