Slow relaxation mode in concentrated oil-in-water microemulsions consisting of repulsive droplets.

International audienceThe present contribution reports on the observation of two diffusive relaxation modes in a concentrated microemulsion made of repulsive droplets. These two modes can be interpreted in the frame of Weissman's and Pusey's theoretical pioneering works. The fast mode is associated to the collective diffusion of droplets whereas the slow one corresponds to the relaxation of droplet concentration fluctuations associated with composition and/or size. We show that (i) repulsive interactions considerably slow down the latter and (ii) a generalized Stokes Einstein relationship between its coefficient of diffusion and the Newtonian viscosity of the solutions, similar to the Walden's rule for electrolytes, holds for concentrated microemulsion systems made of repulsive droplets

Dynamics of a dry-rebounding drop: observations, simulations, and modeling

Dynamics of a dry-rebounding drop was studied experimentally, numerically, and theoretically. Experimental results were reproduced by our computational fluid dynamics simulations, from which time series of kinetic energy, potential energy, and surface energy were obtained. The time series of these energies quantitatively clarified the energy conversion and loss during the dry-rebound. These results were interpreted by using an imaginary spring model and a spherical harmonic analysis. The spring model explained the vertical deformation of the drop, however, could not completely explain the energy loss; the timings of the energy loss did not match. From a viewpoint of the spherical harmonic deformation of a drop, the deformation of the drop after the impact was found to be a combination of two vibrational motions. One of the two vibrational motions is an inertial motion derived from the free-fall and the another is a pressure-induced motion derived from a pressure surge due to the sudden stop of the bottom part of the drop at the impact. The existence of the pressure surge at the impact was confirmed in the simulated results. The pressure-induced motion resists the inertial motion and consequently dumps the kinetic energy of the drop

Complex macromolecular dynamics: I. Estimation technique for time-resolved emission anisotropy ratio of chromophores incorporated into polymer chains

Time-resolved fluorescence emission anisotropy ratios of carbazolyl groups incorporated into polystyrene chains in polyethyleneoxide(PEO)/1,2- dichloroethane mixtures have been measured by the single photon counting method. The fluorescence depolarization method is very excellent to clarify various dynamical modes of polymer chains, and many theoretical and experimental researches have so far been reported in the field of polymer chain dynamics. However there are few reports about the dynamics on the polymer side chain, because the dynamical mechanism of the polymer side chain is very complicated. In this report we tried to analyze the dynamical modes of the polymer side chains by the fluorescence depolarization method. Five dynamical modes of a polymer chain based on the Wöessner model were estimated by our original analytical technique 'χ2-map method'. The value of each mode of a polymer side chain was discussed above the overlap concentration (C *) of PEO and the micro-environments were clarified in the vicinity of the chromophore attached to the polymer side chain

Size evolution of onion structure under oscillatory shear flow

The formation process of onion structure in a quaternary mixture among water, NaCl, octanol and sodium dodecyl sulphate, have been investigated by two dimensional light scattering under oscillatory shear flow. In our experiment, we investigated the size evolution of onion structure estimated by light scattering data with a nonlinear least-squares curve fitting method. The time evolution of onion size showed a good agreement with a stretched exponential function. The effect of oscillatory shear flow on formation process of onions is briefly discussed from the viewpoint of the physical meaning of fitting parameters based on the integral transformation method

Formation Process of shear-induced onion structure made of quaternary system SDS/octanol/water/NaCl

The formation process of onion structure in a quaternary mixture made of water, NaCl, octanol and sodium dodecyl sulphate, have been investigated by two dimensional light scattering under various shear rates. In this paper, we investigated the size evolution of onion structure estimated by light scattering data with a nonlinear least-squares curve fitting method. The time evolution of onion size showed a good agreement with a stretched exponential function. The formation process of onion structure is briefly discussed from the viewpoint of the physical meaning of fitting parameters based on the integral transformation method

Growth of monodisperse mesoscopic metal-oxide colloids under constant monomer supply

In closed systems, control over the size of monodisperse metal-oxide colloids is generally limited to submicrometric dimensions..