High-speed Spinning Research Articles

Prevention of spinning induced sample deterioration during long time solid state NMR experiments of quadrupolar spin systems

A simple solution is proposed to prevent a solid state polycrystalline sample from deterioration during long time high speed spinning experiments in solid state NMR. It is found that if a certain percentage (∼40% volume) of polyethylene glycol (PEG, (HO–CH 2–(CH 2–O–CH 2–) n –CH 2–OH) n ) is mixed with the sample that are subject to deterioration, the quality of the sample can be maintained for a long time under high speed spinning for a few days or longer, sufficient for multi-dimensional and/or low-sensitivity experiments. Both 1D and 2D experimental results are shown to support this idea.

Process aspects of production of polyester textile fibres

Some aspects of high-speed spinning of polyester textile fibres that affect the technology level and product quality are examined. It was shown that uniformity of the melt, extrusion, and cooling of the filaments are the most important process factors in modern plants. Addition of polymer dye concentrates (PDC) (MB) results in physical modification of the polyester fibres that affect the structure formation and deformation properties of POY. This makes it necessary to correct the process parameters of the fibre production process.

Improved magnetization transfer in solid-state NMR with fast magic angle spinning

The efficiency of magnetization transfer between different spins S such as chemically inequivalent carbon-13 nuclei in solid samples that are spinning at high frequencies about the magic angle can be enhanced by a phase- alternated recoupling irradiation scheme (PARIS). Dipolar recoupling is assisted by a radio-frequency ( rf) field applied to the abundant I (proton) spins. In contrast to rotary resonance-based recoupling schemes, the new method does not depend critically on the rf amplitude, which need not be matched with the spinning frequency. Modest rf amplitudes suffice to bring about efficient magnetization transfer even at high spinning speeds, thus avoiding excessive sample heating. The new method compensates efficiently for rf field inhomogeneity, so that the full sample volume is used more effectively.

Design of high-power, broadband 180° pulses and mixing sequences for fast MAS solid state chemical shift correlation NMR spectroscopy

An approach for the design of high-power, broadband 180 degrees pulses and mixing sequences for generating dipolar and scalar coupling mediated (13)C-(13)C chemical shift correlation spectra of isotopically labelled biological systems at fast magic-angle spinning frequencies without (1)H decoupling during mixing is presented. Considering RF field strengths in the range of 100-120 kHz, as typically available in MAS probes employed at high spinning speeds, and limited B (1) field inhomogeneities, the Fourier coefficients defining the phase modulation profile of the RF pulses were optimised numerically to obtain broadband inversion and refocussing pulses and mixing sequences. Experimental measurements were carried out to assess the performance characteristics of the mixing sequences reported here.

Forming method of axial micro grooves inside copper heat pipe

The high-speed oil-filled ball spinning and drawing process was put forward to manufacture the axially grooved heat pipe with highly efficient heat-transfer performance, and the forming mechanism of micro-grooves inside the pipe was investigated. The key factors influencing the configurations of micro-grooves were analyzed. When the spinning depth varies between 0.4 mm and 0.5 mm, drawing speed varies from 200 mm/min to 450 mm/min, rotary speed is beyond 6 000 r/min and working temperature is less than 50 °C, the grooved tubes are formed with high quality and efficiency. The ball spinning process uses full oil-filling method to set up the steady dynamic oil-film that reduces the drawing force and improves the surface quality of grooved copper tube.

High-speed Melt Spinning of Nanoparticle-filled High Molecular Weight Poly(ethylene terephthalate)

Abstract High molecular weight poly(ethylene terephthalate) (HMW-PET) (intrinsic viscosity of 0.809 dL/g) and its nanocomposites with 1 wt.% organoclay C12PPh-Cl− and 1 and 2 wt.% trisilanol isobutyl-poly(hedral oligomeric silsesquioxane) (POSS) were high-speed melt spun over the range of take-up speeds 1 to 4.5 km/min, and the effects of nanoparticle type on the fiber properties were investigated. The clay and POSS nanocomposites exhibited quite different melt spinning behaviors. The neat PET and PET/POSS nanocomposites showed a neck-like deformation distinctly from the take-up speed of 3.5 and 3 km/min while PET/clay nanocomposites did not show any neck-like deformation over the entire spinning speed range. In comparison with nanocomposite chips clay gave rise to re-aggregation of nanoparticles whereas POSS made little change in dispersion. Clay suppressed the crystallization of PET during high-speed spinning although it had more effective nucleation effects at the static state than POSS. Clay nanocomposite fibers gave lower modulus and higher elongation at break than PET fibers. On the other hand, the mechanical properties of POSS nanocomposite fibers were almost equal or slightly better than PET fibers.

