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The use of gold nanoparticles combined with other organic and inorganic materials for designing nanostructured films has demonstrated their versatility for various applications, including optoelectronic devices and chemical sensors. In this study, we reported the synthesis and characterization of gold nanoparticles stabilized with poly(allylamine hydrochloride) (Au@PAH NPs), as well as the capability of this material to form multilayer Layer-by-Layer (LbL) nanostructured films with metal tetrasulfonated phthalocyanines (MTsPc). Film growth was monitored by UV-Vis absorption spectroscopy, atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). Once LbL films have been applied as active layers in chemical sensors, Au@PAH/MTsPc and PAH/MTsPc LbL films were used in an electronic tongue system for milk analysis regarding fat content. The capacitance data were treated using Principal Component Analysis (PCA), revealing the role played by the gold nanoparticles on the LbL films electrical properties, enabling this kind of system to be used for analyzing complex matrices such as milk without any prior pretreatment.

This work aims to evaluate the effect of inclusion of different contents of candeia (Eremanthus erythropappus) essential oil (whose alpha-bisabolol is the main terpene) on the properties of polylactic acid (PLA) nanostructured mats and their relationship with fiber morphology and structure. The interaction occurring between the PLA and the candeia essential oil was confirmed by thermal and microscopy analysis. Addition of candeia essential oil increased nanofiber diameter and decreased the glass transition and melting temperatures of the nanofibers, suggesting lower energy input for processing. Scanning electron microscopy (SEM) images provided evidence of a homogeneous structure for the nanostructured mats. X-ray diffraction did not show differences in the crystallization of the nanofibers. This ongoing research confirms the possibility of incorporation of candeia essential oil in the production of nanofibers that will be studied for multipurpose applications.

The real (e′) and imaginary (e″) components of the complex permittivity of blends of PVDF [poly(vinylidene fluoride)] with POMA [poly(o-methoxyaniline)] doped with toluenosulfonic acid (TSA) containing 1, 2.5, and 5 wt % POMA–TSA were determined in the frequency interval between 102 and 3 × 106 Hz and in the temperature range from −120 up to 120°C. It was observed that the values of e′ and e″ had a greater increase with the POMA–TSA content and with a temperature in the region of frequencies below 10 kHz. This effect decreased with frequency and it was attributed to interfacial polarization. This polarization was caused by the blend heterogeneity, formed by conductive POMA–TSA agglomerates dispersed in an insulating matrix of PVDF. The equation of Maxwell–Garnett, modified by Cohen, was used to evaluate the permittivity and conductivity behavior of POMA–TSA in the blends. A strong decrease was observed in POMA–TSA conductivity in the blend, which was bigger the lower the POMA–TSA content in the blend. This decrease could have been caused either by the POMA dedoping during the blend preparation process or by its dispersion into the insulating matrix. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 752–758, 2003

The environmental degradation behaviour on the physical and mechanical properties of short sisal/PP composites has been studied with special reference to the influence of ageing conditions like treatment with water and UV radiation. The dependence of water uptake on the sorption characteristics of sisal/PP composites was evaluated by immersion in distilled water with respect to fibre loading, temperature and chemical treatment. It is found that water uptake increases with increase of fibre loading due to the increase in cellulose content. The raise of temperature up to 70 °C is accompanied by an increase of the rate and extent of sorption. Chemical treatments such as urethane derivative of PPG, PMPPIC and MAPP were given to sisal fibre. All chemically modified fibre composites showed lower uptake than the unmodified composites. This is because all chemical treatments given to sisal fibre reduce its hydrophilicity thereby favouring strong interfacial adhesion between the fibre and PP matrix. The influence of water uptake on the tensile properties of sisal/PP composites was studied. Tensile properties decreased with water uptake, time of immersion and fibre loading. The behaviour was strongly dependent on the chemical treatment and fibre orientation. The influence of the tensile properties of sisal/PP composites exposed to UV radiation was studied. The tensile properties were found to decrease with increase in the time of exposure to UV radiation. The reduction in properties is due to chain scission and degradation occurring to PP molecules as a result of photooxidation promoted by ultraviolet radiation. As a result of UV irradiation, surface cracks can be seen on neat PP and PP composites which can be evidenced from SEM photos. The retention of tensile properties increased with increase of fibre loading.

Chopped sisal fibers and finely powdered high-density polyethylene were surface functionalized using dichlorosilane (DS) under radio frequency (RF)-plasma conditions and characterized by electron spectroscopy for chemical analysis (ESCA) and fluorescence labeling techniques. A high-capacity (10 L), rotating, 13.56 MHz, electrodeless plasma installation, specially designed to allow the uniform surface modification of powdery and particulate matter of irregular shape, was used. A three-factor fractional experimental design was employed to evaluate the effect of RF-power, pressure, and reaction time on the ESCA-based relative atomic composition of plasma-treated samples. It was demonstrated that SiHxCly functionalities are present on plasma-exposed surfaces and these functionalization reactions can be controlled by selecting proper plasma parameters. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2145–2154, 2002

The latex and natural rubber from rubber trees [Hevea brasiliensis (Willd. exAdr. de Juss.) Muell. Arg.] from clones (RRIM 600, IAN 873, GT 1 and PB 252) recommended to the state of São Paulo, Brazil, were studied in three different tapping systems. The parameters studied were dry rubber content (DRC), percentages of ash and of nitrogen, Wallace Plasticity (P0) and Mooney Viscosity (VR). The rubber properties vary considerably as a function of clone type, tapping method and season of the year. DRC tends to decrease in the beginning of the dry, cold season (May and June), whereas both nitrogen % and ash % increase in the same period. A good linear correlation was obtained for P0 and VR. The highest P0 and VR were obtained for RRIM 600.

