Polymer matrix, mobility

In semi-crystalline polymers the interaction of the matrix and the tiller changes both the structure and the crystallinity of the interphase. The changes induced by the interaction in bulk properties are reflected by increased nucleation or by the formation of a transcrystalline layer on the surface of anisotropic particles [48]. The structure of the interphase, however, differs drastically from that of the matrix polymer [49,50]. Because of the preferred adsorption of large molecules, the dimensions of crystalline units can change, and usually decrease. Preferential adsorption of large molecules has also been proved by GPC measurements after separation of adsorbed and non-attached molecules of the matrix [49,50]. Decreased mobility of the chains affects also the kinetics of crystallization. Kinetic hindrance leads to the development of small, imperfect crystallites, forming a crystalline phase of low heat of fusion [51]. 

In a cation-exchange membrane, the fixed negative charges are in electrical equilibrium with mobile cations in the interstices of the polymer as indicated in Figure 5.1, which shows schematically the structure of a cation-exchange membrane with negative charges fixed to the polymer matrix, and mobile cations and anions. 

PVA, close to 80°C. The polymer chains become mobile at the glass transition, allowing a partial re-organization of the nanotubes in the matrix and a modification of the conducting network. The polymer mobility allows some relaxation in the structure with possible better intertube contacts and loss of nanotube alignment which favors the contact probability. Both mechanisms can explain improvements of conductivity at the glass transition of the polymer. 

There are numerous references that show a correlation between matrix properties and reaction rates (Labuza et al., 1977 Roos, 1993 Bell and Hageman, 1994 Buera and Karel, 1994 Bell, 1996), but arguably not to the exclusivity of solvent-based effects, and never with a direct link to the mobility of the reactant itself rather than the polymer. Yet there are a handful of studies that come very close to showing a direct link between reactant mobility and polymer mobility. 

Contrast arises from polymer matrix The mobility of the net-chains depends on the concentration of a solvent due to the softening influence of the solvent. It is possible to monitor the changes of mobility of the net-chains during a transport process. For responsive polymers, it is also possible to monitor the drastic change in mobility dining the volume phase transition, e.g., induced by heating. 

Considering, for instance, a system containing 1 nm thick plates, Ipm in diameter, the distance between plates would approach 10 nm at only 7 vol% of plates [217]. The behavior of PNCs can be rationalized as follows. The proliferation of internal inorganic-polymer interfaces means the majority of polymer chains reside near an inorganic surface. Since an interface restricts the conformations that polymer molecules can adopt, and since in PNCs with only a few volume percent of dispersed nanoparticles the entire matrix polymer may be considered as nanoscopically confined interfacial polymer, the restrictions in chain conformations will alter molecular mobility, relaxation behavior, and the consequent thermal transitions such as glass transition temperature of the composites [217]. 

CPNCs with a semicrystalline matrix have complex morphology and diverse mobility, as the type and level of crystallinity varies and the Tg of the matrix polymer may be below or above the ambient temperature. There is also a greater diversity of chemical composition of these polymers. Considering the industrial importance of CPNC with PA-6 and PP matrices, only these two types are discussed. 

Some battery separators are swollen by battery electrolyte solutions and function as a solid polymer matrix with mobile conducting ions. In the last few years a number of alkali metal containing polymers, usually based upon poly(ethylene oxide) or derivatives thereof, have been described for use with non-aqueous Li based batteries. 

Figure 7.2 shows that the diffusion coefficient of the plasticizer decreases as the number of carbon atoms in alcohol of phthalate ester increases. It was also found that molecules with a compact structures diffuse slower than extended structures with all other factors being equal. Figure 7.3 shows that the presence of plasticizer increases the diffusion rate. This is caused by an increased mobility in the matrix polymer. Figure 7.4 shows that the rate of diffusion also increases when temperature is increased. These data are in agreement with the principles of free volume theory. 

The example given in Figure 10.30 shows improvement in ionic conductivity due to increased mobility of LT ion in the matrix. Also increased mobihty of matrix polymer increases ionic conductivity as work on dielectric characteristics of highly plasticized membranes shows. Increase in the amount of the plasticizer and decrease in its molecular weight (either acid or alcohol) contributes to the increase in ionic conductivity. ... 

