Method to Measure Surface Tension of Microdroplets Using Standard AFM Cantilever Tips

Area of Science:

• Physical Chemistry
• Materials Science
• Nanotechnology

Background:

• Surface tension is crucial for understanding wetting phenomena and is typically measured using bulk methods.
• Existing atomic force microscope (AFM) techniques for micro-scale surface tension measurement require specialized nanoneedle probes.

Purpose of the Study:

• To develop a simplified AFM-based method for measuring surface tension of microscopic liquid droplets.
• To eliminate the need for custom-fabricated probes, reducing complexity and cost.

Main Methods:

• Utilized standard pyramidal AFM cantilever tips coated with a hydrophilic polymer brush.
• Measured capillary forces between the coated tips and micro-droplets.
• Employed numerical simulations to calculate surface tension from force measurements.

Main Results:

• Successfully measured surface tension of micrometer-sized droplets using standard AFM tips.
• Results for mineral oil, ionic liquid, and glycerol showed good agreement with bulk tensiometer measurements (max 10% error).
• The hydrophilic coating reduced contact angle hysteresis for various liquids.

Conclusions:

• A simplified and cost-effective AFM method for micro-droplet surface tension measurement is presented.
• This approach enables femtoliter-scale surface tension analysis without specialized equipment.
• The findings contribute to advancements in microfluidics and materials characterization.