Conductive Self-healing Composite Materials

Self-healing materials can extend lifespan, reduce production costs and enhance the safety. In recent years, investigation on self-healing materials has become a hot area. The research on conductive self-healing materials is one of the most important. Although a lot of achievements have been made in conductive self-healing materials, there are still some problems. For example, many of the conductive self-healing materials reported could only repair with the aid of external stimuli; there was no report on the conductive self-healing materials working below the room temperature. In this thesis, we chose the supramolecular polymers as the matrix, and combined them with nano-sized carbon materials, including graphene oxide and carbon nanotubes, to construct novel conductive self-healing composites. The structure and property of the composites were characterized carefully.This thesis is mainly composed of two parts.1. Composite of graphene oxide/supramolecular polymerIn this work, we first prepared supramolecular polymers based on proton exchange among citrate acid (CA) and N,N,N’,N’-tetramethyl-l,3-propanediamine (TMPDA) molecules, and then obtained composites by addition of reduced graphene oxide (RGO). WAXD, TEM, FTIR, DSC, rotatable rheometer, and resistance gauge were used to analysis structure of RGO and the composites, in addition to thermal property, viscosity-temperature dependence, conductivity and self-healing ability of the composites. The results showed that the RGO used was sheets of lateral dimension of several micrometers; the electrostatic interactions among the acid and ammonium molecules were weakened; the heat flow in DSC run was lowered; the viscosity of RGO composites greatly decreased. All these results indicated that the RGO isolated some of the CA and the TMPDA molecules that the integrity of pseudo network of the supramolecular polymer was partially destroyed, due to the large dimension of the RGO sheets. It is because of the good conductivity of RGO and the highly flowing ability of the composites, the conductivity of the composites was elevated almost 3 orders of magnitude, and the jump of conductivity with the temperature increasing was more apparent. Compared to the pristine supramolecular polymer, the self-healing efficiency of the RGO composite was better.2. Low temperature self-healing composites possessing conductivityIn this work, supramolecular polymer synthesized from citric acid and tetramethyl propylenediamine was prepared, and a proper amount of carbon nanotubes were added in to obtain conductive composites that can self-heal below room temperature. The results show that the supramolecular polymer can perform self-healing at-24℃ within four hours. The self-healing ability of supramolecular polymer matrix was greatly affected after addition of carbon nanotubes. The conductive self-healing composites could also heal the wounds within four hours. Both of the repaired samples, including the supramolecular polymer and the conductive composites were of good mechanical strength that they could withstand 1×104 Pa tensile stress. Even if the fractured samples were not aligned precisely, both the supramolecular polymer and conductive composites could combine together at-24℃, and withstand the same stress. The conductivity could be restored perfectly together with restoration of the structures. Investigation on the low-temperature self-healing mechanism showed that dynamic exchange among the carboxyl groups and the amine groups was the major reason. Due to the good viscoelasticity and the plasticity, the conductive self-healing composites could be molded into different shapes. Therefore, they can be applied in many different areas.