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1.
Drying dissipative structural patterns of the colloidal crystals of silica spheres were studied under an dc-electric field. Platinum plate electrodes of anode and cathode were set on a cover glass. The broad hills accumulated with the spheres were observed at the outer edges of the dried film without and also with the electric fields. The column-like structures were formed by the electric flux, and movement of the spheres took place toward anode. The dried film kept colloidal crystal structure, where the nearest-neighbored spheres contact each other more compactly in the areas closer to the anode. Drying times needed for the complete dryness of the suspensions decreased as the strength of the electric field increased. Addition of sodium chloride to the suspensions retarded the movement of spheres toward the anode substantially. 相似文献
2.
Sedimentation and drying dissipative structural patterns formed in the course of drying colloidal silica spheres (305 nm in
diameter) in aqueous suspension have been studied in a glass dish and a watch glass. The broad ring sedimentation patterns
formed within several tenth minutes in suspension state by the convectional flow of water and colloidal spheres. The sedimentary
spheres always moved by the convectional flow of water, and the broad ring patterns became sharp with time. The width of the
broad rings was sensitive to the change in the room temperature and/or humidity. In other words, the patterns became sharp
or vague when the room parameters decreased or increased. Colorful macroscopic drying structures were composed of a broad
ring and the wave-formed patterns. Iridescent colored fine patterns formed in the solidification processes on the bases of
the sedimentation patterns. Beautiful drying patterns were observed for the suspension mixtures of CS300 and NaCl, and were
different from the structures of CS300 or NaCl individuals, which support the synchronous cooperative interactions between
the colloidal spheres and the salt. 相似文献
3.
The sedimentation and drying dissipative structural patterns were formed during the course of drying binary mixtures among
colloidal silica spheres of 183 nm, 305 nm, and 1.205 μm in diameter in aqueous suspension on a watch glass, a glass dish,
and a cover glass, respectively. The broad ring-like sedimentation patterns were formed within several hours in suspension
state for all the substrates used. Colorful macroscopic broad ring-like drying patterns were formed for the three substrates.
In a watch glass, macroscopic drying patterns were composed of the outer and inner layers of small and large spheres, respectively.
The two colored layers were ascribed to the Bragg diffractions of light by the dried colloidal crystals of the corresponding
spheres. The width ratio of the layers changed in proportion to the mixing ratio of each spheres. In a glass dish, wave-like
macroscopic drying patterns were observed in the intermediate areas between the outside edges of the broad ring and the inner
wall of the cell. On a cover glass, the sphere mixing ratios were analyzed from the widths of the drying broad rings of the
small spheres at the outside edge. High and distinct broad rings of small spheres and the low and vague broad one formed at
the outer edges and in the inner area, respectively. Drying dissipative pattern was clarified to be one of the novel analysis
techniques of colloidal size in binary colloidal mixtures. 相似文献
4.
Tsuneo Okubo 《Colloid and polymer science》2007,285(13):1495-1503
The sedimentation and drying dissipative structural patterns formed during the course of drying colloidal silica spheres (CS550,
560 nm in diameter) in an aqueous suspension have been studied in a glass dish and a watch glass. Broad ring patterns were
formed within 20 min in the suspension state by the convectional flow of the colloidal spheres and water. The sedimentary
spheres always moved by the convectional flow of water, and the broad ring patterns became sharp with time. The sharpness
of the broad rings was sensitive to the change in the room temperature and/or humidity. Colorful macroscopic structures were
composed of the broad ring and wave-like patterns, and further colorful and beautiful microscopic fine patterns formed during
the solidification processes based on the convectional and sedimentation structures. The drying patterns of the colloidal
suspensions containing sodium chloride were different from the structures of CS550 or sodium chloride individuals, which support
the synchronous cooperative interactions between the colloidal spheres and the salts. 相似文献
5.
