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Herein, a benchtop technique to create one‐to‐one plastic replicas of nanostructured "masters" of various materials and dimensions via polycarbonate (PC) molding under ambient conditions is described. Instead of conventional thermal molding of PC under high temperature and pressure, it is explored to adapt solvent‐assisted method that has been traditionally unpopular due to the alteration of its morphology induced by swelling and recrystallization. A thorough study of how polymer spherulites (spherical domains of semicrystalline polymer chains) develop and whether their growth can be inhibited by nanocontact molding is conducted; it demonstrated not only how molding drastically limits crystallization but also how the crystallization can be controlled in the process of replicating micro/nanostructures. The efficacy of one‐to‐one replication across length scales from 100 nm to 1 mm over large areas (>5 cm2) has been confirmed with high‐resolution scanning electron microscopy and atomic force microscopy. The durable monolithic PC replicas can be used as templates for casting polydimethylsiloxane (PDMS) devices, allowing expensive lithographically designed masters to be preserved and accelerating production by multiplexing. The simplicity and low cost of this benchtop approach augment the feasibility of nanofabrication in resource‐limited settings with reduced costs and processing time. [ABSTRACT FROM AUTHOR]

Physical and chemical degradative effects of etching agents on polymer spherulites have been explored thoroughly to understand the etching mechanism as well as to perceive the polymer crystal structure and assembly. Interior lamellae of an aromatic polyester, poly(trimethylene terephthalate) (PTT), crystallized into a well-defined periodic-birefringent spherulitic structure, are subjected to sequence-assorted etching agents of basic methylamine (MA) vapor, acidic permanganate (KMnO 4) reagent, inorganic acids mixture (H 2 SO 4 :H 3 PO 4), and organic dichloroacetic acid (DCA). The chemistry involved in reactions between the selected etchants with the polymer spherulites was probed and their synergistic effects on exposing the interior 3D assembly were assessed. The exposed circumferential alignment of rod-like polycrystals interconnected by nanofibrils signifies the hidden interfaces between the lamellae that are assembled in a periodic grating structure to form banded PTT spherulites. The synergy of sequential MA- and KMnO 4 -etchings revealing the nano-assembly of PTT banded spherulites that resembles circumferential shish and kebabs. Image 1 • Combinatory dual-solvent-etching reveals interior lamellae assembly without causing severe distortion. • Pathways and proper sequence of etching agents provide avenue to better expose the interior assembly in banded spherulites. • Periodically assembly originates from tangential nanofibrils interconnected with radial micrometer-size lamellae bundles. • Contrary to classical models, periodic grating structure, with discontinuity in lamellae, accounts for banded spherulites. [ABSTRACT FROM AUTHOR]

The evaluation method for a biaxially oriented film was developed using in-situ measurement during the stretching process. It can obtain basic data such as stress-strain curves, birefringence, light scattering, three dimensional refractive indexes and birefringence distribution. Stress and strain as functions of stretching speed and stretching temperature, as well as the deformation of spherulite of semi-crystalline polymer can be obtained by measuring the birefringence and light scattering during the biaxial stretching process with a small piece of polymer sample. The experimental results show the stress, retardation and three dimensional molecular orientations behavior during the simultaneous biaxial stretching and the sequential biaxial stretching process. Stretchability, thickness uniformity and spherulite size can be obtained simultaneously. In this paper, advantages and details of the newly developed system will be discussed with some experimental data. [ABSTRACT FROM AUTHOR]

Most classical crystallization analyses on top surfaces of thin films could not adequately reveal the inner assembly of banded spherulites. Interior dissections by fracturing across various spherulite planes should be conducted to justify the inner lamellar assembly underneath the periodic bands. In this study, self-assembly of poly(dodecamethylene terephthalate) (P12T) into banded spherulites has been explored using powerful microscopy approaches. Results interestingly show a hierarchical ordered sequence of tangentially and radially oriented crystals into alternating polycrystalline layers. The layer width of the inner bands exactly matches with the optical inter-ring spacing (ca. 5 μm), proving emphatically that the interior lamellar assembly accurately accounts for the optical patterns of periodic rings. [ABSTRACT FROM AUTHOR]

