Fabrication And Performance Of Epidermis-like Self-healing Coatings

Due to the green,environmental protection and resource saving advantages,self-healing smart materials have received extensive attention.As research continues,it is found that some factors restrict the development of self-healing materials,such as the difficulty of achieving good self-healing ability and strong mechanical properties at the same time,and the low preparation efficiency of self-repaired materials.At present,the self-healing ability of artificial materials is still difficult to compare with that of natural organisms,and its complicated preparation methods have further hindered the practical application of self-healing materials.In this paper,the biomimetic design is used to simulate the structure of human epidermis,which realizes the effective combination of self-healing performance and high modulus/high hardness,and completes the simple,low-cost and rapid preparation of epidermis-like self-healing coating.And through the dynamic acquisition of iron ions,the self-strengthening of the mechanical properties and anticorrosion properties of the epidermis-like self-healing coating is realized.Inspired by human epidermal multilevel hierarchical structure,a hierarchical epidermis-like hybrid coating was prepared using layer-by-layer self-assembly technology(LBL)and hydrogen bonding as the driving force.In the hybrid coating,the soft bottom layer is an exponential growth multilayer film composed of polyvinyl alcohol(PVA)and tannic acid(TA),while the hard top layer is a linear growth multilayer film composed of PVA with graphene oxide(GO)and TA.When the hybrid coating is damaged,the soft bottom layer can provide more polymers to help the external hard layer to repair,and the external hard layer can act as the sealing barrier layer to promote the self-healing of the soft layer during the process of polymer diffusion.Under the synergistic effect,the hybrid coating can not only be immersed in water for 30 min to achieve 100%recovery of morphology and mechanical properties,but also when the number of multilayer films on the bottom and top layers of the hybrid coating are 80 and 10,respectively,it can be repeate d 30 self-healing cycles.At the same time,the the Young’s modulus and hardness of the hybrid coating can reach 31.4±1.8 GPa and 2.27±0.09 GPa,respectively.These results prove that the design of this bionic structure can improve the mechanical prope rties while maintaining the self-healing ability of the material.Furthermore,in order to prepare high-strength self-healing coatings in a simple,low-cost and rapid manner,a epidermis-like multilevel hierarchical structure is constructed by using doctor blade coating technology(DBC)that is easy to achieve large-scale.In this hierarchical structure,the soft bottom layer is composed of premixed PVA and TA,while the hard top layer is composed of cheap montmorillonite clay nanosheets(MMT),PVA and TA mixture.The DBC can not only complete the preparation of the hybrid coating more than ten times faster than the LBL,but the obtained coating can also achieve 100%morphology and mechanical repair after being immersed in water for 30 min.The DBC also allows easy adjustment of the composition and structure of the coating,so as to achieve synergy and optimization of healing properties and mechanical properties.When the bottom layer of the hybrid coating is 5 squeegee cycles and the content of MMT in the to p layer is70%,it can achieve up to 54 times of repeated self-repair and modulus of 34.3±1.4GPa and hardness of 1.65±0.09 GPa.These high-performance self-healing coatings have high transparency and bactericidal properties and show good adhesion to a variety of substrates including glass,plastic and fibreboard.When used as a surface protection for fiberboard,the coating can be kept at 1000 ~oC for 12 s before it starts to burn,showing good flame retardant properties.In order to construct an ion dynamic acquisition system for synthetic self-healing materials,a DBC epidermis-like coating is applied to the steel and then immersed in a salt solution.The bottom layer of the epidermis-like coating is composed of premixed PVA and TA,and the top layer is composed of a mixture of MMT,PVA and TA.When the epidermis-like coating is immersed in 3.5 wt%sodium chloride for100 d,the content of iron ions in the coating reaches 0.36 wt%,and its Young’s modulus and hardness in the wet state can range from 7.87±0.34 GPa and 0.30±0.02GPa increased to 9.14±0.38 GPa and 0.40±0.02 GPa,respectively.The oxidation reaction and ion diffusion at the interface make it possible to dynamically chelate iron from the in-situ rusted steel,and the formation of metal coordination bonds can continuously improve the modulus and hardness of the coating.In this self-strengthening process,the double-layer structure ensures that the coating has good self-healing performance even after 100 d,and exhibits anticorrosion performance with autonomous protection mechanism,which can achieve 91.6%anticorrosion efficiency.These results indicate that the steel base coating can achieve self-strengthening of its mechanical properties and anticorrosion properties by dynamically acquiring iron ions.This paper is based on the imitation of multilevel hierarchical structure of the human epidermis.With the help of LBL and DBC,a high-strength,self-repairing,self-strengthening epidermis-like coating is prepared,which improves the mechanical properties and achieve self-strengthening of the coating.The research work in this paper will provide a certain theoretical and technical basis for the design and application of high-strength self-healing materials.