Role Of Crystallinity Research Articles

A simple sol–gel method for the synthesis of Pt co-catalyzed spinel-type CuFe2O4 for hydrogen production; the role of crystallinity and band gap energy

In this investigation, spinel-type copper ferrites (CuFe2O4) at different calcination temperatures (600–900 °C) were produced using a facile citric acid-assisted sol–gel method. The crystal structure, morphology, optical, and electrical properties of the as synthesized photocatalysts were comprehensively characterized. XRD and UV–vis diffuse reflectance spectra (UV–vis (DRS)) showed that the phase structure and the band gap energy of the copper ferrite are strongly correlated to the applied calcination temperature. TEM results investigated that the copper ferrites calcined at higher temperatures presented large particle sizes and crystallized very well. In addition, the photocatalytic activity was tested for hydrogen production in the presence of methanol, with and without Pt nanoparticles as a cocatalyst. The results indicated that the CuFe2O4 annealed at 900 °C (CuF-900) has higher hydrogen production activity than photocatalysts calcined at lower temperatures in the presence and absence of Pt, which is mainly assigned to the higher crystallinity, and narrower bandgap energy. Moreover, this study explained in more detail the role of Pt nanoparticles in enhancing the photocatalytic activity of CuF-900. This work introduces a new direction of thinking for the tetragonal phase structure as an efficient photocatalyst for hydrogen production.

Early stages of X-ray induced molecular unit modifications in poly(lactic acid)

Exposure of polymers to ionizing radiation and high-energy particle beams is involved in many processes – from food sterilization to radiotherapy protocols. The resulting effects, at the final stages, determine the functional, structural, and morphological alteration of the material. However, the processes responsible for cumulative chain scission, crosslinking, and reactions with the environment are often difficult to disentangle as a sequence of elementary events. Here we report a spectroscopic study – by attenuated-total reflection Fourier transform infrared spectroscopy and powder x-ray diffraction measurements, together with differential scanning calorimetry and thermogravimetric analyses – that sheds light on the very initial stages of the mechanisms involved in radiation-induced modifications of poly(lactic acid) (PLA). The results, collected on samples from biobased processes and exposed to low x-ray doses in the range of 100–103Gy after different thermal treatments, show spectroscopic evidence of the emergence of molecular unit perturbations – mainly related to methyl and carbonyl groups with the formation of C=C double bonds – with a clear-cut dependence on the polymer conformation. Understanding the mechanisms involved and the role of crystallinity provides information potentially useful for the development of PLA with a suitable radiation hardness for applications in radiotherapy.

NiFe Alloy Integrated with Amorphous/Crystalline NiFe Oxide as an Electrocatalyst for Alkaline Hydrogen and Oxygen Evolution Reactions.

The rational design of efficient and low-cost electrocatalysts based on earth-abundant materials is imperative for large-scale production of hydrogen by water electrolysis. Here we present a strategy to prepare highly active catalyst materials through modifying the crystallinity of the surface/interface of strongly coupled transition metal-metal oxides. We have thermally activated the catalysts to construct amorphous/crystalline Ni-Fe oxide interfaced with a conductive Ni-Fe alloy and systematically investigated their electrocatalytic performance toward the hydrogen evolution and oxygen evolution reactions (HER and OER) in alkaline solution. It was found that the Ni-Fe/oxide material with a crystalline surface oxide phase showed remarkably superior HER activity in comparison with its amorphous or poorly crystalline counterpart. In contrast, interestingly, the amorphous/poorly crystalline oxide significantly facilitated the OER activity in comparison with the more crystalline counterpart. On one hand, the higher HER activity can be ascribed to a favorable platform for water dissociation and H-H bond formation, enabled by the unique crystalline metal/oxide structure. On the other hand, the enhanced OER catalysis on the amorphous Ni-Fe oxide surfaces can be attributed to the facile activation to form the active oxyhydroxides under OER conditions. Both are explained based on density functional theory calculations. These results thus shed light onto the role of crystallinity in the HER and OER catalysis on heterostructured Ni-Fe/oxide catalysts and provide guidance for the design of new catalysts for efficient water electrolysis.

Material Science for catalysis: Quo vadis?

Material Science for catalysis: Quo vadis?

