Degradation modelling size effect

However, the available experimental data about degradation or dissolution of nanocatalysts need theoretical explanation on atomic and molecular levels in different models, with their specific reactions on nanoparticles and size effects in nanosystems. Unfortunately, modem theoretical approaches in simulations often lead to indefinite information about properties of nanoclusters, because of omitting quantum characters of interactions in such systems. 

A reliable procedure for determination of molecular parameters number, weight and z-averages of the molecular weight (Mj, i = n, w and z respectively) for polyethylenes, PE, by means of Size Exclusion Chromatography, SEC, has been developed. The Waters Sci. Ltd. GPC/LC Model 150C was used at 135 C with trichlorobenzene, TCB, as a solvent. The standard samples as well as commercial stabilized and not stabilized PE-resins were evaluated. The effects of sampling, method of solution preparation, addition of antioxidant(s), thermal and shear degradation were studied. The adopted procedure allows reproducible determination of and M , with a random error of 4% and M2, with 9%, within 2 to 72 hrs from the initial moment of preparation of solutions. 

The existence of UCST is typically attributed to the energy differences between polymer and solvent and of LCST to the so-called free-volume effects, which are dne to the differences in size and free-volume between polymer and solvent. Free-volume effects are small for nonpolymeric solutions and are discussed in conjunction with free-volume-based activity coefficient models in Section 16.4. The LCST was first discovered by Freeman and Rowlinson only about 40 years ago, but is now considered to be a universal phenomenon of polymer-solvent systems at high temperatures. In some cases, it is not observed if the polymer degrades before reaching the LCST. 

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