Direct Surface Tension Measurements of Individual Sub-Micrometer Particles Using Atomic Force Microscopy

Area of Science:

• Atmospheric Chemistry
• Physical Chemistry
• Environmental Science

Background:

• Sea spray aerosol (SSA) plays a crucial role in Earth's climate and environment due to its high atmospheric concentration.
• Direct surface tension measurements of sub-micrometer SSA particles are scarce, hindering a full understanding of their properties.

Purpose of the Study:

• To directly measure the surface tension of individual sub-micrometer SSA particle mimics.
• To investigate the influence of relative humidity (RH), chemical composition, and viscosity on SSA surface tension.

Main Methods:

• Utilized atomic force microscopy (AFM) to probe individual sub-micrometer particles.
• Examined model systems including electrolyte salts, dicarboxylic acids, and saccharides, both as single components and mixtures.
• Varied relative humidity and solute concentration to observe changes in surface tension.

Main Results:

• Single particle surface tension was found to be dependent on RH, solute mole percentage, and chemical composition.
• Good agreement was observed between AFM single particle and bulk solution surface tension measurements for liquid droplets within a specific viscosity range.
• Demonstrated AFM's capability for direct surface tension measurements across diverse chemical systems and conditions.

Conclusions:

• AFM provides a viable method for direct surface tension measurements of individual SSA particles.
• The study enhances understanding of SSA's physical-chemical properties relevant to atmospheric processes.
• Results contribute to more accurate climate and environmental modeling involving SSA.