Spherulitic Structure Research Articles

Characterization of the Nanoscale in Triacylglycerol Crystal Networks

Here we report on the characterization of the nanoscale in triacylglycerol crystal networks of edible fats. Blends of tristearin and triolein were prepared in proportions between 20 and 100% w/w to achieve a wide range of supersaturations. Crystal networks were subjected to mechanical disruption using isobutanol at 10 °C and visualized using cryogenic transmission electron microscopy (cryo-TEM). This method allowed the breakdown of spherulitic structures into their primary crystals: nanoplatelets of approximate sizes 150 × 60 × 30 nm to 370 × 160 × 40 nm depending on supersaturation conditions, and a length to width aspect ratio of 2.3. The method also allowed the visualization of bimolecular triacylglycerol lamellae within a cross-section of a nanoplatelet. The tristearin d-spacing (∼4.5 nm) and domain size (30−50 nm) of the (001) plane, by cryo-TEM and small-angle X-ray diffraction, agreed quantitatively. Scherrer analysis provided an accurate estimate of the cross-sectional thickness of the nanoplatele...

Non-isothermal crystallization of poly(ε-caprolactone)-grafted multi-walled carbon nanotubes

Non-isothermal crystallization behavior of poly(ε-caprolactone) (PCL)-grafted multi-walled carbon nanotubes (MWNTs) was studied in order to determine the effects of functionalized MWNTs (f-MWNTs) on its crystallization behavior. Differential scanning calorimeter measurements showed that an introduction of f-MWNTs into the PCL molecules induced heterogeneous nucleation and the crystal growth process was significantly affected. X-ray diffraction showed a decrease in the crystallinity of composites with the addition of f-MWNTs in PCL, likely due to the occurrence of more heterogeneous nucleation induced by f-MWNTs in the samples. The activation energy for crystallization of PCL drastically reduced with the presence of 2 wt.% f-MWNTs in the samples and increased slightly with increasing content of f-MWNTs. A spherulite structure of PCL-grafted MWNTs with MWNTs at the center was developed, clearly indicating the nucleating action of MWNTs in the crystallization process. The experimental data were also analyzed using various kinetic models e.g., Avrami, Tobin, Ozawa, etc.

Spherulites of Amyloid-β42 In Vitro and in Alzheimer's Disease

Several amyloidogenic proteins including insulin, beta-lactoglobulin, and albumin form spherulites in vitro under non-physiological conditions. These micrometer-sized, roughly spherical structures are composed of ordered arrays of amyloid fibrils in radial arrangements which, characteristically, show a typical Maltese cross pattern of light extinction under the polarizing microscope. The physiological significance of amyloid spherulites is unknown though in Alzheimer's disease, senile plaques composed primarily of beta sheets of amyloid-beta (Abeta)42 have, very occasionally, been shown to give a Maltese cross pattern of light extinction under crossed polarizers. Herein we describe the first observation of the formation in vitro of spherulites of Abeta42. They were formed under near-physiological conditions in which the beta sheet conformation of pre-formed aggregates of Abeta42 had been abolished following the addition of an excess of copper. Incubation of these preparations at 37 degrees C for up to 9 months resulted in the formation of globular structures, 5-20 microm in diameter, which exhibited a Maltese cross pattern of light extinction typical of spherulites. Near-identical spherulitic structures were also observed in abundance in 30 microm thick sections of Alzheimer's disease brain tissue. Synchrotron x-ray fluorescence showed that the location of these spherulites in AD tissue coincided with locally elevated concentrations of tissue copper. The formation in vitro of spherulites of Abeta42 which morphologically appeared analogous to spherulitic structures observed in vivo strongly supports the hypothesis that spherulites and senile plaques in AD tissue are one and the same structures and that their ultimate formation may involve copper.

Laser-induced Propagation and Destruction of Amyloid β Fibrils

The amyloid deposition of amyloid beta (Abeta) peptides is a critical pathological event in Alzheimer disease (AD). Preventing the formation of amyloid deposits and removing preformed fibrils in tissues are important therapeutic strategies against AD. Previously, we reported the destruction of amyloid fibrils of beta(2)-microglobulin K3 fragments by laser irradiation coupled with the binding of amyloid-specific thioflavin T. Here, we studied the effects of a laser beam on Abeta fibrils. As was the case for K3 fibrils, extensive irradiation destroyed the preformed Abeta fibrils. However, irradiation during spontaneous fibril formation resulted in only the partial destruction of growing fibrils and a subsequent explosive propagation of fibrils. The explosive propagation was caused by an increase in the number of active ends due to breakage. The results not only reveal a case of fragmentation-induced propagation of fibrils but also provide insights into therapeutic strategies for AD.