The effects of flowing preformed spherulites on shear-induced melt crystallization behaviors of isotactic polypropylene (iPP) had been investigated by using a Linkam shearing cell coupled with an optical microscope, atomic force microscope, and rheometer. By quenching iPP melt to 130 °C for a short time, preformed spherulites were intentionally obtained. While iPP films were heated up to temperatures below the nominal melting point of iPP (164 °C), various shear conditions were applied, and then the crystalline morphologies during crystallization at the isothermal crystallization temperature of 135 °C were traced by alternately using phase contrast optical microscopy and polarized optical microscopy modes. Two distinct highly orientated thread- and cylinder-like crystalline morphologies were induced by shearing with preformed spherulites present, which were dependent on the applied shear rate and temperature. The distinct crystalline morphologies were attributed to relative movements between shear flowing melt and preformed spherulites. Atomic force microscopy was used to reveal the crystal aggregates of the two typical morphologies, indicating that the former was composed of highly packed orientated crystal nuclei, while the latter was composed of loosed packed random crystal nuclei, for which the thin crystal lamellae grew perpendicularly to crystal nuclei, leading to large widths for the cylinders as seen by an optical microscope. Rheological measurements indicated that preformed spherulites were isolated in the iPP films, which could obviously retard the stress relaxation of iPP films at the lower shear temperature. [ABSTRACT FROM AUTHOR]

The crystal structures of poly(L-lactic acid) (PLLA), its stereocomplexes, and some features of its crystallization process are reviewed. PLLA exists in different crystal modifications that are based on two different left-handed helix geometries having three units in one turn (31) or ten units in three turns (103). The stable α-phase with a 103 helix exists in two variants: an ordered α'-phase produced at high crystallization temperature and a less ordered α'-phase produced at low crystallization temperature. Two structures are based on the 31 helical conformation: an elusive γ-phase, obtained so far only by epitaxial crystallization, and a frustrated trigonal ß-phase. The β-phase, first obtained in stretched fibers, could be an intermediate or precursor phase of the low crystallization temperature α'-PLLA variant, which would explain a number of its unusual crystallization features (increased growth rate, thicker lamellae, structural disorder). Stereocomplexes of PLLA and poly(D-lactic acid) (PDLA) are formed through intimate association of left- and right-handed threefold helices. They have remarkably higher melting temperatures than the homopolymers, which is explained by the presence of a dense network of weak CH. . .OC hydrogen bonds. Single crystals of PLLA are obtained both from solution and thin film growth. Spherulites of chiral polylactides are frequently made of twisted lamellae with a large pitch, with the sense of twist depending on the polylactide chirality. [ABSTRACT FROM AUTHOR]

In this study, nanocomposites were prepared by melt blending poly (ε-caprolactone) (PCL) with a (polycarbonate (PC)/multi-wall carbon nanotubes (MWCNTs)) masterbatch in a twin-screw extruder. The nanocomposites contained 0.5, 1.0, 2.0, and 4.0 wt % MWCNTs. Even though PCL and PC have been reported to be miscible, our DSC (Differential Scanning Calorimetry), SAXS (Small Angle X-ray Scattering), and WAXS (Wide Angle X-ray Scattering) results showed partial miscibility, where two phases were formed (PC-rich and PCL-rich phases). In the PC-rich phase, the small amount of PCL chains included within this phase plasticized the PC component and the PC-rich phase was therefore able to crystallize. In contrast, in the PCL-rich phase the amount of PC chains present generates changes in the glass transition temperature of the PCL phase that were much smaller than those predicted by the Fox equation. The presence of two phases was corroborated by SEM, TEM, and AFM observations where a fair number of MWCNTs diffused from the PC-rich phase to the PCL-rich phase, even though there were some MWCNTs agglomerates confined to PC-rich droplets. Standard DSC measurements demonstrated that the MWCNTs nucleation effects are saturated at a 1 wt % MWCNT concentration on the PCL-rich phase. This is consistent with the dielectric percolation threshold, which was found to be between 0.5 and 1 wt % MWCNTs. However, the nucleating efficiency was lower than literature reports for PCL/MWCNTs, due to limited phase mixing between the PC-rich and the PCL-rich phases. Isothermal crystallization experiments performed by DSC showed an increase in the overall crystallization kinetics of PCL with increases in MWCNTs as a result of their nucleating effect. Nevertheless, the crystallinity degree of the nanocomposite containing 4 wt % MWCNTs decreased by about 15% in comparison to neat PCL. This was attributed to the presence of the PC-rich phase, which was able to crystallize in view of the plasticization effect of the PCL component, since as the MWCNT content increases, the PC content in the blend also increases. The thermal conductivities (i.e., 4 wt % MWCNTs) were enhanced by 20% in comparison to the neat material. The nanocomposites prepared in this work could be employed in applications were electrical conductivity is required, as well as lightweight and tailored mechanical properties. [ABSTRACT FROM AUTHOR]

