Carlos J. R. Silva

Organic–inorganic hybrid sol–gel coatings for metal corrosion protection: a review of recent progress

Abstract This paper is a review of the most recent and relevant achievements (from 2001 to 2013) on the development of organic–inorganic hybrid (OIH) coatings produced by sol–gel-derived methods to improve resistance to oxidation/corrosion of different metallic substrates and their alloys. This review is focused on the research of OIH coatings based on siloxanes using the sol–gel process conducted at an academic level and aims to summarize the materials developed and identify perspectives for further research. The fundamentals of sol–gel are described, including OIH classification, the interaction with the substrate, their advantages, and limitations. The main precursors used in the synthesis of OIH sol–gel coatings for corrosion protection are also discussed, according to the metallic substrate used. Finally, a multilayer system to improve the resistance to corrosion is proposed, based on OIH coatings produced by the sol–gel process, and the future research challenges are debated.

A novel class of luminescent polymers obtained by the sol–gel approach

A series of amorphous Eu3+-doped hybrid organic/inorganic materials prepared by the sol–gel process is presented. The host matrix of the so-called ureasils is a silica network to which oligopolyoxyethylene chains are grafted by means of urea bonds. Trivalent europium is present as a triflate salt, Eu(CF3SO3)3. Four different compositions of salt have been considered: n=184, 92, 55 and 37, where n represents the number of (OCH2CH2) polymer repeat units per ion group of Eu(CF3SO3)3. Infrared spectroscopic studies suggest that the doped ureasils contain both free and coordinated triflate ions. The lowest decomposition temperature (about 250°C) occurs with composition n=92. This composition also exhibits the highest conductivity at room temperature (approximately 10−5 Ω−1 cm−1). The photoluminescence spectra of these materials present a series of narrow lines assigned to 5D0→7F0,1,2,3,4 transitions. The high emission intensity observed is a promising property for application of the ureasils in technological luminescent devices.

C-Reactive Protein: Clinical and Epidemiological Perspectives

An important etiopathogenic component of cardiovascular disease is atherosclerosis, with inflammation being an essential event in the pathophysiology of all clinical pictures it comprises. In recent years, several molecules implicated in this process have been studied in order to assess cardiovascular risk in both primary and secondary prevention. C-reactive protein is a plasmatic protein of the pentraxin family and an acute phase reactant, very useful as a general inflammation marker. Currently, it is one of the most profoundly researched molecules in the cardiovascular field, yet its clinical applicability regarding cardiovascular risk remains an object of discussion, considered by some as a simple marker and by others as a true risk factor. In this sense, numerous studies propose its utilization as a predictor of cardiovascular risk through the use of high-sensitivity quantification methods for the detection of values <1 mg/L, following strict international guidelines. Increasing interest in these clinical findings has led to the creation of modified score systems including C-reactive protein concentrations, in order to enhance risk scores commonly used in clinical practice and offer improved care to patients with cardiovascular disease, which remains the first cause of mortality at the worldwide, national, and regional scenarios.

Differential capacitance of liquid/liquid interfaces: effect of electrolytes present in each phase

The effect of electrolyte type and concentration on the differential capacitance of the 1,2-dichloroethane/water interface has been measured. The results show that the differential capacitance is controlled by the pair ion (1)–counter-ion (2), where 1 and 2 denote the different phases. At constant organic electrolyte composition the capacity increases in the order, F– MTMA+ > TBA+ > TOA+, TPB– > TCPB–. In very dilute solutions, the effects are not noticeable.

Preparative effects on poly(ethylene oxide) based polymer electrolytes of lanthanide salts

Abstract A series of solid polymer electrolytes prepared from commercial poly(ethylene oxide) and lanthanide triflates (La 3+ , Nd 3+ and Eu 3+ ), in which the salt ions are solubilised by complexation with the oxygen atoms in the flexible polymer molecule, has been studied using ac conductivity and thermal analysis measurements. Two techniques, solvent casting and hot-pressing, were applied to produce a range of polymer electrolyte compositions. The differences in the behaviour of electrolytes produced using these two preparative techniques have been justified in terms of partial decomposition of the electrolytes, the effects of chain entanglement and the presence of residual solvent molecules increasing the free volume of the polymer chains.

