Contact instability of thin elastic films on patterned substrates

Abstract

The free surface of a soft elastic film becomes unstable and forms an isotropic labyrinth pattern when a rigid flat plate is brought into adhesive contact with the film. These patterns have a characteristic wavelength, lambda approximately 3H, where H is the film thickness. We show that these random structures can be ordered, modulated, and aligned by depositing the elastic film (cross-linked polydimethylsiloxane) on a patterned substrate and by bringing the free surface of the film in increasing adhesive contact with a flat stamp. Interestingly, the influence of the substrate "bleeds" through the film to its free surface. It becomes possible to generate complex two-dimensional ordered structures such as an array of femtoliter beakers even by using a simple one-dimensional stripe patterned substrate when the instability wavelength, lambda approximately 3H, nearly matches the substrate pattern periodicity. The free surface morphology is modulated in situ by merely varying the stamp-surface separation distance. The free surface structures originating from the elastic contact instability can also be made permanent by the UV-ozone induced oxidation and stiffening.

Contact Instability of a Soft Elastic Film Bonded to a Patterned Substrate

“…Since in the linear stability analysis we are looking at only the onset of instability, which occurs at a gap distance of few nanometers in the case of VDW interactions and even higher values (up to the micron range) in the case of a long-ranged electric field, this term is neglected. The range of the film thicknesses of importance considered in the experiments as well as in the simulation studies are generally of the order of few microns [11][12][13][14][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Hence, any destabilizing interactions of the film surface with the substrate are of little consequence and do not contribute to the interaction energy.…”

“…It may be anticipated that a new length scale depending on the substrate topography may arise because the total energy now becomes a function of the substrate pattern parameters. An experimental study of the contact instability on a periodic substrate [38] has focused on the conditions for the alignment of the instability pattern with the substrate pattern. The effect of substrate topography (amplitude and periodicity) was not investigated under a wide range of parameters.…”

Prefracture Instabilities Govern Generation of Self-Affine Surfaces in Tearing of Soft Viscoelastic Elastomeric Sheets

“…The elastomer and cross-linking agent were mixed in the ratio of 100:2 by weight in order to make 2% cross-linked elastomer. 21,22 The solution was prepared in a 25 mL clean glass beaker and degassed under vacuum in order to remove trapped air from the solution. The prepared solutions were cast between two clean glass plates (Figure 1a) with predetermined gap controlled by inserting spacers of known heights between the plates.…”

Large areain situfabrication of poly(pyrrole)-nanowires on flexible thermoplastic films using nanocontact printing

“…After curing, the nanopatterned PDMS stamps were affixed to a semi-automated microcontact printer. The nanopatterned PDMS stamps will produce a high quality printing of PPy-NWs and this technique has been used before within our group for nCP of thiols [56,57,58].…”

“…The nanopatterned PDMS stamps can produce a high quality printing of PPy-NWs and this technique has been used before within our group for nCP of thiols [41,42,43]. Consequently, we describe a simple process to fabricate PPy-NWs supported on thermoplastics films via nanocontact printing techniques combined with controlled catalytic polymerization (nCP-CCP).…”