Laser microstructuring for fabricating superhydrophobic polymeric surfaces

In this paper we show the fabrication of hydrophobic polymeric surfaces through laser microstructuring. By using 70-ps pulses from a Q-switched and mode-locked Nd:YAG laser at 532 nm, we were able to produce grooves with different width and separation, resulting in square-shaped pillar patterns. We investigate the dependence of the morphology on the surface static contact angle for water, showing that it is in agreement with the Cassie-Baxter model. We demonstrate the fabrication of a superhydrophobic polymeric surface, presenting a water contact angle of 157 degrees. The surface structuring method presented here seems to be an interesting option to control the wetting properties of polymeric surfaces. (C) 2010 Elsevier B.V. All rights reserved.

CONTRA: Improving the performance of dynamic investigations in natural abundance organic solids by mirror-symmetric constant-time CODEX

We present a minor but essential modification to the CODEX 1D-MAS exchange experiment. The new CONTRA method, which requires minor changes of the original sequence only, has advantages over the previously introduced S-CODEX, since it is less sensitive to artefacts caused by finite pulse lengths. The performance of this variant, including the finite pulse effect, was confirmed by SIMPSON calculations and demonstrated on a number of dynamic systems. (C) 2007 Elsevier Inc. All rights reserved.

Experimental and theoretical investigation of molecular structure and conformation of the 4-isopropylthioxanthone

In this study, the molecular structure and conformational analyses of the 4-isopropylthioxanthone (4-ITX) are reported according to experimental and theoretical results. The compound crystallizes in the centrosymmetric P (1) over bar space group with only one molecule in the asymmetric unit, presenting the most stable conformation, in which the three fused-rings adopt a planar geometry, and the isopropyl group assumes a torsional angle with less sterical hindrance. The structural and conformational analyses were performed using theoretical calculations such as Hartree-Fock (HF), DFT method in combination with 6-311G(d,p) and 6-31++G(d,p) and the results were compared with infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The supramolecular assembly of 4-ITX is kept by non-classical C-H center dot center dot center dot O hydrogen bonds and weak interactions such as pi-pi stacking. 4-ITX was also studied by (1)H and (13)C NMR spectroscopy. UV-Vis absorption spectroscopic properties of the 4-ITX showed the long-wavelength maximum shifts towards high energy when the solvent polarity increases. (C) 2011 Elsevier B.V. All rights reserved.

Hybrid materials from intermolecular associations between cationic lipid and polymers

Intermolecular associations between a cationic lipid and two model polymers were evaluated from preparation and characterization of hybrid thin films cast on silicon wafers. The novel materials were prepared by spin-coating of a chloroformic solution of lipid and polymer on silicon wafer. Polymers tested for miscibility with the cationic lipid dioctadecyldimethylammonium bromide (DODAB) were polystyrene (PS) and poly(methyl methacrylate) (PMMA). The films thus obtained were characterized by ellipsometry, wettability, optical and atomic force microscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and activity against Escherichia coli. Whereas intermolecular ion-dipole interactions were available for the PMMA-DODAB interacting pair producing smooth PMMA-DODAB films, the absence of such interactions for PS-DODAB films caused lipid segregation, poor film stability (detachment from the silicon wafer) and large rugosity. In addition, the well-established but still remarkable antimicrobial DODAB properties were transferred to the novel hybrid PMMA/DODAB coating, which is demonstrated to be highly effective against E. coli.

