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Shear-induced network-to-network transition in a block copolymer melt
Eric W Cochran1, Frank S Bates
1Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA.
Physical Review Letters
|September 28, 2004
Summary
Shear stress transforms a poly(cyclohexylethylene-b-ethylethylene-b-ethylene) triblock copolymer melt into a single crystal network. This transformation preserves short-range geometry while altering long-range symmetry, indicating stable, nearly degenerate free energies.
Area of Science:
- Polymer science
- Materials science
- Soft matter physics
Background:
- Block copolymers self-assemble into ordered nanostructures.
- Tricontinuous network phases are complex morphologies with potential applications.
- Understanding phase transitions in block copolymers is crucial for materials design.
Purpose of the Study:
- To document a tricontinuous (10,3)c network phase in a specific triblock copolymer.
- To investigate the effect of shear on the self-assembled structure.
- To characterize the topological and symmetry changes induced by shear.
Main Methods:
- Small-angle X-ray scattering (SAXS) was used to analyze the nanostructure.
- Controlled shear was applied to the copolymer melt.
- Structural analysis focused on lattice symmetry and topological features.
Main Results:
- A tricontinuous (10,3)c network phase was identified in the poly(cyclohexylethylene-b-ethylethylene-b-ethylene) triblock copolymer melt.
- Shear induced a transformation to a single crystal (10,3)d network.
- The transformation preserved short-range threefold connectivity but reduced long-range symmetry from Fddd to Pnna.
- Both phases exhibited stability upon annealing, suggesting similar free energies.
Conclusions:
- Shear is an effective method to control the self-assembly and topological structure of block copolymers.
- The observed phase behavior highlights the interplay between short-range order and long-range symmetry.
- The stability of both phases suggests a delicate balance of thermodynamic and kinetic factors.
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