Poly(trimethylene terephthalate) (PTT) with its unique spherulitic morphologies, highly birefringent features, and crystal stability serves as a good candidate to study polymer crystallization and assembly. This review compiles the main findings on crystallization in PTT, including birefringence and morphology, thermal behavior, as well as the interior structure of PTT banded spherulites, in order to elucidate the origin and formation mechanism of banded spherulites. Interior observation through the inner anatomy of crystal assembly in banded spherulites hidden under the top surface is necessary to provide a complete picture for the unsettled arguments about formation mechanism. Careful attention should be taken when selecting the etching agent for exposing the lamellar structure of polymer spherulite, otherwise, misinterpretation could result. [ABSTRACT FROM AUTHOR]

The effects of diffusion of crystallizable polymer to a developing spherulite embryo are treated. Using the classical nucleation theory result for the size of a critical-size embryo and an existing model for the growth of a small pure component sphere in a bicomponent matrix, the time τ d for a critical-size embryo to develop under diffusion control is given. The nucleation rate is lowered inversely proportionally to τ d . The dependence of τ d on crystallization temperature exhibits a minimum. At temperatures above that minimum, τ d for a blend becomes increasingly larger with temperature than the time to form a nucleus in a pure system with similar diffusivity. Below the minimum, τ d decreases with increasing crystallization temperature. Decreasing the activation energy for diffusion causes the minimum to move to higher temperatures. [ABSTRACT FROM AUTHOR]

Polymer crystals usually show a completely different melting behavior than small molecules. Instead of starting from the crystal growth front, the lamellar crystals within polymer spherulites always experience a successive thickening process upon heating before they simultaneously melt. However, a systematic comparative study of the different melting behavior of crystals formed by small and large polymer chains is still scarce. In this work, two PCL oligomers with similar molecular weight are selected to study their crystallization and melting behavior. The defect-free oligomer (PCL2.4) exhibits a similar melting behavior as polymeric crystals (where spherulites melt simultaneously). In contrast, the other oligomer (PCL2.0) with a mid-chain defect shows prominent surface melting starting at the spherulite growth front. SAXS, SSA thermal fractionation, and flash DSC results confirm that an extended chain-like crystal structure could form at relatively high crystallization temperatures. According to the Gibbs-Thomson equation, the melting temperature of PCL2.0 crystals at the spherulite growth front is relatively lower than in the inner part due to different surface free energies. On the other hand, the thermal stability of PCL2.4 is enhanced due to melting and recrystallization during heating, and the spherulites show identical melting points and lamellar thicknesses at their growth front centers. [Display omitted] • The crystallization and melting behaviors of two kinds of PCL oligomers with or with our mid-chain defect were studied in this work. • Defect-free PCL2.4 exhibits a normal simultaneous melting behavior which is similar to polymeric crystals due to the successive melting and recrystallization process during heating. • Because of the topological constraint effect of mid-chain defect, the oligomer PCL2.0 always shows a peculiar surface melting behavior, starting at the spherulite growth front and gradually moving inside the spherulite center like small molecular crystals. • Both oligomers exhibit identical lamellar thickness after crystallization at the same temperature. [ABSTRACT FROM AUTHOR]

ABSTRACT The basic thermal properties, isothermal melt crystallization kinetics, spherulitic morphology, mechanical properties, and hydrolytic degradation behavior of a novel eco-friendly polyester poly(butylene diglycolate) (PBDG) containing ether linkages were systematically studied with several techniques in this research. PBDG is an aliphatic polyester with high thermal stability. It had a glass transition temperature ( Tg) of −25.7 °C, a melting point temperature of 65.1 °C, and an equilibrium melting point of 73.2 °C. During the isothermal melt crystallization, PBDG crystallized slowly with increasing crystallization temperature, but the crystallization mechanism did not change. Negative spherulites were observed for PBDG. The mechanical properties of PBDG were investigated from the tensile testing. As a ductile polyester, PBDG possessed good mechanical properties. PBDG also showed a fast hydrolytic degradation rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44186. [ABSTRACT FROM AUTHOR]

