CONTACT ELECTRIFICATION INDUCED BY MONOLAYER MODIFICATION OF A SURFACE AND RELATION TO ACID-BASE INTERACTIONS

ELECTRICAL charge separation following contact between two materials ( contact electrification or the triboelectric effect) is well known to occur between different materials as a consequence of their different electronic structures1,2. Here we show that the phenomenon occurs betw een two surfaces of the same material if one is coated with a single c hemisorbed monolayer. We use the surface force apparatus3 to study con tact electrification4 and adhesion between two silica surfaces, one co ated with an amino-silane. The presence of this monolayer results in s ignificantly enhanced adhesion between the surfaces, owing to electros tatic attraction following contact electrification, in accord with Der jaguin's electrostatic theory of adhesion5. At the same time, the obse rved increase in adhesion is consistent with Fowkes' acid-base model6 (in which acid-base interactions between surface groups are considered to be the predominant factor determining adhesion), as the monolayer converts the originally acidic silica surface to a basic (amine-termin ated) one. These observations demonstrate a link between acid-base int eractions and contact electrification.