Spinning Conditions Research Articles

In-cell 31P solid-state NMR measurements of the lipid dynamics and influence of exogeneous β-amyloid peptides on live neuroblastoma neuro-2a cells

Non-specific disruption of cellular membranes induced by aggregation of exogeneous β-amyloid (Aβ) peptides is considered a viable pathological mechanism in Alzheimer's disease (AD). The solid-state nuclear magnetic resonance (ssNMR) spectroscopy has been widely applied in model liposomes to provide important insights on the molecular interactions between membranes and Aβ aggregates. Yet, the feasibility of in-cell ssNMR spectroscopy to probe Aβ-membrane interactions in native cellular environments has rarely been tested. Here we report the application of in-cell31P ssNMR spectroscopy on live mouse neuroblastoma Neuro-2a (N2a) cells under moderate magic angle spinning (MAS) conditions. Both cell viability and cytoplasmic membrane integrity are retained for up to six hours under 5 kHz MAS frequency at 277 K, which allow applications of direct-polarization 31P spectroscopy and 31P spin-spin (T2) relaxation measurements. The 31P T2 relaxation time constant of N2a cells is significantly increased compared with the model liposome prepared with comparable major phospholipid compositions. With the addition of 5 μM 40-residue Aβ (Aβ1–40) peptides, the 31P T2 relaxation is instantly accelerated. This work demonstrates the feasibility of using in-cell31P ssNMR to investigate the Aβ-membrane interactions in the biologically relevant cellular system.

Poly(aryl ether ketone) hollow fibers preparation with acid resistant spinnerets

Poly(ether ketone ketone) (PEKK) and poly(ether ether ketone) (PEEK) are high-performing thermoplastics applicable for solvent-resistant nanofiltration due to their outstanding resistance to harsh conditions. However, the polymers require strong acids for solubilization and use as dope solution for membrane preparation. This is the major limitation when targeting hollow fibers (HF) since the metallic spinning line and spinnerets could be prone to corrosion in long term. In this work, we propose the fabrication of an acid-resistant spinneret by 3D printing technology through stereolithography using acrylate and methacrylate-based resins. The hollow fibers are produced by interplaying spinneret designs and spinning conditions with an acid-resistant spinning line. The fabricated hollow fibers exhibited N,N-dimethylformamide (DMF) permeance of 1.4–2.7 L m−2 h−2 bar−1, with a molecular weight cut-off around 246 g mol−1 confirmed with more than 90% rejection of 1,3,5-tri-tert-butyl benzene (TTBB). Furthermore, the hollow fiber modules were tested at high-temperature filtration in DMF with confirmed membrane flux or structural dimension stability.

Preparation and Antibacterial Properties of a Composite Fiber Membrane Material Loaded with Cationic Antibacterial Agent by Electrospinning.

Microbial infections due to bacteria, viruses, and molds are a serious threat to both human life and the health of other organisms. To develop inexpensive, easy-to-prepare, efficient, and portable nano-antibacterial materials, as well as to explore the antibacterial prospects of cationic antibacterial agents, in this work, six different membrane materials were prepared by the electrostatic spinning method and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR). The materials were tested for antimicrobial properties using a modified AATCC100-200 test method. Under the most suitable spinning conditions, the doping amount of the cationic antimicrobial agent, CTAB, had the greatest influence on the antimicrobial performance. The antimicrobial performance of PCL/PEO/CS/CTAB0.4 was the highest among the prepared materials, with 83.7% effectiveness against S. aureus and 99.9% against E. coli. The antimicrobial performance was found to be stable. In our study, we determined the most suitable spinning ratio to prepare an inexpensive and efficient cationic antimicrobial agent. Biodegradable, high-antimicrobial-activity antimicrobial materials can be applied as films, and this new nanofiber material has shown great potential in wound dressings and as a mask material due to its remarkable antimicrobial efficiency.