Excited-State Dynamics in fac-[Re(CO)(3)(Me(4)phen)(L)](+)

Excited-state dynamics in fac-[Re(CO)(3)(Me(4)phen)(cis-L)](+) (Me(4)phen = 3,4,7,8-tetramethyl-1,10-phenanthroline, L = 4-styrylpyridine (stpy) or 1,2-bis(4-pyridyl)ethylene (bpe)) were investigated by steady-state and time-resolved techniques. A complex equilibrium among three closely lying excited states, 3IL(cis-L), (3)MLCT(Re -> me4phen), and (3)IL(Me4phen), has been established. Under UV irradiation, cis-to-trans isomerization of coordinated cis-L is observed with a quantum yield of 0.15 in acetonitrile solutions. This photoreaction competes with radiative decay from (3)MLCT(Re -> Me4phen) and (3)IL(Me4phen) excited states, leading to a decrease in the emission quantum yield relative to the nonisomerizable complex fac-[Re(CO)(3)(Me(4)phen)(bpa)](+) (bpa = 1,2-bis(4-pyridyl)ethane). From temperature-dependent time-resolved emission measurements in solution and in poly(methyl methacrylate) (PMMA) films, energy barriers (Delta E(a)) for interconversion between (3)MLCT(Re -> me4Phen) and (3)IL(Me4phen) emitting states were determined. For L = cis-stpy, Delta E(a) = 11 (920 cm(-1)) and 15 kJ mol(-1) (1254 cm(-1)) in 5:4 propionitrile/butyronitrile and PMMA, respectively. For L = cis-bpe, Delta E(a) = 13 kJ mol(-1) (1087 cm(-1)) in 5:4 propionitrile/butyronitrile. These energy barriers are sufficient to decrease the rate constant for internal conversion from higher-lying (3)IL(me4phen) state to (3)MLCT(Re -> Me4phen), k(i) congruent to 10(6) s(-1). The decrease in rate allows for the observation of intraligand phosphorescence, even in fluid medium at room temperature. Our results provide additional insight into the role of energy gap and excited-state dynamics on the photochemical and photophysical properties of Re(I) polypyridyl complexes.

Evaluation of the light polymerization efficiency of copolymers used in dental formulations by differential scanning calorimetry

Different compositions of visible-light-curable triethylene glycol dimethacrylate/bisglycidyl methacrylate copolymers used in dental resin formulations were prepared through copolymerization photoinitiated by a camphorquinone/ethyl 4-dimethylaminobenzoate system irradiated with an Ultrablue IS light-emitting diode. The obtained copolymers were evaluated with differential scanning calorimetry. From the data for the heat of polymerization, before and after light exposure, obtained from exothermic differential scanning calorimetry curves, the light polymerization efficiency or degree of conversion of double bonds was calculated. The glass-transition temperature also was determined before and after photopolymerization. After the photopolymerization, the glass-transi-tion temperature was not well defined because of the breadth of the transition region associated with the properties of the photocured dimethacrylate. The glass-transition temperature after photopolymerization was determined experimentally and compared with the values determined with the Fox equation. In all mixtures, the experimental value was lower than the calculated value. Scanning electron microscopy was used to analyze the morphological differences in the prepared copolymer structures. (C) 2007 Wiley Periodicals, Inc.

Evaluation of Postpolymerization as a Function of the Storage Time of Triethylene Glycol Dimethacrylate/2,2-Bis[4-(2-Hydroxy-3-Methacryloxy-Prop-1-Oxy)-Phenyl]-propane Bisphenyl-alpha-Glycidyl Ether Dimethacrylate Copolymers Used in Dental Resins by Differential Scanning Calorimetry and Dynamic Mechanical Analysis

The aim of this work was to evaluate the effect of the storage time on the thermal properties of triethylene glycol dimethacrylate/2,2-bis[4-(2-hydroxy-3-methacryloxy-prop-1-oxy)-phenyl]propane bisphenyl-alpha-glycidyl ether dimethacrylate (TB) copolymers used in formulations of dental resins after photopolymerization. The TB copolymers were prepared by photopolymerization with an Ultrablue IS light-emitting diode, stored in the dark for 160 days at 37 degrees C, and characterized with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared spectroscopy with attenuated total reflection. DSC curves indicated the presence of an exothermic peak, confirming that the reaction was not completed during the photopolymerization process. This exothermic peak became smaller as a function of the storage time and was shifted at higher temperatures. In DMA studies, a plot of the loss tangent versus the temperature initially showed the presence of two well-defined peaks. The presence of both peaks confirmed the presence of residual monomers that were not converted during the photopolymerization process. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 679-684, 2009

