Erratum: Influence of oxygen plasma treatment parameters on poly(vinylidene fluoride) electrospun fiber mats wettability

Electrospun poly(vinylidene fluoride) (PVDF) fiber mats find applications in an increasing number of areas, such as battery separators, filtration and detection membranes, due to their excellent properties. However, there are limitations due to the hydrophobic nature and low surface energy of PVDF. In this work, oxygen plasma treatment has been applied in order to modify the surface wettability of PVDF fiber mats and superhydrophilic PVDF electrospun membranes have been obtained. Further, plasma treatment does not significantly influences fiber average size (~400 ± 200 nm), morphology, electroactive -phase content (~80-85%) or the degree of crystallinity (Xc of 42 ± 2%), allowing to maintain the excellent physical-chemical characteristics of PVDF. Plasma treatment mainly induces surface chemistry modifications, such as the introduction of oxygen and release of fluorine atoms that significantly changes polymer membrane wettability by a reduction of the contact angle of the polymer fibers and an overall decrease of the surface tension of the membranes.

Characterization of physical, mechanical and chemical properties of quiscal fibres : the influence of atmospheric DBD plasma treatment

This paper reports the first attempt of characterizing various physical, mechanical and chemical properties of Quiscal fibres, used by the native communities in Chile and investigating the influence of atmospheric dielectric barrier discharge plasma treatment on various properties such as diameter and linear density, fat, wax and impurity%, moisture regain, chemical elements and groups, thermal degradation, surface morphology, etc. According to the experimental observations, Quiscal fibre has lower tenacity than most of the technical grade natural fibres such as sisal, hemp, flax, etc., and plasma treatment at optimum dose improved its tenacity to the level of sisal fibres. Plasma treatment also reduced the amount of fat, wax and other foreign impurities present in Quiscal fibres as well as removed lignin and hemicellulose partially from the fibre structure. Plasma treatment led to functionalization of Quiscal fibre surface with chemical groups, as revealed from attenuated total reflection spectroscopy and also confirmed from the elemental analysis using energy dispersive Xray technique and pH and conductivity measurements of fibre aqueous extract. The wetting behavior of Quiscal fibre also improved considerably through plasma treatment. However, untreated and plasma treated Quiscal fibres showed similar thermal degradation behavior, except the final degradation stage, in which plasma treated fibres showed higher stability and incomplete degradation unlike the untreated fibres. The experimental results suggested that the plasma treated Quiscal fibres, like other technical grade natural fibres, can find potential application as reinforcement of composite materials for various industrial applications.

Effect of chemical and plasma DBD treatments on pseudostem plantain fiber properties

Las fibras del seudotallo de plátano (FSP) fueron modificadas mediante epiclorhidrina (EP), anhídrido acético (AA), y su combinación (AA_EP), y con plasma a tres descargas de barrera dieléctrica (DBD) 1, 3 y 6 kW min m-2. Las FSP tratadas y sin tratar fueron caracterizadas mediante espectroscopia infrarroja por la transformada de Fourier (FT-IR), termogravimetría (TGA), microscopía electrónica de barrido (SEM) y pruebas mecánicas de tensión y de humectabilidad. Los espectros FT-IR, las micrografías SEM, y el análisis TGA indicaron pérdidas de lignina, hemicelulosa, impurezas y ceras. Estos efectos en conjunto con las reacciones de grupos OH y -C-C-, con los tratamientos químicos y de plasma respectivamente, incrementaron la hidrofobicidad de las FSP tratadas. Los tratamientos químicos produjeron reacciones de esterificación, eterificación y entrecruzamiento de los grupos OH libres en las FSP, lo que hizo que mostraran mayor rigidez que las expuestas al plasma. Las micrografías SEM mostraron que las FSP expuestas al plasma quedaron con superficie más irregular y rugosa que la de las FSP tratadas químicamente. La humectabilidad de las fibras, medida mediante pruebas de ángulo de contacto, se redujo como consecuencia de ambos tratamientos, característica importante para un relleno en los materiales compuestos.

