Study of field-induced chain conformation transformation in poly(L-lactic acid) based piezoelectric film by infrared spectroscopy

摘要

In this investigation, the chain conformation transformation of the piezoelectric polymer of a poly(L-Lactic Acid) (PLLA) film was analyzed under an electric field for the first time using infrared spectroscopy. It is revealed that the piezoelectric shear mode coefficient d_(14) (～10 pC/N) of a stretched α form PLLA film mainly comes from the rotation of C = O dipoles inside the polymer main chain. The reorientation of the dipoles causes the deformation of the crystal structure, which corresponds to a shear mode strain macroscopically in the PLLA film along a 45° direction to the polymer length. The back-bone of the molecular chain keeps its own conformation of a 10_3 helix under an external field up to 100 MV/m.