Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 66: Nanotribology I
O 66.1: Vortrag
Donnerstag, 25. März 2010, 10:30–10:45, H36
Tuning mechanical properties of single silica capsules — •Doris Vollmer1, Lijuan Zhang1, Alfons van Blaaderen2, Robert Graf1, and Michael Kappl1 — 1Max Planck Institute for Polymer Research, Mainz, Germany — 2Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands
The shell’s mechanical properties determine their stability and flow behavior. We investigated the mechanical properties of single silica shells by force-distance spectroscopy. The spherical capsules of different diameters (800 nm and 1.9 µm) and shell thickness (15 nm thickness 70 nm) were immobilized on a silicon substrate.
We probed the elastic response of the hollow particles by applying a point load, successively increasing the load until the shell broke. In agreement with the predictions of shell theory the deformation increases linearly with applied force for small deformations. For thicknesses larger than 20 nm the Young modulus is independent of shell thickness. However, it depends on the thermal history of the sample. It increases from 10 GPa for unheated shells to close to that of fused silica (80 GPa) after heating the hollow particles to 1100 ∘C. Heating transforms the large number of silanol groups into Si-Si bonds. This transformation leads to a compaction of the shells, which is reflected in a reduction of the diameter of the hollow particle as well as its shell thickness. Amazingly, tempering at 1100 ∘C induces smoothing of shells although the particles still remain spherical as shown by atomic-force-microscopy and scanning-electron-microscopy.