Ambient Catalytic Spinning of Polyethylene Nanofibers.

A novel single-atom Ni(II) catalyst (Ni-OH) is covalently immobilized onto the nano-channels of mesoporous Santa Barbara Amorphous (SBA)-15 particles and isotropic Anodized Aluminum Oxide (AAO) membrane for confined-space ethylene extrusion polymerization. The presence of surface-tethered Ni complexes (Ni@SBA-15 and Ni@AAO) is confirmed by the inductively coupled plasma-optical emission spectrometry (ICP-OES) and X-ray photoelectron spectroscopy (XPS). In the catalytic spinning process, the produced PE materials exhibit very homogeneous fibrous morphology at nanoscale (diameter: ~50 nm). The synthesized PE nanofibers extrude in a highly oriented manner from the nano-reactors at ambient temperature. Remarkably high Mw (1.62×106  g mol-1 ), melting point (124 °C), and crystallinity (41.8 %) are observed among PE samples thanks to the confined-space polymerization. The chain-walking behavior of surface tethered Ni catalysts is greatly limited by the confinement inside the nano-channels, leading to the formation of very low-branched PE materials (13.6/1000 C). Due to fixed supported catalytic topology and room temperature, the filaments are expected to be free of entanglement. This work signifies an important step towards the realization of a continuous mild catalytic-spinning (CATSPIN) process, where the polymer is directly synthesized into fiber shape at negligible chain branching and elegantly avoiding common limitations like thermal degradation or molecular entanglement.

Effects of Nanoscale Morphology on Optical Properties of Photoluminescent Polymer Optical Fibers.

Bicomponent photoluminescent polymer optical fibers (PL-POFs) have been melt-spun and in-situ drawn to different extents. The results suggest that scattering in the sheath can effectively increase the photoluminescent dye excitation probability in the fiber core. The core/sheath PL-POFs are made of a semi-crystalline fluoropolymer sheath of low refractive index (RI) and an amorphous cycloolefin polymeric core of high RI, which is doped with a luminescent dye. The axial light emission, as well as the guiding attenuation coefficients of the core/sheath PL-POFs, have been measured using a side-illumination set-up. The incident blue laser is down-converted to red light, which is re-emitted and partially guided by the core. The axial light emission is measured at the fiber tip as a function of the distance from the illumination position to the integrating sphere. It is demonstrated that the presence of a semi-crystalline sheath significantly enhances the axial light emission and that it also lowers the attenuation coefficient, compared to the emission and guiding properties of PL core-only fibers. Additionally, the attenuation coefficient has been found to be lower in more strongly drawn PL-POFs. Wide-angle X-ray diffraction and small-angle X-ray scattering experiments reveal structural differences in differently drawn PL-POFs that can be linked to the observed differences in the optical properties.

Structure-Property Relationship in Melt-Spun Poly(hydroxybutyrate-co-3-hexanoate) Monofilaments.

Poly(hydroxybutyrate-co-3-hexanoate) (PHBH) is a biodegradable thermoplastic polyester with the potential to be used in textile and medical applications. We have aimed at developing an upscalable melt-spinning method to produce fine biodegradable PHBH filaments without the use of an ice water bath or offline drawing techniques. We have evaluated the effect of different polymer grades (mol% 3-hydroxy hexanoate, molecular weight etc.) and production parameters on the tensile properties of melt-spun filaments. PHBH monofilaments (diameter < 130 µm) have been successfully melt-spun and online drawn from three different polymer grades. We report thermal and rheological properties of the polymer grades as well as morphological, thermal, mechanical, and structural properties of the melt-spun filaments thereof. Tensile strengths up to 291 MPa have been achieved. Differences in tensile performance have been correlated to structural differences with wide-angle X-ray diffraction and small-angle X-ray scattering. The measurements obtained have revealed that a synergetic interaction of a highly oriented non-crystalline mesophase with highly oriented α-crystals leads to increased tensile strength. Additionally, the effect of aging on the structure and tensile performance has been investigated.

Fitting of 2D WAXD data: Mesophases in polymer fibers.

This data article presents fitting results of wide-angle x-ray diffraction (WAXD) patterns of melt-spun polymer fibers from amorphous materials (polycarbonate (PC), cyclo-olefin polymer (COP), copolyamide (coPA), polyethylene terephthalate glycol (PETG)) and semi-crystalline materials (polyethylene terephthalate (PET), poly-3-hydroxybutyrate(P3HB)). The data was fit using the fitting algorithms, previously described in the publication by Perret and Hufenus 'Insights into strain-induced solid mesophases in melt-spun polymer fibers' [1]. Fitting results of WAXD data and details about azimuthal, equatorial, meridional or off-axis profiles are presented in sections 1.1-1.2. SAXS patterns of fibers, melt-spun from amorphous materials, are shown in section 1.3. Fiber production parameters are given in section 2.1, and a description of the WAXD measurements and fitting details, e.g., the chosen fitting parameters, are given in section 2.2.

X-ray reflectivity theory for determining the density profile of a liquid under nanometre confinement.

