Small-angle neutron scattering from micelles of alkylpolyoxyethylene sulfate: Effect of chain length

Small-angle neutron scattering (SANS) data have been obtained for (i) a series of solutions of C _m H_2m+1(OCH₂–CH₂)₂SO₄Na, for m=18, 16, and 14; (ii) an approximately 0.07M solution of C₁₄H₂₉(OCH₂–CH₂)₂SO₄Na to which different amounts of NaCl were added; and (iii) a series of solutions of variable concentration of C₁₂H₂₅(OCH₂–CH₂)SO₄Na. The increase of the number of carbon atoms of the hydrocarbon chain produces a noticeable increase of the aggregation number of the micelles, while the salt tolerance decreases with increasing m. All the data can be described in terms of a monodispersed, charged, hard-spheres model interacting via a screened Coulombic potential, except the run at highest salt concentration, for which an ellipsoid model gives better results.