Determination of stamp deformation during imprinting on semi-spherical surfaces

We developed a process for double curved injection molding inserts presenting nanostructuredsurfaces. Line gratings with a line width and spacing of 500 nm as well as arrays of pillars,both up to an aspect ratio of unity, have been successfully transferred onto steel mold surfaces. A thin film of sol-gel was applied onto spherical injection mold inserts and subsequently imprinted using a flexible stamp. A hard curing step transformed the sol-gel into a quartz-like and durable material.
As an example, we present theory and results regarding the imprint of pillar nanostructures on semi-spherical mold surfaces. Imprints were realized on three different radii of circumferenceof the spherical mold: R = 0.5 mm, R = 1.0 mm, and R = 2 mm. After hard-curing of theimprinted sol-gel, the inserts were used for cold-mold as well as vario-therm injection molding.The polymer replicas and the inserts were characterized by analyzing the center-to-centerdistance of the pillars at several points across the spheres. From the measurements and the observed deviation of the distance of pillars, the stamp deformation was calculated. Finally, the experimentally determined deformation of the flexible stamp was compared with predictions provided by a geometrical model [1]. Simulated and experimental observations were in good accordance.
Future work will include the application of current results to design nanostructured patterns forwhich the stamp deformation will be compensated to achieve more reliable surface characteristics.