Different Levels Of Crystallinity Research Articles

Mechanisms of Shock Dissipation in Semicrystalline Polyethylene.

Semicrystalline polymers are lightweight, multiphase materials that exhibit attractive shock dissipation characteristics and have potential applications as protective armor for people and equipment. For shocks of 10 GPa or less, we analyzed various mechanisms for the storage and dissipation of shock wave energy in a realistic, united atom (UA) model of semicrystalline polyethylene. Systems characterized by different levels of crystallinity were simulated using equilibrium molecular dynamics with a Hugoniostat to ensure that the resulting states conform to the Rankine-Hugoniot conditions. To determine the role of structural rearrangements, order parameters and configuration time series were collected during the course of the shock simulations. We conclude that the major mechanisms responsible for the storage and dissipation of shock energy in semicrystalline polyethylene are those associated with plastic deformation and melting of the crystalline domain. For this UA model, plastic deformation occurs primarily through fine crystallographic slip and the formation of kink bands, whose long period decreases with increasing shock pressure.

Ni-Fe layered double hydroxides for oxygen evolution Reaction: Impact of Ni/Fe ratio and crystallinity

The Oxygen Evolution Reaction (OER), half-reaction of the water-splitting process for hydrogen production, suffers from sluggish kinetics. NiFe materials appeared as interesting catalytic materials for this reaction in alkaline electrolyzers and have been studied, particularly in the form of NiFe Layered Double Hydroxides (LDH). However, the impact of the specificity of the atomic arrangement in the LDH and of its composition on the catalytic efficiency of the material are still unknown. Herein, LDH are synthesized with Ni/Fe ratios from 2 to 4 and different levels of crystallinity to assess their electrocatalytic behavior in 0.1 M KOH. Statistical analysis of the electrochemical results allows to highlight that, while no effect from the atomic ratio is observed, an increase in the crystallinity of the LDH seem detrimental to the catalytic efficiency.

An Insight into the Correlation between Chemical Composition Changes of Aluminum-Iron-Polyphosphate Glasses and Thermal Properties.

The present study aimed to investigate the influence of the gradual substitution of Fe2O3 by Al2O3 on the thermal properties of polyphosphate glasses. The conducted considerations based on differential scanning calorimetry (DSC) and heating microscopy thermal analysis provided much essential information about the correlation between glass chemical composition and its characteristic parameters, such as transformation temperature, specific heat, crystallization temperature, crystallization enthalpy, the activation energy of crystal growth, melting temperature, and Angell glass thermal stability. The obtained estimation of viscosity changes as a function of temperature could be very helpful for researchers to correctly plan the vitrification process and thus radioactive waste immobilization. A precise analysis of DSC curves and X-ray diffraction patterns revealed the possibility of crystallization process design in order to create materials with different levels of crystallinity and phase composition. The drawn conclusions allow choosing the glass with the optimal concentration of Al2O3 and Fe2O3, which ensures the relatively low melting temperature, viscosity, and glass crystallization ability, with application potential in nuclear waste immobilization.

Modeling Injection Molding of High-Density Polyethylene with Crystallization in Open-Source Software.

This work investigates crystallization modeling by modifying an open-source computational fluid dynamics code OpenFOAM. The crystallization behavior of high-density polyethylene (HDPE) is implemented according to theoretical and experimental literature. A number of physical interdependencies are included. The cavity is modeled as deformable. The heat transfer coefficient in the thermal contact towards the mold depends on contact pressure. The thermal conductivity is pressure- and crystallinity-dependent. Specific heat depends on temperature and crystallinity. Latent heat is released according to the crystallization progress and temperature. Deviatoric elastic stress is evolved in the solidified material. The prediction of the cavity pressure evolution is used for the assessment of the solution quality because it is experimentally available and governs the residual stress development. Insight into the thermomechanical conditions is provided with through-thickness plots of pressure, temperature and cooling rate at different levels of crystallinity. The code and simulation setup are made openly available to further the research on the topic.