Preparation of nano-porous poly(ether ether ketone) hollow fiber membrane and its performance for desalination in vacuum membrane distillation

Nano-porous poly(ether ether ketone) (PEEK) hollow fiber membranes were successfully fabricated from PEEK/polyetherimide (PEI) blends via thermally-induced phase separation (TIPS) followed by chemical extraction of PEI method. The gas permeation rates, morphologies and mechanical properties of membranes were systematically investigated under different spinning conditions. The content of PEEK in blends substantially determined the gas permeation rates following the order: PEEK30/PEI70 (~9000 GPU) > PEEK40/PEI60 (~5100 GPU) > PEEK50/PEI50 (~1700 GPU) > PEEK60/PEI40 (~300 GPU) > PEEK70/PEI30 (below 1.0 GPU). Faster winding rates and bigger N2 bore fluid flow rates would result in bigger pores, higher porosity and larger gas permeation rates, while would cause lower mechanical strength. Furthermore, the silane-grafted hydrophobic PEEK hollow fiber membranes were successfully prepared via one-step reduction followed by silane modification. The performance of virgin and modified membranes was evaluated by treating saline feed containing 3.5 wt% sodium chloride in vacuum membrane distillation (VMD) process. Compared with virgin PEEK membrane, the modified membranes exhibited a more stable flux and higher salt rejection over 99.9 % for 33 h, indicating the significant improvement in the anti-wetting property caused by silane modification. The application attempt expands the research direction of PEEK membranes and promotes its further application potential in VMD process.

The study of correlations among the process condition, structure and property for poly(l-lactide) fibers

This article focus on derive the process-structure-property relationship of Poly(l-lactide) (PLLA) fibers prepared by two-step melt spinning process. The spinning temperature, spinning rate, drawing temperature as well as draw ratio were studied to analyze the influence of process variables on the structure and properties of PLLA fibers. It suggests that the crystallinity, lamellar orientation structure and mechanical properties of fibers are dependent on the spinning conditions, including melt-spinning and hot-drawing process. An approximate linear correlation resulted between the orientation degree and tensile strength of PLLA fibers, which means that the oriented structure plays a dominant role to enhance PLLA fibers. PLLA fibers with high performance of 499 MPa and 5.30 GPa in tensile strength and Young’s modulus separately have been realized by the selected spinning parameters. The results provide a theoretical direction for enhancing PLLA fibers by adjusting the structure characteristic via modifying the spinning parameters.

PLA/starch biodegradable fibers obtained by the electrospinning method for micronutrient mineral release

<abstract> <p>Developments in nanofibers seek to increasingly expand the field of support and release of actives, such as fertilizers. Using nanofibers as materials for mineral nutrients aims to increase the efficiency of contact release of the fertilizer to the plant root in the soil. Poly lactic acid (PLA) is a polymer with biocompatibility characteristics and spinning conditions. The starch biopolymer combined with PLA can improve the biodegradation properties and hydrophilicity of the fibers and allow the solubilization of the fertilizer source for the plant. Thus, the present paper sought to find a polymeric matrix in the form of PLA/starch nanofibers that could act in the release of the mineral micronutrient manganese as a model asset. The electrospinning method was employed to obtain the fibers varying the starch concentration from 10 to 50% (w/w) in the polymeric matrix. The nanocomposite containing manganese carbonate as a source of Mn<sup>2+</sup> ions was produced from the best membrane composition. The results showed that the analyzed PLA/starch blends with 20% (w/w) provided better fiber affinity with water, which is fundamental for fiber degradation time. Regarding fertilizer release, the starch present in the PLA fiber at a concentration of 20% (m/m) promoted better control in the release of Mn<sup>2+</sup>. The total release occurred after 5 d in contact with the 2% citric acid extractive medium. Thus, PLA/starch fiber becomes an alternative in the packaging of particulate fertilizers, providing increased contact area during root application with gradual delivery of mineral nutrients and minimizing loss by leaching.</p> </abstract>

Spin and valley polarization of an MoS2 zigzag nanoribbon with a magnetic barrier via Fano resonance

For monolayer ${\mathrm{MoS}}_{2}$, a magnetic field causes the degeneracy of the $K$ and ${K}^{\ensuremath{'}}$ valleys to be lifted, owing to the valley Zeeman effect. Thus, in a monolayer ${\mathrm{MoS}}_{2}$ nanoribbon system with a magnetic barrier, electrons in these valleys exhibit different conductance behaviors when passing through the barrier. One valley shows a strong dip in conductance caused by Fano resonance, i.e., quantum interference between continuum states and Landau levels in the magnetic barrier. This dip can be modulated by changing the strength and length of the magnetic barrier. By calculating the asymmetric conductance for the $K$ and ${K}^{\ensuremath{'}}$ valleys as a function of incident energy with various values of the physical parameters, optimized conditions for spin and valley polarization can be found. The results presented here provide useful information to enable implementation of spin- and valley-polarized currents in future devices.

