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Shear-induced homogenization of semidilute solutions of polybutadiene and polystyrene mixtures with nearly critical composition was studied by the flow small-angle light scattering method. The dramatic drop of the homogenization temperature ΔTc(S)=Tc(0)−Tc(S) was observed, and studied as a function of shear rate S, where Tc(S) is the homogenization temperature at a given S and Tc(0) is the temperature under the quiescent state. The experimental results showed that ΔTc(S)/Tc(0)=KS0.50±0.02 where the prefactor K was found to be (2.6±0.6)×10−3 for the solutions containing 3.0 wt. % of total polymer weights. This prefactor is much larger than that reported for a case of simple-liquid mixture by 3 or 4 orders of magnitude. The large prefactor is proposed to be due to a long lifetime of the concentration fluctuations in the single-phase state and slow growth rate of the fluctuations in the two-phase state, compared with the corresponding quantities for the simple-liquid mixture. In the shear-induced homogenized state, the light scattered intensity I(qy) perpendicular to the flow direction was found to obey the Ornstein–Zernike equation. The correlation length ξ and the intensity at qy=0, I(0), were found to depend on S, i.e., ξ−2∼S1/2−S1/2c and I(0)−1∼S1/2−S1/2c, and diverge at the critical shear rate Sc. These experimental results on Tc(S), ξ−2 and I(0)−1, suggest the mean-field behavior of the solution of the polymer mixture under shear. The early-stage unmixing behavior after the cessation of the steady-state shear at S>Sc was also examined, the results of which indicate that the hydrodynamic interaction is suppressed, giving rise to the small mode–mode coupling contribution Dhydro/Dapp=0.2 to 0.45, but is not yet completely screened out. Hence the hydrodynamic interaction cannot be still ignored for this system.

A semidilute solution of a polymer mixture with a nearly critical composition was studied by using the small-angle light scattering method as a model system to study ordered structures and critical phenomena of mixtures under shear flow. The experimental studies revealed that there are five regimes in the shear-rate dependence of the concentration fluctuations of the solution, as discussed in the text, including the regime in which the "shear-induced homogenization" takes place. The results were interpreted, as much as possible, with the theories developed for binary mixtures of simple liquids and, when necessary, with a theory proposed here for polymer systems. Unique features of polymer dynamics in comparison with the dynamics for the critical mixtures of simple liquids were presented in the text, e.g., the shear-rate (S) dependence of the cutoff wave number being proposed to be given by qc,s~ (Dc5~) -1/4S 1/4 rather than qc,s~ (61T?]/kB T)1/ 3 S 1/3 for the simple liquids.

Electronic properties of four defect centers (designated as E7, E8, I, and IV) in A1-doped n-CdTe single crystals annealed under various Cd vapor pressures ( pCd) have been investigated by a combined use of photocapacitance, deep level transient spectroscopy (DLTS), and thermally stimulated capacitance techniques. Electron trap E7 at Ec−0.68 eV, a dominant deep defect center in samples quenched after annealing under high pCd, has shown a strong interaction with the lattice vibrations (S≳30, S: electron-phonon coupling parameter). The photoionization threshold energy for electrons E0n for the purely electronic transition has been estimated to be larger than 1.30 eV. Temperature dependence of the capture cross section for electrons σtn has been found to be very weak. The configuration coordinate diagram for E7 has suggested that E7 will nonradiatively capture the free electron. On the other hand, recombination center E8 at Ec−0.74 eV, a dominant deep defect center in samples annealed under low pCd, has shown only a negligible interaction with the lattice vibrations (S∼4) and has the photoionization threshold energies for electrons E0n ( = 0.80 eV) and for holes E0p ( = 0.95 eV) close to the thermal ionization energies for electrons Etn ( = 0.74 eV) and for holes Etp ( = 0.83 eV), respectively. The configuration coordinate diagram for E8 has revealed that E8 can radiatively capture the free electron and the free hole and can emit photons of ∼0.66 and ∼0.75 eV, respectively. E7 and E8 have been proposed to be identical with the levels previously reported as the doubly ionized Cd interstitial and the doubly ionized Cd vacancy, respectively. As to true origins of these centers, the data obtained in this study have suggested that both E7 and E8 may be donorlike complex centers including native defects, or impurities whose solubilities or stable sites in the lattice are strongly dependent on pCd. Hole trap IV at Ev +0.48 eV, which gradually decreases in concentration with decreasing pCd, has shown a weak interaction with the lattice vibrations (S∼6.7). It has been revealed that level IV can capture the free electron with emission of the photon of ∼1.0 eV. This level has been attributed to an impurity whose solubility in the crystal is moderately dependent on pCd. Electron trap I, which exists only in samples quenched after annealing under the highest pCd and have an electron-repelling barrier, has shown a very strong interaction with the lattice vibrations.

A rheo-optical apparatus for simultaneous detection of rheology, small-angle light scattering, and optical microscopy under transient, oscillatory, and continuous shear flows Rev.We presented some experimental results on flow small-angle light scattering ("flow SALS") of lyotropic polymer liqui.d crystals which involved real-time, in situ, and simultaneous measurements of mechanical properties and small-angle light scattering (SALS) of a complex structured fluid. The flow-SALS studies were conducted under steady-state Couette flow and during relaxation process occurring after the cessation of the steady-state shear flow. We found the following universal behavior on the structure and properties for two kinds of the liquid crystal systems, Le., poly (y-benzyI L-glutamate) in m-cresoI and hydroxypropyl cel1ulose in water. 0) Upon increasing shear rate y, the "polydomain" structure gradually tends to be transformed to the essentially "monodomain" texture through annihilation of the disclinations. On the top of this general tendency, we found more specific characteristic of the fluid systems with y, (ii) at y < Ye' a critical shear rate above which a remarkable shear thinning occurs, the disclinations are more or less uniformly distributed in space, while at Y> Yc the disc1inations are localized into domains and dispersed in the more or less uniform medium with a high degree of orientation, (iii) the relaxation after cessation ofthe steady state shear depends on its ybefore the cessation and is quite different below and above Yo and (iv) the cessation from y> i'c involves formation of the "band texture" during the relaxation process of the fluids. 1386