Preparation Of Composite Micro-and Nanostructures Through Interfacial Adsorption And Self-Assembly Process

Nanoparticles exhibit particular optical, electric, and magnetic properties, and have extensive potential applications in catalyst, sensing, biomedicine, and biological ceramic etc. Nanoparticles with high surface-to-volume ratio are usually incorporated in matrices or immobilized on carriers to prevent them from aggregation. Polymers are often used as such matrix due to their chemical and thermal stabilities and easy processing ability. Nanopaticle/polymer composite structures have been fabricated by several approaches. This thesis adopted two facile and effective ways to fabricate inorganic species/polymer composite structures.(1), aqueous solutions of CuSO4, Cu(CHOO)2, and HAuCl4were used as the aqueous phases, and a chloroform solution of amphiphilic poly(2-vinylpyridine)(P2VP) was used as organic phase. When the liquid/liquid interface of the aqueous and organic phases formed, the polymer molecules adsorbed and aggregated at the interface, interacted with inorganic species and then self-assembled into composite structures.(2), a DMF/chloroform solution of polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-b-PAA-b-PS) and an aqueous solution of lead acetate or cadmium acetate form a planar liquid/liquid interface. An emulsion formed in the organic phase gradually with time, and became clear at last. In the meantime, a film appeared at the planar liquid/liquid interface.1. Polymer composite films doped with Cu nanoparticlesWhen the liquid/liquid interface of the chloroform solution of P2VP and the aqueous solution of cupric sulfate (CuSO4) or cupric acetate (Cu(CH3COO)2) formed, a thin composite film formed after15days. Transmission electron microscopic (TEM) investigation shows that microporous structure and nano-shuttles or microbelts were fabricated, respectively. X-ray photoelectron spectra (XPS) and X-ray diffraction (XRD) observation revealed that the nano-shuttles and microbelts are composed of Cu(OH)2when cupric acetate was used. The formation of Cu(OH)2should be attributed to the hydrolysis of Cu2+ions. When CUSO4aqueous solution was used, the protonated pyridine groups coordinate to Cu2+ions to form microporous structures. After treatment with KBH4aqueous solution, the particles transformed to Cu nanoparticles completely. The catalytic activity of the two composite films was evaluated by using the reduction of4-nitrophenol by KBH4in aqueous solutions. The result indicates that there is an incubation time for this catalytic reaction. This should be attributed to the oxidation of the copper nanoparticles in the composite film because the formed nanoparticles are very small and not protected by polymer well. These two composite films exhibit different catalytic behaviors. For the porous film, the apparent rate constant of the reaction increased and then decreased gradually with the used cycles, possibly resulting from the gradually outward diffusion and part leaching and/or aggregation of the incorporated Cu nanoparticles because the size of Cu nanoparticles is so small. Obviously, the film is not an ideal catalyst. The nano-shuttle and microbelt structures exhibited higher and durable catalytic activity.2. Polymer composite films doped with Au nanoparticlesWhen the liquid/liquid interface of the chloroform solution of P2VP and aqueous solution of HAuCl4formed, a free-standing and colourful thin polymer film was formed with time. The formation of the film was attributed to self-assembly of the polymer molecules at the liquid/liquid interface, and interaction between AuCl4-ions and the protonated pyridine groups. TEM investigations indicated that the films were composed of microsphere with the diameter of100-200nm and microcapsules, and nanoparticles exsited in these structures. XPS investigations revealed that two kinds of gold species, Au(0) and AuCl4ions with the relative contents of88%and12%, respectively existed in the film. The formation of Au(0) was ascribed to the reduction of AuCl4-ions by a small amount of ethanol which was used as stabilizer in chloroform. After treatment with KBH4aqueous solution, the AuCl4-ions transformed to Au nanoparticles completely, which was confirmed by UV-vis spectroscopy. Hermogravimetric analysis (TG) showed good thermal stability of the composite films, and the content of Au (0) was estimated to be28.9%. The catalytic activity of the composite films was evaluated by using the reduction of4-nitrophenol by KBH4in aqueous solutions. The results indicated that the composite film have high and durable catalytic activity, the Ea of the reaction was reduced to44.4kJ/mol. 3. Polymer composite films doped with PbS or CdS nanoparticlesAn aqueous solution of lead acetate or cadmium acetate and a DMF/chloroform solution of PS-b-PAA-b-PS form a planar liquid/liquid interface. The aqueous phase and the organic phase were called upper and lower phase, respectively. When the DMF/chloroform volume ratio of1:1was used, the lower phase changed from a clear organic solution to a cloudy dispersion and then to a clear solution again with time. This process was monitored using dynamic laser scattering (DLS) investigation. At the initial stage, the organic phase is clear, and the distribution peak indicates that only one kind of aggregate exists. The mean hydrodynamic diameter was found to be20-30nm. When the organic phase turns to be milky, a distribution peak with a mean hydrodynamic diameter of several hundreds nanometers appears, and the bigger particles is not stable enough. When the organic phase turns to be clear again, the bigger particles disappeared. As revealed by optical microscopic observation, freeze fracture transmission electron microscopic (FF-TEM) observation, and TEM investigation, the micelle formed in the organic phase, and the droplets were generated in the lower phase when the organic turned to be milky. A thin film formed at the liquid/liquid interface after the lower phase turned to be clear again. The TEM investigations reveal that the film is made up of microcapsules. The foam structure is a result of emulsion droplet-directed assembly and adsorption at the planar liquid/liquid interface. The XPS and FTIR observation indicate that metal ions, metal oxide or hydroxide resulting from the hydrolysis of the metal ions and the coordinated metal ions to the carboxyl groups coexist in the formed thin films, which transform to metal sulfide completely after treating with H2S to get quantum dot-doped polymer thin films. The volume ratios of DMF/chloroform have great effects on the film structure. When the volume ratio of3:1was used, the film is made up of interconnected nanotubes and nanospheres; when the volume ratio of1:3was used, round dots organized into a two-dimensional hexagonal close-packing array.