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The sensitivity evaluation of a vanadium pentoxide/poly-o-methoxyaniline hybrid material (V2O5/POMA) using casting deposition for the preparation of an ammonia gas sensor was investigated herein. V2O5/POMA was produced by the intercalation of V2O5 via sol–gel and o-methoxyaniline monomers. V2O5/POMA thin film deposition onto electrodes was performed by casting. The electrical studies confirmed that V2O5/POMA exhibited increased complex impedance as a function of increasing ammonia concentration. The conductivity of the film decreased with increasing ammonia concentration due to the de-doping process. According to theoretical adjustment, a significant increase in the bulk and interfacial electrical resistance in the presence of ammonia was observed. The combination of these effects contributed to the high sensitivity of the prepared film in both the real and imaginary components of the complex impedance for ammonia gas in a range of 0 to 100 ppm, which indicated that the film is a good candidate for use as an ammonia sensing material.

Conducting polymers such as polyaniline (PANi) have been widely investigated as ammonia gas sensors due to their intrinsic redox states, good environmental stability, and suitability for low-cost and variable changing in electrical conductivity when exposed to acid and basic gases. In this paper we used both a hybrid PANi derivative, poly(o-methoxyaniline) (POMA)-vanadium pentoxide (V2O5) film, and new ac electrical measurement strategies to increase the ammonia gas sensor performance. Complex impedance measurements of POMA/V2O5 hybrid film showed linearity in response and a high sensitivity to ammonia in the 0–20 ppm range in both real (around 800%) and imaginary (around 3000%) components, which indicated that the film is a good candidate to use as an ammonia sensing material. FTIR spectra presented typical V2O5 and POMA bands and also presented a shifting to higher wave numbers in bands referring to the vanadyl group and primary amines, which indicated the presence of hydrogen bonds between oxide and polymer. Finally, the Cole–Cole theoretical model with an interface effect provided a good fit for the experimental results from electrical ac measurements.

Studies of xerogel vanadium pentoxide hybrids in the presence of polyaniline (V2O5/PANI) for ammonia gas detection are presented. The hybrid materials were obtained in an oxidative polymerization/intercalation process, in which gel reacted with the monomers of the polymers. In situ characterization revealed V2O5/PANI hybrids with lamellar structure. Finally, the electric impedance technique was used for determining the optimal frequency band for operation of an Ag/V2O5/PANI/Ag amperometric ammonia gas sensor, to achieve linearity and stability. The results indicate that the sensor can detect gaseous ammonia in the 0–54 ppm range of concentrations. This characteristic is important for successful applications in easy to handle and low-cost ammonia gas sensors for animal confinement husbandry, for which current variation and difficulties related to electrode effects and dielectric absorption of V2O5 and PANI are negligible.

Hyperbilirubinemia is a systemic global problem and an often diagnosed pathology in newborns. In most cases, blue-light phototherapy (410–460 nm) is the only treatment required to prevent the bilirubin neurotoxicity, but its effectiveness is dose-dependent and is highly affected by the skills, knowledge, and attention of nurses and clinicians who implement the treatment. This paper presents a novel light-sensitive colorimetric dosimeter to simulate the effect of blue-light phototherapy on the optical properties of in vitro bilirubin. The dosimeter is based on a multilayered organic structure comprising a light-stable green-light emitter (copper phthalocyanine, C 32 Cl 16 CuN 8 ), and a blue-light-sensitive red emitter (poly{[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene]vinylene}, OC 1O C 6 -PPV). The optical and chemical properties of the dosimeter were investigated by fluorescence and FTIR spectroscopies and by color coordinates of CIE (1931) diagram chromatics, while the photochemical processing of bilirubin was evaluated by UV–vis absorption spectroscopy. The optical response of the dosimeter under conventional (10 μW/cm 2 ) and intensive (40 μW/cm 2 ) phototherapy was found to present the same photochemical kinetics as bilirubin. These findings highlight a cutting-edge solution for monitoring bilirubin elimination in neonates as a function of the dosimeter’s color evolution. This novel colorimetric dosimeter provides a standardized method of reporting and measuring phototherapy dose to promote an efficient use of available phototherapy units in health facilities.

With the aim of improving phototherapy for neonatal jaundice (hyperbilirubinemia), this study investigates the degradation of unconjugated bilirubin under irradiance by conventional light and by white, red, green, and blue LED sources in vitro. The absorption spectra of bilirubin under these different light sources are compared. The results demonstrate that white LED phototherapy promotes more efficient bilirubin degradation than conventional blue-light therapy. This study provides a basis for the design of novel phototherapy devices for the treatment of hyperbilirubinemia.

