(381g) Simulation of Marangoni Transport from Two Interacting Surfactant Sources

Surfactant laden aerosols have recently become of interest for their potential use in the treatment of obstructive pulmonary diseases. In one such disease, cystic fibrosis, the lung mucus forms viscous plaques which obstruct the airflow and harbor fatal bacterial infections. Typical aerosolized medication distributes drugs poorly throughout the lung as the aerosols follow the path of least resistance, away from the most obstructed regions and deposit preferentially on branch points in the lung. Including a surfactant along with the aerosolized medication can lead to decreasing the surface tension in the areas of high aerosol deposition which cause Marangoni flow originating in these regions, moving drug deeper into the lung, to where the infection is worst.

Most currently available research on Marangoni transport can be split up into two dissimilar groups: invitro and computational work studying single surfactant sources, and invitro and clinical studies on surfactant laden aerosols. While both types of work yield valuable information for understanding how surfactants can be used to treat obstructive lung diseases. This work is the first to attempt to bridge the gap between the two, by looking at how two simultaneously deposited surfactant sources interact with each other.

The simultaneous spreading of two surfactant disks was simulated using COMSOL Multiphysics. As the two pucks spread and interacted with each other, overall behavior could be grouped into three distinct phases. First, the two pucks are isolated from each other and spread without being affected by the other drop. Second, the two pucks begin to interact. We measure this in three different ways, the fluid flow of the liquid beneath the disks, the height of the interface where the disks reside, and the location of surfactant along that interface. Third, the profiles for fluid flow, surface height, and surfactant location merge together resulting in all extrema to occur at the midpoint between the two disks, resulting in profiles that appear to have come from a single surfactant source. By increasing the ratio of the separation distance to the initial size of the surfactant disk, we delay the onset of these phases, and with sufficient separation, spreading stalls before the interaction phase ends.

This study also gives insight into two phenomena observed during in vitro surfactant aerosol experiments. First, the surfactant droplets are shown to move along the interface away from other surfactant droplets. In the simulations, this behavior occurs when the Marangoni front from one disk moves past the other. A second observation is that drops that are sufficiently close to one another begin to deform. Deformation of the surfactant pucks occurs in the simulations when the surfactant fronts from the two disks interact at the midpoint between the two disks. This work begins the task of bringing together the data from two separate areas in the study of Marangoni driven transport and will lead to the creation of better treatments for obstructive lung disease.