Crosslinked Networks Filled with Gold Nanoparticles

I. E. DELL'ERBA, C.E. HOPPE AND R. J. J. WILLIAMS

Madrid

Conferencia; 6th International ECNP Conference on Nanostructured Polymers and Nanocomposites; 2010

An effective way to disperse metal nanoparticles without the risk of aggregation is to bond them covalently to a crosslinked network. In order to do this, nanoparticles must have reactive functionalities that can undergo a polymerization reaction.   In this work, we show the synthesis of gold nanoparticles functionalized with OH groups (we shall denote them as OH-NPs). These OH-NPs were then reacted with 3-isocyanate propyl triethoxysilane (IPTES) in order to obtain triethoxysilane-functionalized gold nanoparticles (Si-NPs). Finally, Si-NPs were coreacted with a high functionality alkoxysilane to obtain a crosslinked network containing gold nanoparticles.     Gold nanoparticles functionalized with OH groups (OH-NPs) were prepared following Brust-Schiffrin method[1]. HAuCl4 was transferred from an aqueous solution to a toluene solution using tetraoctylammonium bromide (TOAB) as a phase transfer agent. Then, 6-mercapto-1-hexanol (MCH) was added up to the desired S / Au relation. MCH acts as a mild reducing agent, yielding an Au(I)-S polymer[2] which is then reduced with a strong reductant like aqueous NaBH4 to give OH-NPs.   Si-NPs were obtained by reacting OH-NPs with IPTES. OH + NCO reaction was catalyzed by dibutyltin dilaureate (DBTDL 0,2 wt%) taking 1 h to attain complete conversion. OH-NPs and Si-NPs were characterized by FTIR and UV-visible spectrophotometries. The absence of a band in the 2550 cm-1 region (S-H stretching) shows that residual MCH was actually removed and sulfur atoms are joined to the gold core by covalent or ionic bonds. UV-visible absorption spectrum exhibits a weak surface plasmon resonance band centered at 520 nm, which indicates the formation of gold nanoclusters of diameters less than 2 nm.   High functionality alkoxysilane was obtained by reacting glycerine with IPTES in a molar relation Gly/IPTES = 3. Again, DBTDL 0,2 wt % was used as a catalyst taking 3 h to attain complete conversion. Si-NPs were added to this high functionality alkoxysilane and hydrolytic polycondensation was carried out at 50ºC with concentrated formic acid (HCOOH/Si=3) as a catalyst. As a result, a homogeneous network filled with gold nanoparticles was obtained, showing no signs of particle aggregation. NPs concentration can be varied from zero to high values. Crosslinked networks can be obtained as bulk materials or as thin films spread on glass or mica substrates. Many applications can be foreseen for these materials.