The lack of monitoring of food freshness during the cold chain has been reported in the literature as either a problem faced by meat industries enforcing stricter controls and public health security needs. This paper presents an innovative solution for real-time food freshness discrimination: a printable, easy-to-use, and non-toxic two-faced Janus color-indicator label. This sensor is based on the pink to purple variation of a multilayer pH-sensitive composite (cellulose acetate and black carrot anthocyanin) film in the turnover process of fresh to spoilage chicken. The microstructure and permeability of the composite, and also the impact of the psychrotrophic aerobic bacteria on the optical properties of the indicator label, were investigated. This sensor demonstrating a short response time (∼ 2 min), great color stability, and provides interactive information of food freshness, being capable of communicating directly with consumers via two simple images: “happy face” for fresh meat and “sad face” for spoilage. As far as we know, this is the first time that the Janus (or Emoji) principle is designed for tracking food quality to allow consumers to have easy information on food freshness.

This paper describes a variety of experiments that reveal the potential application of impedance spectroscopy (IS) measurements to enhance performance of ultrathin polyaniline (PANI)-based films on flexible substrate to control ammonia gas exposure in the 0–20 ppm range. Further, the device is mechanically robust for making electrical contact without lithography. We have employed the IS technique to proper adjust the optimal operation frequency of an easy-to-process, inexpensive and user-friendly PANI-based resistometric detectors in which drift current and delay problems related to electrode effects and dielectric absorption of PANI are insignificant. These requirements place emphasis upon the material and device configuration, and the range of frequencies from 10 to 100 Hz corresponds to the ideal working region to operate the device to unify sensibility inside 5%, reproducibility, linearity, stability and low response time (

Made available in DSpace on 2018-11-26T17:42:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-12-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) This paper describes a new statistical model to predict the frequency dependence of the conductivity of conjugated polymer-semiconductor nanoparticle composites. The model considers AC conduction in an inhomogeneous medium represented by a two-dimensional model of resistor network. The conductivity between two neighboring sites in the polymer matrix and the semiconductor particles is assumed to obey the random free energy barrier model and the Drude model, respectively. The real and imaginary parts of the AC conductivity were determined using the transfer-matrix technique, and the statistical model was applied to experimental data of thin films composed of polyaniline (PANI) and indium-tin-oxide (ITO) nanoparticles. The conductivity critical exponent (s) obtained in two dimensions for PANI/ITO films below the percolation threshold was found to be 2.7, which is greater than the universal value of s described by the classical percolation theory (s = 1.3). This non-universality is explained by the existence of a local electric field distribution in the bulk of the nanocomposite. Finally, these results are discussed in terms of the distribution of potential barriers that vary according to the concentration of ITO amount in the composite. Univ Sao Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP, Brazil IFMG, Campus Ouro Preto, BR-35400000 Ouro Preto, MG, Brazil Univ Fed Ouro Preto, Dept Fis, BR-35400000 Ouro Preto, MG, Brazil Univ Estadual Paulista, Dept Fis & Quim, Campus Ilha Solteira, BR-15385000 Ilha Solteira, SP, Brazil Univ Estadual Paulista, Dept Fis & Quim, Campus Ilha Solteira, BR-15385000 Ilha Solteira, SP, Brazil

Poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable aliphatic-aromatic copolyester. In this paper, we report the radio induction of photoluminescence (PL) properties in PBAT, after exposure to high doses of gamma radiation. After the previous high-energy irradiation, the material shows the highest photo-stimulated luminescence emission when excited with a light-emitting diode (LED) source at wavelengths ranging from 370 to 405 nm. The PL intensities obtained after excitation with an LED source of 385 nm are proportional to gamma doses ranging from 100 to 1000 kGy in the preirradiation process. FTIR data revealed that the gamma-induced aromatic amine groups may be responsible for the appearance of the postirradiation PL character in PBAT samples. The results indicate that PBAT has great potential for applications in in vitro imaging of human cancer, bioimaging devices, and radiation dosimetry.

Research in hybrid electronics has included advances in materials, devices and architectures. However, in practice, controversy still exists on some details which limit hybrid materials to high-performance applications, such as processing–structure–design–property relations. This paper describes a practical approach to enhancing the sensing performance of a prototype ammonia gas sensor based on electrical conductivity changes, percolation theory and current limitation to a semiconducting polymer-metal oxide medium. This device is based on fully-gravure printed polyaniline/indium - tin oxide nanocomposites, Pani100−xITOx [0 ≤ x≤ 100% (wt/wt)], layers on a freestanding high-density polyethylene substrate. We find that the electrical current of the device decreases and tends to saturate as the gas concentration increases, and the value of this electrical current limit (IL) depends on x: the higher the value of x, the smaller the IL, when the current that flows through the electronic device was dominated by the ITO-nanoparticle filled PAni, which increase the concentration of hopping carriers and contribute to the desired electrical response of a heterogeneous gas sensor. In this regime, we find a good linear relationship between x and ammonia concentration. These findings suggest new directions for future research on the development and investigation of organic-inorganic devices in which the electrical current variation is desired for enhanced sensitivity and stability of hybrid sensors.

