It is shown that the theory of Sogami and Ise leading to an attraction between particles with cha... more It is shown that the theory of Sogami and Ise leading to an attraction between particles with charges of the same sign contains errors. When the errors are corrected the calculated attraction disappears.
ABSTRACT Colloidal crystals can be formed of silica particles while those of titania particles ar... more ABSTRACT Colloidal crystals can be formed of silica particles while those of titania particles are not known under the normal gravitational field, because of their high specific gravity. We found by the Kikuchi--Kossel diffraction technique that, when silica particles (diameter: D = 170 nm; density: ρ = 2.2 g cm−3) are mixed with titania particles (D = 127 nm; ρ = 3.9 g cm−3), colloidal crystals are formed. Colloidal crystals started out with body-centred-cubic structure and changed to face-centred-cubic structures after about 60 days. Transitions began from the bottom of the container. Thus, the transitions are considered to be due to gravitational sedimentation. It is significant that the crystal growth process, which has not been observed in one-component dispersions of the silica particles, was found using titania particles with a wide range of the practical applicability.
It is demonstrated that the Sogami potential, which contains both repulsive and attractive compon... more It is demonstrated that the Sogami potential, which contains both repulsive and attractive components, can account for the experimental data on photothermal compression of colloidal crystals much more satisfactorily than the purely repulsive DLVO potential. The Sogami ...
We report bcc-fcc transitions of colloidal crystals in mixed aqueous dispersions of polystyrene-b... more We report bcc-fcc transitions of colloidal crystals in mixed aqueous dispersions of polystyrene-based latex particles (diameter: D=55.8 nm) and silica particles (diameter: D=170 nm). In the single systems, the silica particles formed bcc crystals and the latex particles did not crystallize. In the binary mixtures of these particles, colloidal crystals with fcc structures were found by the analysis of Kikuchi-Kossel diffraction images. Especially, the samples at low latex fractions started out as bcc structures, and then changed to fcc structures. Due to gravitational sedimentation, the lattice constant increased as the height from the bottom of the dispersion became larger. Furthermore, the lattice constant became smaller at a given silica fraction as the latex fraction increased.
The colloidal and macroionic interaction is discussed within the mean-field approach. Bound pairs... more The colloidal and macroionic interaction is discussed within the mean-field approach. Bound pairs of latex particles are photographed at a low particle volume fraction of 10 −4. The effective pair-potential obtained therefrom has an attractive tail for highly charged samples, while no attraction is detected for a low-charge sample. This attraction also manifests itself in the reversible aggregation of polystyrene sulfonate or DNA double strands by multivalent counterions. It is furthermore found in intra-macroionic interaction, affecting the conformation of flexible macroions. The reason why the DLVO theory predicts only repulsion is discussed. The Fowler-Guggenheim-McQaurrie analysis of the Debye–Hückel theory indicates that electrostatic Helmholtz free energy F el is generally not equal to Gibbs free energy G el. The difference (G el − F el)/V (V: system volume) corresponds to the electrostatic osmotic pressure p el , which increases with increasing charge number. This consideration hints that (G el − F el) might not be negligible for highly charged macroions and colloidal particles. On the other hand, the DLVO approach is based on the assumption of G el = F el. Using a mean-field
It is shown that the theory of Sogami and Ise leading to an attraction between particles with cha... more It is shown that the theory of Sogami and Ise leading to an attraction between particles with charges of the same sign contains errors. When the errors are corrected the calculated attraction disappears.
ABSTRACT Colloidal crystals can be formed of silica particles while those of titania particles ar... more ABSTRACT Colloidal crystals can be formed of silica particles while those of titania particles are not known under the normal gravitational field, because of their high specific gravity. We found by the Kikuchi--Kossel diffraction technique that, when silica particles (diameter: D = 170 nm; density: ρ = 2.2 g cm−3) are mixed with titania particles (D = 127 nm; ρ = 3.9 g cm−3), colloidal crystals are formed. Colloidal crystals started out with body-centred-cubic structure and changed to face-centred-cubic structures after about 60 days. Transitions began from the bottom of the container. Thus, the transitions are considered to be due to gravitational sedimentation. It is significant that the crystal growth process, which has not been observed in one-component dispersions of the silica particles, was found using titania particles with a wide range of the practical applicability.
It is demonstrated that the Sogami potential, which contains both repulsive and attractive compon... more It is demonstrated that the Sogami potential, which contains both repulsive and attractive components, can account for the experimental data on photothermal compression of colloidal crystals much more satisfactorily than the purely repulsive DLVO potential. The Sogami ...
We report bcc-fcc transitions of colloidal crystals in mixed aqueous dispersions of polystyrene-b... more We report bcc-fcc transitions of colloidal crystals in mixed aqueous dispersions of polystyrene-based latex particles (diameter: D=55.8 nm) and silica particles (diameter: D=170 nm). In the single systems, the silica particles formed bcc crystals and the latex particles did not crystallize. In the binary mixtures of these particles, colloidal crystals with fcc structures were found by the analysis of Kikuchi-Kossel diffraction images. Especially, the samples at low latex fractions started out as bcc structures, and then changed to fcc structures. Due to gravitational sedimentation, the lattice constant increased as the height from the bottom of the dispersion became larger. Furthermore, the lattice constant became smaller at a given silica fraction as the latex fraction increased.
The colloidal and macroionic interaction is discussed within the mean-field approach. Bound pairs... more The colloidal and macroionic interaction is discussed within the mean-field approach. Bound pairs of latex particles are photographed at a low particle volume fraction of 10 −4. The effective pair-potential obtained therefrom has an attractive tail for highly charged samples, while no attraction is detected for a low-charge sample. This attraction also manifests itself in the reversible aggregation of polystyrene sulfonate or DNA double strands by multivalent counterions. It is furthermore found in intra-macroionic interaction, affecting the conformation of flexible macroions. The reason why the DLVO theory predicts only repulsion is discussed. The Fowler-Guggenheim-McQaurrie analysis of the Debye–Hückel theory indicates that electrostatic Helmholtz free energy F el is generally not equal to Gibbs free energy G el. The difference (G el − F el)/V (V: system volume) corresponds to the electrostatic osmotic pressure p el , which increases with increasing charge number. This consideration hints that (G el − F el) might not be negligible for highly charged macroions and colloidal particles. On the other hand, the DLVO approach is based on the assumption of G el = F el. Using a mean-field
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