| As the concept of sustainability and green lifestyle arises, many research groups have made some progress in fabrication of green functionalized surface from an environmentally-friendly and economic perspective. Nevertheless, previous strategies in fabrication of functionalized surfaces often require anhydrous and inert conditions. And many catalysts used in former studies are toxic and expensive. These drawbacks limit the development of functionalized surfaces and are against the environmental-friendly and economic perspective. In recent years, visible light induced reactions are diverse in a wide range of applications, which allows the facile and novel method in fabrication of green functionalized surfaces. Besides, polydopamine (PDA) as a green functionalized coating has attracted broad interest due to its facile preparation and wide application as a versatile coating platfoRm with marvelous properties. Due to its insolubility, however, the structure of PDA and the polymerization mechanism remain unclear.In this thesis, by using UV-Vis spectroscopy, single-molecule force spectroscopy(SMFS) and many other measurements, a facile and green strategy in fabrication of polymer brush modified surface with a living nature has been designed. Besides, upon some surface characterizations, the surface initiated polymerization (SIP) progress of dopamine under acidic and alkaline conditions is studied. According to the experimental data, we develop a green and facile strategy in fabrication of functionalized surface. At the meantime, we put forward that free radical polymerization of dopamine as a novel pathway exists in the formation of PDA.In chapter 2, 2-(4-Methoxy-3-methylphenyl)ethylamine (MOE) as a sample system has been applied to develop a green and facile strategy in fabrication of polymer brush on surface. Based on SIP reaction, this sample system is featured with four elements in green chemistry: visible-light exposure, non-toxic and inexpensive initiator, eosin Y (EY), air atmosphere and DI water medium. Green visible light (?= 515 nm) will induce photoredox reaction of the monomer by catalysis of EY. Seen from the data of UV-Vis spectra, atomic force spectroscopy (AFM) imaging and contact angle measurements, it can be observed that as irradiation time prolongs, the UV absorbance, roughness of the surface and contact angles will increase. It indicates that polymer brush will be grafted on amino modified surface via free radical polymerization. As for the fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), they both confirm the formation of secondary amine group and other characteristic groups from the repeating unit of polymer brush via free radical polymerization from surface. Furthermore, typical force-extension (F-E) curves from SMFS could be superposed after normalization. It also confirms the formation of linear polymer brush. According to the study of UV-Vis spectra and SMFS data, we find out that as the conversion of monomer reaches 100%, without any addition of catalyst, the UV absorbance and molecular weight obtained from SMFS all increase quasi-linearly against irradiation time when new monomer is added. It indicates the formation of polymer brush shows a living nature. Herein, we develop a greener and facile strategy to fabricate polymer brush with a "living" nature. This strategy will enlighten a novel synthesis method in fabrication of green functionalized surfaces.In chapter 3, a derivative of DA, 3-methoxytyramine hydrochloride (MOA) that bearing fewer active sites, is used as the simplified model system to investigate the polymerization mechanism of DA under acidic condition. There should exist several pathways in parallel in the formation of PDA. However, the existed pathways cannot explain the formation of PDA initiated by APS under acidic condition. The UV-Vis spectra and SFMS analysis can both confirm the formation of linear polymer that obtained from free radical polymerization pathway. However, after incubation over 18 h, a cross-linked sturcture of polmer of MOA can be obtained via SMFS. Therefore, the pathway of free radical polymerization may exist in the formation of PDA under acidic condition.In chapter 4, MOE bearing only two active sites, is used as the simplified model system to investigate the polymerization mechanism of DA under acidic condition. Based on the study of MOA in chaper 3, it can be observed that the UV absorbance, roughness on the surface and the contact angles will increase as the reaction time prolongs from the UV-Vis spectra, AFM imaging and contact angle measurements. FT-IR and XPS results demonstrate the formation of the secondary amine group and other characteristic groups, which should come from repeating unit of polymer (PMOE). The SFMS analysis further confirms the formation of linear polymer that obtained from free radical polymerization pathway. Based on the Set Theory, the pathway of free radical polymerization should exist in the formation of PDA under acidic condition.In chapter 5, by using the same simplified sample system of MOE, the SIP process of DA under alkaline condition is studied. Similar with the measurements and methods in chapter 3, it can be observed that MOE could polymerize into a linear polymer via free radical polymerization initiated by APS according to UV-Vis spectroscopy, FT-IR, XPS and SMFS measurements. Typical single-chain F-E curves obtained under acidic and alkaline conditions from SMFS are proven to present the same elastic modulus, which indicates that the same species of linear polymer are grafted from the surface. According to the Set Theory,among many other pathways in the formation of PDA, there should exist free radical polymerization pathway in the polymerization of DA no matter under acidic and alkaline conditions. These parallel pathways may be the main reason for the structure complexity of PDA. |
PDF Full Text Request