Research Interests

Periodic Precipitation

    You learned about precipitation reactions in General Chemistry.  You dissolved one soluble salt (like lead nitrate) in water, and added a second (like sodium chloride), and you observed an insoluble product (in this case, lead chloride) form as a cloudy suspension before it settled to the bottom.  Not terribly interesting....  But if you perform the same reaction under a different set of conditions, something very interesting can happen.  Namely, if one salt is dissolved in a gel, and the second is aqueous and allowed to diffuse through the gel, brilliant patterns of precipitate, called Liesegang rings (pronounced lee-seh-gahng), can form spontaneously (see figure below).

                                   Top view of a Liesegang ring formation reaction in a petrie dish.  The dark rings are the precipitate.

    The mechanism behind formation of Liesegang rings is not well understood.  Understanding this mechanism is important because of the ways in which Liesegang rings manifest themselves in nature.  They appear in geologic rock formations, and are believed to be integral in the formation of human gall stones.  Furthermore, they have been linked to cysts, tumors and inflamed tissue in human beings.

    My research aims at better understanding the mechanism of Liesegang ring formation.  Currently there are two disparate theories describing how patterns emerge.  Electrochemical and laser light scattering experiments I will conduct are designed to probe each of these theories, with the hope of producing a clearer picture of the total  mechanism.

    The future direction of my research will involve studying light-dependent Liesegang systems.  These are Liesegang ring formation reactions in which, absent light, no patterns emerge, whereas in the presence of certain wavelengths of light, Liesegang rings do form.  I plan to conduct the same electrochemical and laser light scattering experiments on these systems, both with and without the critical wavelengths of light.  Results from these experiments promise to provide additional insight into the nature of Liesegang ring formation reactions in general.

Resonance versus Inductive Effects