Reptation assumes that the mobility of the matrix polymer plays no role in the relaxation of the tube constraint felt by a test molecule. However, if the matrix chains were very much more mobile than the test chain, additional lateral motion of the chain might be permitted by virtue of the constraining chains themselves moving away. This type of motion is called constraint release or tube renewal , and may be operative if some of the matrix chains are significantly shorter or intrinsically more mobile than the test chain (Green 1991, Composto etal. 1992). 

Akcasu et al. [74] attempted to identify the fast and slow modes with the two modes observed in dynamic scattering experiments from ternary polymer solutions. They defined the vacancies as the third component in a mixture of A and B polymers and concluded that the slow mode was obtained when vacancies were gradually removed, resulting in an incompressible binary mixture of A and B. The fast mode was obtained in the opposite limit of high vacancy concentration or a matrix with very high mobility. Since the polymer mobility and the vacancy concentration are small below, and high above, Tg, this suggested that the slow and fast-mode theories described interdiffusion below and above Tg, respectively. 

In addition to its structure, the dynamics of the interphase are extremely important. Studies on poly(styrene) have shown not only that there exists significant polymer mobility below Tg, but that these nanocomposites display a large range of mobilities both above and below Tg, indicating a large range of distinctly different polymer environments. This, in turn, points to fundamentally different matrix mobility near the silicate surface. Similar results have also been found in poly(methylphenylsiloxane) nanocompos-ites, while a number of other studies on a variety of systems have reached similar conclusions. ... 

The activation energy of dipole-dipole and spin-rotational interaction between carbon atoms for both liquid TBP and supported TVEX resins are collected in Table 8.3. The lower difference on the activation energy of spin-rotational interaction E(,(sj) for the C-4 atom of TBP in TVEX matrix compared with C-4 atom of 100% TBP is connected with effect of polymer matrix on mobility of extractant butyl chains. Increase of activation energy of dipole-dipole interaction for carbon C-3 and C-4 atoms of tri-butylphosphate in TVEX (as compared with liquid TBP) is caused by change of TBP conformation composition due to influence of TVEX matrix. 

It has been shown that interfacial regions in particulate-filled elastomeric nanocomposites represent the polymer layer, adsorbed by nanofiller surface. This layer is formed by a diffusive mechanism. The last is realized at the expense of polymer matrix molecular mobility. 

The mobility of reactants depends not only on the type of reaction as well as the size and shape of reacting groups, but also on the molecular motion and free volume distribution in the matrix polymer. Three types of heterogeneity can be distinguished. Microhetrogeneity due to a heterogeneous free volume distribution would lead to... 

As has been outlined in Chapt 3, the isomerization reactions in amorphous polymer solids are appreciably influenced by local mobility and heterogeneity of reactive sites, often leading to the deviation of reaction profiles from first-order kinetics. However, this situation allows us to obtain an insist into the microstructure of amorphous polymer solids, e.g. distribution of local free volume, by using photoisomerization reactions as molecular probes. Since the photochromic phenomena in polymer solids were reviewed by Smets in 1983, our discussion below will be limited to more recent advances, putting emphasis on the explanation of non-homo-geneous progress of reactions in terms of the distribution of local free volume in matrix polymers. 

The photodecoloration of the cyclized form of fulgide in PMMA film proceeds following first-order kinetics, and its quantum yield (4> = 0.06) is the same as that in toluene solution This fact suggests a very small critical free volume v, and also suggests that the ring-opening decoloration reaction is not restricted by the mobility of Ae matrix polymer at room temperature. The apparent rate of photodecoloration... 

The polymer viscosity influences the mobility of the filaments in the melt and therefore their distribution in the molded parts. The higher viscosities act as shearing forces to degrade the glass bundles and influence the bundle size distribution in the matrix polymer system. 

Understanding the mechanisms of polar order decay is crucial for the tailoring of new exploitable active materials. In contrast with crystals, polymers containing oriented molecules tend to evolve towards a randomization of dipole orientation when the field is removed. Relaxation in such poled systems, following the molecular statistical model, arises from thermal reorientation whose rate is governed by the mobility of the molecules in the matrix. The mobility is in turn determined by a number of parameters including, in particular, glass transition temperature (Tg) and the amount of free volume in the polymer. 

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