New insights into the crystallization process of sol-gel–derived 45S5 bioactive glass

In this work the influence of thermal treatment conditions on crystallization of a sol-gel-derived 45S5 bioactive glass was evaluated using DSC, XRD, TEM, EDX, and X-ray nanocomputed tomography (nano-CT). Temperature and time of the thermal treatment strongly influence the composition of the crystalline phases. At the onset of the glass transition temperature (600°C), combeite crystallizes as the main phase along with a calcium silicate-phosphate phase, which decomposes into rhenanite from 2 hours of thermal treatment at this temperature. At the crystallization temperature (700°C), combeite remains as the main crystalline phase. Additionally, Na₂Ca₂Si₂O₇ crystalline phase is formed. Our results provide a basic platform for tailoring the crystalline phases by controlling the nucleation and growth of crystalline phases via thermal treatments. Different morphologies (round particles, stacked layers, toothpick-like, and long features) were discerned by TEM as a function of temperature and time of treatment. It is the first time that bioactive glass is investigated by nano-CT at laboratory scale. This novel technique enables the 3D visualization of features in the nanometer range, giving clear information about the volumetric distribution of phases in the sample.     

Crystal morphology of rapidly cooled isotactic polypropylene: A comparative study by TEM and AFM

The morphology of crystals, formed at the surface and in the bulk of rapidly cooled and subsequently at elevated temperature annealed films of isotactic polypropylene (iPP) was analyzed by transmission electron microscopy (TEM) and by atomic force microscopy (AFM). Both techniques show a lamellar crystals after melt-crystallization at 12 K s^-1, and a nodules after melt-crystallization at 750 K s^-1. The morphology of crystals is independent on the position of the investigated film of thickness of 100 μm, suggesting (a) that the crystallization at the surface is not affected by the use of a glass substrate for preparation, and (b) that the temperature-gradient during primary crystallization is sufficiently small to ensure identical structure at the surface and in the bulk. AFM suggests a larger size of crystals than TEM, in particular if the absolute size of objects approaches the dimensions of the used tip of the AFM. If the absolute size of objects is distinctly larger, then AFM and TEM yield nearly identical dimensional information.     

Effect of feldspar addition into bioglass 45S5 composition: Crystallization kinetics and thermal transformation

Thermal transformations of glasses with formulations derived from Bioglass 45S5 with Al₂O₃ (≤2.5 wt %) and K₂O additions through K-feldspar were studied. Crystallization kinetics and transformations were followed-up by X-ray diffraction and differential thermal analysis. The activation energy of crystallization of Na₂CaSi₂O₆ was found to be lower than that of Bioglass 45S5 for the prepared samples. This behavior was attributed to an increase in phase separation in glasses. Nevertheless, transformations shifted towards higher temperatures with addition of feldspar, due to a decrease in pre-exponential factor. Cell parameters evolved progressively with increasing temperature without any abrupt changes. Al₂O₃ and K₂O remained as a part of a residual glassy phase.     

Hollow microspheres of NiO as anode materials for lithium-ion batteries

NiO hollow spheres are prepared by heating the NiCl₂/resorcinol-formaldehyde (RF) gel in argon at 700 °C for 2 h, and subsequently in oxygen at 700 °C for 2 h. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to characterize the structure and morphology of the as-prepared NiO hollow spheres. These hollow spheres have a diameter of about 2 μm, which are composed of NiO particles of about 200 nm. The electrochemical properties of these NiO hollow spheres are investigated to determine the reversible capacity and cycling performance as anode materials for lithium-ion batteries, and the advantages of their hollow spherical morphology to the electrochemical performance are discussed.     

