Search

Spherulites are radial distributions of acicular crystals, common in biogenic, geologic, and synthetic systems, yet exactly how spherulitic crystals nucleate and grow is still poorly understood. To investigate these processes in more detail, we chose scleractinian corals as a model system, because they are well known to form their skeletons from aragonite (CaCO 3) spherulites, and because a comparative study of crystal structures across coral species has not been performed previously. We observed that all 12 diverse coral species analyzed here exhibit plumose spherulites in their skeletons, with well-defined centers of calcification (CoCs), and crystalline fibers radiating from them. In 7 of the 12 species, we observed a skeletal structural motif not observed previously: randomly oriented, equant crystals, which we termed "sprinkles". In Acropora pharaonis , these sprinkles are localized at the CoCs, while in 6 other species, sprinkles are either layered at the growth front (GF) of the spherulites, or randomly distributed. At the nano- and micro-scale, coral skeletons fill space as much as single crystals of aragonite. Based on these observations, we tentatively propose a spherulite formation mechanism in which growth front nucleation (GFN) of randomly oriented sprinkles, competition for space, and coarsening produce spherulites, rather than the previously assumed slightly misoriented nucleations termed "non-crystallographic branching". Phase-field simulations support this mechanism, and, using a minimal set of thermodynamic parameters, are able to reproduce all of the microstructural variation observed experimentally in all of the investigated coral skeletons. Beyond coral skeletons, other spherulitic systems, from aspirin to semicrystalline polymers and chocolate, may also form according to the mechanism for spherulite formation proposed here. Understanding the fundamental mechanisms of spherulite nucleation and growth has broad ranging applications in the fields of metallurgy, polymers, food science, and pharmaceutical production. Using the skeletons of reef-building corals as a model system for investigating these processes, we propose a new spherulite growth mechanism that can not only explain the micro-structural diversity observed in distantly related coral species, but may point to a universal growth mechanism in a wide range of biologically and technologically relevant spherulitic materials systems. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Semicrystalline yellow TiO 2 nanoparticles are new synthesized. • Lattice O O bonds is firstly in-situ created within semicrystalline TiO 2. • Lattice O O bonds significantly enhance photocatalytic activity for H 2 production. • Reaction mechanism is proposed that describes the role of lattice O O bonds. Atomic defects (e.g., Ti3+, oxygen vacancies) have been intenstively investigated for modifying TiO 2 in order to reach visible light active photocatalytic H 2 production. However, the atomic defects within TiO 2 could easily act as photo-generated charge-carrier recombination centers, resulting in relatively low H 2 conversion efficiency. In this paper, semicrystalline yellow TiO 2 nanoparticles rich of superoxide ions are new synthesized by a simple aqueous solution method. Instead of introducing atomic defects, we show for the first time that catalytic performance can also be significantly improved via in-situ creating lattice O O bonds within metastable semicrystalline TiO 2. The synthesized semicrystalline yellow TiO 2 exhibits significantly enhanced photocatalytic activity for H 2 production after cycle tests. The formaldehyde in aqueous solution is used as target pollutant to simulate industrial wastewater. In-situ created elastic lattice O O bonds are proposed to improve catalytic performance through facilitating the breakage of C H bonds of HCHO. A series of internally consistent reaction equations is proposed that describes the role of in-situ created lattice O O bonds for improving the catalytic performance. This is strongly supported by that the H 2 production rate at the end of the fourth cycle test is significantly more than that of the beginning of the first cycle test. [ABSTRACT FROM AUTHOR]

Abstarct Small strain deformations below yielding can cause plastic deformation in semicrystalline polymers by a process similar to what is described for filled rubber-like materials known as the Mullins effect. Inter-lamellae chains contribute predominantly in deformations at this level, and the residual plastic strain can be attributed to permanent damage to the tie chains, affecting the long-term mechanical resistance of a molded part. With little detectable alteration of the polymer crystallinity at this early onset of plastic deformation, the primary characterization method applied to date is cyclic tensile loading, which provides information of stress-softening by monitoring the unloading path or relaxed stress behavior. An alternative method for monitoring the development of Mullins effect is proposed that can examine a molded part by using selected modes based on ultrasonic guided waves analysis. The technique was examined to determine if it could follow this effect induced by cyclic strain-controlled tensile deformations since it does not require sample preparation and could ultimately be applied while a part was in-service. Results for different polyethylene grades agree in trend with relaxed stress values over four cycles for tests of increasing applied tensile strain, demonstrated by an increase in the attenuation of ultrasonic guided waves. The correlation reveals a good promise in applying this method to structural health monitoring of plastic parts, while in use, to follow the initiation and progress of early service damage. [ABSTRACT FROM AUTHOR]

