Molecular dynamics primitive relaxation

The evolution of the many-molecule dynamics, with more and more units participating in the motion with increasing time, is mirrored directly in colloidal suspensions of particles using confocal microscopy [213]. The correlation function of the dynamically heterogeneous a-relaxation is stretched over more decades of time than the linear exponential Debye relaxation function as a consequence of the intermolecularly cooperative dynamics. Other multidimensional NMR experiments [226] have shown that molecular reorientation in the heterogeneous a-relaxation occurs by relatively small jump angles, conceptually simlar to the primitive relaxation or as found experimentally for the JG relaxation [227]. 

The advanced molecular models described in this chapter, namely the Milner-McLeish model and the hierarchical model, involve combinations of multiple relaxation mechanisms reptation, primitive path fluctuations, and constraint release described by both constraint release Rouse motion and dynamic dilution. However, all these mechanisms can be captured in algorithms in which entanglements are viewed as slip links between two chains see for example Fig. 9.22. 

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