Microphase Separation in Thin Films of Poly(styrene-block-4-vinylpyridine) Copolymer−2-(4‘-Hydroxybenzeneazo)benzoic Acid Assembly

Abstract

The fine structure of thin films of poly(styrene-block-4-vinylpyridine) copolymer−2-(4‘-hydroxybenzeneazo)benzoic acid (PS-PVP+HABA) assembly has been studied using the combination of atomic force microscopy, ellipsometry, X-ray reflectivity, GISAXS, XPS, and XPEEM. The films consist of cylindrical nanodomains formed by PVP+HABA associates surrounded by PS matrix. Alignment of the domains can be switched upon exposure to vapors of different solvents from the parallel to perpendicular orientation and vice versa with respect to the surface plane. Swelling in 1,4-dioxane leads the system from the cylindrical to the spherical morphology. Solvent evaporation results in a shrinkage of the matrix in the vertical direction and subsequent merging of the spheres into the perpendicularly aligned cylinders. The cylinders form a regular hexagonal lattice with a spatial period of 25.5 nm. On the other hand, vapors of chloroform induce in-plane alignment. The films consist of parallel layers of the cylinders separated by PS matrix and demonstrate the fingerprint-like structure. The nanocylinders of PVP+HABA are packed into a distorted hexagonal lattice exhibiting 31 nm in plane and 17 nm vertical periodicity. In both cases a thin wetting layer is found at the polymer−substrate interface. The free surface is enriched with PS.

Effects of Annealing Solvents on the Morphology of Block Copolymer-Based Supramolecular Thin Films

“…33−35 For supramolecular thin films, the effects of annealing solvents on the morphology of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) with 2-(4′-hydroxybenzeneazo) benzoic acid (HABA) molecules have been reported by Minko and co-workers. 22,36,37 They found that as films were annealed by chloroform, the P4VP(HABA) cylindrical microdomains were parallel to the surface, while annealed by 1,4-dioxane, the cylinders were perpendicular to the surface, which was attributed to the different selectivity of the solvents to each phase. The previous discussions of block copolymer-based supramolecules have been generally under the presumption that the small molecules are firmly grafted on the polymer chains.…”

Creation of lateral structures in diblock copolymer thin films during vapor uptake and subsequent drying – Effect of film thickness

“…Lateral structures are of special interest, e.g. for their use in organized inorganic substrates [3,4] and for the preparation of nanoporous membranes [5,6]. Solvent vapor induced annealing offers a simple and flexible method to create ordered structures with a potentially high degree of controllability through careful choice of solvent [7][8][9][10][11][12][13][14][15][16].…”

Supramolecular Assemblies from Poly(styrene)-block-poly(4-vinylpyridine) Diblock Copolymers Mixed with 6-Hydroxy-2-naphthoic Acid

“…Association of small organic molecules with one of the polymer blocks of the starting block copolymers via weak forces of attractions, like electrostatic interactions, van der Waals forces and hydrogen bonding, has become a widely adopted approach for the fine-tuning of the block copolymer morphology in solution [14], bulk [15,16] and in thin films [17][18][19][20][21][22][23][24][25][26][27]. In a further step, the interacting small molecules can be removed by dissolution in a selective solvent, and nanoporous materials can be obtained [17,18].…”

“…In a further step, the interacting small molecules can be removed by dissolution in a selective solvent, and nanoporous materials can be obtained [17,18].…”

“…Ten Brinke and coworkers have reported the terrace formation in thin films comprising P4VP/PDP supramolecular assemblies [32]. Stamm and coworkers realized homogeneous thin films from the supramolecular assembly of PS-b-P4VP and HABA [17,18,[34][35][36]. The orientation of the resultant cylindrical morphology could be switched from vertical to horizontal, depending on the solvent conditions.…”