Confinement effects on the miscibility of block copolymer blends

Abstract.

Thin films of long and short symmetric AB diblock copolymers are examined using self-consistent field theory (SCFT). We focus on hard confining walls with a preference for the A component, such that the lamellar domains orient parallel to the film with an even number $\nu$ of monolayers. For neat melts, confinement causes the lamellar period, D , to deviate from its bulk value, D_b, in order to be commensurate with the film thickness, i.e., $L=\nu D/2$. For blends, however, the melt also has the option of macrophase separating into $\nu^{(\ell)}$ large and $\nu^{(s)}$ small monolayers so as to provide a better fit, where $L = \nu^{(\ell)} D^{(\ell)}/2 + \nu^{(s)}D^{(s)}/2$. In addition to performing full SCFT calculations of the entire film, we develop a semi-analytical calculation for the coexistence of thick and thin monolayers that helps explain the complicated interplay between miscibility and commensurability.

Graphical abstract