Graduate Research and Discovery Symposium (GRADS)


Entropic Contributions to Shape Memory Induced Self-Healing Polymers

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Self-healable polymeric materials offer many advantages, manifested in their ability to maintain their physicochemical properties and functionality. These studies report the development of polyurethane fibers based on isophorone diisocyanate (IPDI) and polytetrahydrofuran (PTHF) capable of complete recovery of mechanical properties upon damage. To the best of our knowledge, this is the strongest (Sf = 21 mN/tex, or σf ≈ 22 MPa) and stiffest (J = 300 mN/tex, or E ≈ 320 MPa) self-healing polymer capable of complete and autonomous self-repair under ambient conditions. These properties are attributed to the ability of shape memory entropic energy storage during damage, evidenced by the viscoelastic length transition (VLT) detected in dynamic mechanical analysis (DMA) measurements. During self-healing the conformational entropic energy generated upon damage is released, thus facilitating closure of the wound. Mechanical strength is regained by interdiffusion of macromolecular chains and H-bond reformation. Because the shape memory/entropic recovery relies on chain entanglements to act as junctions, self-healing is molecular weight dependent.

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