Study On Preparation And Properties Of Self-healing Organogels

Self-healing gels are promising smart materials, the studies of their preparations and properties have attracted more and more attention from scientific researchers. So far, self-healing gels can divided into two major categories: chemical self-healing gels and physical self-healing gels. Chemical self-healing gels commonly have stable molecular structures and high mechanical strength, but most of them can only self-repair with the assistance of external stimulus, such as light, temperature and redox conditions. Physical self-healing gels can autonomously and rapidly self-heal without the assistance of any stimulus, but their structures are not stable and they often have poor mechanical strength. Therefore, forming gels that possess both excellent self-healing and mechanical properties is the key for designing and preparing self-healing gels. Introducing both stable chemical crosslink junctions and dynamic physical crosslink junctions into the structures of gels seem promising to solve this problem. In this paper, we used the nucleophilic addition-condensation reaction between amine-terminated poly(ethylene glycol) oligomers and paraformaldehyde to prepare a novel organogels. The fabricated organogels were comprised of hemiaminal dynamic covalent networks(HDCN) and hydrogen-bonding bis-hemiaminal moieties. The hemiaminal dynamic covalent networks could serve as chemical crosslink junctions in organogels, which conferred high mechanical strength to organogels. The hydrogen-bonding bis-hemiaminal moieties could serve as physical crosslink junctions in organogels, which sustained the self-healing behavior of organogels.The main contents and results of this paper are as follows:1.The author chemically modified the terminal group of linear poly(ethylene glycol) by two-steps method. Firstly, poly(ethylene glycol) was modified by sulfonylation reaction, and then the sulfonyl group was turned into amino by amination reaction. By this way, we successfully synthesized amine-terminated poly(ethylene glycol) gelators. Structures of the gelators were characterized by Fourier transform infrared spectrometer(FT-IR) and nuclear magnetic resonance(NMR). The computational results from elemental analysis showed that the degree of terminal functionality was about 90.0%.2.The nucleophilic addition-condensation reaction between amine-terminated poly(ethylene glycol) and paraformaldehyde was employed in N-methyl-2-pyrrolidone to successfully prepare a novel organogels. The process of gel formation was studied by NMR, and the self-healing and mechanical properties of the organogels were analyzed by photomicrography, rheological test and tensile test. The results indicate that the fabricated organogels could autonomously and rapidly repair the incisions or cracks within 5 hours at ambient temperature without needing any stimulus. Besides, the tensile strength of the organogels was 100 kPa, the elongation at break was 1072%, and the storage modulus was about 10 kPa. All of these results show that the organogels possess both excellent self-healing and mechanical properties.3.The author used the reaction between amine-terminated poly(ethylene glycol) and paraformaldehyde in N-methyl-2-pyrrolidone and water to form gels. The effects of water on the rate of gel formation were studied by NMR and gel time, while the effects of water on self-healing and mechanical properties of the gels was analyzed by photomicrography, rheological test and tensile test. The results indicate that the presence of water could accelerate the reaction rate of amine-terminated poly(ethylene glycol) and paraformaldehyde, and increase the density of physical crosslink junctions in gels, thus accelerating the rate of gel formation and self-healing, and dramatically reducing the mechanical properties of fabricated gels.