Does nitrogen availability have greater control over the formation of tropical heath forests than water stress?A hypothesis based on nitrogen isotope ratios

Global scale analyses of soil and foliage δ15N have found positive relationships between δ15N and ecosystem N loss (suggesting an open N cycle) and a negative relationship between δ15N and water availability. We show here that soils and leaves from tropical heath forests are depleted in 15N relative to 'typical' forests suggesting that they have a tight N cycle and are therefore limited by N rather than by, often suggested, water availability.

Intermetallic layer formation and influence in solder joints reliability

Dissertação de mestrado integrado em Materials Engineering

Characterization of physical, mechanical and chemical properties of quiscal fibres: the influence of atmospheric dbd plasma treatment

This paper reports the first attempt of characterizing several physical, mechanical and chemical properties of Quiscal fibres, usually used by the native communities in Chile and on investigations concerning the influence of atmospheric dielectric barrier discharge (DBD) plasma treatment on various properties such as diameter and linear density, percent of impurity, moisture regain, chemical elements and groups, thermal degradation, surface morphology, among others.

A systematic study of the structural and magnetic properties of Mn-, Co-, and Ni-Doped Colloidal Fe3O4 nanoparticles

A series of colloidal MxFe3-xO4 (M = Mn, Co, Ni; x = 0–1) nanoparticles with diameters ranging from 6.8 to 11.6 nm was synthesized by hydrothermal reaction in aqueous medium at low temperature (200 °C). Energy-dispersive X-ray microa-nalysis and inductively coupled plasma spectrometry confirms that the actual elemental compositions agree well with the nominal ones. The structural properties of obtained nanoparticles were investigated by using powder X-ray diffraction, Raman scattering, Mössbauer spectroscopy, and electron microscopy. The results demonstrate that our synthesis technique leads to the formation of chemically uniform single-phase solid solution nanoparticles with cubic spinel structure, confirming the intrinsic doping. Magnetic studies showed that, in comparison to Fe3O4, the saturation magnetization of MxFe3-xO4 (M = Mn, Ni) decreases with increasing dopant concentration, while Co-doped samples showed similar saturation magnetizations. On other hand, whereas Mn- and Ni-doped nanoparticles exhibits superparamagnetic behavior at room temperature, ferromagnetism emerges for CoxFe3-xO4 nanoparticles, which can be tuned by the level of Co doping.

O estudo da aplicação de acabamentos funcionais de barreira UV em fibras previamente ativadas por plasma

Tese de Doutoramento Engenharia Têxtil

Antibacterial Ag/a-C nanocomposite coatings: The influence of nano-galvanic a-C and Ag couples on Ag ionization rates

Biofilm formation has been pointed as a major concern in different industrial applications, namely on biomedical implants and surgical instruments, which has prompted the development of new strategies for production of efficient antimicrobial surfaces. In this work, nano âgalvanic couples were created to enhance the antibacterial properties of silver, by embedding it into amorphous carbon (a-C) matrix. The developed Ag/a-C nanocomposite coatings, deposited by magnetron sputtering, revealed an outstanding antibacterial activity against S.epidermidis, promoting a total reduction in biofilm formation with no bacteria counts in all dilution. The open circuit potential (OCP) tests in 0.9% NaCl confirmed that a-C shows a positive \OCP\ value, in contrast to Ag coating, thus enhancing the ionization of biocidal Ag+ due to the nano-galvanic couple activation. This result was confirmed by the inductively coupled plasma-optical emission spectroscopy (ICP-OES), which revealed a higher Ag ionization rate in the nanocomposite coating in comparison with the Ag coating. The surface of Ag/a-C and Ag coatings immersed in 0.9% NaCl were monitored by scanning electron microscopy (SEM) over a period of 24 hours, being found that the Ag ionization determined by ICP-OES was accompanied by an Ag nanoparticles coalescence and agglomeration in Ag/a-C coating.

