Gamma Radiation Chemistry of Polydimethylsiloxane Foam in Radiation-Thermal Environments: Experiments and Simulations

Abstract

The γ radiolysis behavior of polydimethylsiloxane (PDMS) in the radiation-thermal environments (dose rate, 0.2 Gy/s) is studied to pinpoint the basic knowledge of the temperature (20–70 °C) effects. The non-monotonous temperature effects on the formation of gas products, paramagnetic species in silica, and cross-linking density are proposed to correlate with the complex chemical reaction mechanisms. Besides, molecular dynamics simulation and theoretical calculation are first performed simultaneously based on the radical chemistry and intricate material composition, making it easier to comprehend and further harness the radiolysis mechanisms and structure deterioration of PDMS. The γ radiation-induced primary gas products and dominant cross-linking phenomena are reproduced by the molecular dynamics simulations with a reactive force field, and the reaction mechanisms and physicochemical interactions among PDMS chains, gas products, reactive radicals, and silica fillers are thoroughly studied at the atomic scale. The thermochemistry of the barrierless radical coupling reactions and reactions with explicit high-barrier transition states is calculated at the M06-2X theoretical level with the 6-311g­(d, p) basis set. The barrierless reactions are all exothermal with the heat release of 321–618 kJ/mol, while the potential barriers for reactions with explicit transition states vary between 37 and 229 kJ/mol. The results show that γ radiation-induced radicals are crucial for the ensuing gas formation and cross-linking reactions, especially for the radical coupling reactions. The radical chemistry involved in the radiolytic PDMS is the key to understand and simulate its radiolysis behavior, according to the experimental and simulated results.

Molecule Dynamics Simulation of the Effect of Oxidative Aging on Properties of Nitrile Rubber

“…In recent years, molecular dynamics (MD) simulation has been employed as an effective theoretical tool to comprehend quantitatively the structure-performance relationships of polymer materials at the molecular scale, especially in modification of polymers and diffusion of small molecules in polymers [28,29]. Although the molecular dynamics simulation methods were preliminarily applied to estimate the thermal oxidative aging mechanism of rubber materials [30][31][32], the chemical reactions such as oxidation products during the aging process are not fully considered by researchers. For example, Wang et al [30] found that rubber at low compressive strain possesses high fractional free volume, molecular chain movement, and ozone permeability by molecular dynamics simulation.…”

Polymer degradation through chemical change: a quantum-based test of inferred reactions in irradiated polydimethylsiloxane

“…Common vectors for degradation arise from the ready uptake of environmental water [4][5][6][7] or absorption of radiation. [7][8][9][10][11][12] Understanding the degradation responses of PDMS has enormous practical applications, ranging from assessing environmental impacts [13][14][15] to establishing models for the aging and lifetime prediction of silicone components. [4][5][6][7][8][9][10][11][12]16,17 Ionizing radiation is a common cause for polymer degradation that can arise during component sterilization, 1,18,19 as a consequence of planned operation conditions, and as a driver in accelerated aging studies.…”

“…[7][8][9][10][11][12] Understanding the degradation responses of PDMS has enormous practical applications, ranging from assessing environmental impacts [13][14][15] to establishing models for the aging and lifetime prediction of silicone components. [4][5][6][7][8][9][10][11][12]16,17 Ionizing radiation is a common cause for polymer degradation that can arise during component sterilization, 1,18,19 as a consequence of planned operation conditions, and as a driver in accelerated aging studies. [7][8][9][10][11][12] In 1955, Charlesby proposed 20 a set of reaction schemes for crosslinking in irradiated PDMS that were quickly refined by others 21,22 and were based on IR vibrational spectroscopy, titration, mass spectra of off-gassing species, and chromatography (see Fig.…”

“…Common vectors for degradation arise from the ready uptake of environmental water 4–7 or absorption of radiation. 7–12 Understanding the degradation responses of PDMS has enormous practical applications, ranging from assessing environmental impacts 13–15 to establishing models for the aging and lifetime prediction of silicone components. 4–12,16,17…”

“…Ionizing radiation is a common cause for polymer degradation that can arise during component sterilization, 1,18,19 as a consequence of planned operation conditions, and as a driver in accelerated aging studies. 7–12 In 1955, Charlesby proposed 20 a set of reaction schemes for crosslinking in irradiated PDMS that were quickly refined by others 21,22 and were based on IR vibrational spectroscopy, titration, mass spectra of off-gassing species, and chromatography (see Fig. 1).…”