Modification of film thickness by using electro-responsive biolubricants

Electro-responsive fluids present great potential for smart lubrication. The reversible changes attained in such lubricants through the application of an external electric field allow them to adapt to specific operational conditions, which translates to an active control of the lubrication process. However, there are still numerous variables to be studied in the application of these fluids in lubrication, as it remains an emergent area of research. This experimental work focuses on the influence of the electric field on the lubricant film thickness in a non-conformal contact (ball-on-disc), using a simple and sustainable lubricant formulation. The biolubricants studied are composed of a vegetable base oil (castor oil) and a dispersed organo-modified nanoclay (Cloisite 15A) in concentrations between 1 and 6 wt.%. Through an optical interferometry experimental method, it was possible to determine film thickness across the entire contact area, over a range of entrainment speeds. The film thickness variation with the electric field intensity, from 0 to 30 V, was observed. Hence, the effect of combined parameters (nanoparticle concentration, entrainment speed and electric potential difference) on film thickness is reported. This evaluation delves into film thickness along the entrainment direction, with special emphasis on central and minimum film thickness. The results confirm the capacity to electro-modulate film thickness, as the lubricant film effectively thickened when an electric potential was applied, especially at lower speeds. This study underscores the relevance of this type of lubricants, which not only pose a minimum environmental impact but also may improve efficiency. Further research could be carried out to study the influence of electric field on friction in the same test conditions. The comprehension of both friction and film thickness behavior under electric field is fundamental for the design and development of potential applications.