The Pressure and Temperature Dependence of the Low-Shear Viscosity

Protecting Proteins from Desiccation Stress Using Molecular Glasses and Gels

“…Developments by Volgel, Flucher, and Tammann and Hesse led to the Volge–Flucher–Tammann (VFT) equation, η = η ∞ e B T − T 0 with T 0 the temperature where the viscosity diverges, and B is an empirical parameter. B was later related to the fragility through B = DT 0 , with the empirical parameter D < 20 corresponding to a fragile glass former and D > 100 corresponding to strong glass former. , Further improvement to the temperature dependence of the viscosity is given by the Williams–Landel–Ferry (WLF) equation . The dependence of viscosity on external pressure can be modeled by an analog of the VFT equation, η = η 0 e C P P 0 − P where P 0 is the idealized glass transition pressure, η 0 is the extrapolated zero pressure viscosity and C is the empirical pressure fragility parameter.…”

“…The dependence of viscosity on external pressure can be modeled by an analog of the VFT equation, η = η 0 e C P P 0 − P where P 0 is the idealized glass transition pressure, η 0 is the extrapolated zero pressure viscosity and C is the empirical pressure fragility parameter. More complex models for the pressure dependence have also been proposed. , …”

“…More complex models for the pressure dependence have also been proposed. 200,202 Two important theoretical descriptors of mobility in glass and glass viscosity are the free volume and the excess configurational entropy. Under the free volume framework suggested by Doolittle, 203,204 the viscosity increases upon cooling because of the reduced space afforded to each particle.…”