Vesicle-micelle transition in aqueous mixtures of the cationic dioctadecyldimethylammonium and octadecyltrimethylammonium bromide surfactants

The vesicle-micelle transition in aqueous mixtures of dioctadecyldimethylammonium and octadecyltrimethylammonium bromide (DODAB and C18TAB) cationic surfactants, having respectively double and single chain, was investigated by differential scanning calorimetry (DSC), steady state fluorescence, dynamic light scattering (DLS) and surface tension. The experiments performed at constant up to 1.0 mM total surfactant concentration reveal that these homologue surfactants mix together to form either mixed vesicles and/or micelles, or both of these structures in equilibrium, depending on the relative amount of the surfactants. The main transition melting temperature Tm of the mixed DODAB-C18TAB vesicles is larger than that for the neat DODAB in water owing to the incorporation of C18TAB in the vesicle bilayer, however, little amount of C18TAB having a minor effect on the Tm of DODAB. The surface tension decreases sigmoidally with C18TAB concentration and the inflection point lies around xDODAB ≈ 0.4, indicating the onset of micelle formation owing to saturation of DODAB vesicles by C18TAB molecules and formation of vesicle structures. At low C18TAB concentrations When xDODAB > 0.5 C18TAB molecules are mainly solubilized by the vesicles bilayers, while at high C18TAB concentrations but when xDODAB < 0.25 micelles are dominant. Fluorescence data of the Nile Red probe incorporated in the system at different surfactant molar fractions indicate the formation of micelle and vesicle structures. These structures have apparent hydrodynamic radius RH of about 180 and 500-800 nm, respectively, as obtained by DLS measurements.Fundação para a Ciência e a Tecnologia (FCT

Microscopy techniques for dye distribution in DSCs nanocrystalline TiO2 films

Capture of sunlight has attracted an increasing interest in the scientific community and triggered the development of efficient and cheap photovoltaic devices. Amongst recent generation technologies for solar energy conversion, dye-sensitized solar cells (DSCs) show an optimal trade-off between high-conversion efficiency and low-cost manufacturing. For the last two decades, significant progress has been made and best energy conversion efficiency of the DSC at the laboratory scale has surpassed 12% [1]. A lot of work has focused on the enlargement of surface areas to enhance the amount of adsorbed dyes by reduction of nanoparticle sizes or utilization of novel structures. Nevertheless there remain some crucial details of DSC operation for which limited information is available, namely dye diffusion and adsorption, surface coverage and dye distribution throughout the nc-TiO2 film. Microprobe techniques can be powerful tools to evaluate the dye load, the dye distribution and dye depth profile in sensitized films. Electron Probe Microanalysis (EPMA) and Ion Beam Analytical (IBA) techniques using a micro-ion beam, namely micro-Particle Induced X-ray Emission ( PIXE) and Rutherford Backscattering Spectrometry (RBS), were used to quantify and to study the distribution of the ruthenium organometallic (N719) dye in TiO2 films, profiting from the different penetration depth and beam sizes of each technique. Two different types of films were prepared and sensitized, mesoporous nanoparticles and 1D nanostructured TiO2 films (figure 1). Despite the low concentration of Ru, the high sensitive analytical techniques used allowed to assess the Ru surface distribution and depth profile. Fig. 2 shows the PIXE maps of Ru and Ti indicating an homogeneous surface distribution. The same figure presents the RBS spectra obtained with a 2 MeV proton beam of the same sample showing that a good spectra fit is obtained considering only two sample layers: the first one with a 1.7 ìm thickness; the second one being the SiO2 substrate. The Ru RBS signal also shows that the dye has an homogeneous depth distribution. Due to the fine spatial resolution of the EPMA/WDS (Wavelength Dispersive Spectroscopy) technique it was possible to visualise the dye distribution in sample cross-section (with micrometer or submicrometer dimensions) as presented in Fig. 3 for the elemental mapping of a mesoporous nanoparticle TiO2 film. Dye load evaluation by two different techniques (ìPIXE and EPMA/WDS) provided similar results (Ru/Ti values around 0.5 %). The distribution analysis of the organometallic dye (N719) was done through ruthenium distribution via X-ray mapping. RBS was used to assess the ruthenium depth profile. This assessment can lead to a better understanding of the device performance

Valorisation of polyolefins into magnetic carbon nanotubes: application as catalysts in wet peroxide oxidation of paracetamol

This work deals with the application of magnetic carbon nanotubes (MCNTs) in the catalytic wet peroxide oxidation (CWPO) of paracetamol (PCM), a pharmaceutical compound selected as model contaminant of emerging concern (CEC). MCNTs were synthetized by catalytic chemical vapor deposition (CCVD) at 850 ºC, considering low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) as carbon precursors representative of urban plastic solid waste. Magnetite supported in alumina (Fe3O4@Al2O3) nanoparticles previously synthesized by sol-gel were used as catalysts in the CCVD process. The synthesized MCNTs were tested in the CWPO of PCM at 80 ºC, monitoring during 24 h the concentration of H2O2, PCM, Total Organic Carbon (TOC) and aromatic compounds. All MCNT catalysts show activity allowing to decompose completely the pharmaceutical in aqueous solutions after 360 min. In particular, the MCNTs synthesized from HDPE lead to complete removal of the pollutant after 30 min of reaction. By TOC analysis, it was observed that the CNTs led to obtain mineralization degrees higher than 38% of the pollutant after 24 h. Aromaticity test indicated that the catalyst prepared from HDPE promotes more degradation of the intermediates than the catalyst prepared from LDPE and PP.This work was financially supported by project "PLASTIC_TO_FUEL&MAT – Upcycling Waste Plastics into Fuel and Carbon Nanomaterials" (PTDC/EQU-EQU/31439/2017) and CIMO (UIDB/00690/2020) through FEDER under Program PT2020. Fernanda F. Roman acknowledges the national funding by FCT through the individual research grant SFRH/BD/143224/2019.info:eu-repo/semantics/publishedVersio

