Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (02): 351-357.doi: 10.3866/PKU.WHXB201211214

• SOFT MATTER • Previous Articles     Next Articles

Dynamic Surface Adsorption Properties of Sodium Dodecyl Sulfate Aqueous Solution

FAN Hai-Ming, ZHANG Yi-Nuo, ZHANG Jin, WANG Dong-Ying, GAO Jian-Bo, KANG Wan-Li, MENG Xiang-Can, ZHAO Jian, XU Hai   

  1. College of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, Shandong Province, P. R. China
  • Received:2012-09-25 Revised:2012-11-19 Published:2013-01-14
  • Supported by:

    The project was supported by the Taishan Scholars Construction Engineering of Shandong Province (ts20070704), National Natural Science Foundation of China (51234007, 51104169), Natural Science Foundation of Shandong Province, China (ZR2010BQ003, ZR2010EZ006), and National Undergraduate Innovative and Entrepreneurship Training Program of China University of Petroleum (East China), China (201210425011).

Abstract:

The dynamic surface adsorption properties of aqueous sodium dodecyl sulfate (SDS) solutions were investigated at different concentrations of NaCl using bubble pressure tensiometry MPTC. In the case of ionic surfactants, the existence of a diffuse electric double layer on the surface adsorption layer and around the micelle produces a surface charge. Here, we discuss the influence of the surface charge on the dynamic surface diffusion processes and the micelle properties. It was found that the SDS adsorption process occurred in the presence of a 5.5 kJ·mol-1 adsorption barrier (Ea) that was generated by the surface charge; this barrier significantly decreased the effective diffusion coefficient (Deff) of the dodecyl sulfate ions (DS-). The ratio of the effective diffusion coefficient to the monomer self-diffusion coefficient (D) (Deff/D) was only 0.013. This indicated that at the beginning, the adsorption of SDS followed the mixed kinetic-diffusion controlled model; this is different from the behavior observed for nonionic surfactants. The adsorption barrier was reduced when NaCl was added. Ea was less than 0.3 kJ·mol-1 after the addition of 80 mmol·L-1 of NaCl. This resulted in values of between 0.8 and 1.2 for Deff/D, which was consistent with the diffusion-controlled model that describes the behavior of nonionic surfactants. The characteristic constants for the micelle dissociation rate (k2) were determined from the dynamic surface tension of the SDS micelle solutions. The calculated k values decreased as the NaCl concentration was increased, which demonstrated the existence of surface charge on the SDS micelles; this surface charge increased the repulsive forces between the dodecyl sulfate ions, and promoted the dispersion of the micelles.

Key words: Sodium dodecyl sulfate, Dynamic surface tension, Surface charge, Adsorption barrier, Micelle dissociation

MSC2000: 

  • O647