First-Principles Study of the Charge Distributions in Water Confined between Dissimilar Surfaces and Implications in Regard to Contact Electrification

Abstract

The role of humidity in contact electrification is complex and multifaceted. With the aim of elucidating this role, we carry out first-principles molecular dynamics simulations of water confined between dissimilar surfaces. We address water confined between the (0001) surfaces of quartz and sapphire, as these surfaces have simple structures that allow for rigorous simulation while also being amenable to experimental investigation. The water takes on a layered structure, with the molecules somewhat oriented by the electric fields that arise in the system. The simulations find that the quartz charges negatively with respect to the sapphire, which concurs with previous experimental results. Yet interestingly we find that the water phase obtains a significant positive charge; we believe that this effect can have consequences in the contact electrification process, and also elucidate several experimental results for changes in electrostatic charge due to changes in relative humidity or pressure.