Session: 12-22-01: Multiscale Models and Experimental Techniques for Composite Materials and Structures

Paper Number: 144603

144603 - Analysis and Deconvolution of Atomic Force Microscopy Data From Particulate Nanocomposites Through Finite Element Analysis 

Particulate nanocomposites represent a wide range of advanced materials—such as filled rubber composites, carbon nanotubes in a polymer matrix, or polystyrene particles in a hydrogel matrix—with many applications in industry and research, and understanding their material properties and how they change with composition is important for future applications. Characterizing the material properties of such composites is complicated by nano-scale interactions between the particles and the matrix they are embedded in; structural effects, varying geometry, and the presence of an interphase are all factors that can confound results. Atomic force microscopy (AFM) is one technique that is used for characterization of particulate nanocomposites, but interactions between the AFM probe and the embedded particles result in complicated force-displacement data that can be difficult to analyze and interpret. Finite element analysis (FEA) offers a method for deconvoluting complex AFM data, whereby models of nanoscale material behavior and experimental data are be used to simulate AFM indentation and model the response of composites with different geometries and material composition. In this paper, 2D FEA models will be used to simulate and analyze hard particles suspended in a soft matrix in an effort to understand more complicated materials—like polymers with nanoscale fillers and biomaterials—that have similar base geometries at the nanoscale.

Previous studies have used FEA to model and analyze different particulate nanocomposites. One study used FEA to identify the effect of the substrate in rubber nanocomposites on stress fields during AFM indentation and the size and properties of an apparent interphase. Similarly, another study analyzed the modulus of the measured interphase in filled rubber composites and how it is artificially increased by boundary and probe effects. Biomaterials have also been analyzed with this method, with simplified FEA models of polystyrene-hydrogel composites used to simulate more complex biomaterials such as cells. Other studies directly modeled cells as ellipsoidal soft matrices with a hard particle that represented the cell’s nucleus and were able to correlate FEA results with AFM data to determine the elastic modulus and shape of the cell. These studies demonstrate how FEA can be used to determine how complex, heterogeneous geometries impact AFM results and the nanoscale material properties extrapolated from AFM data.

However, many existing studies only examined one geometry or set of boundary conditions, and they did not account for local damage and plastic strain when deconvoluting nanoscale AFM data. This paper will use 2D FEA and the Derjaguin-Muller-Toropov contact mechanics model to analyze probe-particle interactions, with a spherical indenter with a radius of 10 nm and a particle diameter ranging between ~40-300 nm. The focus of this paper will be on particles that have a Young’s modulus ~10-10² times greater than that of the matrix, and particle embedment depths will vary between 2.5-60 nm below the surface of the matrix. To provide a more comprehensive resource for deconvoluting AFM data, different geometries, material properties, and orientations and levels of confinement will be modeled while studying the presence of an interphase and the impact of varying conditions on force-displacement data and hydrostatic pressure. The resulting FEA data was compared to data from AFM performed on hard inclusions embedded in a thermoset epoxy resin in order to supplement and verify FEA.

Presenting Author: Tyler Norkus Arizona State University

Presenting Author Biography: Tyler Norkus is pursing a master's degree in mechanical engineering at Arizona State University, with a focus on carbon nanotube composites, nanoscale mechanics, atomic force microscopy, and finite element analysis. He has published in two previous conference proceedings and plans on publishing a journal paper before graduating with his masters.

Authors:

Tyler Norkus Arizona State University
Masoud Yekani Fard California Polytechnic State University
Maximillian Westby Arizona State University
William Boutin Arizona State University