Morphological study by TEM on uniaxially oriented thin films of PBT

We prepared uniaxially oriented thin films of poly(butylene terephthalate) (PBT) by applying shear strain to the melt and studied their resulting morphology by transmission electron microscopy (TEM), and could show visually that stacked-lamellar structures are formed in aromatic polyesters. On the basis of crystallographic consideration, we assigned each of the recognized stacked-lamellar structures to a shish-kebab structure or a part of it. In addition, we successfully demonstrated that in one shish-kebab structure all or almost all kebabs (namely, lamellae) have a same crystallographic orientation.     

TEM image simulation study of small carbon nanotubes and carbon nanowire

Recent findings of extremely small diameter carbon nanotube and nanowire in the core of a multi-walled carbon nanotube (MWCNT) have attracted interests from broad range of researchers. Direct observation of carbon nanotube is usually done using a transmission electron microscope (TEM). When nanotubes become smaller, it becomes harder to correctly understand the TEM images, not only because of the weak scattering, but also due to the artifact that starts to appear because of the interference effect and the inappropriate defocus condition.In this study, we have shown that the artifact such as ghost fringes due to inappropriate defocus conditions of the TEM appear in the core of an MWCNT, and can be misinterpreted as either carbon nanowire or small carbon nanotube. It is also shown that, in the TEM image, it is hard to distinguish a single-walled nanotube bundle from a double-walled carbon nanotube bundle. Finally, we propose that the cross-sectional observation is necessary for the correct characterization of single- and double-walled carbon nanotube bundles.     

Scanning force microscopy of nanostructured uniaxially oriented ultra thin film surfaces of isotactic polystyrene

Surfaces of ultra thin films of isotactic polystyrene (iPS) drawn from the melt were investigated by scanning force microscopy (SFM). SFM micrographs of iPS surfaces exhibit the morphology of uniaxial orientation resulting from the preparation technique as well as structures pseudomorphic to regularly arranged shish crystals. Their diameters were 60% larger compared to earlier results obtained from dark-field transmission electron microscopy investigations. Furthermore, different defects of the polymer surface morphology were observed. It is supposed that macromolecules of a lower orientational order cover the shish crystals (hair dressing model).     

Structural, electrical and magnetic properties of carbon-nickel composite thin films

Carbon-nickel composite thin films (600 nm thick) were prepared by dc magnetron sputtering of Ni and C at several temperatures (25-800 °C) on oxidized silicon substrates. By transmission electron microscopy it was found that the composite consisted of Ni (or Ni₃C) nanoparticles embedded in a carbon matrix. The metallic nanoparticles were shaped in the form of globular grains or nanowires (of the aspect ratio as high as 1:60 in the sample prepared at 200 °C). The carbon matrix was amorphous, or graphite-like depending on deposition temperature. At low deposition temperatures T_S (25-400 °C) the Ni₃C nanoparticles were of hcp phase. Samples prepared at T_S ? 600 °C contained ferromagnetic fcc Ni nanoparticles. A correlation was found between the structural, electrical and magnetic properties of the composites. To characterise the films, dependences, such as resistivity vs. temperature, current vs. voltage, differential conductivity vs. bias voltage, and magnetoresistivity, were determined. For example, the tunneling effect was found in samples in which the metallic nanoparticles were separated by 2-3 nm thick amorphous carbon. When the metallic nanoparticles were connected by graphite-like carbon regions (having a metallic conductivity, in contrast to a-C), the temperature coefficient of the resistivity became slightly positive. An anisotropic magnetoresistivity of ∼0.1% was found in the sample that contained ferromagnetic columnar fcc Ni. Zero magnetoresistivity was found in the sample in which the metallic nanoparticles were of non-magnetic hcp phase.     

Processing and morphology of molecularly imprinted nylon thin films

The characterization of thin, selectively imprinted films of nylon‐6 was performed. Amino acids were used as template molecules. Spin‐cast films were prepared with sizes ranging from 2 μm to 300 nm, depending on the nylon and template concentration in the casting solution. The morphological characteristics of the film surface were examined by atomic force microscopy, and the structure within the films was observed by freeze‐fracture scanning electron microscopy. The film activity was clearly coordinated with the appearance of nanometer‐sized pores both on the surface and within the film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2919–2926, 2006     

Morphological studies of glass-microbead-filled polyamide 6.6-polypropylene blends

This article deals with the study of the morphology of glass bead (10% in volume) reinforced compatibilized blends of polypropylene (PP) and polyamide (PA) 6.6. The morphology, as well as some physical and mechanical properties, are determined. The blends are studied in relation with the PP-PA ratio and according to the glass bead's sizing. We have seen the existence of a boundary PA-glass beads interface (independently of the sizing), and the best compatibilization effect is obtained with PP size glass beads and for 50% PP content. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 201–208, 1998     

