Marne' Pierre¹, Jada Williams¹, Feng Gao², Weihua Wang^1,

During our study of the synthesis of metal nanoparticles via chemical reduction methods, we found that some colloidal solutions of silver nanoparticles displayed dichroic effect. The dichroic effect is a phenomenon where a material displays two different colors in transmitted light and reflected light. In this study, dichroic silver nanoparticles were obtained via a simple chemical reduction method under ambient conditions. Ascorbic acid was used as the reducing agent and trisodium citrate was used as the stabilizing agent. A colloidal solution of synthesized silver nanoparticles showed an opaque gray color in reflected light and a translucent pink color in transmitted light. Another colloidal solution prepared in the presence of copper (II) sulphate displayed a new combination of dichroic colors: opaque blue and translucent green. To understand the formation of dichroic effect, Transmission electron microscopy (TEM) and UV-Vis spectroscopy were used to characterize and study the silver nanoparticles in these colloids. TEM study showed that silver nanoparticles with different sizes and shapes were present in the solutions that displayed dichroic effect. By comparing the morphology of dichroic silver nanoparticles with that of the silver nanoparticles that exhibited no dichroic effect, we concluded that both the sizes and the shapes of nanoparticles play important roles in the formation of dichroic effect. The small particles are responsible for the absorbance of light, which results in the color in transmitted light. While large particles account for the scattering of light and lead to the color in reflected light. Different combinations of nanoparticles with different sizes and shapes lead to different colors for the dichroic effects

silver nanoparticles, dichroic effect, chemical reduction method, UV-Vis, TEM