John Cahn, an emeritus senior fellow and materials scientist at the U.S. Commerce Department’s National Institute of Standards and Technology (NIST), was recently named to receive the prestigious Kyoto Prize in Advanced Technology. Cahn's numerous major contributions to materials science include developing a fundamental theory that describes the behavior of mixtures of different materials and how they tend to separate at the microscale. The theory established an entire branch of materials research and is particularly important to the rational design of new alloys.
The Cahn-Hilliard equation supplied that basic framework for understanding how an alloy's phase separation and related changes in microstructure play a key role in determining the physical engineering properties of the bulk composite alloy—things like strength, toughness, ductility, magnetic strength and thermal conductance. The equation describes, quantitatively, how the components of a binary mixture that becomes unstable when cooled will separate through a process called "spinodal decomposition." Cahn proceeded to elaborate the theory, showing how basic thermodynamic principles could be used to design alloys that, under spinodal decomposition, would form desired microstructures. His work laid the foundation for the rational design and manufacture of new materials using the Cahn-Hilliard equation as well as for the related "phase-field" method, which uses similar thermodynamic considerations to model the behavior of complicated interfaces in materials.
Like many other fundamental theories, spinodal decomposition has proven relevant to a broad range of seemingly disparate fields. The Cahn-Hilliard equation, among other things, describes how galaxies began forming out of the primal material of the Big Bang in the early stages of the universe.