Chain scission diffusion controlled

As the sensitivity of AS 1160 to humidity is not well understood, the experimental matrix incorporates a controlled humidity experiment (F4). The use of 60 °C combined with 20 % RH correlates to a dew point of 29 °C and simulates relatively humid conditions. Under these conditions, the rate of moisture diffusion through the resin is accelerated with temperature potentially degrading the material either through hydrolysis, chain scission or plasticisation effects. 

In the case of PE irradiation, it has been established that the superficial oxidized layer undergoes essentially chain scission, whereas the behavior of nonoxidized core layers is dominated by crosslinking therefore, the samples become more and more heterogeneous as the dose increases and a skin core structure appears. If in an inert medium, y-rays penetrate in all directions of the material in an oxidative medium, the phenomenon is oxygen diffusion-controlled. A depth distribution will exist in the variation of carbonyl index, crystallinity, melting point, degradation products, and so on. 

The uptake of O2 by films of this polymer was shown to be diffusion controlled. This manifested itself in the small energy of activation of the oxidation process and in the fact that the overall chain scission reaction (i.e. the rate constant) was a function of the... 

Thus, in order to reproduce the effect of an experimentally existing activation barrier for the scission/recombination process, one may introduce into the MC simulation the notion of frequency , lo, with which, every so many MC steps, an attempt for scission and/or recombination is undertaken. Clearly, as uj is reduced to zero, the average lifetime of the chains, which is proportional by detailed balance to Tbreak) will grow to infinity until the limit of conventional dead polymers is reached. In a computer experiment Lo can be easily controlled and various transport properties such as mean-square displacements (MSQ) and diffusion constants, which essentially depend on Tbreak) can be studied. 

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