Complex three-dimensional self-assembly in proxies for atmospheric aerosols

Area of Science:

• Atmospheric Chemistry
• Materials Science
• Nanotechnology

Background:

• Aerosols significantly influence Earth's climate.
• Organic compounds with hydrophilic and hydrophobic parts are common in atmospheric aerosols.
• The internal structure of organic compounds within aerosol droplets is largely unknown.

Purpose of the Study:

• To investigate the self-assembly and nanostructure formation of fatty acids in aerosol proxies.
• To understand how these structures respond to environmental changes like humidity and chemical reactions.
• To explore the implications of these nanostructures for aerosol properties and climate processes.

Main Methods:

• Acoustic trapping of oleic acid/sodium oleate droplets in NaCl solution.
• Simultaneous synchrotron small-angle X-ray scattering (SAXS) and Raman spectroscopy.
• Analysis in a controlled gas-phase environment with varying humidity and chemical conditions.

Main Results:

• Fatty acids self-assemble into highly ordered 3D nanostructures, including hexagonal and cubic close-packed micelles and bilayer stacks.
• These structures exhibit responsiveness to humidity changes and chemical reactions.
• Self-assembly was observed in complex mixtures mimicking atmospheric aerosol compositions.
• Self-assembly reduces the fatty acid reaction rate with ozone.

Conclusions:

• Lyotropic phases form readily in fatty acid-based aerosol proxies.
• These ordered nanostructures likely exist in atmospheric aerosols.
• Lyotropic phase formation can influence aerosol radiative forcing, residence times, and other climate-relevant characteristics.