Plasma levels of immunoinflammatory markers in De Novo coronary atherosclerosis and coronary restenosis postangioplasty

OBJECTIVE: To compare circulating plasma levels of immunoinflammatory markers in patients with known de novo coronary artery disease and patients with postangioplasty restenosis. METHODS: Using enzymatic immunoabsorbent assay, we measured plasma levels of soluble interleukin-2 receptosr, tumor necrosis factor alpha, and soluble tumor necrosis alpha receptors I and II in 11 patients with restenosis postcoronary angioplasty (restenosis group), in 10 patients with primary atherosclerosis (de novo group) who were referred for coronary angiography because of stable or unstable angina, and in 9 healthy volunteers (control group). Levels of soluble interleukin-2 receptors were significantly higher in the de novo group compared with that in the restenosis and control groups. Levels were also higher in the restenosis group compared with that in the control group. Plasma levels of tumor necrosis alpha and receptor levels were significantly higher in the de novo group compared to with that in the restenosis and control groups, but levels in the restenosis group were not different from that in the controls. CONCLUSION: Coronary artery disease, either primary or secondary to restenosis, is associated with significant immunoinflammatory activity, which can be assessed by examining the extent of circulating plasma levels of inflammatory markers. Moreover, patients with de novo lesions appear to have increased inflammatory activity compared with patients with restenosis.

Antibacterial properties of multifunctional coatings Ag-ZrCN for biomedical devices: a novel approach

PhD in Sciences Specialty in Physics

Acabamentos funcionais têxteis aplicados por estamparia digital em substratos têxteis ativados por plasma

Tese de Doutoramento em Engenharia Têxtil

Analysis of Plasma Homocysteine Levels in Patients with Unstable Angina

OBJECTIVE - To determine the prevalence of hyperhomocystinemia in patients with acute ischemic syndrome of the unstable angina type. METHODS - We prospectively studied 46 patients (24 females) with unstable angina and 46 control patients (19 males), paired by sex and age, blinded to the laboratory data. Details of diets, smoking habits, medication used, body mass index, and the presence of hypertension and diabetes were recorded, as were plasma lipid and glucose levels, C-reactive protein, and lipoperoxidation in all participants. Patients with renal disease were excluded. Plasma homocysteine was estimated using high-pressure liquid chromatography. RESULTS - Plasma homocysteine levels were significantly higher in the group of patients with unstable angina (12.7±6.7 µmol/L) than in the control group (8.7±4.4 µmol/L) (p<0.05). Among males, homocystinemia was higher in the group with unstable angina than in the control group, but this difference was not statistically significant (14.1±5.9 µmol/L versus 11.9±4.2 µmol/L). Among females, however, a statistically significant difference was observed between the 2 groups: 11.0±7.4 µmol/L versus 6.4±2.9 µmol/L (p<0.05) in the unstable angina and control groups, respectively. Approximately 24% of the patients had unstable angina at homocysteine levels above 15 µmol/L. CONCLUSION - High homocysteine levels seem to be a relevant prevalent factor in the population with unstable angina, particularly among females.

Lipid peroxidation and nitric oxide inactivation in postmenopausal women

OBJECTIVE: To assess the effect of endogenous estrogens on the bioavailability of nitric oxide (·NO) and in the formation of lipid peroxidation products in pre- and postmenopausal women. METHODS: NOx and S-nitrosothiols were determined by gaseous phase chemiluminescence, nitrotyrosine was determined by ELISA, COx (cholesterol oxides) by gas chromatography, and cholesteryl linoleate hydroperoxides (CE18:2-OOH), trilinolein (TG18:2-OOH), and phospholipids (PC-OOH) by HPLC in samples of plasma. RESULTS: The concentrations of NOx, nitrotyrosine, COx, CE18:2-OOH, and PC-OOH were higher in the postmenopausal period (33.8±22.3 mM; 230±130 nM; 55±19 ng/mL; 17±8.7 nM; 2775±460 nM, respectively) as compared with those in the premenopausal period (21.1±7.3 mM; 114±41 nM; 31±13 ng/mL; 6±1.4 nM; 1635±373 nM). In contrast, the concentration of S-nitrosothiols was lower in the postmenopausal period (91±55 nM) as compared with that in the premenopausal p in the premenopausal period (237±197 nM). CONCLUSION: In the postmenopausal period, an increase in nitrotyrosine and a reduction of S-nitrosothiol formation, as well as an increase of COx, CE18:2-OOH and PC-OOH formation occurs. Therefore, •NO inactivation and the increase in lipid peroxidation may contribute to endothelial dysfunction and to the greater risk for atherosclerosis in postmenopausal women.