Rodrigo S. Neves

Electrochemical immittance spectroscopy applied to the study of the single crystal gold/aqueous perchloric acid interface

The technique of electrochemical immittance spectroscopy has been used for characterisation of the interface at gold single crystal electrodes in aqueous solutions of perchloric acid in the absence of Faradaic processes. The results obtained for low index crystallographic orientations, namely, (100), (110) and (111) are compared to those obtained earlier for the (210) orientation. The experimental results are analysed by fitting them to a simple equivalent circuit consisting of a resistor in series with a constant phase element representing respectively, the solution resistance, Rs, and the distributed impedance of the double layer, ZCPE. The dependence of the parameters constituting the constant phase element, namely the pre-exponential factor, Y0, and the fractional exponent, nf, on the orientation of the electrode surface, on the electrode potential and on the solution concentration are discussed. The relationship of these parameters to the surface energy of the single crystals is discussed.

Characterisation of Au(111) and Au(210) ∣ aqueous solution interfaces by electrochemical immittance spectroscopy

Abstract Gold single crystals oriented to expose the (111) and (210) faces were investigated using electrochemical immittance spectroscopy (EIS) in aqueous solutions of HClO 4 and KF in the double layer region with the aim of identifying and explaining the frequency dispersion of interfacial capacitance known as constant phase angle (CPA) dispersion. Au(111) and Au(210) were chosen as representing the whole range of variance of electrochemical properties of Au( hkl ) electrodes. Au(111) as the most uniform, microscopically smooth surface behaved with almost ideal capacitance in HClO 4 solutions in the whole potential range and also in KF solutions, in that case with the exception of potentials well positive to the potential of zero charge (pzc). Au(210) being microscopically the most corrugated surface displayed significant CPA dispersion in both electrolytes. In HClO 4 , dispersion on Au(210) occurred mostly in the potential region slightly positive to the potential of zero charge where the capacitance hump of the Helmholtz layer appeared. Analogous dispersion occurred on Au(210) in KF solutions only at high concentrations. The behaviour closest to ideal, dispersionless behaviour was always observed at sufficiently negative potentials. In KF solutions at positive potentials dispersion on both electrodes may be attributed to the adsorption (OH − , HF). In the intermediate potential range, close to the Helmholtz capacitance hump it can be attributed to solvent-metal interactions. Dispersion was lower in well conducting (concentrated) electrolytes and this suggests its geometrical nature is related possibly to the fractal pattern of the structured solvent.

Liposuction Induces a Compensatory Increase of Visceral Fat Which Is Effectively Counteracted by Physical Activity: A Randomized Trial

CONTEXT Liposuction is suggested to result in long-term body fat regain that could lead to increased cardiometabolic risk. We hypothesized that physical activity could prevent this effect. OBJECTIVE Our objective was to investigate the effects of liposuction on body fat distribution and cardiometabolic risk factors in women who were either exercise trained or not after surgery. DESIGN, SETTING, AND PARTICIPANTS Thirty-six healthy normal-weight women participated in this 6-month randomized controlled trial at the University of Sao Paulo, Sao Paulo, Brazil. INTERVENTIONS Patients underwent a small-volume abdominal liposuction. Two months after surgery, the subjects were randomly allocated into two groups: trained (TR, n = 18, 4-month exercise program) and nontrained (NT, n = 18). MAIN OUTCOME MEASURES Body fat distribution (assessed by computed tomography) was assessed before the intervention (PRE) and 2 months (POST2), and 6 months (POST6) after surgery. Secondary outcome measures included body composition, metabolic parameters and dietary intake, assessed at PRE, POST2, and POST6, and total energy expenditure, physical capacity, and sc adipocyte size and lipid metabolism-related gene expression, assessed at PRE and POST6. RESULTS Liposuction was effective in reducing sc abdominal fat (PRE vs. POST2, P = 0.0001). Despite the sustained sc abdominal fat decrement at POST6 (P = 0.0001), the NT group showed a significant 10% increase in visceral fat from PRE to POST6 (P = 0.04; effect size = -0.72) and decreased energy expenditure (P = 0.01; effect size = 0.95) when compared with TR. Dietary intake, adipocyte size, and gene expression were unchanged over time. CONCLUSION Abdominal liposuction does not induce regrowth of fat, but it does trigger a compensatory increase of visceral fat, which is effectively counteracted by physical activity.