Desenvolvimento de redes de polímeros interpenetrantes (IPN) para a aplicação como eletrólito polimérico

Uma nova rede de polímeros interpenetrantes (IPN) baseada em poliuretana de óleo de mamona e poli(etileno glicol) e poli(metacrilato de metila) foi preparada para ser utilizada como eletrólito polimérico. Os seguintes parâmetros de polimerização foram avaliados: massa molecular do poli(etileno glicol) (PEG), concentração de PEG e concentração de metacrilato de metila. As membranas de IPN foram caracterizadas por calorimetria diferencial de varredura (DSC) e espectroscopia de infravermelho por transformada de Fourier (FT-IR). Os eletrólitos de redes de polímeros interpenetrantes (IPNE) foram preparados a partir da dopagem com sal de lítio através do inchamento numa solução de 10% em massa de LiClO4 na mistura de carbonato de etileno e carbonato de propileno na razão mássica de 50:50. As IPNEs foram caracterizadas por espectroscopia de impedância eletroquímica e Raman. As IPNEs foram testadas como eletrólito polimérico em supercapacitores. As células capacitivas foram preparadas utilizando eletrodos de polipirrol (PPy). Os valores de capacitância e eficiência foram calculados por impedância eletroquímica, voltametria cíclica e ciclos galvonostáticos de carga e descarga. Os valores de capacitância obtidos foram em torno de 90 F.g-1 e eficiência variou no intervalo de 88 a 99%. Os valores de densidade de potência foram superiores a 250 W.kg-1 enquanto que a densidade de energia variou de 10 a 33 W.h.kg-1, dependendo da composição da IPNE. As características eletroquímicas do eletrólito formado pela IPN-LiClO4 (IPNE) foram comparadas aos eletrólitos poliméricos convencionais, tais como poli(difluoreto de vinilideno)-(hexafluorpropileno) ((PVDF-HFP/LiClO4) e poliuretana comercial (Bayer desmopan 385) (PU385/LiClO4). As condutividades na temperatura ambiente foram da ordem de 10-3 S.cm-1. A capacitância da célula utilizando eletrodos de PPy com eletrólito de PVDFHFP foi de 115 F.g-1 (30 mF.cm-2) e 110 F.g-1 (25 mF.cm-2) para a célula com PU385 comparadas a 90 F.g-1 (20 mF.cm-2) para a IPNE. Os capacitores preparados com eletrólito de IPNE apresentaram valores de capacitância inferior aos demais, entretanto provaram ser mais estáveis e mais resistentes aos ciclos de carga/descarga. A interpenetração de duas redes poliméricas, PU e PMMA produziu um eletrólito com boa estabilidade mecânica e elétrica. Um protótipo de supercapacitor de estado sólido foi produzindo utilizando eletrodos impressos de carbono ativado (PCE) e o eletrólito polimérico de IPNE. A técnica de impressão de carbono possui várias vantagens em relação aos outros métodos de manufatura de eletrodos de carbono, pois a área do eletrodo, espessura e composição são variáveis que podem ser controladas experimentalmente. As células apresentaram uma larga janela eletroquímica (4V) e valores da capacitância da ordem de 113 mF.cm-2 (16 F.g-1). Métodos alternativos de preparação do PCE investigados incluem o uso de IPNE como polímero de ligação ao carbono ativado, estes eletrodos apresentaram valores de capacitância similares aos produzidos com PVDF. A influência do número de camadas de carbono usadas na produção do PCE também foi alvo de estudo. Em relação ao eletrólito polimérico, o plastificante e o sal de lítio foram adicionados durante a síntese, formando a IPNGel. As células apresentaram alta capacitância e boa estabilidade após 4000 ciclos de carga e descarga. As membranas de IPN foram testadas também como reservatório de medicamento em sistemas de transporte transdérmico por iontoforese. Os filmes, mecanicamente estáveis, formaram géis quando inchado em soluções saturadas de lidocaina.HCl, anestésico local, em propileno glicol (PG), poli(etileno glicol) (PEG400) e suas misturas. O grau de inchamento em PG foi de 15% e 35% em PEG400. Agentes químicos de penetração foram utilizados para diminuir a resistência da barreira causada pela pele, dentre eles o próprio PG, a 2-pirrolidinona (E1) e a 1-dodecil-2-pirrolidinona (E2). Os géis foram caracterizados por espectroscopia de impedância eletroquímica e transporte passivo e por iontoforese através de uma membrana artificial (celofane). O sistema IPN/ lidocaina.HCl apresentou uma correlação linear entre medicamento liberado e a corrente aplicada. Os melhores resultados de transporte de medicamento foram obtidos utilizando o PG como solvente.

