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Optical Tuning of Surface Tension at the Air-Water Interface Using a Merocyanine Photoacid
Thien Khuu1, Sean W Parsons1, Jahan M Dawlaty1
1University of Southern California , Los Angeles, California90007, United States.
The Journal of Physical Chemistry. B
|July 16, 2026
Summary
Visible light reversibly controls surface tension in merocyanine photoacid (MCH) solutions. This light-induced modulation, influenced by interfacial electrostatics, offers new ways to control interfacial processes.
Area of Science:
- Photochemistry
- Surface Science
- Physical Chemistry
Background:
- Merocyanine photoacids (MCH) exhibit light-induced proton release and cyclization to spiropyran (SP).
- The photochemistry of MCH/SP is well-studied, but its effect on interfacial properties like surface tension is less understood.
Purpose of the Study:
- To quantify light-driven changes in surface tension of aqueous MCH solutions.
- To investigate the role of interfacial electrostatics in modulating these light-induced surface tension changes.
Main Methods:
- Utilized a Langmuir-Blodgett (LB) trough to measure surface tension.
- Employed a 430 nm LED for illumination and observed reversible changes.
- Introduced LB monolayers with varying headgroup charges (neutral, positive, negative) to probe electrostatic effects.
Main Results:
- Illumination with visible light caused a rapid, reversible decrease in surface tension.
- The surface tension decrease correlated with the enhanced interfacial partitioning of photogenerated spiropyran (SP).
- Positively charged monolayers amplified the light-induced surface tension change, while negatively charged and neutral monolayers suppressed it, indicating electrostatic influence.
Conclusions:
- Established that visible light can reversibly tune surface tension in MCH solutions.
- Demonstrated that interfacial electrostatics significantly impact the light-induced modulation of surface tension.
- Highlighted the potential for light-controlled interfacial processes through MCH/SP systems.
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