New Information on the Hydrophobic Interaction Revealed by Frequency Modulation AFM

Area of Science:

• Physical Chemistry
• Surface Science
• Nanotechnology

Background:

• Understanding hydrophobic interactions is crucial in various scientific fields.
• Previous measurements of forces between hydrophobic surfaces were limited in range.

Purpose of the Study:

• To extend the measurement range of forces between hydrophobic surfaces in water.
• To investigate the dissipative and oscillatory components of these interactions at short distances.

Main Methods:

• Utilizing ultrahigh resolution atomic force microscopy (AFM) in frequency modulation mode.
• Performing simultaneous measurements of force and dissipation between hydrophobic surfaces.

Main Results:

• Extended force measurements down to molecular contact, revealing a transition from attraction to strong repulsion.
• Observed anomalously large dissipation and oscillatory short-range repulsion, indicating molecular ordering of water.
• Determined oscillation period of ~0.5 nm and range of ~1.5 nm for hydrophobic interactions.

Conclusions:

• Hydrophobic surfaces undergo significant changes in interaction forces and medium properties at close proximity.
• The observed phenomena suggest a distinct molecular ordering of water between approaching hydrophobic surfaces.
• These findings provide new insights into the fundamental nature of hydrophobic interactions.