Wetting behavior of block copolymers on self assembled films of alkylchlorosiloxanes: Effect of grafting density

The wetting behavior of thin films of symmetric poly(styrene-b-methyl methacrylate) was investigated on self-assembled (SA) films of octadecyltrichlorosilane on Si/SiOx with varying grafting density. The different types of SA organic films were produced by changing the deposition times (t) in solution. Two types of wetting behavior were observed on partial self-assembled monolayers (SAMs); 8 Angstrom < thickness < 23 Angstrom): (1) for short deposition times with t = 1-10 h, asymmetric wetting with the poly(methyl methacrylate) block wetting the substrate, and (2) for t = 12 h, neutral wetting with lamellae oriented perpendicular to the substrate. For t = 21-24 h, the polymer films dewet complete SAMs (thickness 26 Angstrom (the theoretical thickness for a complete SAM)). A metastable morphology of symmetric wetting with the polystyrene block wetting the substrate was observed on SA films with long deposition times, greater than 30 h (28 Angstrom < thickness < 36 Angstrom). The different wetting behavior of the block copolymer films on the different types of SA films was determined to depend on the chemistry and structure of the surface. These results have important implications regarding the use of SAMs of alkylsiloxanes to control the wetting behavior of block copolymers for patterning applications.