Effect of infrared radiation on interfacial water at hydrophilic surfaces

Abstract

Hydrophilic materials such as Nafion can nucleate the buildup of interfacial water, which shows features different from bulk water. We investigated the effect of infrared (IR) light on a negatively charged, interfacial exclusion zone (EZ) and a positively charged proton zone (PZ) formed in the vicinity of Nafion. After irradiation for 5 min by mid-IR light, EZ size increased with an expansion ratio of 1.41. A significant expansion was also found in the size of PZ, equivalent to an increment of about 1.39 × 1016 molecules of hydronium ions. Thus, IR radiation not only builds EZ, but at the same time drives release of protons from the growing EZ to bulk water. Near-IR illumination also showed expansion of EZ and PZ water. These results imply that incident IR light not only promotes the build-up of interfacial water at the hydrophilic surface, but also provides a driving force for charge separation.