Role of crystallinity on the thermal and viscous behaviour of polyethylene glycol-in-silicone oil (o/o) phase change emulsions

Stable polyethylene glycol-in-silicone oil phase change emulsions were successfully prepared with a selected silicone surfactant. These oil-in-oil (o/o) emulsions have been scarcely examined up, despite the highly remarkable properties of both phases for energy recovery applications and cosmetic/pharmaceutical compositions. The objective of the present work was to study the effect of composition (surfactant and disperse phase concentrations) and the post-processing conditions (further agitation at the processing temperature for 24 h) on the final features of the emulsion. For this purpose, optical morphology, thermo-physical and the rheological behaviour of the emulsions and binary blends of their compounds were measured and analysed. Special attention has been paid to structural changes and crystallinity modifications of the emulsion disperse phase. The observed miscibility of the silicone surfactant and silicone chains with the disperse phase reduces its crystallinity degree and modifies in the crystallization mechanism of the polyethylene glycol, from heterogeneous to homogeneous nucleation. Interestingly, the change in the disperse phase crystallinity remarkably modifies final thermal and rheological properties of the emulsion.

The role of crystallinity and particle morphology on the sorption of dibutyl phthalate on polyethylene microplastics: Implications for the behavior of phthalate plastic additives

The sorption behavior of phthalate additives in plastic and microplastic litter is an important process controlling the exposure, net health risk and ecotoxicity of these co-occurring pollutants. Plastic crystallinity and particle morphology are hypothesized to be important variables for microplastics sorption behavior, but to date there have been few direct studies to explicitly test for the influence of these parameters. To address this, in this study we explored the sorption of dibutyl phthalate (DBP) as a probe molecule to diverse polyethylene microplastics including irregularly-shaped pure polyethylene microplastics (IPPM), black plastic film microplastics (BPFM), white plastic film microplastics (WPFM), and commercial microspheres (CM), which had crystallinities ranging from 17 to 99%. Sorption kinetics for all materials could be well represented with both a pseudo-first-order (R2 = 0.87–0.93) and pseudo-second-order model (R2 = 0.87–0.93). Further, sorption was highly linear in the concentration range of 0.5–10 mg L−1, with no greater performance from a linear sorption model (R2 = 0.96–0.99) than the non-linear Freundlich or Temkin sorption models. The partition coefficient (Kd) of DBP sorption onto IPPM, BPFM, WPFM and CMs were 1974.55 L kg−1, 1483.85 L kg−1, 1477.45 L kg−1 and 509.37 L kg−1, respectively, showing a significant decrease with increasing crystallinity (r2 = 0.98). The particle size of microplastics (27–1000 μm) is, however, an indecisive factor affecting their sorption behavior for DBP in this study. This study provides new insight that crystallinity plays a governing role on the sorption of phthalate from microplastic. This should be considered in future exposure studies and assessments of phthalates from plastics and microplastics.

High Thermal Conductivity in Anisotropic Aligned Polymeric Materials

Because of their low density, high electrical resistivity, and ease of processing, thermally conductive, anisotropic polymers are appealing for thermal management in applications related to personal comfort, sports, electronics, and optics. In this review, we discuss thermal transport in the different classes of anisotropic polymer fibers and films. The role of crystallinity, chain orientation, draw ratio, temperature, and chain length/molecular weight of these materials on the thermal transport will be discussed. A special emphasis is devoted to structure–property relationships and the influence of phonon scattering. Finally, some key challenges and future prospects of the anisotropic thermally conductive polymers and their use in devices are discussed.

Swelling of individual cellulose nanofibrils in water, role of crystallinity: an AFM study

Atomic force microscopy (AFM) can be used to quantitatively study nanomaterials in different media, e.g. vacuum, air, or submerged in a liquid. A technique was developed to study swelling of individual cellulose nanofibrils (CNFs) using AFM. As a case study, CNFs with different degrees of crystallinity (DoC) were examined for swellability going from dry to wet (submerged in de-ionized water). Swelling was found to depend on DoC, but no significant correlation between fibril diameter and swellability was seen. Upon introduction of de-ionized water high DoC samples (65pm 2%) were found to have a diameter increase of 34% on average, whereas low DoC (44pm 2%) were found to have a diameter increase of 44% on average. A tested control, consisting of platinum nanowires on silisium, did not swell.Graphic abstract

Retinal pigment epithelium and age-related macular degeneration: A review of major disease mechanisms.