This study aims to bio-modulate Poly (vinyl alcohol) crosslinked by silver and gold nanoparticles fabricated by one-step laser ablation. The optical, cell viability, and antibacterial characterization of the fabricated films have been studied via different techniques. FTIR and XRD were used to investigate the molecular structures of the polymer matrix of Polyvinyl Alcohol incorporating gold and silver (Ag-Au NPs) created by laser ablation. XRD data illustrate the semicrystalline structure of PVA, with two hump peaks at 2θ = 8.52° and 2θ = 20.17° that are decreased when loaded with Ag-Au nanoparticles at different laser ablation times. The FT-IR spectra demonstrated a variation in the intensity of different peaks compared to the spectrum of the Polyvinyl Alcohol. This suggests that PVA and Ag-Au nanoparticles interacted and complexed in semicrystalline areas. The optical energy gap (Eg) reduces from 5.55 eV to 5.00 eV during direct transition and from 4.79 eV to 3.10 eV during indirect transition. The cell viability value for sample S2 was 91.7 ± 5.8%, indicating that both nanocomposites are biocompatible. S2 represents the high values of the inhibition zone, which make it preferred in antibacterial applications. The results demonstrate that Polyvinyl Alcohol/metal composite materials have excellent cell viability and antibacterial properties, implying that they may be suggested in antibacterial utilizations. [ABSTRACT FROM AUTHOR]

This study investigates the penetrant transport properties of water, oxygen, and carbon dioxide at 35 °C in poly(ethylene 2,5-furanoate) (PEF) isothermally crystallized at 115 and 160 °C. Dual-mode analysis of the water sorption isotherms for the semicrystalline vs. amorphous PEF samples indicates that the Henry’s law sorption parameter ( k D ) is reduced for the semicrystalline samples in direct proportion to the volume fraction crystallinity measured via both density and thermal methods. While the k D for water obeys the simple two-phase model of crystallinity, an unexpected large reduction in the Langmuir capacity constant ( C H ′) for the semicrystalline vs. amorphous samples resulted in an overall reduction in water sorption capacity greater than predicted by the two-phase model. Corroboration of this behavior for water is provided by independent oxygen and carbon dioxide permeation and sorption measurements, which also exhibit larger than expected reductions in solubility for the semicrystalline vs. amorphous samples. This study, which complements prior work, provides an initial look into the effect of crystallinity and morphology on the penetrant transport properties of PEF. [ABSTRACT FROM AUTHOR]

Abstract: Electronic properties of organic semiconductors are often critically dependent upon their ability to order from the molecular level to the macro-scale, as is true for many other materials attributes of macromolecular matter such as mechanical characteristics. Therefore, understanding of the molecular assembly process and the resulting solid-state short- and long-range order is critical to further advance the field of organic electronics. Here, we will discuss the structure development as a function of molecular weight in thin films of a model conjugated polymer, poly(3-hexylthiophene) (P3HT), when processed from solution and the melt. While focus is on the microstructural manipulation and characterization, we also treat the influence of molecular arrangement and order on electronic processes such as charge transport and show, based on classical polymer science arguments, how accounting for the structural complexity of polymers can provide a basis for establishing relevant processing/structure/property-interrelationships to explain some of their electronic features. Such relationships can assist with the design of new materials and definition of processing protocols that account for the molecular length, chain rigidity and propensity to order of a given system. [Copyright &y& Elsevier]

