Variation Of Crystalline Structure Research Articles

Effect of deformation ratio of flow-induced crystallization on polyethylene in crystalline behavior, thermal stability, and tensile loading: A molecular dynamics simulation

Since the physical and mechanical properties of semicrystalline polymers strongly depend on crystalline morphology, understanding the correlation between the crystallization kinetics and crystalline structure of polythene is beneficial for their rational processing and applications. In this study, united-atom (UA) molecular dynamics (MD) simulations were employed to elucidate the variations in crystalline structure, phase transition temperatures, and uniaxial tensile deformation among polyethylene (PE) with randomly oriented and flow-induced crystallization (FIC). The results showed that crystallization occurs in areas with low potential energy. For the FIC process, the entanglement parameter and interplanar spacing was less than for randomly oriented crystallization, and the crystallinity was higher. The relationship between the deformation and the crystallinity of PE with randomly oriented crystallization was expressed, which indicates that the crystalline structure promoted elongation at break of PE in tensile deformation. As PE was oriented to crystallize during the FIC process, the polymer stiffness is positively correlated with the deformation ratio of the PE model, so crystal conformation systems with higher deformation ratios produce higher ultimate stresses in tensile loading. From the visualization results, the crystalline phase was stable and does not easily transform into an amorphous phase during tensile loading. Additional results show that the fracture region of PE at tensile fracture tends to develop in the amorphous phase under tensile loading. Energy analysis showed that the elastic and yield regions were mainly dominated by intra-chain bonds, angles, and dihedral motion of PE, whereas interchain nonbonded interactions mainly dominated strain-hardening regions.

Coherent phonon dynamics in a c-plane sapphire crystal before and after intense femtosecond laser irradiation.

Femtosecond pump-probe experiments with a ∼6.4 fs time-resolution were performed to investigate the coherent phonon dynamics in a c-plane sapphire crystal before and after intense 800 nm femtosecond laser irradiation. The intense femtosecond laser induced defect/distortion and even re-crystallization of crystalline structures, which result in the appearance of new peaks and relative intensity change in coherent phonon and Raman spectra. The combination of these two spectra was found to be beneficial to evidence the variation of crystalline structure and further to differentiate the origins of new Raman peaks after irradiation. Further analysis of time-dependent differential absorbance with damped cosine function fitting and Fourier transfer calculation yields the vibrational parameters, including periods, damping times and initial phases, before and after irradiation. With these parameters, the defect-effects on damping time and the mechanism of coherent phonon generation were addressed.

Synthesis and Characterization of Gamma Irradiated Graphene Oxide-Polypyrrole Nanocomposites

Variations in crystalline structure, optical property, structural bonding in Graphene Oxide (GO) doped polypyrrole (PPy) under gamma irradiation at 100 KGy with effective dose rate of 2.86 KGy per hour have been studied. The crystalline structure has been studied utilizing XRD spectroscopy and it has become clear that as compare to non-irradiated, irradiated sample show more shift toward crystalline nature, this is because of the decrease in d -spacing. The variation in optical properties have been evaluated using UV-VIS spectroscopy, it has been pointed that gamma irradiation reduces the optical band gap due to the chemical reactions, such as chain scissioning etc., induced by gamma exposure, this result is further supported by FT-IR spectroscopy.

Crystalline structure variation within phlogopite, muscovite and talc under 0–1000 kGy γ ray irradiation: A clear dependence on intrinsic characteristic

A clear cognition on how structure difference affects crystalline structure variation within phyllosilicate especially for “2:1” layered phyllosilicate under irradiation is essential to explore the procedure for damage formation within matrix of clay used in disposal high radioactive waste (HLRW) practically and also beneficial for evaluating the effect of nuclear accident to environment, which is of great significance. In this work, phlogopite, muscovite and talc were irradiated by Co-60 γ rays in air at a dose rate of 54 Gy/min with doses at 0–1000 kGy. Then, variation in crystalline structure and intrinsic mechanism were explored. Main results show phlogopite occurred expansion while muscovite and talc occurred shrink in z-direction lattice. Simultaneously, H2O amount declined and valence for metal was elevated. For 1000 kGy-irradiated sample, interlayer space d varied 1% and binding energy for metal was elevated near 1.5–2 eV. It seems phlogopite, muscovite and talc show poor radiation-resistance. Main mechanisms involve intrinsic characteristic, framework break and H2O radiolysis. Upon irradiation, framework break and H2O radiolysis occurred synchronously. Framework break mainly resulted in shrink, H2O radiolysis mainly led extra OH introduction leading expansion. In reality, all these three materials showed extra OH introduction while only phlogopite occurred expansion. It seems the variation trend in lattice mainly relies on material's intrinsic characteristic, H2O radiolysis is secondary. To talc or muscovite, for compact stacking or idle space existence, they are difficult to expand, lattice shrink observed even under extra OH introduction. To phlogopite, for moderate structure, its lattice is easy to expand. For 1000 kGy-irradiated sample, the interlayer space d was enlarged by 1%. For H2O radiolysis, its amount declined and HO• radical was formed, elevating valence for metal as Mg/Al. It seems phyllosilicate shows poor radiation-resistance, and the apparent variation trend in lattice induced by γ ray irradiation seems mainly rely on material's intrinsic characteristic, H2O radiolysis is secondary.