Age‐related macular degeneration (AMD) is a progressive degenerative disease that is the leading cause of vision loss in the elderly population. Degeneration/dysregulation of the retinal pigment epithelium (RPE), a supportive monolayer of cells underlying the photoreceptors, is commonly seen in patients with AMD. While treatment exists for the neovascular/wet form of AMD, there is currently no cure for the non‐exudative/dry form of AMD, making it imperative to understand the pathogenesis of this disease. Although our understanding of the aetiology of AMD has increased over the years, the underlying disease mechanism has not yet been identified, mainly due to the multifactorial nature of this disease. Herein, we review some of the commonly proposed degeneration pathways of RPE cells and their role in the pathogenesis of AMD; including activation of the complement cascade, oxidative stress‐induced cell death mechanisms, dysfunctional mitochondria and the role of crystallins in AMD disease progression.

Tailoring morphology and structure of manganese oxide nanomaterials to enhance oxygen reduction in microbial fuel cells

In this study, 1D structures based on α-MnO2 nanowires and β-MnO2 nanorods were fabricated by a single-step hydrothermal synthesis and evaluated as cathode components for microbial fuel cells (MFCs). The role of crystallinity and morphology on electrocatalytic activity was investigated by combining X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy with an electrochemical analysis of oxygen reduction reaction at the surface of MnO2-based structures. Among the synthesized composites, β-MnO2 nanorods showed higher ORR activity thanks to the synergy between the rod-like morphology and the nitrogen presence in/on the carbon support which provides a more accessible surface for oxygen adsorption and consequent reduction. MFCs assembled with β-MnO2 nanorod cathode allowed achieving a maximum power density of 524 ± 3 mW m−2 and superior cycling stability as compared to α-MnO2 nanowires and control Pt/C.

All carbon based high energy lithium-ion capacitors from biomass: The role of crystallinity

We report all carbon-based high energy Li-ion capacitor from environmentally threatening bio-source, prosopis juliflora. The pyrolyzed carbon exhibits a few layers of graphene-like structure and tubular morphology with multiple inherent heteroatoms like N, S, and Ca. Presence of such heteroatoms are certainly beneficial to the betterment of electrical conductivity, and pore generation which eventually results in an enhancement in capacity/capacitance of carbonaceous materials. The electrochemical pre-lithiation strategy is used to mitigate the irreversibility observed, and eventually employed as a negative electrode in a hybrid configuration. This LIC delivered a high energy density of ∼216 and 185 Wh kg−1 at ambient (25 °C) and elevated temperature (55 °C) conditions, respectively. Further, ∼94% initial capacity is retained after 5000 cycles with minimum fading of 0.0013% per cycle at ambient temperature. This results clearly demonstrate that the surface functionality and heteroatom doping with tubular structure synergistically facilitates the Li+ and electron transport properties to realize higher energy density for this fascinating all carbon-based Li-ion capacitor.

Designing Conjugated Polymers for Molecular Doping: The Roles of Crystallinity, Swelling, and Conductivity in Sequentially-Doped Selenophene-Based Copolymers

Although chemical doping is widely used to tune the optical and electrical properties of semiconducting polymers, it is not clear how the degree of doping and the electrical properties of the doped...

Crystallinity mediated variation in optical and electrical properties of hydrothermally synthesized boehmite (γ-AlOOH) nanoparticles

In this article, nanostructures of boehmite (γ-AlOOH) have been successfully synthesized in a time varied, facile and cost effective hydrothermal route. The samples have been characterized by using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and Fourier Transform Infrared (FTIR) spectroscopy. Our samples exhibit remarkably high photoluminescence emission intensity and dielectric constant (3.71 × 106 for BH12 sample) with a nominal dielectric tangent loss. A detailed growth mechanism including the nucleation and self assembly of our nanomaterial has been discussed. Moreover, we are the first to report here the electrical properties of the boehmite nanoparticles. Present investigation also explores temperature dependent dielectric property and ac conductivity of these samples. The role of crystallinity in the optical and electrical enhancement of our samples has been illustrated with proper analytical details. Not only high emission intensity in the blue and green region of the spectrum makes our sample a strong candidate for bio-imaging and bio-sensing applications, but also high dielectric constant makes them desirable for cost-effective energy storing devices, such as supercapacitors and solar cells.

