Langmuir monolayers, single molecule-thick rafts of surfactant molecules at the air-water

interface, are of great interest due to their similarity to the surfactant system present in the lung. These monolayers are compressed and expanded between two Teflon barriers in order to change the surface pressure of the system. The effects of reduced subphase depth, particle size, and compression frequency on the folding dynamics of Survanta and SDS-DODAB monolayers are observed. A monolayer of Survanta, a bovine lung surfactant is deposited on the surface of an aqueous buffer solution to test the effects of depth on the system. The depth is altered by placing a polydimethylsiloxane substrate at the bottom of the monolayer trough. The presence of this substrate is found to shift surface pressure-area isotherms toward regions of lower area by an average value of 8.9 mN/m. Fluoresecent polystrene micro- and nanoparticles are used to test the effects of particle size on SDS-DODAB monolayers. A phase diagram was generated showing the reversibility behavior of the monolayer under various conditions of compression speed and particle size. Particle diameters of 100 and 500 nm were generally observed to result in irreversible folding behavior at sufficiently low barrier speeds. At barrier speeds of 90 cm2/min, all particle sizes were observed to transition to reversible folding.

The effects of a barrier in proximity to the air-water interface on the dynamics of a Langmuir monolayer system are observed. A monolayer of Survanta, bovine lung surfactant, is deposited onto the interface of an aqueous buffer solution. Polystyrene particles one micron in diameter and tagged with fluorescent carboxylate groups are distributed evenly throughout the monolayer surface. The bead-monolayer system is compressed and expanded to induce folding. A polydimethylsiloxane (PDMS) substrate is placed below the monolayer in the buffer solution to study interactions between the folding monolayer and a barrier. The presence of the substrate is shown to shift surface pressure-area isotherms toward regions of lower area by an average of 8.9 mN/m. The surface of the PDMS substrate can be imaged using fluorescence microscopy to detect the presence of particles or surfactant that may have been transported there from the air-water interface during folding. Images show the transferral of particles and monolayer together suggesting the pinch-off of a fold or the direct interaction of a fold with the barrier.