Silver doped sol-gel hybrid materials as biocide coatings on 316L stainless steel

SILVIA CERÉ; CLAUDIA STUDDERT; RAÚL A. PROCACCINI; SERGIO PELLICE

Praga

Congreso; 63rd Annual Meeting of the International Society of Electrochemistry; 2012

International Society of Electrochemistry

Development of new materials enriched with noble metal ions, such as silver, cobalt or copper, is of great interest in the field of commercial and medical products due to its action against fungus and bacteria. Although a large number of products are chemically active against microorganisms, they are usually limited to fabrics for medical bandages and sportswear in order to avoid, respectively, infections and odours. On the other hand, sol-gel technology becomes the preparation of hybrid materials possible with introduction of different components, as inorganic salts or organic additives within its structure bringing up the possibility to develop functional materials for different purposes. In this work, the development of an antibacterial coating for metallic substrates is presented. The coating consists in a hybrid organic-inorganic sol-gel material doped with silver. The relation between the structure of the hybrid matrix, aggregation state of silver ions, and biocide behaviour is analyzed as a function of the densifying thermal treatment. Sol-gel materials were synthesized through hydrolytic condensation, in acidic conditions, of tetraethoxysilane (TEOS) and methyl-triethoxysilane (MTES). Silica nanoparticles were added in order to give a mechanical reinforcement and silver nitrate as the supplier of Ag+ ions. Coatings were deposited on 316L stainless steel by the dip-coating process at a constant withdrawal rate and densified at 50, 150 and 450 ºC. UV-visible, Fourier transformed infrared (FTIR), X-ray photoelectron (XPS) and X-ray fluorescence (XRF) spectroscopy were used to analyze the silver aggregates and its influence on the structure of hybrid matrix. Biocide behaviour was determined as a function of the inhibitory halo on Escherichia-coli cultures in agar diffusion tests. Electrochemical impedance spectroscopy (EIS) measurements using a 0.35 % NaCl solution (wt/vol) were performed on coated samples with the different thermal treatments and silver contents in the range of 50 kHz to 10 mHz, using a AC voltage signal amplitude of ± 0.05 V rms around the corrosion potential. The results show that when densification change from 50 to 450°C the total impedance increases, indicating a denser structure enhancing the barrier effect. The total impedance for undoped coatings is greater than the corresponding to the doped ones, suggesting that the doping somehow increases the electrolyte penetration into the film.