The interaction of poly( o -ethoxyaniline) (POEA) doped with HCl and sulfonated lignin (SL) was investigated using UV–Vis spectroscopy in order to probe the influence of pH and quantity of SL on the formation of a polyelectrolyte complex. The introduction of SL into the HCl doped POEA solution screens the positive charges of the protonated POEA allowing further protons to be pumped into the conducting polymers thus increasing its doping level. In addition, the strong interaction between these two electrolytes caused POEA to remain doped within a wide pH range. Layers were built from aqueous solutions of the complex formed by POEA and SL which were alternated with either pure POEA or sulfonated polystyrene in the form of layer-by-layer films. The resulting multilayer films remained doped even at pH 9.0, due to the strong complex formation, which prevents POEA from deprotonating. Surface potential measurements showed that the potential for the POEA+SL complex is more positive than for films with each layer investigated separately, thus confirming the strong interaction between POEA and SL.

The fabrication of nanostructured films with tailored properties is essential for many applications, particularly with materials such as polyaniline (PANI) whose electrical characteristics may be easily tuned. In this study we report the one-step synthesis of AgCl–PANI nanocomposites that could form layer-by-layer (LbL) films with poly(sodium 4-styrenesulfonate) (PSS) and be used for electronic tongues (e-tongues). The first AgCl–PANI layer was adsorbed on a quartz substrate according to a nucleation-and-growth mechanism explained using the Johnson–Mehl–Avrami (JMA) model, revealing a 3D film growth confirmed by atomic force microscopy (AFM) measurements for the AgCl–PANI/PSS LbL films. In contrast to conventional PANI-containing films, the AgCl–PANI/PSS LbL films deposited on interdigitated electrodes exhibited electrical resistance that was practically unaffected by changes in pH from 4 to 9, and therefore these films can be used in e-tongues for both acidic and basic media. With a sensor array made of AgCl–PANI/PSS LbL films with different numbers of bilayers, we demonstrated the suitability of the AgCl–PANI nanocomposite for an e-tongue capable of clearly discriminating the basic tastes from salt, acid and umami solutions. Significantly, the hybrid AgCl–PANI nanocomposite is promising for any application in which PANI de-doping at high pH is to be avoided.

In this study poly(lactic acid) (PLA) and polyvinylpyrrolidone (PVP) micro- and nanofiber mats loaded with Copaiba (Copaifera sp.) oil were produced by solution blow spinning (SBS). The Copaiba (Copaifera sp.) oil was characterized by gas chromatography (GC). Neat PLA and four PLA/PVP blends containing 20% (wt.%) oil were spun and characterized by scanning electron microscopy (SEM) and by studying the surface contact angle, in vitro release rate, and antimicrobial activity. All compositions evaluated were able to produce continuous and smooth fibers by SBS. The addition of PVP increased fiber diameter, and decreased the surface contact angle. GC analysis demonstrated that the main component of the Copaiba oil was β-caryophyllene, a known antimicrobial agent. In vitro release tests of Copaiba oil volatiles demonstrated a higher release rate in fibers containing PVP. Fiber mats made from blends containing higher amounts of PVP had greater antimicrobial action against Staphylococcus aureus. The results confirm the potential of the fiber mats for use in controlled drug release and could lead to promising applications in the biomedical field.

In this study, silver nanoparticles were prepared and incorporated into carboxymethylcellulose films to evaluate the antimicrobial activity for food packaging applications. The techniques carried out for material characterization were: infrared spectroscopy and thermal analysis for the silver nanoparticles and films, as well as particle size distribution for the nanoparticles and water vapor permeability for the films. The antimicrobial activity of silver nanoparticles prepared by casting method was investigated. The minimum inhibitory concentration (MIC) value of the silver nanoparticles to test Gram-positive (Enterococcus faecalis) and Gram-negative (Escherichia coli) microorganisms was carried out by the serial dilution technique, tested in triplicate to confirm the concentration used. The results were developed using the Mcfarland scale which indicates that the presence or absence of turbidity tube demonstrates the inhibition of bacteria in relation to the substance inoculated. It was found that the silver nanoparticles inhibited the growth of the tested microorganisms. The carboxymethylcellulose film embedded with silver nanoparticles showed the best antimicrobial effect against Gram-positive (E. faecalis) and Gram-negative (E. coli) bacteria (0.1 microg cm(-3)).

