Production of electricity by friction is well known but poorly understood and it 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 10 65 mechanisms leading to solids contact electrification and/or triboelectric charging? The explanation of the production of electrostatic charge comes from a transfer of electrons, ions or both, which are presented in the literature? 16 Poor knowledge on charge accumulation and dissipation 70 mechanisms 17-19 is a root of large-scale personal and property losses, including serious industrial accidents and explosions that are described further in the next section. This is ultimately due to the lack of scientific understanding of the basic phenomena.On the other hand, fundamental electrostatic concepts are well 75 established for semiconductors and metals. 20 When two metals with different work functions are brought into contact, electrons migrate across the interface creating a potential difference between them.

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.

The electroneutrality principle 1 expresses the fact that all pure substances carry a net charge of zero. However, real substances in the environment are usually under significant static potential gradients and thus under nonzero electric potential. 2 The electrochemical potential (μ) (eq 1) of ions under a given electric potential (V)

An attempt to understand the microscopic origin of the high viscosity of Brazilian heavy crude oils was made combining macroscopic (rheological measurements) and microscopic [small-angle X-ray scattering (SAXS) measurements] techniques. A clear relationship between the asphaltene content and viscosity was found, while the removal of asphaltene via flocculation led to a large viscosity drop, confirming them as the origin of high viscosity. The SAXS analyses of crude oils confirmed the presence of asphaltene aggregates as fractal-like particles of colloidal dimensions. Afterward, a systematic investigation was performed on the effects of a series of additives and physical treatments on the crude oil viscosity. Physical methods did not cause any significant viscosity drop as well as more than 80 additives tested. SAXS measurements on oil samples containing toluene and heptane indicated little effect on the asphaltene nanoaggregates within the dimensions probed by SAXS, confirming a general mode of action based on aggregate dilution instead of disruption.

Asphaltene precipitation is a key problem in the petroleum industry and has been the focus of many studies on their aggregates present in crude oils and on the effects of additives to inhibit their formation and/or deposition. However, most of these studies were performed using model systems, such as asphaltene solutions in organic solvents, making the comparison to real systems more difficult. Herein, we combine different modes (height and phase modes) of atomic force microscopy to identify colloidal particles associated with asphaltene aggregates present in crude oils. Following this methodology, a mica plate is inserted into oil and washed with toluene to remove excess oil. In addition, nanoparticles with dimensions ranging from a few to hundreds of nanometers were observed. Overall, more particles are observed when flocculants, such as heptane, are added, whereas their size decreases when a good solvent for asphaltenes (toluene) is added. Similar colloidal particles are also observed repeating this methodology with asphaltene solutions in toluene, confirming that these somewhat reproduce the asphaltene association observed in crude oils. The addition of an inhibitor, such as dodecylbenzenesulfonic acid, led to observation of more and smaller nanoparticles. The present experimental approach not only confirms the existence of asphaltene colloidal particles in crude oils but also provides an accessible methodology to directly assess how these particles are affected by changes in oil composition or inhibitors.