| Hydrogen bonding as the driving force of LbL self-assembled ultrathin films was first introduced by Zhang et al. and Rubner et al. almost simultaneously in 1997. In their work, a new concept was established for the fabrication of multilayer films by consecutively alternating the deposition of two kinds of polymers, one with hydrogen-bonding-donating groups and the other with hydrogen-bonding-accepting groups. Unlike electrostatically formed polyelectrolyte multilayers constructed in aqueous solutions, however, one of the advantages of the multilayers based on hydrogen bonding is that the formation of the LbL films can be also obtained in organic solvents, which opened a way for preparing multilayer structures using nonionic and water-insoluble polymers instead of water-soluble polyelectrolytes. The investigation of this dissertation is concentrated on the hot discussions in the hydrogen-bonding-directed LbL assembly of water-insoluble polymers. In chapter 2, we reported a way to fabricate microporous films by post-base treatment of hydrogen-bonding-directed multilayer films of poly(4-vinylpyridine) (PVPy) and carboxyl-terminated polyether dendrimer (DEN-COOH). The PVPy/DEN-COOH multilayer film was fabricated by layer-by-layer assembly of PVPy and DEN-COOH from a methanol solution. UV-visible spectroscopy revealed a uniform deposition process. The interaction between PVPy and DEN-COOH was identified as hydrogen bonding through Fourier transform infrared (FT-IR) spectroscopy. Meanwhile, the composition change of a PVPy/DEN-COOH multilayer film in a basic solution was detected by X-ray photoelectron spectroscopy and UV-visible spectroscopy, and the morphology variation was observed by atomic force microscopy. A two-step variation was observed: the dissolution of DEN-COOH from the multilayer into the basic solution and the gradual reconformation of PVPy polymer chains remaining on the substrate, which produced a microporous film. Interestingly, compared with our previous PVPy/poly(acrylic acid) (PAA) system, under the same conditions, the release of DEN-COOH from a PVPy/DEN-COOH multilayer is slower than that of PAA, and the microporous morphology is also different, which indicates that the molecular structure of a building block has a remarkable influence on the variation of a hydrogen-bonding-directed film in a basic solution. In chapter 3, we described the buildup of hydrogen-bonding-directed PVPy/poly(4-vinylphenol) (PVPh) multilayer film that was fabricated by LbL assembly of PVPy and PVPh from an ethanol solution. UV-visible spectroscopy and Fourier transform infrared (FT-IR) spectroscopy revealed a uniform deposition process. The interaction between PVPy and PVPh was identified as hydrogen bonding through FT-IR spectroscopy and temperature-dependent IR spectral changes of the hydrogen-bonded multilayer. Notably, we discussed the effect of solvent conditions on the growth of PVPy/PVPh multilayer films monitored by UV-visible spectroscopy. It was found that increasing the ratio of N,N-dimethylformamide (DMF) in the mixed ethanol/DMF solvents resulted in a marked decrease of the amount of polymers adsorbed, which was attributed to the increased polarity of the adsorption solutions. Furthermore, the solvent stability of PVPy/PVPh multilayer film in mixed ethanol/DMF solvents with different DMF ratios was also investigated. As a result, a new method for tuning the structure of hydrogen-bonding-directed multilayer film was developed. In chapter 4, we investigated the effect of density of hydrogen-bonding donor (HBD) on the formation of LbL assemblies of poly(4-vinylpyridine) and poly(4-vinylphenol). For this purpose, a series of ethyl-substituted poly(4-vinylphenol) (EsPVPhf) with variable ethyl substitute percentage was... |
PDF Full Text Request