Postepy w badaniach struktur nadczasteczkowych segmentowych poliuretanow

A broad review of the literature related to the most important research in the structure of supermolecular segmented polyurethanes has been presented. The structural elements of segmented polyurethanes as well as direct and indirect experimental methods applied in their evaluation have also been described (Figs. 1, 2). Particular attention has been paid to the indirect investigation methods such as electron microscopy, atomic force microscopy and Raman spectroscopy used in the determination of the micro- and nanostructures of segmented polyurethanes (Figs. 3-12). The fact that nanometric structures also known as domains, global and spherulite micrometer structures depend on the type of polyurethane was established. The structural domains can be spherical, ellipsoidal, cylindrical or lamellar in shape. In the case of the presence of micrometric scale structures, nanometric internal lammelles can be found to exist on their internal space while amorphous domains are located on the external side in the regions between spherulites and globules. The important issue of the destructive effect of Transmission Electron Microscopy on the polyurethane samples occurring during analysis has been emphasized.

Structure and properties of biaxial‐oriented crystalline polymers by solid‐state crossrolling

AbstractThe effect of biaxial orientation by solid‐state crossrolling on the morphology of crystalline polymers including polypropylene (PP), high density polyethylene (HDPE) and Nylon 6/6 was investigated with polarized optical microscopy, atomic force microscopy, wide‐angle X‐ray scattering, and small‐angle X‐ray scattering techniques. It was found that crossrolling gradually changed the initial spherulitic structure into a biaxially oriented crystal texture with chain axis of crystals becoming parallel to the rolling direction for all three polymers. The effect of microstructure change on the macromechanical properties was studied in tension at both ambient temperature and −40°C. In tension at room temperature, the localized necking deformation of HDPE and PP control changed upon orientation into homogeneous deformation for the entire sample length. This was attributed to that the oriented crystal morphology eliminated the stress concentration, which existed in the original spherulitic structure from lamellae orientation in the polar and equatorial regions. At ambient conditions, the elastic moduli of HDPE and PP were found to decrease slightly with orientation whereas the modulus of Nylon 6/6 increased with increasing orientation. This was due to the fact that the amorphous chains of HDPE and PP are in a rubbery state and orientation increased the shear relaxation in the orientation direction but the amorphous chains of Nylon 6/6 are in the glassy state inhibited the shear relaxation. Both the yield stress and strain hardening exponent increased with increasing orientation for all three polymers. In tension at −40°C, orientation changed the failure mechanism of all three polymers from brittle fracture into ductile failure, as the original spherulitic structure was changed into an oriented structure with chain axis of crystals becoming parallel to the tension direction, which allowed chain slip deformation of crystals and resulted in oriented samples showing ductile failure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Studies on α to β phase transformations in mechanically deformed PVDF films

AbstractPVDF cast films were drawn at different temperatures to different draw ratios at constant draw rate to understand the mechanism of α to β phase transformation during mechanical deformation. WAXD and FTIR studies were carried out to determine the formation and content of β phase in the drawn films. Lower stretch temperatures gave higher fractions of β phase. The cast PVDF films were also drawn at suitable temperatures below the PVDF ambient melting point to the draw ratio of 6.4. The highest fraction of β phase obtained in these ultra drawn films was 0.98. SALS studies carried out for films at different stretch ratios show the change in spherulitic structure with the stretching parameters and give information for the understanding of phase transformation during stretching of PVDF films. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation and characterization of microporous PVDF membrane by thermally induced phase separation from a ternary polymer/solvent/non-solvent system

