The use of polarised Fourier transform Raman spectroscopy in morphological studies of uniaxially oriented PEEK fibres—some preliminary results

Wide angle X-ray diffraction patterns and 2D-correlation spectroscopy of crystallization in proton irradiated poly(ether ether ketone)

Proton irradiated poly (ether ether ketone) (PEEK) films were crystallized to different extents, and subsequently characterized by wide angle X-ray diffraction technique. The data were analyzed by two-dimensional correlation mapping (2D-CM), in particular: Generalized, hybrid and multiple perturbations correlation approaches. Two asynchronous correlation peaks at (19.1, 18.7) ^o and at (22.5, 19.1) ^o were utilized as a measure the crystal perfection and the preferred process; orientation/crystal growth respectively. Proton irradiation not only favored the formation of crystal form II, but also changed the type of orientation within the irradiated films. Differential scanning calorimetry and Raman spectroscopic analysis confirmed the contribution of the previous two factors. Raman spectra indicated that the intensity of both bands at 1595 and 1608 cm⁻¹ decreased on samples crystallized from the melt, but increased on cold crystallized samples. 2D-CM combined with other suitable techniques is a promising in evaluating the structure of polymers and revealing the effect of proton irradiation.

Quantifying Polymer Chain Orientation in Strong and Tough Nanofibers with Low Crystallinity: Toward Next Generation Nanostructured Superfibers

Advanced fibers revolutionized structural materials in the second half of the 20th century. However, all high-strength fibers developed to date are brittle. Recently, pioneering simultaneous ultrahigh strength and toughness were discovered in fine (<250 nm) individual electrospun polymer nanofibers (NFs). This highly desirable combination of properties was attributed to high macromolecular chain alignment coupled with low crystallinity. Quantitative analysis of the degree of preferred chain orientation will be crucial for control of NF mechanical properties. However, quantification of supramolecular nanoarchitecture in NFs with low crystallinity in the ultrafine diameter range is highly challenging. Here, we discuss the applicability of traditional as well as emerging methods for quantification of polymer chain orientation in nanoscale one-dimensional samples. Advantages and limitations of different techniques are critically evaluated on experimental examples. It is shown that straightforward application of some of the techniques to sub-wavelength-diameter NFs can lead to severe quantitative and even qualitative artifacts. Sources of such size-related artifacts, stemming from instrumental, materials, and geometric phenomena at the nanoscale, are analyzed on the example of polarized Raman method but are relevant to other spectroscopic techniques. A proposed modified, artifact-free method is demonstrated. Outstanding issues and their proposed solutions are discussed. The results provide guidance for accurate nanofiber characterization to improve fundamental understanding and accelerate development of nanofibers and related nanostructured materials produced by electrospinning or other methods. We expect that the discussion in this review will also be useful to studies of many biological systems that exhibit nanofilamentary architectures and combinations of high strength and toughness.