Crystallites with stretched chains

The cluster model assumes availability in the amorphous polymers structure of local order domains (clusters), consisting of several densely packed collinear segments of different macromolecules (amorphous analog of crystallite with stretched chains). These clusters are connected between themselves by tie chains, forming by virtue of this physical entanglements network, and are surrounded by loosely packed matrix, in which all fluctuation free volume is concentrated [107],... 

Lately it was offered to consider polymers amorphous state stmcture as a natural nanocomposite [6]. Within the frameworks of cluster model of polymers amorphous state stmcture it is supposed, that the indicated structure consists of local order domains (clusters), immersed in loosely packed matrix, in which the entire polymer free volume is concentrated [7, 8]. In its turn, clusters consist of several coUinear densely packed statistical segments of different macromolecules, that is, they are an amorphous analog of crystallites with stretched chains. It has been shown [9] that clusters are nanoworld objects (tme nanoparticles-nano clirsters) and in case of polymers representation as natural nanocomposites they play nanofiller role and loosely packed matrix-nanocomposite matrix role. It is significant that the nanoclusters dimensional effect is identical to the indicated effect for particulate filler in polymer nano composites sizes decrease of both nano clusters [10] and disperse particles [11] resrdts to sharp enhancement of nanocomposite reinforcement degree... 

Proceeding from the said above and analyzing values of polymers limiting strains, one can obtain the information about local order regions type in amorphous and semicrystalline polymers. The fulfilled by the authors of Ref [36] calculations have show that the most probable type of local nanostructures in amorphous polymer matrix is an analog of crystallite with stretched chains, that is, cluster. 

It is supposed that geometry, morphology and crystalline phase nucleation and growth mechanism will be defined to a considerable degree by the nature of heterophase fluctuations in the amorphous state. So, the supposition of heterophase fluctuation from folded chains (Yech model [44]) results in the formation of crystallites with folded chains (CFC). In paper [43], an alternative model of heterophase fluctuation supposes the availability of parallel parts of different chains of macromolecules in it. The use of these models supposes the possibility of formation in the crystallisation process of CFC, crystallites with stretched chains (CSC) or some intermediate morphology... 

Using Equations 5.12 and 5.13 for local order domains (clusters) the description of the growth of epoxy polymers and nucleation is based on the fact that clusters by their physical essence are analogous to crystallites with stretched chains (CSC) [5, 6]. The cluster characteristic size is accepted to be equal to the statistical segment length which is calculated according to Equation 1.8. 

It should be noted fliat intermolecular nucleatitm could coexist with intramolecular nucleation. Intermolecular nucleation is often observed with short chains, rigid chains, polymerizing chains, or when chains are stretched. Recently, upon stretching network polymers, the transition from intramolecular nucleation to intermolecular nucleation was observed in Monte Carlo simulations (Nie et al. 2013). By analyzing the probability of adjacent chain-folding of those newly formed crystallites with a size between 50 to 200 parallel packed bonds at each step of stretching, an obvious reduction was observed in its evolution curve under each temperature as shown in Fig. 4.20a. The corresponding critical strain was considered to be the transition point under which intramolecular nucleation is the favorite and above which intermolecular nucleation becomes the dominant. 

According to Hosemann-Bonart s model8), an oriented polymeric material consists of plate-like more or less curved folded lamellae extended mostly in the direction normal to that of the sample orientation so that the chain orientation in these crystalline formations coincides with the stretching direction. These lamellae are connected with each other by some amount of tie chains, but most chains emerge from the crystal bend and return to the same crystal-forming folds. If this model adequately describes the structure of oriented systems, the mechanical properties in the longitudinal direction are expected to be mainly determined by the number and properties of tie chains in the amorphous regions that are the weak spots of the oriented system (as compared to the crystallite)9). 

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