In the present work, we concentrate on the study of effects of metallic electrodes, multilayer thickness and temperature in ac and dc electrical conductivity of polyaniline/poly(vinyl sulfonic acid) (PANI/PVS) ultrathin films. The polymer system was obtained from layer-by-layer (Lbl) self-assembly technique on a glass substrate with an electrode array of adhesion layer of NiCr (20 nm) covered with Au (180 nm). We observed a significant and abrupt increase in the value of dc conductivity and a change of ac conductivity behavior of NiCr/Au–PANI/PVS–NiCr/Au structure when the thickness of PANI/PVS system reaches the Au layer. These effects were ascribed to the ideal contact of Au–PANI/PVS and the relative high interfacial contact resistance between PANI/PVS and NiCr, thus reducing the parallel resistance of NiCr/Au–PANI/PVS interfacial layer in an ideal parallel plate capacitor structure. Atomic Force Microscopy images confirm this assumption. Furthermore, the ac conductivity of Au–PANI/PVS–Au structure was typical of solid disordered materials. A model based on carrier hopping in a medium with randomly varying energy barriers was presented for the ac conductivity of the polymer system, which also encompasses the high dielectric constant of PANI/PVS blended films, the neutral contact Au–PANI/PVS, and the electrical resistance of NiCr–PANI/PVS interfacial layer. The model allowed separating the interface and the bulk effects in the electrical response of NiCr/Au–PANI/PVS–NiCr/Au structure and in addition the highest activation energy (35 MeV) correlated with an optimization of hopping distance (30 nm) for carriers jumps in PANI/PVS system.

Neste trabalho as propriedades ópticas do poli[2-metóxi,5-(2’etil-hexiloxi)-p-fenilenovinileno] - MEH-PPV foram estudadas sob efeito de luz azul proveniente de super LEDs utilizada no tratamento da hiperbilirrubinemia neonatal (ou icterícia). Os resultados mostraram que o MEH-PPV apresenta uma mudança de cor do vermelho-alaranjado para o incolor, passando por diversas tonalidades de amarelo, bem como uma diminuição da intensidade dos espectros de absorção e de fotoluminescência (PL) em função do tempo de exposição à radiação. Essas mudanças foram usadas para projetar um sensor de acúmulo de dose de radiação azul, tipo indicador de cores, para avaliar a dose de radiação recebida por recém-nascidos durante o tratamento da icterícia neonatal. In this work we investigated the optical behavior of poly[2-methoxy-5(2’-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) under the effect of blue-light LED source applied in neonatal hyperbilirubinemia treatment. There is a visible response that covers the electronic absorption of bilirubin (350-500 nm), and hence this material is applicable for controlling the radiation doses in the treatment of jaundice of neonates, which is one of the most common reasons for hospital readmission of newborn infants. The results show that the material presents a gradation of color from orange-red to yellow and quenching on the absorption and photoluminescent (PL) spectra with the radiation exposure time. The rate of these changes can be altered by manipulations of organic solution concentration, suggesting these color and emission/absorption changes can be used to design an indicator-dosimeter that is readily associated with the radiation exposure time used in treating neonatal jaundice.

In this paper, a detailed study of the capacitance spectra obtained from Au/doped-polyaniline/Al structures in the frequency domain (0.05 Hz–10 MHz), and at different temperatures (150–340 K) is carried out. The capacitance spectra behavior in semiconductors can be appropriately described by using abrupt cut-off models, since they assume that the electronic gap states that can follow the ac modulation have response times varying rapidly with a certain abscissa, which is dependent on both temperature and frequency. Two models based on the abrupt cut-off concept, formerly developed to describe inorganic semiconductor devices, have been used to analyze the capacitance spectra of devices based on doped polyaniline (PANI), which is a well-known polymeric semiconductor with innumerous potential technological applications. The application of these models allowed the determination of significant parameters, such as Debye length (≈20 nm), position of bulk Fermi level (≈320 meV) and associated density of states (≈2×1018 eV−1 cm−3), width of the space charge region (≈70 nm), built-in potential (≈780 meV), and the gap states’ distribution.

The central process of neonatal phototherapy by employing blue light has been attributed to the configurational conversion of (4Z,15Z)-bilirubin to (4Z,15E). Indeed, photoisomerization is the early photochemical event during this procedure. However, in this paper, we show that the bilirubin solutions under continuous blue light exposure undergo a photooxidation process. To ascertain the role of this photodegradation in the phototherapy, we evaluated UV–visible absorption spectra obtained from bilirubin solutions in CHCl3, milli-Q water, and physiological saline, as well as FTIR spectroscopy for bilirubin in CHCl3. These analyses also showed that the first 2 h of phototherapy are the most relevant period. In addition, quantum molecular modeling using B3LYP/6-31G(d,p) and ZINDO/S-CIS was performed to evaluate the electronic and structural properties of four bilirubin isomers, showing that the (4Z,15E)-bilirubin isomer is the most polar configuration. Therefore, it can be more soluble in aqueous environments than the other configurations. This clarifies why this is the faster isomer excreted during the phototherapy.

