Self-Assembly in Thin Films of Mixtures of Block Copolymers and Homopolymers Interacting by Hydrogen Bonds

Abstract

We report on the self-assembling behavior in thin films of mixtures of polystyrene-block-poly(ethylene oxide) copolymers (PS-b-PEO), having PEO cylindrical microdomains, with poly(acrylic acid) homopolymers (PAA). We study the effect of adding PAA of different molecular weights, specifically interacting with the PEO block by hydrogen bonding, on the thin film characteristics: morphology, microdomain orientation and spacing. It is found that the addition of PAA induces an orientation of the cylindrical microdomains perpendicularly to the film surface. The lattice spacing increases with the amount of PAA added until a transition toward lamellar morphology is observed. This transition occurs at lower PAA content for PAA of small molecular weight. The experiments also reveal that the PAA homopolymer is localized in the center of the PEO microdomains. The trends observed in the experiments were validated by self-consistent field theory calculations using a newly and specifically developed model.