Spherulitic Growth Research Articles

Spherulitic growth process in Ti-based metallic glass: Microstructure, phase identification, and growth mechanism

Ti40Cu36Zr10Pd14 metallic glass is often considered a promising candidate for biomedical applications, in particular for the manufacturing of small size dental implants. Nevertheless, its processing and limited glass-forming ability leads to the appearance of crystalline spheres called “spherulites”. These spherulites play a major role in the deformation behaviour of this alloy. It is therefore a critical issue for its future industrial use to identify their nature and better understand their growth process to enable control of their size distribution and localisation. This article presents a detailed description of the microstructure of these crystalline defects, from the sub millimetre to nanometric scales, using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS)/electron backscatter diffraction (EBSD) coupled with scanning electron microscopy and X-ray diffraction characterisation. Several phases are identified thanks to the combination of EDS/EBSD and TEM information, in particular a CuTi B2 phase, analogous to the ZrCu B2 phase usually present in other composite metallic glasses. The presence of other phases such as Ti2Cu3 and CuTi3 phases is also detected. The spherulites are studied at different times during their growth process, and a growth scenario is proposed based on the characterisation observations. However, the nucleation step of the spherulites remains unclear despite the in-depth investigation. Thus, different hypotheses are discussed.

Improving powder performances of natural extracted lutein with spherulitic growth control

Lutein tends to form tiny lamellar crystals which result in poor powder performances in uniformity of particle size and flowability. Spherulitic growth technology is developed to obtain uniform lutein spherulites with diameter around 250 μm to improve the powder performances. Operation conditions concerning initial concentration, stirring speed, temperature and cooling rate for spherulitic crystallization of lutein from solution without additives are studied. Lab-scale crystallization process analysis by on-line Raman confirms the critical effect of temperature on spherulitic growth control, and temperature related molecular conformation disorder induced spherulitic growth above 303.15 K is revealed. Particle growth kinetic study using in-situ HSM reveals that lutein spherulites result from spherulitic growth effect. Kinetic coefficients ( k ) and growth rate order (g) of the spherulitic particle are calculated to be 7.7 × 10 −6 cm/s and 0.78. It provides a new strategy to improve the crystal powder performances of carotenoid compounds through spherulitic growth control. • Spherulitic growth technology without additives is established for natural extracted pigment lutein. • Designed products show much better powder performances. • On-line analyzing the crystallization processes are performed. • Mechanism of molecular disorder induced spherulitic growth is investigated. • Growth kinetic of lutein spherulitic particles is calculated.

Epoxy‐Modified Pyrophyllite as a Multifunctional Chain Extender for Poly(latic acid)

AbstractPyrophyllite (Prl), an aluminosilicate with a balanced mineral structure and extremely small particle size, appears to be an ideal filler but is rarely used in polymers. Herein, a method for the application of pyrophyllite in polymers is reported. A multifunctional filler is prepared by epoxy‐modified pyrophyllite and incorporated into poly(latic acid) (PLA) to enhance its processability and crystallization properties. Results show the effectiveness of epoxy‐modified Prl in composite film with a significant reduction in glass transition temperature, and noteworthy increment in crystallinity and spherulite growth rate. Water vapor barrier properties of PLA composite films increase over 30% with a range of Prl Loading. Furthermore, an enhancement of the tensile strength is increased by 30% and strain at break by 337.1% for PLA composite films compared to neat PLA. This work provides a new idea to prepare the functionalized pyrophyllite fillers and a theoretical basis to develop the application of pyrophyllite for polymers.

