Vertical Cylinder-to-Lamella Transition in Thin Block Copolymer Films Induced by In-Plane Electric Field

Abstract

Morphological transition between hexagonal and lamellar patterns in thin polystyrene–block–poly(4-vinyl pyridine) films simultaneously exposed to a strong in-plane electric field and saturated solvent vapor is studied with atomic force and scanning electron microscopy. In these conditions, standing cylinders made of 4-vinyl pyridine blocks arrange into threads up to tens of microns long along the field direction and then partially merge into standing lamellas. In the course of rearrangement, the copolymer remains strongly segregated, with the minor component domains keeping connectivity between the film surfaces. The ordering tendency becomes more pronounced if the cylinders are doped with Au nanorods, which can increase their dielectric permittivity. Non-selective chloroform vapor works particularly well, though it causes partial etching of the indium tin oxide cathode. On the contrary, 1,4-dioxane vapor selective to polystyrene matrix does not allow for any morphological changes.

Effect of In‐Plane Electric Field on the Microphase Separation in Thin Films of a Symmetric ABA Triblock Copolymer

“…In our recent works, [62,63] we addressed how an in-plane electric field affects the microphase-separated morphologies formed in a thin film of AB diblock copolymer. In the present study, we theoretically consider the same problem for a film of the symmetric ABA triblock copolymer.…”

“…Initially we concluded, based on the AFM images and simple geometrical arguments, that an electric field transformed the standing cylinders into the standing lamellas. [ 62 ] However, a more detailed SCFT consideration [ 63 ] demonstrated that such a transition would require a much stronger electric field than was available in our experiments. A new interpretation was proposed that treated the apparent morphological changes as a transformation of vertical cylinders into horizontal ones.…”

“…[6] This issue can be partially resolved by combining an electric field with other factors that enhance the mobility of block copolymer molecules, for instance, heating the copolymer above T g for both blocks, applying shear, [59,60] graphoepitaxy, [49] or selective vapor annealing. [10,61] Recently we have found experimentally that an electric field, either direct (DC) [62] or alternating (AC), [63] applied in-plane to a thin film of polystyrene-poly(2-vinyl pyridine) (PS-P2VP) or polystyrene-poly(4-vinyl pyridine) (PS-P4VP) diblock copolymer and combined with a saturated chloroform vapor, can effectively align fingerprint and cylindrical morphologies along the field direction. Moreover, in the case of standing cylinders formed by PS-P4VP copolymer with the volume fraction of 4VP units equal to f = 0.26, the field with the root-mean-square value of 8 V μm −1 considerably modulated the film thickness.…”

“…Recently we have found experimentally that an electric field, either direct (DC) [ 62 ] or alternating (AC), [ 63 ] applied in‐plane to a thin film of polystyrene‐poly(2‐vinyl pyridine) (PS–P2VP) or polystyrene‐poly(4‐vinyl pyridine) (PS–P4VP) diblock copolymer and combined with a saturated chloroform vapor, can effectively align fingerprint and cylindrical morphologies along the field direction. Moreover, in the case of standing cylinders formed by PS–P4VP copolymer with the volume fraction of 4VP units equal to f = 0.26, the field with the root‐mean‐square value of 8 V µm −1 considerably modulated the film thickness.…”

Block Copolymer Nanocomposites under Confinement: Effect on Frustrated Phases

“…Experimentally, neutral NPs have been found to induce alignment transition in the BCP, from parallel to perpendicular lamellar, driven by the neutralization of the substrate induced by the accumulation of NPs at the substrate. − CdSe NPs were segregated within perpendicular lamellar domains with respect to glass substrates. , Single Au NPs were segregated within the perforation of a PL thin film, achieving a one-to-one correspondence between the BCP features and the NP placement . Segregating metallic NPs within cylinder-forming BCPs has been recently shown to increase the response to electric fields leading to phase transition and alignment …”