1 research outputs found
Controlled Terahertz Birefringence in Stretched Poly(lactic acid) Films Investigated by Terahertz Time-Domain Spectroscopy and Wide-Angle X‑ray Scattering
We
report a correlation between the dielectric property and structure
of stretched polyÂ(lactic acid) (PLA) films, revealed by polarization-sensitive
terahertz time-domain spectroscopy and two-dimensional (2D) wide-angle
X-ray scattering (WAXS). The experiments evidence that the dielectric
function of the PLA film becomes more anisotropic with increasing
draw ratio (DR). This behavior is explained by a classical Lorentz
oscillator model assuming polarization-dependent absorption. The birefringence
can be systematically altered from 0 to 0.13 by controlling DR. The
combination of terahertz spectroscopy and 2D WAXS measurement reveals
a clear correlation between the birefringence in the terahertz frequency
domain and the degree of orientation of the PLA molecular chains.
These findings imply that the birefringence is a result of the orientation
of the PLA chains with anisotropic macromolecular vibration modes.
Because of a good controllability of the birefringence, polymer-based
materials will provide an attractive materials system for phase retarders
in the terahertz frequency range