Practical considerations on the use of low RF-fields and cosine modulation in high-resolution NMR of I = 3/2 spin quadrupolar nuclei in solids

Despite its ease in experimental set up, the low sensitivity of MQMAS experiments is often a limiting factor in many practical applications. This is mainly due to the large radiofrequency (RF) field requirement of the two short hard-pulses often used for the optimum MQ excitation and conversion steps. Very recently, two novel MQMAS experiments have been proposed for I = 3/2 nuclei, namely lp-MQMAS and coslp-MQMAS, enabling an efficient MQ excitation/conversion with a reduced RF requirement, by utilizing two long pulses lasting one rotor period each, with or without cosine modulation. In this study, we focus on the practical considerations of these new methods and discuss their pros and cons to elucidate their appropriate use under both moderate and fast spinning conditions. Using four I = 3/2 (87Rb, 71Ga, 35Cl and 23Na) nuclei at a moderate magnetic field (B0 = 14.1 T), we show the superior use of these experiments, especially for samples with large CQ values and/or low-gamma nuclei. Compared to all other existing sequences, the coslp-MQMAS method with initial WURST signal enhancement is the most robust, efficient and resolved high-resolution 2D method for spin 3/2 nuclei. Furthermore, using {23Na}-1H spin systems, we demonstrate the sensitivity advantage of the WURST coslp-MQ-HETCOR acquisition upon 1H detection and fast MAS conditions.

Impact of physio-chemical spinning conditions on the mechanical properties of biomimetic spider silk fibers

Artificial spider silk has emerged as a biobased fiber that could replace some petroleum-based materials that are on the market today. Recent progress made it possible to produce the recombinant spider silk protein NT2RepCT at levels that would make the commercialization of fibers spun from this protein economically feasible. However, for most applications, the mechanical properties of the artificial silk fibers need to be improved. This could potentially be achieved by redesigning the spidroin, and/or by changing spinning conditions. Here, we show that several spinning parameters have a significant impact on the fibers’ mechanical properties by tensile testing more than 1000 fibers produced under 92 different conditions. The most important factors that contribute to increasing the tensile strength are fast reeling speeds and/or employing post-spin stretching. Stretching in combination with optimized spinning conditions results in fibers with a strength of >250 MPa, which is the highest reported value for fibers spun using natively folded recombinant spidroins that polymerize in response to shear forces and lowered pH.

Influence of formulation and spinning conditions on the morphology of PES and PES/ZIF-8 hollow fiber membrane

Influence of formulation and spinning conditions on the morphology of PES and PES/ZIF-8 hollow fiber membrane

Behavior of melt electrospinning/blowing for polypropylene fiber fabrication

AbstractThe fabrication process of polymer fibers has been analyzed in various ways, and several studies have been conducted to develop new processes and optimize existing ones. Several studies have been conducted on the electrospinning process, which can easily fabricate nanofibers, and the development of materials manufactured through electrospinning has also been investigated. However, research on the nanofiber fabrication and processing of thermoplastic polymers, such as polypropylene (PP), polyethylene and polyethylene terephthalate, is relatively lacking. Therefore, research on nanofiber fabrication is essential. In this study, PP fibers were successfully manufactured through a melt electrospinning/blowing process, which combined melt blowing and electrospinning. To analyze the melt electrospinning/blowing process, the dynamic behavior of the spinning process was observed using a charge‐coupled device camera in real time, and the effects of the different spinning conditions were compared and analyzed. As the hot air or high voltage was increased, the spinning jet area tended to increase. In addition, the average diameter of the fabricated fibers tended to decrease as a high voltage was applied at a hot air pressure of 0.01 MPa; conversely, the average diameter tended to increase at a hot air pressure of 0.03 MPa. A similar trend was observed for the tensile stresses in the PP web fabrics. The polymer fibers produced by this melt electrospinning/blowing process can be applied as a production process for nanomembranes, filters and battery separators. © 2022 Society of Industrial Chemistry.

