Lamellar Orientation and Transition Behavior of PS- b-P2VP Copolymers Supported on Physically Adsorbed Layers

A simple approach to utilizing physically adsorbed layers consisting of nonfunctional random and block copolymer chains is suggested for surface neutrality toward lamella-forming polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) films. A chemically identical, low-molecular-weight (LMW) random copolymer of P(S-r-2VP) and block copolymer (BCP) of PS-b-P2VP are used to form the adsorbed layers on an impenetrable solid substrate. We investigate lamellar orientation and transition behavior of the overlying PS-b-P2VP films with respect to the thickness (had) of the adsorbed copolymer layers. As the had of P(S-r-2VP) increases to 4.0 nm, an increasing population of perpendicular lamellae in high-molecular-weight (HMW) PS-b-P2VP films is attributed to the corresponding increase in the surface neutrality toward the BCP films. Meanwhile, an extremely thin adsorbed layer at had = 1.7 nm, obtained from LMW PS-b-P2VP, is superior in terms of surface neutrality to produce perpendicular lamellae in HMW PS-b-P2VP films. Such a thickness corresponds presumably to the minimum thickness for surface coverage on the solid substrate. The trends for the formation of perpendicular lamellae in HMW PS-b-P2VP films are well consistent with those for lowering the order-to-disorder transition temperature (TODT) in LMW PS-b-P2VP films with respect to had. Furthermore, the film thickness dependence on TODT of BCP films confined in the best neutral layers reveals that the physically adsorbed layers prepared from the BCP itself provide more balanced interfacial interactions toward the overlying BCP films than the adsorbed random copolymer layers.