title: 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.
authors.affiliation: Institute of Materials Science and Technology (INTEMA), University of Mar del Plata , 7600 Mar del Plata, Argentina.
authors.forename: María L
authors.initials: ML
authors.lastname: Gómez
authors.forename: Cristina E
authors.initials: CE
authors.lastname: Hoppe
authors.forename: Ileana A
authors.initials: IA
authors.lastname: Zucchi
authors.forename: Roberto J J
authors.initials: RJ
authors.lastname: Williams
authors.forename: Marina I
authors.initials: MI
authors.lastname: Giannotti
authors.forename: M Arturo
authors.initials: MA
authors.lastname: López-Quintela
mesh_terms: D006046:Gold / Q000737:chemistry*; D008567:Membranes, Artificial; D053768:Metal Nanoparticles / Q000737:chemistry*; D015394:Molecular Structure; D010316:Particle Size; D012821:Silanes / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013499:Surface Properties
chemical_list: C403136:3-glycidoxypropyltrimethoxysilane; D008567:Membranes, Artificial; D012821:Silanes; D013438:Sulfhydryl Compounds; D006046:Gold