The rheological properties of different phases of the CTAB/benzyl alcohol/water system have been studied. The L phase, except the samples close to the hexagonal liquid crystal, is a viscous fluid with a characteristic Newtonian behavior. On the contrary, the L phase samples close to the hexagonal phase are pseudoplastic fluids built up of cylindrical micelles with elastic properties. The hexagonal liquid crystal behaves as a shear thinning fluid with a well-defined zero-shear-rate viscosity, while the lamellar liquid crystal does not show a zero-shear-rate viscosity and it presents yield stress values. Both liquid crystals have significant elastic properties although we could not find any linear region of viscoelasticity in the lamellar phase. The cubic liquid crystal is also an elastic phase with ringing gel properties. The hexagonal and cubic liquid crystals follow the Maxwell treatment only at low angular frequencies. Consequently, from the results the relaxation time and the instantaneous elastic modulus have been obtained. The relaxation times range in these phases from 2 to 9 s while the relaxation times of the cylindrical micelles are three decades smaller. LA9515682
The lysozyme-sodium dodecyl sulfate-water system features several interesting aggregation phenomena and is also of interest as it constitutes a model system for mixtures of a charged colloid with an oppositely charged surfactant, as both colloid and surfactant are pure and monodisperse compounds. The structure of such mixed protein-surfactant systems has been investigated by means of SANS contrast variation experiments. Two interesting issues of protein-surfactant aggregation are discussed. First, a new set of data on the structure of the protein-surfactant complex in solution is added to the discussion of whether the model of "beads on a necklace", "protein decorated micelles", or "flexible helix" is most appropriate. It is our conclusion that the compact globule of lysozyme does not fit well into any of the mentioned models. Instead, transient clusters of lysozyme-SDS aggregates are proposed for the L 1 phase and more strongly bound locally linear clusters for the gel phase. Second, the structure and formation of a homogeneous, transparent gel at room temperature is analyzed and compared to the well-studied heat-set globular gels. The gel structure in different ionic strengths, lower than the one caused by naturally occurring buffer salts has also been analyzed and it seems that small amounts of salt render the system a more repulsive character than salt-free conditions. In addition to the equilibrated samples studied with the contrast variation technique, the complexation has been studied over time.
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