Ken-ichi Kurumada

Synthesis of submillimeter-thick films of surfactant templated mesoporous silica

Abstract Submillimeter-thick mesoporous silica films using tetraethoxysilane (TEOS) as a silica source and the hexagonal mesophase of cetyltrimethylammonium chloride as a template were prepared by solvent evaporation method. The effects of H2O/TEOS molar ratio and drying temperatures on the macroscopic morphology and mesostructure were investigated. Higher H2O/TEOS ratio and higher drying temperature gave a more transparent and smooth-surfaced product. With increasing H2O/TEOS ratio, the order of the mesostructure in the product film was reduced, resulting from the slow formation of surfactant mesostructure and fast silicate gelation. The pore size showed an increase with increasing H2O/TEOS ratio, suggesting mediation by the water layer between the micellar surface and the silicate. The drying temperature affected the rate of silicate condensation and the solvent evaporation, both factors that influenced the mesostructuralization of surfactant molecules. A high drying temperature facilitated the gelation of silicate rather than the evaporation of solvent, resulting in a less ordered mesostructure.

Effects of catalytic acid and templating surfactant concentrations on mesostructure of submillimeter-thick mesoporous silica by solvent evaporation synthesis

Abstract Submillimeter-thick films of mesoporous silica were synthesized by the solvent evaporation method using tetraethoxysilane (TEOS) and cetyltrimethylammonium chloride (CTAC) as the silica source and the templating agent, respectively. The effects of HCl/TEOS and CTAC/TEOS molar ratios were investigated. It was revealed that a high CTAC concentration and a low gelation rate at a low HCl concentration were favorable for the formation of highly ordered mesostructures, since the mesostructure is governed by the concentration of CTAC at gelation of the solution. The pore diameter increased as the CTAC/TEOS ratio decreased, suggesting the intermediation between a silica wall and a CTAC micelle by a water layer whose thickness increases with the increase in the H 2 O/CTAC ratio.

Structure and formation process of silica microparticles and monolithic gels prepared by the sol-gel method

Abstract Silica microparticies and monolithic gels were prepared via the hydrolysis and polymerization of tetraethylortho silicate (TEOS) with NH3 as the catalyst. The scanning electron microscope (SEM) observations revealed that the microparticles were formed through the aggregation of smaller particles. In the small angle X-ray scattering (SAXS) measurements, an abrupt change in the power dependence of the scattered intensity on the wave number was observed, which suggests that both the microparticles and monolithic gels were formed via multi-staged aggregation. Elementary silica particles first assemble into a fractal precursory aggregate, and a further aggregation of the precursory aggregates leads to the resultant structure. The fractal dimensionality of those precursory aggregate was estimated as approximately 1.5, in common both for the formation of the silica dispersed microparticies and monolithic gels.

Effect of addition of polymeric species with ether moieties on porous structure of silica prepared by sol-gel method

The authors have investigated the effect of the addition of polymeric species (polyethyleneglycol, polypropyleneglycol and polytetramethyleneoxide) containing ether moieties in their main chain on the silica porous structure yielded via the sol-gel method. The obtained silica porous structures were characterized by nitrogen adsorption/desorption and SEM. Introducing those polymeric species apparently enhanced the pore formation. The enhancement is more noticeable for higher concentrations of the polymeric species, distributed from the microporous to mesoporous regions. The pore diameter at which the pore enhancement is induced by adding the polymeric species reduces with the fraction of ether moiety. Adding the polymeric species prior to the onset of the hydrolysis of tetraethylorthosilicate (TEOS) was necessary for the enhancement in the mesoporous region to takes place. The pore enhancement was more outstanding when HCL was used as the catalyst for the hydrolysis of the alkoxide than NH3. The mutual affinity between the added polymeric and silica species is considered as an important factor of the pore generation in the micro- and meso-porous regions.

