Physics Department seminar
DIPARTIMENTO DI FISICA, VIA CELORIA 16, MILANO
AULA C in presence and streaming
https://fisica-unimi.zoom.us/my/aula.c?pwd=TnpkbWpDUEFBUjhxZkMwRG52WW5mdz09
17 Febbraio 2023– 11:00
Valeriy V. Ginzburg
Chemical Engineering and Materials Science, Michigan State University

Theories of Glass Transition in Polymers New Thoughts about an Old Mystery

Philip W. Anderson, a Nobel Prize-winning theoretical physicist, wrote in 1995: “The deepest
and most interesting unsolved problem in solid state theory is probably the theory of the
nature of glass and the glass transition.” This challenge is especially intriguing and practically
important for polymers. Many processes (mechanical recycling, lithography, application of
paints to surfaces, extrusion of amorphous plastics, etc.) are designed based on our ability to
understand the glassy dynamics, where the material viscosity can increase by several orders
of magnitude as the material is cooled by only a few degrees. Today, the accepted paradigm is
that as a polymer is cooled below its glass transition temperature, its “free volume” or,
alternatively, “configurational entropy” decrease to zero at some finite temperature T0; at that
temperature, the material becomes completely “frozen” as its relaxation time and/or viscosity
diverge. This is described mathematically using Vogel–Fulcher–Tammann (VFT) or Williams–
Landel–Ferry (WLF) equations. Recently, however, many researchers (G. McKenna, J. Dyre,
H. Winter, and others) demonstrated that in many systems, the VFT formalism breaks down,
and the low-temperature glass is better understood as “just another fluid”, albeit with
extremely slow dynamics (with molecules moving over geological or astronomical timescales).
Our theoretical research aims at developing simple quantitative models capturing this new
understanding. In particular, by combining a simple “two-state” theory for the relaxation
dynamics with a realistic equation of state (modified Sanchez-Lacombe), we are able to
describe the PVT, dielectric, and volume relaxation experiments for a number of polymeric and
molecular organic glass-formers (V. Ginzburg, A. Zaccone, and R. Casalini, Soft Matter, 2022,
18, 8456-8466). I will conclude by discussing future steps in theory development, including its
practical applications (nanocomposites, recycling, membranes, lithography, etc.)

Students are cordially invited

Contact silvia.leoni@mi.infn.it

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