Electrical Conductivity Enhancement of PTFE (Teflon) Induced by Homogeneous Low Voltage Electron Beam Irradiation (HLEBI)

摘要

Electrical conductivity (σ) enhancement, control, aging stability, and linear relation between σ and reciprocal temperature (1/7) in PTFE (Teflon) had been examined by homogeneous low potential electron beam irradiation (HLEBI). Irradiations up-0.432 MGy were found-raise the σ of PTFE more than two orders of magnitude. In addition, control of electron movement or Fermi level by HLEBI on polymers seems possible since at low HLEBI levels up-0.216 MGy, a strong dependence on σ was observed. Aging stability investigation showed the saturated conductivities at 10~6 s (σ_s) (2.5 x 10~(-19) and 3.6 x 10~(-15) S m~(-1)) obtained at EB doses of 0.0432 and 0.432 MGy, respectively were approximately 4.9 and 70.6 times higher than σ of untreated PTFE (5.1 x 10~(-17)Sm~(-1)). Although the aging initially reduced the σ of irradiated samples, σ_s were remarkably higher than the untreated. For example, the lower dose 0.0432 MGy samples decayed significantly, but its σ_s value (2.5 x 10~(-16) S m~(-1)) was still about 490% above untreated condition at 5.1 x 10~(-17) S m~(-1). ESR (electron spin resonance) measurements showed aging for 10~6 s only slightly reduced the peak intensity of irradiated PTFE. This indicated the charge carriers generated did not easily decay. Results agree with the literature where PTFE was irradiated with VUV and radicals such as CF_3+ did not substantially decay with aging. Since the slopes of linear relationships between logarithmic electrical conductivity (In σ) and reciprocal temperature (1/7) of all PTFE samples irradiated were approximately equal-that before treatment from 303-375 K, HLEBI didn't convert the cr system. The small irradiation dose of 0.0432 MGy raised the electrical conductivity at room temperature. At higher temperatures above ~375 K, the 0.0432 and 0.432 MGy-HLEBI generated drops in conductivity cr. When unstable dangling bonds with isolated radicals at terminated sites are assumed-be formed in irradiated PTFE, the cr recovery by heating-424 K as well as high σ of irradiated PTFE could be explained. HLEBI probably generated dangling bonds in the form of radicals acting as acceptors-carry charge. Since a chemical dopant was not needed-act as a charge carrier, HLEBI could probably be an attractive method-attain homogeneous doping of organic films.