In this work, a new type of WO3 and V2O5 photovoltaic cell were fabricated. The oxides were obtained by sol-gel route. Both V2O5 and WO3 presented a lamellar structure with d = 1.17 nm and 0.69 nm, respectively. From SEM of V2O5 was observed ribbons and for WO3 noted a presence of platelets. For WO3, increasing the distance of lamp was observed a decreasing of light intensity: 164 mV in 44000 lux to 42 mV in 60 lux. For V2O5, in 1700 lux it was observed a voltage of 1418 mV and in 15000 lux a value of 1572 mV.

Poly( p -phenylene vinylene) (PPV) derivatives are well known for their applications in polymer light emitting diodes (PLEDs). PPV derivatives are highly susceptible to photo-oxidation though, which is mainly caused by the scission of the vinyl double bond on the polymer backbone. In this work, we show that Langmuir–Blodgett (LB) films are less degraded than cast films of a PPV derivative (OC 1 OC 6 -PPV). Both films had similar thickness (∼50 nm) to allow for a more realistic comparison. Degradation was monitored with UV–vis and FTIR spectroscopies. The results indicated that cast films were completely degraded in ca. 400 min, while LB took longer time, i.e. about four times the values for the cast films. The differences can be attributed to the more compact morphology in the LB than in the cast films. With a compact morphology the diffusion of oxygen in the LB film is hampered and this causes a delay in the degradation process.

We have developed a novel programmable, low cost, spin coater to be used for applications where flat substrates are coated with an uniform thin layer of a desirable material. The equipment is built with dc brushless motor present in most of the hard disk drivers (HDDs). The system offers manual control, wide speed range (from 0 to 10,000 rpm), spin speed stability and compact size. The paper also describes the use of such equipment for the fabrication of thin poly(o-methoxyaniline) (POMA) films, which are of particular interest for design organic electronic devices, such as diodes, transistor, sensors and displays.

In this work, a plasma-enhanced chemical vapor deposition (PECVD) system was used to deposit carbon nitride at low deposition temperatures (ca. 100 °C) to improve the lifetime of polymer light-emitting diodes (PLEDs) and to decrease photo-degradation of MEH-PPV (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinilene]) in air. The characteristics of the carbon nitride and MEH-PPV films are investigated with FTIR and UV–Visible spectroscopies, with particular emphasis on the degradation process of MEH-PPV under illumination. It was shown by absorbance measurements that the coating protects the polymer film since the damage caused by photo-oxidation diminishes considerably. Current vs. voltage curves for PLEDs also indicated that the protection of a carbon nitride layer enhances the device lifetime.

The properties of a commercial indium-tin-oxide (ITO) layer deposited on glass substrates were evaluated as a function of the treatment time in diluted aqua regia solution. The samples were characterized by atomic force microscopy (AFM), bulk conductivity, ellipsometry, energy-dispersive X-ray analysis (EDX), contact angle/surface energy, and work function measurements. The results show that shorter times of treatment do not affect significantly the ITO properties but decrease the ITO thickness. For longer times (more than 30 min), although the work function and In/Sn ratio are not affected by the treatment, conductivity, roughness, UV–VIS absorption spectra, and refraction index values are greatly affected. Contact angle and surface energy data indicated that the dispersive component of the surface energy was not affected by the treatments. However, a strong decrease in the polar contribution occurred, indicating that ITO surface becomes more hydrophobic as the chemical treatment proceeds. These treated surfaces can interact more strongly with nonpolar materials, such as poly-(p-phenylene-vinylene) derivatives, resulting in a strong polymer ITO adhesion that can improve the efficiency of polymer light-emitting diodes (PLEDs).

In this work, the electrical properties of polymeric light-emitting diodes (LEDs) based on poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene), MEH-PPV, were studied by dc current–voltage (I–V) curves and impedance/admittance spectroscopy, at different temperatures. ITO/polymer/metal (Al and Au) structures were used to study the effect of the barrier height on the charge injection at the polymer/metal interfaces. For ITO/MEH-PPV/Al devices, strong temperature influence on the dc conductivity was observed in the forward direction whereas, in the reverse direction, the conductivity was almost temperature independent. On the other hand, ITO/MEH-PPV/Au devices presented temperature dependent conductivities for both polarities. This indicates that, for low barrier height at the interfaces (

Poly(p-phenylenevinylene) (PPV) and its derivatives exhibit strong luminescence, being serious candidates to be used as active layers in organic light-emitting diodes. However, the structural degradation caused by photo-oxidation is an obstacle for commercial applications of such materials. Here, we show that spectroscopy ellipsometry is a useful technique to investigate the photo-oxidation of poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] (MH-PPV), a PPV derivative, which emits a red color light. Spectroscopy ellipsometry enables determination of the complex dielectric function ∈ * (E) of MH-PPV thin-layer films exposed to air, in the 2.1-4.2 eV energy range, as a function of the light exposure time (t e ). By using the Lorentz model to fit the experimental ∈*(E) curves, it was inferred that the interactions among polymeric chains increase with t e . From ∈*(E), it is also possible to obtain the complex refractive index, N*(E) = n + ik. At higher energies (where k << n), n increases from 1.32 to 1.40 with the photo-oxidation progress. The behavior of n was investigated by using the Lorenz-Lorentz equation, taking into account the contribution for n by the chromophores of MH-PPV. The effect of photo-oxidation, mainly due to the replacement of vinyl C=C by the ketone C=O bonds, is confirmed by Fourier transform infrared measurements, an effect that reduces the average effective polymer conjugation length.

