Magnetically Driven Healing of Self-Healing Polymers

Abstract

Damage in materials and structures is unavoidable, leading to the time deterioration of its functional properties (e.g. barrier, load bearing, aesthetics) and ultimate repair or replacement. Lifetime extension can be achieved by using materials with initially higher performance or using materials that can repair themselves (self-healing). The latter are materials capable of repairing themselves autonomously or with little human intervention, thereby partially or fully restoring their original material properties and performance. To be able to heal macroscopic damages a first key requirement is initial contact between broken faces. Only after this first step will the subsequent molecular processes be able to proceed with the healing at the molecular scale. In most studied concepts the contacting stage is performed by hand placing, limiting potential applications and highlighting the need for research to facilitate this necessary first step. This MSc research project addresses this problem by exploring the potential of magnetically induced damage closure. The main underlying idea states that magnetic forces at the crack plane should be sufficient to promote the bridging of broken parts, thereby facilitating the interfacial phenomena leading to healing. Such a concept can conceptually be implemented by using magnetic healable polymers, pending magnetic particles in the polymer or embedding particles as extrinsic phases. In a preliminary stage it was decided to study the latter experimentally as well as computationally. A hydrogel-composite consisting of poly(vinyl alcohol) polymer matrix mixed with iron-oxide (magnetic) particles was used as model system. Experiments showed that the presence or absence of a magnetic field does not affect the ultimate interfacial healing achieved. COMSOL simulations fed with experimental data showed the applicability of the concept in the presence of external magnetic fields for soft polymers and small gap distances. The results obtained demonstrate the viability of the concept to close damages as well as applying some interfacial pressure not affecting the ultimate healing levels.