The Brazilian chemical community shows positive characteristics that improved significantly during the past forty years: the scientific output is substantial, it contributes positively to the ...position of this country in the innovation rankings, the chemical companies create and export technologies and the larger share of post-graduates employed by the Brazilian industry works in chemical or chemistry-based companies. The chemical sector is thus an exception within the country, together with agrosciences. These facts are unexpected, considering that chemical companies do not occupy leading positions in the rankings based on patent filing and other innovation indicators, throughout the world. This article describes the context of Brazilian chemistry in the middle 1970s, the the well-designed government actions that mobilized academic researchers and industry professionals to build complex converging scenarios and a positive S&T culture that is matched in few other areas, in this country.
Production of electricity by friction is well known but poorly understood, and is the source of electrostatic discharge causing serious accidents. Recent results are in agreement with one of the ...conflicting views on this problem, according to which triboelectricity in polymers is triggered by mechanochemical and wear or mass transfer phenomena. These results also challenge the widely accepted paradigm of one-way charge transfer that is the basis of the triboelectric series. Experimental results from powerful analytical techniques coupled to surface charge mapping support the following hypothesis: charge-bearing species are ionic polymer fragments formed through mechanical action. Beyond this, the atmosphere participates through tribocharge build-up and dissipation due to reactive plasma formation and charge exchange at the gas-solid interface, mediated by adsorption of non-neutral water, or ion partition during water adsorption, as in hygroelectricity phenomena.
Mechanochemical reactions during polymer friction or contact produce ionic fragments distributed on positive and negative domains at both surfaces.
Tribocharged polymers display macroscopically patterned positive and negative domains, verifying the fractal geometry of electrostatic mosaics previously detected by electric probe microscopy. Excess ...charge on contacting polyethylene (PE) and polytetrafluoroethylene (PTFE) follows the triboelectric series but with one caveat: net charge is the arithmetic sum of patterned positive and negative charges, as opposed to the usual assumption of uniform but opposite signal charging on each surface. Extraction with n-hexane preferentially removes positive charges from PTFE, while 1,1-difluoroethane and ethanol largely remove both positive and negative charges. Using suitable analytical techniques (electron energy-loss spectral imaging, infrared microspectrophotometry and carbonization/colorimetry) and theoretical calculations, the positive species were identified as hydrocarbocations and the negative species were identified as fluorocarbanions. A comprehensive model is presented for PTFE tribocharging with PE: mechanochemical chain homolytic rupture is followed by electron transfer from hydrocarbon free radicals to the more electronegative fluorocarbon radicals. Polymer ions self-assemble according to Flory–Huggins theory, thus forming the experimentally observed macroscopic patterns. These results show that tribocharging can only be understood by considering the complex chemical events triggered by mechanical action, coupled to well-established physicochemical concepts. Patterned polymers can be cut and mounted to make macroscopic electrets and multipoles.
Kelvin force microscopy measurements on films of noncrystalline silica and aluminum phosphate particles reveal complex electrostatic potential patterns that change irreversibly as the relative ...humidity changes within an electrically shielded and grounded environment. Potential adjacent to the particle surfaces is always negative and potential gradients in excess of ±10 MV/m are found parallel to the film surface. These results verify the following hypothesis: the atmosphere is a source and sink of electrostatic charges in dielectrics, due to the partition of OH− and H+ ions associated to water adsorption. Neither contact, tribochemical or electrochemical ion or electron injection are needed to change the charge state of the noncrystalline hydrophilic solids used in this work.
Human population growth and development has been largely dependent on non-renewable natural resources, which cannot be indefinitely sustained. Beyond, coal and other abundant resources cannot ...continue to be used at current rates due to their impact on the environment and climate. It is thus important to replace as much as possible the fossil fuels and scarce minerals as sources of energy and industrial raw materials. Biomass plays a key role in this scenario, since its availability depends on abundant but often misused resources: air, water, sunlight and land. The “oil shocks”, the recognition of impending resource shortages, the global pollution and climate change led many governments and organizations to create roadmaps to Bioeconomy. This includes the growing use of plants and animals to produce energy and raw materials, but it cannot create food scarcity. Agriculture depends on the plant macronutrients N, P and K, and this article discusses their role in plant and animal growth, production and consumption, dependence on non-renewable minerals and energy and perspectives for increasing their efficiency. Special attention is given to Brazilian agriculture that is heavily dependent on imported NPK, requiring strategic action and research.
Electric energy harvesting mediated by atmospheric humidity was first demonstrated in 2010, followed by the description of different approaches by many authors. Moisture-based energy-harvesting ...devices usually contain metals and/or are fabricated using nanomaterials and lithographic processes. Here we present a flexible energy harvesting device that is an asymmetric capacitor, formed by two electrodes made out of Kraft paper coated with exfoliated and reassembled graphite (ERG). The electrodes are doped with different chemicals and finished using standard papermaking processes. The voltage output of a single ERG-based hygroelectric generator (ERG-HEG) cell is as high as 0.5 V and it can deliver 250 nA of electric current through a 2 MΩ resistor, for days. The voltage and current outputs can be scaled up by connecting ERG-HEGs in series or parallel. Energy harvesting is also achieved by short (5 seconds) cyclic capacitor charge/discharge extending for more than two weeks. Examinaton of the electrodes during their operation, using Kelvin probe and microscopy analysis, showed that negative charge carriers are the main actors in the ERG-HEG devices. The low material cost, the simple fabrication processes and the energy output invite further development and scaling-up of this "green" alternative for producing electricity.
