Ideal and cooperative bond-lattice representations of excitations in glass-forming liquids: Excitation profiles, fragili
- PDF / 195,531 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 178 Views
N
IN considering possible subject matter for presentation at the symposium honoring the contributions of Milton Blander to the physical sciences, in general, and to the thermodynamics of molten salts, in particular, it seemed to us that it might be appropriate to show how his approach to treating multicomponent solution thermodynamics can be related to phenomena of current interest in the area of glassforming liquids. We will, therefore, give a short account of the relation between the treatment of nonideal solution thermodynamics and the treatment of single-component liquid thermodynamics in the “bond lattice” or, more generally, the “elementary configurational excitation” representation, in both “independent-bond”[1,2,3] and “cooperative-bond” approximations. The latter case will be seen to be analogous to the Hildebrand[4] and Guggenheim[5] treatments of multicomponent solution thermodynamics, which were modified by Blander in his well-known treatments of molten salt thermodynamics.[6] Our approach[7] is more directly related to a variety of “two-liquid” models of the behavior of liquids with unusual properties[8,9,10] and, because of its focus on the elementary excitations of some ground-state structure, is still more directly related to the Granato interstitialcy model of single-component liquids.[11] C. AUSTEN ANGELL, Professor, is with the Department of Chemistry, Arizona State University, Tempe, AZ 85287-1604. CORNELIUS T. MOYNIHAN, Professor, is with the Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12181 This article is based on a presentation made at “The Milton Blander Symposium on Thermodynamic Predictions and Applications” at the TMS Annual Meeting in San Diego, California, on March 1–2, 1999, under the auspices of the TMS Extraction and Processing Division and the ASM Thermodynamics and Phase Equilibrium Committee. METALLURGICAL AND MATERIALS TRANSACTIONS B
Although the most interesting aspect of this model probably lies in its predictions of single-component liquid-liquid phase transitions, we will, in fact, give most of our attention to the independent-bond approximation properties of the model, since this is where we can best demonstrate the relation of this model to the currently popular configurationspace or “energy-landscape” representations of liquid and glass phenomenology.[12,13,14] The account of liquid polymorphism (or polyamorphism[15]), which follows from the introduction of cooperativity in the excitations, will be given in Section IV of this article. The parallel we are making between the bond-lattice model for a single-component system and the ideal-solution model for binary solutions is illustrated in Figure 1. The left-hand-side panel shows the ground state of the system, which is depicted as geometrically ordered, for simplicity of representation, although it is to be conceived of as the lowest possible energy state of an amorphous solid. This panel also represents the infinitely dilute state of a binary liquid solution. The middle pane
Data Loading...