Morphological features and crystallization behavior of the conductive composites of poly(trimethylene terephthalate)/graphene nanosheets

Poly(trimethylene terephthalate) (PTT) composites filled with well‐dispersed graphene nanosheets (GNSs) were prepared through a coagulation method. The effects of increased GNS concentration on variations in the structure and properties of the PTT matrix, such as its electrical conductivity, crystallization kinetics, melting behavior, and crystal morphology, were investigated. Several analytical techniques were used, including electrical conductivity measurement, differential scanning calorimetry, Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, polarized light microscopy, transmission electron microscopy (TEM), and thermo‐gravimetric analysis (TGA). Electrical conductivity increased from 1.8 × 10^?17 S/cm for neat PTT to 0.33 ± 0.23 S/cm for PTT/GNS composites with 2.97 vol % GNS content. Percolation scaling laws were applied, and then threshold concentration and exponent were determined. In the case wherein liquid nitrogen was used to quench the melt, a mesomorphic phase was formed despite the extremely short crystallization time after adding high GNS contents. PTT crystallization rate increased with the gradual addition of GNSs. The enhanced crystallization kinetics was attributed to the high nucleation ability of GNSs to induce epitaxially grown lamellae on their surfaces, as revealed by TEM. PTT nuclei were randomly developed on the GNS surface to form the lamellae. However, crystallinity reached its maximum value near the electrical percolation threshold because the PTT chain mobility was confined after the GNS–GNS network formed. The growth of PTT banded spherulites in the bulk was still observed for composites with high GNS content, and TGA results revealed that the GNS‐filled PTT composites had excellent thermal stability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43419.     

Crystallization,properties, and crystal and nanoscale morphology of PET–clay nanocomposites

The crystallization process and crystal morphology of poly(ethylene terephathalate) (PET)–clay nanoscale composites prepared by intercalation, followed by in‐situ polymerization, have been investigated by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), dynamic scanning calorimetry (DSC), and X‐ray techniques, together with mechanical methods. Results of the nonisothermal crystallization dynamics show that the nanocomposites of PET (Nano‐PET) have 3 times greater crystallization rate than that of pure PET. The thermal properties of Nano‐PET showed heat distortion temperature (HDT) 20–50°C higher than the pure PET, while with a clay content of 5%, the modulus of Nano‐PET is as much as 3 times that of pure PET. Statistical results of particle distribution show that the average nanoscale size ranges from 10 to 100 nm. The particles are homogenously distributed with their size percentages in normal distribution. The agglomerated particles are 4% or so with some particles size in the micrometer scale. The morphology of exfoliated clay particles are in a diordered state, in which the morphology of the PET spherulitics are not easy to detect in most of microdomains compared with the pure PET. The molecular chains intercalated in the interlamellae of clay are confined to some extent, which will explain the narrow distribution of the Nano‐PET molecular weight. The stripe‐belt morphology of the intercalated clay show that polymer PET molecular chains are intercalated into the enlarged interlamellar space. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1139–1146, 1999     

Nanoscale copper sulfide hollow spheres with phase-engineered composition: covellite (CuS), digenite (Cu1.8S), chalcocite (Cu2S)

Covellite (CuS), digenite (Cu(1.8)S) and chalcocite (Cu(2)S) are prepared as nanoscaled hollow spheres by reaction at the liquid-to-liquid phase boundary of a w/o-microemulsion. According to electron microscopy (SEM, STEM, TEM, HRTEM) the hollow spheres exhibit an outer diameter of 32-36 nm, a wall thickness of 8-12 nm and an inner cavity of 8-16 nm in diameter. The phase composition is determined based on HRTEM, electron-energy loss spectroscopy, X-ray powder diffraction and thermal analysis. In face of the advanced morphology of the hollow spheres, precise control of its phase composition is nevertheless possible by adjusting the experimental conditions (i.e. type and concentration of the copper precursor, concentration of ammonia inside of the micelle). Such phase-engineering of nanoscale hollow spheres is firstly observed and might allow adjusting even further compositions/structures as well as tailoring of phase-specific properties in the future.     

Chemical reactions between calcium carbide and chlorohydrocarbon used for the synthesis of carbon spheres containing well-ordered graphite

Carbon spheres and carbon nanospheres were prepared through the chemical reactions between calcium carbide and chlorohydrocarbon without using any catalysts. The reactants were sealed in a pressure vessel and heated to temperatures of 210-250 °C. The final products were characterized using scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS) attached to SEM, transmission electron microscopy (TEM), X-ray diffraction and Raman spectroscopy. SEM and TEM examinations show that some of the obtained products are bead-like or roe-like spheres with diameters of 100-2000 nm. The carbon nanospheres have high purity (>95%) and uniform size distribution (100-200 nm). The EDS analyses reveal that the carbon contents of the spheres are 86-94%. The results indicate that the size and the size distribution of the synthesized spheres change with the change of the reactants. The experimental yields of carbonaceous materials relative to the starting materials are about 8.0-14.4% (w/w). The yields of the spheres increase whereas their size distributions decrease with the increase of H atom and the decrease of Cl atom in chlorohydrocarbon. The average graphitization degree of sample 1 and sample 2 are 81.9% and 78.7%.     

