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Elastic moduli of multiblock copolymers in the lamellar phase
R B Thompson1, K Ø Rasmussen, T Lookman
1Theoretical Division, Los Alamos National Laboratory, New Mexico 87545, USA. rthompson@lanl.gov
The Journal of Chemical Physics
|July 23, 2004
Summary
The study reveals that increased monomer mixing, not bridging, drives modulus changes in multiblock copolymers. This occurs via interface widening during extension and molecule unbinding during compression.
Area of Science:
- Polymer physics
- Materials science
- Soft matter theory
Background:
- Multiblock copolymer melts exhibit complex phase behavior.
- Understanding their linear elastic response is crucial for material design.
- The lamellar phase, formed by symmetric AB diblock copolymers, is a key structure.
Purpose of the Study:
- To investigate the linear elastic properties of multiblock copolymer melts in the lamellar phase.
- To determine the relationship between molecular architecture (block number) and mechanical response (tensile and shear moduli).
- To elucidate the underlying mechanisms responsible for changes in modulus.
Main Methods:
- Utilizing self-consistent field theory (SCFT).
- Employing a real-space approach for calculating elastic moduli.
- Analyzing the influence of block number on material properties.
Main Results:
- Tensile moduli show qualitative agreement with experimental data.
- The increase in modulus with block number is attributed to enhanced mixing of repulsive A and B monomers.
- Bridging fraction increase does not directly cause the modulus increase.
Conclusions:
- The primary driver for modulus change in these systems is increased monomer mixing.
- Under extension, modulus increase stems from interface widening and molecule unbinding.
- Under compression, modulus increase is solely due to molecules being pulled free from the interface.