The dynamics of low molecular weight polymer mixtures, in terms of concentration fluctuations near a critical point, in the homogeneous region, has shown a nonlinear behavior in a number of physical properties.1-2 For high molecular weight mixtures, i.e., polymer blends and block copolymers, most of the studies dealt with the dynamics of phase separation and spinodal decomposition and its incidence on the scattering properties of these mixtures.3 For the viscoelastic properties, Bates,[4][5][6] Gouinlock and Porter,6 and Han7-8 have studied block copolymers and observed important discontinuities of their dynamic properties (G' and *) near the microphase separation temperature (TB) when performing temperature steps. Also, an important increase of these properties was observed at low frequencies for temperatures close to TB.

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Two kinds of transitions can occur when an emulsified water-oil-ethoxylated nonionic surfactant system is cooled under constant stirring. At a water-oil ratio close to unity, a transitional inversion takes place from a water-in-oil (W/O) to an oil-in-water (O/W) morphology according to the so-called phase-inversion-temperature method. At a high water content, a multiple w/O/W emulsion changes to a simple O/W emulsion. The continuous monitoring of both the emulsion conductivity and viscosity allows the identification of several phenomena that take place during the temperature decrease. In all cases, a viscosity maximum is found on each side of the three-phase behavior temperature interval and correlates with the attainment of extremely fine emulsions, where the best compromise between a low-tension and a not-too-unstable emulsion is reached. The studied system contains Polysorbate 85, a light alkane cut oil, and a sodium chloride brine. All transitions are interpreted in the framework of the formulation-composition bidimensional map.

A procedure based on a Couette analogy, to quantitatively analyze torque/rotor speed data in order to extract viscosity/shear-rate curves using non-conventional geometries is presented. It is first validated using a relatively simple geometry for which the equivalent internal radius used in the analogy can be analytically obtained. The results showed that the equivalent internal radius depends only slightly on the nature of the fluid and that there is an optimal radial position r* in the analog Couette gap where the calculations can be easily performed for computing the viscosity/shearrate data from torque/rotational speed data. The experimental results with complex geometries and complex fluids are found to coincide, within experimental errors, with those obtained using standard geometries over a wide range of shear rates. The approach is also found to be very useful to evaluate shear-rate and viscosity data in Couette viscometers when large gaps are used with non-Newtonian fluids.Nous présentons une procédure basée sur une analogie Couette, permettant d'analyser de façon quantitative des données couple-vitesse angulaire de rotor afin d'extraire des rhéogrammes dans des géométries non conventionnelles. Cette procédure est tout d'abord validée à l'aide d'une géométrie simple pour laquelle un calcul analytique du rayon interne équivalent est possible. Les résultats montrent que ce dernier dépend peu de la nature du fluide et qu'il existe une position radiale optimale, r*, dans l'entrefer Couette virtuel permettant de calculer simplement les valeurs de viscosité-vitesse de cisaillement à partir des données de couple-vitesse angulaire de rotor. Les résultats expérimentaux obtenus à l'aide de géométries complexes et des fluides non-newtoniens complexes coïncident, aux erreurs expérimentales près, avec ceux obtenus à l'aide de géométries conventionnelles, sur une large place de vitesses de cisaillement. Cette procédure s'est avérée particulièrement utile pour des viscosimètres de Couette à entrefer large. Rheological characterization of complex fluids may in certain circumstances be a challenging task when conventional rheometers are used. Some food materials, for example, have microstructures with characteristic dimensions in the order of magnitude of the gap available for flow in the conventional rheometers. Placing a sample of such fluid in these geometries may result in a partial destruction of the internal structure. In other situations, phase separation of the basic constituents of the fluid to characterize occurs while the measurement is in progress. Mixer-type rheometry, consisting of a mixing device with a more or less complex geometry rotating in a fluid contained in a cylindrical tank, provides an alternative solution to such rheological characterization problems (Choplin and Marchal, 1996). Mixing devices with large local spacing can indeed be used to handle fluids with relatively large heterogeneities while providing continuous mixing. Monitoring torque and rotational speed during the mixing process can ...