Increased Molecular Weight of a Cross-Linkable Polyimide for Spinning Plasticization Resistant Hollow Fiber Membranes

A propanediol monoester cross-linkable (PDMC) polyimide was synthesized for high-speed hollow fiber membrane spinning. The membranes were plasticization resistant and asymmetric, useful for natural gas purification. In fabricating the membrane material, it was found that significant chain scissioning could occur during the monoesterification reaction, which caused problems in subsequent membrane formation processes. Using NMR, GPC, and FTIR, it was observed that hydrolytic degradation occurs at the imide rings from the small amount of water produced during monoesterification. Workable synthesis conditions were found that enabled the cross-linkable polyimide to be synthesized with high conversions and without loss in the polymer molecular weight. The preservation of a high molecular weight (Mw >100 000) was shown to be favorable for hollow fiber membrane formation.

Simulation and design of planarizing materials for reverse-tone step and flash imprint lithography

Reverse-tone step and flash imprint lithography SFIL-R shows promise as a cost-efficient, high-resolution patterning technique; however, the generation of satisfactory patterns requires the successful application of a planarizing topcoat over topography through spincoating. Photopolymerizable nonvolatile fluids are ideal topcoat materials because they planarize better than volatile fluids during spincoating and can continue to level after spincoating. Fluid mechanics analyses indicate that complete planarization using capillary force is slow. Therefore, defining the acceptable or critical degree of planarization DOPcrit becomes necessary. Finite difference simulation of the spincoat and postspin leveling processes was used to determine the planarization time for various topographic and material property combinations. A new material, Si-14, was designed to have ideal planarization characteristics low viscosity-15.1 cP; low shrinkage-5.1% and satisfy SFIL-R processing requirements oxygen etch resistance-33 wt% silicon, photocurable and was used to validate our models through profilometry and interferometry experiments. During spincoating, minimizing the spin speed generates more planar films; however, this increases the spin time. To rectify this problem, a two-stage spincoating process-a first step with high spin speeds to achieve the target thickness quickly and a second step with low spin speeds to improve planarization-was proposed and experimentally demonstrated.

1H homonuclear dipolar decoupling at high magic-angle spinning frequencies with rotor-synchronised symmetry sequences

We demonstrate here application of symmetry-adapted sequences of the form RN n ν to obtain high-resolution 1H spectra in solid-state nuclear magnetic resonance under high-speed magic-angle spinning. Experimental results are shown for samples of alanine and glycine for spinning speeds up to 30 kHz with radio-frequency nutation rates of around 100 kHz.

Control of flexible rotor systems with active magnetic bearings

An approach is presented for the analysis and design of magnetic suspension systems with large flexible rotordynamics models including dynamics, control, and simulation. The objective is to formulate and synthesize a large-order, flexible shaft rotordynamics model for a flywheel supported with magnetic bearings. A finite element model of the rotor system is assembled and then employed to develop a magnetic suspension compensator to provide good reliability and disturbance rejection. Stable operation over the complete speed range and optimization of the closed-loop rotordynamic properties are obtained via synthesis of eigenvalue analysis, Campbell plots, waterfall plots, and mode shapes. The large order of the rotor model and high spin speed of the rotor present a challenge for magnetic suspension control. A flywheel system is studied as an example for realizing a physical controller that provides stable rotor suspension and good disturbance rejection in all operating states. The baseline flywheel system control is determined from extensive rotordynamics synthesis and analysis for rotor critical speeds, mode shapes, frequency responses, and time responses.

Laser copper plasma X-ray source debris characterization

Laser copper plasma sources are a compact, economical means of producing high intensity X-rays at the correct wavelengths for X-ray lithography. Copper debris in the form of vapor, ions, dust, and high speed particles is an unwanted byproduct of the laser copper plasma technique. Improved methods for debris mitigation are essential for production X-ray lithography using laser copper plasma sources.The main objective of this project is to characterize the debris, particularly the size, amount, and velocity spectrum of high speed particles. The measurements used a source-laser-pulse-synchronized high speed spinning disc. An optical scanning boom microscope analyzed debris collected on a target. Kinematic triangulation using the location of the debris indicates the velocity of debris particles.Velocities of copper debris particles were found to be in the hundreds of meters per second, roughly one order of magnitude slower than previously believed. The precision of results was limited by a mismatched sampling rate for particle collection. This discovery opens up the possibility of a host of mechanical debris blocking countermeasures previously thought to be too slow to effectively stop high speed debris particles. This study also suggests that X-rays emitted at high laser pulse rates could be blocked by debris generated during the previous laser pulse. An area requiring further refinement and study is in the mechanics of plasma generation. The target location and laser spot size and focal point are critical factors in the process and have a low tolerance for variation.

