Neutral polymer slow modes

The modes under consideration here are not the same as the two modes considered in the previous section. Dilute chains have a translational diffusion mode, and a prominent internal mode that relaxes more rapidly than the translational mode. 

The term mode carries certain implications that may or may not be physically correct. Consider two possible descriptions of the same intermediate structure factor, namely 

Here A is an amplitude, x and 1 — x are the relative amounts of two exponential decays, and l (t) is a single function that happens to have a rapid decay, an intermediate plateau, and a final long-time decay. WithEq. 11.10 the fast and slow motions are both happening independently at all times. There are thus two modes. In Eq. 11.11 there is a single relaxation of somewhat complex form 4 (t) has fast and slow parts, but the slow part of 4 (r) is actually absent at early times b(r) is a single complex relaxation. 

Several critical experiments show what the slow mode apparently is not. I say apparently because even with modern instrumentation there remain disagreements. Laboratories do not agree on the presence or prominence of the mode under what 

Even with modem instmmentation, there is disagreement as to whether or not a given system has a slow mode. A good example in this lack of agreement is presented by the experiments of Brown and Stepanek(29) and Wang, et a/. (30) on polystyrenes in diethylmalonate. The polystyrenes used in the bulk of both studies 

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The phenomenology of the slow mode is complex. Early suggestions that the neutral polymer slow mode arises from dust or other artifacts are clearly disproved by modern work. However, some systems apparently do not show a slow mode, so there is no reason to doubt early statements that no slow mode had been observed in particular systems(28). 

The properties of the neutral polymer slow mode are remarkably similar to the features of the Kivelson glass model. The one difference is the control variable Kivelson and collaborators treat a Lennard-Jones or similar system in which the control variable is the temperature(88-90).In the largely athermal polymer... 

This section briefly considers the slow mode often seen in S q, t) of polyelectrolytes, especially at low ionic strength. The polyelectrolyte slow mode resembles the slow modes seen with some neutral polymers. While most of the remainder... 

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