聚多巴胺在强负电型微球表面的形貌调控

Morphology Regulation of Polydopamine Self-polymerizationon the Surface of Strongly Electronegative Microspheres

多巴胺(DA)已被证实可在多种材料的表面进行氧化自聚而形成聚多巴胺(PDA),但其在带强负电荷的表面上的聚合机理和所形成的形貌却还不太明确。为考察材料表面的电负性、氧化条件等对DA氧化自聚速度和聚多巴胺层形貌的影响,本文通过无皂乳液聚合制备了以聚苯乙烯(PS)为核、聚丙烯酸(PAA)为壳的纳米粒子(PS/PAA NPs),探究其表面的阴离子在不同pH缓冲液、反应时间下与DA的加入量对聚合过程及其形貌的影响。通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)和Zeta电势对所得纳米粒子的结构、形貌与尺寸等进行分析。结果发现,在pH值为8.5的三羟甲基氨基甲烷(Tris)缓冲溶液中,当DA与PS/PAA NPs的质量比为1∶[KG-3/5]1时,在反应24 h后,PDA以纳米颗粒的形式存在于PS/PAA NPs的表面,即所形成的PS/PAA/PDA NPs为明显的树莓状结构。随着DA含量的增加和反应时间的延长,所形成的树莓状粒子粒径增大;当DA远远过量时,PDA最终在微球表面形成致密、均匀的壳层。Zeta电势结果表明树莓状结构是由于DA在PAA表面聚合过程中受到静电相互作用和电荷排斥作用间的竞争而形成的,随着DA量的增大和反应时间的延长,形成的静电作用增大,使较多的PDA粘附至PAA表面而形成较致密的均匀壳层。同时,DA在电负性较小的PS/SDS微球和非离子的PS微球表面聚合时,均形成致密的PDA壳层。因而,材料表面的电负性大小可以调控DA在其表面的沉积,以制备不同形貌的PDA复合材料。

Dopamine(DA)has been proved to be able to oxidize and polymerize into polydopamine(PDA)on the surface of a variety of materials,however,the mechanism of the DA polymerization on strongly electronegative surfaces and the formed morphologies of PDA are not clear yet.In order to investigate the influence of the surface electronegativity and oxidation conditions on the rate of the oxidized self-polymerization and the morphology of the PDA layer,herein,polystyrene/polyacrylic acid nanoparticles(PS/PAA NPs)with PS as the core and PAA as the shell were prepared by soap-free emulsion polymerization.Then,PDA was coated on the surface of the PS/PAA NPs and the effect of different pH buffers,reaction time and the amount of DA on the polymerization process and the PDA morphologies were investigated.The morphology and size of the nanoparticles were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and Zeta potential.The results show that small PDA NPs are polymerized on the PS/PAA NPs surface to form the raspberry structure in the Tris buffer solution with a pH of 8.5,and the mass ratio of DA to PS/PAA NPs is 1∶[KG-3/5]1.The formed PDA NPs become bigger with higher DA contents and longer reaction time.When DA is excess,it eventually forms a uniform PDA shell on the surface of microspheres.Zeta potential results show that the raspberry-like structure is formed due to the balance between electrostatic interaction and charge repulsion in the surface polymerization of PAA.A larger amount of DA and a longer reaction time result in the reduction of charge repulsion to form a dense uniform PDA shell layer.In addition,uniform PDA shell layers form on the surface of PS/SDS microspheres with less electronegativity and nonionic PS microspheres.Therefore,the PDA deposition on the surface of the anionic materials is influenced by the negative value of the surface.