The effect of hydrophilic head of drag reducing cationic surfactants on the micellar structures has been studied by using fluorescence probe technique. Sodium 3-hydroxy-2-naphthoate, NaHN, has been used as a fluorescence probe in these experiments. Four types of surfactants having the same alkyl chain but different in number of hydroxyethyl, HE, group changed from 0 to 3 have been tested. A method of calculating the molar ratio of free counter-ions is suggested with the fluorescence decay behavior of counter-ion. From the results, it is found that the lifetime of fluorescence decay in micellar interior phase decreases while the molar fraction of free counter-ion increases when the HE group number increases. It is also found from the results on the molar ratio of free counter-ions and the comparison of Stokes diameters that the decrease of the critical Reynolds number is related to the number density of micellar structures and its strength.

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The biaxial extensional characteristics of a cationic surfactant solution system showing an effective drag reduction in pipe flow have been studied by using two opposed nozzle devices. Aqueous solutions of cationic surfactant, oleylbishydroxyethylmethylammonium chloride, at the concentrations varied from 250 to 1,000 ppm with sodium salicylate, which ionized to counter-ion in an aqueous solution, of which molar ratio to surfactant was set at 1.5, were tested. Especially, time characteristics of extensional stress were focused in wide ranges of surfactant concentration and extensional rate. From the results, the apparent extensional viscosity is found to depend on the extensional rate and on the surfactant concentration. For the extensional rate dependency, the extensional viscosity behavior is classified into four regions. This characteristic is considered to be caused by the formation and the deformation of the surfactant rodlike micellar network structure. In each region, the build-up and relaxation times are not strongly affected by the concentration of the surfactant. On the other hand, the build-up time decreases with a gradient of -1 in a double logarithm plot to the extensional rate, while the relaxation time decreases weakly with the extensional rate. The former fact indicates the micellar network formation occurs due to the collision of surfactant micelles. It is also found that two relaxation processes exist for the extensional flow cases. The shorter or the longer relaxation time takes almost the same value as each value corresponding to that for the shear flow release condition. This indicates the network structure size formed in the biaxial extensional flow takes almost the same as that in the shear flow.