3D depth profiling of the interaction between an AFM tip and fluid polymer solutions

Area of Science:

• Materials Science
• Polymer Physics
• Surface Science

Background:

• Investigating soft polymers and liquids with atomic force microscopy (AFM) is complex due to dominant long-range forces (van der Waals, capillary, adhesion).
• AFM tip indentation and polymer filament pull-off complicate accurate measurement of unperturbed polymeric fluid shapes.

Purpose of the Study:

• To investigate tip-sample interactions with polystyrene droplets swollen in chloroform vapor.
• To adjust specimen mechanical properties by controlling solvent vapor concentration.
• To develop a versatile methodology for accurate nanometer-scale dimensional measurements of fluid and gel-like objects.

Main Methods:

• Utilized atomic force microscopy (AFM) with polystyrene droplets swollen in chloroform vapor.
• Employed two AFM force spectroscopy methods: force-distance (FD) curves and amplitude-phase-distance (APD) curves.
• Measured the fluid's intrinsic relaxation time using an AFM-based step-strain experiment.

Main Results:

• Reconstructed three-dimensional (3D) depth profiles of tip-sample interaction from FD and APD measurements.
• Gained detailed insight into the tip-sample interaction mechanism for fluid polymer solutions.
• Demonstrated that intrinsic relaxation time is crucial for understanding tip-sample interactions.

Conclusions:

• Measuring 3D depth profiles provides detailed insight into tip-sample interactions for fluid polymers.
• The intrinsic relaxation time is essential for understanding these interactions.
• The combined use of 3D depth profiling and APD data offers a versatile method for accurate nanometer-scale measurements of fluid and gel-like materials.