Polymer chain motion

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.

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. 

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. 25a and b. A protein resistant surface based on the steric repulsion argument commonly used in the colloid stability field U0). The interaction between a polyethylene oxide grafted surface and a protein solution is shown, a. suggests an excluded volume or steric repulsion mechanism b. the surface dynamics or polymer chain motion mechanism (from Ref., 33))... 

Label Effect. In order to assess at least partially the effect of the label on the chain dynamics, we also performed measurements on dilute solutions of 9,10-dimethyl anthracene. The reorientation time for the free dye in cyclohexane was - 10 psec, 50 times faster than the time scale for motion of the labeled chain in cyclohexane. Hence we conclude that the observed correlation functions are not dominated by the hydrodynamic interaction of the chromophore itself with the solvent, but can be attributed to the polymer chain motions. 

Figure 3.66 shows the steady-shear viscosity for a polymer system at three molar masses. Note the plateau in viscosity at low shear rates (or the zero-shear viscosity). Also note how the zero-shear viscosity scales with to the power 3.4. (This is predicted by Rouse theory (Rouse, 1953).) Figure 3.67 shows the viscosity and first normal-stress difference for a high-density polyethylene at 200 C. Note the decrease in steady-shear viscosity with increasing shear rate. This is termed shear-thinning behaviour and is typical of polymer-melt flow, in which it is believed to be due to the polymer chain orientation and non-affine motion of polymer chains. Note also that the normal-stress difference increases with shear rate. This is also common for polymer melts, and is related to an increase in elasticity as the polymer chain motion becomes more restricted normal to flow at higher shearing rates. 

The rate of polymer chain motion required to decrease the intersite separation allowing electron self-exchange to occur... 

For the CH and CH2 carbons of poly(vinylmethyl ether) in 15% CDCI3 solution, the minimum of nT is observed at 25.15 MHz at a temperature about 110°C lower than that of the bulk poly(vinylmethyl ether) minimum. At the minimum, nTi is 0.070 s, as observed in bulk, and is much higher than the values that can be derived from specific polymer chain motional models. 

It has been shown in chapters 4 and 6 that the individual mechanisms describing polymer chain motion in the bulk are often complex. An individual segment may simultaneously execute small-angle libration or rotational diffusion (10 < Tc < 10 s) and rotational jump motion with a broad distribution of correlation times (10 < < 10 s). An amorphous material may... 

At 77 K the polymer chain motions in PMMA and PS are very restricted, hut as the temperature is increased to room temperature, the side chains become mobile. Thus, the polymer radicals formed in PMMA and PS on radiolysis at 77 K are relatively stable, but they decompose on annealing to higher temperatures. 

Polymer chain motion, Tg Damping, creep and relaxation, dielectric constant... 

The first molecular theories concerned with polymer chain motion were developed by Rouse (57) and Bueche (58), and modified by Peticolas (59). This theory begins with the notion that a polymer chain may be considered as a succession of equal submolecules, each long enough to obey the Gaussian distribution function that is, they are random coils in their own right. These submolecules are replaced by a series of beads of mass M connected by springs... 

The temperatures shown in Figure 2.5b are significantly above the glass transition temperatures of polystyrene, 100°C, and poly(methyl methacrylate), 106°C, so polymer chain motion, reptation, and interdiffusion take place. However, polystyrene and poly(methyl methacrylate) are immiscible, inter-diffusing only 20 to 50 A, as determined via neutron reflection techniques (21-23) see Section 12.3.7.Theoretical calculations (see Section 12.3.7.2) yield an interphase thickness of 27 A (3). 

Concentration of electrons Atomic nuclei concentration, atomic number Polymer chain motion, glass transition temperature... 

Polymer chain motion contributes to damping and dielectric constants, via conversion of mechanical or electrical energy to molecular motion. 

The conventional, and very convenient, index to describe the random motion associated with thermal processes is the correlation time, r. This index measures the time scale over which noticeable motion occurs. In the limit of fast motion, i.e., short correlation times, such as occur in normal motionally averaged liquids, the well known theory of Bloembergen, Purcell and Pound (BPP) allows calculation of the correlation time when a minimum is observed in a plot of relaxation time (inverse) temperature. However, the motions relevant to the region of a glass-to-rubber transition are definitely not of the fast or motionally averaged variety, so that BPP-type theories are not applicable. Recently, Lee and Tang developed an analytical theory for the slow orientational dynamic behavior of anisotropic ESR hyperfine and fine-structure centers. The theory holds for slow correlation times and is therefore applicable to the onset of polymer chain motions. Lee s theory was generalized to enable calculation of slow motion orientational correlation times from resolved NMR quadrupole spectra, as reported by Lee and Shet and it has now been expressed in terms of resolved NMR chemical shift anisotropy. It is this latter formulation of Lee s theory that shall be used to analyze our experimental results in what follows. The results of the theory are summarized below for the case of axially symmetric chemical shift anisotropy. 

Chari et al. (1994) reported the effect of SDS on both local polymer chain motions and long range dimensions of the polymer coil. They showed that when a PEO coil is saturated with SDS micelles, it is more swollen compared to free coils when it is in a good solvent. They also revealed that these swollen chains are not fully stretched. Their results showed that the polymer coil at saturation is more like a swollen cage rather than a necklace. 

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