Microbrownian motion

Dynamic mechanical measurements. Dynamic mechanical measurements 97) of the storage and loss components of the rigidity modulus (G G") at a single frequency are shown in Fig. 31. As is the case with all polyethers, there is a main relaxation region associated with the onset of microbrownian motion of the main chain. In the region of the melting temperature, a catastrophic drop in modulus appears. 

This spatial coil structure represents the most favorable state from the point of view of entropy the macromolecule tends toward this state to the extent allowed by external conditions (mobility). Under conditions of rising temperature or diffusion of solvents into the material, the mobility of the chain segments and side chains increases. Rotations and shifts are more frequent (molecular microbrownian motion). 

The majority of the different chemical and physical properties, as well as the morphology of microemulsions, is determined mostly by the microBrownian motions of its components. Such motions cover a very wide spectrum of relaxation times ranging from a few picoseconds to tens of seconds. Given the complexity of the chemical make up of die microemulsions, diere are many various kinetic units in the system. Depending on their natme, the dynamic processes in the microemulsions can be classified into three types. 

We shall consider a simple model for the a, P and (aj8) processes. We assume that a reference dipole at any instant t = 0) finds itself in a local environment r, and let V be the probability of obtaining this environnient. We assume that as time develops the dipole may partially relax via local motions in this environment r, and characterized by a decay function (pp t). If []r is the average moment observed for a time scale long compared with the local motions (Pr process), but short compared with the time scale for the microbrownian motions (a process), then the P. process has a magnitude —[] . We assume that the a process breaks down the environment r and relaxes the remainder of completely. The correlation function for this scheme is... 

At low temperatures (pp t) decays to zero far faster than cpM so that (pp t)(po, t) (Pp t) in this region. Thus Eq. (7) predicts two relaxation regions, a and p. The a process is due to microbrownian motions, and the faster P process is the net result of partial reorientations in a distribution of local environments. At very high temperatures the time scale required for microbrownian motions becomes shorter than that required for local motions. Physically, the local environment relaxes faster than the local motions. This would mean that the relaxation would occur through (p t) at these temperatures, and Fq(t) = (pa t This also follows from Eq. (6) for (pM(pp t) (p t). 

X21 and 229 2 also shown in Table 2. The calculated values of 3AXiTi is 0.09. For the transition at Tj, we have an approximate agreement with the predicted value of the glass transitions of polymer. This transition temperature is nearly the same as the temperature at which the absorption peak appears on the dynamic loss modulus curve of the wool. Evidence from the dynamic and the thermal expansion experiments suggests that the transition is caused by the onset of the microbrownian motion in the amorphous regions of wool. 

Figure 5 presents the correlation of log(D) and E at 35 C. The correlation between log(D) and E was similar to the correlation between log(D) and CED. These results suggest that gas diffusivity is influenced by motion of not only the side chain but also that of the backbone chain in the polymer because E, which is nearly equal to E in our study, includes effects of both primary dispersion based on microbrownian motion and secondary dispersion based on local relaxation modes or side chain motion. Gas diffusivity may increase as E decreases due to an increase in segmental motion. Elasticity depends on the polymer structure, and E is useful for the estimation and analysis of gas diffusion. Koros et al.(77), Yee et al.(32) and Muruganandam et al.(33) have studied the rdation between diffusivities and results of viscoelastic measurements in polycarbonates. Their values of D and E (E E ) agree well with our results in Figure 5. These results suggest that gas diffusivities may be strongly influenced by total motion of segments in many families of polymers, including polyimide.

Neither does the microbrownian motion of the amorphous mesh inhibit the liquid crystal phase, nor does the positional order of the molecules interfere with the elasticity. Hence, as a hybrid material that combines LC and rubber characteristics, LCEs have unique properties in which the molecular orientation of the liquid crystal is strongly correlated with the macroscopic shape (deformation) which is unparalleled to other materials. The most prominent example in the physical properties derived from this property is the huge thermal deformation. Figure 10.1 shows an example of the thermal deformation behavior of side-chain nematic elastomers (NE) [3]. When the molecules transform from the random orientation in the isotropic phase to the macroscopic planar orientation in the nematic phase, the rubber extends in the direction of the liquid crystal orientation and increases with decreasing temperature as a result of an increase in the degree of liquid crystal orientation. This thermal deformation behavior is reversible, and LCEs can be even considered as a shape-memory material. Figure 10.1 is from a report of the early research on thermal deformation of LCEs, and a strain of about 40 % was observed [3]. It is said that LCEs show the largest thermal effect of all materials, and it has been reported that the thermal deformation reaches about 400 % in a main-chain type NE [4]. 

Many models for motion in amorphous polymers have been proposed. " Amorphous polymers usually exhibit two broad relaxation regions called a (associated with the dynamic glass transition and being due to the microbrownian motions of chain segments) and P (due to local chain motions or side group motions and usually observed in the glassy state). We shall discuss these below in relation to specific cases. 

Solid amorphous polymers normally exhibit two relaxation processes which coalesce to form one process at high temperatures. The a process is observed above the glass transition temperature and is due to the microbrownian motions of the chains. The jS process, which is normally observed below Tg but can also be observed in a limited range above Tg, is due to limited motions of the main chain or, where present, the motions of dipolar side chains. The frequency-temperature location of these processes is indicated schematically in Figure 8 and the coalescence of a and j processes to form the ajS process is seen to occur above Tg. The loci of these processes vary greatly with chemical structure, tacticity, plasticizer content and sample orientation. Transition maps have been given for many amorphous polymers, based on dielectric, NMR and mechanical relaxation results. The loci obtained from the different methods are found to be similar for a given polymer. 

Discussion. In hydrostatic and rheomolded polystyrene, the TSC peak associated with the glass transition is situated, like in reference polystyrene, in the temperature range 90-100 C. Its increasing magnitude has been attributed to conformational changes favoring microbrownian motion. The width of the distribution function of the relaxation time and also the order parameter is... 

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