Preparation of nanoporous ZnO using copolymer gel template

Mesoporous ZnO were prepared using copolymer gel template of hydroxyl ethyl methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA) where the latter worked as the cross-linker. The effects of molar ratio [HEMA]/[EGDMA] in copolymer on the porous structure of ZnO formed in the template gel were investigated. The results indicated that the pore size and its distribution of the mesoporous ZnO could be drastically varied by [HEMA]/[EGDMA] molar ratio which directly affects the templating gel structure. Smaller pores and narrow pore size distribution were obtained with the molar ratio increased. The formation mechanism of mesoporous structure was discussed based on these experimental results.

Preparation of nanoporous silica using copolymer template

Silica solids with different nanoscaled pore diameters were formed from tertraethoxysiliane (TEOS) and copolymer gel of hydroxyl ethyl methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA) where the latter worked as the cross-linker. The effects of molar ratio [HEMA]/[EGDMA] of copolymers on the porous structure of silica formed in the template gel were discussed. The properties and structure of gel and porous silica were characterized by Fourier transform infrared spectrometer (FT-IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results indicated that the pore diameter of silica could be varied by the [HEMA]/[EGDMA] molar ratio which directly affects the templated structure of copolymer gel. The larger pore diameter was obtained with the increased molar ratio, which corresponds to the decrease in the cross-link density. FT-IR and TGA suggested that the silica moiety is bonded to the network of the copolymer gel due to the gel/silica affinity based on the hydrogen bonding.

Preparation of oxide with nano-scaled pore diameters using gel template

Silica, MgO and ZnO with various nano-scaled pore diameters were prepared with template gel synthesized from hydroxyl ethyl methacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA), where the latter worked as the cross-linker. The effects of the molar ratio [HEMA]/[EGDMA] in the gel were discussed in relation to the resultant porous structure. The pore diameter of the oxide was shown to be varied by the molar ratio [HEMA]/[EGDMA] which directly affects the structure of gel, particularly the mesh size. From the different trend in the variation of the pore size in the oxide, a contrasting trend depending on the molar ratio [HEMA]/[EGDMA] has been found for silica, MgO and ZnO. The mesh-filling and hydrogen bonding mechanism has been considered to explain the formation process of gel templated nanoporous silica and ZnO or MgO, respectively.

Structure and properties of bis(2-ethyhexyl)phospheric acid microemulsions with a network structure: Effect of counter-ions

Abstract Several physicochemical properties were experimentally examined for calcium bis(2-ethylhexyl)phosphate (Ca(DEHP) 2 )/water/ n -hexane/calcium chloride systems and compared with sodium bis(2-ethylhexyl)phosphate (NaDEHP)/water/ n -hexane/sodium chloride systems in the Winsor II regime to elucidate the effect of changing counter-ion species on the properties of a microemulsion in the amphiphile-concentrated region characterized by the presence of a network-like structure formed from worm-like molecular assemblies. The measurements of small angle X-ray scattering, shear viscosity, electroconductivity were consistently interpreted in terms of the strong tendency of molecular assemblies to become more elongated for Ca 2+ than for Na + . The dependence of the dynamical correlation length on the volume fraction of molecular assembly obtained from the dynamic light scattering implies that the freely mobile part in the Ca(DEHP) 2 micoemulsion network would be determined by the individual micromechanical property of the worm-like molecular assembly, being different from that in NaDEHP systems determined by the network mesh which becomes more confined with the increase in the volume fraction of the molecular assembly.

Growth of silica particles in surfactant gel

Abstract Growth of silica particles produced by the hydrolysis of tetraethoxy silane (TEOS) in gels of the cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was investigated by static light scattering and dynamic light scattering measurements. The time evolution of the size of the silica particles was estimated by the static and the dynamic correlation lengths obtained from the two measurements. Both the growth rate and the final size were smaller at higher concentrations of CTAB, indicating that a more confined network exerted a more restrictive effect on the particle growth. The random motion of silica particles was more severely restricted when the particle was larger and the network mesh size was smaller at higher CTAB concentrations. This restriction of movement resulted in the cessation of the growth of silica particles.