Photo-induced selforganized pattern formation in bio-synthesized nanomaterials

We have observed a dynamic self-organization of laser scattering from the biosynthesized nanofluids with silver and gold nanoparticles. Various procedures for nanofluid synthesis suitable for different applications are under constant investigation. In our present research the green biosynthesis process has been used for noble nanoparticles production. The aqueous solution of Magnolia Grandiflora leaves has been used as a reductant for silver and gold nanofluids.. We have applied the UV-visible spectroscopy method to control reaction process, fluorescent spectroscopy and nonlinear interferometric imaging experiments for characterization of nanofluids. From the number of laser-induced photothermal interferometric fringes it is possible to estimate the nonlinear refractive index coefficient changes. The kinetics observed in the pump-probe experiments with blue and red CW laser allowed us to estimate a timescale (similar to 1s) of photothermal lens formation and dissipation. Moreover, we have observed the very exciting and unusual phenomena of self-organization of the laser scattering reflected from the fluid's surface. The diverse regular diffraction patterns (hexagons, rolls, squares etc), resembling diffraction of X-rays on crystal structures, were self-organized in biosynthesized solutions of nanoparticles. From the angular size of the observed hexagonal diffraction patterns it was possible to estimate the diameter of diffracting nanoclusters as 18 microns for silver and gold nanofluids and 9 microns for the Magnolia broth. The kinetics of the hexagonal scattering shows a quasiperiodic pattern, with a period of about 12 seconds with the slow build-up and sharp disappearance of scattering.