Types Of Spherulites Research Articles

Influence of starch spherulites with different allomorphs and morphologies on reducing gastrointestinal digestibility in bread

This study aimed to enhance the resistance of bread to gastrointestinal digestion by partially substituting wheat flour with starch spherulites. Three types of starch spherulites, specifically A-type (exhibiting an A-type crystalline pattern with mostly positive birefringence), B(−)-type (B-type crystalline with negative birefringence), and B(+)-type (B-type crystalline with positive birefringence), were investigated. The A-, B(−)-, and B(+)-type spherulites showed significantly higher resistant starch contents of 63.5, 63.8, and 89.2 %, respectively, compared to the control wheat flour (7.4 %). The melting temperatures of A-type and B(+)-type spherulites were notably higher than those of the control wheat flour, suggesting the potential preservation of certain enzyme-resistant starch during the baking process. The partial substitution of wheat flour with spherulites resulted in a denser crumb structure, increased bread hardness and chewiness, and a pale brown color in the case of B(+)-type spherulite. However, these variations in physicochemical properties did not significantly impact consumer acceptability. Remarkably, in bread containing A- or B(+)-type spherulite, residual ordered spherulite structures were present after baking, as confirmed by differential scanning calorimetry. This resulted in significantly lower digestibility during in vitro gastrointestinal digestion. These findings are useful for the rational design of bread with sustained glucose release during gastrointestinal digestion.

Polyethylene oxide mixtures with thymol: Unusual thermal behavior and morphology due to a crystallizable hydrogen-bonded complex

Formation of cocrystals in polymer-containing systems attracts a lot of attention lately due to their promise in pharmaceutics, being a poorly studied phenomenon in polymer science. For the first time, we report on the cocrystallization in mixtures of polyethylene oxide and thymol and study in detail the structure and thermal behavior of the mixtures by differential scanning calorimetry, optical microscopy, wide angle X-ray scattering, attenuated total reflection Fourier-transformed infrared spectroscopy, and quantum chemical simulation. The results are summarized into the experimental phase diagram that describes well all the transformations of the systems during their heating and cooling. On the molecular level, we conclude the existence of noncovalent-bonded complexes composed of three monomeric units of polyethylene oxide and two molecules of thymol, which might become structural units of cocrystals upon cooling. This results in a growth of huge centimeter-sized spherulites in the stoichiometric mixture and to the coexistence of two types of spherulites in the mixtures of other compositions. The peculiarities of thymol release from the complexes into different media are also investigated.

Crystal-by-Crystal Assembly in Two Types of Periodically Banded Aggregates of Poly(p-Dioxanone).

The exterior and interior lamellar assemblies of poly(p-dioxanone) (PPDO) crystallized at 76 °C yield the most regular ones to interpret the 3D assembly mechanisms and potential for structural coloration iridescence, which are investigated using atomic-force microscopy (AFM), and scanning electron microscopy (SEM). PPDO displays two types of ring-banded spherulites within a range of Tc with dual-type birefringent spherulites (positive and negative-type) only within a narrow range of Tcs = 70−78 °C. At Tc > 80 °C, the inter-band spacing decreases from a maximum and the crystal assembly becomes irregularly corrupted and loses the capacity for light interference. Periodic grating assemblies are probed by in-depth 3D dissection into periodically banded crystal aggregates of poly(p-dioxanone) (PPDO) to disclose such layered gratings possessing iridescence features similar to nature’s structural coloration. This work amply demonstrates that grating assembly by orderly stacked crystal layers is feasible not only for accounting for the periodic birefringent ring bands with polarized light but also the distinct iridescence by interfering with white light.

Lamellar Assembly Mechanism on Dendritic Ring-Banded Spherulites of Poly(ε-caprolactone).

The self-assembly structures of lamellae in optical ring bands have a critical effect on their optical and physical arrangements. Two different types of dendritic banded spherulites (namely ring-banded and zigzag ring-banded) are formed in poly(ε-caprolactone)/poly (phenyl methacrylate) blend at crystallization temperatures of 42and 46°C,respectively.The difference in optical birefringence of ring bands in two types of spherulites is resolved by means of direct morphological comparison. Banded spherulites are fractured carefully to facilitate lamellar orientation analyses of both the top surface and the interior surface. The results have revealed the existence of tree-like dendritic fractal growth lamellar assemblies in both banded spherulites. The optical ring patterns of the banded spherulites are differentiated mainly by the fractal orientation of the edge-on crystal branches in the ridge region. On the basis of detailed morphological analysis, 3D-lamellar assembly mechanisms are proposed to explain the growth of dendritic ring-banded spherulites at 42°Cand dendritic zigzag ring-banded spherulites at 46°C.

