Young’s Modulus of Polycrystalline Titania Microspheres Determined by In Situ Nanoindentation and Finite Element Modeling

Peida Hao,Yanping Liu,Yuefei Zhang,Yuanming Du

doi:10.1155/2014/309827

Abstract

In situ nanoindentation was employed to probe the mechanical properties of individual polycrystalline titania (TiO2) microspheres. The force-displacement curves captured by a hybrid scanning electron microscope/scanning probe microscope (SEM/SPM) system were analyzed based on Hertz’s theory of contact mechanics. However, the deformation mechanisms of the nano/microspheres in the nanoindentation tests are not very clear. Finite element simulation was employed to investigate the deformation of spheres at the nanoscale under the pressure of an AFM tip. Then a revised method for the calculation of Young’s modulus of the microspheres was presented based on the deformation mechanisms of the spheres and Hertz’s theory. Meanwhile, a new force-displacement curve was reproduced by finite element simulation with the new calculation, and it was compared with the curve obtained by the nanoindentation experiment. The results of the comparison show that utilization of this revised model produces more accurate results. The calculated results showed that Young’s modulus of a polycrystalline TiO2microsphere was approximately 30% larger than that of the bulk counterpart.

Highlights

Nano/microspheres have wide application in supercapacitors, biosensors, drug delivery, and catalysts [1–3]
SEM observation reveals that the diameters of the TiO2 microspheres are in the range of 200 nm to 1.5 μm
The force-displacement curves produced by the hybrid scanning electron microscope/scanning probe microscope (SEM/SPM) system were the sum of the real penetration depth (h) and the compressive deformation (s) of the microspheres under pressure (Figure 1(b))

Summary

Introduction

Nano/microspheres have wide application in supercapacitors, biosensors, drug delivery, and catalysts [1–3]. Armini et al and Chen characterized the mechanical properties of microspheres for drug delivery and polymer microspheres using the nanoindentation method [5, 6]. In these tests, Hertz’s model for contact mechanics was used to characterize the mechanical properties of the nano/microspheres by measuring the forcedisplacement curves with an AFM cantilever tip. Hertz’s model for contact mechanics was used to characterize the mechanical properties of the nano/microspheres by measuring the forcedisplacement curves with an AFM cantilever tip These tests took the displacement of the tip as the penetration depth and neglected the compressive deformation of the spheres. Finite element modeling (FEM) was used to investigate the deformation mechanism of the microspheres in the nanoindentation tests

Experimental

Results and Discussion

Conclusion