An X-ray reflectivity theory on the determination of the density profile of a molecular liquid under nanometre confinement is presented. The confinement geometry acts like an X-ray interferometer, which consists of two opposing atomically flat single-crystal mica membranes with an intervening thin liquid film of variable thickness. The X-rays reflected from the parallel crystal planes (of known structure) and the layered liquid in between them (of unknown structure) interfere with one another, making X-ray reflectivity highly sensitive to the liquid's density profile along the confinement direction. An expression for the reflected intensity as a function of momentum transfer is given. The total structure factor intensity for the liquid-filled confinement device is derived as a sum of contributions from the inner and outer crystal terminations. The method presented readily distinguishes the confined liquid from the liquid adsorbed on the outer mica surfaces. It is illustrated for the molecular liquid tetrakis(trimethyl)siloxysilane, confined by two mica surfaces at a distance of 8.6 nm.

X-ray data about the structural response of melt-spun poly(3-hydroxybutyrate) fibers to stress and temperature.

Mechanical properties of as-spun, aged and stress-annealed melt-spun poly(3-hydroxybutyrate) (P3HB) fibers are presented in section 1.1. Section 1.2 presents tables with stress/temperature conditions and exposure times during in-situ laboratory WAXD and SAXS experiments, and section 1.3 presents azimuthal profiles of the corresponding WAXD patterns with extracted orientation factors of the α-crystals. Section 1.4 presents the extracted long-spacings, coherence lengths and crystal sizes from SAXS patterns. The corresponding fits of meridional and transversal SAXS profiles are shown in sections 1.5 and 1.6, respectively. In-situ synchrotron measurements during tensile drawing of differently pre-annealed P3HB fibers are presented in section 1.7. A detailed description of the tensile, SAXS/WAXD measurements and analysis is given in the experimental section 2. The laboratory SAXS/WAXD measurements during stress annealing were performed with a Bruker Nanostar U diffractometer (Bruker AXS, Karlsruhe, Germany) and a heating stage H+300 (Bruker AXS, Germany). Different weights were attached to the fibers during heating to apply stress. The synchrotron measurements during tensile drawing were performed at the cSAXS beamline at the Swiss Light Source of the Paul Scherrer Institute in Switzerland. The fibers were drawn with a TS 600 tensile stage (Anton Paar GmbH, Austria) using a 5 N load cell. For more information see 'Structural response of melt-spun poly(3-hydroxybutyrate) fibers to stress and temperature' [1].

X-ray data from a cyclic tensile study of melt-spun poly(3-hydroxybutyrate) P3HB fibers: A reversible mesophase.

Wide-angle x-ray diffraction (WAXD) patterns that show mesophases in core-sheath bicomponent fibers and amorphous fibers are presented in section 1.1 of the article. Section 1.2 presents molecular dynamics simulations and scattered intensity calculations of stretched P3HB chains. Sections 1.3-1.6 summarize WAXD and small-angle x-ray scattering (SAXS) data analysis from a tensile study of melt-spun P3HB fibers. Azimuthal profiles are extracted from 2D WAXD patterns at various angular regions and the positions of equatorial reflections and corresponding d-spacings are summarized. Additionally, the extracted structural parameters from SAXS images are summarized. The tensile stress calculations, crystal orientation calculations, applied intensity corrections, calculations of long spacings, coherence lengths and lamellar diameters are explained in the methods subsections 2.3.1-2.3.7. WAXD and SAXS measurements of P3HB fibers were recorded on a Bruker Nanostar U diffractometer (Bruker AXS, Karlsruhe, Germany). The recorded WAXD/SAXS patterns were analyzed with the evaluation software DIFFRAC.EVA (version 4.2., Bruker AXS, Karlsruhe, Germany) and python codes. For more information see 'Tensile study of melt-spun poly(3-hydroxybutyrate) P3HB fibers: Reversible transformation of a highly oriented phase' (Perret et al., 2019).

Self-consistent algorithm for calibrating spectrometers to picometer accuracy over the entire wavelength range.

Spectrometer calibration accuracies are of high importance for a wide range of applications. Typically, one calibrates the spectrometer with a calibration lamp, providing distinct and well-defined calibration lines. However, for small spectral ranges, where only two calibration lines are present, the calibration becomes inaccurate. We present a high-precision nonlinear wavelength calibration method, which is based on two or more reference lines from a calibration lamp. The additional key element introduced is a Fabry-Perot multilayer structure that yields multiple sharp transmission maxima of similar intensity over the full spectrometer range under broad-band illumination (e.g., white-light source). An iterative algorithm is put forward to obtain a self-consistent calibration of picometer precision over the full spectrometer range. In regions distant from calibration lines the accuracy is enhanced by at least a factor of two compared to conventional methods.

Molecular liquid under nanometre confinement: density profiles underlying oscillatory forces.

Ultrathin (<12 nm) films of tetrakis(trimethyl)siloxysilane (TTMSS) have been confined by atomically flat mica membranes in the presence and absence of applied normal forces. When applying normal forces, discrete film thickness transitions occur, each involving the expulsion of TTMSS molecules. Using optical interferometry we have measured the step size associated with a film thickness transition (7.5 Å for compressed, 8.4 Å for equilibrated films) to be smaller than the molecular diameter of 9.0 Å. Layering transitions with a discrete step size are commonly regarded as evidence for strong layering of the liquid's molecules in planes parallel to the confining surfaces and it is assumed that the layer spacing equals the measured periodicity of the oscillatory force profile. Using x-ray reflectivity (XRR), which directly yields the liquid's density profile along the confinement direction, we show that the layer spacing (10-11 Å) proves to be on average significantly larger than both the step size of a layering transition and the molecular diameter. We observe at least one boundary layer of different electron density and periodicity than the layers away from the surfaces.