Polymers segmental mobility

The analyte sensitivity and response time of a PVC film can also be markedly improved with addition of plasticizers such as tributyl phosphate (TBP) or tripropyl phosphate (TPP), since it is well established that the presence of plasticizer in the polymer-encapsulating medium increases gas diffusion rate by increasing the degree of polymer segmental mobility. It is... 

Nevertheless, the migration of water into the fiber is sufficient to produce the above-mentioned plasticization effect. The chain mobility is inaeased, as indicated by a decrease of the glass transition temperature by 35—50 C This is a very fortunate fact, because dyeing of the fibers is possible only above the Tg, where the increased polymer segment mobility permits dye diffusion within the fiber. For the commercial polyacrylonitrile copolymer fibers, the Tg in water hes in the r on of= 80 so that dyeing at, or slightly below, the boiling point of water becomes... 

Diffusion coefficient D) is the ability of the penetrant to move among the polymer segment. It is a kinetic parameter which depends on the polymer segment mobility. Sorption is a surface phenomenon, and it is an indication of the tendency of the penetrant to dissolve into the polymer. Permeation on the other hand, can be considered as the combined effect of sorption and diffusion process. From equation 22.5, it can be inferred that the sorption process controls the permeability. 

The results are presented in Table 2. Parameter X is a constant related to the structure of the network, and the exponent n is related to the type of diffusion, being Fickian for n values of 0.45-0.50 (rate of diffusion of solvent is less than polymer segmental mobility), whereas 0.50< <1.0 indicates a anomalous transport, non-Fickian diffusion type [8-10, 11]. Equation 2 was applied to... 

Another likely source of error in all three models is related to the very high solubility of CO2 in PPO. In both the Koros and Paul and Barrer models, the characteristic diffusivity parameters are assumed constant on the basis of the assumption that polymer segmental mobility does not significantly change as a result of penetrant-induced dilation. This approximation ultimately breaks down and plasticization begins to dominate the behavior of the system (Fig. 21). 

This arises in polymer/permeant systems which obey Fickian diffusion (described later in Section 20.4). The rate of diffusion of permeant molecules is much less than the polymer segment mobility. Under these conditions, the rate at which sorption equilibrium is approached is independent of swelling kinetics. As shown in Figure 4, the sorption curve vs, t ) is linear in the... 

As described in the previous sections, the diffusivity D is a kinetic parameter and is related to polymer-segment mobility, whilst the solubility coefficient S is a thermodynamic parameter which is dependent upon the strength of the interactions in the polymer/permeant mixture. Hence D and S are affected in different ways by variables such as permeant concentration and type. However, since the permeation behaviour depends on both D and S, it is clear that the permeation coefficient P will vary in a more complex fashion. 

In situ spectroscopy is used to study the plasticisation of glassy polymers by high-pressure and supercritical C02. The methodology for in situ spectroscopic analysis of the interactions between C02 and polymers is described. The changes in IR spectra of C02 incorporated into various polymers indicate a specific interaction between C02 and polymer functional groups. Increased polymer segmental mobility is also observed, indicative of the plasticisation phenomenon. Implications of these discovered molecular interactions are discussed. 25 refs. 

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