Desevolvimento de nanocompósitos de poli(metacrilato de metila)/argila processados por mistura no estado fundido

Poly(methyl methacrylate)/clay nanocomposites were prepared by melt mixing using a montmorillonite-rich clay (MMT). The clay in natura was treated with acrylic acid to facilitate the dispersion in the polymer matrix. A masterbatch of PMMA/clay was prepared and combined with the pure PMMA and then subjected to extrusion process using singlescrew and twin-screw extruders followed by injection. Nanocomposites were processed with clay contents of 1, 3, 5 and 8 wt.%. The effect of shear processing on the morphology of the nanocomposites was evaluated by XRD, SEM and TEM. Thermal and mechanical properties of the nanocomposites were investigated through TGA, DSC, HDT, VICAT, tensile and impact tests, to evaluate the effect of the addition of clay to the PMMA matrix. Flammability tests were also conducted to investigate the effect of the addition of clay on the flame retardation properties. SEM images of the nanocomposites indicated the presence of clay agglomerates, which resulted in the reduction of properties such as thermal stability, mechanical strength and impact resistance, and increased the rate of burning for materials processed by both extrusion routes

Degradação do PMMA através da reação despolimerização uitlizando catalisadores de óxidos mistos

In this work, mixed oxides were synthesized by two methods: polymeric precursor and gel-combustion. The oxides, Niquelate of Lanthanum, Cobaltate of Lanthanum and Cuprate of Lanthanum were synthesized by the polymeric precursor method, and treated at 300 º C for 2 hours, calcined at 800 º C for 6h in air atmosphere. In gel-combustion method were produced and oxides using urea and citric acid as fuel, forming for each fuel the following oxides Ferrate of Lanthanum, Cobaltato of Lanthanum and Ferrato of Cobalt and Lanthanum, which were submitted to the combustion process assisted by microwave power maximum of 10min. The samples were characterized by: thermogravimetric analysis, X-ray diffraction; fisisorção of N2 (BET method) and scanning electron microscopy. The reactions catalytic of depolymerization of poly (methyl methacrylate), were performed in a reactor of silica, with catalytic and heating system equipped with a data acquisition system and the gas chromatograph. For the catalysts synthesized using the polymeric precursor method, the cuprate of lanthanum was best for the depolymerization of the recycled polymer, obtaining 100% conversion in less time 554 (min), and the pure polymer, was the Niquelate of Lanthanum, with 100% conversion in less time 314 (min). By gel-combustion method using urea as fuel which was the best result obtained Ferrate of Lanthanum for the pure polymer with 100% conversion in less time 657 (min), and the recycled polymer was Cobaltate of Lanthanum with 100 % conversion in less time 779 (min). And using citric acid to obtain the best result for the pure polymer, was Ferrate of Lanthanum with 100% conversion in less time 821 (min and) for the recycled polymer, was Ferrate of Lanthanum with 98.28% conversion in less time 635 (min)

