Wide-angle X-ray Diffraction Measurements Research Articles

Influence of Crystallization Kinetics and Flow Behavior on Structural Inhomogeneities in 3D-Printed Parts Made from Semi-Crystalline Polymers.

We report the results of a study focusing on the influence of crystallization kinetics and flow behavior on structural inhomogeneities in 3D-printed parts made from polyamide 12 (PA12) and poly(lactic acid) (PLA) by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), fast scanning calorimetry (FSC), and wide-angle X-ray diffraction (WAXD). Temperature-dependent WAXD measurements on the neat PLA filament reveal that PLA forms a single orthorhombic α phase during slow cooling and subsequent 2nd heating. The PA12 filament shows a well pronounced polymorphism with a reversible solid-solid phase transition between the (pseudo)hexagonal γ phase near room temperature and the monoclinic α' phase above the Brill transition temperature TB = 140 °C. The influence of the print bed temperature Tb on structure formation, polymorphic state, and degree of crystallinity χc of the 3D-printed parts is investigated by height and depth-dependent WAXD scans and compared with that of 3D-printed single layers, used as a reference. It is found that the heat transferred from successive layers has a strong influence on the polymorphic state of PA12 since a superimposed mixture of γ and α phases is present in the 3D-printed parts. In the case of PLA, a single α phase is formed. The print bed temperature has, in comparison to PA12, a major influence on the degree of crystallinity χc and thus the homogeneity of the 3D-printed parts, especially close to the print bed. By comparing the obtained results from WAXD, DMA, DSC, and FSC measurements with relevant printing times, guidelines for 3D-printed parts with a homogeneous structure are derived.

In situ study on the tensile deformation in high-density polyethylene/hexagonal boron nitride composite

Tensile deformation in the post processing of polymer plays a critical role in determining its mechanical properties. In this work, we investigated the structure evolution of high-density polyethylene/hexagonal boron nitride (HDPE/h-BN) composite during stretching in a wide temperature range from 25 °C to 100 °C in order to reveal the suitable post processing temperature of HDPE/h-BN composites fiber. The structure transition of HDPE crystal and the distribution of h-BN were investigated by in-situ small-angle X-ray scattering (SASX), in-situ wide-angle X-ray diffraction (WAXD) measurements, and scanning electron microscopy (SEM). The result shows that the parent HDPE crystal would be broken and recrystallize into highly oriented daughter crystal along the tensile direction when the tensile temperature (Tten) is in the range from 70 °C to 100 °C, though the recrystallization rate is low at high Tten. When Tten is low (25 °C), the crystallinity decreases continuously as no recrystallization takes place. In addition, the h-BN migrates accompany with the HDPE matrix and becomes oriented during the tensile direction. Combining the result of WAXD, SAXS, and the SEM measurement, it is concluded that the temperature of 70 °C is suitable for post processing of the HDPE/h-BN composite fiber.

Investigation of the Hydrolytic Degradation Kinetics of 3D-Printed PLA Structures under a Thermally Accelerated Regime.

The application of biobased and biodegradable polymers, such as polylactide (PLA), in fused deposition modeling (FDM) 3D-printing technology creates a new prospect for rapid prototyping and other applications in the context of ecology. The popularity of the FDM method and its significance in material engineering not only creates new prospects for the development of technical sciences on an industrial scale, but also introduces new technologies into households. In this study, the kinetics of the hydrolytic degradation of samples obtained by the FDM method from commercially available PLA filaments under a thermally accelerated regime were analyzed. The investigation was conducted at the microstructural, supramolecular, and molecular levels by using methods such as micro-computed tomography (micro-CT), wide-angle X-ray diffraction (WAXD), viscosimetry, and mass erosion measurements. The obtained results clearly present the rapid structural changes in 3D-printed materials during degradation due to their amorphous initial structure. The complementary studies carried out at different scale levels allowed us to demonstrate the relationship between the observed structural changes in the samples and the hydrolytic decomposition of the polymer chains, which made it possible to scientifically understand the process and expand the knowledge on biodegradation.

