FIGURE 4.

AFM images of DPPC/POPG/PA + SP-C_ff films. (A) Below the plateau in the isotherm, the fluid phase regions are 1 nm lower (see height trace) than the condensed regions. (B) Above the plateau, the fluid regions have thickened to be ∼5 nm higher than the condensed domains. This is consistent with the formation of three-layer thick areas in the fluid phase. The plateau in the isotherms corresponds to the removal of fluid phase lipids from the interface to form these multilayer patches. SP-C acts to regulate the solid/fluid phase ratio causing the surface viscosity to diverge.