title: Sub-surface imaging of carbon nanotube-polymer composites using dynamic AFM methods.
abstract: High-resolution sub-surface imaging of carbon nanotube (CNT) networks within polymer nanocomposites is demonstrated through electrical characterization techniques based on dynamic atomic force microscopy (AFM). We compare three techniques implemented in the single-pass configuration: DC-biased amplitude modulated AFM (AM-AFM), electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM) in terms of the physics of sub-surface image formation and experimental robustness. The methods were applied to study the dispersion of sub-surface networks of single-walled nanotubes (SWNTs) in a polyimide (PI) matrix. We conclude that among these methods, the KPFM channel, which measures the capacitance gradient (∂C/∂d) at the second harmonic of electrical excitation, is the best channel to obtain high-contrast images of the CNT network embedded in the polymer matrix, without the influence of surface conditions. Additionally, we propose an analysis of the ∂C/∂d images as a tool to characterize the dispersion and connectivity of the CNTs. Through the analysis we demonstrate that these AFM-based sub-surface methods probe sufficiently deep within the SWNT composites, to resolve clustered networks that likely play a role in conductivity percolation. This opens up the possibility of dynamic AFM-based characterization of sub-surface dispersion and connectivity in nanostructured composites, two critical parameters for nanocomposite applications in sensors and energy storage devices.
authors.affiliation: Department of Electrical and Electronic Engineering, Universidad de los Andes, Bogota, Colombia.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Cadena
authors.forename: Rocio
authors.initials: R
authors.lastname: Misiego
authors.forename: Kyle C
authors.initials: KC
authors.lastname: Smith
authors.forename: Alba
authors.initials: A
authors.lastname: Avila
authors.forename: Byron
authors.initials: B
authors.lastname: Pipes
authors.forename: Ron
authors.initials: R
authors.lastname: Reifenberger
authors.forename: Arvind
authors.initials: A
authors.lastname: Raman
mesh_terms: D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D018625:Microscopy, Atomic Force / Q000379:methods*; D008968:Molecular Conformation; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D037742:Nanotubes, Carbon; D011108:Polymers