Reversing-Pulse Electric Birefringence of Poly(γ-methyl l-glutamate) in Hexafluoro-2-propanol

Abstract

Abstract Reversing-pulse electric birefringence (RPEB) signals of poly(γ-methyl l-glutamate) (PMLG) were measured, for the first time, in hexafluoro-2-propanol at 25 °C and at 535 nm. Quantitative analyses were carried out on the steady-state birefringence and the field-free decay time (<τ>EB) in the wide field strength region and also on the rise, reverse, and decay portions in the low field strength region by taking into account the continuous molecular length distribution of a fractionated PMLG sample. The weight-average length (lw), permanent dipole moment (μw), polarizability anisotropy (Δαw), and the degree of polydispersity (lw/ln) were evaluated by two procedures: one from the analysis of the reverse-transient portion and the other from the field-free decay portion of RPEB signals. These two sets of the parameters should be identical with each other, if the electrooptical and hydrodynamic properties of PMLG do not change during the field-on and field-off processes. However, the length of the PMLG helix is shorter by about 18% in the presence of an electric field than that in the absence of the field. In order to explain this discrepancy, a new concept of reversible conformational transition under the external electric field is introduced.