Intercrystalline bridges

Since the increase of the elastic modulus of oriented polymers with draw ratio is, to a large extent, the consequence of the tie molecules or intercrystalline bridges interconnecting crystal blocks within the fibrils 72) one may anticipate a correlation to exist between indentation anisotropy and modulus. Recent data 23) illustrating the... 

Figure 8.2 Schematic diagram indicating the structure of a highly oriented semicrystalline polymer. A, amorphous region B, intercrystalline bridges C, chain-folded crystal block TM, tie molecules.

At A > 5, nearly all crystalline blocks become oriented (s 1). Then and ay become independent of X and the appearance of an intercrystalline bridge becomes a reality. Then the oriented structure can be represented schematically by Figure 8.3. Gibson et al. [77] have suggested on the basis of statistical consideration that the volume fraction of intercrystalline bridge material is... 

Figure 8.4 (a) Schematic diagram of an oriented polymer consisting of an amorphous region (A), intercrystalline bridges (B), crystalline blocks (C) and tie molecules (TM) with volume fractions a -h b H- t = 1. (b) Parallel combination of two phases, (c) Phases TM and S after removal of constraint. 

The structure of high modulus polyethylene fibres obtained by optimized drawing of linear polyethylene is viewed as crystalline lamellae linked by intercrystalline bridges.Accordingly, the component B is then viewed as crystalline, and its content (1 — >1) corresponds to the volume fraction of the material incorporated in the crystalline bridges. A more complex model consisting of four components has been proposed for these fibres by Grubb. 

Differences in the structure of monocrystalline, threshold or bridge type polycrystalline adsorbents are to be manifested in the shape of adsorption - caused response of electrophysical characteristics [25]. The basic models of adsorption - induced response of monocrystalline and barrier poly crystal line adsorbents have been considered in Chapter 1. Here we describe various theoretical models of adsorption-induced response of polycrystalline adsorbents having intercrystalline contacts of the bridge type and their comparison with experimental results. 

Thus, we have considered in detail various theoretical models of effect of adsorption of molecular, atom and radical particles on electric conductivity of semiconductor adsorbents of various crystalline types. Special attention has been paid to sintered and partially reduced oxide adsorbents characterized by the bridge type of intercrystalline contacts with the dominant content of bridges of open type because of wide domain of application of this very type of adsorbents as sensitive elements used in our physical and chemical studies. 

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