Competition between microphase separation and crystallization in self-assembly sPS/PS-PEP blends

The crystallization and the self-assembly of blending system, syndiotactic polystyrene/polystyrene-block-poly(ethylenepropylene) (sPS/PS-PEP), were investigated by transmission electron microscopy (TEM), polarized light microscopy, small angle X-ray scattering and differential scanning calorimetry (DSC). Spherical microdomains with sPS embedded in PS-PEP matrix were obtained after melt mixing as evidenced by TEM observations combined with DSC analyses. The size of spherical microdomains is in the order of tens nanometer. This unique morphology provides an appropriate system to examine the effect of crystallization on microphase-separated morphology. The driving force of sPS crystallization leads the growth of sPS crystals to overcome the effect of spatial confinement and the repulsive barrier of immiscibility, and thus to go across the surrounding PEP domains. As a result, the growth of crystallization interconnects sPS microdomains and forms crystalline lamellae. The overall crystallization rate of sPS in self-assembly sPS/PS-PEP blends increases with increasing the content of sPS. We suggest that the increase on the crystallization rate is attributed to the decrease on the crossing-distance between the crystallizing sPS domains due to an increase on the size of spherical microdomain.     

A comparative study of different techniques for microstructural characterization of oil extended thermoplastic elastomer blends

This paper gives a relative comparison of different microscopic methods that are presently used to visualize polymer blend morphologies, versus the possibility to visualize the three-dimensional structure of the blends with electron tomography. Oil extended thermoplastic elastomer (TPE) blends based on a high amount of rubber phase and low amount of isotactic polypropylene (PP) were used as samples for this study. Low voltage scanning electron microscopy (LVSEM) and transmission electron microscopy (TEM) proved to be far superior to conventional scanning electron microscopy (SEM) and atomic force microscopy (AFM) for obtaining good quality images of the morphology of these blends. In an attempt to visualize the 3D morphology, electron tomography was carried out on these blends and models of the 3D morphologies were constructed. The usefulness of the different microscopic techniques in providing complementary morphological information and the potential of electron tomography as a new tool for constructing 3D-models of polymer blends are highlighted.     

A comparative structure–property study of polyphosphazene micro-nano spheres

Novel fluorinated cross-linked polyphosphazene micro-nano spheres have been prepared by precipitation polymerization of hexachlorocyclotriphosphazene (HCCP) monomer. The influence of molecular structure on the morphology of polyphosphazene micro-nano spheres was investigated by SEM and TEM. The micro-nano spheres were also characterized by Fourier transforms infrared, X-ray photoelectron spectroscopy and thermo gravimetric analysis. The results indicate that the 5 % thermal degradation temperature is 366 °C. It was found that a silicon wafer dip-coated with thus prepared micro-nano spheres has a water contact angle as high as 137° ± 1.5°. Furthermore, the effects of the concentration of HCCP and ultrasonic power on the morphology were also discussed.     

X-ray nano computerised tomography of SOFC electrodes using a focused ion beam sample-preparation technique

High-resolution tomography techniques have facilitated an improved understanding of solid oxide fuel cell (SOFC) electrode microstructures.The use of X-ray nano computerised tomography (nano-CT) imposes some geometrical constraints on the sample under investigation; in this paper, we present the development of an advanced preparation technique to optimise sample geometries for X-ray nano-CT, utilizing a focused ion beam (FIB) system to shape the sample according to the X-ray field of view at the required magnification.The technique has been successfully applied to a Ni-YSZ electrode material: X-ray nano-CT has been conducted at varying length scales and is shown to provide good agreement; comparison of results from X-ray and more conventional FIB tomography is also demonstrated to be favourable.Tomographic reconstructions of SOFC electrodes with volumes spanning two orders of magnitude are presented.     