Electropolymerization Studies of PAni/(poly)luminol Over Platinum Electrodes

This work presents a cyclic voltammetry study of the polyaniline/polyluminol copolymer on platinum electrodes. The results show that under determined conditions it is possible to obtain the copolymer deposited on a metallic surface. The luminol presence clearly affects the oxidation of aniline in the nucleation process and, additionally, changes the cyclic voltammetric characteristics of the obtained material. In this aspect, the copolymer presents hybrid characteristics when compared to the polyaniline and polyluminol separately obtained and seems to present intermediary conductivity.

Monte Carlo simulation of the adsorption of phenol on gold electrodes: a simple model

Canonical Monte Carlo simulations, at 298 K, of the adsorption of phenol in a dilute aqueous solution on gold electrodes, at the potential of zero charge, are presented. The results suggest that the process occurs in two distinct and successive steps. Adsorption starts with the phenol oxygen atom pointing towards the gold surface and the aromatic ring in a quasi-perpendicular orientation relative to the surface. This is followed by the reorientation of the aromatic ring to a parallel configuration. The effect of the solvent is analyzed through the calculation of the potential of mean force acting on phenol. Despite the simplicity of the model and the interaction potentials used in the simulations, the results are in good agreement with experimental observations, giving insight into the microscopic details of the adsorption process of phenol at low concentrations.

Electrochemical Behaviour of the AA2024 Aluminium Alloy Modified with Self-Assembled Monolayers/Polyaniline Double Films

The electrochemical characteristics of the AA2024 aluminium alloy modified with octadecyltrimethoxysilane (ODTMS) + polyaniline (PANi) and propiltrimethoxysilane (PTMS) + (PANi) were studied in the present work. The results show that the different protective coatings shift the values of corrosion and pit potentials to more positive values making the system nobler and indicate that the double film ODTMS + PANi present the best protection against corrosion characteristics, that is probably due to the two contributions: anodic protection associated with the barrier effect.

A time saving algorithm for the Monte Carlo method of Metropolis

A time saving algorithm for the Monte Carlo method of Metropolis is presented. The technique is tested with different potential models and number of particles. The coupling of the method with neighbor lists, linked lists, Ewald sum and reaction field techniques is also analyzed. It is shown that the proposed algorithm is particularly suitable for computationally heavy intermolecular potentials.

Corrosion Protection of AA7075 Aluminium Alloy by Trimethoxy-Silanes Self-Assembled Monolayers

This study presents electrochemical data concerning the aluminium alloy AA7075 surface modified by self-assembled monolayers (SAMs) of octadecyl-trimethoxy-silane and propyl-trimethoxy-silane. Polarisation curves have shown SAMs blocking effect, as they partially block the oxygen reduction reaction and displace the corrosion potential to positive values. Electrochemical impedance spectroscopy experiments have suggested that the protective effect comes from the oxide layer stabilization by the organic monolayers, which block the corroding species diffusion to the surface. These results show the potential of using methoxy-silanes SAMs as corrosion protective coatings; however, they are also indicative of the superior octadecyl-trimethoxy-silane protective characteristics.

Characterization of Polyaniline-Based Blends, Composites, and Nanocomposites

Polyaniline (PANI) and its blends, composites, and nanocomposites are promising systems for development of materials with enhanced characteristics, such as, conductivity, processability, thermal stability, mechanical strength, important for their applications such as electromagnetic interference shielding, protection against corrosion, antistatic coating, to mention few. Nanoscale characterization techniques have been used to study the properties of PANI blends, composites, and nanocomposites aiming to improve their specific features and to expand the field of their application. The main limitation for a massive application of PANI is related to the formation of nitrogen-containing by-products that are normally formed during the synthesis via chemical reactions while other PANI synthesis methods result in a very low PANI yield. In this chapter the main techniques to measure the relevant properties of PANI are exposed.