Investigating Nanoscopic Structures on a Butterfly Wing To Explore Solvation and Coloration

Surface structures on the nanometer size scale can impart new and exciting properties to bulk materials. Nanoscopic structures on hydrophobic materials can result in superhydrophobicity and structural coloration. We present an interdisciplinary experiment that introduces undergraduate students to nanotechnology by manipulating the superhydrophobicity and structural coloration of blue Morpho butterfly wings. The use of detergents can change the surface of the wing from superhydrophobic to hydrophilic, while the use of common solvents can change the ambient index of refraction and shift coherently scattered light to longer wavelengths. Superhydrophobicity and alteration of the index of refraction are readily observable using Morpho menelaus and Morpho rhetenor butterflies: water beads up and rolls off untreated butterfly wings, while detergent-treated wings get wetted by water and change color from bright blue to green. This experiment is a fun and impactful introduction to fundamental physical principles involving solvation and properties of light that exposes students to materials science concepts that go beyond the solution-phase chemistry normally experienced in a general chemistry course.