Porous poly(vinylidene fluoride) (PVDF) microporous membranes were successfully prepared from a ternary system including PVDF, solvent and non-solvent via thermally induced phase separation (TIPS) process. Tributyl citrate (TBC) as solvent and di-(2-ethylhexyl) phthalate (DEHP) as non-solvent were used in this study. The effect of mixed diluent composition on PVDF/TBC/DEHP system phase diagram was studied. Phase separation mechanism changed from solid-liquid phase separation to liquid-liquid phase separation with the increase content of non-solvent DEHP. Effects of mixed diluent composition, polymer concentration, cooling condition on morphology, water permeability, porosity and pore size were studied. The membranes which formation controlled by L-L phase separation mechanism have narrow pore size. For the system of 30 wt/70 wt TBC/DEHP with L-L phase separation, bi-continuous morphology was observed. For the system of 90 wt/10 wt TBC/DEHP with S-L phase separation, spherulites structure was obtained. With the polymer concentration increased, the values of porosity, pure water permeability flux and mean pore radius all decreased. For the same polymer content, the membranes prepared from 30 wt/70 wt TBC/DEHP system have better performance. Membranes possessed nice performance prepared in the 20°C water bath.

Solid-liquid phase separation of poly-4-methyl-1-pentene/diluent system via thermally induced phase separation

Poly-4-methyl-1-pentene (PMP) microporous membranes were prepared via thermally induced phase separation (TIPS) with dioctyl adipate (DOA) as the diluent. Solid-liquid phase separation happened to this PMP/DOA system because of the weak interaction between them, which resulted in the spherulitic structure. Unique and obvious spherulites were formed at low PMP concentration system or low quenching temperature, while the spherulites were destroyed and impinged at high PMP concentration or high quenching temperature. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) were used to analyze the crystallization of PMP in the PMP/DOA system via TIPS. The increase of the PMP concentration delayed the crystallization of PMP, which was inferred from the results of both the isothermal and non-isothermal crystallization of the PMP/DOA system. The crystallization was faster and had more effect on the ultimate membrane morphology when the quenching temperature decreased. Double endotherm peaks emerged on DSC melting curves of PMP/DOA quenched samples were owing to the crystals of different extent formed in primary crystallization and further crystallization during TIPS.

Molecular Structure Modulated Organization and Properties of Azobenzene‐Substituted Polydiacetylene Assemblies Films: Photopolymerization, Morphology, and Thermal Stability

AbstractThree accessible azobenzene mesogen‐substituted diacetylene monomers (DA1, DA2, and DA3) were synthesized and the effect of the molecular structure on the photopolymerization behavior and self‐assembled structures of the resulting azobenzene‐substituted polydiacetylene (PDA) films had been investigated in detail. The films derived from DA1 were substantially polymerized into blue phase. However, the films derived from DA2 and DA3 were polymerized into red phase directly. The morphology, packing structure, and thermal stability of the resulting azobenzene‐substituted PDA films were characterized in detail by SEM, XRD as well as POM measurements. PDA1 formed micrometer‐sized lamellar crystal structures, while PDA2 and PDA3 both formed spherulitic crystal structures. The strong π–π stacking interaction among side chains was essential for maintaining high stability upon thermal stimulus.magnified image

Crystallization behavior of poly(L‐lactic acid)/montmorillonite nanocomposites

AbstractIn this study, we modified montmorillonite (MMT) with dilauryl dimethyl ammonium bromide (DDAB) and then exfoliated the structures in a poly(L‐lactic acid) (PLLA) matrix. We used polar optical microscopy and X‐ray diffraction (XRD) to examine the morphologies of the resulting composites, differential scanning calorimetry to study the melting and crystallization behavior, and Fourier transform infrared (FTIR) and Raman spectroscopy to measure the influence of the intermolecular interactions between PLLA and MMT on the isothermal crystallization temperature. We found that the DDAB‐modified MMT was distributed uniformly in the PLLA matrix. At temperatures ranging from 130 to 140°C, the crystalline morphology resembled smaller Maltese cross‐patterned crystallites; at temperatures from 150 to 170°C, however, the number of crystallites decreased, their sizes increased, and they possessed ringed spherulite structures. In the XRD spectra, the intensity of the diffraction peaks of the 200/110 and 203 facets of the PLLA/MMT nanocomposites decreased as the crystallization temperature increased. In the FTIR spectra, the absorption peak of the CO groups split into two signals at 1748 and 1755 cm−1 when the isothermal crystallization temperature was higher than 140°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of the structure at the micrometer and nanometer scales on the light transmission of isotactic polypropylene

