Fold-speed control in collapsing mixed phospholipid monolayers

Mixed monolayers of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoyl-phosphatidylserine are compressed beyond their collapse pressure. Primary and secondary folds that grow perpendicular to the compression direction are observed using Brewster angle microscopy. The secondary fold velocity is measured with a fast charge-coupled device camera. We observe a reduction in secondary fold speed when increasing the mole fraction of the softer DPPC component in the monolayer. The fracture kinetics follows theoretical predictions for the fold coarsening dynamics of uniaxially stressed three-dimensional systems.