| Layer-by-Layer self-assembly introduced by Decher in the early1990’s is the most promising method to fabricate ultrathin film. This technique enables the development of complex heterostructures and the control of thickness and surface properties at the nanoscale level by changing the proces parameters. This self-assembled film has attracted a lot of interest due to the potential application in the field of micropatterning, porous bomedical thin films or membranes, and bioinert implant coatings, among many others. Chitosan, an unique naturally occurring polycation, shows many advantages over other synthetic polycations including biocompatibility, biodegradability, nontoxicy, antibacterial activity, and procoagulation activity. It can be assembled to fabricate thin films with many other polyanions. If the polyanion used is also naturally occurring polysaccharide, this polysaccharide LBL film can be used as biomaterial without evoking any negative response.The tailored nanostructure chitosan films can be widely used in many biomedical fields, inclding useful bioinert implant coatings, porous biomedical thin films or membrances, controlled release systems, and substrates for biosensors. It can provide theoretical foundation and practical direction for the fabrication of tailored functional chitosan ultrathin films in the future. In this thesis, The effect of pH and NaCl concentration of polyelectrolyte solution on the growth of CMC/CHI film was investigated by quartz crystal microbalance, and the nonline growth mechanism was also discussed using diffusion model. A detailed surface morphology was observed using atomic force microscopy step by step to study the effect of pH and NaCl concentration of polyelectrolyte solution on the morphology evolution as the number of bilayers increased. The main results are as follows:1. Only soluble polyelectrolyte complexes exist in solution(no turbidity), suggestint that the multilayer assembly at pH below2.0would be prohibited. The growth mechanism is exponential independent of the pH in the range of2.0-5.0, which is due to the in and out diffusion proces of CHI chain.2. The adsorption amount of one bilayer increased first when the pH below3.0and then decreased after the pH beyond3.0, indicating that the deposited amount per bilayer at pH3.0is higher than other three pHs. At low ionic strength, the increase in ionic strength results in a more adsorption amount, whereas the deposited amount decreases at NaCl concentration above0.2M. The effect of pH is more significant.3. The multilayer buildup of CMC/CHI was comprised of two distinct regimes. When the films are prepared at pH=3.0and pH=4.0、0.1M NaCl, the first regime, whose relevant number of bilayers is4and6, respectively, was mainly characterized by islet number increase, whereas the second regime involves islet growth with rough surface. Compared with multilayer film prepared at pH=3.0and pH=40、0.1M NaCl, the film buildup mechanism at pH=4.0is quite different. the first regime,8bilayers, was characterized by isolated islet growth with number of bilayers, whereas the second regime involves a more continuous film construction and the surface is more smooth.4. Changes in soultion pH have a stronger effect than that in solution NaCl concentration. The pH=3.0flim has larger islets with the diameter of2μm, and height of700nm at the number of15bilayers. While the diameter of islets on pH=4.0film with15bilayers is80nm, and the height is about80nm. The islets on pH=4.0、0.1M NaCl film have medium size, which is600nm in diameter and200nm in height. The Rms of these films are150nm,20nm, and50nm, respectively.5. Methylene blue absorbance study showed that the formation of the multilayers is driven by the overcompensation of charge at the surface of the multilayer. The contact angles of pure CMC and CHI films are45°and75°, respectively. When CMC is the outermost layer (60°) the pH=4.0surface is mixed with previous CHI chains. While CHI is the outermost layer the surface (75°) is dominated by CHI segment. |
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