Effect of uniaxial stretching on gas separation performance of polyimide membranes

Fine-tuning of the physical stacking structure for microporous polyimide (PI) membranes via the stretching processing is a practical way of achieving advanced membrane materials with improved aging resistance as well as high gas separation performance. Here, a fluorinated polyimide 6FDA:BPDA-TFDB(1:1:2) is used as a prototype and a series of stretched membranes X%-PI are fabricated by uniaxially stretching the membrane to different elongation ratio and then annealing. Based on birefringence and wide-angle X-ray diffraction measurements, it's found that regular orientation of polymer chains along the stretching direction and fine-tuning of d-spaces from interchain packing and π-π stacking happen during the uniaxial stretching process. As such, compared to pristine PI membrane, the stretched membranes show better mechanical and thermal stability, especially for the one with higher stretching ratio. In addition, owing to the increased packing density of polymer chains, the highly stretched membrane of 40%-PI shows significantly improved gas perm-selectivity by 32.8%, 24.3%, and 12.6% for He/CH4, H2/CH4, and CO2/CH4 gas pairs, respectively, in comparison to pristine membrane. Furthermore, 40%-PI exhibits much higher gas permeability retention rate than that of other membranes after three months' aging. We expect that this work can offer polymer materials processing guidance for the preparation of high-performance gas separation membrane in future.

Analysis of the in-plane fiber orientation distribution in carbon fiber composites using wide-angle X-ray diffraction

The orientation of discontinuous carbon fibers (CF) in carbon fiber reinforced plastic (CFRP) influences the various properties, such as mechanical, thermal, and electrical properties. Here, we propose a fast and nondestructive method for evaluating the in-plane orientation distribution of CFs in CFRPs using wide-angle X-ray diffraction (WAXD). A symmetric transmission method was adopted as the specimen configuration to reduce the influence of the CFRP plate thickness on the WAXD measurement. The orientation distribution function was expressed as the sum of several Gaussian functions to analyze the orientation distribution of the uniaxially oriented and randomly oriented CFRP plates. The measurement of this method was accurate when the orientation distribution was wide. Because this method utilizes diffraction from the crystal structure in CFs, it is applicable to CFRPs where the diffraction from the matrix polymer in the azimuthal direction can be corrected with a linear baseline.

Improving Photovoltaic Performance of All-Polymer Solar Cells by Adding An Amorphous B←N Embedded Polymer as the Third Component.

Currently, most of the disclosed ternary strategies to improve photovoltaic performance of all-polymer solar cells commonly focus on the guest polymers having similar structures with the host polymer donors or acceptors. Herein, we develop a distinctive ternary method that adding an amorphous B←N embedded polymer named BN-Cl-2fT to a crystallized host polymer blend of PM6 and PY-TT (a copolymer of Y6 and thieno[3,2-b]thiophene). Although the structures between BN-Cl-2fT and PM6 and PY-TT are completely different, excellent miscibility is found between BN-Cl-2fT and both of the host PM6 and PY-TT, which can be interpreted by the crowded phenyl groups anchoring along the backbone of BN-Cl-2fT, leading to weak self-aggregation. GIWAXS measurements explicitly confirm the crystallization of PM6 and PY-TT and amorphous feature of BN-Cl-2fT. Furthermore, adding 10 wt% BN-Cl-2fT to PM6:PY-TT could significantly enhance the crystallization of the host polymers. Thus the ternary devices based on PM6:PY-TT:BN-Cl-2fT afford promoted JSC (23.29versus 21.80mA/cm2 ), FF (62.4%versus 60.0%), and PCE (13.70%versus 12.23%) in contrast to these parameters of binary devices based on PM6:PY-TT. We provide a unique and enlightening avenue to design high performance all-PSCs by adding amorphous B←N embedded polymers as guest component to enhance host-crystallization. This article is protected by copyright. All rights reserved.

