Evgen Prokhorov
CINVESTAV-Unidad Querétaro. Querétaro, Libramiento Norponiente 2000, Queretaro, México. e-mail: prokhorov@cinvestav.mx
Citosan (CS) is a suitable matrix material for stabilization and homogeneous nanoparticles (NPs) dispersion in the polymer environment. Properties of nanocomposites essentially dependent on the high surface area of the NPs which in turn depend on the dimension and concentration of NPs. Different routes of synthesis of polymer-NPs composites have been proposed. The dimension of NPs can be obtained from TEM or SEM measurements but problem appears how to control NPs concentration. Additionally, one of the most important question of nanotechnology is how to compare properties of nanocomposites obtained using different methods of preparation (precursors, reducing agents, temperature, etc.) and how to find optimum concentration of NPs with the highest surface area in the composites? In this work chitosan (CS) based nanocomposites with high conductivity silver (AgNPs), gold (AuNPs), clay nanoparticles and multiwall carbon nanotubes have been investigated and relation between electrical properties and optimum concentration of NPs for application in biomedicine and sensors have been found. It was shown that the percolation threshold (obtained from impedance measurements) represents a critical concentration above which NPs agglomeration takes place such that the effective surface area of the nanocomposite decrease. Herein we report the successful production of chitosan based nanocomposites: a) CS-Ag films with antibacterial properties, b) CS-Au sensor for detection of Cu++, c) CS-nanoclay sensor for detection of NO3- and CS-carbon nanotubes for vapour sensing. For all these applications the best functional performance of nanocomposites has been observed when NPs concentration increases and approaches the percolation threshold. The obtained relationship between electrical percolation threshold and functional properties of polymer nanocomposites is of primary importance in the design of high-performance applications.
Keywords: chitosan, conductivity nanoparticles, percolation threshold.