Fig. 2: Contact drives evolution.
From: Spontaneous ordering of identical materials into a triboelectric series
a, Towards uncovering what causes the series evolution, we first performed baseline measurements between 24 pairs of pristine samples. These charge randomly about zero with a standard deviation of about 0.007 nC. b, Motivated by the possibility that the act of contact itself could drive the series evolution, we prepare 48 new samples and expose half to 100 prior contacts. Contacting these against unbiased ones and measuring ΔQ5 reveals a marked effect, with the previously contacted samples always charging negative. c, We investigate how this ‘contact bias’ evolves using trios of samples: an ‘advancing’ sample (green A), a ‘lagging’ sample (ivory A) and an ‘extra’ sample (ivory X). We first measure ΔQ5 between the advancing and lagging samples starting from the pristine state. We then subject the advancing sample to 20 contacts with the extra sample. After discharging, we measure ΔQ5 again between the advancing and lagging samples. Repeating this process develops a growing contact bias between the lagging and advancing samples. d, Charge exchange versus advancing (bottom) and lagging (top) contacts for different trios of samples. All advancing samples charge more negatively as their contact bias increases, although each one at a different rate and with a different plateau. As explained in the main text, we assume that the charge exchange in this evolution is caused by a difference in a generalized potential, φ, which obeys equation (2). Solid curves are fits to the model.