Synthesis of Multiblock Copolymer Composed of Biodegradable Poly(butylene succinate) and Poly(2-pyrrolidone): Impact of Each Block Length on the Mechanical Properties.

A series of multiblock copolymers comprising a systematic combination of biomass-originated and biodegradable poly(butylene succinate) (PBS) and poly(2-pyrrolidone) (PA4) units is synthesized with various mean degrees of polymerization (mDP) of each unit. Despite the inherent immiscibility of PBS and PA4, multiblock structure allows to mix the two components in the solution-cast films from solution. The mechanical properties of the cast films are highly dependent on the mDP of each unit, as demonstrated by tensile tests. The film of the copolymer with the lowest mDP of each unit (PBS: 17, PA4: 10) is transparent and exhibits extremely high elongation at break (> 400%) and high tensile stress (39.5MPa) with strain hardening. The films with 50% or higher crystallinity are brittle and opaque, while a decrease in crystallinity can result in higher elongation, as revealed by wide-angle X-ray diffraction measurements.

Application of machine learning to reveal relationship between processing-structure-property for polypropylene injection molding

Revealing relationship between processing–structure-property using machine learning (ML) is beneficial to shorten the development cycle of polymer materials, which could be a promising solution to break through the traditional mode of trial-and-error. In this work, the quantitative data of processing field, polymorphic structure and mechanical properties of samples are successfully obtained based on microfocus wide-angle X-ray diffraction and mechanical property measurements, which provides the dataset for the application of machine learning. An initial step toward predicting the contents of polymorphic structure (α and β) and mechanical properties of isotactic polypropylene injection molding is taken by applying four algorithms of machine learning to establish regression models. The importance of processing descriptors is further analyzed. The prediction models for the contents of polymorphic structure and mechanical properties demonstrate satisfactory performance (R2max = 0.95). Compared with the prediction for the content of α-crystals, the results of feature importance analysis indicates that the injection pressure and shear rate of filling end in the processing descriptors charge higher contribution to the prediction for the β-crystals. And mold temperature plays an important role in predicting mechanical properties, which is consistent with the results of the signal-to-noise (S/N) ratio analysis.

The effect of temperature on the structural evolution of ultra-high molecular weight polyethylene films with pre-reserved shish crystals during the stretching process

The influence of temperature on the structural evolution and macroscopic properties of ultrahigh-molecular weight polyethylene (UHMWPE) films with pre-reserved shish crystals during stretching was investigated by in-situ small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements as well as ex-situ differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) measurements. The UHMWPE films with pre-reserved shish crystals were obtained by compression molding at 135 °C and further stretched at different temperatures of 100, 110, 120 and 130 °C. At all stretching temperatures, the pre-reserved shish can promote the structural evolution of UHMWPE films to form shish-kebab or shish crystals. At 100, 110, and 120 °C, the two-point pattern can be observed for 2D-WAXD, the lamellar crystals fragment to form shish-kebab crystals by epitaxial crystallization on pre-reserved shish crystals. At 130 °C, the two-point pattern signal becomes weak at 2D-WAXD, the lamellar crystals are mainly melted and then recrystallized on the pre-reserved shish crystals to form large-period kebab crystals. Moreover, the temperature of 130 °C favors the growth of kebab crystals with larger lateral size, resulting in a difficult transformation to shish crystals. In addition, at 110 and 120 °C, the crystallinity and orientation of UHMWPE films increase significantly after stretching, resulting in improved mechanical properties.

