Abstract
SANS external and internal contrast variation experiments have been used to determine the structure of dihexanoylphosphatidylcholine micelles. These monodisperse (aggregation number 19 ± 1 from 0.027 to 0.361 M) short-chain lecithin micelles can be well represented by a prolate ellipsoid with two uniform regions. The hydrocarbon chains form a close-packed spheroidal core with a minor axis equal to the fully extended fatty acyl chain (7.8 Å) and a major axis equal to 24.0 Å. Surrounding the hydrocarbon core are the polar head groups, which are distributed in a shell with a thickness of 10 Å in the direction of the minor axis and 6 Å along the major axis. Analysis of the scattering from 1,2-di(hexanoyl-6,6,6-d 3 )phosphatidylcholine micelles indicates that terminal methyl groups are distributed throughout the hydrocarbon core. At high lecithin concentrations attractive interactions between micelles occur. These can be modeled, and the results suggest that the structure of water around the interface is important in determining effective intermicelle interactions. © 1986 American Chemical Society.