John W. Cahn

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John Cahn (1927 - ) is an American Scientist and winner of the National Medal of Science in 1998. Since 1977, he has held a position at the National Institute of Standards and Technology. Cahn has had a profound influence on the course of materials and mathematics research during his forty year career. The foremost authority on thermodynamics since J. Willard Gibbs, Cahn has applied the basic laws of thermodynamics to describe and predict a wide range of physical phenomena.

Cahn received a bachelor's degree in Chemistry in 1949 from the University of Michigan, a Ph.D in Physical Chemistry in 1953 from the University of California at Berkeley.

In 1954 Cahn joined the Chemical Metallurgy research effort at the General Electric laboratory in Schenectady, NY, led by David Turnbull. Turnbull had done pioneering work on the kinetics of nucleation, and there was a focus in the group on understanding the thermodynamics and kinetics of phase transformations.

In 1957, Cahn worked with John E. Hilliard to develop the Cahn-Hilliard Equation which describes the thermodynamic forces driving phase separation in many systems. They also did pioneering work in the quantitative interpretation of metallography -- i.e. microscope images of polished metal samples.

In 1964 Cahn became a professor in the Department of Metallurgy (now Materials Science) at the Massachusetts Institute of Technology. He left MIT in 1978. Since 1984, he has held an affiliate professor position at the University of Washington.

In 1969, Cahn began a long professional relationship with his graduate student Francis Larché, whose work focussed on the effect of mechanical stress on the thermodynamics of solids. The Larche-Cahn approach is the cornerstone of the treatment of the thermodynamics of stressed materials -- for example the regions near a coherent precipitate or the stress field around a dislocation.

In 1972, Cahn worked with David W. Hoffman to formulate a vector-based thermodynamics to describe the thermodynamics of interfaces, a formulation which is necessary to account for anisotropic materials. This is also known as the capillary vector formulation of interface energies. The mathematics of this treatment involves the concept of norms, although Cahn and Hoffman were unaware of it at the time.

In 1975, Cahn worked with his graduate student Sam Allen on phase transitions in Iron alloys, including order-disorder transitions. This work led to the Allen-Cahn equation.

In 1977, Cahn published a simple mathematical treatment of the thermodynamics of wetting: the interaction between a liquid in contact with a solid surface. This paper laid out a simple formulation for describing the wetting transition -- the point at which a liquid changes from forming a droplet on a surface to spreading out evenly as a liquid film over the surface. This theory had wide-ranging implications for many materials processing techniques

In 1982, Dan Shechtman observed a new of crystalline structure with puzzling features. Cahn contributed to the theory of how such a structure could be thermodynamically stable and became co-author of the seminal paper which introduced quasicrystals. His competence in this new domain is widely aknowledged.