When distinction matters: Carbonate shrubs from the Aptian Barra Velha Formation of Brazilian's Pre-salt

Branched, bush- or shrub-like crystals are some of the most striking components of carbonate facies from the Cretaceous South Atlantic Pre-salt carbonate reservoirs. Many different analogues have been proposed to help to understand them, including travertines, lacustrine mounds and alkaline lake deposits, amongst others. Interpretation and genesis of these special facies involve discussions about biogenic vs. abiogenic formation of these branched components, relation with Mg-clays, role of microbes and growth of spherulites, amongst others. The present work shows some examples at microscale from a drilled core from Santos Basin (Brazil).The analyses of the shrub-like crystals present in the studied section allowed the distinction between four different types: (i) Type 1: fan-shaped fibrous-radial crystals; (ii) Type 2: fan-shaped, branched fibrous-radial crystals; (iii) Type 3: dendrite crystals; and (iv) Type 4: laminated crusts. All these components show similarities with their counterparts present in travertines, suggesting similar conditions controlling crystal growth in both Pre-salt and travertines. However, microfacies relationships show clear differences between the Pre-salt and those from travertine in the literature. Such Pre-salt microfacies presented here show a clear relationship between the development of the so called shrub-like crystals and the environment's energy, allowing the establishment of a proximal–distal pattern within a lacustrine environment as well as the identification of microfacies that could be related to (subaqueous?) hydrothermal vents.Distinction between the different types of branched components described here as well as their relationships with other microfacies are critical issues for the differentiation of the processes involved and the interpretation of the environments of formation (e.g., spring-related and proximal–distal environments within a lake). The observations made on samples from a drilled core of Brazilian's Pre-salt allow the discussion on some topics and interpretations involving the Pre-salt facies, providing potential research guidelines on these challenging continental carbonates.

Supernucleation Dominates Lignin/Poly(ethylene oxide) Crystallization Kinetics

The effect of lignin nanoparticles (LNPs) on the crystallization kinetics of poly(ethylene oxide) (PEO) is examined. Lignin from spruce and ionic isolation was used to prepare LNPs with a number-averaged diameter of 85 nm (with a relatively large polydispersity) by an ultrasonication method. PEO-based nanocomposites with four different LNP contents (5, 10, 15, and 20 wt %) were prepared and subject to isothermal and nonisothermal crystallization protocols in a series of experiments. Scanning electron microscopy (SEM) images showed well-dispersed LNPs in the crystallized PEO matrix. The incorporation of LNPs exponentially increases nucleation density at moderate loadings, with this trend apparently saturating at higher loadings. However, the spherulitic growth rate decreases monotonically with LNP loading. This is attributed to the substantial PEO/LNP affinity, which impacts chain diffusion and induces supernucleation effect (with efficiencies in the order of 200%), but leads to slower growth rates. The overall crystallization kinetics, measured by the DSC, shows faster nanocomposite crystallization rates relative to the neat PEO at all LNP contents examined. This indicates that the supernucleation effect of LNPs dominates over the decrease in the growth rates, although its influence slightly decreases as the LNP content increases. The strong hydrogen-bonded interactions between the LNPs and the PEO are thus reminiscent of confinement effects found in polymer-grafted NP nanocomposites (e.g., PEO-g-SiO2/PEO) in the brush-controlled regime.

Dynamically stable and amplified circularly polarized excimer emission regulated by solvation of chiral co-assembly process

Chiral supramolecular assembly has been assigned to be one of the most favorable strategies for the development of excellent circularly polarized luminescent (CPL)-active materials. Herein, we report our study of an achiral boron-containing pyrene (Py)-based chromophore (PyBO) as a circularly polarized excimer emission (CPEE) dye induced by chiral co-assemblies containing chiral binaphthyl-based enantiomers (R/S-M). Chiral co-assembly R/S-M-(PyBO)4 fresh film spin-coated from toluene solution can exhibit orderly nanofibers and strong green CPEE (λem = 512 nm, gem = ±0.45, ΦFL = 51.2 %) resulting from an achiral PyBO excimer. In contrast, only a very weak blue CPL was observed (λem = 461 nm, gem = ± 0.0125, ΦFL = 19.0 %) after 187 h due to PyBO monomer emission as spherulite growth. Interestingly, this kind of chiral co-assembly R-M-(PyBO)4-T film from tetrahydrofuran (THF) solution retains uniform morphology and affords the most stable and strongest CPEE performance (λem = 512 nm, gem = + 0.62, ΦFL = 53.3 %) after 10 days.

