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 tun able P(S-r-MMA) brush surfaces is addressed. Homopolymer dewetting experime nts show an increase in interfacial energy between PI and P(S-r-MMA) with i ncreasing styrene fraction, while the interfacial energy dependence of PnBM A with brush composition was indeterminate. Reflection optical micrographs of block copolymer films cast on PS and PMMA brush surfaces show island/hol e structures that are indicative of a parallel orientation of the block cop olymer domains with respect to the film boundaries. The micrographs are ide ntical in structure and are comprised of the same interference colors, indi cating antisymmetric wetting conditions for films cast upon both PS and PMM A brush surfaces. Thus, for P(S-b-I) and PCS b-nBMA) films cast upon PMMA b rush surfaces, unfavorable wetting of the PS component occurs at the PMMA b rush surface in order to avert PI/PMMA and PnBMA/PMMA interactions which ar e 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 ge neral wetting behavior of block copolymer films on random copolymer surface s is discussed with specific attention being made to wetting condition inve rsions and neutral surfaces.