Template Cross-Linking Effects on Morphologies of Swellable Block Copolymer and Mesostructured Silica Thin Films

Abstract

Mesostructured silica films were formed from cross-linked poly(d8-styrene-block-2-vinylpyridine) (dPS-b-P2VP) diblock copolymer template films by swelling with silica precursor solutions. The mesoscopic and macroscopic morphologies of the resulting materials depended strongly on the extent of P2VP cross-linking. Without cross-linking, extensive rearrangement of the initial 2D hexagonal arrangement of dPS cylinders took place during swelling, leading to wormlike mesostructures. At low extents of template cross-linking, osmotic stresses led to a surface-wrinkling instability with a morphology directed by the anisotropic mechanical properties of the swelled block copolymer mesostructure. At higher degrees of P2VP cross-linking, wrinkling was suppressed, and the composite silica/polymer mesostructures corresponded to essentially affine expansions of the initial template structures normal to the film plane. At low extents of P2VP cross-linking, the mesostructures of the hybrid block copolymer/silica films were preserved during oxidation and removal of the block copolymer template species, leading to stable mesoporous silica films. At high extents of P2VP cross-linking, however, insufficient amounts of silica were incorporated to form stable porous inorganic materials, leading to mesostructural collapse. An intermediate level of cross-linking allowed the preparation of stable mesoporous silica films with structures that closely resembled those of the initial template films.

Block Copolymer Assemblies as Templates for the Generation of Mesoporous Inorganic Materials and Crystalline Films

“…In separate work, Chmelka et al first cross-linked the mesophases of block copolymers featuring additional double bonds, [42] and then the inorganic precursor was infiltrated. This approach reduces the disruption of the BC mesophase upon condensation of the metal salts.…”

Controlled chemical stabilization of self-assembled PS-P4VP nanostructures

“…Cross-linking is known to be important to the preservation of mesostructural ordering during swelling and incorporation of inorganic precursors [3]. Without cross-links, the block copolymer template rearranges extensively upon swelling, destroying the spatial patterning imposed by preprocessing.…”

Crosslinked Poly(styrene)‐block‐Poly(2‐vinylpyridine) Thin Films as Swellable Templates for Mesostructured Silica and Titania

“…[19] The block-copolymer films employed here were ∼ 90 nm thick and had 8-11 % of the P2VP moieties quaternized by DIB, as measured via X-ray photoelectron spectroscopy (XPS) (film thickness and the degree of crosslinking are both important variables in determining the morphologies of the resulting inorganic/block-copolymer films, as elucidated in a separate report). [20] Dynamic secondary-ion mass spectrometry (SIMS) was employed to measure the extent of crosslinking as a function of depth from the film surface. The iodine ( 127 I -) signal in the SIMS depth profile shown in Figure 3a is relatively constant, indicating homogeneous incorporation of the iodine-containing crosslinking agent.…”