Most colored materials owe their color to the absorption of light: certain wavelengths are absorbed and others transmitted. This talk will present experiments and arguments based on scattering theory that shed some light on why red structural colors are difficult to make.
Most colored materials owe their color to the absorption of light: certain wavelengths are absorbed and others transmitted. The color arises from the remaining wavelengths that are reflected or scattered back to the observer. In nature we often see a different type of coloration, known as structural color, which comes from interference or diffraction of light and not absorption: certain wavelengths are transmitted, while others constructively interfere and are reflected. Structural colors are common in birds and particularly in blue feathers, which consist of disordered arrays of pores that scatter light. I will discuss efforts to make synthetic systems that mimic the bird feathers -- that is, systems that show structural colors that are indistinguishable from traditional, absorption-based colors, both in their saturation and their angle independence. The synthetic samples display rich blues and greens, but they do not display red colors. Interestingly, the same trend occurs in birds: there are no known red birds with angle-independent structural color. I will present experiments and arguments based on scattering theory that shed some light on why red structural colors are difficult to make.
Professor Vinothan N. Manoharan
Vinothan N. Manoharan is the Wagner Family Professor of Chemical Engineering and Professor of Physics at Harvard University. His research focuses on understanding how systems containing many particles suspended in a liquid -- such as nanoparticles, proteins, or cells -- organize themselves into ordered structures like crystals, viruses, and even living tissues. His lab uses optical microscopy and holography to watch these systems self-assemble in real time. The goal is to discover new, general physical principles that underlie complex systems and to apply these principles to practical problems in materials science, nanotechnology, and medicine. Manoharan received his Ph.D. from the University of California, Santa Barbara in 2004 and worked as a postdoctoral researcher at the University of Pennsylvania before arriving at Harvard in 2005.