Development of an atomic-force-microscope-based hanging-fiber rheometer for interfacial microrheology

Area of Science:

• Interfacial Science
• Physical Chemistry
• Materials Science

Background:

• Understanding interfacial properties is crucial in various scientific and engineering fields.
• Traditional methods for studying interfacial rheology can be complex and limited in scope.
• Atomic Force Microscopy (AFM) offers high-resolution force sensing capabilities.

Purpose of the Study:

• To develop a novel interfacial microrheology technique.
• To utilize AFM as a precise force sensor for interfacial measurements.
• To investigate the dynamics of the contact line at a water-air interface.

Main Methods:

• A modified AFM probe featuring a glass fiber immersed in a water-air interface was employed.
• The motion of the cantilever was modeled using the Langevin equation for a damped harmonic oscillator.
• Friction coefficients were determined by analyzing cantilever motion and extrapolating to zero immersion length.

Main Results:

• The friction coefficient (xi) was found to have contributions from both bulk fluid and the contact line.
• Bulk fluid contribution increased with the immersion depth of the glass fiber.
• Contact line contribution was isolated by extrapolating measurements to zero immersion length.

Conclusions:

• The developed AFM-based interfacial microrheology technique is effective for studying interfacial phenomena.
• The study successfully quantified the friction associated with the water-air contact line.
• This method provides new insights into interfacial microrheology and contact line dynamics.