Reassessment of the generic features of starch gelatinization: An advanced SAXS study on maize and potato starch

The gelatinization of maize and potato starch granules in excess water [10% starch (w/w)] while heating at 4 °C/min was monitored by time-resolved polarized optical microscopy (POM), synchrotron small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) measurements. POM confirms that gelatinization is the result of a non-synchronous fast gelatinization of the individual granules over a rather wide temperature range. The WAXD based crystallinity of maize and potato starches disappears by gelatinization in the temperature range where DSC reveals endothermic transitions. Room temperature SAXS patterns are understood in terms of the scattering from stacks of alternating crystalline and amorphous layers. During gelatinization, the SAXS stack scattering and the WAXD crystallinity decreases in parallel while additional SAXS appears at very low angles, due to temporarily remaining fragmented sheets of semicrystalline blocklets, being remnants of granules in the course of gelatinization. The amount of such temporarily remaining blocklets is much lower in potato starch than in maize starch likely as a result of a more rapid and complete individual granular conversion for potato starch. Remarkably, in maize starch the blocklet scattering appears prior to crystal melting, suggesting that water sorption induces blocklet separation prior to actual gelatinization. In potato starch, such early separation is not observed, likely because blocklet connecting, long chain amylose molecules prevent the pre-gelatinization separation process. • New SAXS interpretation scheme for non-simultaneously gelatinizing starch granules. • Gelatinization temporarily leaves separated semicrystalline blocklets. • Quantification of closely packed, separated and fully gelatinized blocklet fractions. • Blocklets in A-type maize starch partially disconnect prior to gelatinization. • Quantification of water content in amorphous layers.

TEOS loading effect on the properties of PVA-modified polysulfone membranes

ABSTRACT Novel membranes have been obtained from an aldehyde functionalized-polysulfone and poly(vinyl alcohol), in the presence of tetraethyl orthosilicate (TEOS) by a sol-gel method, and the effect of the amount of TEOS in the membrane formulations has been investigated. The characterization of the prepared membranes has been performed using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), thermal analysis (TGA and DSC), and by wide-angle X-ray diffraction measurements (XRD). Also, the hydrophilicity, the water/alcohol absorption, and permeability of membranes were studied. The novel membranes showed a much lower absorption of water/alcohol than the one without TEOS. The membrane containing 1% TEOS exhibited a porous structure that entailed a permeability toward both polar (water and alcohols like ethanol and butyl alcohol) and nonpolar solvents (toluene, benzene), compared to pristine membrane which is permeable only for nonpolar solvents.

Electric-Field-Induced Phase Transition and Crystal Structural Change of the Oriented Poly(vinylidene Fluoride) β Form as Clarified by the In Situ Synchrotron Wide-Angle X-ray Diffraction Measurement

Electric-Field-Induced Phase Transition and Crystal Structural Change of the Oriented Poly(vinylidene Fluoride) β Form as Clarified by the <i>In Situ</i> Synchrotron Wide-Angle X-ray Diffraction Measurement

Evaluation of microscopic structural changes during strain hardening of polyethylene solids using In situ Raman, SAXS, and WAXD measurements under step-cycle test

We have examined the mechanism of strain hardening of polyethylene (PE) using a step-cycle test with in situ Raman spectroscopy, small-angle X-ray scattering, and wide-angle X-ray diffraction measurements. A stable fibrillar structure was formed at the onset of strain hardening. The fraction of the long-consecutive trans chains increased and decreased with increasing and decreasing strain during the stretching and unloading steps, respectively. The peak shift of the C–C stretching mode showed a red shift by applying the stretching stress to the specimen, accompanied by the broadening of the peak width. The broadening of the Raman band is interpreted as the strong stretching load becoming concentrated on the taut-tie chains. According to these results, we concluded that the strain hardening was caused by the increment of the modulus resulting from the increase in the number of taut-tie chains caused by chain pull-out from the crystalline structure. ・ Strain hardening of PE was investigated via various measurements. ・ The strain-hardening behavior was dominated by plastic deformation. ・ Increasing the amount of taut-tie chains dominates the strain-hardening modulus.

