Nanoscale topographic instabilities of a phospholipid monolayer

Light scattering microscopy reveals previously undetected topographic insta bilities in phospholipid monolayers at the air/water interface far below th e collapse pressure. Following compression through the fluid --> condensed phase transition in monolayers of dipalmitoyl phosphatidylcholine, after th e disappearance of the fluid phase, the contact regions between condensed d omains acquire static roughness as indicated by enhanced light scattering. With further compression, a nanoscale budding process occurs within the rou ghened regions, while the interiors of the condensed domains remain flat an d retain their domain shapes. At monolayer collapse, the buds proliferate a cross the entire interface, suggesting that the buds detected at lower pres sures represent spatially confined fluctuations into the collapse phase. Th e confinement of static roughness formation and budding to domain contact r egions indicates that these topographic instabilities originate from packin g defects created where adjacent domain edges with conflicting molecular or ientations grow together juring the fluid --> condensed phase transition.