Fig 1.
Schematic (A) and photograph (B) of the drainage platform. For the insoluble surfactant experiments, the glass dome is initially submerged in the PBS-filled Langmuir trough (white, teflon container) and DPPC is spread at the air-liquid interface. DPPC is then compressed to the desired surface pressure using a single Delrin barrier and the surface pressure is monitored using a paper Wilhelmy balance (1). For the soluble surfactant experiments, the Langmuir trough is filled with SDS solution of desired concentration. In both cases, the measurement commences once the glass dome is elevated through air-liquid interface with a computer controlled motorized stage (2). A high speed interferometer (black tube) captures the thickness of the draining films as a function of time at the apex of glass dome.
Fig 2.
Characteristic experimental data-set for DPPC film draining at 7 mN m−1 in the LE-LC plateau.
(A) The film thickness (h) as a function of rescaled time (τ) at elevated Ve = 10 mm s−1. The parameter b corresponds to fitting parameter α. (B) Summary of the α values as a function of elevation velocity Ve = [1–10] mm s−1.
Fig 3.
(A, B) Dimensionless variable (1/H2 = (h0/h)2) as a function of rescaled time (τ) for DPPC at 5 mN m−1 and 25 mN m−1 at various elevated velocity (Ve) ranging from 1–10 mm s−1. (C) Summary of the value for the fitting parameter α of DPPC at various surface pressures. (D) Summary of the initial height capture of the aqueous film laden with DPPC at different surface pressures. The standard deviation is calculated from three independent trials.
Fig 4.
[A, B] Dimensionless variable (1/H2 = (h0/h)2) as a function of rescaled time (τ) for SDS at 0.13 cmc and 5 cmc at various elevated velocity (Ve) ranging from 1–10 mm s−1. [C] Summary of the value for the fitting parameter α of SDS at 0.13 cmc and 5 cmc. [D] Summary of the initial height capture of SDS film at 0.13 cmc and 5 cmc. The standard deviation is calculated from two independent trials.
Fig 5.
Photograph (A) and schematic (B) of the surface visualization setup. Instead of a glass substrate, an air bubble is elevated through air-water interface. Thin film color interference patterns are clearly visible under diffused white-light illumination, due to enhanced refractive index mis-match.
Fig 6.
Images of the color interference patterns captured for DPPC at two different surface pressures, Π = 5 mN m−1 and >25 mN m−1 using the surface flow visualization setup. The colormap is a visual tool to determine the corresponding thickness of individual vibrant color. The dark black spot in the center of each frame is the reflection of the camera and the white bright ring at the periphery is the edge of the glass capillary. The scale bar shown is 0.25 mm.
Fig 7.
Snapshots of interference patterns observed for SDS at 0.13 cmc and 5 cmc. The images are attained using the surface flow visualization setup. The colormap is a guide to relate individual vibrant color to its corresponding thickness. The dark black spot in the center of each frame is the reflection of the camera and the white bright ring at the periphery is the edge of the glass capillary. The scale bar shown is 0.25 mm.
Fig 8.
Surfactant stability mechanisms.
Schematic summarizing the two different stabilizing interfacial mechanisms for surfactant films: Viscoelastic interfaces create immobile films that reduce drainage through surface stress dissipation, while surface inviscid surfaces create mobile interfaces and create surface-tension induced Marangoni flows that counter the bulk-flow direction.