Determining liquid substrate cleanliness using infrared imaging

Abstract

Experiments conducted in a modified Langmuir trough are described. Measurements of surface tension were obtained using a Wilhelmy plate, while infrared (IR) images of the water surface adjacent to the Wilhelmy plate were simultaneously recorded. A contaminating surfactant film was allowed to form on the surface while the experiments were being conducted. The data reveal a substantial change in the IR imagery due to the film in all cases. The difference between the appearance of the clean and surfactant-covered regions of the surface is clear and distinct. For some of these experiments the change in the IR imagery is accompanied by no observable change in surface tension. This, along with several other aspects of this work, suggest that IR imagery may be a superior tool, compared to traditional surface tension measurements, for ascertaining the cleanliness of a liquid substrate.

Phase separation in molecular layers of macromolecules at the champagne–air interface

“…Additional insights should be gained from observation over a field of view comparable with the surface of the dish. An infrared imaging technique of recent implementation might be appropriate (Saylor, 2001).…”

An experimental study of Mesler entrainment on a surfactant‐covered interface: The effect of drop shape and Weber number

“…6,23,24 Moreover, even when water is cleaned to the point that a Wilhelmy plate apparatus reveals no surfactant contamination, surfactants may still exist on the water surface, 25 as revealed by infrared imagery. 26 Hence, when using ''clean'' water surfaces, one may simply be creating an environment where Mesler entrainment becomes highly variable due to varying degrees of contamination which occur at the water surface from run-to-run or even from drop-to-drop. This may be the cause of the lack of reproducibility in Mesler entrainment which was observed by, for example, Esmailizadeh and Mesler, 3 and Pumphrey and Elmore.…”

Sherwood–Rayleigh parameterization for evaporation in the presence of surfactant monolayers

“…Several small islands of indigenous surfactant material exist on the clean surface in Figure a. As shown by Saylor, comparing the surfactant images in Figures b–d with the clean surface image in Figure (a) shows that the use of the IR camera allows for the clean surface condition to be easily distinguished. When oleyl alcohol, stearic acid, or stearyl alcohol are present, the fine scale structures disappear and dark, slender sheet regions emerge.…”

“…The surface was then cleaned by sweeping a Kimwipe tissue across the interface to remove indigenous surfactant material. Use of the IR camera allowed the surface cleanliness to be visually monitored, and the sweeping procedure was repeated until the surface was entirely clean. Once the surface was determined to be free of indigenous surfactant material, either the surface was prepared with one of the surfactant monolayers or a clean surface experiment was initiated.…”

“…A second IR camera (not shown in Figure ) was used to observe the entire tank surface. As IR images can be used to ascertain surface cleanliness, the images from this camera were used to ascertain when contamination began, at which time data‐taking for the clean surface run was terminated. The water surface was then cleaned once again to begin a new clean surface run.…”