Converting humidity into useful electrical energy was only recently demonstrated and the improvements presented in this work are not only highly energy efficient, but also contributes to the development of scalable, real-world applications.
Catalytic Nanomotors: Self-Propelled Sphere Dimers Valadares, Leonardo F.; Tao, Yu-Guo; Zacharia, Nicole S. ...
Small (Weinheim an der Bergstrasse, Germany),
February 22, 2010, Volume:
6, Issue:
4
Journal Article
Peer reviewed
Experimental and theoretical studies of the self‐propelled motional dynamics of a new genre of catalytic sphere dimer, which comprises a non‐catalytic silica sphere connected to a catalytic platinum ...sphere, are reported for the first time. Using aqueous hydrogen peroxide as the fuel to effect catalytic propulsion of the sphere dimers, both quasi‐linear and quasi‐circular trajectories are observed in the solution phase and analyzed for different dimensions of the platinum component. In addition, well‐defined rotational motion of these sphere dimers is observed at the solution–substrate interface. The nature of the interaction between the sphere dimer and the substrate in the aqueous hydrogen peroxide phase is discussed. In computer simulations of the sphere dimer in solution and the solution–substrate interface, sphere‐dimer dynamics are simulated using molecular‐dynamics methods and solvent dynamics are modeled by mesoscopic multiparticle collision methods taking hydrodynamic interactions into account. The rotational and translational dynamics of the sphere dimer are found to be in good accord with the predictions of computer simulations.
Catalytic silica–platinum sphere‐dimer nanomotors in solution and nanorotors at the solid solution interface propelled by the decomposition of aqueous hydrogen peroxide on the platinum are probed experimentally and their motion is simulated theoretically for different dimensions of the platinum sphere component. The nature of the interaction between sphere dimer and substrate is analyzed and discussed.
The transition to sustainable standards of production and consumption within a scenario of decreased availability of natural resources, growing population and climate change is essential to meet ...current challenges facing mankind. A strategy to meet these challenges should contain elements different from current approaches for industrial production. This work concentrates on the possibilities for the intensive use of sustainable biomass, abundant minerals and every type of residue, a task that can largely benefit from the application of nanotechnology and biotechnology platforms for material design and transformation. This strategy cannot be solely based on existing knowledge and requires new science, new knowledge including supposedly well-known themes, like the tribochemistry of electrostatic charging and friction. It is especially relevant within the Brazilian context, where many recent successful innovations are related to biomass production and transformation. Implementation of this strategy requires converging efforts by personnel from many different organizations and professions, while making sound risk assessment to produce significant innovation leading to sustainable development.
CsPbX3 perovskite nanoplates (PNPLs) were formed in a synthesis driven by SnX4 (X=Cl, Br, I) salts. The role played by these hard Lewis acids in directing PNPL formation is addressed. Sn4+ disturbs ...the acid–base equilibrium of the system, increasing the protonation rate of oleylamine and inducing anisotropic growth of nanocrystals. Sn4+ cations influence the reaction dynamics owing to complexation with oleylamine molecules. By monitoring the photoluminescence excitation and photoluminescence (PL) spectra of the PNPLs grown at different temperatures, the influence of the thickness on their optical properties is mapped. Time‐resolved and spectrally resolved PL for colloidal dispersions with different optical densities reveals that the dependence of the overall PL lifetime on the emission wavelength do not originate from energy transfer between PNPLs but from the contribution of PNPLs with distinct thickness, indicating that thicker PNPLs exhibit longer PL lifetimes.
CsPbX3 perovskite nanoplate (PNPL) synthesis was driven by SnX4 (X=Cl, Br, I) salts. The role played by these hard Lewis acids in directing the formation of PNPLs is addressed. Sn4+ disturbs the acid–base equilibrium of the system, increasing the protonation rate of oleylamine and inducing an anisotropic growth of the nanocrystals.
Friction between dielectric surfaces produces patterns of fixed, stable electric charges that in turn contribute electrostatic components to surface interactions between the contacting solids. The ...literature presents a wealth of information on the electronic contributions to friction in metals and semiconductors but the effect of triboelectricity on friction coefficients of dielectrics is as yet poorly defined and understood. In this work, friction coefficients were measured on tribocharged polytetrafluoroethylene (PTFE), using three different techniques. As a result, friction coefficients at the macro- and nanoscales increase many-fold when PTFE surfaces are tribocharged, but this effect is eliminated by silanization of glass spheres rolling on PTFE. In conclusion, tribocharging may supersede all other contributions to macro- and nanoscale friction coefficients in PTFE and probably in other insulating polymers.
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