Viscoelastic surfactant solutions: Kinetically controlled viscosities

Hoffmann, H.; Löbl, M.; Rehage, Heinz

doi:10.1007/978-3-642-49337-9_81

Cited by 3 publications

(2 citation statements)

References 6 publications

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“…These large values of T m indicate that the micelles are elongated and exist as a living network. Also the viscosity , for these solutions depends not only on the size of micelles but also on the break probability of micelles. The break of a micelle allows reduction of the shear stress and leads to a lower value of the viscosity.…”

Section: Resultsmentioning

confidence: 99%

Effect of Pentanol and Salt on the Fusion−Scission Kinetics for CTAB Micelles

Michels

Waton

2003

J. Phys. Chem. A

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The kinetic properties of aqueous solutions of CTAB with pentanol and KBr are studied with a T-jump device. The transition range from spherical to cylindrical micelles is determined with a microcalorimeter, and the semidilute range with an Oswald viscometer. The kinetic results show that, for elongated micelles, the value of the relaxation time decreases when the salt or pentanol concentration increases. This variation indicates that the decrease of the potential barrier is larger than the increase of the endcap energy. The observed variation of the potential barrier with salt concentration obeys a scale law, as expected by the DLVO theory. Its variation with pentanol obeys to a linear law. At the transition from spherical to cylindrical micelles the variation of the relaxation time is essentially controlled by the growth in the width of the length distribution.It is well-known 1 that surfactant molecules self-assemble into micelles if the concentration is higher than the critical micelle concentration (cmc). The micelles can undergo uniaxial growth upon an increase of surfactant concentration 2 and upon addition of salt 3,4 or alcohol. 5,6 It is also known that aggregates continuously exchange surfactant molecules with the bulk solution, and that the micelles break and merge. These kinetic processes have been widely investigated theoretically. The theoretical treatment of the exchange of surfactant molecules between micelles and solvent has been worked out by Aniansson et al. 7,8 Experimentally, these kinetics are generally studied by the ultrasonic relaxation absorption method. 9 Kahlweit has performed a theoretical study of the fusion-scission process 10,11 for spherical micelles, Cates 12 has theoretically studied wormlike micelles, and the relaxation time associated with the fusion-scission kinetics has been determined for some micellar shapes. 13 Experimentally, these kinetics are investigated by the T-jump technique with light absorption detection in the case of the fusion-scission process of quasi-spherical micelles. Use of one absorbency probe is often necessary in this last technique. The fusion-scission kinetics can be studied without probes by the T-jump technique with light scattering detection, if the weight aggregation number of the micelles varies sufficiently with temperature. This last technique is the best suited for solutions of micelles from the dilute regime to the beginning of the semidilute regime, but it does not allow observation of the fusion-scission process of micelles when the micelles are strongly entangled.The fusion-scission relaxation process has been studied in CTAB 14 solutions or in SDS 15 solutions at different temperatures and ionic strengths. These studies show that for elongated micelles the relaxation frequency increases as the square root of the average length of the micelles. For short micelles, the variation law of the relaxation time is unknown but it strongly depends on the size distribution of micelles. Zana et al. 16 studied the effect of alcohol molecules of diffe...

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Section: Resultsmentioning

confidence: 99%

Effect of Pentanol and Salt on the Fusion−Scission Kinetics for CTAB Micelles

Michels

Waton

2003

J. Phys. Chem. A

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“…9 Some of the exponents have been explained by different mechanisms. The structural relaxation times in the viscous fluids can be kinetically controlled by the breaking of the micelles 10 or as in polymer networks, by a reptation process. 11 In the first case, the viscosity is due to a product of a single shear modulus, G°and a single relaxation time, (η°= G°τ).…”

Section: Introductionmentioning

confidence: 99%

Evidence of Sticky Contacts between Wormlike Micelles in Viscoelastic Surfactant Solutions

Thurn

Hoffmann

2019

Langmuir

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Many cationic surfactants form highly viscoelastic solutions at concentrations of only a few percent. These solutions contain wormlike micelles (WLM) which can be several micrometers long. The structural relaxation time, τ s in these solutions can be as long as many seconds, and the zero-shear viscosity can be in the range of 10 6 Pas. Electric birefringence measurements on such solutions showed four different relaxation times with increasing concentration. The two shortest ones, τ 1 and τ 2 in the μs region were due to the alignment of small rodlike or ringlike micelles. The third one, τ 3 , was observed in the viscoelastic region in the ms region and finally, a fourth one, τ 4 , which was the same as the structural relaxation time, τ s . In this article, it is shown that the τ 3 process is due to the formation and opening of contacts between the WLM. The reason for the contacts is the attraction between the WLM which is due to the hydrophobic surfaces of the micelles. The contacts crosslink the WLM and thus form a threedimensional network. This network is the reason for the high viscosity and viscoelastic properties of the samples. If the attraction between the WLM is reduced by adding glycerol to the solution, the viscosity of the solution breaks down. The same happens if the surface of the WLM is made hydrophilic by the addition of small amphiphilic molecules. The WLM are not destroyed by these procedures.

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