270155 Effect of Chain Architecture On the Viscoelasticity and Shock Response of Block Copolymers

Wednesday, October 31, 2012: 1:20 PM
Butler East (Westin )
Bedri Arman1, Srinivas Reddy2 and Gaurav Arya1, (1)Department of Nanoengineering, University of California, San Diego, La Jolla, CA, (2)La Jolla Bioengineering Institute, La Jolla, CA

A clear understanding of the molecular mechanisms responsible for energy and shock dissipation in elastomeric materials is essential for the design of next-generation materials for blast mitigation. Even though current high-end, protective gear typically rely on polyurea and polyurea-based materials for protection against blasts, the molecular basis for the dissipative properties of polyurea remains unknown. It may be hypothesized that the multiblock chain architecture of polyurea--repeating units of hard and soft segments--might be partly responsible for its superior dissipative properties. As a first step towards addressing this question, we carry out a detailed comparison of the microstructure, viscoelastic properties, and shock response of coarse-grained models of multiblock  and diblock copolymers using molecular dynamics simulations. We find that the multiblock copolymer forms small, interconnected, rod-shaped, hard domains surrounded by a soft matrix, whereas the diblock copolymer forms larger, unconnected, hard domains. Viscoelastic analyses indicate that multiblock copolymer is not only more elastic but also more dissipative at low to intermediate frequencies. Shock simulations reveal that shock waves propagate slower in the multiblock copolymer compared to the diblock copolymer, which may be due to the more deformable hard domains in the former system. Our results thus suggest that the multiblock architecture of polyurea might endow polyurea with smaller, more deformable, and interconnected hard domains that could lead to improved energy dissipation and lower shock speeds.

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