Polymer chain movement

The primary cause of the shrinkage of cellulosic fibres is the fact that these fibres can readily absorb moisture. This absorbed moisture facilitates internal polymer chain movements in the amorphous fibre areas by lubrication. It disrupts the... 

Several factors affect the permeation rate of the polymer. Temperature increase raises the permeation rate for two reasons. First, solubility of the permeant increases in the polymer at higher temperatures. Second, polymer chain movements are more abundant which allow easier diffusion of the permeant. The permeation rate of gases increases at higher partial pressures. For liquids, permeation rates rise with an increase in the concentration of the permeant. Unless the permeant species are highly soluble in the polymer, the permeation rate increases linearly with pressure, concentration, and the area of permeation. 

Increasing the temperature will increase the permeation rate because the solubility of the permeant in the polymer will increase, and as the temperature rises, polymer chain movement is stimulated, permitting more permeant to diffuse among the chains more easily. 

The degree of crystallinity of the PET polymer is affected by the presence of the nanoparticles. Crystallization temperature increases significantly with the incorporation of the nanoparticle. The glass transition temperature also increases on nanoparticle incorporation and this is due to the restriction of polymer chain movement imposed by the presence of the nanoparticle. Hernandez et al. have performed thermal analysis on SiO -Poly 2-hydroxyethyl acrylate hybrids [77]. 

The charge movement that is most similar to the polymer chain movements discussed in Chapter 1 is dipole orientation. Under the influence of an electric field, dipoles that are originally randomly orientated are turned so that the charged ends are attracted to the appropriately charged electrodes (Figure 12.7). 

Several theories have been developed to account for the observed characteristics of the plasticization process Daniels has recently published a review of plasticization mechanisms and theories [8]. Although most mechanistic studies of plasticization have focused on PVC, much of this information can be adapted to other polymer systems. The lubricating theory of plasticization holds that plasticizers act as molecular lubricants to facilitate polymer chain movement when a force is applied to the plastic. It starts with the assumption that the unplasticized polymer chains do not move freely because of surface irregularities and van der Waals attractive forces. As the system is heated and mixed, the plasticizer molecules diffuse into the polymer and weaken the polymer-polymer interactions. Portions of the plasticizer molecule are strongly attracted to the polymer while other parts of the plasticizer molecule can shield the polymer chain and act as a lubricant. This reduction in intermolecular or van der Waals forces among the polymer chains increases the flexibility, softness, and elongation of the polymer. 

Free volume is a measure of the internal space available within a polymer. As free volume is increased, more space or free volume is provided by molecule or polymer chain movement, making the polymer system more flexible. In the unplasticized polymer, free volume arises from movement of polymer end groups, polymer side chains, and internal polymer motions, while in the amorphous region,... 

Show different ion conduction mechanisms at temperatures above or below Tg. Below Tg, the conduction mechanism is changed from the normal coupling and polymer chain movement to ion decoupling and hopping by thermal excitation, i.e., hopping mechanism and chain-assisted ion transfer. 

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