Tsuneo Okubo 《Colloid and polymer science》2006,284(12):1395-1401
Sedimentation and drying dissipative structural patterns formed in the course of drying colloidal silica spheres (1.2 μm in diameter) in aqueous suspension have been studied in a glass dish and a polystyrene dish. The broad ring patterns are formed within a short time in suspension state by the convection flow of water and colloidal spheres. The broad ring patterns are not formed when a dish is covered with a cap, which demonstrates the important role of the convectional flow of silica spheres and water accompanied with the evaporation of water on the air-suspension interface. The sedimentary spheres always move by the convectional flow of water, and the broad ring patterns became sharp with time. Broad ring and microscopic fine structures are formed in the solidification processes on the bases of the convectional and sedimentation patterns. Drying patterns of the colloidal suspensions containing sodium chloride are star-like ones, which strongly supports the synchronous cooperative interactions between the salt and colloidal spheres. 相似文献
6.
Kinetics of the dissipative structure formation in the course of drying the colloidal crystals of silica spheres (103 nm in
diameter) in aqueous deionized suspension on a rinsed cover glass has been studied by the close-up video observation. The
patterns of the broad ring of the hill accumulated with the spheres coexisted with the many spoke-like cracks. The characteristic
convection flow of the spheres and the interactions between the spheres and substrate were important for the pattern formation.
Cracks formed suddenly in the course of drying along the outside edge first, then toward the center, and stopped around the
middle point between the outside edges and the frontier of suspension area. The further growth of the cracks took place at
the adjacent place of the previous crack side by side and cooperatively. After the fast formation of these cooperative spoke-like
cracks was completed, then all the crack lines further developed very slowly and simultaneously toward the center with the
similar rate as that of the movement of the drying frontier of the suspension area toward center. Rates of the fast and slow
modes of crack formation were 6.2 mm/s and 0.0098 mm/s, respectively, at the sphere concentration of 0.033 in volume fraction. 相似文献
7.
Tsuneo Okubo Hisanori Ishiki Hiroshi Kimura Megumi Chiyoda Kohji Yoshinaga 《Colloid and polymer science》2002,280(5):446-453
Rigidity (G) of colloidal crystals in organic solvents of acetonitrile and nitrobenzene has been measured by reflection spectroscopy
in sedimentation equilibrium. The colloidal spheres used are the silica spheres (136 nm in diameter) modified on their surfaces
with polymers, poly(maleic anhydride-co-styrene) [P(MA-ST)], poly(methyl methacrylate) (PMMA), or polystyrene (PST). Log G increases linearly with the slope of unity as log N (number density of colloidal spheres) increases. The mean values of the b-factor, which is the fluctuation parameter in crystal lattices and should be smaller than 0.1 according to the Lindeman's
rule, are 0.045±0.003, 0.039±0.007, and 0.038±0.003 for P(MA-ST)/SiO2, PMMA/SiO2, and PST/SiO2, respectively. These values are larger than that of colloidal crystals of mother silica spheres in the deionized aqueous
suspension, 0.028. These results support the important role of the excluded volume effects
from the polymer layers formed around the silica surfaces. However, contribution of the excluded volume effects from the electrical double layers formed around the spheres in the organic solvents is also effective in the colloidal crystallization.
Electronic Publication 相似文献
8.
Macroscopic and microscopic dissipative structural patterns formed in the course of drying the deionized aqueous colloidal
crystal suspensions of silica spheres (diameter: 103 nm) on a cover glass have been observed. Spoke-like and ring-like patterns
are formed in the macroscopic scale; the former is the crack in the sphere film and the latter is the hill accumulated with
spheres formed around the outside edge. The neighbored inter-spoke angle, thickness of the film, and other morphological parameters
have been discussed as a function of sphere concentration, concentration of sodium chloride, and the inclined angle of the
cover glass. Fractal patterns of the mud cracks are observed in the microscopic scale. Capillary forces between spheres at
the air-liquid surface and the relative rates between the water flow at the drying front and the convection flow of spheres
are important for the pattern formation.
Electronic Publication 相似文献
9.
