Bridged Silsesquioxane Films Modified with Gold Nanoparticles.

MARÍA L. GÓMEZ; CRISTINA E. HOPPE; ROBERTO J. J. WILLIAMS

Buenos Aires, Argentina

Simposio; 5TH INTERNATIONAL SYMPOSIUM ON METASTABLE, AMORPHOUS AND NANOSTRUCTURED MATERIALS; 2008

Bridged silsesquioxanes are a family of organic-inorganic hybrid polymers synthesized by the hydrolysis and polycondensation of monomers containing an organic bridging group covalently bonded to terminal trialkoxysilyl or trichlorosilyl groups.[1] Different kinds of organic structures with self assembly capabilities have been reported in literature to generate nanostructured bridged silsesquioxanes. Strong hydrogen bonds interactions produced a variety of self assembled structures.[2] Recent efforts toward controlling the physical and chemical properties of nanostructured materials through molecular level design have generated enormous interest in thin films comprised of organically encapsulated metal nanoparticles (Nps).[3] It has been shown that the optical and electronic properties of such films can be tuned by varying the size, shape and concentration of metal Nps.[4] In this work we prepared films of nanostructured silsesquioxanes by hydrolysis and polycondensation of a precursor formed by reaction between glycidoxypropyl (trimethoxysilane) and dodecylamine. The reaction mixture was modified with different amounts of dodecanethiol-coated gold Nps (mean average diameter = 2.0nm). The films were characterized by Uv-Vis spectroscopy, photoluminiscence, ATR, SEM, EDAX, TEM, etc. Figure 1 shows the Uv-Vis spectra of some of the modified films. The absorption band centred at 520nm is consistent with the presence of 2nm spherical gold Nps.[5] The properties of the matrix, such as their FTIR and photoluminescence spectra are not modified by the presence of the Nps. Although many of the incorporated Nps keep their individuality, as was corroborated by TEM, the formation of fractal aggregates at the air-solid interface was also evident. The influence of the evaporation rate on the size of the formed aggregates for films modified with 0.7wt% of gold Nps was investigated by transmission optical microscopy (TOM) and SEM. A clear decrease in the mean size of the structures was observed at lower evaporation rates. This effect could be useful as a tool for the design of new nanostructured composite films and coatings. References: [1] D. A. Loy, K. J. Shea, Chem. Rev. 95 (1995) 1431. [2] C. T. Kresge, M. E. Leonowiwicz, W. J. Roth, J. C. Vartulli, J. S. Beck, Nature 359 (1992) 510. [3] A. N. Shipway, E. Katz, I. Willner, Chem. Phys. Chem. 1 (2000) 18. [4] A. W. Snow, H. Wohltjen, Chem. Mater. 10 (1998) 947. [5] S. Link, M. A. El-Sayed, Int. Rev. Phys. Chem. 19 (2000) 409.