We present a detailed study of the electric mechanism of a thin poly(o-methoxyaniline) (POMA) field-effect transistor. The device was prepared using Al-Si/SiO2/(interdigitated gold lines array)/POMA structure as the gate electrode, insulating layer, source-drain electrodes, and active layer, respectively. A model is presented for the electrical characteristics of such a device that encompasses the disordered properties of the POMA, the source-drain electrical-field dependence of hole mobility, and the carrier and mobility gradients in directions perpendicular to the polymer–oxide interface. The fittings of source-drain current versus source-drain voltage, having as parameters the gate voltage, is in good agreement with the experimental data, and the dependence of both the carrier saturation velocity and of the carrier mobility with the gate voltage are obtained. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 74–78, 2005

Complex conductance,ae ⁄ (f) = ae0(f)+iae"(f), measurements of polyaniline/carnauba wax composites were carried out at room temperature in samples containing different amounts of PAni. While ae"(f) ever grows as a function of the frequency f;ae0(f) was observed to vary as f n (n … 1) in the high frequency domain, and to be frequency-independent for lower frequencies. This is the quasi-universal behavior characteristic of conduction in a disordered medium. Superposed on this, another signal was observed to occur, and the whole impedance response was then analysed in an Argand Diagram, disclosing an electrode process in series with the bulk one. An equivalent conductance expression was used to explain such electrical behavior, in which the bulk properties of the composite were represented through the Random Free Energy Barrier model, while the composite-electrode interface by a simple parallel combination of a capacitor and a resistor. From the theoretical fittings it was concluded that the increase of PAni concentration acts in the sense of increasing not only the sample conductance, but also the bulk capacitance. The separation of the bulk and the interface contributions was then achieved.

This article presents a novel radiochromic film for selective detection of low-medium (0–10 kGy) gamma radiation (60Co) doses. This dosimeter is based on a printed fluorescent multilayer structure comprising a paper substrate having layers of copper phthalocyanine (DY220) (a green emitter material) on the bottom, and layers of poly[2-methoxy-5(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) (a green-light absorber, red emitter, and radiation sensitive polymer) on the top. The effect of gamma radiation on the optical properties of DY220/MEH-PPV was described: it was observed as a strong correlation between radiation dose and fluorescent, color coordinates for CIE (1931) chromatic diagram, and Pantone color reference of the dosimeter. The rate of these changes can be altered by manipulation of top–bottom layers to represent easily the radiation dose to be determined in a wide range. This versatile dosimeter has many uses in the field of food radiation for monitoring, quality assurance, and control of the gamma radiation process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45729.

In this work the electron spin resonance (ESR) and electron detected magnetic resonance (EDMR) are applied in MH-PPV and MEH-PPV, respectively. The ESR measurements revealed that there is a change of lineshape and a clear reduction of spin density on MH-PPV degraded by light and air. This result is in agreament with the fact that the spin density resides predominantly on vinylic carbon. The EDMR measurements in MEH-PPV LEDs provided evidences that there is a spin-dependent fusion of two polarons to spinless bipolaron.

In this paper we present the photoconduction effect of the poly( p -phenylenevinylene) (PPV) and its derivative, the poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] (MH-PPV). The structures used to study photoconductivity were prepared using solutions of either PPV-precursor in methanol or MH-PPV in chloroform, both spin-coated on an interdigitated chromium-gold line array previously deposited onto glass substrate. Currents vs. voltage curves were carried out as well as of the films optical characteristics have been studied by UV-Vis, and photoluminescence and eletroluminescent spectroscopies.

In this paper we study the photo-oxidation phenomenon in the structure of a PPV derivative, the poly[(2-methoxy-5-hexyloxy)- p -phenylenevinylene] - (MH-PPV), using ellipsometry and infrared spectroscopy techniques. Ellipsometric measurements were carried out in MH-PPV films previously exposed to light irradiation in air. It was observed a variation of both real and imaginary components of the refractive index. These variations are related with the replacement of the vinyl C=C bounds by the carbonyl C=O bounds, as confirmed by the infrared absorption measurements.

