Colloquium with

Dr. Will Cantrell

MTU Department of Physics

Nucleation, Thin Films and Deliquescence of Salt

    There is a puzzling asymmetry in the first order liquid/crystal phase transition.
Most liquids can be deeply supercooled, but the corresponding crystal cannot be
superheated. The asymmetry implies that freezing must be nucleated while melting
is not, a behavior that is usually explained in a phenomenological sense by the
existence of a thin film of a quasi-liquid on the surface of the solid at temperatures
less than the melting point. As the melting point is approached from below, the
thickness of the quasi-liquid layer increases. Viewed from this perspective, melting
is simply the increase in the thickness of this layer.
     Deliquescence and efflorescence are the corresponding phase transitions for the
two component system of a soluble salt and water. Supersaturated solutions can
exist for extended periods of time in a manner analogous to supercooled liquids.
Until recently, it was thought that deliquescence, like melting, occurred at a well
defined point, relative humidity in this case as opposed to temperature.
     In an investigation of thin films of water adsorbed to the (001) face of NaCl, my
co-authors and I found that deliquescence is a nucleated phenomenon. I will
discuss why we see this behavior where others have not and discuss its
implications for the more general case of first order phase transitions and surface
melting.

Thursday, November 8, 2001

Fisher Hall 139, 4:00 p.m.

Refreshments will be served