ipyChord: a package for evaluating small-angle X-ray scattering data of fiber symmetry

This article presents a Python-based package, ipyChord, to compute the 2D chord distribution function (CDF) from the small-angle X-ray scattering (SAXS) pattern from polymer materials with fiber-symmetrical nanostructure. The program allows construction of a harmonized SAXS pattern from a raw SAXS pattern, by normalization of the incident-beam intensity, absorption correction for sample thickness, masking blind areas on the detector, and filling in the shadow of the beamstop and its holder using symmetry operations. Patterns from modular detectors with inter-module gaps can still be fully constructed satisfactorily after determining the optimized beam position and a radial basis function. A CDF pattern computed from the full SAXS pattern can be used to determine the domain size and its variability using a graphical method. An interface distribution function computed from Bonart's longitudinal projection or sliced from a CDF meridian can quantify differently stacked hard and soft domains. Two cases of the application of ipyChord are presented. The software is open source and available at https://github.com/isaxs/ipyChord.

The colloidal structure of a cellulose fiber

We present a small angle X-ray scattering (SAXS) study of the colloidal structure of regenerated cellulose fibers, air-gap spun from an ionic liquid solution. Based on the data, and a different interpretation of the anisotropic SAXS pattern, we propose a slightly different colloidal structure of the fibers, than what is commonly assumed for regenerated cellulose fibers. Fibers with two different degrees of orientation, as produced by different draw ratios, DR = 2 and 15, respectively, are analyzed. The 2D SAXS pattern is highly anisotropic with striking cross-like pattern, having scattering predominantly perpendicular and parallel to the fiber axis. This cross-like pattern suggest a colloidal structure with oriented crystalline lamellae of ca. 10 nm thickness, embedded within a continuous matrix of amorphous cellulose. The lamellae are oriented with their normal parallel with the fiber axis. Complementary wide angle X-ray diffraction data confirm that the lamellae normal direction corresponds to the cellulose chain direction (c-direction) in the monoclinic cellulose crystal (Cellulose II). Graphic abstract

SAXS signature of the lamellar ordering of ionic domains of perfluorinated sulfonic-acid ionomers by electric and magnetic field-assisted casting

The origins of the matrix and ionomer peaks of Nafion SAXS pattern are revisited.