Solid state intercalation of barium into poly(para-phenylene): TEM, EELS and ESR characterizations

Compressing together divided barium and poly(para-phenylene) results in the intercalation of the metal into the polymer. Electron energy loss spectroscopy (EELS) analysis indicates that an intercalation level of 0.24 barium ions per phenyl unit can be achieved and that the oxidation state of the intercalated barium is rather +2 (Ba²⁺). Both transmission electron microscopy and electron spin resonance studies show that the distribution of the intercalant in the polymer is very inhomogeneous.     

TEM and electron tomography studies of carbon nanospheres for lithium secondary batteries

The structure of carbon nanospheres of 100-200 nm diameter, which showed superior high-speed charge-discharge behavior as the negative electrode in a lithium ion battery, was investigated with XRD, SEM and TEM with an electron tomography attachment. Observation of carbon 0 0 2 lattice images, as well as electron diffraction patterns, illustrated that heterogeneous microtexture was formed as the polyhedronization of the particle proceeded with heat-treatment. The outside region of the particle heat-treated at 2800 °C has stacking structure of aromatic layers with some distribution of d₀₀₂, while the center region consisted of non-graphitic. Structure defects seemed to be concentrated along the ridgelines of the polyhedronized particles after heat-treatment. The electron tomography technique clarified the morphology of the graphitized particles, although the images should be understood with other crystallographic measurements. A slice image computed in the 3D-reconstruction process showed the inner texture of the graphitized particles more clearly than the conventional TEM bright-field image.     

Study on phase separation of PET/PEN blends by dynamic rheology

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) were processed into biaxially drawn films, and samples taken from the bi‐oriented films were then investigated by dynamic rheology experiments in the melt state. Storage modulus G′ and loss modulus G″ were determined in the frequency range of 10^?2–10² rad/s at temperatures between 260 and 300°C. Although the time–temperature superposition (TTS) principle was found to hold in the high frequency regime, a breakdown of TTS was observed at low frequencies, and the terminal behavior of the storage modulus G′ of the blends departs drastically from the terminal behavior observed for the blend components. This is caused by interfacial surface tension effects. The results indicate that despite the effect of transesterification reactions, the PET/PEN blend systems investigated consist of a microseparate phase of PEN platelets in a matrix of PET. This morphology is produced when the blends are processed into biaxially oriented PET/PEN films, and droplets of PEN are deformed into a lamellar structure consisting of parallel and extended, separate layers. The large interfacial surface area of the bi‐oriented PET/PEN blends leads to remarkably strong interfacial tension effects in dynamic rheology measurements. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Microstructure evolution and cation interdiffusion in thin Gd2O3 films on CeO2 substrates

Thin Gd₂O₃ films with a thickness of about 150 nm were deposited by pulsed layer deposition on polycrystalline CeO₂ substrates to study the structural evolution of the Ce_1−xGd_xO_2−x/2 system with respect to phase formation and cation interdiffusion in the temperature range between 986 °C and 1270 °C. Transmission electron microscopy combined with quantitative energy dispersive X-ray spectroscopy was applied to study the microstructure and to obtain composition profiles across the Gd₂O₃/CeO₂-interface. Gd₂O₃ was observed to occur in the bixbyite structure up to 1175 °C. The fluorite and the bixbyite phase are found at intermediate compositions without any indication for a miscibility gap. Interdiffusion coefficients were obtained from Gd₂O₃/CeO₂-concentration profiles on the basis of the diffusion-couple solution of the diffusion equation. The activation enthalpy and frequency factor of the diffusion coefficient were derived assuming an Arrhenius-type behavior in the investigated temperature range.     

Electrochemical behavior of C60 films and C60/lipid films in ionic liquids

Cyclic voltammograms (CVs) of C₆₀ films and C₆₀ embedded in cast films of triple-tailed cationic surfactant solutions and salt-free zero-charged cationic/anionic (catanionic) surfactant vesicles on glassy carbon electrode in a typical room-temperature ionic liquid (RT-IL), 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), were examined. CVs show typically electrochemical oxidation and reduction. The salt-free zero-charged catanionic surfactant bilayer vesicles were determined by freeze-fracture transmission electron microscopy (FF-TEM) images and small-angle X-ray scattering (SAXS) measurements. The cast films of the salt-free zero-charged catanionic surfactant vesicles incorporated C₆₀ molecules were employed to study the electrochemical properties in RT-ILs, which would open new fields for the bulk electronic properties of fullerenes or their derivatives in ionic liquids.     

