Ion-Selective Marangoni Instability Coupled with the Nonlinear Adsorption/Desorption Rate

Ion-Selective Marangoni Instability Coupled with the Nonlinear Adsorption/Desorption Rate

An oil/water interface containing bis(2-ethylhexyl)phosphate and Ca2+ or Fe3+ exhibits spontaneous Marangoni instability associated with the fluctuation in interfacial tension. This instability rarely appears for oil/water systems with Mg2+, Sr2+, Ba2+, Cu2+, or Co2+. The same ion selectivity is obs...

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Bibliographic Details
Published in:Langmuir Vol. 27; no. 23; pp. 14131 - 14142
Main Authors: Hosohama, Tsugihiko, Megumi, Keitaro, Terakawa, Syuji, Nishimura, Junya, Iida, Youhei, Ban, Takahiko, Shioi, Akihisa
Format: Journal Article
Language:English
Published: Washington, DC American Chemical Society 06-12-2011
Subjects:
Adsorption
Chemistry
Diethylhexyl Phthalate - chemistry
Exact sciences and technology
General and physical chemistry
Hydrogen-Ion Concentration
Interfaces: Adsorption, Reactions, Films, Forces
Ions - chemistry
Metals, Alkaline Earth - chemistry
Metals, Heavy - chemistry
Oils - chemistry
Organometallic Compounds - chemical synthesis
Organometallic Compounds - chemistry
Surface physical chemistry
Surface-Active Agents - chemistry
Water - chemistry
Water
Phosphates
Viscosity
Nitro compound
Interface tension
Selectivity
Density
Convection
Aggregation
pH
Extraction
Fluctuations
Ions
Desorption
Complexes
Equilibrium
Heptane
Exfoliation
Drop
Oil
Adsorption
Benzenic compound
Soluble compound
Instability
Aggregate
Physicochemical properties
Interface
Rheological properties
Neutralization
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Summary:An oil/water interface containing bis(2-ethylhexyl)phosphate and Ca2+ or Fe3+ exhibits spontaneous Marangoni instability associated with the fluctuation in interfacial tension. This instability rarely appears for oil/water systems with Mg2+, Sr2+, Ba2+, Cu2+, or Co2+. The same ion selectivity is observed for n-heptane and nitrobenzene despite their significant differences in density, viscosity, and the dielectric constant of oil. We studied this instability under acidic pH conditions to avoid the neutralization reaction effects. The result of the equilibrium interfacial tension and the extraction ratio of cations indicates that a large number of oil-soluble complexes form at the interfaces of Ca2+-containing systems and probably for Fe3+-containing systems. The results obtained by oscillating drop tensiometry and Brewster angle microscopy indicate that desorption, rather than adsorption, is more significant to the onset of instability and that the resulting complex tends to form aggregates in the interface. This aggregation gives the nonlinear desorption rate of the oil-soluble complex. Then, exfoliation of the aggregating matter occurs, which triggers the Marangoni instability. The induced convection removes the oil-soluble complex accumulated at the interface, creating a renewed interface, which is necessary for the successive occurrence of the Marangoni instability. For the other cations, the oil-soluble compounds are insignificant, and they rarely form aggregates. In such cases, adsorption/desorption proceeds without instability.
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ISSN:0743-7463
1520-5827
DOI:10.1021/la203145f