The use of the active methodology of teaching for braking study / O uso da metodologia ativa de ensino para o estudo da frenagem

Kinematics is one of the most studied concepts in physics because its understanding is connected with the description of movements without caring about its causes. This branch involves the greatnesses: speed, space traveled, time, acceleration, among others. This article studies an actual application of kinematics, in which a motorcyclist travels on an avenue and is alerted about a speed radar. This work has the main objective of designing a mobile application to establish if the rider meets the speed of up to 40 km / h on the avenue. The software elaborated besides contributing to the teaching learning of the one who executes it, solves a very common situation nowadays. Based on the specific analysis of the application, there have been cases in which vehicles travel with speed within the tolerance limit of the place

Emptying time of a swimming pool with cylindrical output duct calculated with practice by a software / Tempo de esvaziamento de uma piscina com duto de saída cilíndrico calculado com a prática por um software

The creation of new methodologies grows along with digital media as more and more solutions to problems encountered in engineering are required. This work has as main objective to develop an application to determine the necessary time of discharge of a fluid in a pool, since this can be established through the flow rate of the liquid in a permanent flow. Besides contributing to solve a problem found in the mechanics of fluids, the application ensures a more effective teaching-learning for the user who executes it. Some considerations have served to show that emptying of the industrial reservoir depends on some variables such as water column, reservoir base diameter, and fluid outlet duct. From the results obtained, it was observed that the larger the outlet duct diameter and, the lower the water column height, the shorter is the fluid emptying time in the pool

Dimensioning of parts exposed to the mechanical turning process through an application for mobile devices / Dimensionamento de peças expostas ao processo de torneamento mecânico através de uma aplicação para dispositivos móveis

The present article aims to study some common equations in calculations of the mechanical turning process, using active teaching-learning methodologies. Thus, this work has as main objective to develop an application to determine the various variables necessary for the dimensioning of the parts to be turned inside the machining. The expressions used in the application show the Cutting Speed, Advance per Rotation, and Cut Time. In addition to the great contribution to the teaching-learning of the user executing the application, it provides solutions to daily activities that involve these types of problems in Mechanical Engineering. From the obtained results, it was observed that the Cutting Speed, Rotation Advance and Cut Time presented modifications with variations of the properties connected to these cutting parameters

Software developed to calculate electric motor power / Software desenvolvido para calcular a potência do motor elétrico

The use of electric motors is common for many types of vehicles, from motorcycles to aircraft or large ships. The electric motor, also called an electric machine, serves to transform electrical energy into mechanical energy. The most commonly used type of electric motor is induction, which is used in almost any application, covering hostile environments, explosives, naval applications, among others. The use of the electric motor is defined from its power. Its determination depends on three important variables, being those the voltage, current, and efficiency. Therefore, the purpose of this work is to produce software for mobile devices to calculate the power of an electric motor. According to the results obtained, it is verified that the parameter analyzed presents several behaviors when related to its dependent parameters

Degradation of paracetamol by wet peroxide oxidation using carbon nanotubes synthesized from plastic solid waste

Within increased production and economic/social dependence of plastic utilization, an environmental problem has also emerged. In this scenario, plastic solid waste (PSW) recycling/management/recovery has become a problem of public concern, with a global generation estimated at 150 million tonnes per year. Materials produced from PSW can be classified as primary (performance/characteristics equivalent to virgin plastic), secondary (performance’s requirement lower than the original application), tertiary (PSW used as feedstock for the generation of chemicals and fuels), and quaternary (energy recovery via incineration) recycled materials [1]. For instance, pyrolysis of PSW has been extensively used for the thermochemical conversion of useless PSW into oil, gas, and carbon materials, thus classified as terciary recycled material.Adriano S. Silva thanks his doctoral Grant with reference SFRH/BD/151346/2021 financed by the Portuguese Foundation for Science and Technology (FCT), with funds from NORTE2020, under MIT Portugal Program. This work was financially supported by UIDB/05757/2020 (CeDRI), UIDB/00690/2020 (CIMO), LA/P/0045/2020 (ALiCE), UIDB/50020/2020, UI-DP/50020/2020 (LSRE-LCM) and funded by national funds through FCT/MCTES (PIDDAC). Fernanda F. Roman acknowledges the national funding by FCT through the individual research grant SFRH/BD/143224/2019info:eu-repo/semantics/publishedVersio

Development of a sequential injection system for the determination of nitrite and nitrate in waters with different salinity: Application to estuaries in NW Portugal

In this work, a sequential injection methodology for monitoring nitrite and nitrate in estuarine waters without any previous treatment is described. The developed system was applied to the measurement of nitrite and nitrate in estuarine waters of three rivers in the NW Portugal, allowing an automatic, fast (ca 60 h 1) and precise method (relative standard deviation lower than 2%). The procedure was based on the reaction between nitrite, sulfanilamide and N-(1-naphthyl)-ethylenediamine dihydrochloride (N1NED), whereas the determination of nitrate resulted from its reduction to nitrite, using an in-line cadmium column, followed by the same reaction. The samples were collected in three locations for each river (Douro, C avado and Ave) covering the lower, middle and upper section of the estuaries. Despite the presence of a salinity gradient, this parameter showed no interference in the accuracy of the determinations. The results obtained for the described method for nitrite were statistically comparable to those obtained by the reference procedure. For the determination of nitrate, recovery tests confirmed that the sequential injection methodology provided good quality results.info:eu-repo/semantics/publishedVersio