Miscibility and crystallization behavior of a polymer blend consisting of two crystalline components, polyoxymethylene copolymer (Co-POM) and poly(ethylene oxide) (PEO), have been investigated. Experimental results indicate that Co-POM is thermodynamically miscible with PEO, as shown by the existence of single-composition dependent glass transition temperature over the entire composition range. The crystal structures and spherulitic morphologies of (Co-POM)/PEO blends were studied by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and polarizing light microscopy. It was found that the PEO spherulites crystallized within the matrix of the crystals of the pre-existing Co-POM phase and resulted in a high extent of interfibrillar segregation. The unique interpenetrated crystalline structure was beneficial for the sufficient contact between the two components and significantly improved both the toughing and the lubricating effect of PEO on the POM matrix. On incorporation of 30 wt% PEO, the notched impact strength of POM was enhanced from 6.7 to 10.3 MPa, by about 53.7%, while the elongation at break increased from 28.5% to 121.0%, by about 3.2 times. Furthermore, the friction coefficient drastically decreased from 0.35 to 0.17, demonstrating the enhanced tribological performance of the miscible blends. J. VINYL ADDIT. TECHNOL., 22:479-486, 2016. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The cracking behavior of spherulites in melt-crystallized poly ( l-lactic acid) and poly [(R)-3-hydroxybutyric acid] was investigated in an isothermal crystallization process. Layered spherulites with dual T were prepared under gradient cooling conditions. As T decreased the crack density reduced obviously, while width and depth of the cracks increased. A comparison of the effects of crystallization temperature ( T ) and spherulite size on cracking behavior in spherulites was present for the first time. Cracks were found to be more sensitive to T than spherulite size. Cracks were healed with a thermal treatment and the process was fully reversible. The crack positions were closely depended on the crystalline lamellae alignment set up at T . [ABSTRACT FROM AUTHOR]

A distinct skin-core-water-channel structure was formed in water-assisted injection molded low molecular weight high density polyethylene. A large number of well-developed banded spherulites were observed in core region. Two types of shish-kebabs, i.e., shish-kebabs without and with twisted lamellae, were appeared in both skin and water-channel region. The results imply that the formation mechanisms of twisted lamellae in banded spherulites and shish-kebabs are different, but both depend on the level of applied shear stress. [ABSTRACT FROM AUTHOR]

Polymeric and non-polymeric materials often crystallize as spherulites when crystallized from viscous melts or solutions at large undercooling. The essential component of a spherulite is fibrillar crystals that grow in predominantly radial directions and branch irregularly. We review the growth, branching and twisting of crystals in the light of theoretical and experimental advances of the last decade, while maintaining an appreciation for historical context. The crucial role of self-generated fields ahead of the crystal–melt interface is developed. Pressure gradients from volume contraction have been treated, as well as impurity gradients ahead of a growing crystal; fibril width W is predicted and found to be proportional to δ 1/2 , where the diffusion length δ = D / G , the quotient of diffusivity and growth rate, conveys the extent of the field gradient. Ribbon-like spherulite radii grow at a constant rate under diffusion-coupled interface control. Non-crystallographic branching is required to maintain the volume occupied by fibrillar crystals as the spherulite radius increases. Topological giant screw dislocations and induced nucleation at cilia tethered to crystals are observed mechanisms leading to branching normal to the wide dimension of lamellar crystals; but the relative importance of each of these is not yet established. Repetitive tip splitting by kinetic interface instability has been suggested as a branching mechanism in the wide dimension of lamellar crystals. Larger molecular mass reduces the spherulite growth rate, more so at low undercoolings, for reasons that remain unresolved. Miscible diluents often profoundly reduce G by lowering both thermodynamic driving force and local transport dynamics that govern the secondary nucleation rate. Spherulite blend morphology is linked to the competition between radial growth rate G and diffusivity D of the diluent, expressed as the diffusion length δ . Polymer crystals in which chain helices all have the same sense show banded spherulites, as do crystals in which the chain axes are not perpendicular to the basal surfaces. Recent analyses with optical birefringence and X-ray micro-diffraction support the presence of helicoidally twisted ribbons, although other structural arrangements have sometimes been revealed by microscopy. Assessments of twist directions in spherulites of chiral polymers point to unbalanced basal surface stress as the source of twisting, although a general mechanical analysis is lacking. Another twisting model employs regular arrays of isochiral giant screw dislocations; results are mixed for this model. [ABSTRACT FROM AUTHOR]

