K. Hamano

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.

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.

Near-critical dynamical behavior of an ionic micellar solution

A series of experiments, static light scattering, dynamic light scattering, and shear viscosity, have been performed to study the critical properties of micellar solution of sodium dodecyl sulfate (SDS) and butanol in an aqueous solution of sodium chloride in terms of the modified dynamical droplet model. The exponents ν and γ for the long range correlation length and the osmotic compressibility were obtained as 0.736 and 1.374, respectively, in agreement with Fisher’s renormalized Ising model. The experimental investigation on the dynamic critical behavior suggests that the modified dynamical droplet model, which assumes that the local fluctuations activated thermally behave as the physical clusters with a fractal dimension of df=2.49 and a polydispersity exponent of τ=2.21, describes well the dynamical behavior of the SDS ionic micellar mixture together with an evaluation of the effective micellar size of 7–8 nm.

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 |.

Double critical behavior and micellar size effect in the multicomponent surfactant solution

Multicomponent surfactant system, sodium dodecyl sulfate and butanol in an aqueous NaCl solution, which exhibits a closed-loop type reentrant phase separation, was investigated by light scattering experiments focusing on the double critical behaviors and the finite micellar size effect on the dynamic critical behavior. The loop size decreased with the decrease of NaCl concentration, and the double critical point appeared. Approaching the double critical point, the critical exponents ν for the long-range correlation length ξ and γ for the isothermal osmotic compressibility χT determined by use of the spinodal divergency theory showed a crossover behavior from Fisher’s renormalized Ising model values to the doubling of them. ξ and χT formed master curves as a function of eUL=|(TU−T)(TL−T)|/TUTL, and had the effective critical exponents ν=0.73 and γ=1.41 ascertaining the validity of Fisher’s renormalized Ising model. Here, TU and TL are the upper and lower critical solution temperatures, respectively. Dynami...

EFFECTIVE VISCOSITIES OF A PHASE-SEPARATING BINARY MIXTURE IMPOSED TO SHEAR

Abstract We report measurements of effective viscosities in a near-critical phase-separating binary mixture in the presence of a flow field. Our experimental results suggest that the viscosity associated with a flow-induced quasi-stationary, two-phase structure obeys Onukis formula, in which a delicate balance between shear and growing domains should be achieved, resulting in significantly extended domain structures in the flow direction. It is observed that the domains break up into spherical ones smaller in size than those in a quiescent mixture when the shear is turned off. This implies that the undulation associated with a tube-like concentration domain could be suppressed by shear.

Experimental studies in a phase‐separating mixture under shear flow

This work is concerned with critical behaviors in a nonionic micellar solution of tetra‐ethyleneglycol N‐decylether (C10E4) in water in the presence of shear flow. We find the measured viscosity can depend weakly on a shear rate S in the form η∝S−ω with ω=0.021±0.003. It is reported that the phase‐separation processes induced by decreasing suddely a shear rate from S to S=0 approximately obey a universal function of spinodal decomposition for a fluid, in conjunction with a S‐dependent temperature shift given by [To(S)−Tc]/Tc =e0Sp with e0=(1.35±0.11)×10−5 and p=0.51±0.03. Here, To(S) is estimated experimentally as an onset of significantly anisotropic patterns of the forward scattered light under shear flows. The viscosity behavior in a phase‐separating mixture of isobutyric acid (IB) in water is also reported.

Phase-separation induced by shear for a near-critical ionic micellar solution

Abstract We report shear effects in a near-critically ionic micellar system of sodium-dodecyl-sulfate (SDS)+butanol+NaCl+water, with varying NaCl concentration and shear rate. In the experiment, when the mixture is imposed to shearing at a homogeneous equilibrium region, highly elongated concentration-domains suggesting phase-separation appear in the direction of flow, and when the shear is turned off, those domains disappear in time and the homogeneous state is recovered. The temperature shift associated by shear, T p − T p,S , strongly depends on shear rate and NaCl concentration, where T p and T p,S are the phase-separation temperature in a quiescent state and that in a sheared state, respectively. These results indicate that the shear-induced phase-separation occurs in the SDS micellar system, in contrast to the shear-induced homogenization observed in nonionic micellar systems.