Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 118, Issue 25, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2024805118
Keywords
foams and emulsions; surface forces; X-ray scattering; soft matter; structural forces
Categories
Funding
- DOE Office of Science [DE-AC02-06CH11357]
- NSF-CBET [1806011]
- UIC College of Engineering
- UCLA Samueli School of Engineering
- Department of Chemical and Biomolecular Engineering
- Div Of Chem, Bioeng, Env, & Transp Sys
- Directorate For Engineering [1806011] Funding Source: National Science Foundation
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The step size in stratifying foam films is inversely proportional to the cubic root of surfactant concentration. Analysis using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols compared with small-angle X-ray scattering provides insights into non-DLVO supramolecular oscillatory structural forces and micellar interactions within foam films.
Ultrathin foam films containing supramolecular structures like micelles in bulk and adsorbed surfactant at the liquid-air interface undergo drainage via stratification. At a fixed surfactant concentration, the stepwise decrease in the average film thickness of a stratifying micellar film yields a characteristic step size that also describes the quantized thickness difference between coexisting thick-thin flat regions. Even though many published studies claim that step size equals intermicellar distance obtained using scattering from bulk solutions, we found no reports of a direct comparison between the two length scales. It is well established that step size is inversely proportional to the cubic root of surfactant concentration but cannot be estimated by adding micelle size to Debye length, as the latter is inversely proportional to the square root of surfactant concentration. In this contribution, we contrast the step size obtained from analysis of nanoscopic thickness variations and transitions in stratifying foam films using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols, that we developed, with the intermicellar distance obtained using small-angle X-ray scattering. We find that stratification driven by the confinement-induced layering of micelles within the liquid-air interfaces of a foam film provides a sensitive probe of non-DLVO (Derjaguin-Landau-Verwey-Overbeek) supramolecular oscillatory structural forces and micellar interactions.
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