Chain motion

At very short times the compliance is low and essentially constant. This is the glassy state where chain motion requires longer times to be observed. 

An important characteristic of biomolecular motion is that the different types of motion are interdependent and coupled to one another. For example, a large-scale dynamic transition cannot occur without involving several medium-scale motions, such as helix rearrangements. Medium-scale motions cannot occur without involving small-scale motions, such as side-chain movement. Finally, even side-chain motions cannot occur without the presence of the very fast atomic fluctuations, which can be viewed as the lubricant that enables the whole molecular construction to move. From the point of view of dynamic... 

Figure 4. Two representations (on the left) of cation motion in a polymer electrolyte assisted by polymer chain motion only, and two (on the right) showing cation motion taking account of ionic cluster contributions.

Glassy state In amorphous plastics, below the Tg, cooperative molecular chain motions are frozen , so that only limited local motions are possible. Material behaves mainly elastically since stress causes only limited bond angle deformations and stretching. Thus, it is hard, rigid, and often brittle. 

Several other points are worth noticing Well-defined motions lead to well-defined spectra. Thus chain motion can be studied, where the analysis of 2H line shapes yields directly the number of conformations accessible for a given segment. Moreover, even more complicated motions not considered explicitely here lead to spectra, the angular dependence of which can be described by Equation (1 a). The corresponding line shapes can easily be calculated facilitating the analysis of the data. In glassy... 

As a first example of applying the techniques described in section 2 let us look at the chain motion of linear polyethylene (LPE). A detailed study of a perdeuterated sample, isothermally crystallized from the melt, has been carried out in our laboratory24,25,44). Since all of this work is published and, in fact, has been reviewed extensively17 we can restrict ourselves to stating the main conclusions here ... 

The number of the constraints to chain mobility shown in Fig. 16 decreases with increasing temperature, reflecting the increase of the free volume. From a comparison of the spectra in Fig. 15 with line shapes calculated for flexible chains on a diamond lattice 23 (one can infer that the average length of the flexible unit increases from 3-5 bonds at room temperyture to about 10-15 bonds at 380 K. Our model thus can quantitatively explain the gradual increase of the number of conformations accessible to the chain motion. The earlier XH wide line data 72 are also in accord with our findings. 

Any polymer contains some inner free space free volume distributed in a dynamic manner between its molecular chains (see Section 23.2). When it is exposed to a fluid (liquid or gas) the physical possibility exists for fluid absorption by the polymer, if the fluid molecules or atoms are small enough to fit into local regions of this distributed space during kinetic movements. As this happens, subsequent kinetic chain motion must allow for the newly absorbed fluid molecules and, hence, the polymer s overall volume will adjust accordingly this action will coincide with the formation of more free space around these fluid molecules—so the polymer will swell a little. This process will be continued until an equilibrium is reached ( equilibrium swelling ), by which time the extent of swelling can be considerable. The amount of fluid taken up and the rate at which this happens are both important, and are discussed in this and following sections. 

The classical example of a soUd organic polymer electrolyte and the first one found is the poly(ethylene oxide) (PEO)/salt system [593]. It has been studied extensively as an ionically conducting material and the PEO/hthium salt complexes are considered as reference polymer electrolytes. However, their ambient temperature ionic conductivity is poor, on the order of 10 S cm, due to the presence of crystalUne domains in the polymer which, by restricting polymer chain motions, inhibit the transport of ions. Consequently, they must be heated above about 80 °C to obtain isotropic molten polymers and a significant increase in ionic conductivity. 

The relaxation data for the anomeric protons of the polysaccharides (see Table II) lack utility, inasmuch as the / ,(ns) values are identical within experimental error. Obviously, the distribution of correlation times associated with backbone and side-chain motions, complex patterns of intramolecular interaction, and significant cross-relaxation and cross-correlation effects dramatically lessen the diagnostic potential of these relaxation rates. 

By application of proton multiple quantum (MQ) NMR experiments, information about the segmental order parameter, which is directly related to the restrictions on chain motion (cross-links) formed upon gelation of PVA, is obtained.103The quantitative study of rigid phase... 

NMR spectra and Tj measurements at different temperatures. The local polymer chain motion varies over a frequency range of 104-106 Hz in the nematic phase. The activation energy of this motion is found to increase with decreasing number ( ) of methylene units in the spacer, and exhibits odd-even fluctuations. In a study of a homologous series of main-chain LC polyesters, 13C CP/MAS and variable-temperature experiments reveal a conformation-ally more homogeneous and a less dynamic nature for the even-chained than for the odd-chained polymer structures.300... 

Fig. 22. Relaxation map for PBLG side chain motion. Experiments except 2H NMR measurements are open symbols, and PBLG-Kdi (filled circle) and PBLG-fd2 (filled triangle).

The jump rates obtained by the line shape simulations are plotted on the relaxation map in Fig. 22 together with values obtained by other experimental methods. The points of the mechanical and dielectric relaxations correspond to the process of the large-scale side chain motions refered to as the -process and follow the WLF equation very well above Jg,. 11 It should be noted that the present 2FI NMR results are located on the curve obtained by other relaxation experiments. This fact shows that... 

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