Multi‐Level Electro‐Thermal Switching of Optical Phase‐Change Materials Using Graphene

Reconfigurable photonic systems featuring minimal power consumption are crucial for integrated optical devices in real‐world technology. Current active devices available in foundries, however, use volatile methods to modulate light, requiring a constant supply of power and significant form factors. Essential aspects to overcome these issues are the development of nonvolatile optical reconfiguration techniques which are compatible with on‐chip integration with different photonic platforms and do not disrupt their optical performances. Herein, a solution is demonstrated using an optoelectronic framework for nonvolatile tunable photonics that uses undoped‐graphene microheaters to thermally and reversibly switch the optical phase‐change material Ge2Sb2Se4Te1 (GSST). An in situ Raman spectroscopy method is utilized to demonstrate, in real‐time, reversible switching between four different levels of crystallinity. Moreover, a 3D computational model is developed to precisely interpret the switching characteristics, and to quantify the impact of current saturation on power dissipation, thermal diffusion, and switching speed. This model is used to inform the design of nonvolatile active photonic devices; namely, broadband Si3N4 integrated photonic circuits with small form‐factor modulators and reconfigurable metasurfaces displaying 2π phase coverage through neural‐network‐designed GSST meta‐atoms. This framework will enable scalable, low‐loss nonvolatile applications across a diverse range of photonics platforms.

Nanoindentation study of time-dependent mechanical properties of ultra-high-molecular-weight polyethylene (UHMWPE) at different temperatures

Ultra-high-molecular-weight polyethylene (UHMWPE) possesses high potential to be utilized as a body armor material due to its outstanding mechanical properties. The UHMWPE materials exhibit property anisotropy in the longitudinal and the transverse directions. In this study, the time-dependent transverse mechanical properties of UHMWPE sheet and fiber samples were systematically studied at different temperatures using the nanoindentation method. The different levels of crystallinity of the sheet and fiber samples were expected to lead to the differences in mechanical properties. These differences were revealed by XRD and DSC studies.

Interface strength of glass fibers in polypropylene: Dependence on the cooling rate and the degree of crystallinity

AbstractThe article experimentally investigates the interface strength of glass fibers in polypropylene (PP) with two different levels of crystallinity. The different degrees of crystallinity, 46.6% and 52.5%, were achieved using fast (quenching, ~4500°C/min) and slow (~2°C/min) cooling, respectively, during production of the PP film. The degree of crystallinity was measured using the differential scanning calorimetry. The mechanical properties of the films were characterized with the dynamic mechanical analysis and with a tensile test on Deben micro‐tester. Interfacial shear strength (IFSS) of glass fiber/PP was determined using fiber fragmentation test. Interfacial normal strength (IFNS) was determined using inverse identification based on finite‐element modeling of transverse tensile loading of a single fiber (Deben micro‐tester with digital image correlation‐based observation of the debonding). The measurements have confirmed the expected trend in mechanical properties of the film: increase of the storage and Young's moduli (room temperature) with the increase of degree of crystallinity, accompanied by the decrease in the loss modulus and tan δ. Interfacial strength followed the trend of the PP stiffness: both the IFSS and IFNS values for the PP with high crystallinity (slow cooling) are three (IFSS) and four (IFNS) times higher than those for the low crystallinity (fast cooling) case.

Synthesis of birnessite-type manganese oxide from two different reducing agents via solvent-free method and the catalytic activity in degradation of POME

Birnessite-type manganese oxide is multifunction material that has been used in various application and the characteristic depends heavily upon its preparation method. In this study, birnessite-type manganese oxide was synthesized using the reaction between KMnO4 (oxidant) and two different reducing agents i.e., citric acid and oxalic acid via a solvent-free method. The characterization of the birnessite was carried out using X-Ray Diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX), and Surface Area Analyzer (SAA). Birnessite from this variation of reducing agents showed different levels of crystallinity, diverse morphology, crystal size, and surface area. The birnessite-type was then applied as a catalyst for the degradation of Palm Oil Mill Effluent (POME) with hydrogen peroxide (H2O2) as an oxidant to reduce the concentrations of Chemical Oxygen Demand (COD). The maximum reduction in COD concentration was obtained using the catalyst concentration of 400 and 800 mg/L for reducing agent of as-synthesized catalyst citric acid and oxalic acid. Birnessite-type manganese oxide shows potential as a catalyst in the degradation of POME with citric acid as reducing agents showed better degradation in reducing COD values.