High‐strength functionalized pectin/fibroin hydrogel with tunable properties: A structure–property relationship study

ABSTRACTHydrogels possessing high mechanical strength and well‐controlled properties are of utmost interest in bone tissue engineering. In the current study, a strong self‐crosslinked hydrogel with variable properties has been developed from a combinatory composition of functionalized pectin and silk fibroin. Pectin chains underwent partial oxidation to be decorated with aldehyde functionalities. Later on, functionalized polysaccharide and protein were blended with different ratios, and corresponding variations in crystalline structure as well as in morphological, mechanical, and rheological properties have been monitored. Some theories have been used to better perceive the relation between blending ratio and hydrogel properties.Avrami equationbased on time sweep rheological analysis elucidated that in sample with equivalent ratio of oxidized pectin and fibroin, the crystallization was highly delayed due to dominance of Schiff's base reaction. The Herschel–Bulkley model based on flow curve rheology test corroborated that aforesaid composition revealed the most noticeable shear thinning behavior and accordingly the strongest crosslinked network. Finally, rubber elastic theory based on dynamic mechanical analysis implied that said formulation possessed the highest crosslinking density due to higher availability of aldehyde to amine functionalities. Moreover, cell culture studies proved that P50 F50 sample prevailed over other compositions with respect to cell viability and function. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48859.

The Variation of Crystalline Structure Induced by Gas Dilution and Thermal Annealing in Silicon Layers Deposited by PECVD Technique

We prepared hydrogenated thick silicon film by plasma enhanced chemical vapor deposition (PECVD) method using SiH4 and H2 gas mixture and we investigated the effect of the hydrogen dilution ratio defined as $$ R=\frac{\left[{H}_2\right]}{\left[{SiH}_4\right]} $$ on the as-deposited and annealed films. With increase in hydrogen dilution ratio, amorphous to microcrystalline transition has been observed. The crystallization has been confirmed from Raman spectroscopy, UV reflectance, low angle X-ray diffraction (XRD), spectroscopic ellipsometry and atomic force microscopy (AFM) analysis. Tauc band gap shows a decreasing trend with increasing H2 dilution of silane. It decreases from 1.8 to 1.57 eV. It has been concluded that H2 dilution of silane in PECVD enhances the crystallinity of the film and affects its optical and structural properties.

Effect of annealing on the properties of polylactide/poly(butylene carbonate) blend

AbstractThe microstructure evolution of partial miscible polylactide/poly(butylene carbonate) (PLA/PBC) blend during annealing, including the variation in crystalline structure of PLA and PBC, the morphologies of PBC particles, and the relaxation of chain segments in the amorphous region of PLA, is investigated in detail. Based on the significant difference in melting temperature, phase separation arises as a result of the occurrence of crystallization of PLA and is further enhanced due to the crystallization of PBC. The glass transition temperature Tg of the PLA phase in the phase separation blend is significantly higher than that of the pure PLA due to increasing crystallinity. The increasing annealing time resulted in enhanced phase separation, as reflected in the harsher morphology, the decrease of molecular dynamics, and the reduction amount of the amorphous domain. It can be verified by the interaction parameter C values at various annealing conditions from the yield stress data. Therefore, blend is aptitude to elongation decrease and the toughening micromechanism changes, while the plastic deformation is the important energy dissipation process for quenched PLA/PBC blend. Debonding of the PBC particles followed by plastic void growth of the PLA matrix is the major toughening micro‐mechanisms for phase separation blend.

Extended-Charge-Transfer Excitons in Crystalline Supramolecular Photocatalytic Scaffolds.

