Single crystals polyethylene

Fig. 3.15. Growth rates of (110) and (200) sectors of polyethylene single crystals grown from solution in tetradecanol (courtesy of S. Organ)...

One of the most remarkable features of polymer crystallization is that such chain molecules can form lamellar crystals that contain heavily folded polymer chains. In experiments, the structural analysis of these lamellar crystals became possible when polyethylene single crystals were first prepared from a solution [100-102]. It was found that the orientation of the polymer chains... 

In the classical Lauritzen-Hoffman theory for the mechanism of polymer crystal growth [106], it is assumed that the observed lamellar thickness corresponds to those crystallites that happen to have the largest growth velocity. However, this picture is hard to reconcile with the experimental observation that the thickness of polyethylene single crystals can be modulated by varying the temperature at which they are grown [117,118]. In fact, simulations by Doye et al. [119,120] suggest that the observed lamellar thickness does... 

Attempts were made to include all hydrogen atoms explicitly in the simulations. This computationally demanding explicit-atom model shows (Fig. 1) that the crystal symmetry is orthorhombic, in agreement with the well-known experimental result for polyethylene single crystals, instead of the hexagonal symmetry seen in united-atom model simulations. 

Keller, A., E. Martuscelli, D. J. Priest, and Y. Udagawa. Fold surface of polyethylene single crystals as assessed by selective d radation studies. III. Application of the improved techniques to single crystak. J. Polymer Sci. Part A-2 9 1807-1837, 1971. 

Figure 1.64 Polyethylene single crystals. Reprinted, by permission, from P. Heimenz, Polymer Chemistry The Basic Concepts, p. 239. Copyright 1984 by Marcel Dekker, Inc.

Very interesting results on polyethylene single crystals have been reported by van Roggen (125). Using a copper substrate and various point metal contacts, a pronounced rectification and /q 20 V (volts)... 

Fig. 9. Negative resistance phenomena, a) 100 A thick polyethylene single crystal using Pt Catswhisker and Copper substrate [after van Roggen (725)], b) 70S A thick silicone polymer film at 300° K, c) 705 A thick silicone polymer film at 4° K [after Mann (726)]...

Roggan, A. van Negative resistance in polyethylene single crystals. Phys. Rev. Letters 9, 369 (1962). 

Fig. 6 Sectorisation of polyethylene single crystals. The upper crystal shows only 110 sectors whereas the lower also has 100 sectors. With permission from Kluwer, Doordrecht, Netherlands [91]...

Fig. 7 Schematic drawing of tent-shaped polyethylene single crystals with only 110 sectors...

Fig. 15 Lateral habit of solution- and melt-grown polyethylene single crystals. The drawing are based on electron micrographs of Organ and Keller [64]—grown from solution—and of Toda [107]—grown from the melt...

To help the reader unfamiliar with polyethylene single crystal habits, Fig. 10 summarizes the most typical types [32] (a) the rhombic lozenge, normally observed in PE solution crystallized at lower temperatures (b) the... 

Statton, W. O. Rate of recrystallization of polyethylene single crystals. J. Appl. Phys. 32, 2332-2334 (1961). 

Fig. 1 Sketch of a polymer single crystal and electron micrograph of polyethylene single crystals (Marlex 50) grown from hot xylene. Chain backbones in the crystals are mostly aligned with the c-crystallographic axis. (From Ref...

Solid-state extrusion has also yielded some of the highest properties for uniaxially oriented morphologies. Tensile moduli (210 GPa) nearing the theoretical value of a polyethylene single crystal have been attained.f ... 

Table 7.2. NMR chemical shifts and crystallographic forms of cyclic paraffins and polyethylene single crystal in the solid state [18]...

The results described above for highly drawn samples of HDPe (EDR > 12) seem to be consistent with such an assumption. However, in some cases, the important role of the shear vs. extensional deformation components (JO. In extrusion of spheruiitic HOPE and the compressive force in extrusion of powders of polyethylene single crystals (21) and ultrahigh MW polyethylene (22) has been suggested. Indeed, we have shown (23) recently that single crystal mats of various poiyethyienes, which couid not be extended by tensile force below can be effectively drawn even at room temperature up to... 

At the initial stage of extrusion, the parallel lamellae rotated or tilted to form inclined lamellar stacks and the perpendicular lamellae tended to increase in number. The perpendicular lamellae increased up to around EDR 4.6 in the second stage where the inclined lamellae started to transform steadily into fibrils. This perpendicular lamellar orientation characteristic for extrusion drawing is likely caused by the compressive force applied for extrusion. Such an effect of the compressive force has bran more clearly observed in our previous study of crystalline-state extrusion of polyethylene single crystal powder (21). 

Let us now consider how this fold conformation fits into the overall morphological featirres of the polymer single crystal. Figure 3.17 is a schematic representation of the top surface of an idealized model of a diamond-shaped polyethylene single crystal as seen along the (001) (c axis). The ctrrved lines. 

Tian MW, Loos J (2001) Investigations of morphological changes during annealing of polyethylene single crystals. J Polym Sci B 39(7) 763-770... 

These earlier papers did not take into account the fact that the oriented polymers were partially oriented. It is therefore now necessary to extend the previous discussion of the aggregate model to the situation where molecular motion occurs. This has been done independently by Olf and Peterlin, McBrierty and Douglass, and Folkes and Ward. McBrierty and Douglass paper gives a formal theoretical treatment, as part of a general discussion of the influence of molecular motions on Tj, Tz and the other papers are particularly concerned with an analysis of the effects of molecular motion on the second moment anisotropy but nevertheless provide explicit results for special types of motion. The results are then applied to oriented mats of polyethylene single crystals and to... 

Fig. 2.15 Several lozenge-shaped polyethylene single crystals grown from xylene solution (from Geil (1963) courtesy of Geil).

Fig. 2.16 A sketch of a 3D view through a polyethylene single crystal showing the planar zig-zag conformation of molecules referred to the orthorhombic lattice of PE (from Lin and Argon (1994b) courtesy of Springer-Verlag).

---