N. Kuwahara

Universal exponents for a nonionic micellar solution of tetraethylene glycol decylether in water

The angular distribution of light intensity scattered from a nonionic micellar solution of tetraethylene glycol n‐decylether (C10E4) in water has been examined close to its critical point of mixing. Including multiple‐scattering corrections to the light‐scattering data, we have found the exponent γ=1.25±0.02 for the osmotic susceptibility χT and the exponent ν=0.63±0.01 for the long‐range correlation length ξ in the temperature range of 1.03×10−4≤e≤4.25×10−3, where e=(Tc−T)/Tc. The values of the critical exponents obtained in this work are in good agreement with the theoretical and experimental ones for three‐dimensional Ising systems.

Dynamics of concentration fluctuations for butylcellosolve in water

The coexistence curve, the shear viscosity, and the angular and the spectral distribution of scattered light have been measured for butylcellosolve in water near its lower critical mixing point. We have examined the validity of the pseudospinodal concept for the interpretation of the diffusion coefficient near the critical point. The critical exponents obtained with the assumption of the pseudospinodal agree with the recent experimental and the theoretical values. The universal dynamic amplitude ratio R=1.03±0.06 obtained in the present work is in disagreement with the value R=1.2 calculated from the renormalization‐group theory but in good agreement with R=1.03 of the prediction by Burstyn et al. The diffusion coefficient as a function of temperature and concentration is well represented in terms of a scaled function.

Dynamic scaling behavior of spinodal decomposition in a critical mixture of 2,5-hexanediol and benzene

Time‐resolved light scattering was used to study the time evolution of phase separation in a critical mixture of 2,5‐hexanediol and benzene in the spinodal region. The early stage behavior of spinodal decomposition where the linearized theory of Cahn–Hillard is valid has been observed. The wave number and the interdiffusion coefficient characteristic of the early stage were well described by three‐dimensional Ising model values, and the symmetric law of critical point universality was ascertained. A shoulder was observed at the higher scattering angle region in the structure factor and its wave number dependence was well expressed by the Porod law in the later stage of spinodal decomposition. The scaled behavior of the scattering function relating to the time evolution of phase separation was examined. The present result is in good agreement with the recent dynamic scaling theory.

Critical behavior of a cationic surfactant in an aqueous salt solution

The critical behavior of a cationic surfactant, butyl‐tetradecyldimethylammonium bromide, in an aqueous 4M–NaBr solution was investigated concerning the isothermal osmotic compressibility and long‐range correlation length by means of light scattering, coexistence curve, and turbidity. The critical exponents were obtained as γ’=1.39±0.04 and ν’=0.70±0.03 together with ξ0=(2.48±0.06) nm, and β’=0.375±0.01. The temperature dependence of turbidity showed a good accordance with the result of light scattering measurement. Negative α’ was obtained from the scaling relation. The critical exponents are in good agreement with the Fisher‐renormalization prediction for the ternary system (almost fully renormalized Ising exponents).

A characteristic temperature for the visibility of phase separation in a binary liquid mixture under shear

Abstract In this work we report a shear-dependent temperature T 0 ( S ) at which the phase separation of critical mixture mo isobutyric acid and water is detected by observation of intense forward-scattered light. We show that T 0 ( S ) is distinct from the shear-dependent critical temperature T c ( S ). We find that T 0 ( S ) is identical with the crossover temperature T s - ( S ) that distinguishes the weak- and strong-shear regimes in the coexisting phases and suggest that the formation of concentration domains in the strong-shear regime below T c ( S ) is suppressed by shear.

Critical anomaly in the viscosity of a nonionic micellar solution

Abstract The critical enhancement in the viscosity has been examined using a low-shear rotational viscometer for a nonionic micellar solution of tetraethylene glycol n -decylether (C 10 E 4 ) in water. The estimated value o =0.041±0.005, which characterizes the temperature dependence of the viscosity very close to its critical point of mixing, is in excellent agreement with that predicted by the dynamical universality for a fluid.

The early stage of phase separation for the system polydimethylsiloxane-diethyl carbonate

Abstract The time evolution of a ring formed by the forward scattered light in the phase separation process was found to be divided into an early and a late stage. The effective concentration diffusivity D ∗ estimated within the linearized approximation in the unstable region was found to be approximately represented by - D ∗ ∝ϵ v ∗ with v ∗ ≈0.6 2 , where ϵ=| ( T-T c )/ T c |.

Spinodal decomposition in a polymer mixture

Light scattering was used to study spinodal decomposition in a critical mixture of polystyrene and polymethylphenylsiloxane. Time dependence of the wave number of the maximum scattering intensity was expressed by power‐law relations. Those exponent values are consistent with the values obtained for the metallic alloys.

Kinetics of spinodal decomposition in a critical polymer solution

Spinodal decomposition in a critical mixture of polydimethylsiloxane and diethyl carbonate was investigated by a time-resolved light-scattering technique in the time region of the early to the intermediate stage of phase separation. The exponential growth of the scattered light intensity without changing the wave number of its peak was observed, in good agreement with the linearized theory of Cahn-Hillard. The quench depth dependences of the interdiffusion coefficient and of the wave number corresponding to the most dominant fluctuation show the three-dimensional Ising-model behavior indicating the validity of the symmetric law of critical-point universality.

Scaled phase separation in a critical nonionic surfactant solution

The time evolution of phase separation in a critical mixture of non-ionic surfactant, pentaethylene glycol n-decylether and water, was investigated by the time-resolved small-angle light scattering in the spinodal region focusing to the scaling concept. The scaled behavior of the wave number and the intensity corresponding to the spinodal ring and of the scattering function are examined in relation to recent theoretical work. Good agreement was obtained with the dynamic scaling theory.