title: Unidirectional crystallization of charged colloidal silica due to the diffusion of a base.
abstract: Dilute aqueous dispersions of charged colloidal silica (particle volume fraction = approximately 0.03-0.04, particle diameter = 110 nm) exhibit unidirectional crystal growth due to the diffusion of a weak base, pyridine (Py). Similar diffusion-crystallization is enabled by a salt of a weak acid and a strong base, sodium hydrogen carbonate (NaHCO3). The resulting crystals consist of columnar (or cubic) crystal grains with a maximum height of a few centimeters and a maximum width of 1 cm. The crystal growth process is attributed to a combination of (i) the diffusion of Py or NaHCO3 accompanied by a charging reaction of the silica particles and (ii) the charge-induced crystallization of the silica colloids. Theoretical growth curves based on the reaction-diffusion model for the case of Py were in good agreement with the observed curves. We also report the immobilization of the resulting large crystals by using a polymer hydrogel matrix.
authors.affiliation: Faculty of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe, Mizuho, Nagoya, Aichi 467-8603, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Murai
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamada
authors.forename: Junpei
authors.initials: J
authors.lastname: Yamanaka
authors.forename: Sachiko
authors.initials: S
authors.lastname: Onda
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Yonese
authors.forename: Kensaku
authors.initials: K
authors.lastname: Ito
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Sawada
authors.forename: Fumio
authors.initials: F
authors.lastname: Uchida
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Ohki
mesh_terms: D000327:Adsorption; D003102:Colloids / Q000737:chemistry*; D003460:Crystallization; D004058:Diffusion; D020100:Hydrogels / Q000737:chemistry; D049329:Nanostructures / Q000737:chemistry*; D036103:Nanotechnology; D010316:Particle Size; D011725:Pyridines / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D017693:Sodium Bicarbonate / Q000737:chemistry; D055672:Static Electricity; D014961:X-Ray Diffraction
chemical_list: D003102:Colloids; D020100:Hydrogels; D011725:Pyridines; D012822:Silicon Dioxide; D017693:Sodium Bicarbonate