Tsuneo Okubo 《Colloid and polymer science》2006,284(10):1191-1196
Sedimentation and drying dissipative structural patterns formed in the course of drying aqueous suspensions of colloidal silica spheres (1.2 μm in diameter) were observed in the various sizes of watch glasses. The macroscopic broad ring patterns were formed on the inner inclined watch glass in suspension state within a short time after suspension was set. The important role of the convectional flow of water and colloidal spheres for the pattern formation is supported. The influence of sodium chloride was also studied. It was clarified that the sedimentary spheres move toward upper and outer edges along the inclined cell wall by the cell convection and hence the patterns are formed by the balancing between the outside movement and the downward sedimentation of the spheres. Beautiful microscopic drying patterns were also observed from the optical microscopy. 相似文献
10.
Drying dissipative structural patterns formed in the course of drying ethyl alcohol solutions of rhodamine 6G, uranine, 7-hydroxy
coumarin, and 7-amino-4-(trifluoro methyl)-coumarin are studied on a cover glass. The macroscopic broad ring patterns form
for all the solutions examined, which supported importance of the convectional flow of ethyl alcohol and dye solutes. Dried
area increases as dye concentration increases above the critical dye concentration. Microscopic fine patterns including street-like,
needle-like, and flower-like crystal structures are formed in the solidification processes. Change in the functional side
group moieties of the dyes gives the strong effect on the microscopic drying patterns; even the main chemical structures are
same. Kinetic aspect of the drying patterns is studied. 相似文献
11.
Tsuneo Okubo 《Colloid and polymer science》2008,286(13):1527-1535
In a series of our studies on the dissipative structure formation, this work focused on the sedimentation and drying patterns
of colloidal crystals of poly(methyl methacrylate) colloidal spheres with different sizes (100, 200, 300, and 1,000 nm in
diameter) in a glass dish. During the course of dryness, the brilliant iridescent colors changed. Drying frontier grew from
the central area of the cell toward the outside edge. Macroscopic and microscopic drying patterns of the resulting film from
dried colloidal suspensions showed outer and inner broad rings. Size of the outer rings increased with increasing sphere concentration
but did not altered sphere size, while these factors affected the inner ring size. These observations do not support the pinning
effect proposed by Deegan et al. 相似文献
12.
T. Okubo 《Colloid and polymer science》1993,271(2):190-196
Close-up color photographs are taken for crystallites (single crystals surrounded by the grain boundaries) in the colloidal crystals of monodisperse silica spheres (diameter: 110 nm±4.5 nm (standard deviation)). Very large crystallites (34 mm) are observed with the naked eye (for the first time) for the completely deionized and diluted suspensions. Deionization is carefully made with the mixed beds of ion-exchange resins more than 2 weeks old. Size of the crystallites increases sharply as the concentration of spheres decreases, and becomes small at the concentrations slightly higher than the critical concentration of melting toward liquid-like structure. Shape of the crystallites, i.e., mixture of triangle, cubic, pentagonal, hexagonal, cone-like, etc., is recognized in the photographs. 相似文献
13.
Macroscopic and microscopic dissipative structural patterns formed in the course of drying the fractionated and monodisperse bentonite particles (plate-like in their shape) in aqueous deionized suspension and in the presence of NaCl have been studied on a cover glass. The patterns coexisted with the broad ring of the hill accumulated with the particles and with the round hills are formed around the outside edges of the film and in the center, respectively, in the macroscopic scale. By the addition of NaCl the pattern shifts from the broad ring to the round hill in the center. The spoke-like cracks, which have been observed for the suspensions of the spherical particles so often hitherto, are not observed at all for the bentonite suspensions. The characteristic convection flow of the particles and the interactions among the particles and substrate are important for the macroscopic pattern formation. Wrinkled, branch-like and/or star-like fractal patterns are observed in the microscopic scale. These patterns are determined mainly by the electrostatic and polar interactions between the particles and/or between the particle and the substrate in the course of drying. 相似文献
14.
Macroscopic and microscopic dissipative structural patterns formed in the course of drying a series of the colloidal silica spheres ranging from 29 nm to 1 m in diameter have been observed in the aqueous deionized suspension on a cover glass. The broad ring patterns of the hill accumulated with the silica spheres are formed around the outside edges in the macroscopic scale for all spheres examined. The spoke-like cracks are also observed in the macroscopic scale and their number decreases sharply as sphere size increases. The pattern area and the time for the dryness have been discussed as a function of sphere size and concentration. The convection flow of water accompanied with that of the silica spheres and interactions among the silica spheres and substrate are important for the macroscopic pattern formation. The microscopic fractal structures of the wave-like patterns and branched strings are formed. Their fractal dimensions are determined. Microscopic patterns form in the narrow range of sphere sizes and concentrations and are determined mainly by the electrostatic and polar interactions between the spheres and/or between the sphere and substrate in the course of solidification. 相似文献
15.
