Radiation Effects on Thermal Properties of Polymers. I. Polyethylene (contd.)

Abstract

The information about radiation effects on the thermal properties of polymeric materials is of special interest as: (1) the temperature regime of technical structural units operated in the radiation fields is determined in many respects by the values of the material thermal constants and the rate of their degradation (2) the temperature and dose dependencies of heat conductivity and, especially, heat capacity characterize the polymer structure. The data on radiation effects on the thermal conductivity, heat capacity and diffusivity, linear thermal expansion, density, degree of crystallinity, heat and temperature of phase transitions were presented in the first part of this paper [ Nucl. Instr. Meth. in Phys. Res. B 185 (2001) 116–122] for polyethylene of high and low density, as a well-known and typical partly-crystalline polymer that is very convenient for investigation of the radiolysis processes. This part of the review examines such problems as reversible radiation effects on heat capacity, analytical models of the radiation-induced changes and anisotropy effects on the thermal conductivity, accumulated radiation energy (‘heat defect’) and important problems of specific action of different kinds of radiation on the thermal properties of the polymer and dose-rate effects, especially under vacuum.

Radiation Effects on Thermal Properties of Polymers. II. Polytetrafluoroethylene

“…The dose dependencies of X, 1 c and 1 a were found by solving the set of equations (2), (3) and (5), the values of 3 c and 3 a were assumed to be independent on irradiation dose. The results of 1 c and 1 a calculation are presented in table 2, and of crystallinity for T ir in table 3.…”

“…Values of X were determined from data on 3 (equation ( 2)) for the initial sample at T m 2 298 K. Then value of 1 a 2 09179 W (m.K) 31 was found from equation (5) for the same temperature. Assuming K II 2 50, the value of K 7 was found to be equal to 0.66.…”

“…The LET effect depends on the energy generation inside the track of charged particles, concentration of radiolysis of active intermediate species, their recombination, migration of energy from the track right up to the formation of intermediate products and migration of the radiolysis products along the matrix. The main aspects of the problem are examined in numerous publications, particularly in our review [43], and briefly for polyethylene in [5].…”

“…An analysis of the effects of radiation on the thermal properties is the objective of a set of planned reviews for a number of model polymers. The first part of the set, Briskman [4] and Briskman and Tlebaev [5], is devoted to polyethylene (PE). The irreversible radiation changes to the properties indicated above are analyzed by Briskman [4].…”

“…The irreversible radiation changes to the properties indicated above are analyzed by Briskman [4]. Reversible radiation effects on heat capacity, analytical models of radiation-induced changes and anisotropy effects in thermal conductivity, specificity of accumulation of ionizing radiation energy, and such important problems as the action of different kinds of radiation, dose rate effects, especially under vacuum, are examined by Briskman and Tlebaev [5].…”