Polymer single crystals

Figure 4.11 Electron micrographs of polyethylene crystals, (a) Dark-field illumination shows crystals to have a hollow pyramid structure. (Reprinted with permission from P. H. Geil, Polymer Single Crystals, Interscience, New York, 1963.) (b) Transmission micrograph in which contrast is enhanced by shadow casting [Reprinted with permission from D. H. Reneker and P. H. Geil, /. Appl. Phys. 31 1916 (I960).]...

Geil, P. H., Polymer Single Crystals, Interscience, New York, 1963. 

Fig. 3. Polymer single crystals (a) flat lamellae and (b) pyramidal lamellae. Two concepts of chain re-entry are illustrated (6).

Lotz, B. and Wittmann, J.-C. (1993) Structure of Polymer Single Crystals, in Structure and Properties of Polymers, ed. Thomas, E.L. Materials Science and Technology, A Comprehensive Treatment, eds. Cahn, R.W., Haasen, P. and Kramer, E.J. (VCH, Weinheim) p. 79. 

With the first successful growth of a polymer single crystal in the 1950s it was found that the polymer chains are folded back and forth many times inside the crystal [161]. 

The fringed micelle theory has been less favoured recently following research on the subject of polymer single crystals. This work has led to the suggestion that polymer crystallisation takes place by single molecules folding themselves at intervals of about 10 nm to form lamellae as shown in Figure 3.3b. These lamellae appear to be the fundamental structures of crystalline polymers. 

Geil PH (1963) Polymer single crystals. Wiley-Interscience, New York... 

Since polymer single crystals prepared these days are too small for x-ray diffraction experiments, the Crystal Structure of a polymer is generally determined from x-ray patterns of a fibre drawn from the polymer. Due to the alignment of the crystalline regions with the long axes of the molecules parallel to the fibre axis, the pattern is essentially identical to a rotation pattern from... 

Electron Microscopy can be used for resolution of smaller objects the practical limit of resolution being a few angstrom units. Electron Microscopy has been used in the study of the morphology of crystalline polymers. The usual techniques of replication, heavy-metal shadowing, and solvent etching are widely used. The direct observation of thin specimens, like polymer single crystals, is also possible and permits the observation of the electron-diffraction pattern of some specimen area, which is invaluable for... 

Crystalline clumps in suspension are ultra-sonicated into thin plates/fragments suitable for TEM investigation [10], but such ultra-sonication may damage the polymer single crystals. 

P.H. Geil, Polymer Single Crystals, John Wiley and Sons (1963)/ (reprint), R.E. Krieger Pub. (1973). 

Note 3 Polymer crystals that can be manipulated individually are often called (polymer) single crystals. A single crystal may contain different fold domains. 

While the lamellar structures present in spherulites are similar to those present in polymer single crystals, the folding of chains in spherulites is less organized. Further, the structures that exist between these lamellar structures are generally occupied by amorphous structures including atactic chain segments, low molecular weight chains, and impurities. 

The. folded-chain lamella theory arose in the last 1950s when polymer single crystals in the form of thin platelets termed lamella, measuring about 10,000 A x 100 A, were grown from polymer solutions. Contrary to previous expectations, X-ray diffraction patterns showed the polymer chain axes to be parallel to the smaller dimension of the platelet. Since polymer molecules are much longer than 100 A, the polymer molecules are presumed to fold back and forth on themselves in an accordionlike manner in the process of crystallization. Chain... 

GeU PH (1963) Polymer single crystals. John Wiley Interscience, New York Mandelkern L (1989) Crystallization and melting of polymers In G Allen (ed) Comprehensive polymer science, vol 2. Pergamon Press, Oxford Avrami M (1939) J Chem Phys 7 1103 Avrami M (1940) J Chem Phys 8 812 Avrami M (1941) J Chem Phys 9 1977 Tohin MC (1974) J.Polym Sci Polym Phys 12,399 Tohin MC (1976) J Polym Sci Polym Phys 14 2253 Nakamura K, Katayama K,Amano T (1975) J Appl Polym Sci 17 1031 Ozawa T (1971) Polymer 12 150... 

Figure 3. Schematic representation of a polymer single crystal, illustrating the principle of chain folding (13)...

Thus, it is concluded that as far as possible experiments should be made on single crystal samples using guard ring techniques under conditions where the ambient atmosphere may be rigorously controlled. In the case of polymers single crystal samples of any size are virtually impossible to obtain. 

Lieser, G. Polymer single crystals of poly(4-hydroxybenzoate). J. Polymer Sci., Polymer Phys. Ed., 27, 1611 (1983)... 

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