Chapter 6
Polymer Deformation
6.1 Characteristics of Polymer Deformation...................
The Brownian motion of a polymer chain for self-diffusion is carried out by the
integration of Brownian motions of monomers. Therefore, the entropic elasticity of
chain conformation in a random coil allows a large-scale deformation, with its extent
subject to the external stress for polymer deformation and flow, and hence exposes
the characteristic feature of a rubber state in a temperature window between the glass
state and the fluid state.
As illustrated in Fig.6.1, within different temperature regimes, the bulk phase of
non-crystalline linear polymers exhibits different characteristics of deformation as
a mechanical response to a small external stress. Below the glass transition temper-
atureTg, the solid polymer can resist the external force without any large deforma-
tion. At the temperatures slightly aboveTg, the polymer chain can experience a
large-scale deformation, and maintains the deformation temporarily, exhibiting a
rubber-like highly elastic behavior. At even higher temperatures, a rubber-fluid
transition occurs, and the bulk polymer becomes a viscous fluid, characterized by
large permanent deformations of flows under the external force. For most of the
synthetic plastics and fibers, their processing needs to be carried out at the fluid state
to achieve sufficient permanent deformations. The viscous fluid state of polymers is
easily available in the industry, since the rubber-fluid transition temperature for
non-crystalline polymers, or the melting temperature for semi-crystalline polymers,
are around 100C, one magnitude lower than 1,000C for the processing of steels.
This is also the reason why we give the name “plastics” to a typical sort of
applications of polymer materials.
Small molecules display both glass and fluid states, but not the rubber state. The
rubber state is a unique feature for non-crystalline or semi-crystalline polymers in
the intermediate temperature regime between the glass and the fluid states. With the
decrease of temperature from the fluid state, various modes of polymer motions will
be gradually frozen, corresponding to their different scales of length and time (a
dynamic structure). First, the fluid-rubber transition occurs, which freezes the
W. Hu,Polymer Physics, DOI 10.1007/978-3-7091-0670-9_6,
#Springer-Verlag Wien 2013
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