Estudo morfológico da blenda polimérica poli(metacrilato de metila)/poli(tereftalato de etileno) reciclado (PMMA/PET)

Among the options for plastics modification more convenient, both from a technical-scientific and economic, is the development of polymer blends by processing in the molten state. This work was divide into two stages, with the aim to study the phase morphology of binary blend PMMA / PET blend and this compatibilized by the addition of the poly(methyl methacrylate-co-glycidyl methacrylate-co-ethyl acrylate) copolymer (MMA-GMA-EA). In the first stage is analyzed the morphology of the blend at a preliminary stage where we used the bottle-grade PET in a Haake torque rheometer and the effect of compatibilizer in this blend was evaluated. In the second stage the blend was processed using the recycled PET in a single screw extruder and subsequently injection molding in the shape of specimens for mechanical tests. In both stages we used a transmission electron microscopy (TEM) to observe the morphologies of the samples and an image analyzer to characterize them. In the second stage, as well as analysis by TEM, tensile test, scanning electron microscopy (SEM) and atomic force microscopy (AFM) was performed to correlate the morphology with the mechanical properties. The samples used in morphological analyzes were sliced by cryo-ultramicrotomy technique for the analysis by TEM and the analysis by SEM and AFM, we used the flat face of the block after cut cryogenic. It was found that the size of the dispersed phase decreased with the addition of MMA-GMA-EA in blends prepared in a Haake. In the tensile test, the values of maximum tensile strength and modulus of elasticity is maintained in a range between the value of pure PMMA the pure PET, while the elongation at break was influenced by the composition by weight of the PMMA mixture. The coupling agent corroborated the results presented in the blend PMMA / PETrec / MMA-GMA-EA (80/15/5 %w/w), obtained by TEM, AFM and SEM. It was concluded that the techniques used had a good morphologic correlation, and can be confirmed for final analysis of the morphological characteristics of the blends PMMA / PET

Efeito da adição dos azocorantes DR73 e DB79 nas propriedades do poli(metacrilato de metila)

Currently new polymeric materials have been developed to replace other of traditionally materials classes. The use of dyes allows to expand and to diversify the applications in the polymeric materials development. In this work the behavior and ability of azo dyes Disperse Blue 79 (DB79) and Disperse Red 73 (DR73) on poly(methyl methacrylate) (PMMA) were studied. Two types of mixtures were used in the production of masterbatches: 1) rheometer 2) solution. Processing by extrusion-blow molding of PMMA was carried out in order to evaluate the applications of polymeric films. Thermal analysis were performed by thermogravimetry to evaluate polymer and azo dyes thermal stability. Colorimetric analysis were obtained through monitoring the spectral variations associated with sys/trans/anti azo dyes isomerization process Colorimetric data were treated and evaluated in accordance to the color system RGB and CIEL*ab, by monitoring the color change as function of time. Mechanical properties, characterized by tensile tests, were evaluated and correlated with the presence and content of azo dyes in the samples. Analyses by scanning electronic microscopy (SEM) were performed on the surfaces of samples to check the azo dye dispersion after the mixing process. It was concluded that the production of PMMA/azo dyes is possible and feasible, and the mixtures produced had synergy of properties for use in various applications

