Dynamic Viscoelasticity and Flow Behavior of a Polyoxyethylene Glycol Nonylphenyl Ether/Toluene/Water System

Abstract

Several samples of a ternary nonionic surfactant/ toluene/ water system at six compositions were characterized on the basis of their rheological and phase behaviors at 25 °C. Different self-association structures were identified: a dispersion of lamellar vesicles embedded in an isotropic phase (D1), a further dispersion (D2) consisting of an aqueous phase dispersed in a continuous medium whose structure is dominated by an incipient lamellar liquid−crystalline structure, three samples located in the lamellar mesophase (Lα) region and an L2 sample. The latter exhibited Newtonian behavior and no viscoelasticity, both phenomena were attributed to the occurrence of reverse globular micelles. Linear dynamic viscoelasticity revealed that samples located well within the Lα region showed mechanical and relaxation spectra typical of highly structured materials. Similar spectra were observed for a D2 sample but with a lower plateau modulus, indicating that the basic structure was the same as for standard Lα samples but with weaker interactions among the liquid−crystalline monodomains. An Lα sample located by the border of the L2 and Lα regions showed more fluidlike viscoelastic properties. Relaxation spectra turned out to be quite sensitive to a change of composition. The different viscoelastic results found for the Lα samples studied were associated with a change of the so-called packing parameter with composition. Apparent viscosities derived from flow curves were compared with complex viscosities. While shear flow provoked an order decrease in the Lα systems, it gave rise to a striking structural build-up process in the dispersions.

Rheological Behavior and Structure of a Commercial Esterquat Surfactant Aqueous System

“…The occurrence of a peak in G" at the onset of nonlinear response of concentrated emulsions was attributed by Lequeux et al to a structural rearrangement preceding its collapse [16]. This response in surfactant lamellar phases and in dispersions of vesicles in an incipient lamellar liquid crystalline matrix was explained on the basis of the existence of small mechanical defects in the closepacked structure, which promote shear-induced rearrangements in the contact zones of monodomains, leading to some mechanical dissipation [17]. The peak in G" tended to disappear as surfactant concentration decreased and the structure was not as tightly packed (see 12 wt % T1 results) in agreement with results obtained for diluted aqueous dispersions of vesicles [17].…”

“…This response in surfactant lamellar phases and in dispersions of vesicles in an incipient lamellar liquid crystalline matrix was explained on the basis of the existence of small mechanical defects in the closepacked structure, which promote shear-induced rearrangements in the contact zones of monodomains, leading to some mechanical dissipation [17]. The peak in G" tended to disappear as surfactant concentration decreased and the structure was not as tightly packed (see 12 wt % T1 results) in agreement with results obtained for diluted aqueous dispersions of vesicles [17]. The case of the most diluted system studied (4 wt % T1) was quite enlightening since both G' and G" fell throughout the whole shear stress range applied.…”

“…A detailed description of the fitting protocol used was reported in [23] and further applications can be found in [17,24]. Fig.…”

“…However, the information provided by the background was not clear enough to assess whether vesicles were dispersed into a micellar solution or were embedded in a tenuous network made by a bilayer matrix. Both types of dispersions were reported to occur in a nonionic surfactant/hydrocarbon/water system depending on composition [17].…”

Microstructure and Lubrication Properties of Lamellar Liquid Crystal in Brij30/[Bmim]PF6/H2O System

“…As for [Bmim]PF 6 , the dependence of loss modulus on the content of [Bmim]PF 6 is negligible because most of the [Bmim]PF 6 molecules locate in the amphiphile layer [16] and the thickness of the solution layer is independent of the content of [Bmim]PF 6 . Besides, the minimal loss modulus G@ mim in each line corresponds to the minimum function work needed to make the La phase flow under the corresponding shear frequency of x mim [28]. The smaller the value of x mim , the easier for the phase to flow.…”