The photodegradation of soluble electroluminescent polymers is one of the greatest problems to be overcome in order to improve their technological applications. Here we will report on preliminary evaluation of the effects of commonly used solvents on the photodegradation of poly(3-methoxy-5-dodecyloxy- p -phenylene-vinylene), MD-PPV. We prepared solutions of similar concentration of MD-PPV in different solvents and recorded the ultraviolet-visible spectra before and after the exposure to a 250 mW/cm 2 light intensity. Also, we prepared cast films with the same solutions (with similar thickness) in order to observe if the solvent also affects the properties of the films. The results showed that the solvent polarity seems to be not the unique factor affecting the photodegradation, since no direct correlation could be made. Among the solvents tested, tetrahydrofuran was the best solvent for preparing films in order to minimize the photodegradation process.

A report is made of Langmuir film of a new semi-amphiphilic alternating N-hexylpyrrole-thiophene AB copolymer (PHPT) that is amenable to transfer as Langmuir–Blodgett (LB) films. PHPT was synthesized by condensation copolymerization via Stille coupling between N-hexyl-2,5-bis(trimethylstannyl)pyrrole and 2,5-dibromothiophene in the presence of Pd(PPh3)2Cl2 as a catalyst in dry DMF and characterized with various analytical techniques. In contrast to homopolymers (e.g. poly(N-alkylpyrrole)s and poly(3-alkylthiophene)s), PHPT formed a reasonably stable monolayer, as inferred through surface pressure and surface potential isotherms, and Brewster angle microscopy (BAM). The dependence of monolayer characteristics on the spreading volume, subphase temperature and compression speeds was also investigated. Electrical characterization revealed the possibility of using PHPT LB films as gas sensors.

Optical absorption and fluorescence measurements have been done on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]/[aluminum-tris(8-hydroxyquinoline)] solutions. The authors show that there is a visible response that covers the electronic absorption of bilirubin ( 350 – 500 nm ) , and hence, this material is applicable for managing the radiation doses planning before treatment of jaundice of neonates, which is one of the most common reasons of hospital readmission of newborns infants. The results show that the material presents a gradation of color from orange to yellow clearly, while its peak position emission shifts from orange-red ( λ max = 571 nm ) to green ( λ max = 540 nm ) with the radiation exposure time. The rate of these changes can be altered by manipulations of organic solution concentration and they are usually slow (from 2 to 8 h ), suggesting these color and emission changes can be used to design an easy to make, easy to read, easy to operate, low cost ( US $0.50) and accuracy for individual monitoring indicator dosimeter in order to represent easily the radiation exposure time usually used in management of neonatal jaundice.

The ac complex conductivity σ*(f) of polyaniline (PAN) films at different doping levels and different temperatures, in the 1–100 KHz frequency range, are reported. The results are typical of a disordered medium where the real component of ac conductivity is frequency independent at low frequencies, rising for higher values of frequencies. In order to interpret both the real and the imaginary components of σ*(f), we developed a model which considers the doped PAN as a disordered insulating matrix, sprinkled with conductive islands generated by doping, as indicated by energy dispersed x-ray microanalysis. The conduction through the insulating matrix obeys the random free energy barrier model, while in the conductive islands a metallic frequency-independent conductivity is considered. From the fittings we obtained the activation energy value of the maximum energy barrier of the doping mechanism and estimated the concentration of hopping sites.

This paper presents a methodology for the preparation of a-HgI2 by Physical Vapor Transport and of PbI2 crystals using the Bridgman technique. The results of the growth of HgI2 diluted in PbI2 by the Bridgman technique are shown for the first time, its limit of solubility having been determined at 600 ppm of HgI2 in the PbI2 matrix. Optical absorption, photoluminescence and electrical conductivity measurements show that the crystals prepared are of good crystalline quality.

The control of the photo degradation of a fluorene–vinylene–phenylene based-polymer, poly(9,9-di-hexylfluorenediylvinylene- alt -1,4-phenylenevinylene) (LaPPS16) was achieved by addition of a radical scavenger (RS) (enhancing photo resistance) or a radical initiator (RI) (reducing photo resistance). Photoluminescence, UV–Vis absorption, 1 H NMR spectroscopies and gel permeation chromatography (GPC) revealed that the incorporating small amounts of RS or RI is an efficient way to control the rates of the photo-oxidation reactions, and thus to obtain the conjugated polymer with foreseeable degradation rates for applications in blue-light sensitive detectors for neonatal phototherapy.

In this paper, we report our experimental design in searching a smart and easy-to-read dosimeter used to detect 6MV X-rays for improving patient safety in radiation oncology. The device was based on an organic emissive solutions of poly(2-methoxy-5(2′-ethylhexyloxy)- p -phenylenevinylene) (MEH-PPV), aluminum-tris-(8-hydroxyquinoline) (Alq 3 ) and additive components which were characterized by UV–Vis absorption, photoluminescence and CIE color coordinate diagram. The optical properties of MEH-PPV/Alq 3 solutions have been examined as function of radiation dose over the range of 0–100Gy. It has shown that MEH-PPV/Alq 3 solutions are specifically sensitive to X-rays, since the effect of radiation on this organic system is strongly correlated with the efficient spectral overlap between Alq 3 emission and the absorption of degraded MEH-PPV, which alters the color and photoemission of MEH-PPV/Alq 3 mixtures from red to yellow, and then to green. The rate of this change is more sensitive when MEH-PPV/Alq 3 is irradiated in the presence of benzoyl peroxide than when in the presence of hindered phenolic stabilizers, respectively, an accelerator and an inhibitor to activate or inhibit free radical formation. This gives rise to optimize the response curve of the dosimeter. It is clear from the experimental results that organic emissive semiconductors have potential to be used as dedicated and low-cost dosimeters to provide an independent check of beam output of a linear accelerator and therefore to give patients the opportunity to have information on the dose prescription or equipment-related problems a few minutes before being exposed to radiation.

