Normal
force response of
polymer glasses (Anny Flory)
The molecular origins of the nonlinear (finite) elasticity
of cross linked rubber and the nonlinear viscoelastic response of
polymer melts and solutions are well understood both
fundamentally and in practical applications. On the other hand,
the impact of molecular structure on the nonlinear viscoelastic (but
sub-yield) behavior of glassy polymers has been little explored and no
chemical structure theory is available to describe this behavior.
In
this research we address this issue. In Particular, we take advantage of torsional measurements because, in order to keep the sample at
constant length it is necessary to apply not only a torque but also a
normal force and the combination of torque, normal force and volume
change during torsion provide more information about the material
behavior than do other modes of deformation. Here, we investigate
how the molecular mechanisms associated with the glass transition (Tg)
and first sub-Tg relaxation (β transition) relate to the
nonlinear viscoelastic behavior of glassy polymers with various chemical
structures.
Funding: Petroleum Research Fund
National Science Foundation
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