Layer-by-layer Assembled Functional Films Of Polymeric Complexes

Layer-by-layer (LbL) assembly, which was developed by Decher and co-workers in the early 1990s, has emerged as a group of versatile and convenient methods for the construction of layered composite films with precise control of film thickness and composition. The LbL assembled films can find multiple applications in areas such as antireflection coatings, superhydrophobic surfaces, nonlinear optics, biosensors, cell adhesion or resistance coatings, drug delivery systems, proton exchange membrane, solar-energy conversion, separation membranes, and so forth. The search for new building blocks is a prerequisite for the fabrication of LbL assembled advanced functional film materials, which is of the same importance as the exploration of driving force for LbL assembly technique. Meanwhile,there are still some challenges for the LbL assembly technique, for example, rapid fabrication of thick LbL assembled films, the LbL assembly of noncharged organic molecules, the homogeneous dispersion of inorganic nanofillers in polymeric LbL assembled films, and so forth. Based on the above mentioned issues, in this dissertation, polymeric complexes were taken as building blocks for the fabrication of LbL assembled films, mainly including the following three parts:In chapter 2, a facile method for rapid fabrication of micrometre-thick films with hierarchical micro- and nanostructures was developed by layer-by-layer (LbL) deposition of hydrogen-bonded complexes of poly(vinylpyrrolidione) (PVPON) and poly(acrylic acid) (PAA) (denoted PVPON&PAA) with poly(methacrylic acid) (PMAA). A non-drying film preparative process was critically important to realize the rapid fabrication of PVPON&PAA/PMAA films with hierarchical micro- and nanostructures because the structure of the adsorbed spherical PVPON&PAA complexes can be well preserved during film fabrication which led to an exponential growth of the PVPON&PAA/PMAA films. After chemical vapor deposition of a layer of fluoroalkylsilane on top of the as-prepared PVPON&PAA/PMAA films with hierarchical micro- and nanostructures, superhydrophobic coatings were conveniently fabricated. The use of polymeric complexes as building blocks for LbL film fabrication not only provides a facile method for the rapid fabrication of micrometre-thick films, but also enables the convenient tailoring of film structures because of the structural diversity of polymeric complexes in solution.In chapter 3, noncharged pyrene molecules were incorporated into multilayer films by first loading pyrene into poly(acrylic acid) (PAA)-stabilized cetyltrimethylammonium bromide (CTAB) micelles (noted as PAA-(Py@CTAB)) and then layer-by-layer (LbL) assembled with poly(diallyldimethylammonium chloride) (PDDA). The stable incorporation of pyrene into multilayer films was confirmed by quartz crystal microbalance (QCM) measurements and UV-vis absorption spectroscopy. The resultant PAA&(Py@CTAB)/PDDA multilayer films show an exponential growth behavior because of the increased surface roughness with increasing number of film deposition cycles. The present study will open a general and cost-effective avenue for the incorporation of noncharged species, such as organic molecules, nanoparticles, and so forth, into LbL-assembled multilayer films by using polyelectrolyte-stabilized surfactant micelles as carriers.In chapter 4, we report an innovative and straightforward method to well-disperse a low loading content of inorganic nanofillers of extremely small size in exponentially growing layer-by-layer (LbL) assembled micrometre-thick polymeric coatings. Complexes of poly(acrylic acid) (PAA) and in situ synthesized CaCO3 nanoparticles (noted as PAA-CaCO3) were alternately deposited with poly(allylamine hydrochloride) (PAH) to fabricate exponentially growing PAA-CaCO3/PAH coatings. The ultrafine CaCO3 nanofillers with a size of ~2 nm were homogeneously dispersed in the hybrid PAA-CaCO3/PAH coatings because of the strong interaction of CaCO3 nanofillers with PAA and the''in-and-out''diffusion of the polyelectrolytes during the LbL assembly process. Thermogravimetric analysis indicates that the PAA-CaCO3/PAH coatings have a loading content of ~4.2 wt% CaCO3 nanofillers. The thermally cross-linked PAA-CaCO3/PAH coatings, which have greatly enhanced hardness and Young's elastic modulus because of the well-dispersed CaCO3 nanofillers, are highly transparent and scratch-resistant. The transparent and scratch-resistant PAA-CaCO3/PAH coatings are further proved to be highly useful as scratch-protection layers of other functional film materials. The present study provides a convenient and rapid method to prepare mechanically robust and transparent coatings for various applications.