In this work we investigate the radio-degradation of MEH-PPV polymer film as a tool for measuring high doses of gamma radiation. In order to produce film samples with thickness in the micron range, we have mixed the photoluminescent poly(2-methoxy-5(2'-ethylhexyloxy)-p-phenylenevinylene) copolymer (MEH-PPV) with a biodegradable poly(butylene adipate-co-terephthalate) copolymers (PBAT). The system was irradiated with a Co-60 source with doses ranging from 1 to 1,000 kGy. Ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopy have been used to investigate the radiation induced changes in the absorption and photon-emission spectra of the irradiated samples. Results indicate that the PL emission intensity varies exponentially with the applied gamma radiation dose for doses ranging from 30 to 500 kGy. The unambiguous relationship between PL & Dose together with the good flexibility of the copolymer films indicate that MEH-PPV/PBAT blends have great potential for applications in high gamma dose dosimetry.

A novel approach for studying the thermal conversion of poly-p-xylylidene tetrahydrothiophenium chloride (PTHT) into poly(p-phenylenevinylene) (PPV) films has been proposed on the basis of calculated optical parameters. Spin-cast PTHT films were thermally converted into partially conjugated PPV films over conversion temperatures ranging from 22 °C to 200 °C. A strong correlation between refractive index (n) and damping constant extinction coefficient (k) was verified by spectroscopic ellipsometry (SE) for the films studied in the visible range of energy. The conversion temperature has a strong influence on the values of n and k, which were theoretically modeled using a Lorentz harmonic oscillator analysis. The films were also studied by spectroscopic techniques (photoluminescence, FTIR, and UV–VIS), and it was verified that the values of n decrease with increasing the amount of C C groups present along the polymer chains, as a strong evidence that both structure and optical properties of thermally converted PPV films can be directly compared. The optical properties of the PPV films were also compared with those of two electroluminescent derivatives in which side chains are introduced into the phenyl ring of PPV, poly(2-methoxy-5-hexyloxy)-p-phenylenevinylene) (MH-PPV) and poly(3-methoxy-5-dodecyloxy-p-phenylene–vinylene) (MD-PPV).

Neste trabalho são apresentadas a fabricação e a caracterização óptica de um novo detector de raios X para monitoramento da dose nos processos de radioterapia empregando fótons de alta energia (6,0 MV). O dispositivo foi fabricado a partir de materiais orgânicos luminescentes consolidados como elemento ativo de displays eletroluminescentes nanoestrurados, mas que, até esse momento, têm sido pouco investigados como detectores de radiação ionizante. Para tanto, foram preparadas soluções à base de tris(8-hidroxiquinolato) de alumínio - Alq3 e poli(2-metóxi-5-(2-etilhexiloxi)-pfenilenovinileno) – MEH-PPV, cujo espectro de emissão do primeiro material se sobrepõe ao de absorção do segundo. Os resultados obtidos mostram que os espectros de emissão do sistema MEH-PPV/Alq3 desloca-se do vermelho-laranja (λmax = 598 nm) para o verde (λmax = 545 nm) quando a dose de radiação vai de 0 a 100 Gy. Essa mudança, consequência da degradação induzida pela radiação do MEH-PPV, foi usada no desenvolvimento de dosímetros para possível futura aplicação no controle do tratamento de pacientes oncológicos. In this work it is presented the characterization and fabrication of a novel ionizing radiation detector for high energy photon beam (6.0 MV). It is used organic luminescent materials usually applied in light-emitting and nanostructure device, but still few explored in radiation dosimetry. Organic solutions of tris(8-hydroxyquinolinato) aluminum - Alq3 and poly[2-methoxy-5-(2’-ethylhexyloxy)-p-phenylene vinylene] - MEH-PPV were prepared to better study the impact of spectral overlap between the Alq3 emission and MEH-PPV absorption. It is observed a blue-shift on the photoluminescence of the MEH-PPV/Alq3 solution system from red-orange (λmax = 598 nm) to green (λmax = 545 nm) when the radiation dose changes from 0 to 100 Gy. This effect is attributed to the photoxidation process of MEH-PPV and was employed to design dose accumulation detector in order to represent easily the radiation dose for cancer treatment.

