Historical Examples of Nanomaterials

While interest in nanotechnology is fairly new, nanomaterials have always existed naturally. A sterling example of a molecular machine in nature is the ribo-some, which produces protein by arranging amino acids in a very specific manner. Certain materials that were highly prized by artisans in ancient and Medieval times were valuable due to the presence of nanomaterials in them, such as “Damascus steel,” which possessed incredible sharpness and strength because they contained carbon nanotubes and nanowires. Nanomaterials are distinguished from their parent material by the fact that at the nanoscale level, material takes on very different properties. As opposed to solid-state physics, in a nanoparticle, the vast majority of atoms lie near the boundaries, and the unique properties of nanostructured materials depend crucially on the departures from regular crystalline states and thus on imperfections, defects, impurities, and dislocations. Indeed, this was first suggested by the German scientist Herbert Gleiter when he proposed in 1981 that material properties will change dramatically when the proportion of atoms near a boundary increases from one in 108 to one in two. Thus, for example, the presence of nano-sized particles of gold in Roman glass gives it remarkable properties, depending on the amount of light falling on it. For industry, two specific characteristics of nanomaterials—flexibility in applications and distributed innovation-enable their application.

Nanomaterials can be traced back to the Mayan age (circa 1500 B.C.E. to 1000 CE.) in South America. Murals and pottery from this period have an incredible blue tint that is vivid and does not deteriorate with time, or on the application of chemical agents. This has been attributed to nanoscale-oxidized metallic impurities in the host clay that has been traced to a mine near Mérida in Yucatán, present day Mexico. The Mayan blue, in addition to the oxidized metals, is the result of a unique way of absorbing light that is influenced by the exact size, shape, and dispersion of the nanomaterials in the material. At the same time, the natural intercalation (inserting foreign atoms into the crystalline lattice of another material) of indigo molecules from local plants in the clay gives it strong anticorrosion properties. Such clay was highly prized by Mayan artists, who presumably did not know the reason behind the material's unique properties.

The same was true for the Romans who used nanomaterials, though they did not recognize it as such. The Lycurgus Cup, dating back to the late Roman Empire (4th and 5th century C.E.), and now in the British Museum, changes color remarkably. Normally green, it becomes red when a light is placed inside it—an amazing [Page 314]phenomenon that can be attributed to the Surface Plasmon phenomenon that occurs when waves of electrons move along the surface of metal particles as light falls upon them. This is achieved since the cup contains nano-sized particles of gold in the glass.

Medieval Europe also has remarkable examples of nanomaterials. The ruby red color of stained glass that lends glass windows in cathedrals in Europe its ethereal beauty, and the decorative glaze, known as luster, that is found in medieval pottery is also due to the presence of nanoparticles in the glass matrix. In fact, many stained glass artists in medieval periods treasured small vials of metallic compounds that were handed down from generation to generation, as for example, cobalt oxide from the mines of Bohemia (in the present day Czech Republic) that were added during the fusion process to achieve deep blue.

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