Effect of the Blending of Low Stereo-regularity Component in High-Speed Melt Spinning of Polypropylene

Effect of the Blending of Low Stereo-regularity Component in High-Speed Melt Spinning of Polypropylene

Anion diffusivity in highly conductive nanocrystalline BaF2:CaF2 composites prepared by high-energy ball milling

We report on the fluorine diffusivity in nanocrystalline BaF2 and CaF2 as well as in BaF2:CaF2 composites prepared by high-energy ball milling. Mechanical treatment of polycrystalline BaF2 together with CaF2 results in a nanocrystalline composite with an unexpectedly high dc conductivity of about 0.1 mS cm−1 at 450 K. X-ray diffraction and 19F magic angle spinning NMR measurements at extraordinary high spinning speeds reveal that this can be explained inter alia by the interplay of structural disorder and the formation of a mixed (Ba,Ca)F2 phase.

Structure of (NH4)3GaF6 Investigated by Multinuclear Magic-Angle Spinning NMR Spectroscopy in Comparison with Rietveld Refinement

The structure of ammonium gallium cryolite (NH(4))(3)GaF(6) was investigated by (19)F and (69,71)Ga magic-angle spinning (MAS) NMR in comparison with X-ray powder diffraction followed by Rietveld refinement. In agreement with previous thermodynamic measurements, NMR experiments on (NH(4))(3)GaF(6) support the model of rigid GaF(6) octahedra. At high spinning speeds (30 kHz), the scalar coupling between the six equivalent (19)F nuclei and (69,71)Ga can be directly observed in the powder spectra. The coupling constants are J(19)F(69)Ga = 197 Hz and J(19)F(71)Ga = 264 Hz. To explain the (71)Ga spectra recorded at 3 kHz a small distribution of quadrupolar frequencies has to be included. The spread of the spinning sidebands hints to a largest nu(Q) value of 28 kHz for (71)Ga. This can be explained by the occurrence of highly symmetric GaF(6) octahedra, which are tilted against the surrounding atoms. In addition, the incomplete motional excitation does not average out the quadrupolar effects. NMR findings are in discrepancy to those of Rietveld refinement. As result it appears that X-ray diffraction is not sensitive enough to deliver proper results.

Continuum model for the simulation of fiber spinning, with quiescent and flow-induced crystallization

A macroscopic model for the description of low- and high-speed fiber spinning of crystallizing polymers is proposed. The model incorporates air drag, air cooling, gravity, surface tension and the viscoelastic rheological behavior of the melt. The crystallization dynamics are formulated through a set of rate equations, which describe the quiescent nucleation and growth of spherulites, as well as the flow-induced nucleation and longitudinal growth of fibrils. The influence of the crystallization, as well as the glass transition, on the rheological response is accounted for through a viscous stress contribution. The proposed model realistically describes the velocity, temperature, stress, apparent viscosity and crystallinity profile along the spinline under different processing conditions. Moreover, using a single set of model parameters a fair description of the experimental velocity and temperature profiles is obtained for both low- and high-speed spinning conditions of nylon 66. For poly(ethylene terephthalate) the model describes high-speed spinning conditions only.

Solution and solid-state 31P NMR study of paramagnetic polyoxometalates

Abstract The “lacunary” sandwich polyoxometalate αβ-[Co 3 Na(H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 17− was characterized by solution and solid-state 31 P NMR. The solution 31 P NMR spectrum shows two relatively broad and two narrow signals, assigned to P atoms close and far from the cobalt paramagnetic nuclei, respectively. Solid-state 31 P NMR spectra enable to obtain supplementary data, like chemical shift anisotropy values. The CSA of P atoms' nuclei close to the metallic centres are very large (∼3300 ppm) as compared to those of P nuclei far from the metallic centres (∼500 and 700 ppm). Cumbersome temperature effects were observed at high spinning speeds. In order to quantify these effects, NMR experiments at variable temperature were performed on another paramagnetic polyoxometalate α 2 -[Ce(III)(P 2 W 17 O 61 )] 7− .

Wplyw grzania strefowego na strukture włokien PET i na dynamike procesu przedzenia ze stanu stopionego. Cz. II. Model matematyczny