We report on the design, fabrication and performance of a poly (2-methoxy-5(2_-ethylhexyloxy)- p-phenylenevinylene)/tris-(8-hydroxyquinoline)aluminum (MEH-PPV/Alq3) X-ray dose detector for improving safety for cancer patients shortly before radiation therapy. The detector consists of an inexpen-sive (

We report on the investigations about the modification of optical properties induced by X-rays onto film detectors of cadmium tungstate (CdWO4), poly[2-methoxy-5(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) and polystyrene (PS) This device takes advantage of reduction of spectral overlap between the radioluminescence (RL) of CdWO4 and the absorption of MEH-PPV as it is exposed to radiation, forming the basis of a new dosimeter that is capable of converting the orange-red radioluminescence of PS:MEH-PPV:CdWO4 into green. We propose an explanation of the optical processes occurring in MEH-PPV:CdWO4 in terms of the radiation hardness of CdWO4 combined to the RL-induced degradation of MEH-PPV.

A fototerapia com luz azul (460 nm - 490 nm) é o procedimento mais utilizado para o tratamento da icterícia em recém-nascidos. Contudo, dois fatores alteraram drasticamente a eficiência desse tratamento: (1) o espectro da fonte luminosa e (2) a dose de radiação absorvida pelos neonatos. Este trabalho apresenta o desenvolvimento de detectores de radiação orgânicos e flexíveis, de baixo custo, de bom desempenho e de fácil operação para monitoramento da radiação incidente em neonatos ictéricos sob tratamento fototerápico. O princípio de funcionamento dos dispositivos baseia-se na resposta óptica de filmes finos à base de dois materiais orgânicos luminescentes: o tris (8-hidroxiquinolinato de alumínio) - Alq3 e o poli[2-metóxi-5-(2’-etilóxi)-p-fenilenovinileno] - MEH-PPV, dispersos em matriz de poliestireno – PS sob efeito de luz azul. Os resultados obtidos mostram que a radiação atua no sentido de alterar a intensidade de máxima emissão do vermelho ao verde, passando pelo amarelo, dos filmes de PS/MEH-PPV/Alq3. Esse resultado é atribuído à fotodegradação do MEH-PPV e, consequentemente, as mudanças na sobreposição entre os espectros de emissão do Alq3 e de absorção desse polímero. A resposta óptica dos filmes com a radiação foi usada para fabricar um sensor orgânico flexível, inédito e de custo inferior a R$ 0,50, para controle das condições de exposição de neonatos ictéricos à fototerapia com luz azul. Blue-light therapy (460 nm - 490 nm) is the most common treatment of jaundice in newborns. However, the efficiency of this treatment is dependent of two factors: (1) the spectrum of light source and (2) the delivered dose to the neonates. This work presents the development of a low-cost, flexible, good performance and an easy detector operation based on organic materials for evaluation of radiation dose delivered by the phototherapy units to jaundice newborns. The operation principles of the device is based on the optical response of poly [2-methoxy-5-(2’-ethylhexyloxy)-p-phenylene - MEH-PPV, tris (8-hydroxyquinolinato aluminum)-Alq3 and polystyrene-PS thin films under the effects of blue-light. It is observed that the optical response of the PS/MEH-PPV/Alq3 films changes from red to yellow, and then to green with the radiation exposure. It is attributed to the photodegradation process of MEH-PPV and also to the spectral overlap between the photoemission of Alq3 and the absorption of MEH-PPV. The optical response of PS/MEH-PPV/Alq3 films was used to develop a novel organic flexible and low cost (

Neste trabalho, é apresentado o desenvolvimento de um novo equipamento para fabricação de filmes finos orgânicos, baseado na tecnologia automotiva de injeção eletrônica. Tal sistema apresenta, dentre as vantagens de disponibilidade comercial e baixo custo, baixas taxas de corrosão química e de problemas de entupimento dos bicos injetores, bem como o controle de taxas de temperatura de deposição. Portanto, apresenta versatilidade para utilização de diversas soluções orgânicas usadas em microeletrônica e eletrônica orgânica, tais como Fotoresistes e polímeros semicondutivos, como o poli(etileno-dioxitiofeno) - PEDOT. Ensaios obtidos com esses materiais mostram que o desempenho do sistema proposto depende de parâmetros como frequência da válvula injetora, diâmetro do orifício ejetor, pressão aplicada na solução impressa e das características da superfície dos substratos, que influenciam diretamente na qualidade dos filmes obtidos. This paper presents the development of a new equipment for manufacturing organic thin-films based on the technology of electronic fuel injection. This system presents, among the advantages of commercial availability and low cost, low rates of chemical corrosion and problems of nozzle clogging, as well as a temperature rate control system for material deposition. Thus, the developed equipment presents the versatility of using several organic solutions, such as Photoresistes and semiconducting polymers, for microelectronic and organic electronics, such as polyethylenedioxythiophene - PEDOT. Tests obtained with these materials show that system performance depends of parameters such as frequency of the injector valve, ejector orifice diameter, pressure applied in the printed solution and the substrates surface characteristics that influence directly in the quality of films obtained.