Molecular Chains, Concatenation

The very idea of an intermolecular chemical bond, in conjunction with crystal periodicity, leads to the concept of chain formation. One is never too careful, however, because crystal structures are by definition periodic in space and, vice versa, the concept of chain can surreptitiously sneak in without the need of a real chemical bond. Once again, there is a dichotomy between geometrical appearance -a ribbon of molecules close to each other - and objective physics, or the presence of an effective electronic interaction between the partners in the supposed periodic structure. The basic question is, how and when is one allowed to trace a chemical bond, and thus legitimately to draw a chain structure The answer - or at least what in this author s opinion is the only objective and physically sound answer - must come from quantitative evaluation of the involved contact energies, as discussed in the next paragraphs. 

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We have not considered the difference between the sol that might be extracted rom a real network and that which is permanently incarcerated by virtue of its concatenation with the network. For more elaborate calculations, chain trajectories %rauld be required to distinguish bet%men molecules of these ttio types. For low molecular weights, e.g. n 50, the proportion of incarcerated sol molecules should be small since the loops that are formed eu e too small to be wrapped euround by another chain. 

Several models for the structure of wheat glutenin have been proposed. One of the earliest molecular models was that of Ewart [62]. He subsequently modified the model. Ewart s latest model shows one disulfide bond between two adjacent polypeptide chains of glutenins, which consist of linear polymers. Ewart pointed out that the rheological properties of dough are dependent on the presence of theologically active disulfide bonds and thiol groups as well as on secondary forces in the concatenations [63]. 

Self-diffusion becomes much slower in high-molecular-weight concentrated solutions. A theory for this process has been developed by deGennes. A chain of N monomers in a semidilute or concentrated solution can be represented as a concatenation of blobs of rms length. The chain is constrained in a tube of other chains of length L = (N/g%, where g is the number of monomers per blob. The chain itself has a mean-squared end-to-end length (r = N / g if. 

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