AbstractThe spherulitic superstructure, crystallinity, and structure and morphology of crystals of isotactic polypropylene were controlled by the conditions of melt crystallization and related to the transmittance of visible light. Spherulitic samples, which contained monoclinic lamellae, were prepared by slow cooling of the quiescent melt at rates lower than 10 K/s and by isothermal melt crystallization at temperatures between 373 and 413 K. Nonspherulitic specimens, which contained nonlamellar mesomorphic domains, in contrast, were obtained by rapid cooling of the melt with rates faster than 100 K/s. The crystallinity and the size of crystals were furthermore fine‐tuned by subsequent annealing at elevated temperatures. Analysis of such films of different structure by ultraviolet–visible spectroscopy revealed that the light transmission was independent of (1) the fraction, (2) the internal structure, and (3) the size of the crystals. In contrast, the light transmission increased with decreasing size of spherulites and finally exceeded 90% in films of 100 μm thickness when spherulites were completely absent. The crystallinity and the structure and size of the crystals of the films of isotactic polypropylene could be adjusted within wide limits without affecting the light transmission. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation and characterization of fluorescence probe from assembly hydroxyapatite nanocomposite.

A new nanocomposite fluorescence probe with thioglycolic acid (TA) functional layers embedded inside the hydroxyapatite nanoribbon spherulites has been synthesized. The fluorescence intensity of the novel probe is about 1.5–3.3-fold increase compared with the probe containing no TA. When used to detect cadmium ion, the most of original assembly nanoribbon spherulites structure in the novel probe is found to have been damaged to new flake structures. The mechanism of determining cadmium ion in alcohol solution has been studied. The present systematic study provides significant information on the effect of assembly nanostructure on the metal-enhanced fluorescence phenomenon.

Effect of Gamma Irradiation on the Microstructure and Morphology of Polyethylene Oxide and Polyvinyl Alcohol Blends

Thin films of a blend of 90, 75, 50 (wt/wt%) percentage of polyethylene oxide and polyvinyl alcohol were synthesized and irradiated with 5, 25, 50, 100 and 200 kGy. The presence of PVA leads to diffusion controlled mechanism where it decreases the crystallinity of PEO as restricted crystallization occurs.Low doses of 5 kGy cause crosslinking of the blends and increase the thermal stability. Higher doses up to 100 kGy cause the PEO crystallite boundaries to be erased and to blur spherulites structure; it also leads to an increase in the crystallinity. Higher doses of 200 kGy cause an increase in the hydrogen bonding where the material is more crystalline in structure and broken down which made more segments available for the hydrogen bonding. Degradation and oxidation of the blends due to the presence of free radicals in the polymer irradiated in air is noticed for blends with very high doses. Never the less, PVA in these blends protects the PEO composite from the effect of radiation.

Isothermal crystallization kinetics of poly(vinylidene fluoride) in the α-phase in the scope of the Avrami equation

Isothermal melt crystallization of poly(vinylidene fluoride) (PVDF) at different crystallization temperatures was studied by differential scanning calorimetry. Analysis by the two different approaches of the Avrami equation was performed: first the classical double logarithmic approximation was used, but a non-linear least squares search showed to clearly improve the fit of the model to the experimental isotherms. The differences found by both methods in the Avrami parameters are discussed. The limitation of the Avrami equation in this polymer has to do not only with the fitting procedure to determine the parameters but also with the lack of a consistent physical interpretation of their temperature evolution. The melting behavior of the samples was analyzed and an equilibrium melting temperature of 190.9 °C was obtained by the Hoffmann–Weeks extrapolation. The samples crystallize in a spherulitic structure, as observed by optical microscopy with polarized light (OMPL). Lauritzen–Hoffmann theory was applied to analyze the crystallization kinetics and the Regime III was found for the crystallization of α-PVDF.

