Crystals Of Silica Spheres Research Articles

Drying dissipative structures of colloidal crystals of silica spheres coated with polymer brushes of poly(carboxymethyl betaine)

Drying patterns of colloidal crystals of colloidal silica spheres coated with the brushes of zwitterionic poly(carboxymethyl betaine) (SiP-PCMB) and their parent silica spheres (SiP) were studied on a cover glass, a watch glass, and a Petri glass dish. Crystal structures kept the whole process of dryness of the suspensions of SiP-PCMB and SiP. Crystal structures of the dried films of SiP-PCMB were kept stable even when the initial suspensions contained 5 mM of sodium chloride, which is the important role of the excluded volume effects of the shells of the polymer brushes. On the other hand, crystal structures of SiP spheres in the dried films were much unstable and melted in the presence of 5 mM sodium chloride. In the suspension state, colloidal crystallization of SiP-PCMB took place stably by the contribution of the excluded volume effects besides the extended electrical double layers compared with that of SiP spheres, where only the double layer effect contributes to the crystallization. The fractal patterns of the complexation of SiP-PCMB or SiP spheres with sodium chloride were observed microscopically in the dried films. Several kinds of dissipative crystallization such as array and/or accumulation of the crystallites were observed, and the importance of the convectional and sedimentation processes during the course of dryness was demonstrated.

Experimental determination of the band structure of photonic crystals of colloidal silica spheres

A photonic band structure of colloidal crystals of silica spheres is analytically determined by a band model with three fitting parameters: the sphere size, the effective refractive index, and the band-gap. Optical properties of the crystals annealed at various temperatures were characterized by a procedure similar to X-ray diffraction technique, and the width of photonic band-gap measured from the transmission spectra experimentally servers as an additional check on the validation of the model. The photonic band structures defined by the band-gap, the refractive index, and the Brillouin zone are obviously superior to the use of the Bragg's expression involving simple zone folding.

Convectional, sedimentation, and drying dissipative patterns of colloidal silica (183 nm in diameter) suspensions in a glass dish and a watch glass

Convectional, sedimentation, and drying dissipative structural patterns formed during the course of drying aqueous colloidal crystals of silica spheres (183 nm in diameter) have been studied in a glass dish and a watch glass. Spoke-like convectional patterns were observed in a watch glass. The broad ring sedimentation patterns formed especially in a glass dish within 30–40 min in suspension state by the convectional flow of water and colloidal spheres. The macroscopic broad ring drying patterns formed both in a glass dish and a watch glass. The ratio of the broad ring size in a glass dish against the initial size of suspension, i.e., inner diameter of the glass dish, d f/d i, in this work, were compared with previous work of other silica spheres having sizes of 305 and 560 nm and 1.2 μm in diameter. The d f/d i values in a glass dish increased as sphere concentration increased, but were rather insensitive to colloidal size. The d f/d i values on a watch glass also increased as sphere concentration increased, and further increased as sphere size decreased. Segregation effect by sphere size in a watch glass takes place by the balancing between the upward convectional flow of spheres in the lower layers of the liquid and the downward sedimentation of spheres. Colorful microscopic drying patterns formed both in a glass dish and a watch glass.

Drying dissipative patterns of colloidal crystals of silica spheres on a cover glass at the regulated temperature and humidity

Influences of temperature and humidity on the drying dissipative patterns of colloidal crystals of silica spheres (103 nm in diameter) were studied. The broad ring pattern, which is one of the typical macroscopic drying structures, became sharp as temperature rose and/or humidity decreased. Furthermore, number of the spoke-like cracks decreased as temperature and/or humidity increased. The water evaporation from a liquid surface to air and the convectional flow of water and colloidal spheres were important for the macroscopic pattern formation.

Thermo-sensitive colloidal crystals of silica spheres in the presence of large spheres with poly (N-isopropyl acrylamide) shells

Thermo-sensitive colloidal crystals are prepared simply by mixing colloidal silica spheres and large thermo-sensitive gel spheres. The thermo-reversible change in the lattice spacing of colloidal crystals of monodisperse silica spheres (CS82, 103 nm in diameter) depends on the size of the admixed temperature-sensitive gel spheres. For spheres with sizes less and greater than that of the silica spheres, the lattice spacing upon temperature increase above the lower critical solution temperature of poly(N-isopropyl acrylamide) decreases (cf. Okubo et al. Langmuir 18:6783, 2002) and increases, respectively. A mechanism, which is able to explain these experimental findings, is proposed. Moreover, crystal growth rates and the rigidities of the thermo-sensitive colloidal crystals are studied.

Video-tape observation of the crystal growth and morphology of colloidal single crystals

Crystal growth and morphology of colloidal crystals of silica spheres (81.2 nm in diameter) are observed directly on a video-tape camera. Crystal growth from the round-shaped, small single crystals to the angular-shaped ones is clear. It is observable that the single crystals are packed densely and separated from each other with the grain boundaries. The morphology of colloidal crystals is quite similar to that of typical crystals such as metals, proteins, and ice.

The layer multiple-scattering method applied to phononic crystals

Abstract After a brief description of the layer multiple scattering method as applied to phononic crystals, we present some results obtained by this method, relating to: crystals of polystyrene spheres in water; crystals of silica spheres in air; and crystals of steel spheres in polyester. We relate the transmission characteristics of slabs of these ma terials to the complex band structure of the corresponding infinite crystals. We emphasize aspects of the underlying physics which have not been discussed previously.

Microgravity experiments on colloidal crystallization of silica spheres in the presence of sodium chloride

Rate coefficients (k) in the colloidal crystallization of monodispersed silica spheres in the presence of sodium chloride are studied in microgravity achieved by parabolic flights of an aircraft. Time-resolved reflection spectroscopy is made with a continuous circulating-type stopped-flow cell system. The k values decrease as the salt concentration increases both at 0 and 1 G and those in microgravity are smaller than those in normal gravity by 16% (maximum), especially in water and in the presence of a small amount of the salt lower than 2 × 10−6 mol/l. The rates in flight at 1 G are larger by 15% (maximum) compared with those at 1 G on the ground. The k values obtained at 0 G, 1 G in flight and 1 G on the ground agree excellently with each other for the suspensions with 3 × 10−6 and 4 × 10−6 mol/l sodium chloride. Disappearance of the downward diffusion of spheres and no convection of the suspensions are important for retardation in microgravity.