New X-ray method for monitoring of polymers radiation crosslinking
- Prof. Boris TOLOCHKO
- Mr. Marat SHARAFUTDINOV
- Prof. Boris TOLOCHKO (Institute of solid state chemistry and mechanochemistry)
In this work the effect of radiation of relativistic electrons on the crystal structure of polyethylene after radiation crosslinking studied. The main attention was paid to changes in the temperature of the Debye. The structure factor equation given earlier yields the diffracted intensities as though all atoms were stationary. As the temperature rises the atoms execute increased excursions from their average position. Such excursions can involve complex coupled motions of several atoms. However if one restricts consideration to just the independent motions of each atom there is a relatively simple trick that can be used which is to (artificially) modify the atomic scattering factors, f, of each atom to represent the net broadening of their electron clouds resulting from atomic motion. For example a given atom will have its "stationary" f changed to fT according to: fT = f exp(−B sin2θ / λ2) where T is the temperature and B = 8π2u2 (units of A2 ), u2 being the root mean square displacement of the atom from its average position. The B values are often referred to as B factors (Debye-Waller is a another, similar, term often used) and increase with temperature (typical values are 0.2 to 0.8 A2 ). So clearly temperature will modify the diffraction intensities by changing the various values of f to fT in the structure factor equation. To determine the Debye powder X-ray series was filmed at different temperatures of the polyethylene samples irradiated by relativistic electrons. The method allows to monitor the changes in the structure upon irradiation.