Self-assembled films of poly(o-ethoxyaniline)—POEA alternated with sulfonated lignin (SL)—were successfully produced, and their kinetics of formation and growth investigated for different dopants (hydrochloric acid, methanesulfonic acid, p-toluenesulfonic acid, and camphorsulfonic acid). These films were characterized by ultraviolet-visible spectroscopy, atomic force microscopy, surface potential, and electrical resistance measurements. It has been observed that the bulkiest dopants led to a greater time for the polymer deposition and greater amount of material adsorbed. This can be explained by the lower mobility and lower solvation of the bulkiest dopant counterions, which led to a higher screening effect of the charges present in the POEA chains and therefore to a more compact molecular conformation. The morphology of the POEA films were also greatly affected by the type of dopant used, being rougher for the bulkiest dopants. The POEA films also exhibited different electrical responses upon ethylene exposure depending on the dopant, indicating a promising use for gas sensor applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1309–1316, 2002

An artificial tongue composed of four sensors made from ultrathin films deposited onto gold interdigitated electrodes has been able to distinguish easily the four basic tastes (salty, sour, sweet, and bitter), in addition to detecting inorganic contaminants in ultrapure water and identifying different brands of coconut water. Some tastants were detected below the human threshold values, for example, 5 mM of NaCl or sucrose. Suppression of quinine by sucrose was also detected. The high sensitivity may be partially attributed to the ultrathin nature of the films as the sensors were produced with Langmuir−Blodgett films of the 16-mer polyaniline oligomer, polypyrrole, and a ruthenium complex and with self-assembled films of an azobenzene-containing polymer. The sensor response was evaluated with ac measurements taken at various frequencies, with the admittance being treated theoretically with an equivalent circuit representing the sensor immersed in a polyelectrolyte solution.

Self-assembled films of Poly(o-ethoxyaniline) (POEA) doped with HCl alternated with sulfonated lignin (SL) were successfully produced under different pHs and their kinetics of formation studied. The adsorption at lower pHs is faster due to the greater electrostatic attraction between the POEA and the SL covered substrate, but a lower amount of POEA is deposited due to charge repulsion of additional POEA chains and conformational steric hindrance. At higher pHs the adsorption of POEA takes longer but it is greater due to the contribution of hydrogen bonding interactions, lower charge repulsion between POEA chains and a more compact polymer conformation. Adsorption of POEA/SL multilayers could be carried out in different types of substrates. Atomic force microscopy (AFM) employed to investigate the morphology of the alternated layers showed that POEA layers exhibited a granular rough aspect, while SL layers presented a much smoother surface.

Mechanical blends of ethylene–vinyl acetate copolymer and polyaniline doped with dodecyl benzene sulfonic acid (PAni–DBSA) were prepared in a two-roll mill at 50°C and in a Haake internal mixer at 150°C. The effects of the blend composition and processing conditions on the electrical conductivity and mechanical properties were investigated. These blends exhibited high levels of electrical conductivity at a small amount of PAni complex. Blends prepared in a two-roll mill displayed conductivity values as high as 1 S/cm and a higher protonation degree than the pure PAni–DBSA, as indicated by X-ray photoelectron spectroscopy. Two different insulator–conductor transition points were observed in these blends. The mechanical performance decreased as the amount of PAni–DBSA increased, indicating blend incompatibility and a plasticizing effect of the DBSA. The morphology of the blends were studied by scanning electron microscopy. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 114–123, 2001

The thermal behavior of blends of poly(vinylidene fluoride), or PVDF, and poly( o -methoxyaniline) doped with toluene sulfonic acid was studied by thermogravimetic analysis, electrical conductivity measurements, differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. Blends with thermal and electrical conductivity stabler than the conductive polymer alone were obtained. Nevertheless, degradation occurs after a long period of time (500 h) at high temperatures. The possible association of the conductivity decay with dopant loss, degradation and structural and morphological changes of the blend is discussed.

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).

Blends of polyaniline (PANI) doped with camphor sulfonic acid and ultra high molecular weight polyethylene were prepared using a mixture of m -cresol and decaline under conditions that promote specific interactions between the polymer, dopant and solvent mixture, leading to films with improved electrical conductivity. Such interactions are in agreement with the formation of supramolecular structures based on hydrogen bonding and phenyl stacking reported in the literature for similar systems. The results from the blend characterization by tensile strength and electrical conductivity measurements, differential scanning calorimetry, UV–Vis spectroscopy, X-ray diffraction and scanning electron microscopy are presented and discussed. Low percolation threshold and high conductivity were obtained, for instance, 10 −6 and 10 −2 S/cm, for blends containing 1 and 5% of PANI, respectively.

In the present article it is shown that a corona discharge can be employed to dope thin films of polyaniline (PANI) coated on poly(ethylene terephthalate) films, allowing the electrical conductivity to be tuned within the range 10−10 to 0.3 S cm−1. A study of the effect of different corona conditions, namely corona treatment for positive and negative polarities, air humidity, treatment time, corona current, and the geometry of the corona triode, on the electrical conductivity of the polyaniline is presented. The results indicate that the corona discharge leads to protonic doping of polyaniline similar to that which occurs in conventional protonic acid solution doping. Atomic force microscopic analysis shows that, as the PANI is exposed to the corona discharge, its globular morphology is disrupted leading to the appearance of droplet-like features and a significant decrease in the average height and surface roughness. Doping by corona discharge presents several advantages over the conventional solution met...