Direct observation of heterogeneous formation of amyloid spherulites in real-time by super-resolution microscopy

Protein misfolding in the form of fibrils or spherulites is involved in a spectrum of pathological abnormalities. Our current understanding of protein aggregation mechanisms has primarily relied on the use of spectrometric methods to determine the average growth rates and diffraction-limited microscopes with low temporal resolution to observe the large-scale morphologies of intermediates. We developed a REal-time kinetics via binding and Photobleaching LOcalization Microscopy (REPLOM) super-resolution method to directly observe and quantify the existence and abundance of diverse aggregate morphologies of human insulin, below the diffraction limit and extract their heterogeneous growth kinetics. Our results revealed that even the growth of microscopically identical aggregates, e.g., amyloid spherulites, may follow distinct pathways. Specifically, spherulites do not exclusively grow isotropically but, surprisingly, may also grow anisotropically, following similar pathways as reported for minerals and polymers. Combining our technique with machine learning approaches, we associated growth rates to specific morphological transitions and provided energy barriers and the energy landscape at the level of single aggregate morphology. Our unifying framework for the detection and analysis of spherulite growth can be extended to other self-assembled systems characterized by a high degree of heterogeneity, disentangling the broad spectrum of diverse morphologies at the single-molecule level.

Organizing Nanoparticles in Semicrystalline Polymers by Modifying Particle Diffusivity.

We have previously shown that semicrystalline polymers can be reinforced by adding nanoparticles (NPs) and then ordering them into specific motifs using the crystallization process. A key result we have found is that when the spherulite growth rate is slowed below a critical value, then, NPs can order into the amorphous interlamellar regions of the semicrystalline structure. The effects of spherulite growth rate in this context have previously been examined, and here we focus on the role of NP diffusivity. We achieve this goal by changing the poly(ethylene oxide) (PEO) molecular weight as a route to altering the matrix viscosity. In particular, four molecular weights of PEO were employed ranging from 5.4-46 kDa. Each sample was loaded with 10 vol % of bare 14 nm diameter silica NPs. After initially studying spherulite growth rates, experiments were designed to fix the spherulite growth rate across sample molecular weights to study particle ordering, induced by polymer crystallization. We find that, at the fastest growth rate studied (12 μm/s), the lowest molecular weight sample showed the highest order, presumably due to enhanced particle mobility. However, as the spherulite growth rate is slowed, the maximum ordering behavior is observed at intermediate molecular weights. The trend observed at slow growth rates is explained by the large-scale segregation of NPs (presumably into the grain boundaries, i.e., the interspherulitic regions); evidence for this is the observed transition of spherulite growth to diffusion-control at slow growth rates in the lowest molecular weight PEO sample studied.

Spherulitic Growth Strategy for Agitation-Induced Formation of Spherical Amoxicillin Sodium Products

Spherulitic Growth Strategy for Agitation-Induced Formation of Spherical Amoxicillin Sodium Products

Development and Characterization of Fully Renewable and Biodegradable Polyhydroxyalkanoate Blends with Improved Thermoformability.

