The assembly of polyelectrolyte multilayer regulated by electrical control using conductive polymer

• Main Authors: Yan-rong Zheng, 鄭晏蓉
• Other Authors: Wei-wen Hu
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/47877952612160419331

碩士 === 國立中央大學 === 化學工程與材料工程學系 === 101 === To regulate the adsorption and the following release of polyelectrolyte on substrate, we developed external electric field to assist layer-by-layer (LbL) assembly in this study. Conductive polymer, polypyrrole, was utilized as the substrate, and DNA as well as chitosan was applied to deposit on the surfaces. To elucidate the effect of electricophoretic deposition, the electric field was solely administrated to chitosan or DNA adsorption. Chitosanase was used to degrade polyelectrolyte multilayers (PEMs) at different bilayer numbers, and the adsorbed chitosan and DNA may thus be quantified. The adsorption results demonstrated that LbL assembled DNA and chitosan can both be augmented under low electric field (0.1~0.2V). However, for the groups using electrical field during chitosan deposition, the improvement began to reduce at 0.5 V. It should be due to that the voltage approach to the reduction potential of dissolved oxygen in solution, and the increased hydroxyl ions decreased the charges on chitosan molecules to inhibit their adsorption. But when the voltage increased to 5V, the adsorption of chitosan was increased. It probably due to that the electrolysis significantly increased pH value to close to the pKa of chitosan, which chitosan precipitation on PEMs. The electrical field treatment during DNA deposition also revealed similar trends that using low voltage can increase deposition. However, the oxidization occurred when the voltage was high which resulted in proton release to decrease pH. Therefore, the charged density of DNA was decreased which decline DNA adsorption to PEMs. Then we soaked PEMs to PBS to determine their DNA release efficiency. Because electric-assisted LbL during DNA deposition highly increased DNA adsorption, their releases were thus also improved. However, this trend was not obvious to the chitosan groups. Interestingly, the group using 5V during chitosan deposition demonstrated highest release. It was consistent to our deduction that 5V led chitosan participation, which weakened the stability of PEM that the DNA can be released easily from loose structure. Finally, these films were illustrated by atomic force microscopy (AFM). When films were treated low voltage (0.1V and 0.2V) for chitosan deposition, surfaces were smoothened, suggesting that surface potential of substrate increased the contact of polyelectrolyte to surfaces that the defects of PEMs can thus be reduced. However, using high voltage increased the roughness of the films. It should be due to that the reduction of charge density of polylelectrolyte on PEM caused their configuration as coiled-form and thus the microstructure of PEMs was not as smooth as those using low voltages. In contrast, for electric field-treated DNA deposition, there was no obvious trend between voltage and roughness. We deduced that chitosan was extremely small compared to DNA, so the surface roughness mainly depended on DNA but not chitosan.