Thursday, January 25, 2007

Wrinkly Silicone

The most recent Proceedings of the National Academy of Sciences (Vol. 104, No. 4, pp 1130-1133) has a free access article which is visually striking, although I was really disappointed in the analysis.  PDMS was exposed to a beam of Ga+ ions, which then forms a stiff upper layer (SiOx - a depletion of carbon is noted) atop the softer underlayer, with the upper layer forming a buckled surface at high enough Ga+ fluences.

Why?  The authors are silent on the subject.

Having a stiff layer of anything over a softer layer doesn't mandate buckling unless there is a difference in stress/strain that is allowed to relax.  I suspect that that is the ultimate cause here - residual stress from the manufacturing of the original PDMS.  This would be easy to verify qualitatively.

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