Active Control of Friction Coefficient with Electro-sensitive Biolubricants

The electro-active control of friction is an incipient area of growing interest, and one of the greatest challenges of Tribology. At present, one of the most promising technological innovations in lubrication is linked to the use of electro-rheological (ER) fluids. These “smart materials” allow instant and on-demand control of their friction behavior through the application of an electric potential. The development of a new generation of instruments aimed to their comprehensive tribological characterization under external electric fields is yet to be explored.

1 Introduction
Current technological strategies developed by the lubricants industry are mainly oriented towards sophisticated formulations capable of reducing energy consumption and extending the useful life of mechanical elements.
Even so, all these advances have only supposed a mere “passive” control of lubrication. Thereby, it continues to be very sensitive to sudden changes in operating conditions, such as vibrations or starting and stopping times, and to wear.
In turn, the use of electro-rheological (ER) fluids constituted by polarizable nanoparticles suspended in a non-conductive oil enables an "active" control of the lubrication process (1). The so-called “electro-viscous” effect arises from the orientation and arrangement of polarized particles into organized columnar structures when subjected to an electric field (Figure 1). Hence, its contribution to lubrication is twofold: i) on-demand control of friction coefficient in order to optimally dampen friction perturbations; ii) enhanced load carrying capacity of the lubricant film to withstand heavier loads.

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