Diblock-copolymer thin films under shear

LS Shagolsem and T Kreer and A Galuschko and JU Sommer, JOURNAL OF CHEMICAL PHYSICS, 145, 164908 (2016).

DOI: 10.1063/1.4966151

The behavior of lamellae forming diblock-copolymer melts confined by two non-selective substrates under shear is studied by means of molecular dynamics simulations. Since the substrate/copolymer preferential interaction is absent, the vertically oriented lamellae (L-perpendicular to) are formed. The response of L-perpendicular to phase under transverse and perpendicular modes of shear is studied for a wide range of shear rates, (gamma) over dot. In particular, shear deformation and reorientation transition, flow behavior, and difference in the macroscopic response under the two modes of shear are discussed. We show that an inclined lamellae state observed for transverse shear below a critical shear rate (gamma) over dot* is stabilized by a cyclic motion of chains close to the substrates. The value of (gamma) over dot*, at which lamellae dissolve and reorient along the flow field during transverse shear, coincides with the onset of shear-thinning. For (gamma) over dot < (gamma) over dot*, the shear viscosity for transverse shear is much larger compared to that observed in perpendicular shear, while there is no difference for (gamma) over dot > (gamma) over dot*. Published by AIP Publishing.

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