Any hints on how to derive the glass viscosity? n=n(0)exp(Q/RT)?

[nomisme]

Any hints on how to derive the glass viscosity? n=n(0)exp(Q/RT)?

 

[Mapes]

Hi nomisme, welcome to PF. This is a very fundamental equation that applies to all events that involve an activation energy, or an energy "hump" that must be overcome for the process or reaction to occur (these are called thermally activated processes). In the case of viscosity, we're talking about molecules sliding past each other. As the bulk fluid flows, the molecules move along an energy landscape with valleys and peaks corresponding to locations where it's more or less energetically favorable to bond to adjacent molecules. At high temperatures, any bonds are easily broken and each molecule traverses this landscape easily; at lower temperatures, the fluid is more viscous because the molecules are less likely to break these bonds.

The equation describes the general likelihood that a particle at a given temperature will reach a particular energy. It should be clear that this is directly connected to the ability of a molecule in a viscous fluid to break the bonds with its neighbors and continue to move independently. Does this help?