Defect induced modification of structural, topographical and magnetic properties of zinc ferrite thin films by swift heavy ion irradiation

Swift heavy ion irradiation provides unique ways to modify physical and chemical properties of materials. In ferrites, the magnetic properties can change significantly as a result of swift heavy ion irradiation. Zinc ferrite is an antiferromagnet with a Neel temperature of 10K and exhibits anomalous magnetic properties in the nano regime. Ion irradiation can cause amorphisation of zinc ferrite thin films; thus the role of crystallinity on magnetic properties can be examined. The influence of surface topography in these thin films can also be studied. Zinc ferrite thin films, of thickness 320nm, prepared by RF sputtering were irradiated with 100MeV Ag ions. Structural characterization showed amorphisation and subsequent reduction in particle size. The change in magnetic properties due to irradiation was correlated with structural and topographical effects of ion irradiation. A rough estimation of ion track radius is done from the magnetic studies.

Role of Crystallinity on Moisture Absorption and Mechanical Performance of Recycled PET Compounds

Recycle poly(ethylene terphthalate) (RPET) was compounded with talc, glass bead and PEG in twin screw extruder with different cooling systems of hot air cooling and water cooling processes. The air cooling system allowed slow cooling and higher crystallized of RPET in the compounds, which resulting in higher crystllinity in the compounds as compared to the water cooling. Moisture content of the compounds decreased when increasing crystallinity. It is interesting to note that tensile properties of the RPET compunds would enhance when incorporated with talc filler and when lower moisture content values in the RPET compounds.

Role of crystallinity on the nanomechanical and electrochemical properties of TiO2 nanotubes

In order to study the effect of annealing on the nanomechanical and electrochemical properties, TiO2 nanotubes synthesized via anodic oxidation were subjected to thermal treatment at various temperatures. Structural studies revealed that as-anodized nanotubes are amorphous, but they become crystalline when subjected to thermal treatment in air. TiO2 nanotubes annealed up to 450°C crystallizes in pure anatase phase, whereas a mixture of anatase and rutile phase was observed for sample annealed at 600°C. Interestingly, the evolution of rutile phase at 600°C leads to decrease in crystallite size of the anatase phase. Nanoindentation studies showed that crystallite size plays a strong role in hardness, whereas porosity has significant influence on the elastic modulus of the nanotubes. Presence of two time constants in electrochemical impedance spectroscopy measurement presumably implies the formation of bilayer passive film. Mott Schottky analysis showed n-type semiconducting behavior with decrease in donor concentration (1019cm−3) upon increasing the annealing temperature. However, the evolution of rutile phase decreases the donor concentration drastically by an order of a magnitude (1018cm−3). Potentiodynamic polarization studies revealed that rutile phase favors enhanced passivation behavior exhibiting lower passive current density (10−7Acm−2) compared to the pure anatase nanotubes (10−6Acm−2). The enhanced passivation behavior of rutile phase was confirmed by Raman spectroscopy.

The role of crystallinity in SWCNT–polyetherimide nanocomposites

Two all-aromatic, high-performance poly(etherimide)s ODPA-P3 (I) and BPDA-P3 (II) are studied as a function of SWCNT loading. Polyetherimide I is amorphous but SWCNTs nucleate crystallization during imidization to produce a nanocomposite (nc-I) with SWCNTs embedded in the crystals. This crystalline interphase, with a radial thickness of ∼8 nm, results in a substantial reinforcement efficacy. Melting the interphase and cooling nc-I yields an amorphous nanocomposite with an interphase thickness (3.6 nm) that is smaller and has a lower reinforcement efficacy. Polyetherimide II was used as a reference since SWCNTs reside in the amorphous fraction of its nanocomposite. Consequently, the reinforcement efficiency of the semi-crystalline nc-II and its amorphous analog (prepared by heating above the crystal melting point and cooling) remains unchanged. A crystalline interphase surrounding SWCNT-reinforced poly(etherimide)s appears to be critical in obtaining high reinforcement efficacies. Most high-performance polyimides and poly(etherimide)s are prepared using a thermal imidization step. Our work emphasizes that care has to be taken in selecting the final imidization temperature to avoid melting the crystalline interphase if one is targeting high modulus materials.