Universidade de Sao Paulo Ciencia e Engenharia de Materiais Area Interunidades, Sao Carlos, SP

The effect of low levels of poly(o-methoxyaniline) (POMA) on the crystallization, morphology, and electrical characteristics of blends with poly(vinylidene fluoride) (PVDF) were studied by infrared spectroscopy, AC electrical measurements, and optical microscopy. Undoped POMA has a strong effect in increasing the α-phase and decreasing the β-phase content of PVDF in blends crystallized from solution. For blends melt crystallized, doped POMA promotes much greater homogeneity than undoped POMA. Interestingly, doped POMA promotes the nucleation and growth of unringed PVDF spherulites, whereas undoped POMA hinders it. The doping state of the POMA was also extremely important in determining the electrical behavior of the blend. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1219–1224, 1999

The effect of different types of acidic dopant namely, poly(vinyl sulfonic) (PVS), camphor sulfonic (CSA) and hydrochloric acids on the electrodeposition of polyaniline (PANI) films by cyclic voltammetry has been investigated and correlated with the morphology and properties of the polymers produced. The polymer films were studied by cyclic voltammetry, electron microscopy, u.v.–visible spectroscopy, X-ray diffraction and conductivity measurements. The nucleation step of the electrodeposition of PANI depends on the counter-ion of the dopant and significantly affects polymer growth as well as the morphology of the polymers produced. The properties of the polymeric films were also greatly influenced by the type of acid dopant used in the electrodeposition. Although all dopants used were protonic acids the conductivity of the polymer was affected by the counter-ion and could be enhanced by exposition to m-cresol due to secondary doping effects.

Adsorption isotherms have been obtained for poly(o-methoxyaniline) (POMA) deposited from aqueous solutions onto glass substrates using UV-visible spectroscopy. Since the peaks in the UV-vis spectra are shifted due to dedoping of POMA during the adsorption process, isosbestic points had to be determined for estimating the amount of polymer adsorbed per unit area. Experiments were carried out at various temperatures. For 25°C, the data could be fitted with a Gu isotherm equation, which indicates that the formation of aggregates occurs for high concentrations. For concentrations below 0.25 g/l, the data could be fitted with a traditional Langmuir-type adsorption isotherm. A Langmuir isotherm also applies to data at the other temperatures employed, viz. 15°C, 40°C, 60°C and 80°C, for which the corresponding equilibrium adsorption constants were calculated. The enthalpy, entropy and free energy adsorption values were then estimated, which showed that POMA adsorption is mostly entropy controlled.

A detailed structural characterization study is presented for composite Langmuir–Blodgett (LB) films containing varying compositions of the 16-mer polyaniline, processed with camphor sulfonic acid and m -cresol, and cadmium stearate. The mixed monolayer approach was selected as it has been proven to yield the most uniform LB films for conducting polymers. Because film uniformity was indeed excellent as verified by visual inspection and also using surface potential measurements, attempts were made to probe whether molecular level mixing occurred. However, X-ray diffraction (XRD) results have shown clearly that the cadmium stearate and the 16-mer molecules are phase separated. Diffractograms were obtained which are very close to that of pure cadmium stearate films, at least for low weight percentages of the 16-mer. When the 16-mer content was increased, the stacking order of the cadmium stearate domains was affected to a large extent, being no longer apparent for 75% of the 16-mer. The presence of cadmium stearate and 16-mer polyaniline in the composite LB film was also detected in a Fourier transform infrared spectroscopy (FTIR) analysis. The deposition of a layer-by-layer structure was confirmed through ellipsometry which also provided film thickness to be compared with the bilayer thickness from XRD data. The thickness was found to be dependent on the film composition, being mostly determined by the cadmium stearate domains up to 50 wt.% of the 16-mer in the composite.

RESUMO: Esse artigo apresenta resultados sobre fabricação e caracterização de um transistor por efeito de campo (FET) tendo a poli(o-metoxianilina) - POMA - como material ativo. Uma adaptação de processos de microeletrônica tradicional foi feita para a confecção desse dispositivo. O FET desenvolvido apresentou modulação por voltagem de porta Vg, mas operou mesmo em Vg=0. A corrente de dreno I D aumentou significativamente sob iluminação na região da radiação visível e infravermelho próximo, mostrando o caráter fotocondutor da POMA dopada e, portanto, do dispositivo. Um modelo teórico baseado nos mecanismos de condução eletrônica da POMA, e de efeitos de interface metal-polímero foi elaborado, ajustando-se muito bem aos resultados experimentais.ABSTRACT: A field effect transistor - FET made from poly(o-methoxyaniline) (POMA), which is a conductive polymer, was developed. Several modifications were carried out to adapt the procedures generally used in traditional device developments. The characteristic of the FET produced was sensible to the gate modulation, but it operates even for V G = 0. The drain current I D enhanced under visible and near infrared radiation, showing the photoconductor character of POMA and, consequently, of the device. A theoretical model, based on the electronic properties of POMA and on the metal-polymer interface, was developed which is in good agreement with the experimental results.

