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

Abstract

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 (2 mol) 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 body-centered cubic (bcc) crystals of about 20 nm diameter were formed in the first step, in which the 2 nm gold NPs kept their individuality (high-resolution transmission electron microscopy, field emission scanning electron microscopy, and small-angle X-ray diffraction). In the second step, bcc crystals aggregated, forming compact micrometer-sized spherical particles. Under particular evaporation rates a third step of the self-assembly process was observed where micrometer-sized 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.

Hybrid Films Based on a Bridged Silsesquioxane Doped with Goethite and Montmorillonite Nanoparticles as Sorbents of Wastewater Contaminants

“…Synthesis of Silsesquioxanes Films. The synthesis of the films based on SSO was reported before [13]. The precursor of SSO was synthesized employing stoichiometric amounts of DA and GPTMS (1 : 2).…”

“…For instance, it was possible to synthesize SSO films doped with safranin, in which the light energy collected by the matrix is efficiently transferred to the fluorescent dye [12]. It was also possible to synthesize new SSO films with pendant dodecyl chains able to disperse metallic nanoparticles [13,14], gold thiolates [15], and silver thiolates [16]. On the other hand, the incorporation of porphyrin or Re(I) complexes in these materials proved to be very effective in generating reactive oxygen species…”

Photophysical Behavior of Modified Xanthenic Dyes Embedded into Silsesquioxane Hybrid Films: Application in Photooxidation of Organic Molecules

“…Silsesquioxane films were obtained following the method reported by Gómez et al [12]. Figure 2(a) shows the film preparation procedure.…”

“…These materials are attractive for several reasons: they show intrinsic luminescence, are easy to synthesize, and have high chemical, mechanical, and thermal resistance [12][13][14][15]. Furthermore, because SSO are porous and/or mesoporous materials, they can be used for homogeneously dispersing within its matrix's diverse kinds of compounds producing materials with new properties for interesting applications [9,[14][15][16].…”

“…The synthesis of dye-doped silsesquioxane films was performed using a hydrolysis polycondensation method [12].…”