Extracting Ion Transport Properties from Scanning Probe Measurements on Smectite Clay Nanoparticles

Using finite element modelling, electronic simulations under an electrical load can be designed to better understand ion transport properties of smectite clay nanoparticles (NP). Smectite clay is a layered, porous material capable of changing its physical properties when hydrated upon exposure to water vapor. With a conducting atomic force microscope (AFM) tip, scans on the surface of these particles were done; data relating to particle topography and frequency-dependent electric forces was extracted from these experiments. A finite element method (FEM) model and Matlab programs were constructed to facilitate simulation of AFM system parameters, measurements, and computation. The equivalent charge method offered an advanced approach to computing NP electric properties with the irregular shaped AFM tip by modeling the force resulting from a series of test charge-image interactions. FEM simulations revealed that dielectric phase shift followed a power law with increasing voltage frequency on the AFM tip. With different conductivity anisotropy, force derivative and phase shift values were observed to have different frequency dependencies. Computational results were paired with experimental findings to extract frequency dependant NP conductivity to compare to bulk measurements.