Relaxation Phenomena in Chitosan-Au Nanoparticle Thin Films.

Elodie Strupiechonski,Gabriel Luna-Barcenas,Dora I Medina,Marisa Moreno-Ríos,Erika O Ávila-Dávila,Diana G Zárate-Triviño,Evgeny Prokhorov,Ramón Román-Doval,Yuriy Kovalenko

doi:10.3390/polym13193214

Abstract

Chitosan–gold nanoparticle (CS/AuNP) thin films were synthesized through the chemical reduction of HAuCl4 in sodium citrate/chitosan solutions. The dielectric and dynamic mechanical behaviors of CS/AuNP films have been investigated as a function of moisture and HAuCl4 content. Two relaxation processes in the nanocomposites have been observed. The α-relaxation process is related to a glass transition in wet CS/AuNP films. However, in dry composites (with 0.2 wt% of moisture content), the glass transition vanished. A second relaxation process was observed from 70 °C to the onset of thermal degradation (160 °C) in wet films and from 33 °C to the onset of degradation in dry films. This relaxation is identified as the σ-relaxation and may be related to the local diffusion process of ions between high potential barriers in disordered systems. The α- and σ-relaxation processes are affected by the HAuCl4 content of the solutions from which films were obtained because of the interaction between CS, sodium succinate, and gold nanoparticles. With about 0.6 mM of HAuCl4, the conductivity of both wet and dry films sharply increased by six orders, corresponding to the percolation effect, which may be related to the appearance of a conductivity pathway between AuNPs, HAuCl4, and NaCl.

Highlights

Chitosan (CS) is a natural polymer derivate of chitin
The dielectric and dynamic mechanical behaviors of CS/AuNP films were investigated as a function of moisture and HAuCl4 content
We showed two relaxation processes in the nanocomposites

Summary

Introduction

Chitosan (CS) is a natural polymer derivate of chitin. Its structure comprises glucosamine and N-acetylglucosamine unit residues, and it exhibits properties such as biocompatibility, biodegradability, and low toxicity [1,2,3,4]. The proper combination of such properties allows for the formation of CS–metal nanoparticle bionanocomposites. Among CS-based nanocomposites, CS/gold nanoparticles (CS/AuNPs) are attractive biocomposites because of their great potential in biomedicine [5,6,7,8,9] and in different biosensor [10,11,12,13,14,15] for detecting protein [16], fetoprotein [17,18] and DNA glucose [16,19,20,21], etc. Several methods have been employed to fabricate Au nanoparticles in a wide variety of shapes and dimensions [22]. The most common methods, are based on the reduction of HAuCl4 with sodium citrate (SC) at high temperatures, as first introduced by Turkevitch [23]. The average particle diameter can be tuned over a wide range

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