Sei Hachisu

Direct observation of ordered latex suspension by metallurgical microscope

Abstract Ordered structures of monodisperse latex suspensions are visually observed under a modified metallurgical microscope. A pinhole of about 0.1 mm in diameter is used as the field aperture iris of the illumination tube of the microscope in order to reduce the background caused by scattered light from the latex particles themselves. Using this method the ordered structure of the latex particles, which are about 0.2 μm in diameter, can be observed. Two dimensional hexagonal patterns orienting parallel to the wall of the container are observed in most cases. In some cases square patterns are observed. Dislocation, defects of the ordered structure, domains of microcrystals, and Brownian-like motion of the particles around the lattice points are also observed.

Phase separation in monodisperse latexes

Abstract The conditions for the occurrence of ordered and disordered structures in monodisperse polystyrene latexes are studied, making use of iridescence exhibited by the ordered structures as the indicator. The conditions can be characterized for a given latex by its solid content and the electrolyte concentration of its aqueous phase. A phase diagram is constructed with the solid content as the ordinate and the electrolyte concentration as the abscissa. The result is a diagram comprised of three regions, each representing the states of the ordered and disordered structures and the state of coexistence of the two structures, respectively. In the coexistent state, the ordered structure separates out as an iridescent sediment while the disordered structure remains as a white supernatant. The sediments are 1.2–1.4 times more concentrated than the supernatants. This phase separation can be explained neither by the so-called second minimum of colloid interaction potential nor by the electric repulsion between the latex particles; in other words, the present theory of colloid interaction is unable to account for this phenomenon. Though this separation is very similar to tactoids, the particles in this case are spherical, so that the explanation based on Onsagers concept would not be applicable.

Kirkwood—Alder transition in monodisperse latexes. II. Aqueous latexes of high electrolyte concentration☆

Abstract Phase separation in aqueous monodisperse latexes of high electrolyte concentration being stabilized with nonionic surfactant is studied, in order to confirm the Kirkwood-Alder transition as its explanation. Concentrated latexes were produced by ultrafiltration and the phase separation was detected by observing the appearance of iridescent sediment at the bottom of the containers. The phase transition starts at volume fraction of 0.39–0.49 and is completed at 0.48–0.55. These values depend upon the electrolyte concentration and the surfactant used; high electrolyte concentration and short polyoxyethylene chains give larger values. For short chain length surfactant, the results are in good agreement with Alder, Hoover and Youngs [ J. Chem. Phys. 49 , 3688 (1968)] prediction that the transition starts at about 0.5 and is completed at about 0.55. The effects of the van der Waals force on the phase separation seems to be negligible. Above results, thus, substantiate the computer experiments of Alder, Hoover, and Young on the transition between fluid and solid states in hard sphere systems.

Kirkwood—Alder transition in monodisperse latexes. I. Nonaqueous systems☆

Abstract Spontaneous phase separation phenomenon in a nonaqueous monodisperse latex system is studied to verify the Kirkwood-Alder transition in colloid systems. The nonaqueous system might be suitable for our purpose, because both electrical double layers and van der Waals force effect could be negligible therein. Polymethyl methacrylate latex cross-linked with divinylbenzene was dried and then dispersed in benzene at various concentrations. The phase separation occurs in certain particle concentration ranges, depending upon the degree of the cross-linking. The values of the concentration at which the phase separation starts are in the range of from 0.105 to 0.195 by measured volume fraction; smaller values correspond to lower degrees of cross-linking. Correction of the measured volume fractions for the swelling of the particles gives values very close to 0.5, which are independent of the degree of the cross-linking. This is in good agreement with the value 0.497 predicted by Alder, Hoover, and Young [J. Chem. Phys. 49, 3688 (1968)]. In the phase-separated state the ordered phase which forms a sediment exhibits a beautiful opal-like iridescence (demonstrating the existence of polycrystalline structure), while the disordered state is rather translucent and gives weakly iridescent scattering, which would be attributed to the presence of spatial local order, that is, the liquid-like structure. Experimental evidence seems to support the conclusion that the phase separation which occurs in monodisperse latexes cannot be explained by the DLVO theory but could be attributable to the Kirkwood-Alder transition in a hard sphere system.

