Dynamic surface dilational properties of anionic Gemini surfactants with polyoxyethylene spacers

The dynamic interfacial dilational properties of anionic Gemini surfactants (oligooxa)-alpha,omega-bis(m-octylbenzene sulfonate) (C8E4C8 and C8E8C8) with polyoxyethylene spacers at the water-air interface were investigated by means of oscillating the drop profile method. The influences of temperature and salt on dilational properties were explored. The experimental results show that the special structure of surfactant C8E8C8 is a principal factor to control the nature of interfacial adsorption film. The distinct two peak values appear in dilational modulus vs. time curves for surfactant C8E8C8, which is different from that of traditional surfactants with low molecular weight. The first peak is believed to be related to the molecular diffusion-exchange process between the bulk and interface, and the second peak may be due to the formation and collapse of interfacial sublayer by ethylene oxide groups. In addition, the temperature has obviously effect on the second peak value of dilatioanl modulus. However, there is nearly no effect on the value of the second peak by addition of NaCl. The mechanisms responsible for unique interfacial behaviors mentioned above have been provided schematically. (C) 2015 Elsevier B.V. All rights reserved.