The Study Of Carboxymethyl-Chitosan Self-Assembled Films By Atomic Force Microscopy

Attributed to the convenient adjustability of structure and function, the electrostatic self-assembled film has attracted a lot of interest in the field of control release, ultra thin porous films'fabrication and surface patterning. In the last decade, most of the relevant studies on self-assembly of weak polyelectrloytes focoused on the synthetic or natural macromolecules which have only one protonatable/deprotonatable group. Studies on the self-assembly of polyampholyte is quite rare. Carboxymethyl-chitosan, a derivative of chitosan, is a typical polyanpholyte, which is introduced the carboxymethyl group to C6 site while maintaining the amino group in C2 site. Thus, the electric property of carboxymethyl-chitosan can be inversed easily by adjusting the concentration of proton. Obviously, architecture electrostatic self-assembled film from carboxymethyl-chitosan by LBL technique not only an important complement to the theoretic study but also an impetus to the practical application. In this paper, we choose mica as substrate, the effect of pH value of carboxymethyl-chitosan aqueous and rinse bath to the structure and morphology of carboxymethyl-chitosan self-assembled monolayer were investigated thoroughly by atomic force microscopy. In addition, the effect of preparation condition of carboxymethyl-chitosan self-assembled monolayer to the adsorption of surface charged polystyrene/acrylic acid nanospheres was studied. The main results are as follows:1.Polystyrene, polystyrene/acrylic acid nanospheres was prepared by emulsion polymerization. The morphology analysis by AFM indicates that the nanospheres are approximately monodisperse while the surface is clean and the shape is regular. "Profile analysis" indicates that the diameter of nanospheres increased with the content of acrylic acid decreasing; IR spectrum shows that the co-polymerization of styrene and acrylic acid is successful.2.A series of carboxymethyl-chitosan self-assembled monolayers were prepared in carboxymethyl-chitosan aqueous with different concentration of proton. The morphology analysis by AFM indicates that the thickness of monolayer increases gradually and the morphology develops to a homogeneous structure from the original "sea-island" structure with increasing the concentration of proton. The monolayer obtained with a pH value of 1.7 has a perfect morphology. The roughness of surface is less than 1.0 nm.3.The induction of rinse bath pH value to the morphology of monolayer is significant. The theoretical approximation indicates that the molecules source for the formation of "aggregates" and "crater" are the non-specific adsorbed carboxymethyl-chitosan molecules.4.The "crater" structure can be observed when the pH value of rinse bath in the rangs of 2.2-3.2 to the monolayer obtained with a 1.7 pH value. After a 24h immersion in aqueous with a 7.0pH value, the "crater" structure disappears while the compaction of monolayer decreses. However, the monolayer is still homogeneous, which provide a guaranty to the subsequent electrostatic adsorption.5.The studies of adsorption kinetics show that the most apprapriate ionic concentration for PS nanospheres adsorption is 0.5mol/L, and the equilibrium adsorption time in 25℃is 20min. The higher adsorption temperature induces a higher coverage rate. The maximal coverage rate is 65.0% in this work and the corresponding process of fabrication is:a 10 min self-assembly in carboxymethyl-chitosan aqueous with a pH value of 1.8→rinsed by aqueous with a pH value of 2.8→a 20min drying in vacuum (30℃)→a 20min adsorption in PS nanosphere emulsion while the concentration of salt, pH value of emulsion and temperature are 0.5mol/L,6.0 and 60℃→rinsed by aqueous with a pH value of 6.0→a 20 min drying in vacuum (30℃).