Pressure of Kirkwood–Alder transition in monodisperse latex

Monodisperse latex, a colloid system consisting of uniform sized spherical particles of synthetic resin, shows a phase transition phenomenon from ordered state to disordered state. In view of the fact that repulsive interaction prevails in stably dispersed colloid, the transition must be of Kirkwood–Alder transition type. In the present work, the pressure of phase transition has been studied, making use of sedimentation equilibrium, at several electrolyte concentrations of the medium. The magnitude of the transition pressure changed as the electrolyte concentration of the medium varied. The transition pressure expressed in terms of reduced pressure at melting point was 13 to 15 when the electrolyte concentration was around 10−2 mole/liter. These values are very close to computational value 11.6 by Alder, Hoover, and Young, indicating that the particles behave as hard spheres under such condition. At low electrolyte concentrations, the value was larger, about 30 at 10−3 mole/liter and 230 at about 10−6 mol...

Ordered structure in weakly flocculated monodisperse latex

Abstract Flocculation of a monodisperse polystyrene latex by the addition of sodium polyacrylate (SPA) is studied by bulk observation and in situ observation of the particles by an optical microscope. The results of the bulk observation, namely, the apparent feature of flocculation produced by various amount of SPA added, are in accordance with knowledge now widely known, except that in the presence of certain amounts of SPA the subsided sediment and the wall of the vessel are tinted with iridescence. But the results of the microscopic observation are rather striking; (1) the particles in each floc are arranged in highly regular hexagonal arrays, (2) the flocs (preferably called crystallites) grow and finally attain an equilibrium state with the environment, (3) nucleation, segregation and so forth are observed. These processes are reversible; namely, by shaking the vessel, the flocs are decomposed into a dispersion of single particles and upon quiet standing form again. The behavior of the particles closely resembles what we picture about the growth of real crystals (of atoms or molecules) from vapor.

Ordered structure in monodisperse gold sol

Abstract The three-dimensional ordered structure in a concentrated monodisperse gold sol (particle diameter was ≈ 4000 A) was studied by optical microscope. When the particle concentration was high enough, the sol showed iridescent color, indicating the formation of a three-dimensional ordered structure. Observed in this structure, were hexagonal and cubic patterns, lattice defects, dislocations, grain boundaries, and segregation phenomena. When the concentration was low the particles were packed at random and moved actively by Brownian motion. At the intermediate concentration, coexistence of the ordered and disordered regions was observed, and the boundary line fluctuated continually. In the disordered region near the boundary, the Brownian movement of the particles was highly restricted and coordinated vibrations were observed, suggesting the presence of a so-called “short range order” or “liquid-like structure.” Gold sol particles are very easy to observe and photograph as compared with those of the monodisperse latex. The sol would be an excellent model system for the study of the dynamic features in the structure of solid and liquid.

The observation of grain boundary structure and studies of boundary diffusion in colloid crystals

Abstract Grain boundary of polystyrene latex and gold sol crystals were observed by light microscope. Ordered boundary structures were observed. Brownian motion of the particles in the boundary suggested that the thermal vibration and diffusion in the boundary of metals differ largely from those in the lattice. The elementary process of the boundary diffusion was in the form of an “avalanche” involving a chain of particles. Thermally activated boundary phenomena such as diffusion, migration and sliding may be understood as physical quantities produced by the same elementary process.

On the long-range attractive force between plate-like gold particles: I. Fibrous aggregation

Abstract A formation of fibrous aggregates of plate-like gold particles dispersed in an aqueous solution was observed under an optical microscope. The suspension of gold particles, which were about 2 μm in diameter and 100–200 A in thickness, was prepared by reducing a dilute chloroauric acid solution with salicylic acid. When the concentration of NaCl in the suspension medium came within 7 × 10 −4 to 2 × 10 −3 moles/liter a large number of the particles aggregated face to face and formed long fibrous aggregates. These individual fibers of aggregates then lined up parallel to one other to form larger aggregates. Brownian motion was perceptible in individual particles, but these particles did not separate from the fibrous aggregates. This aggregation was reversible, since the particles redispersed by the reduction of the ionic concentration or by mechanical turbulence. This aggregation can be explained by the secondary minimum in the interaction potential curve in the theory of Derjaguin and Landau and Verwey and Overbeek.

Simulation Study of Equation of State of Simple Liquid by the Use of Monodisperse Latex

The equation of state of concentrated monodisperse polystyrene latex has been studied by sedimentation equilibrium method. Two curves are obtained, one of them is supposed to correspond to slightly modified hard sphere system by repulsive potential, while the other by weak attractive potential. First order transition from fluid to crystalline state has distinctly been observed, which is,in essence, the so-called Kirkwood-Alder transition.