CdS quantum dots sensitized ZnO spheres via ZnS overlayer to improve efficiency for quantum dots sensitized solar cells

This paper reports the preparation of three-dimensional ZnO spheres by using a hydrothermal method and their application to quantum dots sensitized solar cells (QDSSCs). After achieving the desired thickness of sensitized CdS quantum dots (QDs) for ZnO spheres, ZnS overlayer was deposited on the surface of CdS/ZnO photo-anodes to further improve the photoelectric properties. CdS QDs and ZnS overlayer were deposited by successive ionic layer adsorption and reaction (SILAR) method. The surface morphology and crystal structure of the samples were verified by field-emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM) and X-ray diffraction (XRD). The CdS QDs sensitized solar cells were ameliorated via using ZnS as a protection-layer between quantum dots and electrolyte. As a result, the power conversion efficiency (η) has been increased from 0.60 to 1.43% after being treated by ZnS overlayer for CdS/ZnO photo-anodes.     

The Effect of Sodium Dodecyl Sulfate (SDS) and Cetyltrimethylammonium Bromide (CTAB) on the Properties of ZnO Synthesized by Hydrothermal Method

ZnO nanostructures were synthesized by hydrothermal method using different molar ratios of cetyltrimethylammonium bromide (CTAB) and Sodium dodecyl sulfate (SDS) as structure directing agents. The effect of surfactants on the morphology of the ZnO crystals was investigated by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. The results indicate that the mixture of cationic-anionic surfactants can significantly modify the shape and size of ZnO particles. Various structures such as flakes, sheets, rods, spheres, flowers and triangular-like particles sized from micro to nano were obtained. In order to examine the possible changes in other properties of ZnO, characterizations like powder X-ray diffraction (PXRD), thermogravimetric and differential thermogravimetric analysis (TGA-DTG), FTIR, surface area and porosity and UV-visible spectroscopy analysis were also studied and discussed.     

On the structure and morphology of polyvinylidene fluoride-nanoclay nanocomposites

Polyvinylidene fluoride (PVDF)-nanoclay nanocomposites were prepared by both solution casting and co-precipitation methods with the nanoclay loading of 1-6 wt%. The structure and morphology of the nanocomposite were investigated by wide angle X-ray diffraction (WAXD), polarized light microscopy and transmission electron microscopy (TEM) techniques. PVDF phase transformation behavior was investigated using differential scanning calorimetry and in situ thermal WAXD. All the three typical nanoclay morphologies, namely, exfoliated, partially intercalated and phase separated morphologies, were observed in the PVDF-nanoclay nanocomposites prepared by different methods. In solution-cast samples, phase separation and intercalation occurred depending upon the organic modifiers while complete exfoliation of the nanoclays was observed in the co-precipitated nanocomposites. Furthermore, unique parallel orientation of the nanoclay layers and polymer film surface was achieved in solution-cast samples. β-form PVDF was observed in all the nanocomposites regardless of the nanoclay morphology and contents. Both crystallization and melting temperatures of PVDF were increased with the addition of nanoclay, possibly due to the formation of the β-form PVDF.     

Isothermal crystallization of lightly sulfonated syndiotactic polystyrene/montmorillonite clay nanocomposites

Lightly sulfonated syndiotactic polystyrene (sPS) nanocomposites were prepared using a solution intercalation technique, and the effect of montmorillonite clay on the crystallization kinetics of sulfonated sPS ionomer nanocomposites was systematically studied. Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to evaluate the dispersion of clay platelets within sPS and sulfonated sPS ionomer (SsPS) matrices. Experimental results obtained from WAXD and TEM revealed a predominately exfoliated morphology within the SsPS ionomer containing 5 wt.% of organically-modified clay. The corresponding non-sulfonated sPS control exhibited a mixed morphological structure consisting of intercalated platelets and many platelets that were present as micron-sized agglomerates. Using differential scanning calorimetry (DSC), the Avrami approach was used to elucidate information related to nucleation and growth within the sPS and SsPS systems during the isothermal crystallization process. Pristine and organically-modified clays significantly increased the overall crystallization rate of the SsPS ionomer, while the nanoclays slightly decreased the crystallization rate of the non-ionic sPS. The mechanistic origins of increased crystallization rates within the SsPS ionomer clay nanocomposites were attributed to multiple phenomena including disruption of the ionomer electrostatic network and a nucleating effect due to the presence of well-separated, homogeneously dispersed clay platelets.     