Simulador radiográfico antropomórfico de mama humana

Mammography is a diagnostic imaging method in which interpretation depends on knowledge of radiological aspects as well as the clinical exam and pathophysiology of breast diseases. In this work a mammography phantom was developed to be used for training in the operation of mammographic x-ray equipment, image quality evaluation, self-examination and clinical examination of palpation. Polyurethane was used for the production of the phantoms for its physical and chemical properties and because it is one of the components normally used in prostheses. According to the range of flexibility of the polyurethane, it was possible to simulate breasts with higher or lower amount of adipose tissue. Pathologies such as areolar necrosis and tissue rejection due to surgery reconstruction after partial mastectomy were also simulated. Calcifications and nodules were simulated using the following materials: polyethylene, poly (methyl methacrylate), polyamide, polyurethane and poly (dimethyl silicone). Among these, polyethylene was able to simulate characteristics of calcification as well as breast nodules. The results from mammographic techniques used in this paper for the evaluation of the phantoms are in agreement with data found in the literature. The image analyses of four phantoms indicated significant similarities with the human skin texture and the female breast parenchyma. It was possible to detect in the radiographic images produced regions of high and low radiographic optical density, which are characteristic of breasts with regions of different amount of adipose tissue. The stiffnesses of breast phantoms were adjusted according to the formulation of the polyurethane which enabled the production of phantoms with distinct radiographic features and texture similar to human female breast parenchyma. Clinical palpation exam of the phantoms developed in this work indicated characteristics similar to human breast in skin texture, areolar region and parenchyma

Processamento e caracterização de compósitos Poli(METACRILATO DE METILA)/Sílica (PMMA/SiO2)

Currently the search for new materials with properties suitable for specific applications has increased the number of researches that aim to address market needs. The poly (methyl methacrylate) (PMMA) is one of the most important polymers of the family of polyacrylates and polymethacrylates, especially for its unique optical properties and weathering resistance, and exceptional hardness and gloss. The development of polymer composites by the addition of inorganic fillers to the PMMA matrix increases the potential use of this polymer in various fields of application. The most commonly used inorganic fillers are particles of silica (SiO2), modified clays, graphite and carbon nanotubes. The main objective of this work is the development of PMMA/SiO2 composites at different concentrations of SiO2, for new applications as engineering plastics. The composites were produced by extrusion of tubular film, and obtained via solution for application to commercial PMMA plates, and also by injection molding, for improved the abrasion and scratch resistance of PMMA without compromising transparency. The effects of the addition of silica particles in the polymer matrix properties were evaluated by the maximum tensile strength, hardness, abrasion and scratch resistance, in addition to preliminary characterization by torque rheometry and melt flow rate. The results indicated that it is possible to use silica particles in a PMMA matrix, and a higher silica concentration produced an increase of the abrasion and scratch resistance, hardness, and reduced tensile strength

Influência de tratamentos térmicos no comportamento mecânico da blenda poli(metacrilato de metila) / poli(tereftalato de etileno) reciclado

Studies indicate that a variation in the degree of crystallinity of the components of a polymer blend influences the mechanical properties. This variation can be obtained by subjecting the blend to heat treatments that lead to changes in the spherulitic structure. The aim of this work is to analyze the influence of different heat treatments on the variation of the degree of crystallinity and to establish a relationship between this variation and the mechanical behavior of poly(methyl methacrylate)/poly(ethylene terephthalate) recycled (PMMA / PETrec) with and without the use of compatibilizer agent poly(methyl methacrylate-al-glycidyl methacrylate-al-ethyl acrylate) (MMAGMA- EA). All compositions were subjected to two heat treatments. T1 heat treatment the samples were treated at 130 ° C for 30 minutes and cooled in air. In T2, the samples were treated at 230 ° C for 5 minutes and cooled to approximately -10 ° C. The variation of the degree of crystallinity was determined by the proportional relationship between crystallinity and density, with the density measured by pycnometry. The mechanical behavior was verified by tensile tests with and without the presence of notches and pre-cracks, and by method of fracture toughness in plane strain (KIC). We used the scanning electron microscopy (SEM) to analyze the fracture surface of the samples. The compositions subjected to heat treatment T1, in general, showed an increase in the degree of crystallinity in tensile strength and a tendency to decrease in toughness, while compositions undergoing treatment T2 showed that the opposite behavior. Therefore, this work showed that heat treatment can give a polymer blend further diversity of its properties, this being caused by changes in the crystal structure