Gold fractal structures spontaneously grown in sheared lamellar phase

In this paper, we report the effect of membrane composition and time on the morphology of gold nanoparticles grown in sheared lamellar phases from a 10(-3) M KAuCl4 solution, using monoolein as the chemical reductant. Fractal, dendritic gold structures are synthesized when octadecylamine (ODA) is inserted in phosphatidylcholine (PC) or PC - monooleine bilayers, while without ODA, gold sphere-like particles are synthesized. Each morphology ( dendrite or sphere-like particles) is macroscopically revealed by sample color. Time favors the growth of fractals at the expense of spherical particles as shown by a statistical analysis performed on 5 day-old and 21 day-old samples. Fractal structures disturb the lamellar arrangement as evidenced by small angle X-ray diffraction experiments, so that no multilamellar vesicles, usually resulting from dilution of the sheared lamellar phase, can be obtained as imaged by cryo-TEM analysis. Possible reasons for the formation of fractal structures are given.