Native and structurally modified gum arabic: exploring the effect of the gum's microstructure in obtaining electroactive nanoparticles.

Electroactive nanoparticles combining gum arabic (GA) and polyaniline (PANI) were prepared by chemical synthesis. The gum consists of highly branched anionic polysaccharides with some protein content. GA was structurally modified by Smith controlled degradation, in order to reduce its degree of branching (GAD), aiming the elucidation of the relationship between the structure and the properties of complex polysaccharides. The modification was studied by SEC, GC-MS, (13)C NMR and colorimetric methods. GAD has lower molecular mass, lower degree of branching and lower uronic acid content. Besides it is enriched in galactose and protein when compared with GA. The obtained composites (GA-PANI and GAD-PANI) were thoroughly characterized. Although the use of both polysaccharides (GA and GAD) produced highly stable electroactive nanoparticles, the best combination of properties was achieved for GA-PANI. The sample GAD was not able to prevent the occurrence of crosslinking between PANI chains, possibly due to its lower microstructural complexity which diminishes the occurrence of hydrogen bonds between the polymers.

The use of gum Arabic as "Green" stabilizer of poly(aniline) nanocomposites: a comprehensive study of spectroscopic, morphological and electrochemical properties.

Herein we show the synthesis and characterization of water dispersible composites formed by poly(aniline) and the natural polymer gum Arabic (GA), used as stabilizer. The materials were synthesized via a rapid and straightforward method and were fully characterized by different techniques such as UV-Vis, Raman, FTIR, TEM, SEM and cyclic voltammetry. TEM and SEM images revealed that the proportion of stabilizer highly influences the growth mechanism of the nanostructures. It was found spherical particles, elongated structures and large agglomerates at the lower, intermediate and at the higher GA amount, respectively. Accordingly to fluorescence spectra, different hydrophobic structures are formed depending on the GA amount in aqueous solutions, possibly acting as hosting sites for the PANI growth. In order to further study the PANI polymerization in the presence of GA, kinetics experiments were performed and showed that nucleation is the limiting step for the composite growth and a model is proposed. Spectroscopic experiments showed that the presence of GA affects the PANI conformation, avoiding the formation of phenazine structures which highly impairs the electroactivity of PANI. The material integrity is achieved by strong hydrogen bond interactions between PANI and GA as evidenced by the study of specific NH bands in FTIR and Raman analyses. The intensity of the hydrogen bonds decreased upon higher amounts of GA, probably due to steric impediment around the NH sites. Cyclic voltammograms showed a good electroactivity behavior of the modified electrodes presenting distinguishable diffusional processes through the adsorbed composites. By this way, we have thoroughly investigated the formation and properties of new conducting polymer composite materials. Taken into account the low toxicity of GA and the excellent dispersity in water, the materials can successfully be applied in bioelectrochemical applications or as green corrosion inhibitors.