Spherulitic and rotational crystal growth of Quartz thin films

To obtain crystalline thin films of alpha-Quartz represents a challenge due to the tendency for the material towards spherulitic growth. Thus, understanding the mechanisms that give rise to spherulitic growth can help regulate the growth process. Here the spherulitic type of 2D crystal growth in thin amorphous Quartz films was analyzed by electron back-scatter diffraction (EBSD). EBSD was used to measure the size, orientation, and rotation of crystallographic grains in polycrystalline SiO2 and GeO2 thin films with high spatial resolution. Individual spherulitic Quartz crystal colonies contain primary and secondary single crystal fibers, which grow radially from the colony center towards its edge, and fill a near circular crystalline area completely. During their growth, individual fibers form so-called rotational crystals, when some lattice planes are continuously bent. The directions of the lattice rotation axes in the fibers were determined by an enhanced analysis of EBSD data. A possible mechanism, including the generation of the particular type of dislocation(s), is suggested.

Novel green and sustainable shape-stabilized phase change materials for thermal energy storage

Poly (ethylene glycol) (PEG) blended with poly (L-lactic acid) (PLLA) as novel green and sustainable shape-stabilized phase change materials (PCMs) were prepared and characterized in this study. The miscibility and morphology of the blends played an important role in the properties of the PCMs. The partial miscibility between PEG and PLLA resulted in suitable latent heat and a low leakage percentage of PCMs. The typical spherulite structure with a Maltese cross was examined in neat PLLA, as observed using polarized optical microscopy. However, the addition of PEG to PLLA led to the formation of ring-banded spherulites due to the presence of PEG altering the aggregation and twisting the PLLA lamellae. These PLLA crystalline structures can capture liquid (including molten PEG), stabilize the shape, and prevent leakage. The thermal mechanical analysis results indicated that the thickness of the PEG/PLLA blends was not significantly changed during the phase change process. The PEG/PLLA 75/25 blends exhibited appropriate film forming properties and mechanical strength. Moreover, differential scanning calorimetry analysis demonstrated the largest latent heat of melting (130.26 J/g), which could have great potential for developing novel phase change materials for thermal energy storage.

Texture Induced by Molecular Weight Dispersity: Polymorphism within Poly(L-lactic acid) Spherulites

Poly(L-lactic acid) (PLLA) has drawn much attention due to its excellent medical and pharmaceutical applications for decades. As a semi-crystalline polymer, morphology and crystal structure of PLLA greatly determine its properties. Here, we demonstrate, for PLLA films, a non-conventional texture featuring two types of spherulites emerging in pairs to form a distinct nested structure where a small spherulite (~10 µm) is embedded in a large one (100 µm to 300 µm). In addition to the size, the molecular weight and polymorph are different in the large and small spherulites. Crystallographic α-form and relatively low molecular weight are identified in the large spherulites, while meta-stable α′-form and relatively high molecular weight in the small ones. These differences suggest that the polydisperse PLLA polymers fractionate during film formation and the high-molecular-weight fraction crystallizes into the small spherulites with meta-stable structure because of its complicated polymer entanglement and high viscosity. In contrast, the rest of polymers crystallize into the large spherulites with the thermodynamically stable polymorph. Furthermore, this texture exhibits accelerated PLLA degradation initiated from the small spherulites, which is distinct from the typical PLLA spherulites. Insights provided by this work may lead to new texture-properties relationship associated with polydispersity of molecular weight.