Coupling among chromophores in molecular assemblies is responsible for phenomena such as resonant energy transfer and intermolecular charge transfer. These processes are central to the fields of organic photovoltaics and photocatalysis, where it is necessary to funnel energy or charge to specific regions within the system. As such, a fundamental understanding of these transport processes is essential for developing new materials for photovoltaic and photocatalytic applications. Recently, photocatalytic systems based on photosensitizing perylene monomimide (PMI) chromophore amphiphiles were found to show variation in hydrogen gas (H2) production as a function of nanostructure crystallinity. The 2D crystalline systems form in aqueous electrolyte solution, which provides a high dielectric environment where the Coulomb potential between charges is mitigated. This results in relatively weakly bound excitons that are ideal for reducing protons. In order to understand how variations in crystalline structure affect H2 generation, two representative PMI systems are investigated theoretically using a modified Holstein Hamiltonian. The Hamiltonian includes both molecular Frenkel excitations (FE) and charge-transfer excitations (CTE) coupled nonadiabatically to local intramolecular vibrations. Signatures of FE/CTE mixing and the extent of electron/hole separation are identified in the optical absorption spectrum and are found to correlate strongly to the observed H2 production rates. The absorption spectral signatures are found to sensitively depend on the relative phase between the electron and hole transfer integrals, as well as the diabatic energy difference between the Frenkel and CT exciton bands. Our analysis provides design rules for artificial photosynthetic systems based on organic chromophore arrays.

Effect of host structure on the photoluminescence properties of Ln3TaO7:Eu3+ red phosphors

Eu3+ doped Ln3TaO7 (Ln=La, Gd, Y, Lu) red phosphors were prepared using a solid state route. The Ln3+ substitution induces variation of crystalline structure from a defect fluorite to weberite types with increased ordering of the cations from Lu to La. These phosphors show strong absorptions at near UV wavelength and emit orange–red luminescence. The increased trend in luminescence lifetime further surmises uniform distribution of Eu3+ ions from Lu to La. The luminescence intensity and quantum efficiency are closely related to the degree of ordering of the cations in the lattice. The Eu3+ luminescence in La3TaO7 embodies the structural variation through intense multiband 5D0→7F0,1,2,4 transitions to only dominant hypersensitive electric dipole 5D0→7F2 transition. All the Eu3+ emission transitions (5D0→7F0,1,2,4) are more intense in La3TaO7 host due to increased polarizability and covalent nature of Eu3+ bonding environment with the surrounding.

Secondary Doping of Vapor Phase Polymerization Based on Conductive PEDOT Thin Film by Sulfuric Acid Treatment

This paper reports the effect of sulfuric acid treatment of vapor phase polymerization (VPP) based poly(3,4- ethylenedioxythiophene) (PEDOT) thin film in order to improve electrical property of the conductive film. The trans- parency of PEDOT film can be controlled by varying the thickness of the film with changing the content of iron(III)- p-toluenesulfonate (FTS) as an oxidant for VPP. Acid treated VPP based PEDOT thin film showed fairly good trans- parency (~80%) and electrical conductivity (>1000 S/cm). It is postulated that the conductivity enhancement of the PEDOT film caused by not variation of crystalline structure of PEDOT, but additional p-dopings by HSO4 - ion dissociated from sulfuric acid aqueous solution to PEDOT + chain from the analysis by X-ray diffractometer (XRD) and X-ray pho-

Mechanical properties and oxidation resistance of reactively sputtered Ta1 − xZrxNy thin films

ABSTRACT Ta1 − xZrxNy coatings were fabricated using reactive direct-current magnetron cosputtering on silicon and cemented carbide substrates. The oxidation resistance of the Ta1 − xZrxNy coatings was evaluated by annealing the samples in a 15-ppm O2–N2 atmosphere at 600 °C. The variations in crystalline structure, mechanical properties, and surface roughness values after annealing were investigated. One commercial moldable glass material, a SiO2–B2O3–BaO-based glass, was used to evaluate the chemical inertness of Ta1 − xZrxNy coatings, applied as protective coatings in glass molding processes. Thermal cycling annealing at 270 and 600 °C, with the temperature strictly maintained at 600 ± 10 °C for 1 min/cycle, was conducted in a quartz tube furnace to simulate a glass molding process in a continuous flow of 15 ppm O2–N2. Up to 500 thermal cycling annealing tests were conducted for the glass and coating assemblies.