In this work the electrochemical synthesis of polyanilne (PAni) in propylene carbonate (PC) medium in the presence of lithium perchlorate and di- (DCA) and tri-chloroacetic (TCA) acids was studied. In order to determine the best experimental conditions to grow an electroactive film of PAni by cyclic voltammetry, the effects of the supporting electrolyte and acid concentration were analysed. These experiments allowed us to conclude that although the degradation processes associated with the polymer are always present for both acids they are much stronger for DCA, probably due to its dimerization capability. In the presence of TCA a maximum ratio between polymer growth and polymer degradation was achieved. For aniline concentrations of 0.25 M and 0.5 M LiClO 4 , the electroactive PAni growth occurs only for acid concentrations higher than 1 M and 2 M, respectively for TCA and DCA.

This study addressed the effects of chitosan-based nanoparticles on microbiological quality, colour, polyphenol oxidase (PPO) and peroxidase (POD) and firmness of fresh-cut ‘Gala’ apple slices during storage at 5 °C for 10 days. The treatments carried out were as follows: (i) slices pulverised with 110-nm chitosan nanoparticles, (ii) slices pulverised with 300-nm chitosan nanoparticles, (iii) 2 g L−1 chitosan dissolved in 2% citric acid and (iv) noncoated samples. There was an increase in chroma and a proportional decrease in hue angle and lightness. Browning of the slices coated with conventional chitosan and control was slightly intense than those coated with chitosan nanoparticles of 110 and 300 nm. The PPO and PDO activities increased with time for all samples, with irrelevant difference among the treatments. Flesh firmness did not change for any treatment and period. Coatings with chitosan nanoparticles of 110 nm showed higher antimicrobial activity against moulds and yeasts, and mesophilic and psychrotrophic bacteria than the other treatments. No Salmonella, and total and faecal coliforms were detected. This investigation supports the potential use of chitosan nanoparticles as edible coatings in controlling microbial activity in fresh-cut apples.

Nanocomposite materials have been incorporated into biopolymers, (e.g. hydroxypropyl methylcellulose), to improve their physical and chemical properties and enable them to be applied in food packaging, especially for their biodegradable and renewable properties. With this addition, fruit puree has been incorporated into the films to confer nutritional properties besides color and flavor. Chitosan is of interest in the packaging field since it is a biodegradable, bioabsorbable, antimicrobial agent. Furthermore, chitosan nanoparticles have been widely explored for their interesting properties and potential applications in food packaging. This work was divided into two stages: (1) chitosan nanoparticle synthesis; (2) addition of nanoparticles into HPMC and papaya puree films. Addition of chitosan nanoparticles to HPMC and papaya puree films improved film properties: mechanical, thermal and water vapor barrier. We have developed a novel nanomaterial with great potential for application in packaging to prolong the shelf life of food.

As técnicas de microscopia de varredura por força tem promovido um grande impacto em ciência dos materiais devido a possibilidade de obtenção de imagens em escala que pode chegar no nível atômico. Neste trabalho serão apresentados o princípio básico de funcionamento da microscopia de varredura por força, os vários modos de operação e as forças envolvidas e medidas. O potencial de aplicação destas técnicas no estudo de materiais, e em particular de polímeros, serão discutidos. Uma comparação da microscopia de força atômica com outras técnicas de microscopia será apresentada, assim como exemplos da utilização da técnica de microscopia de força atômica para o estudo de polímeros.

The kinetics of adsorption of poly(o-methoxyaniline) (POMA) via self-assembly has been investigated using UV-vis spectroscopy. Though experimental conditions, including type of substrate, affect the amount of polymer adsorbed, adsorption of the first POMA layer on glass substrates was shown to occur in two stages, reaching saturation within a few minutes. The first stage is represented by a first-order kinetics with characteristic times of 5-10 s. The second stage also has an exponential behavior with t 1.5 and characteristic times of hundreds of seconds, which was valid for all substrates when the shift in the polaronic band in the beginning of adsorption was taken into account. The t 1.5 within the exponential is believed to indicate a diffusion-controlled growth of small domains formed during the first stage of adsorption. The appearance of small domains and their subsequent growth are consistent with scanning electron micrographs obtained at distinct time periods of adsorption. When a POMA layer was made to adsorb on an already formed POMA/poly(ethenesulfonic acid) self-assembly multilayer, the adsorption process became faster as the number of bilayers already deposited increased.

Solubility tests were performed at room temperature for poly ( o -methoxyaniline) (POMA) in N,N -dimethylformamide (DMF), 1-methyl-2-pyrrolidone (NMP), m -cresol, acetonitrile, chloroform, dichloromethane and xylene, and compared with those for polyaniline. A reversible solvatochromic transition from green to blue was observed in dilute POMA solutions in DMF, NMP and m -cresol indicating the occurrence of deprotonation-protonation processes. The solvent NMP more readily induced deprotonation processes at higher concentrations than those observed in DMF solutions. On the other hand, m -cresol exhibited an ability to protonate POMA in solution regardless of its undoped or doped state. Ultraviolet-visible spectra confirmed modifications of electronic transitions in agreement with the color changes. Correlations among crystalline properties, electron paramagmetic resonance results and electric conductivity of POMA films processed from DMF, NMP and m -cresol solutions are discussed.

