Characterization of micellar aggregates in viscoelastic surfactant solutions. A nuclear magnetic resonance and light scattering study

Olsson, Ulf; Soederman, Olle; Guering, P.

doi:10.1021/j100412a066

Cited by 150 publications

(146 citation statements)

References 2 publications

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“…For instance, the CTAB and salicylate ions form 1-1 complexes (10). At high salt concentrations, the micelles become negatively charged due to the dominating counterion condensation (33). Then, the effect of Coulomb interactions produces a decrease of micellar length and therefore a lower viscosity.…”

Section: Resultsmentioning

confidence: 99%

Rheological behaviour of wormlike micelles : effect of salt content

et al. 1993

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We study the effect of salt content on the rheological properties of wormlike micelles formed from hexadecyltrimethylammonium bromide (CTAB) in presence of potassium bromide (KBr) and of cetylpyridinium chlorate (CPC10,) in presence of sodium chlorate (C10,Na). Upon increasing the salt concentration, at fixed surfactant concentration, we observe for both systems a maximum of the zero-shear viscosity %. For salt concentrations less than that corresponding to the maximum of qO, the variation of qo with the surfactant concentration C can be described by a reptation model. Beyond the maximum, the scaling laws obtained for qo(C) are characterized by values of the exponent much smaller than those predicted by the existing theoretical models. The results are qualitatively interpreted by a description based on a structural evolution upon increasing salt content from a system of entangled linear micelles to a multiconnected network. Measurements of the plateau modulus of CTAB solutions, as a function of KBr, give results supporting the above hypothesis.Nous prtsentons une ttude de l'influence de la teneur en sel sur les propriktks rhwlogiques de solutions de micelles cylindriques form& i partir de bromure d'hexadecyltrimethylammonium (CTAB) en prksence de bromure de potassium (KBr) et de chlorate de cetylpyridinium (CPC10,) en presence de chlorate de sodium (C10,Na). Lorsqu'on fait varier la concentration en sel, i concentration en tensioactif constante, on observe pour les deux syst&mes un maximum de la viscositk h gradient nu1 7,. Pour des concentrations en sel infkrieures i celle correspondant au maximum de qo la variation de qo avec la concentration en tensioactif C peut Ctre d6crite par un modtle de reptation. Au-delh du maximum les lois d76chelles obtenues pour qo(C) sont caractkriskes par des valeurs de l'exposant beaucoup plus faibles que celles praites par les modtles thbriques existants. Les rksultats sont interprttts qualitativement 2 partir d'une description fond& sur l'kvolution de la structure micellaire lorsqu'on augmente la teneur en sel, d'un systkme de micelles lintkires enchev2trks vers un rkseau interconnectk. Les mesures du plateau du module de cisaillement en fonction de la concentration en KBr pour des solutions de CTAB donnent des rksultats ktayant cette hypothbse.Article published online by EDP Sciences and available at http://dx

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Section: Resultsmentioning

confidence: 99%

Rheological behaviour of wormlike micelles : effect of salt content

et al. 1993

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“…For example, the Sal ions can penetrate in the interface of the cetyltrimethylammonium-micellar cores, making the micelles more flexible, as observed in NMR studies and molecular simulations (39)(40)(41). Double peaks of the zero-shear viscosity have also been observed with increasing organic salt concentrations.…”

Section: Effect Of Salt On Branched Wormlike Micellesmentioning

confidence: 90%

Microstructure and rheology of a flow-induced structured phase in wormlike micellar solutions

Cardiel

Dohnálková

Dubash

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Surfactant molecules can self-assemble into various morphologies under proper combinations of ionic strength, temperature, and flow conditions. At equilibrium, wormlike micelles can transition from entangled to branched and multiconnected structures with increasing salt concentration. Under certain flow conditions, micellar structural transitions follow different trajectories. In this work, we consider the flow of two semidilute wormlike micellar solutions through microposts, focusing on their microstructural and rheological evolutions. Both solutions contain cetyltrimethylammonium bromide and sodium salicylate. One is weakly viscoelastic and shear thickening, whereas the other is strongly viscoelastic and shear thinning. When subjected to strain rates of ∼10 3 s −1 and strains of ∼10 3 , we observe the formation of a stable flow-induced structured phase (FISP), with entangled, branched, and multiconnected micellar bundles, as evidenced by electron microscopy. The high stretching and flow alignment in the microposts enhance the flexibility and lower the bending modulus of the wormlike micelles. As flexible micelles flow through the microposts, it becomes energetically favorable to minimize the number of end caps while concurrently promoting the formation of cross-links. The presence of spatial confinement and extensional flow also enhances entropic fluctuations, lowering the energy barrier between states, thus increasing transition frequencies between states and enabling FISP formation. Whereas the rheological properties (zero-shear viscosity, plateau modulus, and stress relaxation time) of the shear-thickening precursor are smaller than those of the FISP, those of the shear-thinning precursor are several times larger than those of the FISP. This rheological property variation stems from differences in the structural evolution from the precursor to the FISP. microfluidics | microrheology | mesh size S urfactant molecules in aqueous solutions can self-assemble into different structures, such as spherical micelles, cylindrical micelles, lamellar phases, and vesicles (1). The morphology of these self-assembled structures is influenced by surfactant concentration, temperature, external additives (e.g., cosurfactants or salts), and flow conditions. Cylindrical micelles in the presence of inorganic or organic salts can self-assemble into large, flexible, and elongated wormlike micelles that exhibit viscoelastic properties (2-4). The ionic strength of the salt screens the electrostatic repulsions between the charged surfactant head groups, promoting cylindrical micellar growth (1-3). At higher salt concentrations, the entangled linear micelles can transition to branched and multiconnected micellar networks, as evidenced by rheological measurements, light scattering techniques, and electron microcopy (EM) imaging (5-18). Additionally, wormlike micellar solutions are known to exhibit a variety of interesting phenomena, some of which are shear banding (19-21), shear thickening (22, 23), shear-induced transitions and insta...

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“…Here, the on further increasing to n Ç 1-2, D mix values remain conmicelles become negatively charged, and for geometrical stant. A slight increase in D mix values is, however, noted at packing reasons the micelles undergo an elongated-to-sphern ú 2. ical transition, which is with a concomitant to an increase At n õ 0.95 the self-diffusion coefficient, D slow , obtained in headgroup area (17).…”

Section: Self-diffusion Coefficients Of the Mixed System Sn-do-tac-d mentioning

confidence: 90%