Characterization of the keratin/polyamide 6 composite fiber's structure and performance prepared by the optimized spinning process based on the rheological analysis

The complex chemical structure of polypeptide and the imperfection of processing technology cause the mechanical properties of regenerated keratin to be hard and brittle. This defect seriously affects the application prospects of keratin materials. To solve the above problems, α-lipoic acid modified keratin (KER) was blended with Polyamide 6 (PA6) and prepared into composite fibers via the wet-spinning method in this work. The spinnability and spinning conditions of the KER/PA6 blend solution were analyzed by rheological theory. The results illustrated that keratin solution will easily form a gel state under certain temperatures and concentrations, which was not conducive to the preparation of regenerated fiber. When the temperature was 45 °C and the mass fraction was 10 %, the viscosity and rheology of the solution were appropriate. The rheological properties of the blend solution showed that too much keratin would make the solution easy to gel, which was not conducive to the preparation of regenerated fibers and may affect the fiber properties. On this basis, the prepared composite fibers were characterized to explore the macromolecular aggregation state of keratin and PA6 in fibers. FT-IR and XRD results proved that there was no chemical reaction between keratin and PA6 in the composite fibers, which belonged to physical blending. At the same time, the two polymers had good compatibility and can be blended at the molecular level. SEM, DSC, and tensile strength test results indicated that when the proportion of keratin was too high, the structure and properties of the composite fibers will have obvious defects, which was consistent with the rheological analysis. Therefore, the blend ratio of keratin/PA6 was determined to be 3:7. Under this condition, the fibers exhibited a homogeneous structure and good thermal properties, especially its mechanical properties were close to wool fibers. The KER/PA6 composite fibers show important research value and can also provide technical reference for the development of regenerated biomass materials.

Impact of Co2+ on the magneto-optical response of MAPbBr3: An inspective study of doping and quantum confinement effect

The current work establishes the excitonic magneto-optic (M − O) effects of magnetic circular dichroism (MCD) in Cobalt (Co2+) doped diamagnetic organic−inorganic hybrid CH3NH3PbBr3 perovskites at low magnetic field and room temperature. The solution-processed perovskites are prepared in the form of single crystal thin films and quantum dots. The structural studies confirm the successful doping of the Co2+ in the perovskite lattice. Further, the perovskites are investigated as diluted magnetic semiconductors (DMSs) related to the dopant concentration effect and the size effect on their M − O properties. Magnetic dopant Cobalt leads to the strong sp-d exchange coupling that generates higher values of Zeeman splitting (ΔEZ) than the pristine MAPbBr3 due to the excitonic 1s Pb–Br absorption quantified by analysis of MCD. The ΔEZ value increases with the Co concentration up to 10 mol % and then starts decreasing. This concentration dependency can be linked with the luminescence of the perovskites with the Co2+ doping. The rise and fall of the MO and PL properties can be defined by the formation of Co–Co pairs in heavily doped perovskites which can influence the spin conditions of the paramagnetic Co ions. Using the Kramers–Kronig relations with MCD, the calculated Verdet constant exhibits a massive increase in value with the doping of cobalt, much higher than the industry standard Faraday rotator indicating their probable usability in this industry. Further in the quantum dots, the quantum confinement effect is pronounced that increases the MCD and hence the ΔEZ multiple times higher than the bulk perovskite films. These results provide a promising pathway for the study of solution-processed hybrid perovskites as DMSs for spintronics.

