Luiz H. C. Mattoso

A simple method to estimate the oxidation state of polyanilines

Abstract The electrical conductivity and other properties of polyaniline (PANI) and its derivatives are highly dependent on its oxidation states. In order to obtain a simple method to determine the oxidation state, a systematic study was performed to investigate the interconversion between pernigraniline (PB) PANI form to emeraldine (EB) one, and from EB to leucoemeraldine (LEB), by ultraviolet/visible (UV/Vis) spectroscopy. UV/Vis spectra were carried out for different oxidation degrees of PANI/N-methyl-2-pyrrolidinone (NMP) solutions. The redox states interconversion was made in NMP solutions in ambient air and/or inert atmosphere. LEB base presents only one peak in the absorbance spectra, associated with the π–π* transition, while the other two forms, EB and PB, exhibit another peak of lower energy. This second peak, related to a molecular exciton in EB, has its maximum intensity diminished as the EB is reduced or oxidized. By plotting the relative intensity of these peaks vs. the oxidation degree, it was possible to identify, with a reasonable accuracy, the oxidation state of PANIs. This method was also applied to poly(o-methoxyaniline) (POMA).

Nanocellulose Reinforced Chitosan Composite Films as Affected by Nanofiller Loading and Plasticizer Content

UNLABELLED Chitosan is a biopolymer obtained by N-deacetylation of chitin, produced from shellfish waste, which may be employed to elaborate edible films or coatings to enhance shelf life of food products. This study was conducted to evaluate the effect of different concentrations of nanofiller (cellulose nanofibers, CNF) and plasticizer (glycerol) on tensile properties (tensile strength-TS, elongation at break-EB, and Youngs modulus-YM), water vapor permeability (WVP), and glass transition temperature (T(g)) of chitosan edible films, and to establish a formulation to optimize their properties. The experiment was conducted according to a central composite design, with 2 variables: CNF (0 to 20 g/100 g) and glycerol (0 to 30 g/100 g) concentrations in the film (on a dry basis), which was produced by the so-called casting technique. Most responses (except by EB) were favored by high CNF concentrations and low glycerol contents. The optimization was based on maximizing TS, YM, and T(g), and decreasing WVP, while maintaining a minimum acceptable EB of 10%. The optimum conditions were defined as: glycerol concentration, 18 g/100 g; and CNF concentration, 15 g/100 g. AFM imaging of films suggested good dispersion of the CNF and good CNF-matrix interactions, which explains the good performance of the nanocomposite films. PRACTICAL APPLICATION Chitosan is a biodegradable polymer which may be used to elaborate edible films or coatings to enhance shelf life of foods. This study demonstrates how cellulose nanofibers (CNF) can improve the mechanical and water vapor barrier properties of chitosan films. A nanocomposite film with 15% CNF and plasticized with 18% glycerol was comparable to some synthetic polymers in terms of strength and stiffness, but with poorer elongation and water vapor barrier, indicating that they can be used for applications that do not require high flexibility and/or water vapor barrier. The more important advantage of such films when compared to synthetic polymer films is their environmentally friendly properties.

Effect of fiber treatments on tensile and thermal properties of starch/ethylene vinyl alcohol copolymers/coir biocomposites.

Coir fibers received three treatments, namely washing with water, alkali treatment (mercerization) and bleaching. Treated fibers were incorporated in starch/ethylene vinyl alcohol copolymers (EVOH) blends. Mechanical and thermal properties of starch/EVOH/coir biocomposites were evaluated. Fiber morphology and the fiber/matrix interface were further characterized by scanning electron microscopy (SEM). All treatments produced surface modifications and improved the thermal stability of the fibers and consequently of the composites. The best results were obtained for mercerized fibers where the tensile strength was increased by about 53% as compared to the composites with untreated fibers, and about 33.3% as compared to the composites without fibers. The mercerization improved fiber-matrix adhesion, allowing an efficient stress transfer from the matrix to the fibers. The increased adhesion between fiber and matrix was also observed by SEM. Treatment with water also improved values of Youngs modulus which were increased by about 75% as compared to the blends without the fibers. Thus, starch/EVOH blends reinforced with the treated fibers exhibited superior properties than neat starch/EVOH.

Investigation of corrosion protection of steel by polyaniline films

In the present study potentiodynamic polarisation curves were obtained for carbon and stainless steel in contact with 3% sodium chloride aqueous solution saturated with air in order to evaluate the capacity of polyaniline in the emeraldine oxidation state to protect the surface against corrosion processes. A high stability of the PAni films was observed with a gain of the corrosion potential around 270 mV more positive in the substrate covered with PAni than in the case without it. Corrosion of steel could be prevented using the conducting polymers as a protective layer.

