Preview of conclusions

A preliminary view of the conclusions reached in later chapters is given in the next four sections. 

A material s stiffness or viscosity is its resistance to change of type (ii), and it must be possible to find a change of type (i) that is exactly as sluggish that is to say, there must be a distance Lq such that journeys of type (i) 

Such a distance Lq is an inherent property of the material, along with other properties such as its density and viscosity. For water, L(, is about 1 nanometer, whereas for fused silica it seems to be 10 or 20 nanometers. Driving material to a new orientation is very like driving it to a new location whatever the means by which material travels, both operations are described in continuum terms as loss, gain or translation of infinitesimal wafers. Deformation occurs as if the transport distance were Lq, while stress-driven self-diffusion operates usually over greater distances. 

Even when a sample is not in equilibrium (and hence some process of adjustment toward equilibrium is running, such as diffusion of material from one point to another) for each component at a point, an associated equilibrium state can be identified. Then one can say that the component s behavior will be very much as if it had the chemical potential it would have if it were in the associated equilibrium state. For example, material will tend to migrate from a site where the associated equilibrium potential is high to a site where the associated equilibrium potential is lower this is a reliable 

For a sample where the stress state is nonhydrostatic, with more compression across some planes at a point than across other planes at the same point, the equilibrium state associated with one plane is different from the equilibrium state associated with another plane. Hence, the chemical potential associated with one plane is different from the chemical potential associated with another a range of chemical potentials is associated with a single point, in the same way as the range of compressive stresses. 

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