Shear Ordering in Thin Films of Spherical Block Copolymer

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• 作者：Gaurav Arya ; Jö ; rg Rottler ; Athanassios Z. Panagiotopoulos ; David J. Srolovitz ; and Paul M. Chaikin
• 刊名：Langmuir
• 出版年：2005
• 出版时间：November 22, 2005
• 年：2005
• 卷：21
• 期：24
• 页码：11518 - 11527
• 全文大小：834K
• 年卷期：v.21,no.24(November 22, 2005)
• ISSN：1520-5827

文摘

We have investigated shear-induced alignment of a bilayer of spherical diblock copolymer micelleswithin thin films using molecular dynamics simulations at two different levels of coarse-graining. At themicroscopic level, the copolymers are modeled as bead and spring chains with specific interaction potentialswhich produce strongly segregated spherical micelles. The simulations qualitatively reveal that long-range shear-induced ordering of hexagonally arranged micelles arises because of the tendency of micellesto pursue trajectories of minimum frictional resistance against micelles in the opposing layer. This influencestheir alignment in the direction of shear without them breaking apart and reforming within the time scaleof the simulations. As observed in experiments, the ordering is shown to be very sensitive to the filmthickness and shearing rates. To access larger lengths and longer time scales, we further coarse-grain oursystem to a mesoscopic level where an individual micelle is represented by a spherical particle, whichinteracts with other micelles through an effective potential obtained from the microscopic simulations.This approach enables us to follow the time evolution of global order from locally ordered domains. Anexponentially fast growth of the orientational correlation length of the hexagonal pattern at early times,followed by a crossover to linear growth, is found in the presence of shear, in contrast to the much slowerpower-law scalings observed in experiments without shear.