Journal of Colloid and Interface Science 313 (2007) 680–685 www.elsevier.com/locate/jcis Viscoelastic behavior of surfactants worm-like micellar solution in the presence of alkanolamide Dharmesh Varade, Suraj Chandra Sharma, Kenji Aramaki ∗ Graduate School of Environment and Information Sciences,Yokohama National University,79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan Received 19 March 2007; accepted 27 April 2007 Available online 3 May 2007 Abstract A study of the phase and rheological behavior of anionic surfactant sodium dodecyl trioxyethylene sulfate (SDES) and nonionic poly- oxyethylene sorbitan monooleate (Tween-80) with alkanoyl-N -methylethanolamide (C 12 , NMEA-12; and C 16 , NMEA-16) in aqueous system is presented. Upon addition of NMEA to the semi-dilute solution of SDES or Tween-80, induces micellar growth leading to the formation of a gel-like highly viscoelastic solution in the maximum viscosity region. These solutions obey the Maxwell model of a viscoelastic fluid. It was observed from rheological measurements that NMEA-16 is more effective than NMEA-12 to induce the micellar growth of surfactants. The rela- tionship between the marked changes in viscosity with surfactant-cosurfactant mixing ratio based on the experimental observations is discussed.  2007 Elsevier Inc. All rights reserved. Keywords: Rheology; Phase behavior; Worm-like micelles; Viscoelasticity; Alkanolamide 1. Introduction Rheological studies have attracted much interest because of their peculiar properties and potential industrial applications, including food emulsion, cosmetics, paints, pharmaceuticals, adhesives, and many household products [1]. In all these appli- cations, knowledge of the structure and dynamics of the worm- like micellar systems is vital for the optimization of the process. In the charged micelles, micellar growth occurs as a conse- quence of the reduction of the repulsion between the surfactant headgroups, which can be induced by adding salts, strongly binding counterions or cosurfactants [2–10]. Reported systems mainly include cationic surfactants with aromatic counterions or halide anions. Among the few reports on anionic surfac- tant, majorities have focused on sodium dodecyl sulfate. Some nonionic surfactants can also form worm-like micelles under certain conditions [11–17]. Recently our group has reported the formation of a highly viscoelastic worm-like micellar so- lution upon addition of a lipophilic nonionic surfactant such as short hydrophilic chain poly(oxyethylene) alkyl ether or alka- * Corresponding author. Fax: +81 45 339 4300. E-mail address: aramakik@ynu.ac.jp (K. Aramaki). nolamides to the dilute micellar solution of hydrophilic surfac- tants [12,18–24]. Alkanolamides are well known as foam-booster in surfac- tant aqueous solution [25,26] as a thickening agent in shampoo, and also as anti-static and anti-corrosion agents in detergents. It seemed appealing to investigate its rheological behavior with anionic surfactant sodium dodecyl trioxyethylene sulfate (SDES) that has vital application in health care products and a hydrophilic nonionic surfactant Tween-80, frequently used in pharmaceutical formulations and cosmetic industries [27]. Anionic systems tend to be an economical, and less toxic com- pared to cationic ones and are therefore considered to be more environment friendly. Mu and Li [28,29] have reported worm- like micelles with highly viscoelastic properties in SDES in presence of multivalent cations, where as, we are first to report it recently for Tween-80 in the presence of polyoxyethylene alkyl ether surfactants [30]. Looking to the importance and scarcity of the published literature for both the surfactants, SDES and Tween-80, the present contribution aims at gaining a better understanding of the rheological behavior of the micellar solutions of wa- ter/SDES/NMEA and water/Tween-80/NMEA mixed systems, which could be of use for vital applications. At first, a par- 0021-9797/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2007.04.065