Multi-Function Integrated Layer-by-Layer Assembled Multilayer Films

The layer-by-layer (LbL) assembly technique has been proven to be a promising method to fabricate various kinds of coatings with well-tailored chemical compositions and architectures on the micro- and nanoscales. The LbL assembly technique for coating fabrication mainly involves multiple dipping, water rinsing and drying steps, which is easy for large-scale production. The versatility of the LbL approach has allowed a broad range of materials (e.g., polymers, nanoparticles, lipids, proteins, dye molecules) to be assembled on various substrates, on the basis of not only electrostatic interactions but also hydrogen bonding, hydrophobic interactions, covalent bonding, and complementary base pairing. During the past decades, although much attention has been paid on this effective multilayer fabrication method, it remains a big challenge for the fabrication of the functionalized especially the multi-funcion integrated LbL assembled multilayer film. In this dissertation, we focus on the fabrication of multi-function integrated LbL assembled films, mainly includes the following aspects:In Chapter 2, a facile method for preparing a superhydrophobic surface was first developed by layer-by-layer deposition of poly(diallyldimethylammonium chloride) (PDDA)/sodium silicate multilayer films on a silica-sphere-coated substrate followed with a fluorination treatment. First, a silica-sphere-coated substrate that contains loosely stacked silica spheres of 600 and 220 nm was prepared and cross-linked with SiCl4. PDDA was then alternately assembled with sodium silicate on the silica-sphere-coated surface to prepare a micro- and nanostructured hierarchical surface. After chemical vapor deposition of a layer of fluoroalkylsilane, a superhydrophobic surface with a water contact angle of 157.1°and sliding angle of 3.1°was successfully fabricated. Then, we extend this method of fabrication of a superhydrophobic surface to the preparation of a broad-band superhydrophobic antireflective (AR) coatings in near infrared (NIR) region. The introduction of superhydrophobicity endows the AR coating with the water-repellent ability and makes the resultant AR coating applicable under humid environments. Additionally, the present method for preparing superhydrophobic AR coatings has the advantage of simplicity in fabrication, easy availability of the materials, and applicability to prepare large area coating on non-flat surface. Potential applications of this kind of superhydrophobic AR coatings in areas such as NIR analysis, NIR sensors and so forth are highly anticipated.In Chapter 3, we reported a facile and cost-effective method for the fabrication of mechanically stable antireflection and antifogging silica coatings by LbL deposition of PDDA&silicate complexes with PAA on quartz substrates followed by calcination. Calcination removed the organic components in PAA/PDDA&silicate multilayer films and introduced three-dimensional nanopores in the resultant silica coatings. In this way, highly porous silica coatings with a reduced refractive index and superhydrophilic properties can be fabricated simultaneously, which can be used as multifunctional AR and antifogging coatings. Calcination cross-linked the resultant silica coatings via the formation of stable siloxane bridges, which endows the AR and antifogging coatings with high mechanical stability and excellent adhesion to the substrates. We believe that the AR and antifogging silica coatings with a high durability can be widely useful in the production of eyeglasses, swimming goggles, periscopes, lenses in laparoscopic and gastroscopic surgery, and so forth.In chapter 4, we developed a facile and cost-effective method to the direct fabrication of highly porous TiO2 coatings by non-drying LbL deposition of sodium silicate and TiO2 nanoparticles without any post treatment. The rigid nature of sodium silicate and the non-drying LbL deposition process are critically important to prohibit the self-healing and lead to the formation of porous TiO2 coatings. Meanwhile, the present method is suitable for the fabrication of large-area porous TiO2 coatings on substrates with complicated morphologies. The as-fabricated porous TiO2 coatings, which can be easily recovered through UV irradiation for recycling usage, show a good ability to remove organic pollutants in wastewater because of their high porosity. The present study creates a novel route of using rigid building blocks and non-drying LbL assembly to prohibit self-healing for the direct fabrication of porous coatings, which we believe to be useful to fabricate other kinds of functional porous coatings.