ORDER IN THE BILAYERS OF GEL-PHASE SODIUM SULFOPROPYL OCTADECYL MALEATE - WIDE-ANGLE X-RAY-SCATTERING AND MOLECULAR MODELING

The order in the bilayers of a metastable gel state of the long-chain surfactant sodium sulfopropyl octadecyl maleate (SSPOM) is investigate d by wide-angle X-ray scattering (WAXS) and molecular modeling. The WA XS patterns indicate an ordered and rather dense in-plane structure, c onsisting of hexagonally packed, untilted, and interdigitated molecule s. Three hexagonal reflections are found for a 60 wt % sample. Fourier analysis of the WAXS data reveals that the spatial correlation betwee n the chains reaches almost 50 Angstrom. The estimated area per molecu le in the bilayer is 40.0 Angstrom(2). Based on the experimental resul ts, the in-plane packing is simulated and the hexagonal arrangement of molecules proves to be energetically possible. A model packing with t he majority of the sodium counterions in the water phase near the SSPO M packing surface shows the best agreement with the experimental WAXS data.