Orientation of Microphase in Polystyrene-b-polyisoprene Thin Film under Solvent Vapor Annealing

Abstract

We investigated the microphase in thin films of polystyrene-b-polyisoprene showing cylinder morphology to elucidate the orientation mechanism of the cylinder phase during solvent vapor annealing (SVA). For the purpose, we examined the effects of swelling ratio of the film, annealing time, and selectivity of the solvent as well as molecular weight and composition of the block copolymers on the orientation of the nanostructure using grazing incidence small-angle X-ray scattering and transmission electron microscopy. In general, the orientation of the cylinders proceeds from disordered state in a spin-coated film to horizontally oriented cylinder phase via vertically oriented cylinder phase. The rate of the orientation change is strongly affected by the SVA condition as well as the nature of the block copolymers. The orientation change rate is slower for higher molecular weight block copolymers under a more selective solvent and at a lower swelling ratio seemingly due to the low mobility of polymer chains. Therefore, the vertically oriented cylinder morphology is more favorably observed at these SVA conditions while the general orientation behavior is the same regardless of the SVA condition and the nature of the block copolymers.

Control over microphase separation and dielectric properties via para-fluoro thiol click reaction

“…Therefore, a change in swelling capability can govern the orientation. 36 Here, the capability of swelling by acetone decreases with the addition of non-polar dodecane chains. Therefore, we assume that this reduction enables the vertically oriented acrylic acid cylinders.…”

Assembling Vertical Block Copolymer Nanopores via Solvent Vapor Annealing on Homopolymer-Functionalized Substrates

“…However, reported studies frequently use very thin BCP films, thereby yielding low-aspect ratio (<∼2) vertical domains. Indeed, as shown by Lee et al in an investigation of SVA using different solvents for thick asymmetric polystyrene- block -polyisoprene films, while SVA reinforces incipient vertical cylinder orientation at the free interface in as-cast films, cylinders near the selective substrate interface remain horizontal . Eventually a gradual cylinder reorientation propagates throughout the film from the substrate surface.…”

“…Indeed, as shown by Lee et al in an investigation of SVA using different solvents for thick asymmetric polystyrene-block-polyisoprene films, while SVA reinforces incipient vertical cylinder orientation at the free interface in as-cast films, cylinders near the selective substrate interface remain horizontal. 18 Eventually a gradual cylinder reorientation propagates throughout the film from the substrate surface. Nonselective (i.e., "neutral") solvents actually promote faster reorientation as a result of enhanced assembly kinetics due to screening of net repulsive block interactions by the solvent (i.e., reduced effective χ).…”