Effect of Raw Material Powder on Melt-Drawing Behavior of Ultrahigh-Molecular-Weight Polyethylene

Ultrahigh-molecular-weight polyethylene (UHMW-PE) can be drawn even from the molten state owing to its high melt viscosity. Molten UHMW-PE exhibits elastic deformability, which is homogeneously transmitted within the entire sample through molecular entanglements, resulting in oriented crystallization. Thus, entanglement characteristics are a dominant factor for the drawability of molten UHMW-PE. The entanglement characteristics of a UHMW-PE reactor powder will be retained for a film prepared by melt-processing due to the long relaxation time of UHMW-PE chains. Therefore, in this study, the melt-drawing behavior of UHMW-PE film prepared from different raw material powders was investigated. Three kinds of commercially available UHMW-PE reactor powders with comparable MW (viscosity average MW of 3×106) were used as a raw material. The UHMW-PE film was melt-drawn at 150℃, well above the sample melting temperature. The stress-strain curves recorded during melt-drawing exhibited a yield point, plateau stress region, and strain-hardening region for all films, although the stress level was different, indicating that the entangled state depends on the kind of raw material powder. In-situ wide-angle X-ray diffraction (WAXD) measurements during melt-drawing revealed two oriented crystallization mechanisms : the characteristic orthorhombic crystallization via transient hexagonal crystallization derived from deep entanglements, and the direct orthorhombic crystallization derived from shallow entanglements. Consequently, the entanglement characteristics of a UHMW-PE reactor powder dominate the melt-drawing behavior of the film. The obtained results are promising for developing the industrial melt-processing of UHMW-PE starting from a supplied UHMW-PE raw material powder.

Chemoenzymatic Polymerization of l-Serine Ethyl Ester in Aqueous Media without Side-Group Protection.

Poly(l-serine) (polySer) has tremendous potential as a polypeptide-based functional material due to the utility of the hydroxyl group on its side chain; however, tedious protection/deprotection of the hydroxyl groups is required for its synthesis. In this study, polySer was synthesized by the chemoenzymatic polymerization (CEP) of l-serine ethyl ester (Ser-OEt) or l-serine methyl ester (Ser-OMe) using papain as a catalyst in an aqueous medium. The CEP of Ser-OEt proceeded at basic pH ranging from 7.5 to 9.5 and resulted in the maximum precipitate yield of polySer at an optimized pH of 8.5. A series of peaks detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that the formed precipitate consisted of polySer with a degree of polymerization ranging from 5 to 22. Moreover, infrared spectroscopy, circular dichroism spectroscopy, and synchrotron wide-angle X-ray diffraction measurements indicated that the obtained polySer formed a β-sheet/strand structure. This is the first time the synthesis of polySer was realized by CEP in aqueous solution without protecting the hydroxyl group of the Ser monomer.

Strengthening of mille-feuille structured high-density polyethylene by heat elongation

We found the strengthening of the extruded high-density polyethylene (HDPE) film by heat elongation perpendicularly to the longer direction of the lamellae, i.e., the yield point disappeared and the tensile strength at break increased from 35 MPa to 170 MPa by the elongation up to 400%. Tear-drop pattern was observed in the small-angle X-ray scattering of the extruded HDPE and it changed to the layer one by the heat elongation, suggesting that mille-feuille structure consisting of hard crystalline lamella layers and soft amorphous ones is formed in the extruded HDPE and the lamellar length becomes shorter by the elongation. DSC and wide-angle X-ray diffraction measurements revealed that irregularly tilted lamellae of the extruded film were arranged to regular ones by elongation and the chain orientation increased with increasing the elongation ratio without change of the crystallinity and lamellar thickness. The strengthening by the elongation might be attributed to the chain orientation and regular arrangement of the short lamellae tied in the mille-feuille structure, which suppress the yielding behavior by preventing the fracture of lamellae and void formation.