Abstract: Nylon 13,6 was successfully synthesized and its chemical composition, thermal properties, crystal structure, and moisture absorption characterized. Melting temperature and glass transition temperature were determined to be 206 °C and 60 °C, respectively, while the equilibrium melting temperature was determined to be 248 °C. Characterization of the crystallization kinetics showed that nylon 13,6 exhibits very fast crystallization compared to the industrially important nylons, nylon 6 and nylon 6,6. In addition, the moisture absorption of nylon 13,6 was dramatically lower than nylon 6 and nylon 6,6 which is consistent with the much lower amide content of nylon 13,6. The crystal structure was determined to be different from the expected γ-form, which possess a pseudohexagonal unit cell. Instead, the x-ray scattering pattern was more similar to the α-form. A similar result has been obtained for other odd–even nylons including nylon 5,6, nylon 5,10, nylon 9,2, nylon 11,10, and nylon 11,12. [Copyright &y& Elsevier]

Abstract: We report the visualization of the electrodeposition of chitosan hydrogels and structural characterization of such materials. An electrode embedded microfluidic device is used to visualize the gel deposition process as a distinguishable sol–gel interface separating the clear electrolyte solution region and the orderly textured gel region. The crystalline structure and the nanostructure of the as-deposited gel is characterized with synchrotron X-ray scattering measurements, confirming the semicrystalline nature of the deposited chitosan gels by a neutralization process at the cathode. [Copyright &y& Elsevier]

Abstract: Tin dioxide is emerging as an important material for use in copper indium gallium diselenide based solar cells. Amorphous tin dioxide may be used as a glass overlayer for covering the entire device and protecting it against water permeation. Tin dioxide is also a viable semiconductor candidate to replace the wide band gap zinc oxide window layer to improve the long-term device reliability. The film properties required by these two applications are different. Amorphous films have superior water permeation resistance while polycrystalline films generally have better charge carrier transport properties. Thus, it is important to understand how to tune the structure of tin dioxide films between amorphous and polycrystalline. Using X-ray diffraction (XRD) and Hall-effect measurements, we have studied the structure and electrical properties of tin dioxide films deposited by magnetron sputtering as a function of deposition temperature, sputtering power, feed gas composition and film thickness. Films deposited at room temperature are semicrystalline with nanometer size SnO2 crystals embedded in an amorphous matrix. Film crystallinity increases with deposition temperature. When the films are crystalline, the X-ray diffraction intensity pattern is different than that of the powder diffraction pattern indicating that the films are textured with (101) and (211) directions oriented parallel to the surface normal. This texturing is observed on a variety of substrates including soda–lime glass (SLG), Mo-coated soda–lime glass and (100) silicon. Addition of oxygen to the sputtering gas, argon, increases the crystallinity and changes the orientation of the tin dioxide grains: (110) XRD intensity increases relative to the (101) and (211) diffraction peaks and this effect is observed both on Mo-coated SLG and (100) silicon wafers. Films with resistivities ranging between 8mΩ cm and 800mΩ cm could be deposited. The films are n-type with carrier concentrations in the 3×1018 cm−3 to 3×1020 cm−3 range. Carrier concentration decreases when the oxygen concentration in the feed gas is above 5%. Electron mobilities range from 1 to 7cm2/Vs and increase with increasing film thickness, oxygen addition to the feed gas and film crystallinity. Electron mobilities in the 1–3cm2/Vs range can be obtained even in semicrystalline films. Initial deposition rates range from 4nm/min at low sputtering power to 11nm/min at higher powers. However, deposition rate decreases with deposition time by as much as 30%. [Copyright &y& Elsevier]

Abstract: Polymerized n-octadecylsiloxane (PODS) was prepared by coating glass substrates with liquid ocatdecyltrichlorosilane (OTS) followed by dipping-in a solvent. The morphology control of PODS was investigated by the post curing temperature as well as the use of different solvents. The resulting substrates were characterized by scanning electron microscopy (SEM), contact angle measurements, and wide angle X-ray diffractometry (XRD). It is shown that both post curing temperature and extracting solvents affect the morphology of PODS. The temperature dependent morphology was investigated and is ascribed to the physiochemical properties of PODS. For the solvent-dependent morphology, it is proposed that the solvation capability of a solvent to OTS and the presence of a hydrophilic/hydrophobic interface are critical in the PODS morphology. This paper shows the controlling parameter and possible explanation in the crystallinity and wettability of PODS films, which may be useful to other silane-based systems. [Copyright &y& Elsevier]

