Reneker defect

Typical crystalline macromolecular substance lattice defects result from end groups, kinks, jogs, Reneker defects, and chain displacements. Distortion of the whole crystal lattice can be conceived in terms of the paracrystal. The defects can be classified in terms of point, line, and network defects. 

Figure 5-12. Some lattice defects in poly (ethylene). From left to right aW-trans conformation (defect-free), Reneker defect, kink, and jog.

Kinks Jogs, and Reneker defects are conformational defects (see Figure 5-12). With kinks and j ogs, a part of the chain is displaced perpendicular to the long axis by false conformations. This kind of defect is called a kink when the displacement is smaller than the interchain distance (example ... 

Finally, for the kinetics of lamella thickening it is essential to know the lattice resistance to the motion of dispiration loops. This has been estimated by Reneker and Mazur (1983) to be describable by a diffusion constant 1 x 10 cm /s at 343 K. They consider that dispiration loops are likely to have a thermal equilibrium concentration of roughly one defect per molecule stem in a lamella, or a linear concentration of roughly 10 m ... 

Reneker, D. H. and Mazur, J. (1982) Stochastic defect diffusion model for relaxation effects in crystalline polyethylene, Polymer, 23, 401-412. 

The agreement with experiment shown in Fig. 14 is fascinating, and with the vast increase in computer power since 1986, it would be valuable to follow up the approach pioneered by Termonia and Smith for models which included the possible defects in the structure. In HMPE fibres, it seems right to attribute creep to the movement of whole molecules past one another, which eventually leads to separation. However, the most likely mechanism would be the movement of defects such as those described by Reneker and Mazur (1983). A kink in a polyethylene chain due to an extra -GHj- group could move like a ripple in a carpet. 

Finally, a rotation of 180° can be combined with a translational defect of c/2 to achieve crystalline register above and below the defect. Such combination of disclination and dislocation is call a disfMration. The nomenclature of chain dislocation, disclination and dispiration was developed by Reneker and Maair [14]. 

The fibers obtained under the best electrospinning conditions are generally of circular cross-section, continuous, and bead free. However, the literature on electrospinning reports other geometries of nanofibers (Koombhongse et al. 2001 Larsen et al. 2004a Reneker et al. 2002). Figure 1.10 show defect-fi ee nanofibers of PS electrospun from methylene chloride solution. 

Venugopal et al. 2005a), DMFrCHCls mixtures (Bolgen et al. 2005), CHCI3 (Yoshimoto et al. 2003), or acetone (Reneker et al. 2002), to obtain continuous defect-free nanofiber mats. 

Figure 1. Representative conformation defects in polyethylene chains, (a) Pech-hold kink, (b) Reneker twist, and (c) smooth twist.

The crux of the present method is how well the relaxation portion converges. Some experience has now been gained with it (11,12,13). Figure 4 shows results of calculations made in our laboratory (11,13) on the energies of three conformational defects in polyethylene crystals. These are a kin)c (15, ), a Reneker twist (Ig) and a smooth twist (12) (see Figure 1). The first two have been proposed as stable point defects cind the last one as a transition state for the motion that accomplishes... 

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