Figure 6.

Schematic diagram indicating key features of the H_II phase. The gray rings with the sketch of an individual phospholipid represent the cylindrical monolayers surrounding the white aqueous core. The arrows indicate: the lattice constant obtained directly from measurements of diffraction (a_o); the radius at the Luzzati surface at the outer surface of the aqueous core (R_w); the radius at the outer surface of the monolayer (R_o); the radius at the pivotal plane (dashed ring), where the molecular cross-sectional area remains constant during bending (R_p); and the molecular volume that separates the pivotal plane from the Luzzati surface $(\Delta {\overline{\text{V}}}_{\text{p}})$. The crosshatched areas represent regions that would be unfilled if the monolayers were circular with a uniform thickness.