Spherulites of A[beta]~42~ in vitro and in Alzheimer's disease

AbstractSeveral amyloid-forming proteins and peptides, including insulin^1^, [beta]-lactoglobulin^2^ and albumin^3^, form spherulites in vitro under non-physiological solution conditions. These micrometer-sized, roughly spherical structures are composed of ordered arrays of [beta] sheets of amyloid fibrils in radial arrangements which, characteristically, show a typical Maltese cross pattern of light extinction under the polarizing microscope. The physiological significance, if any, of these amyloid super assemblies is unknown although in Alzheimer's disease there is the suggestion that senile plaques composed primarily of [beta] sheets of A[beta]~42~ are spherulitic^4^. Herein we describe the first observation of the formation in vitro of spherulites of A[beta]~42~. They were formed under near-physiological conditions in which the [beta] sheet conformation of pre-formed aggregates of A[beta]~42~ had been abolished following the addition of an excess of copper. Incubation of these preparations at 37^o^C for up to 9 months resulted in the formation of spherulites. These were globular in appearance, 5 - 20 microns in diameter, and exhibited the typical Maltese cross pattern of light extinction. Similarly to other amyloid spherulites formed in vitro they bound Congo red without giving apple-green birefringence^5^ while also being thioflavin T-positive when viewed by fluorescence microscopy^3^. Near-identical spherulitic structures were also observed in abundance in 30 micron thick sections of Alzheimer's disease brain tissue. Synchrotron x-ray fluorescence showed that the location of these spherulites in AD tissue coincided with locally elevated concentrations of tissue copper. The formation in vitro of spherulites of A[beta]~42~ which morphologically appeared analogous to spherulitic structures observed in vivo strongly supports the hypothesis that spherulites and senile plaques in AD tissue are one and the same structures and that their ultimate formation involves copper.

Self-assembly in the growth of precious opal

It is proposed that primary nucleation of amorphous microspherulites of hydrated silica in natural proto-precious-opal can be followed by a long range superlattice ordering process by means of electrostatic self-assembly. Necessary conditions in the thermodynamics are a high surface charge density on microspherulite surfaces, a long Debye length and an appropriate number density of nucleation centres. A further chemical requirement is a high alkaline environmental pH ∼9–10. It is also proposed that the characteristic concentric spherical shell-like structure of spherulites, centred on primary nuclei, are due to sequential deposition of intrinsic salts, which precipitate out when the corresponding solubility limits in the liquid are successively exceeded. It can be that the better-known sedimentation of microspherulites under gravity only plays part in the final stabilization period of overall growth.

Electrospinning of poly(ethylene‐co‐vinyl acetate)/clay nanocomposite fibers

AbstractPoly(ethylene‐co‐vinyl acetate)/clay nanocomposite fibers were fabricated using electrospinning. The fiber diameters were controlled by varying the polymer/chloroform concentration, which resulted in fibers with diameters ranging from 1 to 15 μm. The clay concentration was varied from 0.35 to 6.6 wt %. Scanning electron microscopy revealed that the fiber diameter increased with increasing clay concentration, whereas beading decreased. Transmission electron microscopy revealed a disruption of the spherulite structures by clay, which is consistent with heterogeneous nucleation. Shear modulus force microscopy indicated a reduction in melting point (Tm) with decreasing diameter for fibers thinner than 15 μm, which was confirmed by temperature dependent X‐ray diffraction data. For fibers thinner than 8 μm, the presence of clay further enhanced the reduction of Tm. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2501–2508, 2009

Influence of the thin‐film thickness and crystallization temperature on the spherulitic structure of polymer thin films

AbstractThe spherulitic structure and morphology of poly(3‐hydroxybutyrate) (PHB) thin films crystallized from the melt were observed with a polarizing optical microscope. Depending on the thickness of the PHB thin film and crystallization temperature, banded and nonbanded spherulites could form. Reducing the thin‐film thickness and crystallization temperature was favorable for the formation of the banded structure. The morphology transition from banded spherulites to nonbanded spherulites was related to the ratio of the crystallization rate to the diffusion rate. The formation mechanism of the banded structure was examined with the discontinuity growth theory. A depletion zone was considered to appear periodically at the crystal growth front because of the slow diffusion rate, and this may have resulted in the banded spherulites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Penetrant diffusion in polyethylene spherulites assessed by a novel off-lattice Monte-Carlo technique

Semi-crystalline polymers have a complex hierarchical structure. The purpose of this study was to mimic the real structure of polyethylene spherulites by computer simulation using an off-lattice method in order to predict their diffusion properties. The principles used to build the spherulites were based on established findings obtained by electron microscopy. Spherulites in the crystallinity range of 0–55 vol% were built. Diffusion of small-molecule penetrants assuming no interfacial trapping at the amorphous-crystal boundary was studied using a Monte-Carlo technique. The main findings were: (i) diffusion was isotropic; (ii) diffusion was independent of the aspect ratio of the crystal building bricks, clearly in disagreement with the Fricke model; (iii) the geometrical impedance factor showed a dependence on the average free path length of the penetrant molecules in the amorphous phase; and (iv) data for the geometrical impedance factor obtained by simulation compared favourably with experimental data obtained for several penetrants showing limited interfacial trapping.