TEMPERATURE-DEPENDENCE OF THE GROWTH OF DIHEPTANOYLPHOSPHATIDYLCHOLINE MICELLES STUDIED BY SMALL-ANGLE NEUTRON-SCATTERING

The growth of diheptanoylphosphatidylcholine (diheptanoyl-PC) micelles with increasing concentration was studied by small-angle neutron scattering techniques in the temperature range of 25-45°C. Diheptanoyl-PC forms polydisperse spherocylindrical micelles in aqueous solutions. The mean micellar aggregation number increases with increasing concentration. At a constant concentration, the mean micellar aggregation number is found to decrease with increasing temperature. A thermodynamic model called the ladder model is employed in the analyses of the measured neutron scattering data. Both the thermodynamic parameters and the structural parameters that characterize the structure and size distribution of the micellar system are determined at each temperature. The growth of the rodlike micelles with increasing concentration is driven by the total free energy difference of the monomers in the two end caps of one micelle and the same number of monomers in the cylinder section of the micelle. The magnitude of this free energy difference in units of kT is found to decrease with increasing temperature, and it is responsible for the decrease of the mean aggregation number with increasing temperature. © 1990 American Chemical Society.