Poly (ethylene terephthalate) (PET)-silica (SiO2)/polystyrene (PS) nanocomposite films were prepared by melting PET with the core-shell SiO2/PS nanoparticles. Differential scanning calorimetry (DSC) results showed that the crystallization temperature of PET-SiO2/PS nanocomposite films with 2 wt.% PS-encapsulated SiO2 nanoparticles reached 205.1 °C, 11.6 °C higher than that of PET. For crystallized PET-SiO2/PS nanocomposite films, double melting peaks appeared in DSC curves similar to PET. Scanning electron microscopy revealed a netlike fibre morphology for the amorphous PET-SiO2/PS nanocomposite films with 2 wt.% PS-encapsulated SiO2 nanoparticles. The light transmittance of these amorphous PET-SiO2/PS nanocomposite films reached 87.9%, compared to 84.2% for PET. With the increase of annealing temperature from 110 to 150 °C, the transmittance of PET-SiO2/PS nanocomposite films decreased slowly from 69.9 to 46.9%, while their haziness increased slightly from 45.8 to 48.2%. All these phenomena are suggested to result from the strongly heterogeneous nucleation of PS-encapsulated SiO2 nanoparticles in PET. 相似文献
Silica (SiO2) nanocomposite spherical particles coated with polyimide had been synthesized by a dispersion polymerization method. The chemical structure of polyimide/silica (PI/SiO2) nanocomposite spherical particles was investigated by using FT-IR, and the surface morphology characterization was performed with SEM. The TEM showed that SiO2 core was surface-coated with a multilayer composite and the multilayer thickness was about 20 nm. Moreover, the particles were homogeneously distributed and interconnected very fine. Basing the results, it was found that the PI/SiO2 nanocomposite particles were core–shell structure. 相似文献
A novel process for polyethylene terephthalate (PET) surface modification with a silica-like thin layer is proposed. 3-Aminopropyltrimethoxysilane was employed to react with acetone to form dimethyliminopropyltrimethoxysilane (DIPTMS) after aging for 10 days at room temperature. After hydrolysis of alkoxy groups in DIPTMS, dimethylimine-modified silica clusters occurred resulting in an increase of the solution viscosity. Consequently, a dense and homogeneous thin layer was easily dip-coated onto a PET film. After heat treatment at 150 °C, a smooth, flexible and transparent silica-like film (about 70 nm thick) was formed via dehydration and condensation. The surface of the PET dramatically changed from hydrophobic (water contact angle: 70±2°) to hydrophilic (45±3°). As an attempt for application, a dense film of lithium metasilicate (Li2O·2SiO2·nH2O) was successfully prepared by dip coating on the modified PET film, which appeared very low oxygen permeability of about 0.17 cm3/m2 day atm at 23 °C and 85% humidity. 相似文献
Developing high dielectric performance of polymer nanocomposites is still a long-standing issue to simultaneously inherit the high dielectric constant of nanofillers and maintain the high breakdown strength of polymer matrix. In the current study, a tri-layered nanocomposite film is fabricated by a simple and effective solution-casting and dip-coating method, where graphene oxide nanosheets (GONSs) were modified by insulating SiO2 layer (SiO2@GONSs) and polyvinylidene fluoride (PVDF)/SiO2@GONS nanocomposite inner layer was sandwiched by polycarbonate (PC) layers. The surface modification could minimize the local electric field concentration and block conductive path. Furthermore, the sandwich or tri-layered structure inhibited the relaxation and migration of space charge or impurity ions and suppressed the charge injection, thus achieving enhanced breakdown strength and discharged energy efficiency. As a result, the as-prepared tri-layered nanocomposite film exhibited a dielectric constant of 5.2 and a low dielectric loss (tanδ) of 0.013 at 1 kHz, and breakdown strength of 219 MV m?1, which was significantly higher than single-layered nanocomposite films and its counterpart without SiO2 modification. The corresponding discharged energy density was 1.20 J cm?3 with an excellent efficiency of 86.2% at 200 MV m?1. More interestingly, the insulating SiO2 modification layer and PC outer layers could also effectively restrict the relaxation or migration of impurity ions at a high temperature of 120 °C, endowing excellent high-temperature dielectric performance to the as-prepared tri-layered nanocomposite film. The combination of surface modification and sandwich structure opens up an avenue to fabricate GONS-based dielectric nanocomposites with low dielectric loss, high breakdown strength, high efficiency and high temperature tolerance.
