Wormlike Micelles Formed by Synergistic Self-Assembly in Mixtures of Anionic and Cationic Surfactants

Abstract

Self-assembly in mixtures of cationic and anionic surfactants occurs synergistically because of attractive interactions between the oppositely charged headgroups. Here, such effects are exploited to obtain highly viscoelastic fluids at low total surfactant concentration. The systems considered are mixtures of the C18-tailed anionic surfactant, sodium oleate (NaOA), and cationic surfactants from the trimethylammonium bromide family (C n TAB). In particular, mixtures of NaOA and C8TAB show remarkably high viscosities: for 3% surfactant, the zero-shear viscosity η 0 peaks at ca. 1800 Pa·s for a weight ratio of 70/30 NaOA/C8TAB. The high viscosities reflect the growth of giant, entangled wormlike micelles in the solutions. Mixtures of NaOA with a shorter-chain analogue (C6TAB) have much lower viscosities, indicating a weak micellar growth and hence a weak attraction between the surfactants. On the other hand, increasing the C n TAB tail length to n = 10 or 12 leads to much stronger interactions between these surfactants and NaOA. Consequently, both micellar and bilayer structures are formed in these mixtures, and the samples separate into two or more phases over a wide composition range. Thus, the synergistic growth of wormlike micelles in cationic/anionic mixtures is maximized when there is an optimal asymmetry in the surfactant tail lengths.

Self‐assembled, wormlike‐cylinder network of polystyrene‐block‐poly(ethylene oxide) micelles in solution

“…Also, the viscosity of a wormlike-cylinder micelle solution increases with increasing worm length. 32 A worm network can be considered a wormlike cylinder with an infinite length, in contrast to individual wormlike-cylinder micelles, which would have a finite length. Thus, for an entangled and interconnected worm network (Fig.…”

A Dually Effective Inorganic Salt at Inducing Obvious Viscoelastic Behavior of both Cationic and Anionic Surfactant Solutions

“…1À6 The rheology of these viscoelastic surfactant fluids is similar to that of the solutions of flexible polymers. 7 However, unlike covalent chemical bonding polymers, self-assembled wormlike micelles are in dynamic equilibrium with their monomers, which are called "living polymers" owing to their ability to break and recombine rapidly. 8,9 The viscoelastic wormlike micelles often show relaxation behavior that can be described by a Maxwell model with a single relaxation time, a living polymer model proposed by Cates et al 9À11 Viscoelastic wormlike micelles formed by ionic surfactants, especially cationic surfactants, upon addition of various additives have been studied extensively.…”

A systematic rheological study of alkyl amine surfactants for fluid mobility control in hydrocarbon reservoirs

“…In this case, surfactants with coco-based tails, such as ARM and ECA, typically contain 12-16 carbon atoms, while surfactants with tallow-based tails, such as DTTM and EDM, consist of 14-18 carbons. According to Raghavan et al (2002), as the alkyl tail length lessens, synergism in self-assembly decreases, leading to weak micellar growth and a small rise in viscosity. When the tail length increases, the interaction among the tail groups becomes stronger and more entangled causing a dramatic growth of micellar chains and a rise in viscosity (Raghavan et al 2002).…”

“…The presence of hydrophobic terminals, such as methyl groups found in DTTM and ARM, can dehydrate the surfactant molecules with excess salt in the aqueous solution. This hydrophobicity favors the growth of long micelles, since hydrophobic molecules have higher end-cap energies, and end-cap energy is exponentially proportional to the micellar length (Berret 2006;Raghavan and Kaler 2001;Raghavan et al 2002). End-cap energy represents the excess packing energy for surfactants with preferential cylindrical aggregation and is defined as the energy required to create two new chain ends for neutral micelles (Berret 2006).…”