The drying dissipative patterns of aqueous solutions of simple electrolytes, KCl, NaCl, CaCl2, and LaCl3, were observed on a cover glass. The macroscopic broad rings were formed at the outside edge of the drying film area, which
shrunk from the initial solution area especially at low salt concentrations. The drying area and the broad ring size decreased
as the salt concentration decreased. The microscopic block-like and dendritic cross-like patterns were observed for all the
salts. Size of single crystals dried on a cover glass increased as salt concentration increased. The drying patterns of the
binary mixtures of the salts were also observed. Size of the broad ring increased sharply by mixing. The microscopic patterns
were, on the other hand, insensitive to the mixing. 相似文献
16.
Tsuneo Okubo 《Colloid and polymer science》2006,285(2):225-231
Convectional, sedimentation, and drying dissipative structural patterns formed in the course of drying ethanol suspensions of colloidal silica spheres (110 nm in diameter) were studied in a glass dish and a watch glass. Vigorous cell convectional flow was observed with the naked eye, and the patterns changed dynamically with time. Broad-ring-like sedimentation patterns were observed in the suspension state just before the suspension was dried up, and the principal macroscopic patterns of the drying patterns were also broad-ring, though the colorful and fine microscopic structures were observed from optical microscopy. 相似文献
17.
Tsuneo Okubo 《Colloid and polymer science》2008,286(11):1307-1315
Direct observation of the convectional dissipative patterns at room temperature was successful on a cover glass during the
course of dryness of colloidal crystals of poly(methyl methacrylate) colloidal spheres. Formation processes of the convectional
patterns of spoke-like lines were observed as a function of sphere size and also sphere concentration. During dryness of the
suspensions, the brilliant iridescent colors changed beautifully. Macroscopic and microscopic drying patterns of the dried
film were observed. Multiple broad ring-like patterns were observed especially at low sphere concentrations. The water evaporation
accompanied with the convectional flow of water and the colloidal spheres played an important role for the dissipative structure
formation. 相似文献
18.
Direct observation of the convectional dissipative patterns was successful during the course of dryness of colloidal crystals
of poly (methyl methacrylate) spheres on a cover glass. Formation processes of the convectional patterns of spoke-like lines
were observed as a function of sphere size and also sphere concentration. During dryness of the suspensions, the brilliant
iridescent colors changed beautifully. Macro- and microscopic drying patterns and thickness profiles of the dried film were
observed. Sharp broad rings were observed especially at low sphere concentrations. The water evaporation accompanied with
the convectional flow of water and the colloidal spheres played an important role for these dissipative structure formation. 相似文献
19.
Tsuneo Okubo Tomio Yamada Keisuke Kimura Akira Tsuchida 《Colloid and polymer science》2006,284(4):396-404
Macroscopic and microscopic dissipative structural patterns formed in the course of drying a series of poly (ethylene glycol)
(PEG) having molecular weights ranging from 1,000 to 2×106 in aqueous solution have been studied on a cover glass. The broad ring patterns of the hill accumulated with the polymers
are formed irrespective of the molecular weights of PEG molecules. The single round hills are formed also in the center in
the macroscopic scale, when the molecular weight is large. The characteristic convection flow of the polymers and the interactions
among the polymers and substrate are important for the macroscopic pattern formation. Cross-like fractal patterns are observed,
especially for the diluted solutions in the microscopic scale. These patterns are determined mainly by the electrostatic and
polar interactions between the polymers and/or between the polymer and the substrate in the course of solidification. Interestingly,
these microscopic patterns are reflected based on the shape and size of the PEG polymers. 相似文献
20.
Tsuneo Okubo 《Colloid and polymer science》2008,286(12):1411-1423
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. 相似文献