Wang Xiao-Xin,Cao Yun-Qing,Fu Hong-Li,Jiang Mei-Yan,Hu Ji-Ming
This work aimed at understanding the role of silane pretreatment layer in an organic coating system. The study consists of two parts. In the first part, the anticorrosion performance and interfacial property of silane-pretreated epoxy coatings were studied. The results showed that pretreatment with functional 3-glycidoxypropyl-trimethoxysilane (GPTMS) strongly improves the adhesion of epoxy-coated AA2024-T3 aluminum alloy due to the high interfacial compatibility between silane and epoxy coatings and that pretreatment with nonfunctional bis-1,2-[triethoxysilyl]ethane (BTSE) remarkably reduces the adhesion to the alloy because of low compatibility. Nevertheless, the BTSE film provides higher resistance to corrosion than the GPTMS-pretreated coating system, because the former is more hydrophobic and thicker.
Xiang Gao,Ke Lu,Lei Xu,Hua Xu,Haifeng Lu,Feng Gao,Shifeng Hou,Houyi Ma
A novel, highly effective and environmentally friendly film-forming material, phytic acid (PA)/silane (denoted as PAS) hybrid with a three-dimensional (3D) network structure, was prepared through a condensation reaction of PA with methyltrihydroxysilane generated from the hydrolysis of methyltriethoxysilane (MTES). Two kinds of PAS-based pretreatment layers, namely NaBrO3-free and NaBrO3-doped PAS layers, were fabricated on iron substrates using the dip-coating method. SEM and AFM observations showed that the as-fabricated PAS-based layers possessed a 3D porous microstructure at the nanoscale and a rough surface morphology. X-ray photoelectron spectroscopic (XPS) and attenuated total reflection infrared (ATR-IR) spectroscopic characterization demonstrated that the above PAS layers bound to the iron surface via the –P–O– bond. Moreover, analyses of steady-state polarization curves and electrochemical impedance spectroscopic (EIS) data indicated that the corrosion rates of the iron substrates decreased considerably in the presence of the two PAS-based pretreatment layers. In particular, the NaBrO3-dosed PAS layer displayed the better corrosion resistance ability as well as maintaining the original microstructure and surface morphology. The PAS-based pretreatment layers are expected to act as substitutes for chromate and phosphate conversion layers and will find widespread application in the surface pretreatment of iron and steel materials due to the advantages of being environmentally friendly, the rapid film-forming process, and, especially, the nanoporous microstructure and rough surface morphology.
A novel and environmental-friendly pretreatment layer was prepared on a mild steel from an aqueous solution of polyvinyl alcohol (PVA)-grafted phytic acid (PA). This composite pretreatment layer provides greatly improved adhesion to the metal substrate, owing to the strong chelation and coordination interaction between PA and metals. Meanwhile, PVA modification produces highly porous structure in the hybrid layer. This is beneficial to the improvement of adhesion between metal substrates and subsequent polymer coatings. Further, the highly porous structure is good at loading -corrosion inhibitors, and the polymeric coatings painted on PVA-PA pretreatment layer pre-encapsulated with inhibitors exhibit satisfactory anticorrosion performance.
Jianxin Wen,Xiaomei Liu,Zhuoyue Han,Zhijuan Wang,Hidetoshi Saitoh,Hua Li
Biofouling has been persisting as a global problem due to the difficulties in finding efficient and environmentally friendly antifouling coatings for long-term applications. Initial attachment of bacteria on material surface and subsequent formation of biofilm are the predominate phenomena accounting for subsequent occurrence of biofouling. Among the various factors influencing the bacterial attachment, conditioning layer formed by organic macromolecules usually plays the key role in mediating bacterial attachment through altering physicochemical properties of substrate surface. In this study, a guanidine-modified polysaccharide conditioning layer with the capability of tuning the bacterial attachment is constructed and characterized. Dextran, a polysaccharide widespread in bacteria extracellular polymeric substances (EPS), is oxidized by sodium periodate, and cationic polymer polyhexamethylene guanidine hydrochloride (PHMG) is anchored to oxidized dextran (ODEX) by Schiff base reaction. AFM characterization reveals morphological changes of the polysaccharide conditioning layer from tangled chain to island conformation after the PHMG modification. The guanidine-based dextran conditioning layer promotes attachment of both P. aeruginosa and S. aureus and disrupted bacterial cytomembranes are seen for the attached bacteria due to electrostatic interaction of the electropositive guanidine group with the electronegative bacteria. The guanidine-based dextran conditioning layer shows a low survival ratio of 22 %-34 % and 1 %-4 % for P. aeruginosa and S. aureus respectively after incubation in the bacterial suspension for 72 hours. The results would give insight into further exploring the potential applications of the newly designed polysaccharides conditioning layer for combating occurrence of biofouling.
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