Zarzycki,J (1982): Les Verres et l'état vitreux.Götze,W (2009): Complex Dynamics of glass forming liquids.This theory describes a slowing down of structural relaxation on cooling towards a critical temperature Tc, typically located 20% above Tg. In the opposite case, when a high-viscosity liquid is displaced by a low-viscosity one (a classic technique in applied geophysics for oil recovery), the interface between the liquids turns out to be unstable. The microscopic dynamics at low to moderate viscosities is addressed by a mode-coupling theory, developed by Wolfgang Götze and collaborators since the 1980s. Thus, when a low-viscosity liquid is displaced by a high-viscosity one in a homogeneous porous medium, a stable interface is formed. More recently, the fragility has been quantitatively related to the details of the interatomic or intermolecular potential, and it has been shown that steeper interatomic potentials lead to more fragile liquids. Materials with a higher enthalpy of configuron formation compared with their enthalpy of motion have a higher Doremus fragility ratio, conversely melts with a relatively lower enthalpy of configuron formation have a lower fragility. Bond breaking modifies the properties of an amorphous material so that the higher the concentration of broken bonds termed configurons the lower the viscosity. Fragility is related to materials bond breaking processes caused by thermal fluctuations. Strong melts are those with (R D-1) < 1, whereas fragile melts are those with (R D-1) ≥ 1. The fragility of amorphous materials is numerically characterized by the Doremus’ fragility ratio R D=Q H/Q L. Amorphous materials are classified accordingly to the deviation from Arrhenius type behaviour of their viscosities as either strong when Q H-Q L
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