Abstract
A clear ruby-colored gold hydrosol was obtained by a reduction of chloroauric acid solution with sodium citrate. In the presence of hydrophilic nonionic surfactants, such as polyoxyethylene hydrogenated castor oil (60 E. O.) (HC 60) or polyoxyethylene sorbitan monooleate (20 E. O.) (PO 20), the hydrosol showed high stability against the addition of electrolytes as well as freezing. This remarkable stability of the hydrosol can be ascribed to both the effect of the electrical repultion of negatively charged particles and the steric barriers of surfactants. A lotion and a cream colored with gold hydrosol containing HC 60 exhibited enough stability to withstand color change after three years of exposure to sunlight.
Subsequently, we succeeded in producing a reddish-purple silk powder by vigorously stirring a mixture of gold hydrosol and a silk fibroin solution. An electron microscopic observation indicated that ultrafine particles of gold were taken in and dispersed uniformly throughout the silk fibroin. The color of the silk powder showed high stability against heat and light, and did not bleed even in water nor various oils.
