Microphase separation of block copolymer solutions in a flow field

Abstract

Films of polystyrene–polybutadiene–polystyrene (PS/PB/PS) triblock copolymer and polystyrene‐poly(ethylene/propylene) (PS/PEP) diblock copolymer were cast from toluene solutions subjected to hydrodynamic flow at room temperature using a device based on a novel casting method we term ‘roll‐casting.’ Polymer solutions were rolled between two corotating eccentric cylinders while at the same time the solvent was removed at a controlled rate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. A discussion of the flow field that develops during roll‐casting is presented and specific attention is given to the importance of the shear and elongation rates present. For the triblock and diblock, respectively, the processed structures consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix, and unidirectional lamellae of alternating polystyrene and polyethylene/propylene. Small‐angle x‐ray scattering (SAXS) and transmission electron microscopy (TEM) indicated the near single‐crystal structure both types of films. SAXS also showed the styrene cylinders and the alternating lamellae to be packed closer together in roll‐cast films than in simple quiescently cast films. A molecular orientation mechanism is proposed to describe both these results as well as the changes in packing and in macroscopic sample dimensions measured after complete solvent evaporation and after sample annealing. © 1993 John Wiley & Sons, Inc.

Hierarchical Assemblies of Block-Copolymer-Based Supramolecules in Thin Films

“…3,4,[36][37][38] With subsequent solvent annealing, the solvent mediates interactions between each component and with the underlying substrate and imparts mobility to the copolymer. 3,4,[38][39][40] Thus, highly oriented arrays of nanoscopic microdomains with a high degree of long-range lateral order can be produced. In the case of BCP-based supramolecules, two assembly processes occur simultaneously on two different length scales; i.e., the BCP phase separates to form microdomains tens of nanometers in size, and the P4VP(PDP) comb blocks assemble into lamellar structures, a few nanometers in size.…”

Understanding and controlling the morphology of styrene–isoprene side-group liquid crystalline diblock copolymers

“…Samples were prepared by slowly evaporating a 5 wt.% solution of the polymer in toluene followed by thermal annealing at 140ЊC in vacuum. Both small and wide angle X-ray scattering were used to determine the orientation of the mesogens with respect to the IMDS in globally well oriented samples produced by roll-casting [29] and oscillatory shear. For cylinders of the LC block, as well as cylinders of styrene and lamellae, the mesogens were found to orient parallel to the IMDS (i.e.…”

“…Oscillatory shear [27], electric fields [28] and roll-casting [29] have all been applied to produce various well aligned morphologies in di-and triblock copolymers. The presence of mechanical anisotropy on two different length scales due to two different but necessarily interacting sets of structures Illustration of a section of the inter-material dividing surface, IMDS, for a cylindrical microdomain in a PS/PI-LC diblock copolymer.…”

Flow-Induced Alignment of Block Copolymer−Sol Nanoparticle Coassemblies toward Oriented Bulk Polymer−Silica Hybrids

“…After flow alignment, hexagonal hybrids with an inorganic matrix did not show quasi-single-crystalline patterns but exhibited similar order parameters around 0.4 for the orientation distribution of the cylinders along the flow direction as in the regular hexagonal samples. The present extension of the roll-casting technique 21 thus holds promise for considerably improving the macroscopic order of sol-gel-derived bulk polymerinorganic hybrids. Alignment of these technologically relevant materials is vital for realizing their true potential, and development of simple techniques such as the one described in this work may hold the key for successful implementation of these functional materials in real applications.…”

“…6 While these techniques clearly demonstrate the ability to achieve orientation effects in nanostructured silica-type hybrids, they are usually applicable only to thin films and/or not adaptable to large-scale synthesis of bulk materials. Here we present a straightforward scheme for the macroscopic alignment of bulk polymer-nanoparticle hybrid materials from solutions subjected to hydrodynamic flow based on a simplified version of the "rollcasting" method used by Albalak et al 21 to produce oriented pure block copolymer samples. The technique requires initially relatively low-viscosity starting solutions.…”