Folded-chain model, semicrystalline

Reference 109 contains the full NSCFT for both neat copolymers and copolymer-solvent mixtures, but we restrict attention here to the neat copolymer case. Each layer of thickness d contains amorphous and semicrystalline subdomains of thickness dA and ds, respectively. All the A-B joints are assumed to be localized within a narrow interphase of thickness a and, except for this interphase, all A and B monomers are assumed to be in their respective subdomains. This assumption is consistent with the strong segregation that occurs in these systems. The amorphous A blocks are treated in an NSCFT. The B blocks are modeled as semicrystalline, folded chains, characterized by the heat of fusion per unit volume, AHf, the degree of crystallinity of the B block, tc, and the energy of each fold, fifoid-... 

Fig. 5.12 Model for the lamellar organization in semicrystalline PE-PVCH diblocks crystallized from the ordered melt (Hamley et al. 1996b). The PE chains are folded with stems parallel to the lamellar interface. The convention for labelling of the axis system with respect to the shear direction is also indicated.

As discussed earlier, solid polymers can be distinguished into amorphous and the semicrystalline categories. Amorphous solid polymers are either in the glassy state, or - with chain cross linking - in the rubbery state. The usual model of the macromolecule in the amorphous state is the "random coil". Also in polymer melts the "random coil" is the usual model. The fact, however, that melts of semi-crystalline molecules, although very viscous, show rapid crystallisation when cooled, might be an indication that the conformation of a polymer molecule in such a melt is more nearly an irregularly folded molecule than it is a completely random coil. 

DiMarzio et al. developed a scaling model for semicrystalline lamellar structures with alternating layers of amorphous and crystalline blocks, with crystalline chains folded perpendicular to the interface [24]. The model system in-... 

Physical Properties. All polyethylene above 0.86 g/cm density is semicrystalline. The basic crystalline structure for most commercial LLDPE is chain-folded lamellae (Fig. 7). The body of the crystal consists of polymer backbone segments, and the surfaces are a collection of chain folds, loose cilia, and tie chains (chains incorporated into more than one crystal). When crystallized isothermally, it has been foimd that 95% of the lamellae in a given sample are within 5% of the same thickness (10). There is some debate over the mechanism of chain folding and of the subsequent fold loops. The most likely model includes adjacent reentry, loose adjacent reentry, and nonadjacent reentry. Short-chain branch length... 

In comparison with the simple case of para-aramid fibres, formulation of the structure-modulus relationships for semicrystalline fibres is much more complex. This is due to the segregation of crystalline and noncrystalline regions and to chain folding. The usual approach is based on recasting the structural models into mechanical models proposed by Takayanagi et as shown in... 

Fig. 8.13. Four-phase model of highly oriented semicrystalline fiber, (a) crystalline lamellae, (b) fully extended tie segments, (c) non-extended tie segments, (d) matrix (folds, ciliae, broken chains).

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