Rubber state of ionic fluorozirconate glasse

Abstract

Long-chain, and network polymers are elastic over a range of temperature, known as the rubbery or plateau region¹. On cooling they become rigid, or glassy, with a shear modulus of ∼10 GPa and, on heating, if crystallization or decomposition does not intervene non-network polymers become fluid with a shear modulus approaching zero. In the rubbery zone, the real component of their shear modulus, G', remains nearly constant and the mechanical loss factor, tan ψ, reaches a minimum value¹. The occurrence of the rubbery state is exclusively a property of polymers in which topological constraints, resulting from chain entanglements, or junction points forming the network, exist². These obviously involve flexible covalent bonds at junction points and intermolecuiar or interchain forces at entanglements. Here, we report the first observation of rubber-like behaviour in an ionic fluorozirconate glass³, currently of great interest for use as optical waveguides and infrared windows, and examine its implications for concepts of polymer rheology. These results are significant for they suggest that ionic bonds in non-polymers can provide the same configurational restrictions as covalent bonds in a macromolecule or a polymer.