Improving the picture of atomic structure in nonoriented polymer domains using the pair distribution function: A study of polyamide 6

Abstract

Investigations of the atomic structures within polyamides started over 80 years ago and continue today. These weakly ordered materials diffract X‐rays poorly and typically require postprocessing to obtain idealized samples for structural studies. An important goal remains to develop techniques to study the local structure in its natural state, with atomic resolution, and with sensitivity to subtle changes due to synthesis conditions or other technologically relevant processing procedures. Here, we compare the structures of as‐produced, nonoriented polyamide 6 ([C6H11NO] n) from both hydrolytic and anionic processes. A total scattering pair distribution function approach is used to elucidate information about the atomic bonding, molecular conformation, chain packing, crystallite size, and ratio of ordered to disordered domain content. The results are compared with those from standard analytical methods.

Total scattering reveals the hidden stacking disorder in a 2D covalent organic framework

“…To gain further insight into the samples' atomic-scale details, we performed pair distribution function (PDF) analysis. [34][35][36][37][38] We collected total scattering data using synchrotron radiation, which was rst converted into the reduced total scattering structure function F(Q) (Fig. 5A, cf.…”

Cross-examining Polyurethane Nanodomain Formation and Internal Structure

“… 29 , 30 It was also shown that a longer distance assessment can provide information about domain sizes and relative phase fractions. 31 Here, we demonstrate further the use of lower energy laboratory X-ray diffraction data for observing real-space correlations of chain packing over longer distances, which we distinguish as density distribution functions (DDFs) due to the lack of atom-pair resolution compared to the PDF. In general, the idea of density distributions can be generalized for all scattering regimes: the isotropic atomic-pair density correlations obtained from different regions of X-ray scattering momentum transfer imbue useful differences in structural length-scale resolution.…”

“…(b) TPU-06 is compared to polyamide 6 (PA6). 31 (c) The long-range ordered signal in TPU-30 is indexed to the hard phase (HP3: 1:1.2 MDI-BD) measured at NSLS (100 K). 28 Data sets in (c) were both processed with Q max = 15 Å –1 and a Lorch modification for comparison.…”

“…The resolution of features over longer distances allows information to be extracted from the additional damping effects on the profile due to the domain size and shape profiles, once the instrumental effects have been accounted for (see Supporting Information Section S4.8). Recent studies, for example, have demonstrated comparisons of lab and synchrotron data for polyamide 6 31 and low- and high- Q max synchrotron data measured at different detector distances. 47 The more complex structural damping profiles for the TPUs here were confirmed using PDFs obtained from a higher resolution measurement (longer sample-to-detector distance and smaller pixel size), using a Pilatus detector from DECTRIS at the ESRF, as shown in Figures S12 and S13 .…”

“…In particular, we focus on the use of pair distribution functions (PDFs) obtained from total scattering measurements, which allow us to extract details of atomic bonding, molecular chain packing arrangements, and domain size distributions from X-ray scattering data, , even when no long-range structuring is present . PDF analysis has been used on polymers as early as 1936 but often with low-resolution data or analysis over only short distances. , Recent investigations have shown utility for determining structures of TPU hard domains and quantifying the magnitude of local symmetry breaking offsets in stacked, two-dimensional (2D) porous polymers. , It was also shown that a longer distance assessment can provide information about domain sizes and relative phase fractions . Here, we demonstrate further the use of lower energy laboratory X-ray diffraction data for observing real-space correlations of chain packing over longer distances, which we distinguish as density distribution functions (DDFs) due to the lack of atom-pair resolution compared to the PDF.…”