In Situ Synchrotron Radiation Techniques: Watching Deformation-induced Structural Evolutions of Polymers

Synchrotron radiation （SR） provides highly brilliant light with tunable wavelength from hard X-ray to far infrared, on which scattering, spectroscopy and imaging techniques with high time and spatial resolutions have been developed for in situ study on biological system and materials like polymer. With examples on flow-induced crystallization of polymer, deformation of nanoparticle filler network in rubber composite and necking propagation in tensile stretch, current work attempts to demonstrate the advantages of in situ synchrotron radiation X-ray scattering, X-ray nano-CT and infrared imaging in the study of deformation-induced multi-scale structural evolutions of polymers. With time resolution up to sub-ms, synchrotron radiation is expected to play a great role in understanding non-equilibrium polymer physics under processing and service conditions, while high-throughput characterization platform based on synchrotron radiation opens the possibility to establish polymer Materials Genome database in processing parameter space within reasonable time, which can serve as the roadmap for industrial polymer processing and accelerate material innovation.

Synchrotron radiation photoemission study on growth of gadolinium film over Ni(110)surface

The growth of Gd film on Ni(110) surfaco was studied by synchrotron radiation photoemission spectroscopy and XPS techniques. It is revealed that in the coverage range of 0—0.22 nm Gd4f core level showed a single-peak structure, therefore Gd film grows over Ni(110) in the layer-by-layer mode. However, when Gd coverage was larger than 0.22, nm the Gd4f peak turned gradually into double-peak and a double-peak structure with 2.3 eV separation was formed at 1.51 nm, meanwhile similar phenomenon was observed in the Gd4d XPS spectra. It is suggested that the double-peak structure of Gd4f was derived from the growth of Gd film in cluster mode and the Gd atomic clusters may exhibit different electronic states from Gd metal owing to their special structures. The Gd4f double-peak evolved into a single-peak on annealing at 600 K, implying that Gd clusters are thermodynamically unstable.

Structural Evolution of UHMWPE Fibers during Poststretching with Distinct Initial Structures

By adopting a homemade extension apparatus and wide-angle X-ray diffraction(WAXD)technique,the structural evolutions of the extracted ultra-high molecular weight polyethylene(UHMWPE)fibers with different spinning draw ratios were investigated during the poststretching process.Molecular chains oriented along the axis quickly at the early stage of drawing,which is quite different from the situation of drawing with solvents.The crystal regions,which have not melted at higher temperature,show stronger rigidity in the absence of solvents.Rigid characteristics show faster response to the external field.Also,the surface morphologies of fibers after poststretching are characterized by scanning electron microscopy(SEM).The lamellae stack disordered before stretching,but arranged in order along the draw direction when the draw ratios were larger than 1.

AN ANALYTICAL CALCULATION FOR THE LASER GAIN IN A LONG PULSE FREE-ELECTRON LASER

For a long pulse free-electron laser(FEL)in the low gain regime,an approximate expression is given to describe the optical field gain from the small signal to the weak saturation.The result is shown to agree with those from a 1-D computer simulation.

A Preliminary Raman Investigation of the Lead Titanate Thin Films via Sol-Gel Process

Raman spectra of the PbTiO3 films via sol-gel process were investigated by using a Jobin Yvon U1000 system. Compared with the Raman spectra of the PbTiO3 single crystals, Raman peaks of PbTiO3 films shift downward, which is attributed to the stress effect in the PbTiO3 films exerted by the substrate and the size effect on the Raman frequencies.

Improving the Softness of BOPP Films： From Laboratory Investigation to Industrial Processing

Young＇s modulus of biaxially oriented polypropylene （BOPP） films prepared with homemade film stretcher was investigated, which can be used to indicate the softness of films. It was found that the modulus of films was decreased by about 69% as the content of polyethylene （PE） added into polypropylene （PP） reached 30%. Also, increasing draw temperature can induce lower stress level during stretching, which may lead to the formation of crystals with low orientation level and thus decreased modulus of films. Based on laboratory study, BOPP films produced on commercial line were studied by differential scanning calorimetry （DSC）, wide and small-angle X-ray scattering （WAXS, SAXS） with varying contents of PE. SAXS results show that the crystals are oriented in both machine direction （MD） and transverse direction （TD）, and the crystals are more oriented in TD than MD according to the WAXS results for all films. Also, the orientation parameter of crystal along TD increases from 0.68 to 0.83 as the contents of PE increase from 0% to 25%. Meanwhile, the modulus of films in MD declines with increase of PE contents generally, improving the film softness. Orientation of crystals is thus an effective structure parameter to adjust the film softness. The relationship of processing-structure-property is also established.

