Colors without the use of pigments: what nature can teach us

In all the materials to be used for decorative applications, color is of strategic importance and requires the development of continuous innovative solutions. The problems of the raw materials that are commonly used to impart the colors are mainly related to their toxicity, their cost and the difficulty of compatibilization, while the request to obtain variations in the tonalities, to increase the brightness and achieve new color effects is continuosly increasing. A particularly intriguing strategy is to abandon the idea of "chemical" colors obtained from traditional sources (minerals, organic pigments) to move to a "physical" type of color given by replication in organic polymeric powders of nanostructures with properties of photonic crystal. It is in fact possible to develop new inert, emulsifiable and / or easily dispersible polymeric materials in formulations (coating, packaging, cosmetics, etc) capable of imparting color with hue, brilliance, brightness and innovative iridescence effects. These properties derive from a series of chemical-physical principles consolidated in the fields of photonics and optoelectronics, which are inspired by the natural colors present for example on the wings of some species of butterflies, on the elytra of some beetles or some flowers, and they can also be reproduced synthetically. The natural colors not due to pigments derive from the presence of nanostructures properly arranged on the surfaces, which produce interference effects in the interaction with sunlight, so that the color of the surface is often different depending on the angle of view, ie changing. These are surfaces with ordered repetitive structures of the order of hundreds of nanometers, which produce completely new colors and effects and also offer great advantages, not requiring the toxicological characteristics necessary for the development of new pigments.