Resolving Multi-Asperity Contacts at the Nanoscale through Super-Resolution Fluorescence Imaging

Area of Science:

• Contact mechanics
• Surface science
• Nanotechnology

Background:

• Multiscale random roughness in contacts presents challenges for experimental validation of theories.
• Understanding multi-asperity rough contacts is crucial for predicting failures like earthquakes and for technological applications.

Purpose of the Study:

• To introduce a super-resolution microscopy method for visualizing nanoscale contact mechanics.
• To investigate the impact of material stiffness on the real contact area of rough surfaces.

Main Methods:

• Utilized spontaneous millisecond ON/OFF fluorescence blinking of contact-sensitive molecular rotors.
• Achieved approximately 55 nm lateral imaging resolution for rough polymer and glass sphere contacts.
• Compared contact areas for soft polymer and hard glass spheres against diffraction-limited imaging.

Main Results:

• Super-resolution imaging revealed nanoscale contact structures.
• For soft polymer spheres, real contact area was unaffected by resolution improvement due to plastic deformation.
• For hard glass spheres, the real contact area was 2.4 times smaller than observed with diffraction-limited imaging.

Conclusions:

• Material stiffness significantly influences the nanoscale structure within the real contact area.
• Super-resolution microscopy provides direct visualization of contact mechanics at the nanoscale.
• This technique enhances understanding of contact phenomena across various scales.