Liquid-like amorphous component

Our broad-line XH NMR analysis showed that this type of sample generally consists of the phase structure of lamellar crystallites and noncrystalline overlayer with a negligible amount of the noncrystalline amorphous phase [16,62]. In broad-line H NMR spectra of solution-grown linear polyethylene samples, a narrow component that suggests the existence of a liquid-like amorphous phase is hardly recognized. In Table 2, the three-component analysis of the broad-line XH NMR spectra of linear polyethylene samples with different molecular weights that were crystallized isothermally from 0.08% toluene solution at 85 °C for 24 hours under a nitrogen atmosphere is summarized. 

To elucidate the phase structure in detail it is necessary to characterize the molecular chain conformation and dynamics in each phase. However, it is rather difficult to obtain such molecular information, particularly of the noncrystalline component, because it is substantially amorphous. In early research in this field, broad-line H NMR analysis showed that linear polyethylene crystallized from the melt comprises three components with different molecular mobilities solid, liquid-like and intermediate molecular mobility [13-16]. The solid component was attributed to molecules in the crystalline region, the liquid component to... 

Finally, it is worth mentioning that the linear relationship between H and Tg has been derived only from one-phase systems (amorphous homo- and copolymers. Table 3.2). However, it can be applied to explain the micromechanical behaviour of multicomponent or multiphase systems containing at least one liquid-like component or phase (see Chapter 5). Another peculiarity of the polymers listed in Table 3.2 is that their main chains comprise only single C-C, C-0 or C-N bonds... 

Summarizing one can conclude that due to the empirical linear relationship between H and Tg in a rather broad range of Tg (-50 up to 250°C) which covers most commonly used polymers of the polyolefin-type and also polyesters and polyamides, it is possible to calculate the microhardness value of any amorphous polymer provided its Tg is known H =. 91Tg - 571). Furthermore, one can account for the contribution of soft liquid-like components and/or phases (characterized by a negligibly small microhardness) to the microhardness of the entire system. As we shall see in Chapter 5 the plastic deformation mechanism of such systems is different from that when all the components and/or phases are solid, i.e. have Tg above room temperature. 

In this form, in contrast to the traditional one (eq. (1.5)), the additivity law is applicable to multicomponent or multiphase systems comprising liquid-like components or phases displaying a more complex deformation mechanism than the case in which all the amorphous components have a Tg above room temperature. 

Most polymers that have been of interest as membrane materials for gas or vapor separations are amorphous and have a single phase structure. Such polymers are converted into membranes that have a very thin dense layer or skin since pores or defects severely compromise selectivity. Permeation through this dense layer, which ideally is defect free, occurs by a solution-diffusion mechanism, which can lead to useful levels of selectivity. Each component in the gas or vapor feed dissolves in the membrane polymer at its upstream surface, much like gases dissolve in liquids, then diffuse through the polymer layer along a concentration gradient to the opposite surface where they evaporate into the downstream gas phase. In ideal cases, the sorption and diffusion process of one gas component does not alter that of another component, that is, the species permeate independently. 

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