Dynamic characteristics of PET fibers melt spinning with online zone heating was studied by computer simulation using mathematical model of the process of stationary spinning of a single filament from polymer melt, with stress-induced crystallization. The system of four differential equations (first-order ones) of the model were solved applying Runge - Kutta method using standard numerical procedures (see Eqs. 1-4). The axial local velocity profiles [V(z)], velocity gradient (dV/dz), temperature [T(z)], tensile stress [Ap(z)] and crystallinity degree [X(z)] of molten polymer were calculated for the processes with the same heating zone temperature ranges, take-up velocities, fixed fibers' diameters and limited viscosity number values as in case of PET fibers described in Part I [9] (Table 1, Fig. 5-14). Model calculations predict an occurring of maximum take-up velocity resulting from strong increase in polymer viscosity due to fast oriented crystallization at higher take-up velocities. The maximum velocity and, connected with it, the range of take-up velocity not available for the process depend on the heating zone temperature (T K ). Calculated axial velocity profiles strongly change because of zone heating and the range of melt stretching with the maximum velocity gradient undergoes considerable shift from the spinneret to the heating zone. It results in considerable decrease in the fiber take-up stress, predicted by model, due to shortening of the filament section moving with the final take-up velocity. On the basis of calculations we conclude that the introduction of zone heating of temperature higher 30-40 °C than glass transition temperature (Tg) leads to online crystallization of the melt at lower take-up velocities, similar to crystallization at high-speed spinning without heating zone. The decrease in take-up velocity, related to crystallization predicted, is a consequence of repeated polymer transition through crystallization temperature range. Melt stream crystallization, caused by fast oriented crystallization affected by high tensile stress is predicted in the model at very short section of the process line and is correlated with strong increase in tensile stress and reaching the take-up velocity level. The correlation of the calculated amorphous orientation just before the solidification point (Fig. 19) with experimental values of amorphous orientation factor for PET fibers investigated indicate that amorphous orientations of taken-up fibers is formed by tensile stress at solidification point. The comparison of experimentally determined amorphous orientation and crystallinity degree of the fibers tested with the model predictions (Fig. 17-19) shows that the oriented crystallization parameter A depends on the polymer temperature. In the investigated range of heating zone temperature between Tg and temperature of maximum crystallization rate parameter A should increase with increasing temperature.

In vivo three-dimensional microelectromechanical endoscopic swept source optical coherence tomography

In clinical applications, three-dimensional (3-D) microscopic image volume reveals tissue morphological changes, which are closely related to pre-cancer and early stage disease, much better than two-dimensional images. However, the traditional endoscope only achieves two-dimensional surface images. In this paper, a 3-D endoscopic microscope was developed based on a rotational microelectromechanical system (MEMS) probe [1]. The 3-D helix scan mode was realized by combining a MEMS motor rotational scan and linear stage transversal movement. In order to coordinate the high spin speed of MEMS motor inside the endoscope, an optical coherence tomography (OCT) system with a broadband fast swept laser was used. In vivo 3-D image volumes of rabbit esophagus and trachea were demonstrated.

27Al NMR Study of the Structure of Lanthanum- and Yttrium-Based Aluminosilicate Glasses and Melts

We have investigated by (27)Al nuclear magnetic resonance spectroscopy some compositions in the Ln(2)O(3)-Al(2)O(3)-SiO2 (Ln = Y or La) ternary phase diagram containing more than 60 mol % of SiO2. One- and two-dimensional high-field (17.6 T) high-speed (30 kHz) magic angle spinning experiments have been performed along with simulations of the spectra to quantify the amount of penta-coordinated aluminum present in those glasses as a function of composition. Very high-temperature experiments have allowed to follow selected samples from 2200 degrees C down to 1700 degrees C and hence to characterize the aluminum coordination state and dynamics in those liquids. The present study re-enforces the current view that "minor" species such as penta-coordinated aluminum are actually present in a considerable amount in aluminosilicate glasses, and high-temperature liquids at and above the charge compensation join. The high-field strength of Y3+ and La3+ reveal, for the first time in glasses, a different mean electric field gradient perceived by the tetra- and penta-coordinated aluminum environments. The movements responsible for the NMR relaxation of aluminum in the high-temperature liquid are shown to be uncorrelated with the movements responsible for the macroscopic shear viscosity. Results obtained both on glasses and in situ at high-temperature suggest a preferential localization of Ln3+ nearby tetra-coordinated aluminum species, with possible formation of tricluster and/or Ln3+ coordination changes.

2D Modeling of high-speed fiber spinning with flow-enhanced crystallization

A two-dimensional (2D) analysis of fiber spinning is presented based on a modified version of the two-phase model [Shrikhande et al., J. Appl. Polym. Sci. 100, 3240–3254 (2006); Kohler et al., J. Macromol. Sci. Phys. 44, 185–202 (2005)] that accounts for flow-enhanced crystallization (FEC). The modified model employs the extended pom-pom (XPP) constitutive equation for the amorphous phase and the rigid rod equation for the semicrystalline phase. Calculations are carried out for the high-speed spinning of nylons, polyethylene terephthalate (PET), and pure poly(L-lactic acid) (PLLA), as well as racemic mixtures of the latter (rPLA). Radial variations in temperature and degree of crystalline transformation and microstructure for the PLLA, rPLA, and higher speed PET examples show significant patterns in the skin and core regions of the fiber that reflect the interplay between FEC and thermal-induced crystallization (TIC). Insight is gained into the relationship of TIC and FEC in determining radial birefringence profiles. Likewise, similar considerations for the particular Nylon and lower speed PET examples indicate their less pronounced radial effects are the result of the same interplay.