A decrease in the electrical durability, which is defined as an amount of time required for dielectric breakdown at a constant electric field strength, of polyethylene and Lavsan (polyethylene terephthalate) films under tensile loading is registered in a temperature range from 100 to 300 K. It is established that the pulling apart of the axes of neighbor chain molecules in consequence of tensile loading gives rise to a decrease in the energy level of the intermolecular electron traps. In the amorphous region of a polymer, this accelerates the release of electrons from the traps through over-barrier transitions at higher temperatures ranging from about 230 to 350 K and quantum tunneling transitions at lower temperatures in the range from about 80 to 200 K. As a result, the time required for the formation of a critical space charge, i.e., the waiting period of dielectric breakdown, decreases, which means a reduction in the electrical durability of polymers.

Зарегистрировано снижение электрической прочности (измеряемой как время ожидания пробоя диэлектрика в постоянном по знаку и величине электрическом поле) при растягивающем нагружении пленок полиэтилена и лавсана (полиэтилентерефталата) в области температур 100-300 K. Установлено, что вызываемое растягивающим нагружением полимера раздвижение осей соседствующих цепных молекул приводит к уменьшению энергетической глубины межмолекулярных ловушек электронов. Это ускоряет высвобождение электронов из ловушек посредством надбарьерного перехода при повышенных температурах (~230-350 K) и туннельного перехода при пониженных температурах (~80-200 K) в аморфных областях полимеров. В результате происходит сокращение времени формирования критического объемного заряда --- времени ожидания пробоя, что и означает снижение электрической прочности полимеров. DOI: 10.21883/FTT.2017.01.43972.258

The kinetics of electrical damage (breakdown) of polymer films 20–50 μm thick in a constant-sign field of 0.5–0.6 GV/m at 77–300 K has been studied. At elevated temperatures (250–300 K), the exponential temperature dependence of the durability and the above-barrier thermal-fluctuation mechanism of electron emission from traps, i.e., space charge accumulation leading to breakdown, take place. At low temperatures (77–200 K), there are separate local decreases in the durability (minima) at the athermal durability level. The identity of the temperatures of durability minima and measured thermoluminescence maxima of polymers was found. A conclusion is made about the mechanism of thermally stimulated tunneling (subbarrier emission) of electrons from traps.

The time of expectation for breakdown (life-time, tau) was measured as a function of temperature (T) and tensile stress (sigma) for a variety of polymers, including nylon-6, polyethylene, poly(ethylene terephthalate) and poly(tetrafluoroethylene). At moderate temperatures (above approximately 200 K), the tau(1/T)-sigma-dependences are exponential (of the Boltzmann-Frenkel type). The elementary acts of polymer fracture occur at these temperatures through the thermal-fluctuation above-barrier transitions. At low temperatures (below approximately 200 K), tau is T-independent (an athermic plateau) and, therefore, the above-barrier mechanism is ruled out. It is concluded that the elementary acts of fracture proceed at low temperatures via the tunnel below-barrier mechanism. Possible types of tunnel processes (tunneling of atoms or electrons) are discussed.