Figure 2. The schematic of ion/electron dynamic transfer between two different size sands with an adsorbed water film.

(a) The electroneutral sands would initially have the same temperature, T₀. (b) The internal energy conversion by collision would cause a temperature rise of the sands while increasing the ion concentration in the adsorbed water film. The ion would migrate from the high temperature sands to low temperature particles through the contacting interface. (c) The high temperature particles would become negatively charged while the low temperature sands become positively charged due to the mobility of H⁺ being greater than that of OH⁻.