The formation of Langmuir monolayers and Langmuir−Blodgett films is reported for the first time for a polyaniline oligomer, 16-mer, that was mixed with cadmium stearate. The processibility of this oligomeric material was greatly improved as compared to the parent polyaniline, which allowed one to use common solvents like chloroform as the spreading solvent. Analogously to composite polyaniline monolayers, the stability and the transferability are found to depend on the 16-mer content in the composite film, with poor stability and low transfer ratios above 60% of 16-mer. Deposited Langmuir−Blodgett films were found to be undoped (or only weakly doped) since they were obtained from monolayers spread onto aqueous subphases (pH = 6.0). Uniform Langmuir−Blodgett (LB) deposition was confirmed by optical microscopy and UV−vis spectra whose intensity increased linearly with the number of layers deposited and also with the 16-mer content. Fourier transform infrared (FTIR) results revealed that cadmium stearate was...

Structural changes in poly(vinylidene fluoride)-trifluoroethylene [P(VDF-TrFE)] copolymers caused by X-ray irradiation were investigated by molecular weight determination, EPR analysis, FTIR spectroscopy, gel content, DSC thermal analysis, X-ray diffraction, and piezoelectricity measurements. Samples exhibit radiation-induced conductivity (RIC) due to the formation of radical ions. These radicals are generated by bond cleavage, which could react, leading to structural changes such as oxidation, double bond formation, chain scission, and crosslinking. The increasing gel content with radiation dose indicated that crosslinkings of the polymer chains predominate. Irradiation on P(VDF-TrFE ) caused the melting temperature, heat of fusion, and Curie temperature to decrease. These results are consistent with the partial destruction of crystalline domains.

This paper reports on the development of bioactive edible films based on pectin as a dietary matrix and magnesium hydroxide (Mg(OH)2) nanoplates as a reinforcing filler. Nanocomposites of high-methoxyl (HM) and low-methoxyl (LM) pectins were prepared using the casting method at concentrations of Mg(OH)2 ranging from 0.5 to 5 wt %. Atomic force microscopy and FTIR spectroscopy were employed to characterize the nanocomposite structure. The tensile properties and thermal stability of the nanocomposites were also examined to ascertain the effect of Mg(OH)2 inclusion and degree of methoxylation. The results provided evidence that the Mg(OH)2 nanoplates were uniformly dispersed and interacted strongly with the film matrix. The mechanical and thermal properties were significantly improved in the nanocomposite films compared to the control. Mg(OH)2 nanoplates were more effective in improving properties of LM pectin. Preliminary migration studies using arugula leaves confirmed that pectin-Mg(OH)2 nanocomposites can release magnesium hydroxide by contact, demonstrating their potential for magnesium supplementation in bioactive packaging.

Silver nanoparticles have high temperature stability and low volatility, and at the nanoscale are known to be an effective antifungal and antimicrobial agent. The present investigation involves the synthesis of silver nanoparticle/carboxymethylcellulose nanocomposites. The nanoparticles synthesised in this study had sizes in the range of 100 and 40 nm. The nanocomposites formed by a combination of metallic nanoparticles and carboxymethylcellulose were characterised by contact angle measurements, solubility tests, thermal and mechanical analyses, and morphological images. Improvements in the hydrophobic properties were observed with inclusion of the nanoparticles in the nanocomposites, with the best results occurring after the addition of 40 nm nanoparticles in a carboxymethylcellulose matrix. The silver nanoparticles tend to occupy the empty spaces in the pores of the carboxymethylcellulose matrix, inducing the collapse of these pores and thereby improving the tensile and barrier properties of the film.

The effect of pH and type of doping acid on monolayer behavior is investigated for poly(o-ethoxyaniline). Doping during monolayer formation is essential for high-quality Langmuir-Blodgett (LB) films to be obtained. Langmuir films were spread on a variety of subphases, containing trifluoroacetic, hydrochloric, sulfuric or perchloric acids at different concentrations. Doping of the polymer occurs at pH values lower than 3 when spreading of the solution is improved. Pressure-area isotherms display less hysteresis and higher collapse pressures when the polymer is pre-doped and spread on a pH = 1 subphase. Under these conditions monolayers could be transferred from the aqueous subphase onto hydrophilic substrates in the form of Z-type LB films.

Conducting Langmuir-Blodgett (LB) films have been fabricated from parent polyaniline (PAni) which was doped with functionalized acids. In order to optimize experimental conditions for the formation of stable Langmuir monolayers and their subsequent transfer onto solid substrates, PAni was dissolved in ten different combinations of chloroform solutions. Use was made of camphor sulfonic acid, dodecyl benzene sulfonic acid, and toluenesulfonic acid, and of the solvents N-methyl pyrrolidine and m-cresol as processing agents. Because acidic subphases have been employed, as-deposited LB films were already doped, which was confirmed by the appearance of a polaronic band in the UV-Vis absorption spectra. The absorbance peak increases with the number of deposited layers indicating that a suitable multilayer buildup is accomplished. When analysed by atomic force microscopy, PAni LB films show a fibrillar structure with the fibril width ranging from ≈60 to 160 nm.

