Studies On Morphology Regulation Of Polydopamine On The Surface Of Ionic Polymeric Microspheres

Dopamine(DA)is a class of biologically-derived,multi-reactive,multifunctional compounds.It has been proved to be able to oxidize and self-assembling polymerize into polydopamine(PDA)on the surfaces of a variety of materials.However,the mechanism of the DA polymerization on different surfaces is not clear yet,and the formed morphologies of PDA are not controllable.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,a series of ionic polymeric nanoparticles with polystyrene as the core and a variety of ionic polymers as shell were prepared in this paper.Then,the ions on the surface of the polystyrene-based ionic nanoparticles and effect of polymerization conditions on the polymerization process and the PDA morphologies were investigated.In order to investigate the effect of cation on DA polymerization,polystyrene/polydimethyldiallyl ammonium chloride nanoparticles(PS/PDMDAAC NPs),and polystyrene/polyvinylpyrrolidone nanoparticles(PS/PVP NPs)were prepared,and effects of different pH buffers and amounts of DA on the formation process and the morphologies of PDA were investigated.The morphology and size of the nanoparticles were analyzed by scanning electron microscope(SEM),transmission electron microscope(TEM)and Zeta potential and nanoparticle size analyzer.The results showed that DA oxidized to form PDA and deposited on the surfaces of the nanoparticles to form a dense PDA layer.As increasing the amount of DA,the thickness of the PDA layer deposited on the surface of the nanoparticles gradually increased.However,the thicknesses of the PDA layer deposited on the surfaces of the different nanoparticles were different.When the mass ratio of DA and the substrate nanoparticles in the system was 2:1,the PDA shell layer deposited on the surface of PS/PDMDAAC NPs reached 50 nm,while the thickness of PDA deposited on the surface of PS/PVP NPs was only 25 nm.This may be because PVP can form a strong non-covalent bond(hydrogen bond)with the catechol group,and then interfere with the formation of PDA by inhibiting the non-covalent assembly and covalent polymerization of DA.Then,the anion polystyrene/poly(acrylic 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 effects of different pH buffers,reaction times and amount of DA on the polymerization process and the PDA morphologies were investigated.Morphology and size of the nanoparticles were characterized by SEM,TEM and Zeta potential and nanoparticle size analyzer.The results showed that DA were 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 was 1:1.The formed PDA NPs became bigger with the higher DA contents and the longer reaction times.When the DA amount was large,it eventually formed a uniform PDA shell layer on the surfaces of the nanoparticles.In addition,the method of adding monomer DA did not affect the morphology of PDA on the surface of PS/PAA NPs,whether it was a one-time feeding method or a slow dropping method.Zeta potential result showed that the raspberry-like structure was formed due to the balance between electrostatic interaction and charge repulsion in the surface polymerization of PAA.While the larger amount of DA and the longer reaction time resulted in the reduction of charge repulsion,forming a dense uniform PDA shell layer.In order to further observe the influence of anions on the polymerization behavior of DA,polystyrene nanoparticles(PS/SDS NPs)with sodium dodecyl sulfonate on the surface were prepared by changing the ion types and chain segment compositions on the PS surfaces.It was found that a dense PDA shell layer was formed when DA polymerized on the surface of PS/SDS microspheres with low electronegativity and non-ionic PS microspheres.In other words,the surface charge intensity can indeed affect the polymerization of DA,and it is further proved that the strong charge repulsion in DA polymerization can reduce its deposition and polymerization on the surface of polymer microspheres.In summary,the electronegativity of the material surface can regulate the deposition of DA on its surface to prepare PDA composites with different morphologies.