Shear-induced long-range alignment of BCC-ordered block copolymers |
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Authors: | Prashant Mandare H Henning Winter |
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Institution: | (1) Department of Chemical Engineering, University of Massachusetts, Amherst, MA, USA |
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Abstract: | Effect of large shear on an asymmetric block copolymer with nanospherical domains has been studied using rheology and small
angle X-ray scattering. The material investigated was a triblock copolymer polystyrene-b-(ethylene-co-butylene)-b-styrene] swollen in a midblock-selective solvent. When cooled below the order–disorder transition temperature (T
ODT), the system forms a locally ordered structure of grains with body-centered cubic (BCC) lattice. Isothermal shearing, either
at constant rate or with large amplitude oscillatory shear (LAOS) at low frequencies and strain amplitude greater than or
equal to 2.0, leads to the destruction of the BCC lattice (isothermal “shear melting”). Upon cessation of the shear, the BCC
structure recovers with kinetics similar to the one after thermal quench from above T
ODT. Under certain experimental conditions, LAOS leads to alignment of the BCC lattice. The lattice orientation depends primarily
on shearing frequency. At low frequencies, there exists an upper and lower bound on strain amplitude where monodomain textures
can be obtained. Upon alignment, the modulus drops by about 30% of that of the polycrystalline structure. Measurement of rheological
properties offers an indirect method for distinguishing between polycrystalline structure (grains) and monodomain texture. |
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Keywords: | Block copolymer Large amplitude oscillatory shear Flow induced orientation BCC order Monodomain |
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