A glass can be made by rapidly cooling a liquid. As a result of this procedure, in the glassy state the atoms are in a disordered form, as in a liquid.
Unlike the latter, however, their configuration remains almost fixed, that is, the atoms are constrained to their equilibrium position and can move within the material only over extremely long periods of time. Recently it has been found that by exposing glasses to an X-ray beam of sufficient intensity, it is possible to induce displacements of atoms within the glasses: subjected to X-rays, glasses flow, like liquids.
The origin of this phenomenon is still debated, and the research titled “Stochastic atomic acceleration during the X-ray-induced fluidization of a silica glass” published in “PNAS”-born out of a collaboration of the Department of Physics and Astronomy of the University of Padua with the Institute of Physics of the University of Amsterdam, DESY research center in Hamburg and Department of Physics at the University of Trento – sheds new light on how atoms, exposed to X-rays, can move within the disordered structure of glass over distances otherwise unreachable in such a short time.
“With a series of measurements performed with a technique known as X-photon correlation spectroscopy (XPCS) and carried out in the PETRA III synchrotron at the DESY research center in Hamburg,” says Francesco Dallari, a postdoctoral researcher in the Department of Physics and Astronomy at the University of Padua, it has been possible to trace these shifts from the interatomic scale, which is of the order of the angstrom, equal to one ten millionth of a millimeter, to distances of several hundred angstroms, to be more precise, the size of a coronavirus.”
The observed dynamics, Unipd explains, follows the laws of what is called “hyper-transport,” which is a type of motion where the distance traveled by atoms increases with time faster not only than in simple diffusion (think of a drop of coffee extending into a cup of milk) but even faster than when a particle is moving at a constant speed in a certain direction.
“In practice,” explains Professor Giulio Monaco of the Department of Physics and Astronomy at the University of Padua, “X-rays reaching glass generate defects within the material. These induce force fields that behave like compressed springs that in turn move nearby atoms to distances on the order of hundreds or thousands of angstroms.”