title: Characterizations of the Formation of Polydopamine-Coated Halloysite Nanotubes in Various pH Environments.
abstract: Recent studies demonstrated that polydopamine (PDA) coating is universal to nearly all substrates, and it endows substrates with biocompatibility, postfunctionality, and other useful properties. Surface chemistry of PDA coating is important for its postmodifications and applications. However, there is less understanding of the formation mechanism and surface functional groups of PDA layers generated in different conditions. Halloysite is a kind of clay mineral with tubular nanostructure. Water-swellable halloysite has unique reactivity. In this study, we have investigated the reaction of dopamine in the presence of water-swellable halloysite. We have tracked the reaction progresses in different pH environments by using UV-vis spectroscopy and surface-enhanced Raman spectroscopy (SERS). The surface properties of PDA on halloysite were clarified by X-ray photoelectron spectroscopy (XPS), SERS, Fourier transform infrared (FTIR) characterizations, zeta potential, surface wettability, and morphological characterizations. We noticed that the interaction between halloysite surface and dopamine strongly influences the surface functionality of coated PDA. In addition, pH condition further modulates surface functional groups, resulting in less content of secondary/aromatic amine in PDA generated in weak acidic environment. This study demonstrates that the formation mechanism of polydopamine becomes complex in the presence of inorganic nanomaterials. Substrate property and reaction condition dominate the functionality of obtained PDA together.
authors.affiliation: Department of Chemistry, Renmin University of China , 100872 Beijing, People's Republic of China.
authors.forename: Junran
authors.initials: J
authors.lastname: Feng
authors.affiliation: Department of Chemistry, Renmin University of China , 100872 Beijing, People's Republic of China.
authors.forename: Hailong
authors.initials: H
authors.lastname: Fan
authors.affiliation: School of Science, Beijing Jiaotong University , No. 3 Shang Yuan Cun, Haidian District, Beijing 100044, People's Republic of China.
authors.forename: Dao-An
authors.initials: DA
authors.lastname: Zha
authors.affiliation: Department of Chemistry, Renmin University of China , 100872 Beijing, People's Republic of China.
authors.forename: Le
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Renmin University of China , 100872 Beijing, People's Republic of China.
authors.forename: Zhaoxia
authors.initials: Z
authors.lastname: Jin