Fig. 3.

High-resolution AFM images, as indicated by rectangular boxes in Fig. 2, demonstrating detailed structural features of surfactant films. A. DPPC monolayer at 4.0 mN/m. The height profile shows the surface topography along the line tracing indicated in the AFM image. It shows that the tilted-condensed (TC) phase consists of both leaf-like microdomains and worm-like nanodomains, both ~1 nm higher than the surrounding liquid-expended (LE) phase. B. Collapsed DPPC monolayer at 72 mN/m, showing the formation of bilayer stacks ejected from the interfacial monolayer at the collapse pressure. C. Monolayer of DPPC:POPG (7:3) at 40 mN/m, showing that the condensed domains merge into a continuous phase with “holes” of LE phase ~0.5 nm lower. D. Surface plot (three-dimensional topographic image) of DPPC:POPG film at the collapse pressure (i.e., 72 mN/m), showing film folding along the direction of lateral compression. E. Surface plot of Survanta film at 50 mN/m. It shows that the TC microdomains are traced out by higher multilayers that originate from the surrounding LE phase. F. Survanta film at 60 mN/m, illustrating an increasing multilayer density in the lateral dimension while the height of multilayers does not increase significantly, compared to 50 mN/m. G. Curosurf monolayer at 40 mN/m shows a single microdomain with lines of nanodomains, as indicated by the intensive fluctuations in the height profile. H. Curosurf film at 50 mN/m, showing a single TC microdomain with moderate film buckling, indicated by vertical lines of collapse sites of only ~1.5 nm high. I. Infasurf monolayer at 20 mN/m shows the cholesterol-mediated liquid-ordered (LO) phase and a unique TC-in-LO structure as a consequence of cholesterol partitioning into the TC phospholipid phase. The lipid chain order of the LO phase is intermediate between the TC and LE phases, as indicated by height differences detected by AFM (i.e., TC>LO>LE in height). J. Infasurf monolayer at 40 mN/m, demonstrating a single TC-in-LO domain with an increasing number of nanodomains and evident shrink of the TC core (2.5 µm vs. 5 µm at 30 mN/m). K. BLES monolayer at 40 mN/m, showing clearly a decrease of microdomains in size and increase of nanodomains in number. L. BLES film at 50 mN/m, showing TC microdomains traced out by multilayers formed from the surrounding LE phase. M. BNS monolayer at 40 mN/m, showing the detailed morphology of nanodomains and some high spots, likely SP-A aggregates squeezed out of the monolayer at this pressure. N. BNS film at 50 mN/m, showing detailed multilayer structure.