Influence of Surface Flows on the Shape of Fractal Domains

Tidal breathing is associated with a 30% change of thesurfactant-coveredalveolar surface occurring about 16 times per minute. To model thishighly dynamic process, erucic acid monolayers at the air-waterinterface were compressed fast. Brewster angle microscopy imaged thefractal liquid-condensed (LC) domains and quantified the surface flowin size, direction, and duration. Radial branch distribution of thedomains has a minimum in the flow direction, as was shown with directionalityhistograms. The fast Fourier transform of the domains shows a preferentialgrowth perpendicular to the flow direction. Additionally, at thebeginning of the flow, the downstream side of the domain grows fasterthan the upstream side. Surface flows act on the mm to cm scale, causean anisotropic flow in the liquid expanded phase surrounding the LCdomain, and affect the overall domain shape. On the & mu;m-scale,the dendritic or seaweed domains' branches were only slightlydisturbed. These results may help to understand pulmonary surfactantlayers.