Langmuir Monolayer Flow across Hydrophobic Surfaces. 3. Influence of Acyl Chain Structure on Supported Bilayer Formation Rates

The bilayer formation properties of single-component acyl chains of varying length and extent of unsaturation are compared using Langmuir monolayer flow. Four series of structural motifs in the flowing film were considered: linked oleyl chains; chains with a single cis double bond over a range of total chain lengths; chains of the same length with 1−5 cis double bonds; molecules which flow that do not have the standard cis double bond in the chain. Slower flow rates were observed for Langmuir films with increased numbers of linked oleyl chains due to the enhanced interlayer coupling between the flowing and stationary films. Slower flow rates were also observed with increased acyl chain length due to the increased intralayer coupling between the flowing molecules. More rapid flow rates were observed as the number of double bonds within the film forming material was increased, due to both the decreased inter- and intralayer coupling. While no single structural feature is common to molecules that undergo monolayer flow, all molecules that have been observed to flow exist at a liquid expanded phase state at the equilibrium spreading pressure.