Exchange-bias field induced by surface inhomogeneities in ferromagnetic/charge-ordered bilayer structure

Epitaxial bilayer structure consisting of ferromagnetic metallic Pr0.7Sr0.3MnO3 (PSMO) and charge-ordered insulator La0.5Ca0.5MnO3 (LCMO) was fabricated on (001) SrTiO3 substrate by pulsed laser deposition. High-resolution synchrotron X-ray diffraction showed high quality of epitaxial layer. However, besides diffraction peaks from PSMO layer, LCMO layer and SrTiO3 substrate, we observed an additional shoulder peak, which might stem from the inhomogeneities of composition in PSMO/LCMO. Further the atomic force microscopy measurement showed the presence of non-stoichiometric large particulates at surface, imparting an overall inhomogeneous composition to the film. This implied that the variation of crystalline structure of PSMO/LCMO occurred due to inhomogeneous composition. Moreover, studies on magnetic properties showed that surface inhomogeneities and ferromagnetic clusters at the PSMO/LCMO interface probably influenced the ferromagnetism of the bilayer film together, tuning exchange bias effect.

Oxidation behavior and mechanical properties of laminated Hf–Ta coatings

This study explores the internal oxidation of laminated Hf–Ta coatings with a cyclically gradient chemical concentration distribution along the growth direction. The oxidation behavior was examined by annealing the coatings at 400–600°C in a 15ppm O2–N2 atmosphere for 30min. The variations in crystalline structure, nanohardness, chemical states, and chemical composition profiles in depth after various annealing conditions were investigated. The results indicate that all the Hf–Ta coatings maintain a laminated structure after annealing at 400–600°C. Internal oxidation conducts during 500 and 600°C annealing, but part of the outmost layers exhibits complex oxides after annealing at 600°C. The nanohardness of annealed Hf–Ta coatings related to the formation of HfO2, Hf6Ta2O17, and amorphous Ta-oxide were studied.

Effect of surface inhomogeneities on crystalline structure and magnetic properties of epitaxial Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3 film on (001) SrTiO3

Epitaxil Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3 (PSMO/LCMO) bilayer structure was grown on (001)-oriented SrTiO3 (STO) substrate by pulsed laser deposition. High-resolution synchrotron X-ray diffraction showed high quality of epitaxial layer. However, besides diffraction peaks from PSMO layer, LCMO layer and STO substrate, we observed an additional shoulder peak, which might stem from the inhomogeneities of composition in the film. Grazing incidence X-ray reflectivity (GIXRR) was employed to investigate the surface and interfacial crystalline structure of PSMO/LCMO. The fitting results of GIXRR indicated negligible interdiffusion and roughness at interface. Further atomic force microscopy measurement showed the presence of non-stoichiometric large particulates at surface, imparting an overall inhomogeneous composition to the film. This implied that the variation of crystalline structure of PSMO/LCMO film occurred due to inhomogeneous composition. Moreover, studies on magnetic properties showed that surface inhomogeneities and ferromagnetic clusters at the PSMO/LCMO interface probably influenced the ferromagnetism of the bilayer film together, tuning exchange bias in the film.

Thermal stability of TaN, CrTaN, TaSiN, and CrTaSiN hard coatings in oxygen-containing atmospheres

The feasibility of applying Ta-containing nitride protective coatings on glass molding dies was examined by conducting thermal cycling annealing. TaN, CrTaN, TaSiN, and CrTaSiN coatings are prepared by reactive co-sputtering. The thermal cycling annealing was performed at 270°C and 600°C in a 15-ppm O2–N2 atmosphere, a realistic glass molding atmosphere for mass production. This study investigated variations in crystalline structure, surface oxide scale, mechanical properties, surface roughness, and residual coating stress after thermal cycling annealing up to 2000cycles. The results indicated that the near-amorphous Cr6Ta25Si11N58 coating exhibited a nanohardness of 19GPa, a Young's modulus of 230–240GPa, a surface roughness of 1nm, and a consistent residual stress during the 2000 thermal cycles of annealing. The Cr6Ta25Si11N58 coating is proposed as an appropriate coating for molding glass.

Monitoring of Recrystallisation of Microcrystalline Cellulose inside Pharmaceutical Tablets during Storage Using near Infrared Diffuse Reflectance Spectroscopy

Changes in the crystallinity of microcrystalline cellulose (MCC) inside pharmaceutical tablets during storage were monitored by near infrared (NIR) diffuse reflectance spectroscopy to investigate transient variation at the molecular level. The MCC used in the tablets was ground before tablet formulation to intentionally cause a decrease in crystallinity. The variation in crystalline structure of MCC was evaluated from the intensity of NIR spectra peaks ascribed to OH groups in the crystalline region. The MCC exhibited clear signs of recrystallisation during 63 days of storage. In addition, the recrystallisation became even more pronounced when the MCC was stored under high-humidity conditions. Results also showed that the inclusion of anhydrous silicic acid induces a clear delay in recrystallisation by restricting the penetration of water molecules into the tablets. The findings derived from NIR spectra were substantiated by differential thermal analysis. The results from this study suggest that crystallinity of MCC inside tablets can be controlled by other excipients during storage, which has useful applications for controlling pharmaceutical product performance during storage.