Controlled synthesis of high molecular weight polyaniline and poly(o-methoxyaniline)

The molecular weight of polyaniline can be substantially increased from that normally obtained (Mw ≈ 53 000) by the oxidative polymerization of aniline with ammonium peroxydisulfate at about 0 to 3 °C up to about 218 000 by the presence of selected dissolved neutral salts. A further increase up to Mw ≈ 385 000 can be obtained by carrying out the polymerization at about −40 °C. Similar results are obtained for the polymerization of o-methoxyaniline to yield a maximum Mw ≈ 221 000 at 0 to 3 °C and Mw ≈ 417 000 at about −40 °C. The results are consistent with a reduction in the rate of the initiation step in solution and an increase in the rate of the chain propagation step at the solid polymer/solution interface caused by Donnan equilibrium effects.

An artificial taste sensor based on conducting polymers.

Pure and composite nanostructured films of conducting polymers were used as individual sensing units constituting an electronic tongue. The use of extremely thin films for signal transduction via impedance spectroscopy measurements in the frequency range 10-1 MHz allows the detection of trace amounts of tastants and inorganic contaminants in liquid systems. In addition, the sensor could detect the suppression of sourness by sweetness displaying similarities with the biological system. Brands of several commercial beverages could be easily distinguished without complex analysis, including the discrimination of waters, tastants and wines.

Preparation of chitosan nanoparticles using methacrylic acid.

In this work the preparation of chitosan nanoparticle was investigated using methacrylic acid in different conditions and studied by particle size analyzer, zeta-potential, Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM). The particle size was dependent on the chitosan concentration used during the preparation method. Nanoparticles with sizes as small as 60 nm were achieved, that can be extremely important for several applications. The nanoparticles solution was also pH-sensitive, due to swelling and aggregation of the nanoparticles. The nanoparticles obtained presented a very homogeneous morphology showing a quite uniform particles size distribution and a rather spherical shape.

Electrochemical detection of Salmonella using gold nanoparticles.

A disposable immunosensor for Salmonella enterica subsp. enterica serovar Typhimurium LT2 (S) detection using a magneto-immunoassay and gold nanoparticles (AuNPs) as label for electrochemical detection is developed. The immunosensor is based on the use of a screen-printed carbon electrode (SPCE) that incorporates a permanent magnet underneath. Salmonella containing samples (i.e. skimmed milk) have been tested by using anti-Salmonella magnetic beads (MBs-pSAb) as capture phase and sandwiching afterwards with AuNPs modified antibodies (sSAb-AuNPs) detected using differential pulse voltammetry (DPV). A detection limit of 143 cells mL(-1) and a linear range from 10(3) to 10(6) cells mL(-1) of Salmonella was obtained, with a coefficient of variation of about 2.4%. Recoveries of the sensor by spiking skimmed milk with different quantities of Salmonella of about 83% and 94% for 1.5×10(3) and 1.5×10(5) cells mL(-1) were obtained, respectively. This AuNPs detection technology combined with magnetic field application reports a limit of detection lower than the conventional commercial method carried out for comparison purposes in skimmed milk samples.

Preparation and characterization of thermoplastic starch/zein blends

Blends of starch and zein plasticized with glycerol were prepared by melting processing in an intensive batch mixer connected to a torque rheometer at 160 °C. The resulting mixtures were compression molded and then characterized by scanning electron microscopy, differential scanning calorimetry, wide-angle X ray diffraction and water-absorption experiments. The blends were immiscible, showing two distinct phases of starch and zein. The water uptake at equilibrium and its diffusion coefficient were determined. The water uptake at equilibrium decreased with increasing zein content. The diffusion coefficient fell sharply on addition of 20% zein and remained constant as zein content was increased. No appreciable effect of zein on starch crystallization was observed by X ray diffraction. The use of zein in thermoplastic starch compositions causes a decrease in the water sensitivity of these materials and lower its melt viscosity during processing making zein a suitable and very promising component in TPS compositions.

Electrospun Polyamide 6/Poly(allylamine hydrochloride) Nanofibers Functionalized with Carbon Nanotubes for Electrochemical Detection of Dopamine

The use of nanomaterials as an electroactive medium has improved the performance of bio/chemical sensors, particularly when synergy is reached upon combining distinct materials. In this paper, we report on a novel architecture comprising electrospun polyamide 6/poly(allylamine hydrochloride) (PA6/PAH) nanofibers functionalized with multiwalled carbon nanotubes, used to detect the neurotransmitter dopamine (DA). Miscibility of PA6 and PAH was sufficient to form a single phase material, as indicated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), leading to nanofibers with no beads onto which the nanotubes could adsorb strongly. Differential pulse voltammetry was employed with indium tin oxide (ITO) electrodes coated with the functionalized nanofibers for the selective electrochemical detection of dopamine (DA), with no interference from uric acid (UA) and ascorbic acid (AA) that are normally present in biological fluids. The response was linear for a DA concentration range from 1 to 70 μmol L(-1), with detection limit of 0.15 μmol L(-1) (S/N = 3). The concepts behind the novel architecture to modify electrodes can be potentially harnessed in other electrochemical sensors and biosensors.