Session: 04-28-02: Modeling and Experiments in Nanomechanics and Nanomaterials

Paper Number: 113071

113071 - Investigation of Nanomechanical Properties and Interphase of Variable-Size Hard Particles in a Soft Matrix in Atomic Force Microscopy and Finite Element Analysis 

Hard particles suspended in a soft matrix significantly change the properties of the surrounding matrix via the interphase that surrounds the particles, and atomic force microscopy (AFM) is one of the techniques that has been used to characterize the nanoscale properties of such composites. AFM performed on particle-matrix composites results in complicated force-displacement data when indenting on the particles, and significant effort must be made to analyze that data. Finite element analysis (FEA) will be used in conjunction with different models of nanoscale mechanical behavior and experimental data to deconvolute and analyze the complex interactions between the AFM probe and hard particles. Polymers with nanoscale fillers and biomaterials can both be modeled with simpler particle-matrix composites, with this study focusing on materials with particles that have a Young’s modulus that is roughly ~10³-10⁵ times greater than that of the matrix.

Previous work has been done to characterize both filled rubbers and biomaterials, with special attention being paid to their hyperelastic nature and complex geometry. For polymers with hard, nanoscale fillers, AFM was performed on a layered silicon-rubber composite to characterize the rubber interphase, and FEA helped to extract the interphase properties from the AFM data while avoiding boundary and edge effects from the silicon layer. In another study, polystyrene particles were placed within hydrogel in order to model biomaterials with similar geometries, and limited FEA was used to analyze anomalies in the AFM data the resulted from indenting on particles. FEA was used to interpret the materials’ response to AFM indentation, but the scenarios that were considered did not portray the full extent of the AFM probe’s interactions with the hard particles or substrate.

To address this gap in knowledge, this paper creates the FE geometry of a hard particle-soft matrix composite, with particle diameter ranging between ~0.04-3 microns. The embedment depth of the particles will range between ~1 micron above and ~3 microns below the surface of the matrix. Two AFM probes are modeled, a spherical indenter with a radius of 200 nm and a conical indenter with an effective tip radius of 12 nm, and a tapping force between ~0.5-100 nN is used for indentation, depending on the probe tip and material beings studied. A neo-Hookean constitutive material relation is assigned to the soft matrix, and the modified-Hertz and JKR contact mechanic models are considered during analysis of the probe-particle interactions. In order to fully understand how the probe indenting on the particle affects measured AFM data, especially under different boundary conditions, several different scenarios are considered: the probe contacting the exact center of the particle; offsetting the probe contact; and vertical confinement, horizontal confinement, and both vertical and horizontal confinement. Data from AFM performed on hard carbon nanotube particles embedded in thermoset epoxy resin and hard polymer particles embedded in a soft polymer such as LDPE will be collected to supplement and verify FEA. Simulated force-displacement and stress field data are analyzed in order to extract nanoscale mechanical properties and identify the key impacts indentation on the hard particles has on collected AFM data.

Presenting Author: Tyler Norkus Arizona State University

Presenting Author Biography: Tyler Norkus is an undergraduate student at Arizona State University pursuing a degree in Mechanical Engineering. He is entering his senior year and will graduate in May 2024, with the intention to seek a master's degree after graduation. He is interested in nanocomposites and atomic force microscopy and focuses on how to characterize the mechanical properties of such composites.

Authors:

Tyler Norkus Arizona State University
Masoud Yekani Fard Arizona State University