Optical properties of PVDF-TrFE and PVDF-TrFE-CTFE films in terahertz band

Abstract

Polymers have enormous potential in the optoelectronic and biomedical fields due to flexibility, biocompatibility, and ease of fabrication. Recent developments in the use of terahertz (THz) waves for biomedical and security applications demand information on the optical properties of the polymers and polymer composites in this region. In the present work, transmission, refractive index (n), and extinction coefficient (k) of PVDF-TrFE (75/25 mol.) copolymer and PVDF-TrFE-CTFE (73/23/4 mol.) terpolymer films with different thicknesses (40 µm, 60 µm, 80 µm) are measured by the THz-TDS system (up to 1 THz). PVDF copolymer and terpolymer films show average transmission of more than 90% irrespective of thickness. The average refractive index of PVDF-TrFE (75/25 mol.) copolymer and PVDF-TrFE-CTFE (73/23/4 mol.) terpolymer films are 1.50±0.04 and 1.45±0.05 respectively. The estimated extinction coefficient is considerably low for both polymer films for frequencies less than 0.6 THz. The average indices for PVDF-TrFE and PVDF-TrFE-CTFE films are close, however, the loss in PVDF-TrFE films is larger than the PVDF-TrFE-CTFE films. High transmission, low loss and ferroelectric properties make these PVDF based polymers highly desirable in light-wave manipulation, flexible electronic and solar devices.

Structure and Dielectric Properties of Poly(vinylidenefluoride-co-trifluoroethylene) Copolymer Thin Films Using Atmospheric Pressure Plasma Deposition for Piezoelectric Nanogenerator

“…In general, in the case of increasing a film thickness, piezoelectric polymer film can improve an electrical property, such as dielectric strength and energy density, especially in a piezoelectric nanogenerator [ 34 ], whereas, for the optical properties of PVDF-TrFE film, the optical transmission of PVDF-TrFE film is reported to be reduced due to a loss of light, thus resulting in increasing the refractive index with an increase in the film thickness [ 35 ]. It will be necessary to carry out further study on effects of the film thickness change through both an increase in the concentration of the precursor and the deposition time on the electrical property for an application of a piezoelectric nanogenerator.…”

“…Before post-heating, the sample was predominantly coated with the DMF layer, and then P[VDF-TrFE] nanoparticles (NPs) were not observed.After post-heating at 160 • C for 3 h, the deposited film had a smooth surface with P[VDF-TrFE] NPs, as shown in Figure6b. Moreover, the FE-SEM measurement confirmed a small amount of bubble particles due to DMF solvent attached to the P[VDF-TrFE] thin film.In general, in the case of increasing a film thickness, piezoelectric polymer film can improve an electrical property, such as dielectric strength and energy density, especially in a piezoelectric nanogenerator[34], whereas, for the optical properties of PVDF-TrFE film, the optical transmission of PVDF-TrFE film is reported to be reduced due to a loss of light, thus resulting in increasing the refractive index with an increase in the film thickness[35]. It will be necessary to carry out further study on effects of the film thickness change through both…”