Origins and Applications of London Dispersion Forces in
Ceramics: Electronic Structure and Chemistry, Roger H.
French, DuPont Co. Central Research, Wilmington DE 19880; Univ. Of Pennsylvania,
Materials Science Dept. Philadelphia PA, 19104
The London dispersion forces are a universal component of
long-range vdW forces and arise from the electronic structure of materials and
their optical behavior. They play a role in interface and surface energies,
wetting, surficial and interfacial films, flocculation of colloidal systems, and
force microscopy. These vdW dispersion forces are represented by the Hamaker
constant (A), and can be calculated directly from optical property-based
electronic structure spectra using Lifshitz theory. Recent access to new
experimental and ab initio tools for determination of optical properties
of materials has created new opportunities for detailed studies of dispersion
forces.
The close relationship between the London dispersion forces
and the material’s chemistry and electronic structure represents an avenue for
materials design as has been exploited in ceramics processing and applications.
For flocced ceramic systems exhibiting equilibrium intergranular glass films
(Igf), such as Pb2Ru2O7 thick film resistors or
Si3N4, the Igf thickness results from a force balance
where the dispersion force can be varied by Igf chemistry. The interlayer
material, the Igf, serves to shield the vdW attraction of the grain’s dipoles.
Finally, new results on the effects of retardation of the
London dispersion interaction at large distances are discussed with an emphasis
on novel wetting phenomena such as equilibrium surficial films of water on ice
and bimodal wetting/dewetting systems.