The role of crystallinity and viscosity in the formation of submarine lava flow morphology

Submarine lava flow morphology is commonly used to estimate relative flow velocity, but the effects of crystallinity and viscosity are rarely considered. We use digital petrography and quantitative textural analysis techniques to determine the crystallinity of submarine basaltic lava flows, using a set of samples from previously mapped lava flow fields at the hotspot-affected Galapagos Spreading Center. Crystallinity measurements were incorporated into predictive models of suspension rheology to characterize lava flow consistency and rheology. Petrologic data were integrated to estimate bulk lava viscosity. We compared the crystallinity and viscosity of each sample with its flow morphology to determine their respective roles in submarine lava emplacement dynamics. We find no correlation between crystallinity, bulk viscosity, and lava morphology, implying that flow advance rate is the primary control on submarine lava morphology. However, we show systematic variations in crystal size and shape distribution among pillows, lobates, and sheets, suggesting that these parameters are important indicators of eruption processes. Finally, we compared the characteristics of lavas from two different sampling sites with contrasting long-term magma supply rates. Differences between lavas from each study site illustrate the significant effect of magma supply on the physical properties of the oceanic upper crust.

Surface energy engineering for tunable wettability through controlled synthesis of MoS2.

MoS2 is an important member of the transition metal dichalcogenides that is emerging as a potential 2D atomically thin layered material for low power electronic and optoelectronic applications. However, for MoS2 a critical fundamental question of significant importance is how the surface energy and hence the wettability is altered at the nanoscale in particular, the role of crystallinity and orientation. This work reports on the synthesis of large area MoS2 thin films on insulating substrates (SiO2/Si and Al2O3) with different surface morphology via vapor phase deposition by varying the growth temperatures. The samples were examined using transmission electron microscopy and Raman spectroscopy. From contact angle measurements, it is possible to correlate the wettability with crystallinity at the nanoscale. The specific surface energy for few layers MoS2 is estimated to be about 46.5 mJ/m(2). Moreover a layer thickness-dependent wettability study suggests that the lower the thickness is, the higher the contact angle will be. Our results shed light on the MoS2-water interaction that is important for the development of devices based on MoS2 coated surfaces for microfluidic applications.

Role of crystallins in ocular neuroprotection and axonal regeneration.

Neuroprotection is an emerging challenge in ophthalmology due to the particularly exposed location of retinal neurons and to the steadily increasing rate of intraocular surgical and pharmacological treatments applied to various eye diseases. Within few decades neuroprotection has developed from strongly contested approaches to being recognized and introduced as a potentially clinical application. One of the groups of putative substances for neuroprotection comprises αA- and αB-crystallins, which are types of heat-shock proteins and are considered to be molecular chaperones. The β/γ-crystallins form their own superfamily and are characterized as proteins with a distinct structure containing four Greek key motifs. Besides being abundant in the ocular lens, crystallins are also expressed in both the developing and mature retina. Crystallins are dramatically up-regulated in numerous retinal pathologies, including mechanical injury, ischemic insults, age-related macular degeneration, uveoretinitis, and diabetic retinopathy. Crystallins of the α family are thought to play a crucial role in retinal neuron survival and inflammation. Crystallins of the β/γ superfamily are also small proteins with a possible emerging role in retinal tissue remodeling and repair. One of the typical retinal diseases associated with crystallins is the experimental glaucomatous neuropathy that is characterized by their expression. Another typical retinal disease is the atrophy that occurs after mechanical injury to the optic nerve, which is associated with the need to regrow retinal axons. We have shown in regenerative models invivo and invitro that βB2-crystallin actively supports the regenerative growth of cut retinal axons, thereby offering targets for neuroprotective and regenerative treatments. In this review we discuss the discovery that βB2-crystallin is clearly up-regulated in the regenerating retina invitro. βB2-Crystallin is produced and secreted during axon elongation, while β/γ-crystallins promote axon growth both invivo and invitro by acting either directly by uptake into cells, or indirectly by enhancing the production of ciliary neurotrophic factor from astrocytes to synergistically promote axon regrowth. We also discuss methods to induce the continuous production of crystallins at the site of injury and repair based on the use of transfected neural progenitor cells. This review ultimately leads to the conclusion that the postinjury fate of neurons cannot be seen merely as inevitable, but instead should be regarded as a challenge to shaping the neuroprotective and regenerative conditions that promote cell survival and axon repair.