Semicrystalline polymers are composed of crystalline structures together with amorphous polymer chain networks and therefore they exhibit deformation mechanisms of both crystalline materials and amorphous polymers. One of the most common microstructures observed in semicrystalline polymers is the spherulite microstructure in which crystalline lamellae are embedded in a matrix of amorphous material and grow out from a common central nucleus in radial directions. The mechanical behavior of semicrystalline polymers is strongly dependent on the underlying spherulite microstructure. Therefore, characterization of the deformation of spherulites is very important to understand the mechanical behavior of semicrystalline polymers. In this work, we propose a new FEM-based model for semicrystalline polymers which explicitly discretizes the spherulite microstructure consisting of crystalline and amorphous phases. In the model, a viscoplastic crystal plasticity model is employed for the crystalline phase, whereas 8-chain model is employed for the amorphous phase. The model captures the evolution of inhomogeneous plastic deformation activity in a spherulite microstructure, as well as the important features of the spherulite deformation reported in the literature. [ABSTRACT FROM AUTHOR]

Amorphous calcium carbonate films synthesized by the polymer-induced liquid-precursor (PILP) process convert into crystallographically complex calcite spherulites. Tuning the experimental parameters allows for the generation of crystal lattice tilting similar to that found in calcareous biominerals. This contribution evidences the role of spherulitic growth mechanisms in pseudomorphic transformations of calcium carbonate. [ABSTRACT FROM AUTHOR]

ABSTRACT Blending ionic liquid with crystalline polymer permits the design of new high-performance composite materials. The final properties of these materials are critically depended on the degree of crystallinity and the nature of crystalline morphology. In this work, nonisothermal crystallization behavior of poly(ether- b-amide) (Pebax®1657)/room temperature ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [bmim]PF6) was investigated by differential scanning calorimetry. The presence of [bmim]PF6 can retard the nucleation of Pebax®1657 and lead to the crystallization depression of the PA block and the crystalline disappearance of the PEO block. However, the dilution effect of the IL results in a higher growth rate of crystallization of PA block. The influence of [bmim]PF6 content and cooling rate on crystallization mechanism and spherulitc structures was determined by the Avrami equation modified by Jeziorny and Mo's methods, whereas the Ozawa's approach fails to describe the nonisothermal crystallization behavior of Pebax®1657/[bmim]PF6 blends. In the modified Avrami analysis, the Avrami exponent of PA blocks, n > 3, for pure Pebax®1657, while 3 > n > 2 for Pebax®1657/[bmim]PF6 blends testifies the transformation of crystallization growth pattern induced by [bmim]PF6 from three-dimensional growth of spherulites to a combination of two- and three-dimensional spherulitic growth. Further, lower activation energy for the nonisothermal crystallization of PA blocks of Pebax®1657 can be observed with the increase of [bmim]PF6 content. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42137. [ABSTRACT FROM AUTHOR]

Magnetic resonance imaging is an excellent technique to achieve anatomical details and highly resolved images. The search for efficient contrast agents to increase the signal to background ratio led us to evaluate paramagnetic spherulites as potential Magnetic Resonance Imaging (MRI) contrast agents. Spherulites are supramolecular assemblies, made of lipidic concentric multilayers, able to encapsulate with high efficiency soluble macromolecules. Despite their highly interesting structure, spherulites have never been proposed as imaging agents. We proposed here three approaches to render spherulites paramagnetic: encapsulating a soluble contrastophore, inserting a lipidic contrastophore derivative or grafting a soluble contrastophore at the surface of the spherulites. Following similar strategies, liposomes were prepared for comparison. The conservation of the spherulite structure, throughout these three strategies, was shown by cryoelectron microscopy and small angle light scattering. The effect of the paramagnetic spherulites was studied by magnetic resonance imaging at different magnetic fields. The results showed that insertion of a contrastophore lipidic derivative into spherulite bilayers and grafting a contrastophore at the surface of the spherulites were the two strategies which led to the highest MRI contrast improvement. [ABSTRACT FROM AUTHOR]

Crystalline polymers form complex spherulitic morphologies upon crystallization from the melt. The spherulites are made of thin lamellae, frequently twisted, in which the long chains span the lamellar thickness and are folded back and forth at the lamellar surface. Investigation of the crystalline and lamellar structures becomes, however, possible by using single crystals, the size and thickness of which are well adapted for transmission electron microscopy. Imaging in bright and dark field modes, electron diffraction and specific decoration techniques have made it possible to reach a detailed understanding of lamellar and surface structures as well as the crystallization processes. These insights are transferable to the more complex bulk architectures and thus help analyze some of their most striking features. Electron microscopy turns out to be a major tool and in many cases the only possible tool to reach such molecular and even sub-molecular understanding. Some of these insights are illustrated, based mostly on work performed in our laboratory. They involve some original experimental techniques that should be useful in materials science. [ABSTRACT FROM PUBLISHER]