Absorptive Dissolution Testing: An Improved Approach to Study the Impact of Residual Crystallinity on the Performance of Amorphous Formulations

Amorphous solid dispersions typically improve the oral bioavailability of poorly soluble drugs. However, residual crystallinity is always a concern, in terms of potential impact on the product stability and performance. Consequently, in vitro tools that allow biorelevant assessment of residual crystallinity are of interest. The goal of the present study was to use absorptive dissolution testing to evaluate the impact of different levels of crystallinity in an amorphous formulation on membrane mass transport kinetics and supersaturation-time profiles. Partial crystallinity was induced in commercially available tacrolimus formulations by exposure to moderate temperature and high relative humidity. A hollow fiber membrane was coupled to a dissolution vessel to create an absorptive dissolution testing apparatus, and concentration-time profiles were simultaneously monitored during dissolution (donor compartment) and after absorption across the membrane (receiver compartment). The coupled dissolution-absorption measurements indicated that residual crystallinity impacted the absorption profiles in a manner that depended on the volume of fluid used for the dissolution measurement. A high percentage of residual crystallinity hampered the drug release from the formulation. Higher supersaturation in nonsink dissolution conditions improved mass transfer rates; however, the presence of seed crystals led to rapid desupersaturation. Further systematic studies to delineate the interplay between the rate of absorption and desupersaturation revealed that for a given dissolution rate, the crystallization rate would supersede the absorption rate only at high supersaturations. Thus, seeds have a lower impact on absorption when the overall supersaturation generated is lower. This study underscores the importance of considering competing physical processes when evaluating amorphous formulations. A further consideration highlighted is that different fluid volumes may impact the absorption profile for supersaturating dosage forms. Absorptive dissolution testing appears to be a potentially valuable tool to mechanistically investigate amorphous solid dispersion formulation release and phase behavior under more biorelevant conditions.

Quantifying crystallinity in carbon nanotubes and its influence on mechanical behaviour

The different fabrication methods that have been developed for making carbon nanotubes will provide materials with different levels of crystallinity. As crystallinity is qualitatively known to have a profound influence on material properties, this raises the need for standardised quantitative analysis. Here we show how transmission electron microscopy can be used to provide quantitative information about effective crystallite sizes in individual nanotubes which we link to the mechanical behaviour of the tubes. The method relies on a thorough analysis of diffraction patterns and a careful extraction of instrumental and sample contributions to the peak shapes. We find that arc-discharge grown tubes have crystallite sizes that are comparable to the circumference of the outer tube walls, while commercial catalytically grown tubes have much smaller crystallites implying that each cylindrical nanotube wall can be thought of as a patchwork of small graphene-like grains. The clear differences in crystallite sizes are then compared to known differences in mechanical behaviour, such as a substantial disparity in stiffness and significantly different behaviours under bending stress.

Synthesis and Characterization of Alginate-Based Sol–Gel Synthesis of Lithium Nickel Phosphate with Surface Area Control

A sol–gel method in which alginate was used to help prepare carbon-coated LiNiPO4 nanocrystal aggregates with controllable surface area is reported. Nickel alginate prepared from NiCl2 and sodium alginate was blended with stoichiometric LiOH and H3PO4 to produce a single-source precursor gel. Calcining the gel in air at 400–800 °C produced LiNiPO4 nanocrystal aggregates with different levels of crystallinity, sizes, and surface areas. Powder X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and Brunauer–Emmett–Teller analyses collectively showed that 600 °C was the optimal calcination temperature that gave LiNiPO4 with an average crystallite size of 43 nm, a surface carbon coating of 2–4 nm, and a surface area of 27.47 m2/g. The method allows simultaneous achievement of four features, namely, surface carbon coating, high crystallinity, control of primary particle size, and high surface area. Simple modification of the method would allow the...

