Suppressing interfacial instability with nanoparticles

Fabrication of flexible mirrors requires deposition of relatively rigid thin films on soft compliant substrates. Due to film instability induced by substrate compression beyond a critical strain, direct deposition of a rigid film on soft substrates often suffers from wrinkling. We report a novel technique to fabricate wrinkle free rigid thin films in polymer by suppressing such instabilities with a nm layer of “jamming” nanoparticles. The thickness of the jamming layer can be used to control the wrinkle periodicity and amplitude. For demonstration, we selected Poly(dimethylsiloxane) as the compliant substrate, poly(monochloro-p-xylylene) as jammer, and various metals (e.g., Cu, Al, Ti) as film. An atomic force microscopy reviews that as the jammer thickness increases, the wrinkle wavelength increases accordingly, and when the thickness exceeds a certain threshold, wrinkles are completely suppressed. Nanoindentation measurements show that the interfacial stiffness increases by two orders of magnitude as the jammer thickness increases. On-going experiments using various elastomeric hydrogels will examine the effect of bulk substrate properties on interfacial jamming by NPs and assess its applications in distrubted wall stress (shear/normal) sensor for near wall flow investigations.