X-ray tomography image of open cell polyurethane foam

If a gas is injected into a liquid it forms a cellular foam structure. When a thermoset prepolymer of low viscosity is foamed, the polymer can drain from the cell walls (driven by surface tension) before it sets at the cell edges, leaving an open-celled foam. The cell edges have three concave sides. The average co-ordination number for the nodes (where struts meet) is four, giving tetrahedral junctions. The deformation behaviour of the foam was observed by X-ray microtomography at the ESRF in Grenoble. X-ray tomography overcomes the limitations of MRI in terms of contrast, and those of confocal optical microscopy in terms of depth of field