Sole components of titania (TiO2), silica (SiO2) nanoparticles, and binary TiO2–SiO2 nanocomposites with various molar ratios of silica contents were prepared by modified sol–gel method. The samples were calcined at 500 °C for 5 h and characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, Brunauett–Emmett–Teller (BET), and photoconductivity. The crystallite size for TiO2/SiO2 nanocomposites was calculated using Scherrer’s formula and found to be 5 nm for TiO2 nanoparticles. The binary oxide shows the anatase type of TiO2 at the mole ratio up to 80 mol% of TiO2 added. The band gap for as-synthesized nanocomposites was calculated and it was found that the band gap decreases with increase of SiO2 content and then decreases with excess SiO2 content. FTIR confirms that both TiO2 and SiO2 phases have been formed. The BET surface area for TiO2/SiO2 nanocomposite is found to be 303 m2/g, and pore size distribution has an average pore diameter about 10 nm for 40 mol% of TiO2 added. It also confirms the absence of macropores and the presence of micro and mesopores. The field-dependent dark and photoconductivity studies reveal that the dark and photocurrent increase linearly with applied field confirming the ohmic nature of the electric contacts. The dark and photocurrent increase slightly with increase of SiO2 content and decrease with excess amount of SiO2. 相似文献
The photoactive SiO2/WO3–TiO2@rGO nanocomposite was fabricated through sol–gel, microwave, and hydrothermal approaches for the photodegradation of methylene blue (MB) as an organic-colored pollutant. The nanocomposite photocatalysts were formulated by adjustment of the ingredients content to achieve efficient synergic effects on photocatalyst performance. The results exhibited that optimum amount of SiO2 and rise in WO3/TiO2 ratio as well as incorporation of reduced graphene oxide in structure can be led to further efficiency of degradation under visible light. The effect of sunlight irradiation, pH of MB solution, MB concentration, and lamp distance on photodegradation reaction were also investigated. The best performance about 99.9% MB degradation was obtained based on using 0.3 g/L of optimum photocatalyst to remove the 5 ppm MB solution with pH of 5.41 during 3 h irradiation by visible-light source with 30 cm distance from MB solution. As well, results showed that photocatalyst performance under visible light is better than sunlight irradiation. The most favorable photocatalyst indicated surface area of 60.9 m2/g. Furthermore, the reusability test indicated a proper activity after three cycles under the same conditions. So, the introduced efficient visible photoactive SiO2/WO3–TiO2@rGO nanocomposite can be considered as an appropriate potential to remove organic pollutants in colored effluents.
A new kind of superparamagnetic luminescent nanocomposite particles has been synthesized using a modified Stöber method combined with an electrostatic assembly process. Fe3O4 superparamagnetic nanoparticles were coated with uniform silica shell, and then 3-aminopropyltrimethoxysilane was used to terminate the silica surface with amino groups. Finally, negatively charged CdSe quantum dots (QDs) were assembled onto the surface of the amino-terminated SiO2/Fe3O4 nanoparticles through electrostatic interactions. X-ray diffraction (XRD), transmission electron microscopy (TEM), microelectrophoresis, UV-vis absorption and emission spectroscopy and magnetometry were applied to characterize the nanocomposite particles. Dense CdSe QDs were immobilized on the silica surface. The thickness of silica shell was about 35 nm and the particle size of the final products was about 100 nm. The particles exhibited favorable superparamagnetic and photoluminescent properties. 相似文献
Hybrid organic-inorganic materials, silica-poly(ethylene glycol) (PEG) blends, were prepared by the sol-gel process from mixtures of tetraethoxysilane and PEG of low molecular mass. The synthesis scheme (acidic [HCl] or nucleophilic [NH4F] catalysis) influences the structure of these materials and consequently their properties. Two different methods were used to investigate the structure of these blends: a) X-ray diffraction techniques; b) 29Si NMR spectroscopy. A new x-ray diffractometry technique identifies precise interference functions and radial distribution functions of these blends. The comparison of predicted radial distribution functions of the Bell and Dean's physical model refined by Gaskell with the radial distribution function obtained from this technique is implemented to identify the structure of these blends. Analysis by amorphography has identified the existence of SiO2 silica grains and provides only about the positional disorder of these grains in continuum random network. The NMR spectroscopy discriminates the different silicon sites and demonstrates the changes of the morphology and structure when the nature of the catalyst is modified. These results indicate that the structure of non-crystalline SiO2 aggregates inside nanocomposites differs from fused glass by their compositional disorders. These nanocomposites could be described as an agglomerate of SiO2 objects with the pores filled by disordered polymer chains. When these materials are obtained under acidic conditions, the polymer chains are linked to the SiO2 grains forming an ideal composite. 相似文献
