Molecular orientation in lipid bilayers

The optical anisotropy of phospholipid bilayers with different alkyl chain lengths has been measured using optical waveguide light-mode spectroscopy. All the bilayers showed positive birefringence. Considering the bilayers as being composed essentially of aqueous and oleaginous moieties, this implies that the molecular arrangement of the lipids is best described as apolar cylinders perpendicular to the plane of the bilayer and sheathed in water, rather than as a laminar apolar core sandwiched between polar layers.