High yield one-step synthesis of carbon spheres produced by dissociating individual hydrocarbons at their autogenic pressure at low temperatures

Hydrocarbons containing 5–14 carbon atoms (pentane, cyclohexane, camphorquinone, xylene, mesitylene, camphene, decahydronaphthalene, diphenylmethane, and anthracene) are individually dissociated under their autogenic pressure developed at 700 °C to produce pure carbon moieties from the respective hydrocarbon precursor. From all of the hydrocarbons, more than 99% pure carbon is obtained in spherical, filament- or egg-like microstructures. One of the key peculiarities in the thermal dissociation of various hydrocarbons, followed by solidification under autogenic pressure, is the formation of products in micrometer dimensions. It is in contrast to previous work with organometallic precursors, which yield nanometric products via a similar method. These results are compared with those obtained for the thermal dissociation of the same hydrocarbons under flow conditions. Specific systematic morphological, structural, and compositional analysis is presented for the products obtained from the thermal dissociation of diphenylmethane. A possible formation mechanism for the obtained products is provided.     

Morphological study of thin films: Simulation and experimental insights using horizontal visibility graph

We studied the morphological nature of various thin films such as silicon carbide (SiC), diamond (C), germanium (Ge), and gallium nitride (GaN) on silicon substrate Si(100) using the pulsed laser deposition (PLD) method and Monte Carlo simulation. We, for the first time, systematically employed the visibility algorithm graph to meticulously study the morphological features of various PLD grown thin films. These thin-film morphologies are investigated using random distribution, Gaussian distribution, patterned heights, etc. The nature of the interfacial height of individual surfaces is examined by a horizontal visibility graph (HVG). It demonstrates that the continuous interfacial height of the silicon carbide, diamond, germanium, and gallium nitride films are attributed to random distribution and Gaussian distribution in thin films. However, discrete peaks are obtained in the brush and step-like morphology of germanium thin films. Further, we have experimentally verified the morphological nature of simulated silicon carbide, diamond, germanium, and gallium nitride thin films were grown on Si(100) substrate by pulsed laser deposition (PLD) at elevated temperature. Various characterization techniques have been used to study the morphological, and electrical properties which confirmed the different nature of the deposited films on the Silicon substrate. Decent hysteresis behavior has been confirmed by current-voltage (IV) measurement in all the four deposited films. The highest current has been measured for GaN at ～60 nA and the lowest current in SiC at ～30 nA level which is quite low comparing with the expected signal level (μA). The HVG technique is suitable to understand surface features of thin films which are substantially advantageous for the energy devices, detectors, optoelectronic devices operating at high temperatures.     

A TEM study of microstructure of carbon fiber/polycarbosilane-derived SiC composites

The structures of two types of mesophase pitch-based carbon fibers (M30 and M70) reinforced SiC composites, prepared by the polycarbosilane impregnation-pyrolysis process, were investigated using transmission electron microscopy (TEM). It was found that M70 possessed a highly-ordered graphite structure despite occasional misorientation of some crystallites. However, the skin of M70 was less ordered than the interior of M70. The structure of M30 was uniform throughout, and was less ordered than that of M70. The fiber and matrix in M70/SiC bonded weakly, whereas the fiber and matrix in M30/SiC bonded tightly and locked together. This difference in the interface feature originates from the difference of the surface crystalline structures of M30 and M70, and is formed during the first impregnation-pyrolysis cycle of polycarbosilane.     

Morphological study of the structure developed during the polymerization of a series of segmented polyurethanes

The morphology developed during the polymerization of a series of linear polyurethanes ranging from 10–77% by wt. hard segment has been characterized by a variety of techniques. The polyurethanes were batch reacted using poly (propylene oxide) endcapped with poly(ethylene oxide) as the polyol, 4,4′-diphenylmethane diisocyanate and 1,4-butanediol. Hard segment-rich globules and two types of hard segment spherulites have been observed. The size and number of these microstructures depends on cross-sectional location in the mould and hard segment content. A possible polymerization scheme to account for the complex sample morphology is discussed. The importance of these structures on the mechanical properties is illustrated.     

