Electrical charges and tribology of insulating materials

Abstract

Résumé. La description de la génération de charges électriques lors du contact entre isolants a été faite de longue date. En revanche, la prise en compte quantitative des effets de ces charges est rarement évoquée dans les bilans énergétiques concernant les problèmes de frottement. En nous appuyant sur des résultats publiés et sur nos propres expérimentations sur le piégeage des charges dans les isolants, nous montrons l'importance de l'action de ces charges électriques sur l'énergie d'interaction pendant le frottement. Enfin, nous proposons d'évaluer quantitativement cette contribution grâce à l'utilisation complémentaire de la méthode « miroir » et de mesures de forces de surfaces. caractérisation diélectrique / frottement / triboélectrification / interactions interfaciales / énergie libre de surface / charge d'espace / forces de surface Abstract. Electrical charges generation occurring during contact and friction of insulating materials has been identified for a long time. However the contribution of these electrical charges to the friction behaviour is usually neglected in the energetical balances. Based on published results and on our own experimental results on the ability of the dielectric materials to trap charges, we show in this study that the interaction energy during friction depends markedly on these trapped charges. Eventually, we propose the complementary use of the "mirror " method and of surface forces measurements to obtain a quantitative evaluation of this contribution. dielectric behaviour / friction / triboelectrification / interfacial interactions / surface free energy / space charge / surface forces IntroductionSurface forces act between two surfaces when they are in close proximity. They are very well known in the field of colloid science [1, 2] and they have also a strong impact in other fields like adhesion, wetting or friction. Resulting from very complex phenomena, these forces include mechanical, physico-chemical and electrical effects. This paper is focused on one phenomenon which is often neglected : the effects of electrical charges trapped in the near surface or in the bulk of dielectric materials (ceramics, polymers...). In section 2, the various types of surface forces according to their range are recalled. Then, it is shown that some published results in the friction and adhesion domains suggest the major role of these electrical charges. This is followed by an overview on charge generation and trapping during contact or friction in section 3. Our own results are used in section 4 to discuss how electrical charges can influence the friction behaviour of dielectrics. In order to go further, the complementary use of the "mirror " method and of surface forces measurements is proposed in the aim to obtain a quantitative evaluation of this contribution.

Influence of Lateral Movement on Level Behavior of Adhesion Force Measured Repeatedly by an Atomic Force Microscope (AFM) Colloid Probe in Dry Conditions

“…Therefore, trapped surface charges on the microsphere surface cannot leak effectively. Secondly, the transfer of charges into the microsphere body is also difficult [37,38], although charge on Au film may dissipate gradually. Lastly, charge dissipation to gas is difficult in dry conditions (water content < 0.5 ppm).…”

Interpretation of the human skin biotribological behaviour after tape stripping

“…The small variation in the a parameter is probably due to the modification of the skin surface roughness after tape stripping [29].…”

Polymeric Bio‐Inspired Dry Adhesives: Van der Waals or Electrostatic Interactions?

“…[24][25][26][27][28]77] More specifically, insulators are prone to get highly charged at their surface as surface charges via CE cannot efficiently transfer into their matrix, [82][83][84][85] leading to accumulation of electric charges at the surface; by trapping excessive amounts of electric charges at the surface, insulators can generate enhanced electrostatic interactions through CE. [24][25][26][27][28]77] More specifically, insulators are prone to get highly charged at their surface as surface charges via CE cannot efficiently transfer into their matrix, [82][83][84][85] leading to accumulation of electric charges at the surface; by trapping excessive amounts of electric charges at the surface, insulators can generate enhanced electrostatic interactions through CE.…”

“…Even though the understanding about triboelectric charging at the surface of insulators is relatively superficial, it has been illustrated that insulating materials are excellent candidates for promoting adhesion via CE-driven electrostatic interactions. [24][25][26][27][28]77] More specifically, insulators are prone to get highly charged at their surface as surface charges via CE cannot efficiently transfer into their matrix, [82][83][84][85] leading to accumulation of electric charges at the surface; by trapping excessive amounts of electric charges at the surface, insulators can generate enhanced electrostatic interactions through CE. To this day, promoting adhesion through surface charging of insulators has been successfully applied in various technologies as photocopying and laser printing, [23] which essentially deal with charging of micron-sized particles.…”