Collaborative Research: Template-Free Manufacturing of Regular Microstructures by Ribbing-Enhanced Roll Coating

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A technology that can reduce the friction or drag on ship hulls would have a substantial economic and environmental impact by improving fuel efficiency. Microstructured superhydrophobic surfaces may retain air pockets that can act as gas lubrication between the water and the ship hull. Although the superhydrophobic surfaces have been studied for nearly two decades, it is only recently that periodic linear-trench structures have been shown to be effective for marine crafts traveling in open water, which represents sea, oceans, and lakes. The manufacturing of such well-defined micro-trenches has relied on silicon-based microfabrication based on semiconductor manufacturing approaches. These silicon processes are prohibitively expensive and not scalable for large surface areas, such as ship hulls. To address these challenges, a team from North Carolina State University and University of California at Los Angeles would like to utilize roll coating methodology, which is well known for cost-effective and large-scale production, to form the periodic microstructures on large substrates. This new process is researched to develop friction-reduction coatings for ship hulls and study their physical and chemical durability. Hence, outcomes from this research will benefit a wide array of marine applications, including commercial and military ships, which play a significant role in the national and global economies and security applications. This project is investigates the spontaneous pattern generation by ribbing on polymer surfaces during roll coating in an ordered manner using a fundamentally new approach to manufacture three-dimensional micro and nano-scale structures on a large-area substrate. The objectives are to establish the scientific foundation to control the microstructures formed during the roll coating, and to fabricate and validate the drag reduction efficiency of the surfaces in realistic flow conditions of open water and Reynolds number greater than 1 million. The research team will utilize computational modeling to predict the deformation behavior of the viscoelastic polymer verified by the experimental observations. For the proof-of-concept of drag reduction in realistic flows, a microstructured film and a smooth film will be layered on the bottom of a motorboat specifically outfitted to reliably compare the fluid shear stresses on the two. This project will educate the next generation of engineers and scientists through multidisciplinary research involving manufacturing, materials science, computational modeling, and fluid mechanics. The research outcome will be also used to educate K-12, undergraduate, as well as graduate-level students through various formats such as outreach activities and innovative curricular efforts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.