Nanocomposites of polymers and metals or semiconductors: Historical background and optical properties

Feature Article: Upon transmission of visible light through composites comp rising of a transparent polymer matrix with embedded particles, the intensi ty loss by scattering is substantially reduced for particle diameters below 50-100 nm (nanoparticles, nanosized particles). As a consequence, related materials (nanocomposites) have found particular interest in optical studie s. The first part of this article deals with a historical survey on nanopar ticles and nanocomposites and the importance of small particle sizes on the ir optical properties. The second part focuses on results from our laborato ry concerning nanocomposites with extremely high or low refractive indices and dichroic nanocomposites and their application in bicolored liquid cryst al displays (LCD). The inorganic colloids required for these studies (lead sulfide, iron sulfides, gold and silver) were prepared in situ in presence of a polymer or isolated as redispersable metal colloids modified at the su rface with a self-assembled monolayer (SAM) of an alkanethiol. The nanocomp osites themselves were finally obtained by coprecipitation, spin coating, s olvent casting or melt extrusion, with poly(ethylene oxide), gelatin, poly( vinyl alcohol) and polyethylene as matrix polymers.