Theory Versus Experiment. What is the Charge at the Surface of Water?
1Department of Applied Science, London South Bank University, 103 Borough Road, London SE10AA, UK
Key Words: interfacial water, surface charge, water-gas interface, surface tension, surface spectroscopy
Received 11 November 2008; revised 14 December 2008; accepted 6 February 2009. Published 1 July 2009. Available online 1 July 2009.
There is considerable disagreement over whether the gas/liquid surface of water is positive due to the presence of surface-active hydrogen ions or negative due to the presence of surface-active hydroxyl ions. Much has been written and many experimental and simulation studies have been undertaken. We critically analyze these studies to establish what is known unambiguously and what assumptions underlie these opposite views. The conclusion reached after this examination is that there is much misunderstanding over the strength of the evidence for hydrogen ions being surface active and less support for the positive surface than generally regarded. The surface of neutral water is negatively charged.