Diffusion potential at the adsorbate–liquid interface releases H⁺ from the adsorbate, leaving it negatively charged (a surplus of OH⁻). Salt impairs adsorbate formation, and an asymmetry in adsorbate thickness on either side of a membrane is the force behind osmosis. Aquaporins are apertures through that adsorbate — a break in an otherwise uniform field — and the local non-uniform field can propel water through the channel by dielectrophoresis.