Microstructure Investigation of Oil-Bearing Rhyolites: A Case Study from the Hailar Basin, NE China

Understanding the microstructure of rhyolites may greatly promote exploration efforts on rhyolitic hydrocarbon reservoirs; however, related studies are sparse. In this contribution, the microstructure and related porosity of oil-bearing rhyolitic lavas from the Hailar Basin (NE China) were investigated using a combination of optical microscopy, fluorescence image analysis, and scanning electron microscopy. The direct visual and quantitative analyses show that the rhyolites are heterogeneous and porous rocks and have complex microstructures. Phenocryst-rich rhyolitic lava, perlitic lava, and spherulitic rhyolite may be favorable targets for rhyolitic hydrocarbon exploration. For the phenocryst-rich rhyolitic lavas, embayment pores, cleavages, cavitational and shear fractures, and intracrystalline sieve pores are commonly observed in the phenocrysts; while flow-parallel laminar and micropores are ubiquitous in the groundmass. Perlitic lavas are characterized by the occurrence of numerous perlitic fractures which can also be produced in the glassy groundmass of other lavas. Spherulitic rhyolites mainly consist of small-sized (<1 mm) clustered or large-sized (>1 mm) isolated spherulites. Clustered spherulites are characterized by the development of interspherulite pores. Isolated spherulites contain numerous radiating micropores. Both types of spherulites may have water expulsion pores formed in the spherulite–glass border. The formation of the microstructure and related porosity of rhyolites is controlled by pre-, syn- (e.g., deuteric crystal dissolution, cavitation, ductile–brittle deformation, and high-T devitrification), and post-volcanic (e.g., hydration and low-T devitrification) processes. Although pores with diameters > 50 μm are often observed, small pores dominate in pore-size distribution. Small (<15 μm) and large (>300 μm) pores give the most volumetric contribution in most cases. Medium-sized pores with diameters ranging from ~150–300 μm are the least developed and contribute the least to the total volume. The results of this paper can be beneficial to further the understanding of the microstructure and pore system of rhyolites and may be applied to rhyolitic lava hydrocarbon reservoirs elsewhere.

Crystallization of triethyl‐citrate‐plasticized poly(lactic acid) induced by chitin nanocrystals

ABSTRACTThe aim of this study was to gain a better understanding of the crystallization behavior of triethyl‐citrate‐plasticized poly(lactic acid) (PLA–TEC) in the presence of chitin nanocrystals (ChNCs). The isothermal crystallization behavior of PLA–TEC was studied by polarized optical microscopy, scanning electron microscopy, differential scanning calorimetry, and X‐ray diffraction (XRD). Interestingly, the addition of just 1 wt % ChNCs in PLA–TEC increased the crystallization rate in the temperature range of 135–125 °C. The microscopy studies confirmed the presence of at least three distinct types of spherulites: negative, neutral, and ring banded. The ChNCs also increased the degree of crystallinity up to 32%, even at a fast cooling rate of 25 °C min−1. The XRD studies further revealed the nucleation effect induced by the addition of ChNCs and thus explained the faster crystallization rate. To conclude, the addition of a small amount (1 wt %) of ChNC to plasticized PLA significantly affected its nucleation, crystal size, and crystallization speed; therefore, the proposed route can be considered suitable for improving the crystallization behavior of PLA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47936.

The Influence of DMDBS on Crystallization Behavior and Crystalline Morphology of Weakly-Phase-Separated Olefin Block Copolymer.

Olefin block copolymer (OBC), with its low hard segments, can form unique space-filling spherulites other than confined-crystallization morphologies, mainly due to its weak phase-separation. In this work, 1,3;2,4-Bis(3,4-dimethylbenzylidene) sorbitol (DMDBS), a well-known nucleating agent, was used to tailor the crystallization behavior and crystalline morphology of OBC. It was found that DMDBS can precipitate within an OBC matrix and self-assemble into crystalline fibrils when cooling from the melt. A non-isothermal crystallization process exhibited an increased crystallization rate and strong composition dependence. During the isothermal crystallization process, DMDBS showed a more obvious nucleating efficiency at a higher crystallization temperature. OBC showed typical spherulites when DMDBS was added. Moreover, a low addition of DMDBS significantly decreased the crystal size, while a large addition of DMDBS induced aggregates, due to the limited miscibility of DMDBS with OBC. The efficient nucleating effect of DMDBS on OBC led to an increased optical transparency for OBC/DMDBS composites.

Polarization switching, dielectric, structural and elastic properties of 2-Methylbenzimidazole crystals and films

Single crystals and films of 2-methylbenzimidazole were grown from ethanol solution by slow cooling and evaporation method. 3D XRD study confirms pseudo tetragonal structure of MBI crystals. MBI films have a texture formed by spherulite type blocks with in-plane orientation of pseudo-tetragonal [001] axis. MBI crystals and films surface were studied by atomic force microscopy to evaluate Young’s modulus and surface potential distributions related to small charge of domain walls. Dielectric hysteresis loops were simulated in frames of particular case of KAI model. Strong decrease of activation field with temperature increase indicates a potential ferroelectric transition above melting point.