Vortex characteristics in rotating rotor cup of rotor spinning based on large eddy simulation

Large Eddy Simulations (LES) are performed to study the vortex characteristics in a rotating rotor cup of rotor spinning. The instantaneous evolution process of vortex in the cup is analyzed, and the effects of rotor speed, slip surface angle, and rotor diameter on the airflow field in the rotor cup are examined. The numerical results show that vortices mainly concentrate at the outlet of the transfer channel, which may be due to the collision between the high-speed air stream from the transfer channel and the rotating wall. The strengths of these vortices gradually decrease as they are transported downstream due to the rotating of the cup. To analyze the impact of the parameters on the airflow field and yarn formation, a vortex area ratio (S) is defined which characterizes how much the rotor cup is occupied by vortices. A larger S value usually means a more chaotic and less structured flow field, thus is undesired for the spinning as it may adversely affect the slip and assemble of fibers in the rotor cup. Our parametric study indicates that the largest S value is found at 80,000 rpm for a 50 mm-rotor with a slip surface angle of A rotor speed close to this thus may be unfavorable in spinning according to our criterion. For a rotor speed of 100,000 rpm and a diameter of 50 mm, the optimal slip surface angle is found to be about which brings a smallest S value. For a rotor speed of 100,000 rpm and a slip surface angle of the S value is observed to drop dramatically when the rotor diameter reaches 60 mm, a large enough rotor cup thus can efficiently alleviate the chaotic level of the airflow field. The numerical results may provide a preliminary guideline for the choice of spinning conditions that would be better for rotor spinning.

Response to Comment on "Pushing the frontiers of density functionals by solving the fractional electron problem".

Gerasimov et al. claim that the ability of DM21 to respect fractional charge (FC) and fractional spin (FS) conditions outside of the training set has not been demonstrated in our paper. This is based on (i) asserting that the training set has a ~50% overlap with our bond-breaking benchmark (BBB) and (ii) questioning the validity and accuracy of our other generalization examples. We disagree with their analysis and believe that the points raised are either incorrect or not relevant to the main conclusions of the paper and to the assessment of general quality of DM21.

Laser-Assisted Melt Electrospinning of Poly(L-lactide-co-ε-caprolactone): Analyses on Processing Behavior and Characteristics of Prepared Fibers.

The laser-assisted melt electrospinning (LES) method was utilized for the preparation of poly(L-lactide-co-ε-caprolactone) (PLCL) fibers. During the process, a carbon dioxide laser was irradiated, and voltage was applied to the raw fiber of PLCL. In situ observation of fiber formation behavior revealed that only a single jet was formed from the swelling region under the conditions of low laser power and applied voltage and feeding rate, whereas multiple jets and shots were produced with increases in these parameters. The formation of multiple jets resulted in the preparation of thinner fibers, and under the optimum condition, an average fiber diameter of 0.77 μm and its coefficient of variation of 17% was achieved without the formation of shots. The estimation of tension and stress profiles in the spin-line was also carried out based on the result of in situ observation and the consideration that the forces originated from surface tension, electricity, air friction, and inertia. The higher peak values of tension and stress appearing near the apex of the swelling region corresponded to the formation of thinner fibers for the condition of single-jet ejection. Analyses of the molecular orientation and crystallization of as-spun fibers revealed the formation of a wide variation of higher order structure depending on the spinning conditions.

Geometric phase effect study in electric dipole moment rings

Several proposals to measure a possible small electric dipole moment (EDM) of charged particles aligned with the spin and the well-known magnetic dipole moment (MDM) are based on the concept to circulate bunches with an initial polarization in the horizontal plane and to observe the buildup of a vertical spin component caused by the EDM. Most proposals aim at operating the ring with ``frozen spin,'' such that, with an MDM only, the spin remains aligned with the trajectory. The signature of a finite EDM is the buildup of a vertical spin component. Machine imperfections may lead as well to a vertical spin buildup, which can be misinterpreted as an EDM and thus limit the sensitivity of the experiment. For that reason, a good understanding of spin dynamics is mandatory to estimate and limit such systematic errors in the measurement. In this paper, a coordinate system attached to the trajectory is introduced to expand the spin. This is of particular interest for fully electric EDM rings operated at the ``magic energy'' to satisfy the frozen spin condition. The procedure is used for a straightforward analysis of geometric phase and other second order effects, which limit the possible sensitivity, i.e., the smallest EDM which can be detected in presence of systematic effects.