The magnet design for the HLS storage ring upgrade project

In order to improve the performance of the Hefei Light Source （HLS）,in particular to get higher brilliance synchrotron radiation and increase the number of straight section insertion devices,an upgrade project called HLSII will be launched soon.The storage ring lattice,which has a double bend achromatic structure with four periods,comprises eight dipoles,32 quadrupoles and 32 combined function sextupoles.The design and analysis of the magnets are shown in this paper,along with the optimization of the multipurpose combined function magnet,which consists of three magnets：skew quadrupole,horizontal dipole and vertical dipole,with the main sextupole magnet.This type of magnet is the first one that has been designed and used in China.The mechanical design and fabrication procedures for the magnets are also presented.

The Spatial Correlation between Crystalline and Amorphous Orientations of Isotactic Polypropylene during Plastic Deformation:An in situ Observation with FTIR Imaging

On the basis of research method in FTIR imaging, we made a heterogeneous thin film of isotactic polypropylene （iPP） that contains a few large spherulites （-150 μm） which are surrounded by small spherulites （-15 μm） for tensile testing. The evolution processes of crystalline and amorphous orientations of iPP are monitored with its characteristic peaks at 998 and 973 cm^-1, respectively. By introducing the correlation images, the analysis demonstrates the relationships between the orientation evolutions of crystalline and amorphous phases in a space of 250 μm × 250 μm detecting area. During the plastic deformation, crystalline orientation is higher than amorphous orientation outside the large spherulite, while that is opposite inside the region. In addition, the evolutions of crystalline and amorphous orientations almost keep a positive correlation.

Low emittance lattice optimization using a multi-objective evolutionary algorithm

A low emittance lattice design and optimization procedure are systematically studied with a non-dominated sorting-based multi-objective evolutionary algorithm which not only globally searches the low emittance lattice, but also optimizes some beam quantities such as betatron tunes, momentum compaction factor and dispersion function simultaneously. In this paper the detailed algorithm and lattice design procedure are presented. The Hefei light source upgrade project storage ring lattice, with fixed magnet layout, is designed to illustrate this optimization procedure.

A Theoretical Interpretation of Free Volume at Glass Transition

We device a relaxed lattice model （RLM） to study the mechanism of glass transition, which unifies the cage- effects from particle-particle interaction and entropy. By analyzing entropy in RLM with considering the influence of interactions on equilibrium, we demonstrate that glass transition is a second-order phase transition. For a perfect one- dimensional linked particle system like linear polymer under normal pressure, the free volume at glass transition is rigorously deduced out to be 2.6%, which provides a theoretical basis for the iso-free volume of 2.5% given by Willian, Landel and Ferry （WLF） equation. Extending to system with dead particles linked with higher dimensions like branched or cross-linked chains under positive or negative pressure, free volume at glass transition is varied, based on which we construct a phase diagram of glass transition in the space of free volume-dead particle-pressure. This demonstrates that free volume is not the single parameter determining glass transition, while either dead particles like cross-linked points or external force fields like pressure can vary free volume at the glass transition.

How the Aggregates Determine Bound Rubber Models in Silicone Rubber? A Contrast Matching Neutron Scattering Study

The correlation between aggregates and bound rubber structures in silicone rubbers(S(phr)) with various silica fractions(ΦSi) has been investigated by contrast matching small-angle neutron scattering(SANS), swelling kinetics, and low-field nuclear magnetic resonance(NMR).Mixed solvents with deuterated cyclohexane fractions of 4.9% and 53.7% were chosen to match the scattering length densities of the matrix(SMP(phr)) and the filler(SMS(phr)), respectively. All the data consistently suggest that:(i) There is a critical threshold ΦSic between 10 and 30 phr;below ΦSic, the isolated aggregates are dominant, while beyond ΦSic, some rubber fraction is trapped among the agglomerate;(ii) ΦSiindependent thicknesses around 7.5 nm(NMR) and 8.6 nm(SANS) suggest that the bound rubber formation is determined by inherent properties of the components, and the power-law around 4.2 suggests an exponential changed gradient density of the bound rubber;(iii) SMS(80) presents a bicontinuous bound rubber with three characteristic lengths of 41, 100, and 234 nm. The expanded correlation length, a 20 nm smaller aggregate sizes suggest that such existent bicontinuous network in dry samples with less ΦSi is kind of impacted by swelling. With the obtained bound rubber models, the reinforcing mechanism of filled silicone rubber is elucidated.

