Shinsuke Nagamine

Preparation of Porous Poly(L-lactic acid) Honeycomb Monolith Structure by Phase Separation and Unidirectional Freezing

A honeycomb monolith structure with micro/nanoscale porous walls was successfully fabricated in poly(l-lactic acid) (PLLA) by integrating polymer-solvent and polymer-polymer phase separations induced during a pseudosteady-state unidirectional freezing process. Poly(ethylene glycol) (PEG) and PLLA were dissolved in 1,4-dioxane to prepare a single phase polymer solution. The direction of freezing created a honeycomb monolith structure of PLLA/PEG polymers. Crystallization of the solvent reduced the solvent concentration and induced liquid-liquid phase separation during the unidirectional freezing. A sea-and-island morphology, where PEG domains were dispersed in the PLLA matrix, was developed, and pores were created in the channel walls of the honeycomb monolith structure by leaching out the PEG domain. The effects of the PEG molecular weight and the PLLA/PEG weight ratio on the aligned honeycomb structure and the pores in the channel walls were investigated. A ternary phase diagram for PLLA, PEG, and 1,4-dioxane was created from cloud point temperature measurements. Based on this phase diagram, hypotheses for the mechanism of the cellular-dendritic transition and the formation mechanism of the pores in the channel walls are proposed.

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.

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.

Periodic Porous Stripe Patterning in a Polymer Blend Film Induced by Phase Separation during Spin-Casting

A periodic striping pattern with microscale pore size is observed on the surface of thin films prepared by spin-casting from a polystyrene (PS) and polyethylene glycol (PEG) blend solution. The pattern is created by the convection generated by thermal gradients in the solution between the substrate and film solution during solvent evaporation, the radial flow of the spin-coated solution, and the primary and secondary phase separation of the PS and PEG solutions. The formation mechanism of the periodic porous stripe pattern is discussed, wherein the effects of the polymer blend weight ratio, polymer concentration, and drying rate on the formation of the periodic porous striping pattern are investigated using scanning electron and atomic force microscopy.

Interconnected pores on the walls of a polymeric honeycomb monolith structure created by the unidirectional freezing of a binary polymer solution

Interconnected submicron pores were created on the walls of a honeycomb monolith structure by the unidirectional freezing of a binary polymer solution. Agglomerated globules of polyethylene glycol (PEG) in a binary solution of polystyrene (PS) and PEG in 1,4-dioxane solvent were frozen unidirectionally in a liquid nitrogen bath. Removing the frozen solvent and the agglomerated globules of PEG by freeze-drying and leaching, respectively, enabled us to create interconnected pores in the PS walls. The combination of PS and PEG was effective in creating interconnected pores in the walls because PS and PEG are poorly soluble in one another. The higher freezing rate and lower PEG weight fraction of the binary solution effectively reduced the pore size in the microtube walls.

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.