Journal article
Surface Tension Measurements of Aqueous Liquid-Air Interfaces Probed with Microscopic Indentation
Langmuir, Vol.37(7), pp.2457-2465
02/23/2021
DOI: 10.1021/acs.langmuir.0c03507
PMID: 33576233
Abstract
To elucidate the intricate role that the sea surface microlayer (SML) and sea spray aerosols (SSAs) play in climate, understanding the chemical complexity of the SML and how it affects the physical-chemical properties of the microlayer and SSA are important to investigate. While the surface tension of the SML has been studied previously using conventional experimental tools, accurate measurements must be localized to the thickness of the air-liquid interface of the SML. Here we explore the atomic force microscopy (AFM) capabilities to quantify the surface tension of aqueous solution droplets with (sub)micrometer indentation depths into the interface. Sample droplets of hexanoic acid at molar concentrations ranging from 0.1 to 80 mM and SML from a recent wave flume study were investigated. A constant-radius AFM nanoneedle was used to probe ca. 200 μL droplets with 0.3-1.2 μm indentation depths. As a comparison, the surface tension of bulk samples was also measured using a conventional force tensiometer. The data for the hexanoic acid show an excellent overlap between the AFM and force tensiometer surface tension measurements. For the surface tension measurements of the SML, however, the measured values from the AFM were 2.5 mN/m lower than that from the force tensiometer, which was attributed to the structural and chemical complexity of the SML, differences in the probing depth for each method, and the time scale required for the surface film to restructure as the needle is retracted away from the liquid surface. Overall, the study confirmed the accuracy of the AFM method in quantifying the surface tension of aqueous solutions over a wide range of concentrations for surface-active organic compounds. The methodology can be further used to reveal small, yet important, differences in the surface tension of complex air-liquid interfaces such as liquid systems where the type and concentration of surfactants vary with the distance from the air-liquid interface. For such complex systems, AFM measurements of the surface tension as a function of the probing depth and pulling rate may reveal a sublayer film structure of the liquid interface.
Details
- Title: Subtitle
- Surface Tension Measurements of Aqueous Liquid-Air Interfaces Probed with Microscopic Indentation
- Creators
- Chathuri P Kaluarachchi - Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United StatesHansol D Lee - Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United StatesYiling Lan - Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United StatesThiranjeewa I Lansakara - Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United StatesAlexei V Tivanski - Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
- Resource Type
- Journal article
- Publication Details
- Langmuir, Vol.37(7), pp.2457-2465
- DOI
- 10.1021/acs.langmuir.0c03507
- PMID
- 33576233
- ISSN
- 0743-7463
- eISSN
- 1520-5827
- Grant note
- DOI: 10.13039/100000165, name: Division of Chemistry, award: 1305427
- Language
- English
- Date published
- 02/23/2021
- Academic Unit
- Chemistry
- Record Identifier
- 9984216690202771
Metrics
9 Record Views