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Small-angle neutron scattering; small-angle X-ray scattering; charged micelle; counterion condensation

We report a combined use of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to the study of counterion condensation in ionic micelles. Small-angle neutron and X-ray scattering measurements have been carried out on two surfactants cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium chloride (CTACl), which are similar but having different counterions. SANS measurements show that CTABr surfactant forms much larger micelles than CTACl. This is explained in terms of higher condensation of Br⁻ counterions than Cl⁻ counterions. SAXS data on these systems suggest that the Br⁻ counterions are condensed around the micelles over smaller thickness than those of Cl⁻ counterions.

V K Aswal¹ P S Goyal² H Amenitsch³ S Bernstorff⁴

1. Solid State Physics Division, India
2. Mumbai Centre, Bhabha Atomic Research Centre, IUC-DAEF, Mumbai - 400 085, India
3. Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Graz, Austria
4. Sincrotrone Trieste, Trieste, Italy

Published

August 2004