Kaoru J. Takano

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...

Pressure of disorder to order transition in monodisperse latex

Abstract Monodisperse latexes show a first order phase transition from the disordered to the ordered state under certain conditions. In the present study, the osmotic pressure and the volume fraction are measured at the phase transition (melting) point by the use of sedimental equilibrium. At relatively high electrolyte concentration (around 10 −2 mol/l) of the medium, the pressure is very near the value of the Alder transition, though the volume fraction is less than 0.55 (the theoretical value for the melting point in the transition). At low electrolyte concentration (⋍10 −3 mol/l), the pressure is higher, showing the effect of the repulsive potential. At high concentration (5 × 10 −2 mol/l), the pressure is markedly depressed due to the effect of the van der Waals force or of the secondary minimum. The effect of the colloid interaction on the transition condition is that: 1) the inner part of the potential that is strongly repulsive does not influence the transition pressure but only works to increase the effective size of the particles; and 2) the pressure is affected only by the outer part of the potential.

Effect of hydrostatic pressure on the crystallization of lysozyme based on in situ observations

The growth rate (R) and solubility (cs) of the tetragonal crystals of hen egg-white lysozyme were determined under hydrostatic pressure up to 350 MPa based on the observations through transparent windows. When the pH is 4.6 and the NaCl concentration 3.0% (w / w), cs (in % (w / w)) increases with pressure p (in MPa) at 23°C approximately as cs = 0.78 + 0.0152p. In contrast to the linearly increasing cs, R decreased non-linearly with pressure, and was practically zero in a wide pressure range from about 100 to 200 MPa. This means that conventional methods of determining the solubility based on the concentration change are difficult to be used under high pressure. This problem can be overcome by combining in situ observations with image analyses.

NEW HIGH-PRESSURE PHASES OF CARBON

Reversible phase transformations with volume contractions were found at 18 GPa and 22 GPa when graphite was compressed at room temperature. Volume contraction was detected in a diamond anvil cell by observing a plateau in the curve of generated pressure versus the cell load. The phase realized at 18 GPa is thought to work as an intermediate phase in the transformation from graphite to hexagonal diamond. A structure of this phase, though not yet identified, is also discussed.

An optical high pressure cell with spherical sapphire anvils

An optical high pressure cell has been constructed of spherical sapphire anvils (9.53 mm in diameter). The anvil has a small flat compression face (1.5 mm or 2.5 mm in diameter), which is perpendicular to the crystal c axis. Pressure is generated using a gasket, typically made of phosphorus bronze. A maximum pressure of 12.6 GPa was generated at room temperature in a liquid pressure medium. Pressures up to 10 GPa have been generated stably without appreciable damage of the anvils. The capability of optical observations for a photon energy region up to 6.4 eV was confirmed with this anvil, at high pressure. An advantage of the spherical anvil is ease in production.

Spectroscopic study of monodisperse latex: I. Short-range order in monodisperse latex

Abstract Concentrated monodisperse latex, which is usually described as milky white is tinted with very faint diffuse color. This is due to the presence of the so-called short-range order in it. In this work, backward scattering from this latex was measured spectroscopically at several volume fractions of the polymer and it was found that this order appeared at higher particle concentration than 0.3 in effective volume fraction. As a by-product, this measurement gives a phase diagram of monodisperse latex which is significantly different from the original one presented by Hachisu et al. [J. Colloid Interface Sci.42, 342 (1973)].

Spectroscopic study of monodisperse latex: II. Phase diagram of monodisperse latex

Abstract The phase diagram of a monodisperse latex was constructed by the use of a spectroscopic method. The volume fraction of the polymer particles was determined from peak wavelength of Bragg reflection of the ordered phase. The diagram obtained has very narrow region of coexistence of the ordered and disordered phases. In high electrolyte concentration region, its precision has been much improved over the original diagram proposed by Hachisu et al. [ J. Colloid Interface Sci. 42, 342 (1973)]. At low electrolyte concentration region, however, some abnormal behavior is still recognized, which is of the same nature as in Part I [ J. Colloid Interface Sci. 66, 124–129 (1978)].

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.

Development of an optical liquid high pressure cell and its application to visual observation of pressure-driven crystal growth

Abstract An optical liquid high pressure cell generating pressures up to 1 GPa was developed for visual observation of crystal growth, which can settle a supersaturation very rapidly by a pressure operation. By using a soft transparent sample bag, the cell provides high reliability of pressure control (less than ± 1 MPa) and easy handling. The method of constructing a phase diagram was developed for deducing the supersaturation. The pressure and supersaturation dependences of the nucleation and the growth form of p-xylene crystals were observed, which can be explained by the pressure and concentration dependence of the surface and the edge free energy, respectively.

Topotaxial and some other characters of the transformation from hexagonal to wurtzitic BN

Abstract Wurtzitic BN was formed at high pressure from compacted powder of hexagonal BN with c -axes preferentially oriented in one direction. X-ray diffraction on the recovered sample revealed that c -axes of the formed phase had the same orientation distribution as that of the starting phase. The revealed topotaxy confirms a diffusionless mechanism for this transformation, which has been supposed so far on the basis of the known simple correspondence between crystal structures of both phases and some kinetic features of this transformation. Further, the transformation could be caused more easily by the use of larger crystals of hexagonal BN regrown in a flux, which supported the diffusionless mechanism, too. By in sutu X-ray diffraction, the temperature dependence of the pressure for inducing the transformation was determined. No intermediate phase was detected.