The Role Of Silane Films And Some Other Pretreatments In Protective Painting System:the Experimental Study And Molecular Dynamic Simulation

The organic coating system is a commonly used and effective measure for corrosion prevention of metals, and adhesion strength and corrosion performance are our most concern issues. The two most important properties can be easily assessed by experiments, but the molecular-level mechanisms of coating deterioration that happen at the silane/polymer or metal/polymer interface are not fully understood and are very difficult to explore. Molecular dynamics (MD) simulation is an important computer simulation method, which has been applied to study the composite materials and surface/interface properties at atomic level. In this thesis, we combined experiments and theoretical calculation to quantify the effect of two kinds of silane pretreatment films on adhesion strength and corrosion protection of subsequent epoxy coating on aluminum alloy. In addition, we also studied the interaction energy between the other kinds of pretreatment layers and different polymer coatings with the MD method. The specific contents are listed as follows:(1) The adhesion strength and corrosion protection of the coating systems with BTSE and GPTMS silane films were studied. Pull-off test, EIS and SVET tests were used. The results indicate that the GPTMS silane film can significantly improve the interfacial adhesion strength, while BTSE silane film has the opposite effect. Two kinds of silane pretreatment layer both can dramatically improve the corrosion resistance of the coating system. However, GPTMS silane film has an advantage in the short term protection, and BTSE silane film can provide a long-term protection. Molecular dynamics simulation results show that the system with GPTMS has the largest interface interaction energy both in the dry and wet states. From the perspective of the concentration distribution at the interface, the wider cross area between GPTMS and epoxy means a better compatibility with coating and is helpful to increase interaction energy. When the coating system is subjected to the invasion of water molecules, both the silane films can influence the water absorption process of the epoxy and the mobility of the polymer chain. GPTMS film itself will be slightly inflated and become less dense, while BTSE film shrinks slightly and tends to be more uniform and dense to have a effective protection for a long time.(2) The MD method was also applied to study the interaction energy between the other kinds of inorganic oxide pretreatment layers and different polymer coatings. The results show that the interaction energies of the systems without any pretreatment are very weak. The pretreatment layers not only can significantly enhance the adhesion strength of the coating system, but also are non-selective to subsequent organic coating. The morphologies and concentration distributions of polymer chains indicate that the interaction energy is affected by two factors together: one is the contact state between polymer coating and surface, another is the distribution of functional groups in polymer chains.