Observing broken inversion symmetry in solids using two-color high-order harmonic spectroscopy

We experimentally investigate the manifestations of broken inversion symmetry in solids in two-color interferometric measurements. Polarization-resolved, high-order harmonic spectra of ${\mathrm{SiO}}_{2}$ with different levels of crystallinity are obtained. In amorphous and polycrystalline ${\mathrm{SiO}}_{2}$, both even and odd harmonics of the two-color interferogram beat four times per fundamental period, which is similar to what was observed in atomic gases or nonoriented molecules. In contrast, when a crystalline ${\mathrm{SiO}}_{2}$ sample is utilized, the competition between the contributions of broken inversion symmetries of the medium and the incident electric field results in a distinctive feature: Both odd and even harmonics beat two times per fundamental period [as predicted in Phys. Rev. B 94, 115164 (2016)]. Our observations are explained by an intuitive model. Moreover, they are fully supported by numerical simulations based on semiclassical transport theory. Our experiments highlight the considerable potential of polarimetry in two-color interferometric measurements, which allow pure and unambiguous characterization of the complex polarization response and thus consequent studies of electron dynamics in solids.

Thermal Diffusivity of High-Density Polyethylene Samples of Different Crystallinity Evaluated by Indirect Transmission Photoacoustics

In this work, thermal diffusivity of crystalline high-density polyethylene samples of various thickness, and prepared using different procedures, was evaluated by transmission gas-microphone frequency photoacoustics. The samples’ composition analysis and their degree of crystallinity were determined from the wide-angle X-ray diffraction, which confirmed that high-density polyethylene samples, obtained by slow and fast cooling, were equivalent in composition but with different degrees of crystallinity. Structural analysis, performed by differential scanning calorimetry, demonstrated that all of the used samples had different levels of crystallinity, depending not only on the preparing procedure, but also on sample thickness. Therefore, in order to evaluate the samples’ thermal diffusivity, it was necessary to modify standard photoacoustic fitting procedures (based on the normalization of photoacoustic amplitude and phase characteristics on two thickness levels) for the interpretation of photoacoustic measurements. The calculated values of thermal diffusivity were in the range of the expected literature values. Besides that, the obtained results indicate the unexpected correlation between the values of thermal diffusivity and thermal conductivity with the degree of crystallinity of the investigated geometrically thin samples. The results indicate the necessity of additional investigation of energy transport in macromolecular systems, as well as the possible employment of the photoacoustic techniques in order to clarify its mechanism.

Effect of Level of Crystallinity on Melt Memory Above the Equilibrium Melting Temperature in a Random Ethylene 1-Butene Copolymer

A strong memory effect of crystallization has been observed in melts of random ethylene copolymers even above the equilibrium melting temperature. Melt memory is correlated with self-seeds that increase the crystallization rate of ethylene copolymers. The seeds are associated with molten ethylene sequences from the initial crystals that remain in close proximity and are unable to diffuse quickly to the randomized melt state. Fast diffusion is restricted by topological chain constraints (loops, knots, and other entanglements) that build in the intercrystalline region during crystallization. The effect of topological constraints on melt memory, or on number of remaining self-seeds in the melt, is analyzed studying the melting and subsequent crystallization of a model ethylene 1-butene copolymer with 2.2 mol% ethyl branches prepared with different levels of crystallinity. There is a critical threshold level of crystallinity of 6–12% to observe the effect of melt memory on the subsequent crystallization rate of this copolymer. A faster development of the initial crystallinity may more efficiently trap knots and loops around the crystallites, leading to a lower crystallinity threshold than for slow or isothermally crystallized copolymers.

Nanostructures formed on carbon-based materials with different levels of crystallinity using oxygen plasma treatment

Nanostructure formation was explored for various carbon-based materials, such as diamond, carbon fiber, polyethylene terephthalate and poly (methyl methacrylate), which have different levels of crystallinity, ranging from perfect crystal to polymeric amorphous. After treatment of oxygen plasma glow discharge, the nanostructures on these carbon-based materials were found to evolve via preferential etching due to the co-deposition of metal elements sputtered from the metal cathode plate. Local islands or clusters formed by the metal co-deposition have a low etching rate compared to pristine regions on each material, resulting in anisotropic patterns on the carbon-based materials. This pattern formation mechanism was confirmed by covering the cathode or preventing the co-deposition of metallic sources with a polymeric material. Regardless of the level of crystallinity of the carbon-based materials, no patterns were observed on the surfaces covered with the polymeric material, and the surfaces were uniformly etched. It was found that the materials with low crystallinity had a high etching rate due to low carbon atom density, which thus easily formed high-aspect-ratio nanostructures for the same plasma treatment duration.

