SNM: Physical Nano-Engineering Approaches to Surface Coloration and their Industrial Scale Implementation in Anodized Aluminum

Brown University, Providence RI

Investigators

Abstract

Currently the color of aluminum surfaces is achieved via dye- and pigment-based coating methods that have limited functionality, are vulnerable to scratching, and subject to color degradation when exposed to ultra-violet, heat, and the elements. This award supports fundamental research to investigate a novel method based on physical rather than chemical processes that will expand the range of color, function, and therefore, application of surface treatment. Chemical coloration methods rely on mostly absorption of light by dyes and pigments deposited on the surface, whereas physical coloration creates color by controlling the interaction of light with nano-engineered surfaces, coatings, and materials. The researched "color-by-design" method draws inspiration from brilliant examples of bio-physical color found in nature, such as peacock tail feathers, butterfly wings, and the iridescent scales of a jewel beetle. Anodized aluminum is a commonly used material in many industries, including automotive, aerospace, and consumer products. The reseached physical coloration method, which will enhance the appearance, durability, scalability, and functionality of anodized aluminum, has the potential to be broadly applied across many areas of manufacturing. Efforts will be made to involve under-represented groups in the research, train students at various levels and include the research results in curricula and outreach. The impact on device technology is expected to be significant. The goal of the research project is to develop an industry-scalable method for the physical, rather than chemical coloration of aluminum surfaces. The resultant colors will have higher hue, saturation, and brightness values, as well as improved functionality, ease of maintenance, and resistance to the elements. The method will control optical properties, interference and diffraction in materials at the nano- and micro-scales. Key physical phenomena to be investigated and utilized include local electronic processes and quantized plasmonic resonances in metal nanoparticles, long-range optical diffraction in periodic, or random and quasi-periodic nano-patterned dielectrics, as well as wave-phase modulations in ultra-thin (less than 10 nm) absorbing layers. These processes will be implemented via inherently scalable manufacturing techniques, including sputtering thin-film deposition, spray and dip coating, electrochemical baths, electroless deposition, and nano-stamping. The combination of these approaches is expected to expand the colors and finishes currently available in industry catalogs, enable the control of opacity, luster, brightness, and iridescence via purely physical means, and yield actionable and test-backed approaches for transitioning physical coloration techniques to a manufacturing setting.