This line of our investigations concerns the dynamic properties of the air/water interface. While spectroscopic methods have provided experimental insight as to the structure of the air/water interface, the dynamic properties of the air/water interface have remained experimentally inaccessible. Our research seeks to bridge that gap. Through the use of self-positioning "line" microelectrodes, we perform 2D voltammetric experiments on amphiphilic probes adsorbed at the air/water interface. Numerical simulations allow us to interpret our results in terms of the lateral diffusion of probe species at the interface as well as their desorption rate constants. Our current results suggest that the rate of lateral diffusion at the interface of shallowly immersed probes such as TEMPO is about one order of magnitude greater than its diffusion in the bulk water.

These measurements are of fundamental significance and are relevant to the understanding of the uptake of surfactants by atmospheric water droplets. New directions in this line of projects include measurements of the lateral mobility of probes as a function of hydrogen bond strength with water as well as the immersion depth of the polar fragment. Combination of these measurements with detailed molecular dynamics calculations is intended to increase our understanding of the dynamic properties of water itself in its gas/liquid interfacial region. Our recent progress has been reported in the following papers.

M. Majda, “Electrochemistry of Monolayer Assemblies at the Air/Water Interface” in Encyclopedia of Electrochemistry, Vol 10, Modified Electrodes, Bard, A.J.; Stratman, M. Eds.; Fujihira, M.; Rubinstein, I.; Rusling, J. F., volume Eds., Chapter 5, 211-235, Wiley-VCH, Weinheim, 2007.

N. Glandut, C. Monson and M. Majda. “Electrochemistry of TEMPO in the Aqueous Liquid/Vapor Interfacial Region: Measurements of the Lateral Mobility and Kinetics of Surface Partitioning”. Langmuir 2006, 22, 10697–10704.

N. Glandut, A. Malec, M. Mirkin, and M. Majda. “Electrochemical Studies of the Lateral Diffusion of TEMPO in the Aqueous Liquid/Vapor Interfacial Region”. J.Phys.Chem B 2006, 110, 6101-6109.

D. G. Wu, A. Malec, J. Majewski and M. Majda. "Orientation and Lateral Mobility of Insoluble Tempo Amphiphiles at the Air/Water Interface". Electrochimica Acta, 2005, 51, 2237-46.