Hierarchical Assemblies of Gold Nanoparticles at the Surface of a Film Formed by a Bridged Silsesquioxane Containing Pendant Dodecyl Chains

M. L. GÓMEZ; C. E. HOPPE; I. A. ZUCCHI; R. J. J. WILLIAMS; M.I. GIANNOTTI; M. A. LÓPEZ-QUINTELA

LANGMUIR

American Chemical Society

Año: 2009 vol. 25 p. 1210 - 1217

0743-7463

Hierarchical aggregates of gold nanoparticles (NPs) on different length scales were in situ generated at the surface of a bridged silsesquioxane during the process of film formation by polycondensation and solvent evaporation. A precursor of a bridged silsesquioxane based on the reaction product of glycidoxypropyl(trimethoxysilane) (GPMS) (2 moles) with dodecylamine (1 mol) was hydrolytically condensed in a THF solution at room temperature, in the presence of formic acid, water, and variable amounts of dodecanethiol-stabilized gold NPs (average diameter of 2 nm). The initial compatibility of the precursor with gold NPs was achieved by the presence of dodecyl chains in both components. Phase separation of gold NPs accompanied by partitioning to the air-polymer interface took place driven by the polycondensation reaction and solvent evaporation. A hierarchical organization of gold NPs in the structures generated at the air-polymer interface was observed. Small bcc crystals of about 20-nm diameter were formed in a first step, in which the 2-nm gold NPs kept their individuality (HRTEM, FESEM and small-angle XRD). In a second step, bcc crystals aggregated forming compact micron-size spherical particles. Under particular evaporation rates a third step of the self-assembly process was observed where micron-size particles formed fractal structures. Increasing the initial concentration of gold NPs in the formulation led to more compact fractal structures in agreement with theoretical simulations. The surface percolation of NPs in fractal structures can be the basis of useful applications