Abstract: Dynamic mechanical analysis (DMA) was applied to investigate the correlation between dynamic mechanical behaviors of regenerated silk fibroin (RSF) and its structural transition which was characterized by near-infrared (NIR) spectroscopy. The tan δ peak split of DMA demonstrated that the apparent glass transition of amorphous RSF film (at around 177°C) was the contribution of both uncrystallizable and crystallizable segments through homogeneous amide–amide hydrogen bonds, which were gradually separated from each other and produced disordered and β-sheet domains during ethanol treatment. Furthermore, DMA was also applied as “thermal fingerprint” to investigate water effect on the disordered domains of silk fibroin. The results showed that glass transition temperature of permanently disordered domains in crystallized RSF films was increased from 155°C to 190°C after thermal dehydration, and even approached 205°C for stretched RSF films. [ABSTRACT FROM AUTHOR]

Abstract: We have previously shown that most small-angle scattering (SAS) patterns from a range of polymer fibers can be best fit using elliptical coordinates, where the minor axis of the ellipse is parallel to the fiber axis. Analysis of small-angle X-ray scattering patterns obtained during elongation of poly(ethylene-co-1-octene) films now shows that elliptical coordinates also provide a natural way to fit four-point radiating-out patterns, also called “butterfly” or “eyebrow” patterns. To fit this type of pattern the minor axis of the ellipse is tilted away from the fiber draw direction by some angle α, and as the films have rotational symmetry, the pattern is fitted with the sum of two ellipses, at +α and −α. As a result, the reflections appear to fall on a hyperbolic arc – the butterfly pattern. The Matlab code to carry out this analysis on full 2D data is available on request. The elliptical analysis is primarily an empirical fit, much strengthened by its ability to be applied to all observed types of SAS patterns and by its relevance to the mechanical behavior of polymers. [Copyright &y& Elsevier]

Abstract: The successful application of zeolite A membranes in the industrial market has thus far been restricted to the pervaporative dehydration of solvent streams in the pharmaceutical and engineering industries. Their application in gas separation processes remains elusive, largely due to the existence of uncontrollable, intercrystalline diffusion pathways in the boundary regions of neighbouring crystals. In this study the gas permeation characteristics of an unconventional, semicrystalline (70%) zeolite NaA layer, where the boundary phase is filled with amorphous aluminosilicate, was examined and compared to a traditional polycrystalline membrane. To this end, we used single gas permeation of H2, N2 and SF6 at two temperatures. In general, the permeances of all gases through the conventional layer increased in response to temperature, indicating a governing contribution of activated (gaseous) diffusion over the temperature interval tested. Typical permeances of H2 were in the order of 4.8×10−7 (23°C) to 6.5×10−7 molm−2 s−1 Pa−1 (107°C). For the semicrystalline layer, the same trends were observed for N2 and SF6, while the permeance of H2 decreased from 8.7×10−7 (23°C) to about 3.9×10−7 molm−2 s−1 Pa−1 at 107°C. This was attributed to the expansion of the crystal/amorphous interface at higher temperature. By comparing the permselectivity values with the respective Knudsen factors, it was shown that diffusion through the semicrystalline layer, at lower temperature, was predominantly based on molecular sieving (PS H2/SF6 =63.8), which yielded higher selectivities than the traditional membrane under the same conditions (PS H2/SF6 =11.4). However, at higher temperature the H2/SF6 permselectivity of the crystalline layer (5.7) was somewhat higher than that of the semicrystalline membrane (5.2). Based on theoretical considerations, it was concluded that the crystal/amorphous interface in the semicrystalline membrane constituted a denser closure of the boundary interface, which could be attributed to a lower charge barrier presented by the amorphous phase (Si/Al>1), but this integrity was lost at higher temperature due to the thermal instability of the amorphous material. The results therefore suggested that future research should focus on lowering the intercrystalline charge barrier during synthesis, which could reduce the intercrystalline porosity and improve the gas separation properties of NaA membranes in general. [Copyright &y& Elsevier]

