Chitosan/silver nanoparticles composite: Molecular relaxations investigation by dynamic mechanical analysis and impedance spectroscopy

Abstract

By impedance spectroscopy, Gonzalez‐Campos et al. J Polym Sci Part B: Polym Phys 2009, 47, 932–943, reported the first evidence of a glass transition in a polysaccharide. To gain a better understanding on the molecular relaxations in polysaccharides, we study composites of chitosan (CS)/silver nanoparticles (AgnP) films by dynamic mechanical analysis (DMA) and dielectric spectroscopy in the 2–250 °C temperature range. CS/AgnP films conductivity increases in two orders of magnitude in comparison with pristine CS. Three relaxation processes ascribed to the α‐relaxation, σ‐relaxation, and degradation process have been observed for the first time. Molecular dynamics and conductivity strongly depends on moisture content; since a plasticizing effect on the glass transition temperature is observed, similarly the increase in AgnP weight percent leads to a glass transition temperature decrease and also increases CS thermal stability. Infrared spectroscopy analysis reveals the AgnPs interaction with OH, NH2, CO.NH2, and COC groups implying an evident redistribution of the vibration bands for these groups. These new bonds affects the molecular dynamics of the CS chain bearing important changes in relaxations processes when compared CS/AgnP composite with pristine CS. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 739–748, 2010

Revisiting the thermal relaxations of poly(vinyl alcohol)

“…The direct‐current conductivity (σ dc ) behavior of the PVA films was analyzed by DS with the methodology that we described previously 29–31. Resistance ( R dc ) was obtained from the intersection of the semicircle and the real‐part axis on the impedance plane ( Z ″ = 0), as shown in the inset of Figure 1(a); hence, σ dc could be calculated by the following relationship: where d is the thickness and A is the area of the PVA film, respectively.…”

Chitosan/silver nanocomposites: Synergistic antibacterial action of silver nanoparticles and silver ions

“…Figure 7a shows the plots of the DC electrical conductivity obtained from impedance measurements as a function of the AgNP and Ag ions wt. % in dry films at room temperature [55]. At low concentration of AgNP and Ag + ions, a decreasing in CS/Ag + ion (silver acetate) composite films exhibited higher conductivity (approximately one order of magnitude) compared with CS/AgnP's composite films with the same Ag content ( Figure 7b).…”

“…Neat chitosan exhibits low ionic conductivity that can be related to the presence of small concentration of conductive species in the form of OH + and H + ions [55]. At ambient conditions, film's water content is ca.…”

“…The DC conductivity of the composites was obtained from the extrapolation of impedance measurements to zero frequency and by using the dimensions of each film [55]. Neat chitosan exhibits low ionic conductivity that can be related to the presence of small concentration of conductive species in the form of OH + and H + ions [55].…”

In Situ Generation of Silver Nanoparticles in Poly(Vinyl Alcohol)/Poly(Acrylic Acid) Polymer Membranes in the Absence of Reducing Agent and their Effect on Pervaporation of a Water/Acetic Acid Mixture

“…The intensity of the peak at 810 cm −1 , attributable to out‐of‐plane PAA OH vibration, marginally increased, and peak broadening due to silver nanoparticle addition was observed. This may be attributable to the interaction of silver nanoparticles with the PVA OH groups and the PAA COOH groups and the formation of hydrogen bonds . The increased intensity and broadening of peaks at 1390 and 1260 cm −1 was assigned to the symmetric and antisymmetric stretches of the COO − groups and it revealed that PAA molecules were adsorbed on the surface of silver nanoparticles through the bidentate band .…”