Spherulite morphologies of a highlyasymmetrical double crystallizablepoly(ε-caprolactone-b-ethylene oxide) diblockcopolymer in solution-cast films were explored from a unified standpointof tuning radial lamellar organization via controlled evaporation.Besides Maltese cross spherulites, three kinds of ring-banded spherulitesthat display non- and half-birefringent concentric ringed featuresas well as extinction banding were first encountered in the same polymer.Structural analyses based on atomic force microscopy, transmissionelectron microscopy, and grazing incidence X-ray technique revealedthat concentric ringed spherulites possess the nature of a rhythmicvariation of the radial lamellar packing and extinction banded spheruliteshave the origin of a periodic change of the radial lamellar orientation.Morphological transitions among different kinds of spherulites wereachieved by altering the drying condition. PEO segment crystallizedat low temperatures even if it is being confined by PCL lamellae.Combined with poly(ε-caprolactone) and poly(ethylene adipate),the influences of structural feature and crystallization conditionon radial lamellar organization of polymer spherulites were discussed.These present findings are encouraged to enhance our understandingand then governing generation of expected polymer crystal morphologyfor special material performance. [ABSTRACT FROM AUTHOR]

The formation of ring-banded spherulites in double-layer semicrystalline polymer films has seldom been a concern. In this study, the nucleation and growth of ring-banded spherulites in poly(ethylene oxide)/ poly(L-lactide) (PEO/PLA) double-layer films during isothermal crystallization at various temperatures above the melting point of the PEO layer have been investigated by using polarized optical microscopy (POM). The sequential crystallization of PLA and PEO components in the double-layer films was confirmed by a double quench crystallization procedure. The surface morphologies of ring-banded spherulites were examined by using scanning electron microscopy. The experimental results are compared with those for PLA/PEO blend films with 25 wt% PEO composition. It is interesting to find that the changing trend of band space in ring-banded spherulites at different isothermal crystallization temperatures in PEO/PLA double-layer films is more complex than that in PLA/PEO blend films. For the former ones, the ring-banded spherulites form at the lowest temperature approaching 65 °C and the band space slightly increases from 65 to 90 °C, is absent from 90 to 105 °C, obviously decreases from 105 to 115 °C, and significantly increases from 115 to 135 °C. For the latter ones, the band space only shows a monotonic increase with increasing temperature at above 105 °C. The mechanism for the formation of ring-banded spherulites in the PEO/PLA double-layer film system is proposed. The experimental results may shed some light on explaining the formation mechanism of ring-banded spherulites in semicrystalline polymers. [ABSTRACT FROM AUTHOR]

To improve physical motivation of mechanical modeling for semi-crystalline polymers, a better understanding of micro-mechanisms and a quantification of the mechanical response at the microstructure scale are needed. Strain field evolutions during deformation would be useful information but experimental techniques are still lacking for these materials. In this paper, an in-situ Digital Image Correlation (DIC) technique in the Scanning Electron Microscope (SEM) was developed to access strain fields at the spherulitic scale of a polypropylene. The evolution of strain heterogeneities during deformation were analyzed and correlated to the microstructure. [ABSTRACT FROM AUTHOR]

The aim of this study is to assess the interactions between the constituent phases of poly(ethylene terephthalate) and thereby analyse the validity of a hybrid interaction model in a mean-field micromechanical model based on layered two-phase inclusions. Two different modelling approaches are used to simulate the behaviour of semicrystalline polymers. The first approach is the micromechanical model based on interactions of the crystalline lamellae and the adjacent amorphous layers. The second approach is a two-scale finite-element model of the spherulitic microstructure. Isotropic poly(ethylene terephthalate) is selected as the model material. The deformation mechanisms at the microscopic scale are examined. Various crystal geometries are used in the finite-element model to analyse the case when the crystalline regions do not form an interconnected network. It is shown that the predictions of the microscopic deformation measures obtained with the micromechanical and the finite-element models are similar. Experimental evaluation of the elastic moduli has been performed to further estimate the applicability of the micromechanical model to PET. [ABSTRACT FROM AUTHOR]

