Microstructure and dynamics of wormlike micellar solutions formed by mixing cationic and anionic surfactants

被引:245
作者
Koehler, RD
Raghavan, SR
Kaler, EW [1 ]
机构
[1] Univ Delaware, Dept Chem Engn, Ctr Mol & Engn Thermodynam, Newark, DE 19716 USA
[2] DuPont Co Inc, Cent Res & Dev, Expt Stn, Wilmington, DE 19880 USA
关键词
D O I
10.1021/jp0018899
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Small-angle neutron scattering (SANS) and rheology are used to probe the wormlike micelles formed in mixtures of a cationic (cetyl trimethylammonium tosylate, CTAT) and an anionic surfactant (sodium dodecyl benzene sulfonate, SDBS). For a fixed composition of 97/3 CTAT/SDBS, the zero-shear viscosity eta (0) initially increases rapidly with surfactant concentration, but decreases beyond an intermediate concentration phi (max). The solutions show a scattering peak in SANS and the height of the scattering peak also exhibits a maximum around phi (max). These results are interpreted in terms of a maximum in the linear micellar contour length (L) over bar at phi (max), and suggest that the hydrodynamic and electrostatic correlation lengths reach an optimal ratio at this point. For a fixed total surfactant concentration, the viscosity eta (0) also reaches a maximum at an intermediate SDBS fraction. The decrease in eta (0) at high SDBS fractions is interpreted in terms of the polyelectrolyte nature of the micelles and the increased chain flexibility caused by the rising ionic strength of the solutions. An alternate possibility may involve a progression from linear to branched micelles with increasing SDBS content.
引用
收藏
页码:11035 / 11044
页数:10
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