Morphology of paraffin crystals in waxy crude oils cooled in quiescent conditions and under flow

The gel formation in waxy crude oils is a major concern for oil production and transportation. When oil is extracted, the decrease in temperature induces a partial crystallisation of paraffins by a supersaturation mechanism, involving in the first place the longest alkane molecules. Gel formation appears for very low amounts of crystals (around 1-2%) when the oil is cooled in quiescent conditions. However, during normal extraction conditions (pumping or well pressure gradient) the oil remains fluid, although crystallisation still takes place. This investigation deals with the morphology of paraffin crystals in crude oils, cooled either in quiescent conditions or under extensive shearing, controlled by different shear rates. The technique of observation is transmission electron microscopy after cryofixation, cryofracture and replica preparation. The images of gels made under quiescent conditions, distinctly show a lamellar structure: the lamella thickness of the order of the size of a paraffin molecule, the inter-lamella distance decreases with the total amount of crystals. Individual disc-like particles also appear occasionally, which probably constitute the nuclei of crystallisation. Under flowing conditions, only disc-like particles are observed, either isolated or assembled into clusters whose size depends on the shear rate. The discussion deals with the crystallisation mechanism in quiescent conditions and under shear and with the consequences upon rheology of the suspensions.     

Preparation,structural development,and mechanical properties of microfibrillar composite materials based on polyethylene/polyamide 6 oriented blends

The preparation of microfibrillar composites (MFCs) based on oriented blends of polyamide 6 (PA6) and high‐density polyethylene (HDPE) is described. By means of conventional processing techniques, the PA6 phase was transformed in situ into fibrils with diameters in the upper nanometer range embedded in an isotropic HDPE matrix. Three different composite materials were prepared through the variation of the HDPE/PA6 ratio with and without a compatibilizer: MFCs reinforced by long PA6 fibrils arranged as a unidirectional ply; MFCs containing middle‐length, randomly distributed reinforcing PA6 bristles; and a nonoriented PA6‐reinforced material in which the PA6 phase was globular. The evolution of the morphology in the reinforcing phase (e.g., its visible diameter, length, and aspect ratio) was followed during the various processing stages as a function of the blend composition by means of scanning electron microscopy. Synchrotron X‐ray scattering was used to characterize selected unidirectional ply composites. The presence of transcrystalline HDPE was demonstrated in the shell of the reinforcing PA6 fibrils of the final MFCs. The impact of the compatibilizer content on the average diameter and length of the fibrils was assessed. The influence of the reinforcing phase on the tensile strength and Young's modulus of the various composites was also evaluated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and structural characterization of thin multi-walled carbon nanotubes with a partially facetted cross section by a floating reactant method

Here we describe synthesis of very unusual multi-walled carbon nanotubes through a catalytic chemical vapor deposition method using a floating reactant method and subsequent thermal treatment up to 2600 °C in a large quantity. Main characteristics of these nanotubes are (1) relatively wide distribution of diameters ranging from 20 to 70 nm and linear, long macro-morphology (aspect ratio >100), (2) highly straight and crystalline layers, (3) high purity through removal of metallic impurity, (4) very low interlayer spacing (0.3385 nm) and low R value (I_D/I_G = 0.0717), (5) high G′ intensity over intensity of G band (G′/G = 0.85) and strongly negative magnetoresistance value of −1.08% at 77 K and 1 T. The unusual microstructure of thin multi-walled carbon nanotubes with a partially facetted cross-sectional shape caused by thermal treatment is mainly ascribed to abrupt density changes (from 1.89 to 2.1 g/cm³) within a confined nanosized space, accompanying with the phase separation.     

Magnetic and high resolution TEM studies of nanographite derived from nanodiamond

The time evolution of graphitization was analyzed based on the structural and magnetic properties of nanodiamond samples annealed at 1600 °C for various time intervals. High resolution TEM and XRD show that the nanodiamond particles are converted to spherical onions for short annealing time intervals, and then they are completely transformed to polyhedral nanographite through the annealing for 120 min. The in-plane orbital susceptibility χ_orb (300 K) analyzed on the basis of Kotosonov’s equation remains fairly constant in the range −5.5 × 10⁻⁶ to −5.9 × 10⁻⁶ emu/g, suggesting that the coherent scattering region (CSR) and the Fermi energy are independent of the annealing times. It also indicates the presence of serious defects affecting the electronic structure of nanographite. As the annealing time increases from 2 to 120 min, the Pauli paramagnetic susceptibility decreases. The broad ESR signal is associated with the spins localized on the edge states of the π-electron graphite network. The ESR linewidth becomes nine times less as the heat-treatment time rises from 2 to 120 min. The relatively large linewidth is associated with the scattering of π-electrons by the edge phonon modes and magnetic interaction between the edge-localized spins. During continuous annealing the nanoparticle structure changes from more defective to less defective and the number of edge-localized spins in a particle drops from ca. 2 to ca. 1 despite the CSR size and the Fermi energy remain practically the same.