SDS MICELLES AT HIGH IONIC-STRENGTH - A LIGHT-SCATTERING, NEUTRON-SCATTERING, FLUORESCENCE QUENCHING, AND CRYOTEM INVESTIGATION

Sodium dodecyl sulfate (SDS) in 0.8 M NaCl in D2O has been studied by small-angle neutron scattering (SANS), dynamic light scattering (DLS), and time-resolved fluorescence quenching (TRFQ) measurements in the c oncentration range from 10 to 80 mM and at temperatures from 25 to 45 degrees C. Examination by cryo-transmission electron microscopy reveal ed the presence of a variety of structures, from broad band-like or la ce-like aggregates to multiconnected threads. It is suggested that the se structures are formed at the air-solution interface. To verify that they are not present in the bulk solution, SANS, DLS, and TRFQ were s tudied on the same solutions. The SANS results confirm, on the length scale available using this technique, a local cylindrical structure fo r the micelles. Assuming a rod model, with the slow mode corresponding to translational diffusion and the fast mode to the rotational dynami cs of cylindrical SDS micelles, the DLS data at 25 degrees C in 0.8 M NaCl would correspond to a hydrodynamic length L approximate to 150 mn , employing a radius of about 2 nm. The TRFQ shows a transition from s mall micelles at high temperature and low surfactant concentration to long structures at low temperature and high concentration. (C) 1998 Ac ademic Press.