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6.2 Crystallite Size and Lamellar Thickness by X-Ray Methods

1980; Elsevier BV; Linguagem: Inglês

10.1016/s0076-695x(08)60757-7

1875-6514

Jing-I Wang, I. Harrison,

Rheology and Fluid Dynamics Studies

Publisher Summary This chapter discusses the ways in which lamellar thickness (fold period or long period) and crystallite size can be measured using x-ray techniques. In the study of crystalline polymers, two sizes of interest to polymer scientists are reported—microparacrystal or mosaic block size and lamella thickness. Polymer chains crystallize in the form of lamellae (platelet-like objects). Their thickness is of the order of 50–500 A and their lateral dimensions usually lie in the range of 1–25 μm. Within these platelets, the polymer chains are arranged to be approximately perpendicular to the top and bottom surfaces. Because the individual chains are many times longer than the crystal thickness, they are envisioned as folding back on themselves and reentering the crystal core. The concept of chain folding implies that lamellae are two-phase systems, at least in the simpler models. There exists a top and bottom (fold) surface of a more or less disordered structure and a crystalline core is sandwiched in between. In this chapter, instrumentation used for small-angle x-ray work is discussed, and different corrections used in x-ray studies are considered. Results on a variety of polymers are reported, and an attempt is made to examine the implications of alternative explanations.