Poly(3-hydroxybutyrate-co-3-valerate) (PHBV), being one of the most studied and commercially available polyhydroxyalkanoates (PHAs), presents an intrinsic brittleness and narrow processing window that currently hinders its use in several plastic applications. The aim of this study was to develop a biodegradable PHA-based blend by combining PHBV with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), another copolyester of the PHA family that shows a more ductile behavior. Blends of PHBV with 20% wt., 30% wt., and 40% wt. of PHBH were obtained by melt mixing, processed by cast extrusion in the form of films, and characterized in terms of their morphology, crystallization behavior, thermal stability, mechanical properties, and thermoformability. Full miscibility of both biopolymers was observed in the amorphous phase due to the presence of a single delta peak, ranging from 4.5 °C to 13.7 °C. Moreover, the incorporation of PHBH hindered the crystallization process of PHBV by decreasing the spherulite growth rate from 1.0 µm/min to 0.3 µm/min. However, for the entire composition range studied, the high brittleness of the resulting materials remained since the presence of PHBH did not prevent the PHBV crystalline phase from governing the mechanical behavior of the blend. Interestingly, the addition of PHBH greatly improved the thermoformability by widening the processing window of PHBV by 7 s, as a result of the increase in the melt strength of the blends even for the lowest PHBH content.

In Situ Atomic Force Microscopy Tracking of Nanoparticle Migration in Semicrystalline Polymers.

We present in situ tracking of silica nanoparticle (NP) migration from a poly(ethylene oxide) (PEO) melt into interlamellar region using in situ atomic force microscopy (AFM). Our results confirm the previous hypothesis that NPs migrate into the interlamellar regions at crystallization growth rates smaller than a critical value under isothermal conditions. Under these slow crystallization conditions, bare silica NPs are rejected as defects by the growing crystal of PEO, and the in situ imaging on the large (50 nm) NPs helps track the migration into the amorphous zones. We extend this AFM technique to estimate lamellar growth rates that correlate with spherulite growth rates determined by polarized light optical microscopy (PLOM) but at smaller undercoolings than are typical for PLOM.

Spherulitic Crystal Growth Drives Mineral Deposition Patterns in Collagen‐Based Materials

AbstractThe formation of the hard tissues that provide support and mobility to organisms is achieved through the interplay of inorganic crystals and an organic framework composed of collagen and a small percentage of non‐collagenous proteins. Despite their clinical relevance, the mechanisms governing mineralization of the extracellular matrix are still poorly understood. By using 3D electron tomography and high‐resolution electron microscopy imaging and spectroscopy, it has been demonstrated that mineralization proceeds through a spherulitic‐like crystal growth process. First, aggregates of disordered crystals form in the interfibrillar spaces, which lead to the mineralization of adjacent fibrils. Mineral propagates steadily through the inter‐ and intrafibrillar spaces of the collagen structure forming layered spherulites that grow to confluence. The structure of the collagen fibrils serves as a protein scaffold to guide the formation of a myriad of platelet‐shaped crystallites that make up each of these spherulites. At their periphery, nanosized unmineralized areas remain, leading to the formation of the characteristic lacy pattern observed in the transversal cross‐section of mature calcified tissues. This study provides fundamental insights into the bone formation process and represents a potential strategy for complex materials design.

Spherulites: How Do They Emerge at an Onset of Nonequilibrium Kinetic-Thermodynamic and Structural Singularity Addressing Conditions?

This communication addresses the question of the far-from-equilibrium growth of spherulites with different growing modes. The growth occurs in defects containing and condensed matter addressing environments of (bio)polymeric and biominerals involving outcomes. It turns out that it is possible to anticipate that, according to our considerations, there is a chance of spherulites’ emergence prior to a pure diffusion-controlled (poly)crystal growth. Specifically, we have shown that the emergence factors of the two different evolution types of spherulitic growth modes, namely, diffusion-controlled growth and mass convection-controlled growth, appear. As named by us, the unimodal crystalline Mullins–Sekerka type mode of growth, characteristic of local curvatures’ presence, seems to be more entropy-productive in its emerging (structural) nature than the so-named bimodal or Goldenfeld type mode of growth. In the latter, the local curvatures do not play any crucial roles. In turn, a liaison of amorphous and crystalline phases makes the system far better compromised to the thermodynamic-kinetic conditions it actually, and concurrently, follows. The dimensionless character of the modeling suggests that the system does not directly depend upon experimental details, manifesting somehow its quasi-universal, i.e., scaling addressing character.

