Linear and nonlinear rheology of micellar solutions in the isotropic, cubic and hexagonal phase probed by rheo-small-angle light scattering
✍ Scribed by Reinhard Linemann; Jörg Läuger; Gudrun Schmidt; Krystyna Kratzat; W. Richtering
- Publisher
- Springer-Verlag
- Year
- 1995
- Tongue
- English
- Weight
- 967 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0035-4511
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✦ Synopsis
Aqueous solutions of a branched nonionic surfactant were studied in the isotropic, cubic and hexagonal phase by means of theological and small-angle light scattering (SALS) experiments. The isotropic phase behaved like a Newtonian liquid. An increase of activation energy of viscous flow was found near the overlap concentration of spherical micelles, but no shear thinning was observed. The viscosity of low concentrated samples increased slightly when the lower critical solution temperature was approached. This increase of viscosity was much smaller compared to common nonionic surfacrants. The cubic phases behaved as elastic solids with a high plateau modulus, and shear melting occurred at high shear stresses. The hexagonal phase showed complex behavior. Shear orientation could be achieved by large amplitude oscillatory shear and was proved by rheo-small-angle light scattering. Two orientations were observed, at first perpendicular to the flow direction, i.e., log-rolling state and, secondly, an in-shear-plane orientation parallel to the flow direction. The linear viscoelastic region of the hexagonal phase was extremely small and was detected by simultaneous rheo-small angle light scattering. Shear alignment lead to a decrease of the moduli.