Dynamic Properties of Salt-Free Viscoelastic Micellar Solutions

Abstract

Rheological experiments were carried out on aqueous micellar solutions of the "dimeric" surfactant ethanediyl-a,a>-bis(dodecyldimethylammonium bromide) as a function of surfactant volume fraction and temperature. The aim was to investigate the effect of electrostatic interactions on the micellar size through the linear viscoelastic properties of the system. The zero-shear viscosity results indicate a sharp crossover from a dilute regime in which the micelle growth is very weak to a regime of rapid growth, in agreement with the theoretical predictions. However, upon increasing further the volume fraction, a maximum of the zero-shear viscosity is observed which suggests that the micellar length also goes through a maximum. This is confirmed by the ánalysis of the viscoelastic spectra on the basis of the recently developed models taking into account both reptation and Rouse processes. The decrease of micellar length observed in the high volume fraction range has been interpreted as due to the decrease of the effective end-cap energy associated with the theoretically predicted increase of the micelle ionization degree with volume fraction. The effect of the electrostatic interactions also appears in the behavior of the plateau modulus that exhibits a larger volume fraction dependence than in highly screened micelles.

Effect of Screening of Intermicellar Interactions on the Linear and Nonlinear Rheology of a Viscoelastic Gel

“…7(c)) where η • shows a decrease with c N aCl . In contrast to previous experiments with gemini surfactants [3], there is a regime of weak decrease of η • (regime II) followed by a much stronger decrease on increasing c N aCl (regime III). At the cross-over between regimes II and III (c N aCl = 60mM), the change in the slope of η • (Fig.…”

“…Experimentally, a purely exponential stress relaxation has been found in many surfactant solutions [1,2,3,4] where the dynamics obey τ break << τ rep . In such cases, the relaxation spectrum shows a single-exponential behavior and the viscoelastic moduli of the material are given by the well-known Maxwell model [2,9] …”

Effect of ionic strength on rheological behavior of polymer-like cetyltrimethylammonium tosylate micellar solutions

“…8,[15][16][17][18][19] Some authors have added another inorganic salt, such as NaCl or KBr, to further screen the electrostatic interactions in these surfactant/salt (inorganic or organic)/water micellar systems. 16,[20][21][22] By contrast, the structural and rheological reports on salt-free viscoelastic micellar solutions are scarce. Kern et al 22 investigated the linear viscoelastic behavior of salt-free polymer-like a Departamento de Ingenier ıa Qu ımica, Universidad de Guadalajara, Boul.…”

“…16,[20][21][22] By contrast, the structural and rheological reports on salt-free viscoelastic micellar solutions are scarce. Kern et al 22 investigated the linear viscoelastic behavior of salt-free polymer-like a Departamento de Ingenier ıa Qu ımica, Universidad de Guadalajara, Boul. M. Garc ıa Barrag an # 1451, Guadalajara, Jal., 44430, M exico.…”

Mobility of Spin Probes in Micelles of Cationic Gemini Surfactants Having Dodecyl Groups.

“…On the other hand , gemini surfactants are made up of two identical amphiphilic moieties connected at the level of the head groups or very close to head groups by a spacer group [ 12,131, which are also referred to as dimeric or bipolar surfactants [14,15]. Although the properties of the gemini surfactant micelles have been extensively studied by Zana et al [16][17][18][19][20][21][22][23][24], the gemini surfactants have not been applied as dyeing auxiliaries. To use the surfactants as dyeing auxiliaries, it is necessary to get an information about the microenvironments of the gemini surfactant micelles and the behavior of small molecules in them.…”