Chapter 2: Wormlike Micelles: Solutions, Gels, or Both?
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Published:17 Mar 2017
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Special Collection: 2017 ebook collectionSeries: Soft Matter Series
S. R. Raghavan and Y. Feng, in Wormlike Micelles: Advances in Systems, Characterisation and Applications, ed. C. A. Dreiss and Y. Feng, The Royal Society of Chemistry, 2017, ch. 2, pp. 9-30.
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Wormlike micelles (WLMs) formed by the self-assembly of surfactants in water typically form transient networks of entangled chains, and as a result exhibit viscoelasticity, i.e., a combination of elastic rheology at short timescales and viscous rheology at long timescales. This chapter focuses on the unusual case of some micellar systems that instead exhibit gel-like (elastic) rheology regardless of timescale (i.e., their relaxation time and zero-shear viscosity are infinite). Gels are shown to form when the surfactants have ultra-long hydrophobic tail(s) (with a total of 22 carbons or more). In such cases, the micellar chains are expected to have exceptionally large contour lengths and also to have very long breaking times. These chains are then believed to undergo strong topological interactions (‘entanglements’) that give rise to a relatively permanent network, thereby explaining the gel-like behaviour.