Synthesis of ultrafine amorphous PtP nanoparticles and the effect of PtP crystallinity on methanol oxidation

Ultrafine amorphous PtP nanoparticles supported on carbon black were prepared. Comparison of electrocatalytic performance of the samples with different levels of crystallinity showed ultrafine amorphous PtP nanoparticles have high catalytic activity for methanol oxidation due to their small particle size and amorphous structure.

Irradiation‐induced grafting of poly(vinylidene fluoride)‐graft‐poly(styrene sulfonic acid) for the preparation of planar and tube‐shaped air‐drying membranes

AbstractA novel air‐drying membrane was developed and investigated as an alternative for planar and tube‐shaped drying membranes composed of Nafion®. The new membrane is based on poly(vinylidene fluoride) (PVDF) polymer types grafted with polystyrene sulfonic acid. Modification of the PVDF membrane by chemical grafting was initiated via γ‐irradiation of pre‐made film and tube‐shaped samples. The grafting was conducted while the pre‐irradiated PVDF samples were immersed in styrene monomer solution. Three unique characterization methods were introduced to evaluate the ion exchange and barrier functions of the membrane. This investigation focuses on optimizing the degree of grafting yield, and subsequently the control of the membrane's overall functional performances, through (1) monitoring the PVDF's degree of crystallinity and (2) monitoring the styrene monomer solution temperature, respectively. Different levels of crystallinity were achieved by melt blending the PVDF‐copolymer with PVDF‐homopolymer, in various mixing ratios. Another variable examined in this investigation was the introduction of an ionic complex on the sulfonic acid end groups, and its effect on the membrane functional performance was studied. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Debranched cassava starch crystallinity determination by Raman spectroscopy: Correlation of features in Raman spectra with X-ray diffraction and 13C CP/MAS NMR spectroscopy.

Because starch crystallinity influences the physical, mechanical, and technological aspects of numerous starch-based products during production and storage, rapid techniques for its assessment are vital. Samples of different levels of crystallinity were obtained by debranching gelatinized cassava starch, followed by subjection to various hydrothermal treatments. The recrystallized products were further subjected to partial hydrolysis with a mixture of α-amylase and glucoamylase prior to freeze-drying. Crystallinities were determined using X-ray diffraction (XRD) and 13C CP/MAS NMR spectroscopy, and correlated with FT-Raman spectra features. XRD crystallinities ranged between 0 and 58%, and agreed with crystalline-phase fractions (R2=0.99) derived from the respective 13C CP/MAS NMR spectra. A strong linear correlation was found between crystallinities and integrated areas of the skeletal mode Raman band at 480cm-1 (R2=0.99). With appropriate calibration, FT-Raman spectroscopy is a promising tool for rapid determination of starch crystallinity.

Synthesis and properties of A 6B 2(OH) 16Cl 2·4H 2O (A = Mg, Ni, Zn, Co, Mn and B = Al, Fe) materials for environmental applications

Double layered hydroxide materials of composition A 6B 2(OH) 16Cl 2·4H 2O (A = Mg, Ni, Zn, Co, Mn and B = Al, Fe) were synthesized by chemical precipitation at 60 °C. Different levels of crystallinity and ordering degree were observed depending upon the chemical environment or the combination between divalent and trivalent cations. The results from high-resolution transmission electron microscopy revealed that nanostructured layered samples were obtained with interplanar spacing compatible with previous literature. Raman scattering was employed to investigate the complex band structure observed, particularly the lattice vibrations at lower frequencies, which is intimately correlated to the cationic radius of both divalent and trivalent ions. The results showed that strongly coordinated water and chloride ions besides highly structured hydroxide layers have a direct influence on the stability of the hydrotalcites. It was observed that transition and decomposition temperatures varied largely for different chemical compositions.

Copolymers of pyromellitic tetranitrile and urea: Synthesis, structure, and magnetic properties

The methods of synthesis of metal-free and copper-, iron-, and manganese-containing copolymers of pyromellitic tetranitrile with urea and thiourea are developed. The structural, physical, and physicochemical properties of the copolymers are studied. The copolymers have different levels of crystallinity, demonstrate stability during heating in air to 300–400°C, and exhibit paramagnetic properties. Some copolymers feature weak ferromagnetism at room temperature.