Anatomy into Interior Lamellar Assembly in Nuclei-Dependent Diversified Morphologies of Poly(l-lactic acid)

Sophisticated dissection into the interiors of the three different birefringent types of poly(l-lactic acid) (PLLA) spherulites via delicate fracturing across the thickness sections, coupled with proper etching techniques, was adopted to reveal the correlations between the diversified birefringence patterns and interior lamellae assembly. The three types of spherulites are circularly ringed spherulite (type 1), hexagon-shaped axialite (type 2), and circularly core–stripe dendrites (type 3). Such morphological diversification originates from different nuclei geometries. For all three different types (circularly ringed, hexagonal, and core–stripe) of PLLA aggregation into spherulites or dendrites/axialites, the dissected inner lamellar arrangement shares universal commonality of intersecting at a 60° angle in the intersection between different lamellar species, with distinct discontinuity in the grating structures being characteristic of all three types of aggregated PLLA spherulites. This kind of grating a...

Structural and Dielectric Properties of Organic Ferroelectric 2-Methylbenzimidazole

2-methylbenzimidazole single crystals and films are obtained by evaporation from an ethanol solution. The films have a texture with a predominant orientation of the pseudotetragonal axis in the film plane. The blocks are split crystals of the spherulite type, in which the pseudotetragonal axis rotates around the block center. Dielectric hysteresis loops are investigated in the crystals and films in the temperature range of 290–350 K. In the films, loops are observed for both in-plane and out-of-plane electric-field orientation. The maximum value of polarization in the films is close to that observed in single crystals P s ~ 5 μC/cm2. The difference in the temperature behavior of the hysteresis loops in the crystals and films is associated with the specific structure of the blocks.

Nonisothermal crystallization studies of PBT/ZnO compounds

Compounds of poly(butylene terephthalate) (PBT) and zinc oxide (ZnO) with filler content between 1 and 10% were prepared in a laboratory internal mixer. The processing parameters did not damage PBT thermal stability or its molecular weight as evidenced by torque rheology. The melt crystallization of PBT/ZnO compounds was investigated by differential scanning calorimetry and their morphology by scanning electron microscopy and optical microscopy. From morphological analyses, ZnO particles are well dispersed in PBT matrix, which crystallizes in typical spherulites. The melt crystallization temperatures and maximum melt crystallization rates are almost unaffected by the filler. Equally the overall crystallinity did not show any dependence on the filler content or the cooling rate. Mo’s model was found to be suitable for a description of the melt crystallization kinetics, while Ozawa model turned out to be inadequate.

Orientation of polymer chains in spherulites of poly(ethylene oxide)-urea inclusion compounds

Orientation of polymer chains in the spherulites of polymer-small molecule inclusion compounds (IC) is an interesting issue. Two kinds of spherulite morphologies were observed in the metastable β phase of poly(ethylene oxide) (PEO)/urea IC under the same isothermal crystallization temperature. Via polarized micro-Fourier transform infrared spectroscopy and two-dimensional wide angle X-ray diffraction technique, we found that PEO chains in the two morphologies oriented differently: one along the radius and the other along the tangential direction of the spherulites. The β IC spherulites with polymer chains along the radial direction crystallized directly from melt. In contrast, the metastable spherulites with polymer chain oriented along the tangential direction among the preformed urea crystals. The phase transition from the metastable β spherulites to the stable α IC during heating was examined as well. For the both types of spherulites of the β IC, the conversion rate along polymer chain direction was lower than that perpendicular to the polymer chain. After phase transition, the orientations of PEO chains almost did not change. The two types of morphologies with different orientations of β IC crystals in the spherulites can be attributed to the competitive nucleation behavior of the β PEO-urea IC and pure urea crystals, which varies with the EO/urea molar ratio in the mixture melt. With the increasing EO/urea molar ratio, the fastest growth direction of β IC will change from the direction along the PEO chain to that normal to the PEO chain. Namely, the polymer/small molecule molar ratio has profound effect on the growth behavior of the β phase IC crystals.

