Fracture-induced formation of parallel silicone strips
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Fracture-induced formation of parallel silicone strips Yangjun Cai and Bi-min Zhang Newbya) Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, Ohio 44325-3906 (Received 21 October 2009; accepted 4 January 2010)
This study reports the generation of periodic parallel silicone strips by simply peeling a silicone sheet, oxidized by UV/ozone, from its bonded substrate. This spontaneous formation of strips is initiated by a mixed mode of separation along the peeling direction and subsequent channeling of initiated cracks. The periodicity of the strips is tuned by the bending strain acting on the silicone sheet during peeling, and the regularity and the locus of failure are determined by the extent of oxidization. Spontaneous pattern formation is an attractive approach for developing simple and inexpensive alternatives for high-throughput patterning. Among various features, strip-like patterns are the most common for various fundamental studies, including confinement of polymer thin films,1 alignment of cells and micro-organisms,2 tuning wettability,3 and grating.4 The silicone-based strips on the solid substrates are even more attractive, since their topographically patterned substrates can be used for microelectronic devices,5 microfluidic channels,5 membrane microreactors,6 photo masks,7 and etching resists.5 One elegant technique for transferring silicone features onto a silicon oxide (SiOx) substrate is decal-transfer lithography (DTL)5 or its variations.7 However, this method still requires a prefabricated silicone stamp with features that rely on conventional photolithography during its fabrication process. Attempts have been made to produce parallel wrinkled strips on silicone surfaces by surface buckling.8 Transferring the wrinkles to a rigid support, however, might not be feasible due to the relatively small wrinkle height. Therefore, a nonlithographic method that allows spontaneous formation of silicone patterns on an SiOx substrate is more attractive. Recently, a simple and nonlithographic method was reported to spontaneously generate ordered strips by splitting a thin glassy polymer layer sandwiched between two rigid substrates.4,9 However, this method is not suitable for cross-linked elastomers (e.g., silicone). Here, we report a simple and novel approach for fabricating highly regular parallel strips of a silicone elastomer on an SiOx substrate by peeling a thin flat sheet of silicone with its oxidized surface chemically bonded to the substrate. The strips are spontaneously induced by fracture instabilities during a mix-mode of separation a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0106 J. Mater. Res., Vol. 25, No. 5, May 2010
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and subsequent channeling of initiated cracks. The processing conditions, specifically the bending strain and bonding strength, are controlled to achieve various periodic structures over a large area (i.e., centimeters). Figure 1(a) shows the pr
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