The precursor ZrW1.6Mo0.4O7(OH)2(H2O)2 was characterized by IR and XRD methods. δ′-ZrW1.6Mo0.4O8 was prepared by careful controlling the annealing conditions from the precursor and was determined to have the formula as o-ZrW1.6Mo0.4O8·H2O by TG-DSC, IR, and XRD methods. The relation between o-ZrW1.6Mo0.4O8·H2O and o-ZrW1.6Mo0.4O8 was discussed through variable temperature XRD patterns. Further more, the mechanism of the precursor dehydration was suggested. 相似文献
IntroductionIn the past two decades, because of its potentialindustrial applications, organic-inorganic compositeshave attracted the attention of both researchers andacademicians. Organic-inorganic hybrids offer the pos-sibility to combine both the advant… 相似文献
A series of W/O/W or O/W/O emulsion stabilized solely by two different types of solid nanoparticles were prepared by a two-step method. We explored the option of particular emulsifiers for the multiple Pickering emulsions, and a variety of nanoparticles (silica, iron oxide, and clay) only differing in their wettability was used. The primary W/O emulsion was obtained by the hydrophobic nanoparticles, and then the hydrophilic nanoparticles were used as emulsifier in the secondary emulsification to prepare the W/O/W emulsion. In a similar way, the primary O/W emulsion of the O/W/O emulsion was stabilized by the hydrophilic nanoparticles, while the secondary emulsification to prepare the O/W/O emulsion was effected with the hydrophobic nanoparticles. The resultant multiple Pickering emulsion was stable to coalescence for more than 3 months, except the W/O/W emulsions of which the secondary emulsion stabilized by clay nanoparticles became a simple O/W emulsion in a day after preparation. Moreover, the temperature and pH sensitive poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAm-co-MAA)) microgels were introduced as an emulsifier for the secondary emulsification to obtain the stimulus-responsive multiple W/O/W emulsion. Such microgel-stabilized multiple emulsions could realize the efficient controlled release of water-soluble dye, Rhodamine B (RB) on demand in a multiple-emulsion delivery system. 相似文献
Polystyrene/silica composite nanoparticles were synthesized via precipitation and emulsion polymerization methods, in the presence of a basic co‐monomer (e.g., 4‐VP and 1‐VID), and a colloidal aqueous silica solution. The effects of key process parameters, that is, solvent type, monomer/co‐monomer volume ratio and total monomers concentration for precipitation polymerization, and reaction temperature, pH value, initial silica‐sol concentration and initial monomer/co‐monomer molar ratio for emulsifier‐free emulsion polymerization on the particle morphology, silica content, and particle size distribution of the composite nanoparticles were experimentally investigated. Stable, spherical, and uniform in size composite nanoparticles were synthesized by both techniques. The average particle diameter varied from 108 to 182 nm for the emulsifier‐free emulsion polymerization and from 400 to 800 nm for the precipitation polymerization, while the silica content was as high as 38.3 wt.‐% for the former method and up to 15.5 wt.‐% for the later. The synthesized composite polymer/silica particles were then electrolytically co‐deposited with zinc on steel plates to improve the corrosion resistance of the metal's surface.
