Sub-surface imaging of carbon nanotube-polymer composites using dynamic AFM methods

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Polymer nanocomposites require detailed characterization of internal structures for optimal performance.
• Understanding the dispersion and connectivity of carbon nanotubes (CNTs) within polymer matrices is critical for applications.
• Sub-surface imaging techniques are needed to complement surface analysis of nanocomposites.

Purpose of the Study:

• To demonstrate high-resolution sub-surface imaging of CNT networks in polymer nanocomposites using dynamic atomic force microscopy (AFM).
• To compare the efficacy of DC-biased amplitude modulated AFM (AM-AFM), electrostatic force microscopy (EFM), and Kelvin probe force microscopy (KPFM) for sub-surface imaging.
• To establish KPFM as a robust method for characterizing CNT dispersion and connectivity.

Main Methods:

• Dynamic atomic force microscopy (AFM) in a single-pass configuration.
• Comparison of AM-AFM, EFM, and KPFM techniques for sub-surface imaging.
• Analysis of capacitance gradient (∂C/∂d) images from KPFM to assess CNT dispersion and connectivity.

Main Results:

• KPFM, measuring the capacitance gradient (∂C/∂d) at the second harmonic, provides high-contrast, surface-condition-independent images of sub-surface CNT networks.
• AFM-based sub-surface methods effectively probe deep enough to resolve clustered networks relevant to conductivity percolation.
• The proposed analysis of ∂C/∂d images allows for characterization of CNT dispersion and connectivity.

Conclusions:

• Kelvin probe force microscopy (KPFM) is the superior AFM technique for high-resolution sub-surface imaging of CNTs in polymer nanocomposites.
• Dynamic AFM-based sub-surface characterization enables assessment of dispersion and connectivity, critical parameters for nanocomposite applications.
• This work opens possibilities for advanced characterization of nanostructured composites for sensors and energy storage.