UNIVERSITY OF MISSOURI LOCAL

SECTION

November, 2000

Volume 4, Number 3

OUR LOCAL SECTION WEB SITE

This newsletter, along with lots of other information about the local section is online:

http://www.chem.missouri.edu/acslocal/acslocal.htm

The November Meeting will be held in on Wednesday, November 8^th at 7:30 pm in Schlundt 103  on the University of Missouri Campus. The speaker will be Professor Joel Harris from the University of Utah. The title and abstract for his talk are below.

Measurement of adsorption kinetics at liquid/solid interfaces is challenging, requiring selective detection of interfacial species and rapid change in surface concentrations or activities to observe rates of adsorption. Since rapid changes in concentration near solid surfaces are hindered by slow diffusion through a poorly mixed boundary layer, a relaxation approach (where the system is shifted away from equilibrium followed by a kinetic relaxation back to equilibrium) can be used to measure kinetics at solid/liquid interfaces. Fast temperature-jumps based on laser or Joule-discharge heating, for example, can be employed to perturb adsorption equilibria for high-surface area porous or dispersed solids. A novel relaxation approach that avoids the need for an external perturbation is based on random fluctuations of the number of molecules near the interface in a volume defined by internal-reflection excitation of fluorescence. The adsorption kinetics that govern these random fluctuations can be measured by determining how fast the deviations from equilibrium evolve in time. Since the fluctuations arise from molecular statistics, the magnitude of the signal variance can used to determine the number of molecules at the interface without need for standardization or calibration. Example applications in studying model chromatographic interfaces and transport in thin sol-gel films. Extension of the quantitative interfacial measurements into the single-molecule counting domain will be discussed.