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Tracking Giant Folds in a Monolayer

Year: 2010

Journal: Langmuir (2010), 26(15), 12755-12760, 20121205

Authors: Boatwright, Thomas; Levine, Alex J.; Dennin, Michael

Organizations: Department of Physics & Astronomy, University of California, Irvine, California 92697; Department of Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California 90095; California Nanosystems Institute, University of California, Los Angeles, Los Angeles, California 90095

The collapse dynamics of giant folds in a catanionic monolayer at the air−water interface are examined. A monolayer of dioctadecyldimethylammonium bromide (DODAB) and sodium dodecyl sulfate (SDS) in a 1:1 ratio is the system of study that previously was found to fold upon compression in a Langmuir trough. Carboxylate-coated polystyrene beads (1 μm diameter) are deposited and bound to the monolayer. Displacement of the beads is measured with epifluorescence microscopy and particle image velocimetry, yielding a measurement of the velocity of the monolayer around the fold. Reversibility is confirmed by measuring the amount of monolayer material entering and leaving the fold. Material near folds are found to have a maximum relative velocity on the order of 0.1 mm/s, and fold depths are found to be on the order of 1 mm. The folds exhibit regular unfolding behavior, which can be explained qualitatively by a simple mechanical model.