Observation of banded spherulite in a pure compound by rhythmic growth

Banded spherulitic growth of crystals is observed in some materials with spherically symmetric growth front and periodic radial variation of birefringence. This variation of birefringence in quasi-two-dimensional geometry produces concentric interference color bands when viewed through crossed polarizers. In most materials, the banded spherulites are found to be formed by radially oriented periodically twisted fibrillar crystallites. Here, we report the formation of banded spherulites due to the rhythmic growth of concentric crystallite-rich and crystallite-poor bands for a pure compound consisting of strongly polar rodlike molecules. The compound exhibits coexistence of untwisted fibrillar crystallites and an amorphous phase in its most stable solid state. On sufficient supercooling of the sample from its melting point, the banded spherulites are formed with a periodic variation of composition of untwisted radially aligned fibrillar crystallites and an amorphous solid phase. We have developed a time-dependent Ginzburg-Landau model to account for the observed banded spherulitic growth.

Hierarchical Organization of Single Crystal Polymorphs of Azobenzene Chromophore in Anisotropic Media Subjected to Local Thermal Gradients upon Cold Spraying.

The present article entails the emergence of diverse crystal polymorphs following thermal quenching into various coexistence regions of binary azobenzene chromophore (ACh)/diacrylate (DA) solution and of azobenzene/nematic liquid crystal (E7) mixture. Development of various crystal topologies encompassing rhomboidal and hexagonal shapes can be witnessed in a manner dependent on thermal quenched depths into the crystal + liquid coexistence region of ACh/DA system. Upon spraying with compressed carbon dioxide (CO2 ) fluid, the local temperature gradient is generated resulting in spherulitic morphology showing discrete lamellae undergoing twisting locally in some regions and branched dendrites or seaweeds in another. When ACh/E7 blend is sprayed using compressed CO2 fluid, hierarchical organization of various discrete faceted single crystals including needle, rectangular, rhombus, and truncated hexagonal crystals radiating from the spherulite core can be discerned in a brighter region (off cross-polarization) polarized optical microscopy (POM) and nematic disclination in a darker cross-polarized region. Of particular interest is that the observed faceted single-crystal polymorphs in ACh/E7 may be contrasted to the lamellar twisting and branching observed in the ACh/DA system and plausible mechanisms of polymer spherulitic growth are discussed.

Kinetics of Polymer Crystallization with Aggregating Small Crystallites.

The isothermal crystallization near the glass transition temperature from the melt state of poly(trimethylene terephthalate) has been studied by wide-angle x-ray diffraction (WAXD), small-angle x-ray scattering (SAXS), and optical microscopy. The SAXS and WAXD results show the crystallization mechanism in which the crystalline nodules cover the entire sample with the formation of aggregation regions. The analysis of the SAXS results using Kolmogorov-Johnson-Mehl-Avrami theory indicates that the formation kinetics of the aggregation regions is of three-dimensional homogeneous nucleation type. The analysis of the SAXS profiles using Sekimoto's theory provides the growth velocity and the nucleation rate of the aggregation region. The temperature dependence of the growth velocity of the aggregation region is a natural extrapolation of that of spherulite to the high supercooling region. The temperature dependence of the nucleation rate of the aggregation region is also represented by the parameters of the spherulitic growth rate. The result of the growth velocities of the aggregation region and the spherulite suggests the existence of precursors at the front of the crystal growth.

