A small angle neutron scattering study of an SDS micellar solution confined in sodium bentonite

Abstract

The effect on the structure of a Sodium Dodecyl Sulphate (SDS) micellar solution confined within the porous structure of a bentonite has been investigated using Small Angle Neutron Scattering. Normal bentonite and that saturated with sodium of varying molar concentrations were infused with SDS. From X-ray diffraction, the interplanar separation in normal bentonite is 13 Angstrom while in the clay saturated with Na+ ions and loaded with SDS solution it is 20 Angstrom. Similarly, pore sizes from SANS for bentonite and Na bentonite were 13 Angstrom and 20 Angstrom respectively. For an unconfined SDS solution, the aggregation number, effective charge and intermicellar distance are known to increase with concentration of SDS but decrease when SDS is confined in sodium saturated bentonite. These parameters were here found to substantially decrease by up to 50% for increasing SDS concentrations confined in the bentonite. The Na+ ion in the sodium saturated bentonite is thought to play a vital role in the change of these parameters by effectively reducing charge on the micellar aggregates.