Abstract: The crystalline/crystalline polymer blend of poly(butylenes succinate)/poly(ethylene oxide) (PBS/PEO) exhibited lower critical solution temperature (LCST) phase separation behavior at temperatures above the melting point of PBS, which was measured by phase contrast optical microscopy (PCOM) technique. In this work, we determined the LCST phase diagram of PBS/PEO blends, and then investigated the effect of liquid–liquid phase separation (LLPS) on the crystallization kinetics and morphologies of PBS/PEO (40/60 wt/wt) blend. Based on polarized optical microscopy (POM), scanning electron microscopy (SEM) and differential scanning calorimeter (DSC) results, we found that the spherulite morphology and crystallization kinetics of PBS were strongly influenced by the initial LLPS structure; because the kinetics of liquid–liquid phase dissolution was much slower than that of crystallization. The effect of LLPS on the primary nucleation density and crystal growth rate of PBS were strongly dependent on the crystallization temperature of PBS. After a second quench to a temperature below the melting point of PEO, the fractionated crystallization of PEO was observed. The competition between the kinetics of LLPS and the driving force of PBS crystallization controlled the spatial distribution of PEO in PBS spherulites, thus essentially determined the confined conditions of the PEO crystallization. The results indicated that the LLPS was an effective process to control the crystallization kinetics and morphology in crystalline/crystalline polymer blend systems. [Copyright &y& Elsevier]

The chemical and the molecular chain orientation imageof a bandedspherulite of crystalline polymers, poly(l-lactic acid) (PLLA)and poly(3-hydroxybutyrate) (PHB), are visualized using FT-IR imagingwith a newly proposed multipolarization calculation method. The vectorrepresentation of FT-IR image at different absorption spectral peaksvisualizes the magnitude and direction of molecular chain orientationdirectly in comparison with the retardation and the slow-axis azimuthalimages obtained by birefringence imaging. We found for the first timethat the wavenumber dependence of in-plane orientation function inthe band structure of a PHB spherulite, which is known as a double-bandstructure originated from a biaxial refractive index ellipsoid. The15 absorption peaks in the IR spectrum of PHB can be classified intothree groups by a different appearance of a band structure in viewof the magnitude of molecular chain orientation. The azimuthal imageof birefringence also shows the double-band structure; however, theFT-IR azimuthal images of orientation axis indicate the completelydifferent distribution in which there is no band structure at anyIR absorption peaks. By contrast, a good correspondence between theazimuthal image of the slow axis of birefringence and the orientationaxis of FT-IR is observed in the spherulite of PLLA, which has a uniaxialrefractive index ellipsoid. The advanced FT-IR imaging method clarifiesthe wavenumber-dependent two-types single-band structures of PHB,indicating the local molecular chain orientation along the crystallographicaxes in a unit cell. [ABSTRACT FROM AUTHOR]

Ring-banded spherulite is an important morphology ofpolymer crystals, and its formation mechanism is still under debate.In this study, we synthesized poly(trimethylene terephthalate)-co-poly(trimethylene sebacate) copolyesters (PTT-co-PTS) by melting copolycondensation and studied the influenceof PTS segments on the crystallization and ring-banded morphologyof poly(trimethylene terephthalate) spherulites by using a moderateetching technology. It is found that he band spacing of PTT-co-PTS spherulites decreased sharply with PTS segmentscontent. It is confirmed by experiments that there are twofold reasonsfor the sharp decrease of band spacing in PTT-co-PTS ring-banded spherulites. First, PTS segments acted as diluentsfor PTT molecules, which intensified the unbalanced surface stressat the fold surfaces for the PTT lamellar twisting. Second, incorporationof PTS segments decreased the thickness of PTT lamellae, and the greaterthe PTS content, the thinner the lamellae. Both these two changessignificantly enhance the helical twisting power of twist PTT lamellae. [ABSTRACT FROM AUTHOR]

Abstract: The plastic deformation mechanism of polymer materials was observed during the equal channel angular extrusion process with polypropylene as crystal polymer. The variations of the crystalline morphology, microstructure, and microhardness were discussed during the process. The extent of plastic deformation increased from the top surface to the bottom surface, and the maximum molecular orientation increased from R =1 near the top surface to R =2.2 near the bottom surface. The plastic deformation at the surface was small, especially in the range of 400μm distance from the top surface, without definite change of the crystalline structure. The plastic deformation was obvious when the sample was pressed into the outer corner of die. The spherulitic structure extended to the ellipsoidal shape along the 45° direction of the diagonal line because of the shear strain. The plastic deformation led to the destruction of spherulites near the bottom surface. However, the spherulites were not destroyed at center part, so their refinement as metallic material could not be expected. The variation of internal structure and material orientation increased along the direction of the maximum molecular orientation. [Copyright &y& Elsevier]

