a1 Department of Materials Science & Engineering, Stanford University, Stanford, California 94305
a2 Tsukuba Research Laboratory, JSR Corporation, Tsukuba, Ibaraki 305-0851, Japan
a3 Department of Materials Science & Engineering, Stanford University, Stanford, California 94305
The fracture of nanoporous methylsilsesquioxane thin-film glasses in moist air and aqueous solutions was investigated. We demonstrate the effects of controlled volume fractions of nanometer sized pores on the films resistance to fracture. Subcritical cracking accelerated by the presence of moisture, controlled pH, and hydrogen peroxide solutions is reported. Surprising changes in the near threshold growth rate behavior were observed for buffered solutions. We demonstrate that these changes are related to the unexpected diffusion of the aqueous solutions into the highly hydrophobic films. The presence of the solution changes the surface stress of the internal pore surfaces, which changes the stress state of the film. The change in film stress surrounding the crack alters the crack driving force and has profound effects on the resulting crack-growth threshold behavior.
(Received August 01 2005)
(Accepted December 16 2005)
(Online publication April 2006)
p1 Present address: Exponent Failure Analysis Associates, Menlo Park, CA, 94025