Internal oxidation and mechanical properties of Ru based alloy coatings

Ru based laminated coatings with various transition metal solutes were deposited on silicon wafers using a direct current magnetron cosputtering system. After annealing in a 1% O2–Ar atmosphere at 600 °C for 30 min, Ti–Ru, Zr–Ru, Mo–Ru, Hf–Ru, and W–Ru coatings were internally oxidized and maintained a laminated structure, consisting of alternating oxygen-rich and deficient layers stacked along the original growth direction. Conversely, V–Ru and Cr–Ru coatings exhibited external oxidation and failed to maintain the laminated structure after annealing, due to the fast outward diffusion of V and Cr. The variations in crystalline structure and nanohardness of Ru based coatings caused by oxidation after annealing were investigated.

The Surface and Interface Microstructure of Epitaxial Pr<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub>/La<sub>0.5</sub>Ca<sub>0.5</sub>MnO<sub>3</sub> Bilayer Structure

Epitaxial bilayer structure consisting of ferromagnetic (FM) metallic Pr0.7Sr0.3MnO3 (PSMO) and antiferromagnetic (AFM) insulator La0.5Ca0.5MnO3 (LCMO) was fabricated on (001)-oriented single crystal SrTiO3 (STO) substrate by pulsed laser deposition technique. We studied the surface structure and interdiffusion at interface between PSMO and LCMO by using atomic force microscope and grazing incident x-ray reflectivity (GIXRR). The perfect data fitting result of GIXRR indicated that interdiffusion at the interface of Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3 (PSMO/LCMO) could not be negligible; there was a large interdiffusion zone at the PSMO/LCMO interfaces with a thickness of about 7 nm. We found that the thickness of the top layer at air/PSMO interface was about 2.5 nm and the mass density of the top layer was about 76.53% of that of PSMO layer. The surface roughness was about 1.6 nm which was consistent with observation by atomic force microscopy. Normal X-ray diffraction (NXRD) was also employed to investigate the average structure. Except from PSMO and LCMO layer diffraction peaks, we observed another additional peak, which was developed from the large disordered layer resulting from interdiffusion at the interface of PSMO/LCMO. This implied that the variation of crystalline structure of PSMO/LCMO film occurred due to interdiffusion. Surface roughness and interdiffusion played an important role in magnetic properties of FM/AFM bilayer.

Thermal stability of Ir–Re coatings annealed in oxygen-containing atmospheres

Ir–Re coatings are widely applied as protective coatings on glass molding dies. Because the glass molding process in mass production is conducted in an oxygen-containing atmosphere at a high temperature, the protective coatings must endure cyclic annealing treatments. Oxidation and thermal stability of Ir–Re coatings has received scant attention. In this study, Ir–Re coatings were prepared using co-sputtering. Constant-temperature annealing treatments were conducted at 600°C under a 1% O2–Ar atmosphere, which is an oxidation-accelerating atmosphere. The thermal cyclic test was performed at 270 and 600°C under atmospheres of 1% O2–Ar and 15ppm O2–N2, respectively. The 15ppm O2–N2 atmosphere is glass molding atmosphere suitable for mass production. The variations in crystalline structure, nanohardness, surface roughness, and residual stress after various annealing treatments were investigated. The more elevated Ir content coating, namely, Ir0.77Re0.23, displays superior thermal stability compared with the lower Ir content coating, namely, Ir0.53Re0.47.

Enhancing chain segments mobility to improve the fracture toughness of polypropylene

As a part of a serial work about the annealing inducing improvement of fracture toughness of polypropylene (PP) articles, in this work, a highly efficient mobilizer was introduced into PP and the injection-molded samples were annealed at different temperatures. The mobility of chain segments of PP was investigated by measuring the glass transition temperature. Differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) were used to characterize the variation of crystalline structure of PP during the annealing process. The fracture behaviors including notched Izod impact fracture and universal tensile fracture were investigated to detect the mechanical properties in response to the variations of both chain segments mobility and crystalline structures. It was found that the mobilizer greatly improved the chain segments mobility. Further results showed that the mobilizer also induced apparent changes of the glass transition temperature and the degree of crystallinity of PP during the annealing process. Consequently, the annealed PP samples containing a few amount of mobilizer exhibited largely increased fracture toughness.