Conductivity studies of a polymer electrolyte based on europium trifluoromethanesulphonate

Abstract An electrolyte prepared from poly(ethylene oxide) and europium trifluoromethanesulphonate has been studied using ac conductivity and thermal techniques. The results obtained indicate that the levels of ionic conductivity registered in this system are not markedly different from other multivalent ion based electrolytes. A pseudo-equilibrium phase diagram, constructed on the basis of optical microscopy and differential scanning calorimetry (DSC) experiments, demonstrates that this system has a notably large amorphous window.

The study of a lanthanum triflate based polymer electrolyte using electrochemical and thermal techniques

Abstract Ionic conductivity, differential thermal analysis and optical microscopy studies have been carried out on polymer electrolytes obtained from the addition of lanthanum trifluoromethanesulphonate to commercial poly (ethylene oxide). The combination of information from the techniques used allows the form of the pseudo-equilibrium phase diagram of this system to be determined.

Efficient dispersion of multi-walled carbon nanotubes in aqueous solution by non-covalent interaction with perylene bisimides

A selection of bolaamphiphilic perylene bisimides (PBI) were prepared from the reaction of perylenetetracarboxylic dianhydride with α-amino acids. These molecules were obtained in good yield using a simple synthetic protocol and avoiding the need for complex purification methods, a major advantage for future applications. Carbon nanotubes (CNT) were dispersed in an aqueous solution of the PBI, buffered at pH 7, and the suspension was studied by absorption and emission spectroscopy. PBI functionalized with Boc-lysine and phenylalanine led to an excellent suspension of CNT in water, stable for at least 24 h at room temperature. Theoretical calculations were used to support and explain the experimental observations.

Fast and fully reversible photochromic performance of hybrid sol–gel films doped with a fused-naphthopyran

A new type of photochromic naphthopyran with a fused structure was embedded in an organic–inorganic amine–alcohol–silicate hybrid gel producing colourless, transparent and flexible photochromic films. Under UV-vis light these materials developed, in less than 30 s, intense yellow-orange colours that faded completely in the dark in 3 min. This behaviour contrasts with the usual performance of common naphthopyrans that always generate two coloured species which fade with different kinetics, leading to the formation of a residual colour that persists for several minutes/hours. The structural design of this new naphthopyran prevents the formation of the long-lived coloured species and therefore fully reversible photo-switchable materials can be easily obtained.

The use of thermal techniques in the determination of the phase diagram of lanthanide salt based polymer electrolytes

Differential thermal analysis, optical microscopy and ionic conductivity studies have been carried out on polymer electrolyte films prepared by deposition of solutions of neodymium trifluoromethanesulphonate and poly(ethylene oxide). A wide range of electrolyte concentrations were examined and a partial pseudo-equilibrium phase diagram of the system was determined. From the results obtained it is evident that the presence of relatively high concentrations of ionic guest species in the polymer host results in an inhibition of the growth of crystalline material (polymer spherulites or a polymer—salt coordination complex).ZusammenfassungDurch Abscheidung der Lösungen von Neodymtrifluormethansulfonat und Poly (ethylenoxid) wurden Polymer-Elektrolytfilme hergestellt, die als Untersuchungsobjekt für DTA-, Lichtmikroskopie- und Ionenleitfähigkeitsuntersuchungen dienten. Dabei wurde ein breiter Bereich für die Elektrolytkonzentration untersucht und ein partielles Pseudogleichgewichts-Phasendiagramm des Systemes erstellt. Aus den Resultaten ist ersichtlich, daß die Gegen-wart von relativ hohen Konzentrationen von ionischen Gastspezies in den polymeren Wirtspezies zu einer Hemmung des Wachstumes des kristallinen Materiales (polymere Sphärolithe oder ein Polymer—Salz Koordinationskomplex) führt.