A master dynamic flow diagram for the shear thickening transition in micellar solutions

Abstract

The shear thickening behavior of dilute micellar solutions of hexadecyltrimethylammonium-type surfactants with different counterions (tosylate, 3- and 4-fluorobenzoate, vinylbenzoate and salicylate) and of n-alkyltetradecylammonium bromide (C_nTAB), with n = 14, 16 and 18, is examined here. These solutions undergo a shear thickening transition due to the formation of shear-induced structures (SISs) in the shear range studied. Here we report a relationship between the shear thickening intensity and the differences in the hydrophobicity of counterions according to the Hofmeister-like anion series, which leads to a master flow diagram. This master flow diagram is produced by plotting a normalized shear thickening intensity (I_η − 1)/(I_max − 1) versus C_D/C_D,max, where I_η is the shear-thickening intensity, defined as the largest viscosity obtained in the shear-thickening transition (STT) at a given surfactant concentration C_D divided by the Newtonian viscosity η₀, and I_max is the largest intensity value obtained in the STT at a surfactant concentration C_D,max. The master flow diagram is built using several cetyltrimethylammonium-type surfactants with different counterions, according to a Hofmeister-like series, and by n-alkyltetradecylammonium bromide surfactants with different alkyl chain lengths.