Controlled adsorption of end-functionalized polystyrene to silicon-supported tris(trimethylsiloxy)silyl monolayers

Chemically grafted tris(trimethylsiloxy)silyl (sub)monolayers [tris(TMS)] were prepared on the native oxide of silicon by vapor-phase reaction of the corresponding mono chlorosilane at elevated temperatures. By exploiting the inherently sluggish kinetics of the silanization reaction, the grafting density of the tris(TMS) (sub)monolayer can be tuned. Water contact angle, ellipsometry, and X-ray photoelectron spectroscopy were used to determine the surface coverage. Unreacted silanol groups on the substrate surface were used as adsorption sites for carboxylic acid end-functionalized polystyrenes (PS-COOH). The thickness of the adsorbed layer could be controlled by the tris(TMS) surface coverage, adsorbing solvent, and polymer molecular weight. Amino-tris(TMS) mixed monolayers were prepared by the reaction of (4-aminobutyl)dimethylmethoxysilane (ABDMS) with tris(TMS) submonolayers. Polymer adsorption to tris(TMS)/ABDMS mixed monolayers did not occur as readily as it did to the tris(TMS)/silanol surfaces. Aggregates of adsorbed PS were observed on the tris(TMS)-modified surfaces, with an average separation distance that increased with increasing tris(TMS) coverage. The effectiveness of these adsorbed layers in suppressing dewetting of a thin PS film was examined.