I. Saito, R.J. Sheridan, D. French, S. Zauscher, L.C. Brinson
Duke University,
United States
Keywords: nanocomposite material, interphase, nanoindentation
Summary:
Atomic Force Microscopy (AFM) is a powerful technique for characterizing the local properties of multiphase materials, such as the interphase in nanocomposites, due to its high resolution and sensitivity. In particular, Fast Force Mapping (FFM) enables the nanoscale mapping of mechanical properties by accurately correcting the force-deformation relationship as the tip indents the material. However, indentation in nanocomposite materials introduces a challenge known as the "substrate effect," where the structural stress field of the rigid body distorts the apparent local modulus measurement. Using a systematically controlled artificial interphase and FEA simulation, we previously established a practical criterion: when the tip’s contact radius exceeds one-third of the interphase thickness, the substrate effect dominates and obscures the true interphase properties [1][2]. In this presentation, we investigated the interphase modulus of the Si/Polystyrene system across different geometries. To achieve this, we developed a “combinatorial” model composite that enables the characterization of local mechanical properties under varying topological confinement. By analyzing the modulus map with our established criterion, we found that topological confinement enhances the modulus compared to flat surfaces, with the effect scaling with the degree of confinement. Our findings offer deeper insights into the local mechanical behavior of heterogeneous materials. [1] Collinson, D. W.; Eaton, M. D.; Shull, K. R.; Brinson, L. C. Deconvolution of Stress Interaction Effects from Atomic Force Spectroscopy Data across Polymer−particle Interfaces. Macromolecules 2019, 52, 8940–8955. [2] Saito, I.; Sheridan, R. J.; Zauscher, S.; Brinson, L. C. Pushing AFM to the Boundaries: Interphase Mechanical Property Measurements near a Rigid Body. Macromolecules 2024, 58, 980–988.