Tahar Tajouri

Simple-Complex Fluid Transition in Microemulsions

The aim of this work was to study the rheological behavior of water in-oil microemulsion formulated with AOT (sodium bis(2-ethylhexyl) sulfoccinate) in isooctane over a temperature range from 25°C to 55°C for the oil/AOT volume fraction φ m =0.1 and various AOT and H2O molar ratios, W0, ranging from 0 to 45. The apparent viscosity was measured vs. shear rate by a rotational concentric cylinder viscometer. It was shown that above s−1, the solutions utilized behaved as Newtonian liquids. The absolute viscosities were deduced from the shear stress- shear rate rheograms. For W0 < 17, the solutions behaved as simple fluids, where the viscosities decrease as the temperature increases. However, an opposite behavior was observed for W0 > 17; the viscosity remained constant and then increased above a critical temperature, Tc, depending on W0. For the molar ratio W0,c = 17; the studied viscosity remained constant, η(W0,c) = (1.17 ± 0.04) cP, for the temperature range studied. Thus, a simple–complex fluid transition was evident in the studied system. For the simple fluids, W0 < W0,c, the total activation energy vs. W0 showed three linear parts. The different slopes were attributed to the change of the microscopic structure of the formed micelles. For the critical molar ratio W0,c = 17, the total activation energy vanished. So, according to the Eyring lattice model, the jump of the formed micelles from one site to another was not permitted and the entire molecular groups were in vibration and rotation motions. For W0 > W0,c, where the formed micelles were fully hydrated, the relative viscosity of the studied solutions vs. temperature was fitted according a polynomial law, where the exponent was found to be dependent on W0.

Study by 1H NMR of the Influence of the Porosity and Solvent on the Conformations of Macromolecules at an Interface: Poly(Ethylene Oxide) Grafted on Silica

ABSTRACT The 1H NMR technique was used to study the behaviour of poly(ethylene oxide) chains grafted chemically on silica. A noticeable influence of the nature of the surface and solvent on the conformation of the grafted macromolecules was observed. For precipitated silica the chains adopted a disordered conformation whereas for pyrogenic silica they formed a more uniform layer. The grafting ratio and the solvent can both modify the conformations of the chains. The dependence of the relaxation times (T1 and T2) on the grafting ratios is discussed qualitatively from a phenomenological point of view. Different models are proposed for the two extreme grafting ratio levels in both the absence and the presence of solvent. Without solvent, for both grafting ratios, the macromolecules lie very flat on the silica and the layer is more organized, especially at high grafting ratio. In the presence of solvent the chains spread out in the solvent, adopt a more extended conformation and the local concentration of monomers at the surface decreases.

Effect of Temperature and a Non-Solvent Addition on the Specific Volume of Poly (Sodium-4-Styrene Sulfonate) in Water

ABSTRACT The effect of temperature and a non-solvent, ethanol, addition on the specific volume of poly (sodium 4-styrene sulfonate) in water was investigated. The refractive indices of the studied solutions were measured over the 298.15–323.15 K temperature range. Then, the specific volumes of the polyelectrolyte were calculated according to the Lorentz–Lorenz and Gladstone–Dale equations. The relative deviations of the specific volumes between measured and calculated according to these equations did not exceed 2.5%. Several empirical equations were deduced to describe the variations of the refractive index increment and the specific volume versus the temperature and the mixture composition.

A Novel Interpretation of Polymer Viscosity in Mixed Solvents

A novel interpretation of the viscosity of a polymer in mixed solvents in the dilute concentration regime is presented. The ternary system polymer/solvent 1/solvent 2 was considered as a quasi-binary system and the presence of the polymer acts as a perturbation on the mixed solvents where the interaction between unlike molecules was quantified by the Grunberg–Nissan constant, . Thus, a pseudo-Grunberg–Nissan constant, , was introduced to quantify the interaction between the unlike molecules of the mixed solvents in the presence of the polymer. The effect of the polymer addition on the interaction between unlike molecules was quantified by introducing the deviation of the Grunberg–Nissan constant, , concept which is connected to both the intrinsic polymer viscosity and the Huggins constant in pure and mixed solvents. This novel interpretation of the viscosity data was used to study the effect of polystyrene dissolution on the interaction between benzene and ethyl acetate at 20°C.