Enhancing Toughness and Microstructural Memory by Coupling Crystallinity, Elasticity, and Plasticity in Layered Materials Composed of Liquid Crystalline Oligomers

MK Das and FA Escobedo, MACROMOLECULES, 57, 11550-11564 (2024).

DOI: 10.1021/acs.macromol.4c01919

Molecular dynamics simulations are used to show that triblock oligomers, which are first preassembled into a lamellar phase and then cross- linked, exhibit high extensibility and toughness in response to uniaxial tensile deformation parallel to the layer stacking. A coarse-grained model is adopted based on a coil-rod-coil oligomer capped with cross- linkable units. Upon uniaxial strain, a buckling instability ensues in the uncross-linked systems, which eventually leads to defective lamellar "islands" as the stress drops off. In contrast, a toughening behavior, manifested as a "sawtooth" stress-strain profile, is observed in the cross-linked systems, which is associated with "recrystallization" of the rod domains mediated by the interlayer bonds formed upon cross- linking. It is also shown that this toughening mechanism can be encoded in longer multilayer-spanning oligomer designs that forsake the cross- linking step. These structures, which integrate rigidity, elasticity, and plasticity, could be leveraged to experimentally realize novel materials with shape-memory and self-healing properties.

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