Multishell Oblate Spheroid Growth in Poly(trimethylene terephthalate) Banded Spherulites

Unique interior dissection coupled with selective etching techniques for exposing the interiors of poly(trimethylene terephthalate) (PTT) banded spherulites. Three banded PTT spherulite types are present, originating from different nuclei geometries and corresponding to different assemblies of interior lamellae, but all possess similar multishell spheroid layered structures, each with their layer thickness exactly equal to the optical interband spacing. Interior lamellae are alternatingly intersected with mutually perpendicular orientations and clear discontinuity, which evidently disagrees with the conventional models of continuous helical twisting for banding. Interior 3D lamellae assemblies also have been fittingly correlated with top-surface banding patterns.

The crystal morphology and mechanical properties based on poly(l-lactic acid)/silica nanocomposites

Nano silica (SiO2) was introduced into Poly(L-lactic acid) (PLLA) matrix to prepare PLLA/SiO2 nanocomposites, and the crystal morphology, crystallization behavior and mechanical performance were investigated. The XRD experimental data indicated that nano SiO2 could improve the crystallization of PLLA, and PLLA/SiO2 nanocomposites exhibited sharp diffraction peak after isothermal crystallization. In addition, through the POM analysis, PLLA/SiO2 sample had the typical spherulite structure, and the size of the spherulite became larger with the increase of crystallization temperature. The tensile testing showed that a small amount of SiO2 could improve and retain the mechanical performance of PLLA

Distribution of Polymorphic Crystals in the Ring-Banded Spherulites of Poly(butylene adipate) Studied Using High-Resolution Raman Imaging

Poly(butylene adipate) (PBA), an important biodegradable polymer, can crystallize into a particular type of ring-banded spherulite, in each of which two crystal forms, α and β, coexist. However, the distribution of the polymorphic crystals and the molecular chains orientation within the ring-banded PBA spherulites are still unclear. To determine these, in our present study, Raman spectroscopy and high spatial resolution Raman imaging were used. Characteristic Raman peaks were identified for both the α- and β-forms and for amorphous structures. Using these peaks, we investigated the polymorphic crystal distribution and molecular chain orientation within the spherulites through Raman imaging. The two crystal forms are found to be unevenly distributed in the center, ring-banded, and out-layer ringless region. The results of this study also suggested that the two crystal forms can nucleate and grow in the same temperature range (31–33 °C), but the relative content of the α-form in the ring-banded region becom...

Interior Dissection on Domain-Dependent Birefringence Types of Poly(3-hydroxybutyrate) Spherulites in Blends

The mechanisms and correlations between the rotation of Maltese cross axis, optical birefringence types, and lamellar reassembly induced by phase-separation domains, in poly(3-hydroxybutyrate) (PHB)/poly(1,4-butylene adipate) (PBA). In this work, a novel approach via interior dissection into spherulites in correlations with the top-surface morphology of the PHB/PBA (50/50) blend crystallized at a series of Tc’s with various domain sizes. The PHB/PBA blend is used as the model system in comparison to alternative blends of PHB with other polyesters of various extents of phase-separated domains. Domains of optimal sizes were found to be essential in lamellar reassembly, which strongly affects the birefringence types of spherulites. Via the proven approaches, this work expounds how domain sizes and lamellar reorientation in partially miscible blends cause changes in the birefringence types of PHB spherulites, while, in contrast, complete miscibility or extreme phase separation with large domains does not.

Shapes and Origins of Cracks and Correlations with Lamellae Assembly in Poly(L‐lactic acid)

SummaryJust like ring bands in spherulites are not all of a simple type, cracks in crystallized spherulites of polymers can display a wide variety of patterns. Poly(L‐lactic acid) (PLLA) upon crystallization and cooling was found to exhibit as many as four crack types of different directions and patterns, which cannot be feasibly explained simply by the directional difference in coefficients of thermal expansion. Depending on crystallization temperature (Tc), PLLA crystallizes into ringless or ring‐banded spherulites; whereas, the crack patterns are dramatically different in these two types of spherulites. In ring‐banded spherulites of PLLA crystallized at intermediate Tc, two uniquely different crack types are present: (1) twin‐circumferential cracks coinciding with the dark‐bright and bright‐dark boundary, and (2) radial short‐segmental voids coinciding on the bright bands in spherulites. By contrast, only circumferential cracks are present in PLLA ringless spherulites, where crack patterns are influenced by Tc's. Although all cracks in PLLA spherulite are triggered by cooling from Tc, evidence indicates that the crack patterns and ring‐band types (or ringless) are highly correlated and likely both are associated with the lamellar orientation, patterns, and coarseness in spherulites.