Epoxy-silica/clay nanocomposite for silver-based antibacterial thin coatings: structure and ionic mobility

A novel material was developed using sol-gel chemistry and an environmental-friendly grafting process of clay nanoparticles. In a previous work of our group, highly compact coatings had been generated using silicon alkoxides, as tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS), with the incorporation of silver ions and synthetic smectite -type clay nanoparticles, demonstrating antibacterial behaviour against Escherichia coli cultures. By controlling the loading, the exfoliation and the grafting processes of the clay nanoparticles, it was possible to control the migration kinetics of silver ions from the coating matrix to the surface. Morphological and structural studies, through SEM-FIB, revealed the effect of clay nanoparticles leading to the development of a homogeneous structure in 2-μm thickness coatings. Grazing incidence small angle X-ray scattering (GISAXS) experiments demonstrated that silver is distributed in a strongly anisotropic arrangement when clay nanosheets are absent. The size of the silver particles developed on the surface is rather different from that of those developed in the bulk of the coating. Scattering patterns also revealed that the incorporation of clay nanosheets promotes the development of less anisotropic structures. Electrochemical impedance spectroscopy (EIS) measurements confirmed the integrity of the material and the applicability of a physical model with normal distribution of resistive and capacitive elements.