Layer-by-Layer Assembled Films With Large Dimensional Building Blocks

Layer-by-layer (LbL) assembly has been demonstrated to be a convenient and flexible method to fabricate functional film materials with precise control of chemical composition and architecture on micro-and nanoscales. Although the LbL assembly has gained great progress during the past two decades, the search for new building blocks for LbL film deposition has never been stopped. Building block is the foundation of LbL assembled films. The diversity of building blocks contributes to the fabrication of advanced and composite LbL assembled film materials. Up to now, various kinds of materials have been successfully incorporated into LbL assembled films, which greatly expands the application area of LbL assembled films. However, previous to our works, the building blocks used for LbL assembly mainly focus on small dimensional materials such as linear or branched polymer, small molecules, nanoparticles and so forth. There lacks systematical research on the fabrication of LbL assembled films with large dimensional materials. Meanwhile, how to realize the rapid fabrication of LbL assembled films especially for the one with micrometer-thick is still a big challenge for LbL assembly. Base on the above issues, in this dissertation, systematically investigation has been made to study the LbL film fabrication by using materials with large dimensions. We demonstrated that (1) rapid fabrication of LbL assembled films can be realized by using large dimensional materials as building blocks; (2) using polyelectrolyte complexes (PECs) as building blocks provide a facile way to the fabrication of functional film materials which can not be obtained by LbL assembly of uncomplexed polymers.In chapter 1, an introduction on the importance and challenges of LbL assembly has been provided. In general, the LbL assembly has been developed to be a mature technique to fabricate advanced film materials with various functions. However, it still faces some challenges. For example, it is generally a time consuming process to fabricate LbL assembled films especially for those with micrometer-thick. Therefore, novel facile methods for rapid construction of LbL assembled multilayer films are still highly desirable because of the importance of thick films in practice applications. Moreover, little attention has been paid to investigate the fabrication of LbL assembled films with large dimensional building blocks. In this dissertation, we use materials with large dimensions as building blocks to solve the problems mentioned above.In chapter 2, a LbL assembly process for the direct and rapid preparation of coatings which are micrometer-thick and macroporous was developed by alternate deposition of two kinds of oppositely charged PECs of poly(acrylic acid) (PAA)-Diazoresin (DAR) and DAR-poly(sodium 4-styrenesulfonate) (PSS). Upon UV irradiation, the electrostatic interaction within the coatings can be converted into covalently bonds, which improves the stability of the coatings. The rapid fabrication was realized because of the large dimensions of the building blocks. Meanwhile, the nondrying LbL deposition process also enables the highly porous film structures. When a N2 drying step is conducted after each layer deposition, it produces a thin and compact film without any porous structures. The macroporous coatings are proved to be highly efficient adsorbents for selective adsorption of cationic dyes. This work establishes a facile way to the fabrication of macroporous polymeric coatings.In general, there are both PEC particles and free polyelectrolytes in aqueous dispersions of PECs. In chapter 3, we take DAR-PAA dispersions as a typical example to elucidate the simultaneous LbL deposition behaviors of DAR-PAA complexes and the coexisted free polyelectrolytes DAR with oppositely charged PAA. Under a nondrying LbL deposition process, the codeposition of DAR-PAA complexes and DAR with PAA produces bilayered thick polymeric films with the hierarchical structures rooting in the underlying continuous films The hierarchical structures were mainly produced by the alternate deposition of DAR-PAA complexes with PAA, while the underlying continuous film was formed because the LbL assembly of free DAR and PAA. The two processes took place simultaneously, but the more rapid deposition of PAA/DAR-PAA coatings than that of the PAA/DAR films accounts for the formation of bilayered polymeric films. Moreover, the structure of the bilayered polymeric films can be finely tailored by changing the mixing ratio of DAR and PAA in dispersions. After chemical vapor deposition of a layer of fluoroalkylsilane, the bilayered polymeric coatings with hierarchical structures can be easily converted into stable superhydrophobic coatings.In chapter 4, the effect of salt on the structural tailoring of the LbL assembled polymeric films composed of PECs and oppositely charged polyelectrolyte were systematically investigate. (1) The structural tailoring of LbL assembled films by adding NaCl in PEC dispersions was studied. At pH 6.5, salt-containing poly(allylamine hydrochloride) (PAH)-PAA complexes can be LbL assembled with oppositely charged PSS to fabricate dewetting-induced porous PSS6.5/PAH-PAAm films. The structure of the PAH-PAA complexes is dependent on the concentration of NaCl added to their aqueous dispersions, which can be used to tailor the structure of the LbL assembled films. Porous films are fabricated when salt-containing PAH-PAA complexes with a large amount of added NaCl are used for LbL assembly with PSS. In-situ and ex-situ atomic force microscopy measurements disclose that the dewetting process composed of pore nucleation and pore growth steps leads to the formation of pores in the LbL-assembled PSS6.5/PAH-PAAm films. (2) The deposition behavior and film structural tailoring of PEC films by adding salt in polyelectrolyte was then systematically studied. At pH 9.3, PSS solutions with different NaCl concentration were LbL depositied with PAH-PAA9.3 complexes to fabricate PSSm/PAH-PAA9.3 films. The addition of NaCl in PSS solution can produce a rough film with hierarchical structures which can be well tailored as a function of NaCl concentration in PSS. The films with hierarchical structures can be easily converted into superhydrophobicity after chemical vapor deposition of a layer of fluoroalkylsilane.In chapter 5, the concept for rapid fabrication of LbL assembled films using large dimensional building blocks was further extended to realize the rapid fabrication of antifogging-and antireflection-integrated coatings. Herein, a rapid, straightforward and substrate-independent method for the fabrication of antireflection-and antifogging-integrated coatings was developed by LbL deposition of mesoporous silica (MSiO2) nanoparticles and poly(diallyldimethylammonium chloride) (PDDA). Quartz substrates covered with (MSiO2/PDDA)*3 coatings exhibit both antireflection and antifogging properties because the highly porous MSiO2 nanoparticles and their loose stacking in MSiO2/PDDA coatings enable the fabrication of superhydrophilic porous coatings with a low refractive index. A maximum transmittance of 99.9% in the visible spectral range is achieved for the (MSiO2/PDDA)*3 coatings deposited on quartz substrates. The rapid fabrication of the antireflection and antifogging (MSiO2/PDDA)*3 coatings is benefited from the large dimension and the fast adsorption kinetics of MSiO2 nanoparticles. Moreover, the antireflection and antifogging coatings can be conveniently deposited on daily used plastic substrates such as polycarbonate and Columbia resin CR-39. The facile, rapid and substrateindependent fabrication process and the easy availability of the MSiO2 nanoparticles promise the potential applications of the MSiO2/PDDA coatings on the production of eyeglasses, swimming goggles, periscopes, lenses in laparoscopic and gastroscopic surgery, and so forth.