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The diagram
shows the structure of two condensed phases, (a) is a solid and (b) a
liquid. The solid has a regular three-dimensional spatial array of atoms and
the liquid, which has a similar density, has a disordered structure. In the
liquid phase, the mean free path of the atoms is on the order of the atom diameter
and instead of behaving as free particles as do atoms in a gas, the atoms
in the liquid are always interacting with several neighbors. This will alter
the temperature dependence of the viscosity. |
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Moving
parts of the liquid with respect to other parts requires that the interatomic
attractive forces between these regions be overcome by the application of
shears. The thermal motion of the liquid atoms will determine how large these
forces need to be. The probability of an atom getting enough energy from the
thermal motion of its neighbors to move to another location increases exponentially
with increasing temperature. The viscosity of the liquid, therefore,
decreases as the liquid temperature increases and has the form:
m(T) =
m0exp(E/kT)
or Ln
m(T) = Ln m0 + (E/kT)
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