Depth-sensing indentation was applied to three-dimensionally ordered silica foams of two different pore diameters - 500 nm and 850 nm - formed by colloidal crystal templating. The contact responses of indentations with Berkovich and hemispherical indentation tips are presented over a load range of 1 mN to 100 mN. Scanning electron microscopy images of residual indentation impressions showed homogeneous deformation for small loads in which the peak displacement was shallow relative to the film-substrate interface. The characteristics of the load-displacement responses changed from periodic discontinuities, associated with cell wall fracture and pore collapse, to smooth and increased stiffness, as a result of densification due to the accumulation of material under the indentation tip and proximity (and contact) of the substrate. Load-displacement responses were translated into pressure-volume space, in which the average pressure during indentation is a measure of the crushing pressure of the cell walls.
Bibliographical noteFunding Information:
The authors thank Hongwei Yan for film synthesis. This work was sponsored by the Industrial Partnership for Research in Interfacial and Materials Engineering (IPrime), www.iprime.umn.edu.