EMBRAPA CNPDIA, Natl Nanotechnol Lab Agribusiness, Rua 15 Novembro 1452, BR-13560970 Sao Carlos, SP, Brazil

Puree prepared from over-ripe peeled bananas was used as raw material for films processing in a laboratory padder. Pectin and glycerol as plasticizer were added in small concentrations and chitosan nanoparticles (88.79 ± 0.42 nm medium size) incorporated at 0.2% (dry weight basis) as reinforcement material. The mechanical properties, water vapor transmission, thermal stability, and scanning electron microscopy of fractured film surfaces were characterized. Both pectin and glycerol demonstrated an important role in promoting elongation and film handability as was expected. The incorporation of nanoparticles promoted noticeable improvement of the mechanical properties and acted in reducing the water vapor permeation rate, by 21% for films processed with pectin and up to 38% for films processed without pectin, when compared to the control (puree films with no pectin and nanoparticles additions). Microscopic observation revealed a denser matrix when nanoparticles are incorporated into the films. Practical Application: The development of films from fruit purees head to a new strategy for plastic processing from natural resources. The over-ripe or even waste banana can be adequately prepared for batch films processed with reasonable mechanical and barrier properties, suitable for applications in the food segment. The addition of small fractions of chitosan nanoparticles, form nanocomposites enhancing mechanical and thermal stability broadening potential film applications.

Neste estudo, fibras de coco verde foram incorporadas em uma matriz composta de glúten de milho (GM) e poli(hidroxibutirato-co-valerato) (PHBV). As composições foram processadas por extrusão, onde o teor máximo de glúten adicionado à matriz para obter misturas com viscosidade suficientemente baixa para o processamento foi de 50% (em peso) em relação ao teor de PHBV. O teor de fibras nos compósitos variou de 5 a 20% por peso em relação ao peso total dos polímeros. Os plastificantes usados foram acetil tributil citrato (ATBC) e glicerol. Os materiais extrudados foram moldados por compressão a quente para obtenção de corpos de prova para a caracterização das propriedades de absorção de água, solubilidade em água, resistência mecânica, além de propriedades termo-dinâmico-mecânicas (DMTA) e morfológicas. Foi observado que as matrizes apresentaram duas transições vítreas (Tg's) uma para cada componente, indicando que as mesmas são compostas de duas fases (GM) e PHBV. A adição do PHBV ao glúten favoreceu ao aumento da rigidez e houve diminuições significativas na absorção de água e na solubilidade em água, enquanto a presença das fibras provocou, em algumas composições, um aumento no módulo de elasticidade e na resistência à tração. Green coconut fibers were added as reinforcement in polymer matrices comprised of corn gluten meal (GM) and PHBV. The composites were processed by extrusion. The maximum gluten content added in the matrix to obtain mixtures with low enough viscosity for the extrusion process was 50% (by weight) in relation to PHBV content. The content of fibers used in the composites varied from 5% to 20% (by weight) of the total polymers weight (GM and PHBV). Glycerol and acetyl tributyl citrate (ATBC) were used as plasticizers. The matrices and composites obtained were molded by heat compression and further characterized. Water absorption at equilibrium and water solubility decreased as the PHBV content increased. The Young's modulus and ultimate tensile strength increased with fiber content in the matrix for some compositions. GM/PHBV matrices exhibited two distinct glass transitions, one for each component, indicating a two-phase system. DMTA results and the morphology of the composites analyzed under the scanning electron suggested that the reinforcing effect of the green coconut fibers in GM/PHBV matrices was not homogeneous.

Poly(o-ethoxyanilines) (POEA) were synthesized electrochemically and chemically in aqueous acid media. POEA films were readily obtained during the electrochemical deposition on platinum electrodes, while the chemically synthesized material was processed in the form of films either by drop coating or by Langmuir-Blodgett (LB) deposition. The open circuit potential values measured during the chemical synthesis, as well as the color changes observed, are in close agreement with those of the electro-polymerization indicating basically the same changes in oxidation states of the polymer structures. The electrochemical response of all films was investigated by cyclic voltammetry. Two redox processes were observed after stabilization in the electrolyte solution, which are associated with interconversion reactions involving different oxidation and protonation states. Ultra-thin LB films required the shortest time for stabilization. POEA films displayed electrochromism, with color changes from yellow to violet as a function of the potential.

SYNOPSIS Syntheses of parent polyaniline and methyl, methoxy, and ethoxy ortho-substituted polyanilines were performed using the conventional chemical methodology and monitored using the new open-circuit-potential ( V,) profile technique. The intermediate pernigraniline oxidation state was identified and isolated at the V,,, maximum (A) during the conventional chemical synthesis of poly(o-methoxyaniline) in the emeraldine oxidation state. The introduction of the substituent on the aniline ring leads to longer polymerization times and lower V,, values. Syntheses in the presence of two different monomers in solution were also investigated and showed preferential polymerization of the monomer with the lowest V, potential. All polymers produced were characterized by elemental analysis, gel permeation chromatography, UV-VIS spectroscopy, and cyclic voltammetry. The influence of the substituent on the V,, profile and on the polymer characteristics are rationalized in terms of steric and electronic effects. 0 1995 John Wiley & Sons, Inc.

