We have studied the effect of the lipophilicity of the counterions Xon the rheological properties of aqueous solutions of cetyltrimethylammonium-based surfactants (CTAX): cetyltrimethylammonium n-hexane sulfonate (CTAC6SO3), cetyltrimethylammonium n-heptane sulfonate (CTAC7SO3), and mixtures of cetyltrimethylammonium 3-hydroxy-2-naphthalenecarboxylate (CTAHNC) and cetyltrimethylammonium bromide (CTAB) in the molar ratio 1:1 and 2:1. Both linear and nonlinear viscoelasticity properties have been investigated as a function of surfactant volume fraction and temperature. For the system CTAHNC + CTAB (1:1), the effect of added salt (NaBr) was also studied. In the concentration and temperature ranges used in this study, all the systems exhibit a viscoelastic behavior characteristic of wormlike micellar solutions. By changing the lipophilic character of the counterion, one varies the net electrical charge carried by the micelle, which allows us to present a general description of the effect of the electrostatic interactions on the viscoelasticity of micellar systems.

Amorphous silver nanoparticles of ca. 20 nm size have been prepared by the sonochemical reduction of an aqueous silver nitrate solution in an atmosphere of argon-hydrogen. The silver nanoparticles have been characterized by TEM, X-ray diffraction, absorption spectroscopy, differential scanning calorimetry and EPR spectroscopy. The mechanism of the sonochemical reduction has been discussed, and occurs through the generation of hydrogen radicals during the sonication process.Today, nanoparticles have become the focus of intensive ( TEM ). The silver nanoparticles are also characterized using powder X-ray diffraction ( XRD), plasmon spectroscopy, research, owing to their numerous applications in diverse fields differential scanning calorimetry (DSC ), and EPR such as catalyst production, ultramodern electronic and elecspectroscopy. trooptical devices, supermagnets, photographic suspensions, etc.1,2Nanoparticles have a large surface-to-volume ratio, and

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