Synthesis and surface properties of amphiphilic copolymer consisting of hydrophobic perfluorocarbon and hydrophilic zwitterionic blocks

Amphiphilic copolymers are receiving increasing attention due to their special features in solubility and self-assembling. Random and block copolymers containing superhydrophobic 2-perfluorooctylethyl acrylate (FA-C8) and superhydrophilic 3-[dimethyl (2′-methacryloyloxyethyl) ammonio] propanesulfonate (MAPS) segments were designed and synthesized in this work, namely PFA-C8-b-PMAPS and P(FA-C8-ran-MAPS). Synthesized polymers were characterized by 1H nuclear magnetic resonance and differential scanning calorimetry (DSC) measurements, proving the achievement of copolymers without residual PFA-C8. The molecular aggregation structure of FA-C8 in PFA-C8-b-PMAPS and P(FA-C8-ran-MAPS) was revealed by DSC and wide-angle X-ray diffraction measurements. On one hand, the PFA-C8 segments in P(FA-C8-b-MAPS) formed hexagonal packing with lamellar structures. On the other hand, although the lamellar structure is not observed in P(FA-C8-ran-MAPS) samples, the hexagonal packing of FA-C8 exhibited higher thermal stability than that of those in the PFA-C8 sample. Moreover, the polymeric film of P(FA-C8-ran-MAPS) exhibited strong oleophobicity under both air and water conditions.

One-Pot Synthesis of Supertough, Sustainable Polyester Thermoplastic Elastomers Using Block-Like, Gradient Copolymer as Soft Midblock

It remains challenging to synthesize supertough thermoplastic elastomers (TPEs) since the stretchability and tensile strength are mutually exclusive. Here, we report a one-pot strategy for the prep...

Control of parallel versus antiparallel molecular arrangements in crystalline assemblies of alkyl β-cellulosides

HypothesisThe precise control of parallel versus antiparallel molecular arrangements in synthetic assemblies of biorelated molecules is an attractive research focus from both scientific and technological viewpoints. However, little is known about cellulose-based synthetic assemblies. We hypothesized the existence of potential parameters, such as temperature, salt concentration, salt species, and solvent species, for controlling the molecular arrangement in assemblies of alkyl β-cellulosides with different alkyl chain lengths. ExperimentalThe self-assembly of alkyl β-cellulosides was triggered by neutralization-induced water insolubilization. The crystal structures of the cellulose moieties in the assemblies were characterized by attenuated total reflection-Fourier transform infrared absorption spectroscopy and wide-angle X-ray diffraction measurements. The morphologies of the assemblies were also characterized by scanning electron, atomic force, and transmission electron microscopy. FindingsThe temperature for the self-assembly, the concentration and species of inorganic salt in the self-assembly solution, and the solvent species (namely, the addition of water-miscible organic solvents into the self-assembly solution) strongly affected the molecular arrangement of the assemblies. The observations suggested that hydrophobic effects between the alkyl groups of the alkyl β-cellulosides and/or interactions of the alkyl β-cellulosides with solvent species were potential factors for controlling the molecular arrangement.

An effect of crystallographic distortion on carrier mobility in poly(3-hexylthiophene) thin films

The aggregation states and physical properties of polymers in thin films deviate from those found in the bulk. Although an effect of the thickness on the carrier mobility for thin films of poly(3-hexylthiophene) (P3HT) has been widely studied, there is a lack of discussion in terms of crystallographic distortion. Here, we demonstrate how the out-of-plane hole mobility in P3HT, which is a typical semiconducting polymer, changes with decreasing film thickness. Time-of-flight measurements with an analysis using the Gaussian disorder model revealed that the zero-field out-of-plane hole mobility decreased with decreasing thickness because of an increase in the energetical and spatial distribution of hopping sites. Grazing incidence wide-angle x-ray diffraction measurements revealed that such distributions of charge carriers were induced by the crystallographic distortion of P3HT in the thin films.