Light scattering microscopy reveals previously undetected topographic instabilities in phospholipid monolayers at the air/water interface far below the collapse pressure. Following compression through the fluid → condensed phase transition in monolayers of dipalmitoyl phosphatidylcholine, after the disappearance of the fluid phase, the contact regions between condensed domains acquire static roughness as indicated by enhanced light scattering. With further compression, a nanoscale budding process occurs within the roughened regions, while the interiors of the condensed domains remain flat and retain their domain shapes. At monolayer collapse, the buds proliferate across the entire interface, suggesting that the buds detected at lower pressures represent spatially confined fluctuations into the collapse phase. The confinement of static roughness formation and budding to domain contact regions indicates that these topographic instabilities originate from packing defects created where adjacent domain edges with conflicting molecular orientations grow together during the fluid → condensed phase transition.

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Many biominerals are laminated such that crystal shape or habit changes from layer to layer thus yielding exquisitely designed composite materials with tightly controlled properties. Although lamination in biominerals is usually performed using peptides and proteins, here we introduce a new strategy by which sequential addition or depletion of inorganic trivalent ions in a supersaturated solution can be used to switch the surface morphology of calcium oxalate monohydrate (COM) back and forth, resulting in either the growth of flat crystalline sheets or of nanostructures oriented perpendicular to the surface. We propose that the occupation of a Ca(2+) site by Eu(3+) ion switches the orientation of the COM unit cell. The need to compensate the third charge forces coordination of Eu(3+) to an additional oxalate ion ((-)OOC-COO(-)) in an orientation that is not compatible with the initial unit cell. This mechanism of switching the orientation of the unit cell is unique, as it does not involve the use of expensive and thermally labile biomolecules. Suggestions of how to extend this strategy to engineer non-biological nanocomposites are given.