Studies On The Fabrication And Properties Of Organic-inorganic Composite Films With Layered Structure

Recently, organic-inorganic composite materials have attracted much attention in catalysts, photovoltaic devices, biological nanotechnology as well as energy storage and conversion, owing to their unique properties which can not be obtained in the individual component. In this dissertation, a series of functional thin film materials have been fabricated by using layered double hydroxides (LDHs) as host material and azobenzene-containing polymer (PAZO), poly(sodium styrene 4-sulfonate) (PSS), cobalt phthalocyanine (CoPcTs) and poly(vinyl alcohol) (PVA) as guest molecules respectively. The properties of the resulting films (including photoswitching, antireflection/antifogging, electrochemical sensor and mechanical properties) were investigated in order to explore novel organic-inorganic composite materials. The relationship between the superlattice structure, molecular orientation, host-guest interactions and the performance of the composite films was revealed by a combination study based on experimental techniques and molecular dynamics simulation. The framework of this study are shown below. The main results of this thesis are as follows:1. Unilamellar, positively charged LDHs nanosheets were obtained by delaminating highly crystalline M(II)A1-NO3 LDHs (M=Co, Ni, Mg) in formamide. By using these LDHs nanosheets and PSS as building blocks, a series of heterogeneous ultrathin films were fabricated via electrostatic layer-by-layer (LBL) technique. Taking into account the highly tunable compositions of LDHs nanosheets, the fabrication strategy of heterogeneous ultrathin films opens avenues for their applications in the fields of catalysts, sensors and photovoltaic devices.2. The (LDHs/PAZO)n multilayer films with photoswitching properties were fabricated, in which azobenzene chromophore exhibits reversible photoisomerization. The isolation effect of LDHs nanosheets imposes enough free volume for the photoisomerization of the azobenzene group in PAZO, accounting for its complete trans-cis isomerization (isomeric ratio:～100%) as well as high reversibility (isomeric ratio for cis-trans:-51%) and reproducibility. These multilayer films can be potentially applied in the fields of photoresponsive coatings, molecular switch and optical information storage.3. Multilayer films containing exfoliated LDHs nanosheets and CoPcTs were assembled using the LBL technique on ITO substrates, which exhibit a broad linear response range (2.0×10-5～1.4×10-4 mol/L), low detection limit (3.2×10-7 mol/L) and fast response (2 s) for the detection of dopamine. The long range order stacking of organic-inorganic species facilitates the electron transfer between CoPcTs and the underlying electrode. This work provides a novel approach to immobilize electroactive molecule into inorganic layered matrix, for the purpose of technological applications in electrochemical analysis and biodetection.4. The mixed metal oxide (MMO) coatings with antireflection (AR) property were fabricated via LBL deposition of LDHs nanoparticles with PSS on quartz glass substrates followed by calcination. The AR property of MMO films is related to the low refractive index originating from the nanoporous structure. Significantly, the AR property can be switched on and off between the porous (MMO film) and non-porous state (LDHs film) based on the "reconstruction effect" of LDHs materials. The AR/antifogging (AF) multifunctionality of MMO films was further investigated. A maximum transmittance of 98.7% at 650 nm and a minimum time of 0.2 s for a droplet to spread flat (water contact angle～0°) were achieved by tuning the film thickness, porosity and surface toughness. These multifunctional coatings can be potentially used in photovoltaic devices, eyeglasses and lenses in endoscopic surgery.5. Inspired by the biomineralization process, we obtained organic-inorganic composite films with simultaneously enhanced strength and ductility by using LDHs nanoplatelets and PVA as building blocks. The combination of strength and toughness was accomplished by delicately tailoring inorganic platelets with a specific aspect ratio (16～22), enhancing compatibility at the nanoscale level as well as incorporating strong interfacial interactions between organic and inorganic components. Further extension of the present strategy should allow access for the fabrication of hybrid materials with applications in gase barrier, magnetic films and biomedical membrane.