The aim of the project NILstream is the production of patterns for viscous drag reduction by a roll-to-roll nanoimprinting (R2R-NIL) approach. This work will be directly supported by the development of nanostructures targeting on dirt-repellent and other customer-required additional functionalities â?? also fabricated by R2R-NIL. Drag effects of objects in air are a highly discussed, very central topic in various fields from civil transport to energy market. More precisely they cause performance losses, noise (planes, wind turbines), pollution and therefore extended costs.

A promising technique for achieving drag reduction is the implementation of surface riblets â?? small surface protrusions aligned to the direction of the flow - that create an anisotropic roughness on the surface [MAY08]. Riblets of very different geometries have been tested for different applications with varying results [BEC97].

However, these high-potential structures did â?? up to now - not find its way into market because of significant fabrication issues and the requirement of a detailed simulation and design of the pattern geometry adapted to a certain application (speed of object, motion dynamics). 

By now, nanoimprinting processes are well-developed in batch respectively wafer-level. The NILstream project goes one step further and innovatively suggests to use a roll-to-roll nanoimprinting approach based on UV- or thermal NIL for riblet structure fabrication. This will be done on a self-adhesive foil, selected with respect to customer-defined requirements concerning stability and mechanical issues. The structured foil will be sticked to several different end-user products and afterwards aerodynamically tested.

The industry partner Bionic Surface Technologies is interested in offering a complete solution to end-users, from pattern geometry simulation (which is their core competency) over optimization of the fabrication process to small series production (done at JOANNEUM RESEARCH). The project NILstream covers material evaluation (substrate foil and imprint resist), the development of a well-performing R2R imprinting process based on the chosen materials, simulation of riblet structures perfectly matching with product requirements, pattern fabrication by R2R NIL and drag reduction tests on end-user products.

The analysis of imprinted patterns concerning structure quality, layer properties before and after imprinting and pattern stability during test runs will be done by the Center for Electron Microscopy (ZFE). They have outstanding experience in FIB-cutting of polymeric substrates and SEM- and TEM-measurements of samples with nanometer resolution.


[MAY08] R. Garcia Mayoral, J. Jimenez, Physical mechanisms for turbulent drag reduction in riblet-like surfaces, European Drag Reduction and Flow Control Meeting 2008, Germany

[BEC97] D. W. Bechert, M. Bruse, W. Hage, J. G. T. Van der Hoeven, G. Hoppe, J. Fluid Mech. 338 (1997)