Shear-induced parallel and transverse alignments of cylinders in thin films of diblock copolymers

Abstract

Coarse-grained Langevin dynamics simulations were performed to investigate the alignment behavior of monolayer films of cylinder-forming diblock copolymers under steady shear, a structure of significant importance for many technical applications such as nanopatterning. The influences of shear conditions, the interactions involved in the films, and the initial morphology of the cylinder-forming phase were examined. Our results showed that above a critical shear rate, the cylinders can align either along the shearing direction or transverse (log-rolling) to the shearing direction depending on the relative strength between the interchain attraction in the cylinders (εAA) and the surface attraction of the confining walls with the film (εBW). To understand the underlying mechanism, the microscopic properties of the films under shear were systematically investigated. It was found that at low εAA/εBW, the majority blocks of the diblock polymer that are adsorbed on the confining walls prefer to move synchronously with the walls, inducing the cylinder-forming blocks to align along the flow direction. When εAA/εBW is above a threshold value, a strong attraction between the cylinder-forming blocks restrains their movement during shear, leading to the log-rolling motions of the cylinders. To predict the threshold εAA/εBW, we developed an approach based on equilibrium thermodynamics data and found good agreement with our shear simulations.

How does Micro‐ and Macro‐Phase Separation of Block Copolymers Affect the Formation of Integral Asymmetric Isoporous Membranes? A Review on Effective Factors

“…For example, long-range ordering, the orientation of self-assembled BCP nanostructures, the structure formation controllability and process reproducibility may be influenced, as reported for BCP thin films and hollow-fiber isoporous membranes. [102,159,160]…”

Developing Anisotropy in Self‐Assembled Block Copolymers: Methods, Properties, and Applications

“…[264] In general, BCP nanodomains are commonly aligned parallel to the velocity direction of the shear (or normal to the shear direction for lamellae), however when very high strain rates are imposed, the transverse arrangements of nanostructure can be formed due to the extensive polymer chain elongation in the shear direction. [265][266][267] For shear aligning BCP thin films, required stress is often applied by flowing a highly viscous silicone oil or using a crosslinked elastomeric PDMS cap in contact with the film surface. [243,257,268,269] (Figure 7).…”

Facilitated Structure Formation in Isoporous Block Copolymer Membranes upon Controlled Evaporation by Gas Flow

“…Experimentally, many approaches like blending or additives in the casting solution [29][30][31][32][33][34][35][36], solution compositions [27], an electric field on as-cast polymer film [37], shear during fabrication [38,39], temperature [40], evaporation rate [41] and humidity [42] have been reported to influence the long-range order and the orientation of self-assembled nanostructures. Solvent evaporation has proven to be a remarkably effective tool for directing the self-assembled nanostructures in the block copolymer thin films.…”