Synthesis of oligomer betaine surfactant (DDTPA) and rheological properties of wormlike micellar solution system

Novel oligomer betaine surfactant penta sodium N, N', N ''- dodecyl diethylene triamine pentaacetic acid (DDTPA) with three dodecyls, five carboxylic acid groups and three quaternary ammonium were synthesized through two steps in this paper. Rheological properties of mixed oligomer betaine surfactant DDTPA/anionic surfactant sodium dodecylsulfonate (SDS) solution systems were studied as functions of SDS concentration, inorganic salt KCl dosage and temperature. Stable and dynamic viscoelastic measurements were carried out to investigate the characters of wormlike micelles formed in certain condition. In the 2.5 wt% DDTPA, 4 wt% KCl and SDS system, the optimal SDS concentration is 1.2 wt%, at which the viscosity reaches a maximum. Interestingly, with adding inorganic salt KCl to mixed surfactant solution(2.5 wt% DDTPA, 1.5 wt% SDS), the water-like fluid turns into gel-like viscoelastic wormlike micellar solution immediately owing to the screening electrostatic repulsion among the surfactant charged groups by counterions. When KCI concentration is 3 wt%, the micellar solution obtains a peak value in viscosity. For the system with 2.5 wt% DDTPA, 1.5 wt% SDS, 4 wt% KCl, the micellar contour length decreases with increasing temperature, leading to an exponential decrease in the values of eta(0) and tau(R) This work provides a clear understanding of the profound relationship between surfactant wormlike micellar characteristic and the rheological properties. The dynamic viscoelastic behavior of wormlike micelles usually fits for the Maxwell mode in low oscillation frequency region, but in medium and high frequency region it fits for t the modified Maxwell model. (C) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.