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  • chromatography  (2)
  • microporous crystals  (2)
  • porous silica gel  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Porous Gels Made by Phase Separation: Recent Progress and Future Directions (2000)
    Springer
    Journal of sol gel science and technology 19 (2000), S. 65-70 
    Details
    ISSN: 1573-4846
    Keywords: porous material ; phase separation ; microporous crystals ; chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Recent progress in the sol-gel science concerning the porous gels made by phase separation has been reviewed. Based on the principle and technique explored for monoliths, the material shape has been extended to a macroporous thick film and a macroporous gel in a confined space such as capillary, both of which are expected to find useful applications in the chromatography. The modifiable size range of the additional porosity within the micrometer-sized gel skeleton has been broadened from micropores by zeolite, mesopores by surfactant templates to macropores by intensive hydrothermal treatments. A detailed investigation of 3D interfacial structure in real space has been performed using the laser scanning confocal microscope, which enabled quantitative comparison of the structure with those of other phase-separating systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008710104904
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  • 2
    Electronic Resource
    Electronic Resource
    Polymerization-induced phase separation in silica sol-gel systems containing formamide (1993)
    Springer
    Journal of sol gel science and technology 1 (1993), S. 35-46 
    Details
    ISSN: 1573-4846
    Keywords: Flory-Huggins' theory ; phase separation ; spinodal decomposition ; sol-gel method ; porous silica gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Silica gels with well-defined pores both in micrometer and nanometer ranges were obtained by acid-catalyzed hydrolysis and polymerization of tetramethoxysilane in the presence of formamide. The micrometer-range structures of these gels are studied in terms of the phase diagram of the quasi two-component system, namely solvent-rich and silica-rich end compositions. The resulting interconnected structures and aggregates of particles are related to the occurrence of spinodal phase separation. The composition region that gave interconnected structures for the present system was much more limited and their characteristic sizes were much smaller than those for the previously reported systems containing an organic polymer. These results could be explained qualitatively by the effect of the degree of polymerization on the Flory-Huggins' type free energy change of mixing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00486427
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  • 3
    Electronic Resource
    Electronic Resource
    In situ observation of phase separation processes in gelling alkoxy-derived silica system by light scattering method (1994)
    Springer
    Journal of sol gel science and technology 3 (1994), S. 169-188 
    Details
    ISSN: 1573-4846
    Keywords: porous silica gel ; light scattering ; phase separation ; spinodal decomposition ; Cahn's theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The investigation of phase separation processes induced by polymerization reactions of tetramethoxysilane (TMOS) was attempted by a time-resolved light scattering method for TMOS-formamide-water system under the acid-catalyzed condition. Since the early stage of the phase separation exhibits very fast kinetics and weak scattering intensity, the experimental set-up was designed so as to reduce the experimental error and to obtain higher time resolution by using a laser beam expander. For the gels whose morphologies are ‘interconnected structure’ and ‘aggregates of particles,’ it was experimentally found that the wavelength of the concentration fluctuation in the early stage of phase separation was time-independent and its amplitude grew exponentially with time. This suggests that these samples phase-separate by spinodal decomposition mechanism. In the later stages of phase separation, the coarsening process and the following structure-freezing process by gel-network formation were observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00486556
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  • 4
    Electronic Resource
    Electronic Resource
    Preparation of Silicalite-1 Within Macroporous Silica Glass (2000)
    Springer
    Journal of sol gel science and technology 19 (2000), S. 769-773 
    Details
    ISSN: 1573-4846
    Keywords: silica ; macropores ; deposition ; silicalite-1 ; microporous crystals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Microcrystalline silicalite-1 was formed on the inner surface of macroporus silica glasses prepared by the sol-gel process. By heating a homogeneous precursor solution at 100°C under a hydrothermal condition, 2–5 μm of plate-like particles of silicalite-1 were deposited. With an increase of mixing time of the precursor solution, the number of silicalite-1 particles increased, accompanied by the relative decrease of the particle size. Depending on the temperature and the duration of the heat-treatment of the macroporous silica, the amount of deposited silicalite-1 varied. Below 1000°C, the amount increased with the heat-treatment temperature, as a result of the competition between the precipitation of silicalite-1 and the dissolution of silica from the macroporous silica glass under a strongly basic condition. On the other hand, above 1000°C the amount of deposited silicalite-1 decreased in accordance with the decrease of the macropore diameter by the heat-treatment, because of the limited transport of the dissolved silicate species through the smaller macropores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008756015692
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  • 5
    Electronic Resource
    Electronic Resource
    Pore Structure Control of Silica Gels Based on Phase Separation (1997)
    Springer
    Journal of porous materials 4 (1997), S. 67-112 
    Details
    ISSN: 1573-4854
    Keywords: pore structure control ; silica gels ; phase separation ; spinodal decomposition ; chromatography ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In the alkoxy-derived sol-gel system, various macroporous morphologies can be obtained by inducing the phase separation parallel to the sol-gel transition. This principle of macroporous morphology control can be best applied to pure silica and silica-based multicomponent oxide systems. The earlier the phase separation takes place than the sol-gel transition, the larger the characteristic sizes of pores and gel skeletons become. The time resolved light scattering measurements revealed that the morphology formation process exhibits the features of spinodal decomposition and that the final gel morphology is determined by the competitive kinetics between the domain coarsening and the structure freezing by sol-gel transition. The mesopore structure of such macroporous gel skeletons could be easily tailored by the solvent exchange procedures. Silica gels with controlled macropores and mesopores were successfully applied as a material for the continuous rod type column for high performance liquid chromatography.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009627216939
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