Prof. Ranganathan alerted me to the news of Prof. John Cahn’s passing away; here is the obituary in Washington Post. Prof. John Cahn made fundamental contributions to several branches of materials science and engineering. He is probably most well known for his work on diffuse interface models; there are two non-linear diffusion equations named after him — Cahn-Hilliard and Allen-Cahn equations — which form the basis of all the phase field models.
Our group is one among the many in India using phase field models to understand microstructures, their formation and evolution; all of us have found the selected works of John Cahn to be a great book to have, read, consult to and argue about, and, I have met Prof. Cahn in 2005 in a Phase Transformations conference (PTM) that he helped start (though I did not discuss with him).
Cahn has also made several significant contributions including to the areas of wetting, solidification, symmetry breaking transitions and so on. One of the important charactersistics of Cahn’s work is the mathematisation of materials science and the close attention that he paid to general principles (and that included thermodynamics). I also believe that his theory of spinodal decomposition is one of the (relatively rare) instances in materials science wherein the theory was formulated fairly comprehensively before experimental confirmation was obtained. Of course, like in the case of dislocations, this scenario lead many to doubt the existence of spinodal itself. To quote Cahn’s reminiscence:
Borelius fully accepted the interpretations of the results. When I met him in 1961, he was unwilling to acknowledge my spinodal theory, and kept apologizing for having caused me to waste my time with what he now felt to be a fallacious concept.
May be I will write a more detailed appreciation at a later point in this blog. In the meanwhile, here are some videos at YouTube where you can listen to the pioneer himself.