Simulation of SAXS patterns from oriented lamellar structures and their elliptical trajectories. (2nd April 2021)

• Record Type: Journal Article
• Authors: Grubb, David T.; Kennedy, W. Joshua; Koerner, Hilmar; Murthy, N. Sanjeeva
• Is Part Of: Polymer. Volume 220(2021)
• Publication Date: 2021-04-02
• Subjects: Small-angle scattering. lamellar structures. polymer crystal lamellae. eyebrow pattern -- Butterfly pattern -- Diffraction pattern simulation; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2021.123566
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Small-angle X-ray Scattering (SAXS) patterns are useful for studying the organization of crystalline and amorphous regions that make up a semi-crystalline polymer and influence its properties. To understand how these patterns originate and evolve during deformation, three distinct SAXS patterns (2-point, 4-point 'eyebrow', and 4-point 'butterfly') were generated using simple microstructural models and compared in detail with experimental data from poly(ethylene- co -octene). As the patterns typically contain a single unique reflection, it is not possible to fully determine the structure from the patterns alone. Therefore, structural models with lamellar stacks were used to simulate SAXS patterns. When stack orientation (interlamellar shear) and chain slip act to rotate lamellae in the same sense, the result is an 'eyebrow' pattern. Opposite senses give a 'butterfly' pattern. Experimental patterns often have reflections where the peak position traces out an ellipse. Adding moderate amounts of rotational disorder to the models produces this effect without any elliptical correlations or deformed lattice in the material. Graphical abstract: Image 1 Highlights: A simple and rapid FFT method is used to simulate SAXS form lamellar structures. Structural features determined by optimizing structure against experimental data. Lamellar stacks are modified by chain slip and stack rotation or interlamellar shear. Stack rotation and lamellar tilt determine if the pattern is eyebrow or a butterfly. Range of lamellar tilts produced by a range of stack rotations give elliptical tracks.