In this study, hollow silica particles were fabricated by atomizing the dispersion of silica nanocolloids synthesized by modified Stober method and self-organization of the particles by spray drying technique. Rapid evaporation of the droplet containing the silica nanoparticles resulted in the formation of hollow microparticles at high evaporation temperature due to hydrodynamic instability of the droplet. Similar strategy was adopted for the fabrication of macroporous silica particles by the sol spray drying of the hetero-colloidal dispersion of polystyrene nanospheres and commercial silica nanoparticles. The morphologies of the porous particles were observed by scanning electron microscope with varying drying temperature. As a demonstrative purpose, the results using emulsion droplets as confining geometry was compared with the porous particles obtained from spray dryer. Collectively, spray drying was found to be more efficient manner to prepare the porous materials with continuous way in the view of production efficiency and time. 相似文献
The efficient synthesis of all-acrylic, film-forming, core-shell colloidal nanocomposite particles via in situ aqueous emulsion copolymerization of methyl methacrylate with n-butyl acrylate in the presence of a glycerol-functionalized ultrafine silica sol using a cationic azo initiator at 60 °C is reported. It is shown that relatively monodisperse nanocomposite particles can be produced with typical mean weight-average diameters of 140-330 nm and silica contents of up to 39 wt %. The importance of surface functionalization of the silica sol is highlighted, and it is demonstrated that systematic variation of parameters such as the initial silica sol concentration and initiator concentration affect both the mean particle diameter and the silica aggregation efficiency. The nanocomposite morphology comprises a copolymer core and a particulate silica shell, as determined by aqueous electrophoresis, X-ray photoelectron spectroscopy, and electron microscopy. Moreover, it is shown that films cast from n-butyl acrylate-rich copolymer/silica nanocomposite dispersions are significantly more transparent than those prepared from the poly(styrene-co-n-butyl acrylate)/silica nanocomposite particles reported previously. In the case of the aqueous emulsion homopolymerization of methyl methacrylate in the presence of ultrafine silica, a particle formation mechanism is proposed to account for the various experimental observations made when periodically sampling such nanocomposite syntheses at intermediate comonomer conversions. 相似文献
The guanidine group-modified silica particles were used as emulsifier to obtain a CO2-responsive Pickering emulsion. To compare the wettability effect of the particles on the stability of the emulsion, both guanidine and alkyl chain were attached on the surface of silica particles. The influences of tension, particles concentration, oil-water fraction, NaCl concentration, and CO2 on Pickering emulsion properties were investigated. Although the particles did not decrease the surface and interfacial tensions of the air/oil-water interfaces, they attached on the oil–water interfaces and stabilized the emulsions at room temperature for at least 4 weeks. Addition of salt increased the emulsion stability and induced phase inversion at high salt concentration. The stabilization–destabilization cycles of the emulsion could be successively controlled by alternative CO2/heating triggers due to the protonation-deprotonation of guanidine groups on the particle surfaces. 相似文献
The morphology regulation of hollow silica microspheres is significant for their properties and applications. In this paper, hollow silica microspheres were formed through the hydrolysis and condensation reaction of tetraethyl orthosilicate (TEOS) at the interface of the emulsion droplet templates composed of liquid paraffin and TEOS, followed by dissolving paraffin with ethanol. The effects of various factors including the emulsifier structure and content, TEOS content, catalyst type, and the ethanol content in the continuous water phase on the particle size, shell thickness and morphology of the prepared hollow silica microspheres were studied in detail. The results show that the diffusion and contact of TEOS and water molecules as well as the hydrolysis condensation reaction of TEOS at the oil-water interface are two critical processes for the synthesis and morphological regulation of hollow silica microspheres. Cationic emulsifier with a hydrophobic chain of appropriate length is the prerequisite for the successful synthesis of hollow silica microspheres. The ethanol content in water phase is the dominant factor to determine the average diameter of hollow microspheres, which can vary from 96 nm to 660 nm with the increase of the volume ratio of alcohol-water from 0 to 0.7. The silica wall thickness varies with the content and the hydrophobic chain length of the emulsifier, TEOS content, and the activity of the catalyst. The component of the soft template will affect the morphology of the silica wall. When the liquid paraffin is replaced by cyclohexane, hollow microspheres with fibrous mesoporous silica wall are fabricated. This work not only enriches the basic theory of interfacial polymerization in the emulsion system, but also provides ideas and methods for expanding the morphology and application of hollow silica microspheres. 相似文献
Mesoporous silica microspheres were synthesised through a sol–emulsion–gel process using Span 80 as the surfactant in silica
sol/n-hexane water in oil emulsion system. Surface modification of the microspheres was done with trimethylchlorosilane to obtain
hydrophobic silica microspheres. Various parameters related to the synthesis of microspheres, including concentration of surfactant
and viscosities of sol were studied. The hydrophobicity (wettability), thermal stability, porosity, and morphological features
were also investigated. 相似文献
Monomeric emulsifiers with different copolymerization reactivities were used as stabilizers in emulsion polymerization of styrene initiated by 2,2′ azobisisobutyronitrile (AIBN). A significant change in emulsifier function was observed between equal micellar concentrations of surface-active sodium sulfopropyl alkyl maleates and the corresponding sodium sulfopropyl dodecyl fumarate. In the presence of less reactive maleates, copolymerization mainly occurs in the interface of the monomer swollen particles, while copolymerization with the fumarate in the first period of emulsion polymerization leads to polyelectrolyte formation in the water phase. 相似文献
