Direct Measurement of Lateral Correlations under Controlled Nanoconfinement

Area of Science:

• Surface science
• Materials science
• Physical chemistry

Background:

• Hydrophobic surfaces exhibit complex lateral correlations.
• Understanding forces between neutral surfaces is critical in various applications.
• Cationic surfactants can modify surface properties.

Purpose of the Study:

• To measure lateral correlations along hydrophobic surfaces with variable separation.
• To investigate the role of counterion redistribution in surface interactions.
• To characterize the structural changes of hydrophobic surfaces using X-ray scattering.

Main Methods:

• Utilized a modified Surface Force Apparatus coupled with synchrotron radiation (SFAX).
• Employed X-ray scattering to probe lateral correlations on mica surfaces.
• Varied the separation distance between hydrophobic surfaces to observe structural changes.

Main Results:

• Observed weak isotropic diffuse scattering indicating a lateral surface correlation length of approximately 12 nm.
• Found that scattering patterns are stable for gap widths larger than the lateral period.
• Detected changes in scattering intensity and shape below this correlation length, linked to counterion redistribution.

Conclusions:

• Adsorbed surfactant stripes on hydrophobic mica surfaces create lateral correlations.
• Counterion redistribution is a key mechanism influencing interactions between neutral surfaces.
• The observed phenomena provide insights into electrostatic attraction between like-charged surfaces.