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Polymer film embossed with microfeatures can reduce drag, enhance sealing between unlike materials, control wettability, increase antibiofouling, or provide faux surface texturing. Engineers at Battelle, Columbus, Ohio, have used their knowledge of materials science, chemistry, physics, and polymer processing to develop a patterntransfer technique used to fabricate specialized microfeatured polymeric film in a fast and costeffective manner.
The first step is to create a master pattern of the microfeatures of interest. These features are highly specialized for each application, but typically consist of precisely spaced square or cylindrical wells and pegs, or raised and indented rows or grids, one to several hundred micrometers in size. One example where this technology could be used is in diagnostic biomedical devices to increase reagent flow in microchannels, without introducing potential biocontaminates that can affect test results. The microfeature master patterns can be created using standard lithography techniques on silicon wafers, machining metals using single-pointdiamond turning, or using products from nature. Next, a silicone negative is cast of the micropattern. Battelle can cast multiple negatives and tile them next to each other to create large repeating patterns.
Once tiling is complete, the entire pattern is transferred to another polymeric material, generating a positive micropattern. The micropattern gets electroplated with nickel, creating a durable and flexible nickel “shim.” The shim is wrapped around a roll on an embossing stack. A polymer film or polymer extrusion melt is fed into the embossing nip (where the two embossing rollers come into contact with the polymeric material) and heat and pressure are applied. This transfers the micropattern to the polymer substrate.
It’s feasible to run the embossing process — a type of highspeed, roll-to-roll nanoimprint lithography (R2RNIL) — to create high volumes of polymeric microfeatures. On the lab scale, Battelle has processed a 1-ft-wide polymer web with microfeatures at a line speed on the order of single feet per minute. As the process is scaled-up through the pilot scale to production, the polymer web will be widened and the line speeds will be increased to increase production rates. Battelle has also shown that microfeatures can be formed on high-melt-temperature polymers such as Ultem. Materials like Ultem can be used in harsh environments such as aerospace.
Battelle has demonstrated R2RNIL, on the lab scale, to impart hydrophobicity to tens of square feet of polymer film. Hydrophobic microfeatures were formed on silicon wafers by photolithography then transferred through the process to emboss polymer film with the same microfeatures. The patterns increase the water-contact angle, causing water to bead up on the surface, rather than wet out.
Battelle technologists also fabricated a prototype Fresnel lens that concentrates the sun’s rays. The lens can focus sunlight on a tree branch, making it smoking hot in less than a second.