超细ZSM-5分子筛的制备及其形貌表征

对比考察了模板剂的种类、晶化温度以及铝含量等影响因素对超细ZSM-5分子筛晶化行为的影响,采用扫描电镜（SEM）、透射电镜（TEM）和X射线衍射光谱（XRD）技术对所制备的超细产物的结构及形貌进行了表征。结果表明,模板剂的种类对分子筛的晶化过程有重要影响,四丙基氢氧化铵是优良的制备超细ZSM-5分子筛的模板剂;以四丙基氢氧化铵为模板剂,适宜采用静态法制备超细ZSM-5分子筛的晶化温度为70～ 120 ℃;凝胶体系中铝的存在抑制ZSM-5分子筛晶核的生长,无铝条件下,分子筛的晶化速度最快;随着铝含量的增加,分子筛的晶化速度变慢,在相同的晶化时间内,生成的分子筛的粒径更小。     

Morphology of an asymmetric ethyleneoxide-butadiene di-block copolymer in bulk and thin films

We present experiments on the melt and crystal morphology of a asymmetric semi-crystalline poly(ethylene/butylene-b-ethyleneoxide) diblock copolymer (PB_h-b-PEO) in bulk as well as in thin films. Simultaneous small- and wide-angle X-ray scattering combined with AFM and TEM images reveal in the melt a bulk morphology of hexagonally packed cylinders of PEO in a PB_h matrix, that transforms into a hexagonal perforated lamellar phase upon crystallization. X-ray reflectivity of thin films of PB_h-b-PEO in the melt indicates wetting layers at the top and bottom interfaces, which force the cylinders in the interior to orient parallel to the substrate. Crystallization of the PEO block leads to roughening of the air/film interface and causes lateral structuring coexisting with planar lamellar layers in thinner films.     

New N-(2-carboxybenzyl)chitosan composite scaffolds containing nanoTiO2 or bioactive glass with enhanced cell proliferation for bone-tissue engineering applications

In the present study N-(2-carboxbenzyl)chitosan (CBCS) 3D macroporous hybrid scaffolds with interconnected pore system, containing 0.5, 2.5, and 5?wt% TiO₂ nanoparticles (nTiO₂) and 2.5?wt% Bioglass 45S5 (BG) have been synthesized using freeze-drying technique. Compressive strength values verified that the modification of chitosan combined with the presence of inorganic fillers can attribute significant mechanical stiffness to the scaffold. The in vitro biomineralization test confirmed that all samples were bioinert as mineral deposits were detected with X-ray diffractometry after incubation in SBF. Cytotoxicity and biocompatibility of all scaffolds were tested by using and Wharton’s jelly–derived mesenchymal stem cells (WJ-MSCs) and human embryonic kidney 293 (HEK 293) cell line. Metabolic activity, proliferation, migration, and attachment to the scaffolds were examined. Cells appeared to attach around the superficial pores and migrate in them. Cells also maintained their morphology, proliferated, and migrated across the scaffolds and showed consistent and proved compatibility.     

Preparation of ZnO nanorod by solvothermal reaction of zinc acetate in various alcohols

Solvothermal reaction of zinc acetate in various alcohols resulted in the formation of zinc oxide (ZnO) nanorods. The effects of reaction conditions on the product morphology as well as crystallization mechanism were investigated by using X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) techniques. It was found that average diameter and length of the nanorods increased with an increase in reaction temperature or the initial concentration of zinc acetate. On the contrary, the aspect ratio of the product depended upon type of alcohol used as the reaction medium. The aspect ratio of ZnO nanorods increased from 1.7 to 5.6 when the alcohol was changed from 1-butanol to 1-decanol. An investigation of the reaction mechanism suggested that the formation of ZnO nanorods was initiated from the esterification reaction between zinc acetate precursor and alcohol to form ZnO seeds.