Tracking capsule activation and crack healing in a microcapsule-based self-healing polymer

Structural polymeric materials incorporating a microencapsulated liquid healing agent demonstrate the ability to autonomously heal cracks. Understanding how an advancing crack interacts with the microcapsules is critical to optimizing performance through tailoring the size, distribution and density of these capsules. For the first time, time-lapse synchrotron X-ray phase contrast computed tomography (CT) has been used to observe in three-dimensions (3D) the dynamic process of crack growth, microcapsule rupture and progressive release of solvent into a crack as it propagates and widens, providing unique insights into the activation and repair process. In this epoxy self-healing material, 150 µm diameter microcapsules within 400 µm of the crack plane are found to rupture and contribute to the healing process, their discharge quantified as a function of crack propagation and distance from the crack plane. Significantly, continued release of solvent takes place to repair the crack as it grows and progressively widens

Spin tunnelling in mesoscopic systems

We study spin tunnelling in molecular magnets as an instance of a mesoscopic phenomenon, with special emphasis on the molecule Fe8. We show that the tunnel splitting between various pairs of Zeeman levels in this molecule oscillates as a function of applied magnetic field, vanishing completely at special points in the space of magnetic fields, known as diabolical points. This phenomena is explained in terms of two approaches, one based on spin-coherent-state path integrals, and the other on a generalization of the phase integral (or WKB) method to difference equations. Explicit formulas for the diabolical points are obtained for a model Hamiltonian.Comment: 13 pages, 5 figures, uses Pramana style files; conference proceedings articl

Pressurized vascular systems for self-healing materials

An emerging strategy for creating self-healing materials relies on embedded vascular networks of microchannels to transport reactive fluids to regions of damage. Here we investigate the use of active pumping for the pressurized delivery of a two-part healing system, allowing a small vascular system to deliver large volumes of healing agent. Different pumping strategies are explored to improve the mixing and subsequent polymerization of healing agents in the damage zone. Significant improvements in the number of healing cycles and in the overall healing efficiency are achieved compared with prior passive schemes that use only capillary forces for the delivery of healing agents. At the same time, the volume of the vascular system required to achieve this superior healing performance is significantly reduced. In the best case, nearly full recovery of fracture toughness is attained throughout 15 cycles of damage and healing, with a vascular network constituting just 0.1 vol% of the specimen.</p

Autonomic self-healing and materials regeneration

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Self-healing of impact damage in 3d micromolecular composites

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A new self-healing epoxy with tungsten (VI) chloride catalyst

Using self-healing materials in commercial applications requires healing chemistry that is cost-effective, widely available and tolerant of moderate temperature excursions. We investigate the use of tungsten (VI) chloride as a catalyst precursor for the ring-opening metathesis polymerization of exo-dicyclopentadiene (exo-DCPD) in self-healing applications as a means to achieve these goals. The environmental stability of WCl6 using three different delivery methods was evaluated and the associated healing performance was assessed following fracture toughness recovery protocols. Both as-received and recrystallized forms of the WCl6 resulted in nearly complete fracture recovery in self-activated tests, where healing agent is manually injected into the crack plane, at 12 wt% WCl6 loading. In situ healing using 15 wt% microcapsules of the exo-DCPD produced healing efficiencies of approximately 20%

Self-healing PMMA biomaterials

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