A Universal Equipment for Biaxial Stretching of Polymer Films

A biaxial stretching equipment was designed and constructed to enable fundamental studies of the relationship between film processing conditions and structures of oriented film products. With programmable drive motors and scissorlike mechanism, all stretching modes, including uniaxial stretching with constant and free width, simultaneous and sequential biaxial stretching, can be applied to a square-shaped sheet. Parameters related to film stretching manufacturing, such as temperature, draw ratio and stretching speed can be set independently to meet the requirement of different polymers. The force information during stretching is recorded by two miniature tension sensors in two directions independently, which can monitor the mechanical stimulus and stress response. Using this equipment, experiments are conducted to investigate the influence of stretching parameters on the structure of polypropylene films, which provides an effective method to tailor the processing conditions to obtain the films with desired properties.

Design of proton beam optics to realize beam distribution transformation in C-ADS HTBT

The linac to the transmuter beam transport line （LTBT） connecting the end of the linac to the spallation target is a critical sub-system in the accelerator driven system （ADS）. It has the function of transporting the accel-erated high power proton beam to the target with a beam footprint satisfying the special requirements of the minor actinide （MA） transmuter. In this paper, a preliminary conceptual design of the hurling magnet to transmuter beam transport section （HTBT）, as a part of the LTBT, for the China ADS （C-ADS） system is proposed and developed. In this design, a novel hurling magnet with a two dimensional amplitude modulation （AM） of 1 kHz and scanning of more than 10 kHz at 360 in transverse directions is used to realize a 300 mm diameter uniform distribution of beam on target. The preliminary beam optics design of C-ADS HTBT optimized to minimize the beam loss on the vacuum chamber and the radiation damage caused by back-scattering neutrons will be reported.

A Universal Blown Film Apparatus for in Situ X-ray Measurements

A setup of blown film machine combined with in situ synchrotron radiation X-ray diffraction measurements and infrared temperature testing is reported to study the structure evolution of polymers during film blowing. Two homemade auto-lifters are constructed and placed under the blown machine at each end of the beamline platform which move up and down with a speed of 0.05 mm/s bearing the 200 kg weight machine. Therefore, structure development and temperature changes as a function of position on the film bubble can be obtained. The blown film machine is customized to be conveniently installed with precise servo motors and can adjust the processing parameters in a wide range. Meanwhile, the air ring has been redesigned in order to track the structure information of the film bubble immediately after the melt being extruded out from the die exit. Polyethylene（PE） is selected as a model system to verify the feasibility of the apparatus and the in situ experimental techniques. Combining structure information provided by the WAXD and SAXS and the actual temperature obtained from the infrared probe, a full roadmap of structure development during film blowing is constructed and it is helpful to explore the molecular mechanism of structure evolution behind the film blowing processing, which is expected to lead to a better understanding of the physics in polymer processing.

Study on the selection of BLM detector for C-ADS Injector Ⅱ

The injector of C-ADS （Chinese Accelerator Driven Sub-critical System） project is a high current, fully super-conducting proton accelerator. Meanwhile, a BLM system is indispensable for this facility, especially in low energy segments. This paper presents some basic simulations for 10 MeV proton by Monte Carlo program FLUKA, as well as the distributions on different secondary particles in three aspects： angular, energy spectrum, and current. These results are beneficial to selecting the detector type and its location and determining its dynamic range matching different requirements for both fast and slow beam loss. Furthermore, in this paper the major impact of the background is also analyzed, such as superconducting cavity X radiation and radiation caused by material activation. This work is meaningful in BLM system research.

Study of Robinson instabilities with a higher-harmonic cavity for the HLS phase Ⅱ project

In the Phase Ⅱ Project at the Hefei Light Source, a fourth-harmonic ＂Landau＂ cavity will be operated in order to suppress the coupled-bunch instabilities and increase the beam lifetime of the Hefei storage ring. Instabilities limit the utility of the higher-harmonic cavity when the storage ring is operated with a small momentum compaction. Analytical modeling and simulations show that the instabilities result from Robinson mode coupling. In the analytic modeling, we operate an algorithm to consider the Robinson instabilities. To study the evolution of unstable behavior, simulations have been performed in which macroparticles are distributed among the buckets. Both the analytic modeling and simulations agree for passive operation of the harmonic cavity.

Soft X-ray in-line holographic experiment

Water window" soft X-ray has some advantages in the microimaging of biological specimens. Soft X-ray holography can give us three-dimensional images of biological cells in their natural condition. Quasi-monochromatic soft X-ray from the polymonochromatic synchrotron radiation is obtained by a zone plate-pinhole linear monochromator at National Synchrotron Radiation Laboratory (NSRL) at Hefei. The pinhole is used to increase the temporal coherence of the soft X-ray, and also to increase the spatial coherence of it. An in-line holographic experiment has been finished with soft X-ray of main wavelength 4.5 nm and pinhole of diameter 0.03 mm. The magnified hologram is reconstructed with He-Ne laser. A smaller pinhole is wanted to be used to improve the coherence of the soft X-ray so as to improve the quality of the hologram.