Look closely at Hokusai's The Great Wave off Kanagawa, one of Japan's most famous works of art, and the brilliant whites seem almost painted onto the scene. Yet the white foam of the waves, the snow covering Mount Fuji, and the clouds in the sky contain no white pigment at all. Their brightness comes from light scattering off the exposed fibers of the traditional washi paper.
This effect is known as structural whiteness. Rather than relying on a colored substance, it emerges from the way a material's microscopic structure interacts with light. The same basic phenomenon appears throughout nature.
Sea spray, clouds, and snow all look intensely white because their structures scatter visible light extremely efficiently. Similar effects can be found in plant tissues and even in the foamy protective nests made by some frogs. In many cases, these structures consist largely of air, yet they can produce striking whiteness without any pigment.
That natural strategy inspired an international team led by Professor Easan Sivaniah of Kyoto University's Institute for Integrated Cell-Material Sciences (iCeMS), working with researchers from Tokyo Metropolitan University and Donghua University. Their goal was to create a new foam-based materials platform that could address two major challenges facing commonly used materials. Alternatives to Titanium Dioxide and PFAS White packaging, films, and coatings often depend on titanium dioxide (TiO2), which provides both brightness and opacity.
However, safety concerns recently prompted the European Union to ban titanium dioxide as a food additive. Another widely used group of chemicals, known as PFAS, helps materials repel water and oil. These fluorinated substances are increasingly under scrutiny because they can persist in the environment and may pose environmental and health risks.
Those concerns have intensified efforts worldwide to find alternatives. The researchers approached both problems by focusing on physical structure rather than added chemicals. They engineered carefully controlled porous materials that imitate the way natural foams scatter light while also drawing inspiration from water-repellent surfaces found on leaves and flower petals.
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