Effect of crystallinity on the relaxation behavior of normal and waxy rice starches was examined by differential scanning calorimetry (DSC). Starch samples with different crystallinities were prepared by heating granular rice starch (14% moisture) in DSC pans to different temperatures (170 and 200 °C), and an amorphous sample was prepared by dissolving the starch in dimethylsulfoxide and then recovering it in absolute ethanol. The heat capacity increment (ΔCp) at the glass transition decreased with increasing sample crystallinity. The glass transition temperature (Tg) of native granular starch was higher than that of partially melted starches, but the starch heated to 200 °C displayed a higher Tg than did the starch heated to 170 °C, suggesting the occurrence of additional changes besides crystal melting during heating to 200 °C. Moreover, network structure formed between crystalline and amorphous regions could affect the amorphous transition. With regard to amorphous structural relaxation, the peak temperature of relaxation endotherm (Tp) increased linearly with log aging time (ta), but the rate of the relaxation temperature increase (dTp/d log ta) depended on residual crystallinity. The temperature of the relaxation endotherm positively correlated with glass transition. For partially melted starches, the extent of relaxation increased proportionally with the level of amorphous fraction, whereas the rate of relaxation decreased as the amorphous fraction increased. [Copyright &y& Elsevier]

Semicrystalline polymers often show a spherulitic morphology, consisting of a radial assembly of twisted crystalline lamellae and amorphous layers. A multiscale numerical model is used to investigate the mechanics of intraspherulitic deformation of polyethylene. The model establishes links across the microscopic, the mesoscopic, and the macroscopic levels. Constitutive properties of the material are identified for the crystallographic and amorphous domains. The averaged fields of an aggregate of individual phases, having preferential orientations, form the constitutive behavior of intraspherulitic material. The spherulitic macrostructure is described by finite element models. The macroscopic stress–strain response resembles that of a previous random polycrystalline model. However, the current model includes the geometrical effect of the anisotropic structure within a spherulite, causing strain concentrations in the centers, which spread out in the equatorial region for uniaxial loading conditions and in inclined directions for plane strain loading. The deformations are linked to microstructural processes as interlamellar deformation and intralamellar crystallographic slip. [Copyright &y& Elsevier]

The impact strength of many semicrystalline polymers can be improved by the dispersion of second-phase rubber particles. A criterion for the effect of this practice is based on the average interparticle matrix ligament thickness. The critical interparticle distance, below which a substantial toughness increase can be observed, is considered to be an intrinsic material property of the matrix. A toughening mechanism has recently been suggested which considers a layer of transcrystallized material around well-dispersed particles, having a reduced yield strength in certain preferentially oriented directions, thereby opening the possibility of using mineral fillers. In this work, the potential of toughening of semicrystalline polymeric material by local anisotropy in combination with soft rubber and hard mineral filler particles is investigated. The matrix material is modeled within the framework of anisotropic Hill plasticity with a rate dependent and hardening yield stress. Various particle/matrix interface conditions are used to study the role of debonding and cavitation. The presence of debonded moderately stiff or hard fillers is found to affect the shear yielding effect of local anisotropy that was found for voided material. [Copyright &y& Elsevier]

Acid resistance membrane plays a key role in membrane extraction of lithium ions for ensuring performance stability, yet many are not suitable because of their high ion diffusion resistance. We report here our endeavor in further reducing the ion diffusion resistance of a novel poly (ether ether ketone, PEEK) membrane for lithium extraction from salt-lake brine. We blended PEEK with sulfonated PEEK (SPEEK) and their miscibility was researched by evaluating the mixing free energy and glass transition temperature in the whole mixing range. Using methanesulphonic acid (MSA) and sulfuric acid (SA) as the solvent and water as precipitation media, thermodynamic and kinetic behaviors in phase separation were analyzed. Cloud point of a quasi-ternary PEEK/SPEEK-MSA/SA-H 2 O indicated a low water tolerance; the nominal diffusion coefficient showed maximal value at 50/50% mixing ratio, indicating the quickest demixing. PEEK/SPEEK 50/50 showed the highest water permeability and lithium diffusion, extraction and stripping fluxes. Nearly five times lithium extraction flux and about two times stripping flux as compared to the PEEK membrane were obtained. Disruption of crystalline formation in PEEK by amorphous SPEEK contributed to the open morphology and reduced resistance. The results widen the scopes of membrane materials for membrane extraction of lithium and other ions. • Amorphous SPEEK and semicrytalline PEEK blend was researched for membrane extraction. • Lowest resistance for lithium diffusion was obtained at a weight ratio of PEEK/SPEEK 50/50. • Tortuosity factor was evaluated as a quantitative measure for membrane resistance. • Unprecedented lithium flux was achieved using SPEEK/PEEK blends. [ABSTRACT FROM AUTHOR]