Glassy polymers elements

We present a finite element study which includes both shear yielding and crazing within a finite strain description. This provides a way of putting together all aspects of glassy polymer fracture crazing and shear yielding but also thermal effects. 

In contrast to the LCP results just presented, in glassy polymers used as gas separation membranes, free volume influences diffusion coefficients much more than solubility coefficients. Figure 6 provides an example of this effect. In this figure, the solubility, diffusivity, and permeability of methane in a series of glassy, aromatic, amorphous poly(isophthalamides) [PIPAs] are presented as a function of the fractional free volume in the polymer matrix. (More complete descriptions of the transport properties of this family of materials are available elsewhere (59, 40)). The fractional free volume is manipulated systematically in this family of glassy polymers by synthesizing polymers with different substituent and backbone elements as shown in... 

The size of free volume elements in a glassy polymer can be estimated from the dependence of AHra on solute size [31]. A plot of against Vc, where 14 is the critical volume of the solute, generally passes through a minimum at a value of 14 that corresponds to a mean size of free volume elements. The data for n-alkanes in Table 2.5 show increasingly negative values of AH up to decane. Unfortunately, temperature limitations meant that... 

An unportant and generally accepted assumption is that the dye molecule does not influence its surroundings, i.e. it does not interact with the polymer matrix and it does not change the free volume itself. The polymer chain dynamics must be sufficiently slow that there is no significant relaxation of the free volume elements on the time scale required for the trans-cis transition. The latter makes this method only suitable for glassy polymers at temperatures sufficiently far below the glass transition. 

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