The conditions for processing and doping of blends of poly( o -alkoxyaniline)s and poly(vinylidene fluoride) were investigated. Flexible, free-standing and stretchable films of blends of various compositions were obtained by casting. A low percolation threshold was observed with the onset of conductivity at low polyalkoxyaniline contents (i.e. 5%). Interestingly, these blends displayed electrochromism with colour changes similar to those of the parent conducting polymer, as observed from cyclic voltammetry measurements. This behaviour is seen even for low contents of the conducting polymer, indicating that a continuous conducting pathway, which is capable of exchanging charge, is formed within the insulating matrix.

A sensor array made up of nanostructured Langmuir-Blodgett (LB) films is used as an electronic tongue capable of identifying sucrose, quinine, NaCl, and HCl at the parts-per-billion (ppb) level, being in some cases 3 orders of magnitude below the human threshold. The sensing units comprise LB films from conducting polymers and a ruthenium complex transferred onto gold interdigitated electrodes. Impedance spectroscopy is used as the principle of detection, and the importance of using nanostructured films is confirmed by comparing results from LB films with those obtained from cast films.

Citrus canker is one of the most important agricultural citrus diseases worldwide. It is caused by Xanthomonas citri subsp. citri (Xcc) bacterium that infects leaves and the fruits produce a cysteine peptidase (CPXaC), which makes it a potential target for the development of effective and rapid detection methods for citrus canker. We report here the studies on the development of piezoelectric immunoassay for CPXaC using a polyclonal antibody against CPXaC (anti-CPXaC). Three different strategies for covalent immobilization of anti-CPXaC on gold surfaces were evaluated by monitoring the frequency (Δf) and energy dissipation (ΔD) variation in real time when 64.5×10−8 mol L−1 CPXaC was added. Anti-CPXaC immobilized with 11-mercaptoundecanoic acid (MUA) showed the best relation between the frequency and dissipation factor variation, and strong values for the kinetic and equilibrium binding constant were obtained. The immunosensor showed a detection limit of 13.0 nmol L−1 with excellent specificity, showing no response for different proteins that include another cysteine peptidase that is used as a target to detect Xylella fastidiosa bacterium, responsible for another important citrus disease. These results provide good perspectives for the use of CPXaC as a new biomarker for citrus canker.

In this paper the mechanical reinforcement of nano-sized brucite, Mg(OH) 2 in a series of bionanocomposite films based on starch was investigated. Brucite nanoplates with an aspect ratio of 9.25 were synthesized by wet precipitation and incorporated into starch matrices at different concentrations (0–7.5 wt.%). Scanning electron microscopy revealed a high degree of nanoplate dispersion within the starch bionanocomposites and good interfacial adhesion between the filler and matrix. The brucite nanoplates formed agglomerates at high concentrations. The reinforcement factor values of the bionanocomposites were higher than the values predicted from the Halphin–Tsai model, which was attributed mainly to the high surface area of the nanoplates. Brucite (1 wt.%) nearly doubled the elastic modulus of starch films. Thermogravimetric analyses indicated some interaction between starch and the brucite that modified their decomposition profiles. Mechanical tests of glycerol plasticized bionanocomposites showed that the reinforcing efficiency of brucite remained high even at 10 wt.% and 20 wt.% of plasticizer.

One of the overall goals of industries is to use packages that do not cause environmental problems at disposal time, but that have the same properties as the conventional ones. The goal of this study is to synthesize edible films based on hydroxypropyl methylcellulose (HPMC) with guava puree and chitosan (CS) nanoparticles. This was divided into two stages, the first is the synthesis of chitosan nanoparticles and the second is the production of the films. For the nanoparticles, average size and zeta potential measurements were performed. The characterizations of mechanical and thermal properties, solubility and water vapor permeability tests were conducted in the films. It was observed that when the nanoparticles were added to HPMC and guava puree films, they improved their mechanical and thermal properties, as well as decreased the films solubility and permeability. The potential application of the films prepared would be in edible films with flavor and odor to extend the shelf life of products.

Nanocomposite fibers based on multi-walled carbon nanotubes (MWCNT) and poly(lactic acid) (PLA) were prepared by solution blow spinning (SBS). Fiber morphology was characterized by scanning electron microscopy (SEM) and optical microscopy (OM). Electrical, thermal, surface and crystalline properties of the spun fibers were evaluated, respectively, by conductivity measurements (4-point probe), thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), contact angle and X-ray diffraction (XRD). OM analysis of the spun mats showed a poor dispersion of MWCNT in the matrix, however dispersion in solution was increased during spinning where droplets of PLA in solution loaded with MWCNT were pulled by the pressure drop at the nozzle, producing PLA fibers filled with MWCNT. Good electrical conductivity and hydrophobicity can be achieved at low carbon nanotube contents. When only 1 wt% MWCNT was added to low-crystalline PLA, surface conductivity of the composites increased from 5 x 10(-8) to 0.46 S/cm. Addition of MWCNT can slightly influence the degree of crystallinity of PLA fibers as studied by XRD and DSC. Thermogravimetric analyses showed that MWCNT loading can decrease the onset degradation temperature of the composites which was attributed to the catalytic effect of metallic residues in MWCNT. Moreover, it was demonstrated that hydrophilicity slightly increased with an increase in MWCNT content. These results show that solution blow spinning can also be used to produce nanocomposite fibers with many potential applications such as in sensors and biosensors.