(Nanowerk Spotlight) Creating materials that change color based on viewing angle represents a significant challenge at the intersection of art and science. Natural examples of this phenomenon, called iridescence, appear in butterfly wings, peacock feathers, and opals. Unlike traditional pigments that absorb specific wavelengths of light, these natural materials use microscopic structures to split light into different colors. This “structural color” approach creates pure, vibrant hues that don’t fade over time and require no potentially toxic pigments.
Despite these advantages, recreating natural iridescence in synthetic materials has proven extraordinarily difficult, especially at large scales. The challenge lies in creating and maintaining precise structures that are just hundreds of nanometers thick across surfaces many meters wide. Previous attempts using various nanomanufacturing techniques proved either too expensive or impossible to scale up.
A collaboration between Cornell University materials scientists and Korean-American artist Kimsooja has now yielded a practical solution to this challenge. The team developed a method for creating large-scale, durable iridescent coatings, demonstrated through a 46-foot-tall architectural installation titled A Needle Woman: Galaxy was a Memory, Earth is a Souvenir. Initially exhibited at Cornell under the auspices of the Cornell Council for the Arts, the installation now stands as part of the permanent collection at Yorkshire Sculpture Park in Wakefield, UK, where it has maintained its striking optical properties for over a decade.
A Needle Woman: Galaxy Was a Memory, Earth is a Souvenir (Kimsooja). Cornell Arts Quad. Steel installation (1.3 m diameter at base, ∼14 m height), window panels coated with iridescent self-assembled lamellar block copolymer film whose lamellar sheets were oriented vertically along the tower long axis. Today, this structure is part of the permanent museum collection at Yorkshire Sculpture Park in Wakefield, UK. (Image: Reprinted with permission by Wiley-VCH Verlag)
The breakthrough relies on custom-designed plastic molecules that automatically arrange themselves into regular patterns. These molecules consist of two different types of plastic chemically bonded together – polystyrene and poly(tert-butyl methacrylate). When properly designed, thousands of these dual-component molecules spontaneously stack into alternating layers, creating a natural grating that splits light into different colors.
The key innovation came in synthesizing these molecules at unprecedented sizes – about 1000 times longer than typical plastic molecules. At this scale, the self-assembled layers naturally form patterns around 300-400 nanometers in spacing, large enough to interact with visible light. The researchers then developed a precise coating method to apply these materials while maintaining their self-organized structure.
The scale-up process presented numerous challenges. Each production batch yielded only about 35-40 grams of usable material, with half the attempts failing due to the extreme sensitivity to air and water during synthesis. The installation required roughly 500 grams of material to coat all panels. The team developed a custom two-liter reactor equipped with specialized mixing equipment to increase production scale while maintaining precise control over reaction conditions.
Color consistency posed another challenge. Different batches of the polymer produced slightly different colors due to variations in molecular size. The researchers developed two solutions: blending multiple batches to achieve consistent colors and adding precise amounts of shorter polymer chains to fine-tune the optical properties.
Window panel design. a) Schematic illustration of the window panel design. The PET-StB-PET sandwich is laminated to the concave side of the curved PMMA window panel. b) Final window panel of the installation. (Image: Reprinted with permission by Wiley-VCH Verlag)
The team also solved the challenge of applying these coatings to curved surfaces through a specialized lamination technique. They first created the color-shifting layer on flat, flexible plastic sheets, then sandwiched it between protective layers before carefully adhering it to curved acrylic panels. This approach preserved the optical properties while protecting the coating from environmental damage.
The research opened new possibilities beyond architecture. The team successfully applied their coating technique to paper, creating iridescent origami artwork that maintains flexibility without cracking. They also developed a variant using different molecular components that could be converted into color-shifting ceramic materials, potentially enabling applications in harsh environments or high-temperature settings.
This work demonstrates how artistic vision can drive scientific innovation. The specific requirements of Kimsooja’s installation pushed the researchers to solve fundamental challenges in polymer synthesis and processing. The resulting techniques could enable new types of displays, security features, or artistic materials that manipulate light in previously impossible ways.
The successful decade-long performance of the installation at Yorkshire Sculpture Park proves that self-assembling molecules can create durable, practical materials for architectural applications. More broadly, this collaboration shows how bridging the gap between laboratory materials science and artistic practice can lead to innovations that serve both fields, creating new possibilities for incorporating complex optical effects into human-scale structures.
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