ELECTROSTATIC PROPERTIES OF ZWITTERIONIC MICELLES

The electrostatic properties of zwitterionic micelles of 3-(N-hexadecyl-NN-dimethylammonio)propanesulfonate (HPS) have been investigated by light scattering and conductivity, and a simple electrostatic model in the Debye-Hueckel approximation, containing no adjustable parameters, is presented which accounts qualitatively for the main experimental results on second virial coefficients and conductivity, as well as for fluorescence quenching reported in earlier work. Additional photochemical data concerning reprotonation rates of 8-hydroxy-1,3,6-pyrenetrisulfonate in HPS micelles are also presented and interpreted by the electrostatic model. The model involves the superposition of solutions for concentric, oppositely charged spherical micelles. This leads to a broad maximum in the curve of the absolute value of surface potential and second virial coefficient vs ionic strength. It further implies a significant sequestering of mobile anions in the dipole layer (positive inner surface, negative outer) and low net mobile ion charge densities outside the micelle. These effects are observed experimentally.