Sensitivity of viscoelastic characterization in multi-harmonic atomic force microscopy

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Accurate nanomechanical property quantification of soft matter is vital for polymers, coatings, and biological systems.
• Multi-frequency atomic force microscopy (AFM) utilizes cantilever spectral components for characterization.
• Complex multi-parameter optimization in AFM can lead to over-determined estimations and unclear parameter-data relationships.

Purpose of the Study:

• To investigate the sensitivity of viscoelastic characterization in polymers using multi-frequency intermodulation AFM.
• To identify challenges in parameter estimation and their influence on experimental data.
• To propose a refined approach for accurate nanoscale viscoelastic property mapping.

Main Methods:

• Performed simulations and experimental studies on polymeric samples.
• Analyzed the sensitivity of experimental observables to surface and bulk viscoelastic properties.
• Investigated the impact of parameter estimation on objective function minimization (gradient and convexity).

Main Results:

• Surface viscoelasticity was found to have a negligible effect on experimental data.
• Including surface dependency led to inconsistent and non-physical parameter identification.
• Removing surface dependency simplified the model, enabling unambiguous characterization of bulk properties.

Conclusions:

• The study highlights sensitivity issues in AFM when optimizing numerous parameters and observables.
• A simplified model focusing on bulk properties enhances characterization accuracy and reliability.
• Development of advanced nanoscale viscoelastic models and computational methods is recommended for AFM applications.