Neutrality conditions for block copolymer systems on random copolymer brush surfaces

The wetting behavior of P(S-b-I) and P(S-b-nBMA) thin films placed upon tunable P(S-r-MMA) brush surfaces is addressed. Homopolymer dewetting experiments show an increase in interfacial energy between PI and P(S-r-MMA) with increasing styrene fraction, while the interfacial energy dependence of PnBMA with brush composition was indeterminate. Reflection optical micrographs of block copolymer films cast on PS and PMMA brush surfaces show island/hole structures that are indicative of a parallel orientation of the block copolymer domains with respect to the film boundaries. The micrographs are identical in structure and are comprised of the same interference colors, indicating antisymmetric wetting conditions for films cast upon both PS and PMMA brush surfaces. Thus, for P(S-b-I) and PCS b-nBMA) films cast upon PMMA brush surfaces, unfavorable wetting of the PS component occurs at the PMMA brush surface in order to avert PI/PMMA and PnBMA/PMMA interactions which are more unfavorable. Consequently, the dependence of the interfacial energy between PI or PnBMA with P(S-r-MMA) random copolymer brushes as a function of styrene content does not influence the behavior of these systems. The general wetting behavior of block copolymer films on random copolymer surfaces is discussed with specific attention being made to wetting condition inversions and neutral surfaces.