Mysteries of the glass transition

With the very noncrystalline nature of the state labeled “glass,” the use of terms like “lattice sites” by some physicists is misleading if not erroneous. Having spent nearly 40 years researching solid-state chemistry using diffraction methods, I can say that the glass state is not just limited to glass—that amorphous state of polymeric silicon oxide with doping of other oxides, including boron oxide. In fact, all polymers, including those extensively used in daily life starting with organic monomers, show the “mysterious” glass transition.

A study of the glass transition in any polymeric material is necessarily dictated by complex variations in the motions of the polymeric chain segments, which form as sheets, coils, helices, and the like. The glass transition in the case of doped silicon oxides may be ascribed to the conformational changes in the vicinity of the tetrahedral silicon, while in polymers it involves oxygen atoms in the polymeric helices or sheets.

One can draw inferences from the crystal structures of pure silicon oxides such as quartz in that even those crystals enter the glass state upon heating. ¹ Then it is very difficult to recover the original crystal with the same characteristics.

When melted, even crystals of sucrose, a simple everyday compound, lead to a glassy state that is far more mysterious than the glass itself.

To understand the underlying principles of the behavior of the glass state, we must use radial distribution functions from diffraction data to study these mysterious glass transitions, particularly in regard to their structural details at the molecular level.