Deformation-induced phase transitions and superstructure formation in poly(ethylene
terephthalate) (PET) were studied by means of in-situ synchrotron small-angle X-ray scattering (SAXS)
and wide-angle X-ray diffraction (WAXD) as well as Raman spectroscopy. The deformation conditions
involved uniaxial stretching of quenched PET films at a temperature just below its glass transition
temperature (T
g), where a notable “plastic deformation” stage was observed. WAXD results indicated
that the initial sample contained a “slush” structure (amorphous + nematic), whereby deformation induced
oriented amorphous, nematic, smectic (C and quasi-A), and stable triclinic crystalline phases. SAXS results
indicated that the fibrillar superstructure was formed upon the formation of oriented slush. In-situ Raman
spectroscopic data revealed the orientation information on ethylene glycol and benzene ring as well as
the gauche
−
trans transition in deformation of PET chains, which are in good agreement with X-ray results.
A mechanism for deformation-induced phase transitions and for hierarchical structure formation has
been proposed to correlate the structural information with the mechanical properties.
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