Quantitative contribution of each component to secondary nucleation in the blends of homopolymer and its random copolymers

In homopolymer/random copolymer blends, it is still unclear how the two crystallizable components contribute to secondary nucleation and the radial growth rate of spherulites. There are two highly possible nucleation pathways in the blends of homopolymer and the random copolymer with a low content of amorphous co-monomers. One, similar to regime II, the spherulitic growth rate G of the blends is affected by both secondary nucleation and tertiary nucleation, with the former contributed by homopolymers and the latter by random copolymers. The other, similar to regime I and III, the growth rate G of the blends is mainly determined by secondary nucleation, which is involved by both homopolymer and random copolymer. For the two cases, quantitative equations are established to correlate the spherulitic radial growth rate with the volume fraction of the homopolymer and the volume percentage of the crystallizable repeating units in the random copolymer. By analyzing the radial growth rate of the spherulites of poly(butylene succinate)/poly(butylene succinate-co-butylene 2-methylsuccinate) blends, we reveal the microscopic mechanism for the nucleation of homopolymer and random copolymer chains in the blends. Fitting of the experimental results with the theoretical equations precludes the first regime II like possibility that the homopolymer and the random copolymer contribute to secondary nucleation and tertiary nucleation, respectively. It is shown that both the homopolymer and the random copolymer contribute to secondary nucleation in the blends. Namely, a critical secondary nucleus of the blends consists of the crystallizable units from both homopolymer and random copolymer chains. The higher the homopolymer content, the more crystallizable units in a critical nucleus are derived from the homopolymer. In contrast, when the concentration of crystallizable units in the random copolymer becomes larger, more crystallizable units in a critical nucleus come from the random copolymer. Combining theory and experiments, we could determine the quantitative contribution of each crystallizable component to the secondary nucleation in the blends.

End groups affected crystallization behavior of unentangled poly(ε-caprolactone)s

The dynamics of polymer chains containing various topology including entanglement loops, tie molecules and end groups plays an important role in polymer crystallization. Poly(ε-caprolactone)s (PCL) with different end groups including phenyl, naphthyl and anthracenyl were synthesized with low molecular weight to avoid entanglement. The crystallization behavior of the synthesized PCLs was investigated via DSC, POM and X-ray, and the rheology property of the PCL melts was characterized. The largest end group resulted in the smallest spherulite growth rate and the longest half-time of crystallization. However, the effect of naphthyl and phenyl on the crystallization rate is close. The rheology results show low viscosity of naphthyl modified PCL, which is due to the compatibility of naphthyl and PCL. The master curves of the spherulite growth rate and the half-time of crystallization were obtained with the same supercooling regardless the end groups, which indicates that the polymer chains containing different end groups experience the possible same conformation changes during crystallization. Simultaneous SAXS/WAXS investigations on the heating samples with different end groups after isothermal crystallization all show doubled lamellar thickness during melting, which is possibly due to the transition from folded chains to extended chains in the dynamic favored metastable structures.

Heterogeneous Bubble Nucleation by Homogeneous Crystal Nuclei in Poly(l‐Lactic Acid) Foaming

AbstractA novel method to enhance and control bubble nucleation in poly(l‐lactic acid) (PLLA) foaming, not relying on external nucleating agents, is presented. Amorphous PLLA is annealed at temperatures close to its glass transition, to allow local alignment of polymer chains in the form of nanosized aggregates, called homogeneous crystal nuclei (HCN). PLLA containing HCN is then foamed after sorption of CO2 at 120 °C and 10 MPa. Under the chosen experimental conditions, HCN can promote growth of PLLA spherulites that can be controlled by thermal‐pressure history. Foam morphology is strongly affected by the presence of HCN, which act as heterogeneous nucleation sites for bubbles. Resulting foams are characterized by a bimodal morphology, with bubbles of about 50–70 µm in diameter developed in the bulk, and much smaller cells of few µm, grown upon pre‐existing crystal aggregates. The method detailed here to attain PLLA foams with tailored morphology can be exploited also for other semicrystalline polymers.

Correction: Effects of structurally-related impurities on the crystal growth of curcumin spherulites

Correction for ‘Effects of structurally-related impurities on the crystal growth of curcumin spherulites’ by Claire Heffernan et al., CrystEngComm, 2022, 24, 5156–5169, https://doi.org/10.1039/D2CE00223J.