Microstructure and Dynamics of Wormlike Micellar Solutions Formed by Mixing Cationic and Anionic Surfactants

Abstract

Small-angle neutron scattering (SANS) and rheology are used to probe the wormlike micelles formed in mixtures of a cationic (cetyl trimethylammonium tosylate, CTAT) and an anionic surfactant (sodium dodecyl benzene sulfonate, SDBS). For a fixed composition of 97/3 CTAT/SDBS, the zero-shear viscosity η 0 initially increases rapidly with surfactant concentration, but decreases beyond an intermediate concentration φ max . The solutions show a scattering peak in SANS and the height of the scattering peak also exhibits a maximum around φ max . These results are interpreted in terms of a maximum in the linear micellar contour length L h at φ max , and suggest that the hydrodynamic and electrostatic correlation lengths reach an optimal ratio at this point. For a fixed total surfactant concentration, the viscosity η 0 also reaches a maximum at an intermediate SDBS fraction. The decrease in η 0 at high SDBS fractions is interpreted in terms of the polyelectrolyte nature of the micelles and the increased chain flexibility caused by the rising ionic strength of the solutions. An alternate possibility may involve a progression from linear to branched micelles with increasing SDBS content.

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

“…This can indicate hydrodynamic instabilities above a critical shear rate in the solution, most likely attributed to the formation of nonequilibrium, shear-induced, micellar phase transitions (Barentin and Liu 2001;Berret 2006;Hu et al 1998). In addition, shear thickening under steady shear can occur when the surfactant concentration is close to the critical micelle concentration (Koehler et al 2000). To confirm this statement, future experiments will be conducted to determine the critical micelle concentration of DTTM at various conditions.…”

“…Researchers have noted micelles grow and entangle before the inflection point due to the minimization of free energy, but after the inflection point, the onset of micellar branching occurs leading to a decrease in viscosity Petroleum Science (Calabrese et al 2015;Koehler et al 2000;Trickett and Eastoe 2008). Trickett and Eastoe (2008) observed only a range of surfactant concentrations display this viscosity enhancement phenomenon and the critical temperature where the turning point exists is a function of surfactant concentration and shear rate.…”

“…Depending on internal and external parameters, the morphology can transition from one division to another. When the micelles organize into cylindrical aggregates or entangle wormlike structures, the solution transforms into a viscoelastic state (Hull et al 2015;Koehler et al 2000).…”

Viscoelastic properties of new mixed wormlike micelles formed by a fatty acid salt and alkylpyridinium surfactant

“…Long entangled wormlike micelles of surfactants can impart to aqueous solutions pronounced viscoelastic properties [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], which are quite sensitive to external stimuli: ionic strength [2,8], type of salt [11,15], temperature [10], various additives including polymers [6,7] and hydrocarbons [12][13][14]. Such responsiveness is provided by the self-assembled character of micellar chains formed by weak non-covalent interactions [1,9].…”

“…An alternative approach to obtain wormlike micelles consists in the use of the mixture of two oppositely charged surfactants [3][4][5][6][7]. In this case, the screening of repulsion is even more effective because cationic and anionic surfactant heads are located in close proximity to each other.…”