Simulations, evidence analysis techniques

Finally we should consider the location of the chain ends. On physical groimds it can be argued that a chain with its end near a surface suffers a smaller loss of entropy by virtue of the surface than does a chain with a middle segment at the surface, so that the density of chain ends at the surface should be somewhat enhanced. This picture is supported by simulations for example in the variable density self-consistent mean field study of PDMS of relative molecular mass 3270 already cited, more than 50% of the population of the outermost layer of the polymer consisted of chain ends, even though chain ends represented only 17% of the total mass. On the other hand experimental evidence for chain-end segregation is much more equivocal. The reason for this is that, in order to detect such segregation, it is necessary experimentally to label the end of the chain in some way so that a surface analysis technique may be used to detect an excess of the ends. However, as we shall see in chapter 6, even a very small substitution at the end of a polymer chain may lead it to be... 

As we observed that a dozen of carbon atoms in the alkane chain is sufficient to simulate the electronic properties of polyethylene, it becomes evident that the XPS technique, by the analysis of the valence bands, will not be able to distinguish between polymers with different high molecular weights. 

The structure, conformation and intramolecular hydrogen bonds of crystalline and aqueous sucrose have been discussed in detail. Evidence for a transient inter-residue hydrogen bond in aqueous sucrose (0-2- -H O-T) has been discovered by ROESY spectroscopy imder supercooled conditions.Combined use of high resolution NMR techniques and dynamics simulations furnished a new model for the dynamical conformational behaviour of sucrose in water in which internal motions occur at the same rate as overall tumbling. A GROMOS force field analysis, modified to include a potential energy term for the fxo-anomeric effect, has been assessed for efficiency by application to a conformational analysis of a-maltose. ... 

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