Some surprises in confined electrolytes: Electroneutrality breakdown and extreme cryotolerance*

When electric double layers overlap in a charged nanopore, classical Poisson-Boltzmann theory predicts uniform screening charge of ions in equilibrium with a bulk electrolyte reservoir. The dominance of surfaces, however, foreshadows extreme sensitivity to boundary conditions, which leads to some surprising phenomena of biological relevance: (1) The sacred assumption of local electroneutrality breaks down, as ions evacuate the pore in favor of the reservoir, leaving the surface charge unscreened, if electric fields leak into the solid matrix; this phenomenon may explain the collapse of conductivity of nanopores at low salt concentration, as well as unscreened ion transport through biological ion channels; (2) If ions are unable to escape a nanopore as temperature is lowered, they can enable extreme freezing-point depression and large disjoining pressures, consistent with extreme cryotolerance in biology and freeze-thaw damage in concrete.