Structured pattern hollow fiber membrane designed via reverse thermally induced phase separation method for ultrafiltration applications

AbstractMembrane fouling is a major problem that hinders the application of the membrane in water filtration. To address this issue, a novel reversed thermally induced phase separation (RTIPS) process is applied to fabricate a patterned polyethersulfone (PES) hollow fiber (HF) membrane using a structured spinneret. Surface patterning could induce turbulence, thereby preventing the accumulation of foulants on membrane surface. The RTIPS method requires lesser material with similar mechanical strength compared to that of conventional TIPS method. The fabrication process is optimized by changing the spinning conditions. A dope composition of 24 wt% PES is chosen to prepare the membrane. The chemical composition of the membrane is confirmed via sophisticated techniques such as Fourier‐transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) images of the sample indicates the successful formation of the pattern on the shell side of the HFs. The prepared patterned HF membranes exhibits a high rejection of 97% of bovine serum albumin (BSA), which is comparable to or higher than that of commercial membranes. Moreover, the patterned membrane demonstrates better performance, thereby confirming the effectiveness of this modification in enhancing the antifouling nature.

Carbon nanotube yarns derived from gamma irradiated carbon nanotube forests

Gamma irradiation has been recognised as an effective microengineering tool for improving interfacial adhesion of carbon nanotubes (CNTs) in their macroscopic structures. In this study, we applied γ-irradiation directly to vertically aligned CNT forests (grown on iron coated silicon wafers) in the presence of air, and the irradiated CNT forests were then spun into CNT yarns under various applied tensions. The effect of γ-irradiation on the CNT forest morphology, spinning performance and mechanical and electrical properties of the resultant CNT yarns were evaluated and compared with the unirradiated controls. The results revealed that CNT yarns spun from the gamma irradiated CNT forests had higher tensile strength and lower breaking elongation than the yarns spun from the unirradiated CNT control forests under the same spinning conditions. Increasing spinning tension improved the strength of CNT yarns spun from both the irradiated and unirradiated forests, but the tension-induced improvements from the irradiated forests were much more profound. The relative improvements in the yarn tenacity due to the γ-irradiation were in the range from 14% to 26% under various spinning tension applied. This study also showed that the gamma irradiated CNT forests retained good spinnability under relatively low spinning tension, but exhibited significantly inferior spinnability at high spinning tension, compared to the unirradiated controls. Possible mechanisms for the spinnability of CNT forests and the mechanical properties of CNT yarns were discussed. Further improvement in the CNT forest spinnability may be needed through the optimisation of γ-irradiation doses applied to the CNT forests.

Formylation of Recombinant Spider Silk in Formic Acid and Wet Spinning Studied Using Nuclear Magnetic Resonance and Infrared Spectroscopies.

We reported wet spinning of recombinant spider silk protein (RSSP) and formylation of RSSP in formic acid (FA). First, FA was selected as the spinning solvent and the detailed spinning condition was determined. Next, the mechanical property was compared between the RSSP fiber spun after allowing the spinning solution dissolved in FA to stand for 2 days and the fiber spun immediately after being dissolved in FA for 4 h. The tensile strength of the former fiber was lower than the strength of the latter fiber. This difference can be explained by the difference in the degree of formylation as follows. FA is a known formylating agent, although most researchers who prepared silk fiber by wet spinning with FA have not pointed out about formylation. The formylation of the Ser OH group was confirmed by 13C solution nuclear magnetic resonance (NMR), and the time course of formylation of the RSSP film prepared from the FA solution was tracked by Fourier transform infrared spectroscopy. The 13C solid-state NMR spectra were also compared between two kinds of the formylated RSSP fibers and indicated that the packing state was tighter for the latter fiber than the former one, which could explain higher tensile strength of the latter fiber in the dry state. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis indicated that the RSSP sample decomposed gradually with storage time in FA and the decomposition has begun partly even at 2 h after dissolution in FA. The decomposition by formylation seems to have no significant effect on the backbone structure of the RSSP fiber, although the packing of the fiber becomes loose as a whole. Finally, preliminary trial of deformylation of the formylated RSSP fiber was performed.