Structure changes of syndiotactic polypropylene (sPP) under uniaxial stretching are studied with the combination of micro-tensile tester and in situ wide angle X-ray diffraction (WAXD) measurement. Lamellae stacked 'vertically' and 'parallel' to the stretching direction (defined as 'V' and 'P' part) are separated on the basis of two-dimensional WAXD patterns. For all samples with different lamellar thickness, two critical points named as b and b were found in the stress-strain curves, while b and b points are the onsets of the rotation for the lamellae of 'V' part and 'P' part, respectively. The corresponding true stress and true strain for b point are bigger than that of b, demonstrating that for samples with initial isotropic lamellar orientation, inhomogeneous deformation of crystalline skeleton induced by uniaxial stretching is universal. And after b point, 'stress-induced melting' always occurs simultaneously with lamellar slips. Furthermore, the relationship between lamellar thickness and the true stress for b and b point was also studied, illustrating a linear correlation between ln σ and 1/ l ( σ is the corresponding true stress, l is the lamellar thickness), consistent with Young's model. However, the critical true strains for these two points did not change with the varying thickness. [ABSTRACT FROM AUTHOR]

Spherulitic growth rates of blends of polyhydroxybutyrate (PHB) with oligomers of atactic R,S-PHB-OH (Mn = 610, 910, and 2670 g/mol), as well as atactic R,S-PHB (Mn = 30 000 g/mol), were investigated by polarized light optical microscopy in the range from 50°C to 110°C. The temperature of maximum growth rate of PHB spherulites was affected by the molecular weight of the second amorphous component of atactic R,S-PHB-OH and the content of R,S-PHB-OH, Mn = 910 in PHB blends. It shifted from 90°C to 65°C with the presence of 75 wt% R,S-PHB-OH, Mn = 910. In order to apply the Boon and Azcue theory to experimental spherulitic growth rate data, the activation energy, U* ∼ 13.8 kJ/mol, which accounts for the molecular mobility, was calculated by using dielectric spectroscopy measurements. The equilibrium melting temperature,To m , was used as a fitting parameter for applying the Boon and Azcue theory to experimental growth rate data. From the fitting results, the value of the parameter Kg of the PHB blends virtually did not change with addition of the second component, i.e., R,S-PHB-diol or R,S-PHB; the crystallization of pure PHB and PHB blends was in regime III. [ABSTRACT FROM AUTHOR]

Linking the microstructure to the mechanical properties is a key feature in the design and assessment of the durability of semi-crystalline polymers. This paper addresses the importance of a particular architecture inside spherulites. The use of the theoretical tools of continuum mechanics has been combined with experimental observations of the deformation of the microstructure. Microstructural heterogeneities at various scales induced critical regions in the spherulite where voiding has been reported. The local stress state has been investigated using a Finite Element code. A simple Hooke's law was used for meshes accounting for the alternating crystalline and amorphous lamellae. This allowed a better understanding of the loci of void nucleation in the equatorial region, as well as in the "polar fans", and were explained by using a criterion based on stress equi-triaxiality. [ABSTRACT FROM AUTHOR]

Lamellar assembly with fractal-patterned growth into dendritic and ringed spherulites of crystallized poly(l-lactic acid) (PLLA), of two molecular weight (MW) grades and crystallized at (temperature of crystallization) Tc = 120 and 130 °C, respectively, are evaluated using optical and atomic-force microscopies. The results of surface-relief patterns in correlation with interior microscopy analyses in this work strongly indicate that the observed birefringence changes in PLLA polymer dendritic or ringed spherulites (from blue to orange, or to optical extinction) need not be definitely associated with the continuous helix twisting of lamellae; they can be caused by sudden and discontinuous lamellae branching at intersected angles with respect to the original main lamellae, as proven in the case of dendritic and zig-zag rough-ringed spherulites. Intersection angles between the main stalks and branches tend to be governed by polymer crystal lattices; for PLLA, the orthorhombic lattice (α-form) usually gives a 60° angle of branching and hexagonal growth. The branching lamellae then further bend to convex or concave shapes and finally make a 60–90° angle with respect to the main stalks. Such mechanisms are proven to exist in the straight dendritic/striped high-molecular weight (HMW)-PLLA spherulites (Tc = 120 °C); similar mechanisms also work in circularly ringed (Tc = 130 °C) HMW-PLLA spherulites. [ABSTRACT FROM AUTHOR]