The Variation Of A Hydrogen Bonding Directed Layer-by-layer Self-assembled Multilayer Films In A Base Aqueous Solution

The research of self-assembled multilayer films has attracted attention of scientists from all areas in recent years. Numerous materials, including charged and uncharged materials have been incorporated into multilayers by exploiting various techniques. In general, self-assembled multilayer films exist at the interfaces of gas/liquid or liquid/solid and are easy to achieve by self-assembly techniques. In 1991, G. Decher developed a way to fabricate multilayer structures which makes full use of the electrostatic interaction between cationic and anionic groups as driving force. This technique has been proven to be a rapid and experimentally very simple way to produce complex layered structures with precise control of layer composition and thickness. It is gradually recognized that the driving force for multilayer construction is not restricted to electrostatic interaction. Other kinds of weak interactions such as hydrogen bonding, co-ordination bonding, charge transfer, molecular recognition can also be explored for multilayer construction. The research work of this dissertation mainly focuses on two aspects: (1) fabrication of multilayer films of poly(acrylic acid) (PAA) /poly(2－vinyl pyridine) (P2VP) based on hydrogen bonding as driving force; (2) by selective dissolution of PAA component from the hydrogen-bonding directed PAA/P2VP films, a novel kind of microporous films were fabricated. The influence of molecular weight of P2VP on the formation of porous films was investigated. Meanwhile, microporous films prepared from PAA/P2VP and PAA/P4VP (brief name of poly (4-vinylpyridine)) was compared, which will be helpful to understand how to tune the pore structure by simply changing the original film components.In chapter II, multilayer films of PAA/P2VP were successfully prepared based on hydrogen bonding as driving force. The assembly process was monitored by UV-Vis spectroscopy and an uniform film deposition process was confirmed. Fourier transform infrared (FTIR) spectroscopy shows that the driving force for multilayer deposition is hydrogen bonding interaction. The surface of the as-prepared PAA/P2VP films was quiet smooth as confirmed by atomic force microscopy and x-ray diffraction patterns which show a series of Kiessig. The thickness of PAA/P2VP films was calculated form the x-ray diffraction patterns. The average thickness of one bilayer of PAA/P2VP films prepared from the low and high molecular weight of poly (2-vinylpyridine) (noted as LP2VP and HP2VP) is almost the same as confirmed by the UV-Vis spectroscopy and X-ray diffraction.In chapter III, a novel microporous film was fabricated by immersion of the PAA/P2VP films in basic aqueous solutions. Our study indicates that the variation of a PAA/P2VP film in a basic solution underdoes two steps. At the beginning of the immersion, the basic solution breaks the hydrogen bonding interaction between the neighboring layers, which results in the leaving of the soluble poly(acrylic acid) from the multilayer films into the solution. Afterwards,the prolonged immersion time induces the re-conformation of the remaining poly(2-vinyl pyridine) on the surface under the effect of the basic solution, which brings out the observed microporous suface morphology. FTIR spectra of the PAA/P2VP films before and after the immersion into the basic solution show that the leaving of the soluble poly (acrylic acid) from the multilayer film into the solution is quiet rapid, as previously observed for the hydrogen-bonding directed multilayer films of PAA/P4VP. AFM images of PAA/HP2VP and PAA/P4VP films indicate that the speed of configurational change of HP2VP is faster than that of P4VP in their corresponding films although the molecular weight of HP2VP and P4VP is in the same order. This might be that the configuration of LP2VP in PAA/P2VP film is easier for configurational change than that of P4VP in PAA/P4VP film. While for the films of PAA/LP2VP and PAA/LP2VP, the configurational change of HP2VP is faster than that of LP2VP. When considering the fact that...