Layer-by-layer Assembled Antibacterial And Free-standing Films

In the past decade, the layer-by-layer (LbL) assembly technique has been proven to be a versatile method to fabricate multilayer films with well-tailored architectures and compositions on the nano- and micro-scales. The LbL deposition technique introduced in the early 1990s by Decher is a versatile technique to fabricate multilayer films, which has attracted an increasing number of researchers in recent years due to their wide range of potential applications in the fields of biomedical materials, tissue engineering, regenerative medicine, antireflective coatings, anti-foggy coatings, antifouling coatings, protective (anti-corrosion and scratch-resistant) coatings, chemical or bio-sensors, optical and electronic devices, separation films, and so on. The versatility of the LbL assembly has allowed a large numbers of materials (e.g., polymers, nanoparticles, proteins, dendrites et al.) to be assembled, on the basis of electrostatic interactions, hydrogen bonding, covalent bonding, and so on. The procedure is simple and in principle applicable to many different kinds of substrates. It is still a big challenge for fabrication of potential useful multilayer films in the past 20 years. In this thesis, we mainly focus on the fabrication of antibacterial films, high-strength free-standing films and ion separation free-standing films.In chapter 2, we reported a facile method to directly fabricate antibacterial coatings on hydrophobic plastic surfaces by layer-by-layer deposition of cross-linked poly (allylamine hydrochloride) and dextran microgels containing silver nanoparticles (Ag@PAH-D) with poly (sodium 4-styrene sulfonate) (PSS). The as-prepared Ag@PAH-D/PSS microgel multilayer films were effective in prohibiting the growth of Escherichia coli. The antibacterial activity of the Ag@PAH-D/PSS microgel multilayer films could be easily controlled by tailoring the number of coating deposition cycles. The antibacterial coatings of Ag@PAH-D/PSS microgel films were stable and had satisfactory adhesion to the underlying plastic substrates, which guarantee the long-term application of the coatings.In chapter 3, free-standing films of diazonium resin (DAR)/poly (acrylic acid) (PAA) with excellent mechanical stability were released from substrates by an ion-triggered exfoliation technique. After UV light cross-linking, the electrostatic interactions of the LbL assembled DAR/PAA film were translated into covalent bonds, which improves the stability of the DAR/PAA film. Tow kinds of exfoliation methods have been used to produce free-standing DAR/PAA multilayer films. Although it takes a relatively long time for the DAR/PAA films to exfoliate from the substrate when using 1M NaCl solution as the exfoliation solution, the as-prepared free-standing film has an excellent mechanical stability with the ultimate tensile strength and Young's modulus being 353.3±100.2 MPa and 24.5±5.3 GPa, respectively. On the contrary, the exfoliation time is relatively short when using pH 11 NaOH as the exfoliation solution. However, the mechanical strength of the free-standing films released in NaOH. The underlying mechanisms of ion-triggered exfoliation technique were investigated in detail.In chapter 4, we developed a facile method to prepare ion-permselective films by layer-by-layer deposition of poly (acrylic acid)-tannic acid (PAA-TA) complex with poly (allylamine hydrochloride) (PAH). The PAA-TA/PAH multilayer films were peeled off from substrates in alkaline aqueous solution after thermal cross-linking to form free-standing films. The free-standing films had uniform holes after thermal cross-linking, which were permeable for small positively charged ions and impermeable for both negatively charged ions and large positively charged ions. The free-standing PAA-TA/PAH film with high mechanical strength would be used for filtration and separation without the supporting substrates.