2 research outputs found

    Guiding Block Copolymers into Sequenced Patterns via Inverted Terrace Formation

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    Corrugated SiCN ceramic substrates fabricated by a facile replication process using nonlithographic PDMS masters were employed for the directed assembly of block copolymer microdomains. During thermal annealing of polystyrene-<i>b</i>-polybutadiene diblock copolymer, the material transport was guided by a wrinkled substrate to form regular modulations in the film thickness. As a consequence of the thickness-dependent morphological behavior of cylinder forming block copolymer, the film surface appears as sequenced patterns of alternative microphase-separated structures. The ordering process is attributed to the formation of inverted terraces which match the substrate topography, so that the resulting surface patterns are free from the surface relief structures within macroscopically large areas. The issues of the film thickness, the substrate surface energy, and the pattern geometry are addressed. Our approach demonstrates an effective synergism of external confinement and internal polymorphism of block copolymers toward complex hierarchically structured patterned surfaces

    Silicones for Stretchable and Durable Soft Devices: Beyond Sylgard-184

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    This paper identifies and characterizes silicone elastomers that are well-suited for fabricating highly stretchable and tear-resistant devices that require interfacial bonding by plasma or UV ozone treatment. The ability to bond two or more pieces of molded silicone is important for creating microfluidic channels, chambers for pneumatically driven soft robotics, and other soft and stretchable devices. Sylgard-184 is a popular silicone, particularly for microfluidic applications. However, its low elongation at break (∼100% strain) and moderate tear strength (∼3 N/mm) make it unsuitable for emerging, mechanically demanding applications of silicone. In contrast, commercial silicones, such as Dragon Skin, have excellent mechanical properties yet are difficult to plasma-bond, likely because of the presence of silicone oils that soften the network yet migrate to the surface and interfere with plasma bonding. We found that extracting silicone oligomers from these soft networks allows these materials to bond but only when the Shore hardness exceeds a value of 15 A. It is also possible to mix highly stretchable silicones (Dragon Skin and Ecoflex) with Sylgard-184 to create silicones with intermediate mechanical properties; interestingly, these blends also only bond when the hardness exceeds 15 A. Eight different Pt-cured silicones were also screened; again, only those with Shore hardness above 15 A plasma-bond. The most promising silicones from this study are Sylgard-186 and Elastosil-M4130 and M4630, which exhibit a large deformation (>200% elongation at break), high tear strength (>12 N/mm), and strong plasma bonding. To illustrate the utility of these silicones, we created stretchable electrodes by injecting a liquid metal into microchannels created using such silicones, which may find use in soft robotics, electronic skin, and stretchable energy storage devices