  Small angle neutron scattering (SANS) on the unilamellar vesicle populations
(diameter 500 and 1000 angstrom) was used to characterize lipid vesicles from
dimyristoylphosphatidylcholine (DMPC) at three phases (gel, ripple, and
liquid). Parameters of vesicle populations and internal structure of the DMPC
bilayer were characterized on the basis of the Separated Form Factor (SFF)
model. Parameters of the internal bilayer structure (thickness of the membrane
and the hydrophobic core, hydration, and surface area of lipid molecule) were
determined on the basis of the Hydrophobic-Hydrophilic (HH) approximation of
neutron scattering length density across the bilayer r(x) and of the Step
Function (SF) approximation of r(x). It was demonstrated in frame of HH
approximation that DMPC membrane thickness in liquid phase (T=30 degrees)
depends on the membrane curvature. The dependence of the DMPC membrane
thickness on temperature was restored from the SANS experiment.
