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

Abstract

Traditional approaches to the formation of mesostructured inorganic films from block-copolymer and surfactant templates rely on simultaneous assembly of amphiphilic structure-directing agents and inorganic sol-gel precursor species into ordered hybrid structures. [1][2][3][4] Variations in sample composition and processing conditions have afforded considerable control over the local (nanometer-scale) morphology of the composite mesostructures formed via such routes.[5] However, the ability to manipulate mesophase orientation and longrange ordering in these systems has been relatively limited so far, [6][7][8][9][10][11][12] largely due to restrictions on the timescale and conditions for processing that are imposed by network formation of the inorganic component. Here, we demonstrate an alternative approach to forming mesostructured inorganic thin films that can potentially circumvent these limitations. Pre-organized block-copolymer films are first crosslinked, allowing their morphology to be preserved as they are subsequently infiltrated with sol-gel species to form hybrid inorganic/organic materials. Specifically, thin films of poly(d 8 -styrene)-blockpoly(2-vinylpyridine) (dPS-b-P2VP) diblock copolymer were thermally annealed to produce a well-ordered mesostructure consisting of dPS cylinders surrounded by a P2VP matrix. The cylinders were oriented parallel to the film plane due to preferential wetting of dPS at the free interface and P2VP at the substrate. As shown schematically in Figure 1, this morphology was fixed by chemical crosslinking of the majority P2VP component, allowing films to be swelled by aqueous solutions with essentially affine deformation of the polymer mesostructure. Sol-gel precursors for silica or titania present in the swelling solution were sequestered into the P2VP component of the polymer, producing composite inorganic/organic replicas of the initial block-copolymer morphology. Subsequent oxidation to remove the block-copolymer template species led to mesoporous inorganic oxide films that closely resembled the original block-copolymer mesostructure. This decoupling of self-assembly from inorganic infiltration provides the possibility of first processing the block-copolymer film to obtain the desired mesostructural ordering, domain alignment, and surface patterning (using a variety of recently reviewed methods [13] ) and subsequently forming a mesostructured inorganic replica of the starting template film. Recently, other approaches have been described for the preparation of mesoporous silica from pre-formed films of organic templates. Sol-gel precursors were infused via supercritical CO 2 [14] or via the vapor phase [15,16] into pre-formed films of non-crosslinked structure-directing agents, where they were subsequently condensed to produce ordered silica/organic hybrid materials. These approaches, and the current technique, can be thought of as an extension to thin films of the "true liquid-crystal templating" [17] approach for the formation of bulk mesoporous silica, wherein a pre...

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

“…3 Without cross-links, the block copolymer template rearranges extensively upon swelling, 2,3 destroying the spatial patterning imposed by preprocessing. By introducing cross-links, however, it is possible to restrict rearrangement of the block copolymer during swelling and thereby produce inorganic oxide films with mesostructures that closely mimic those of the template films.…”

Responsive Polyelectrolyte Gel Membranes

“…P2VP was crosslinked via the quaternization (S N 2) reaction of pyridine rings with 1,4-diiodobutane (DIB) [11,12] to form a polymer network (gel). P2VP gels are known to show pH-dependent swelling properties.…”

Polymeric Janus nanoparticles templated by block copolymer thin films

“…[13][14][15][16] At this point, it is important to mention that neither the alkyne functionalization nor the cross-linking affects the thin film morphology as verified by AFM (Fig. S2).…”